Building Materials and Concrete Technology Unit 2

NRI INSTITUTE OF TECHNOLOGY DEPARTMENT OF CIVIL ENGINEERING
1
B U I L D I N G M A T E R I A L S A N D C O N C R E T E T E C H N O L O G Y
UNIT II {CO 2,3}
Aggregates: Classification of aggregate, Bond, Strength and other mechanical
properties of aggregate, Physical properties of aggregate, bulking of sand, Deleterious
substance in aggregate, Soundness of aggregate, Alkali-Aggregate reaction – Thermal
properties, Sieve analysis – Fineness modulus – Grading curves – Grading of fine and
coarse aggregates as per relevant IS code, Maximum aggregate size
Portland Cement: Chemical composition, Hydration, Structure of hydrated cement –
Setting of cement, Fineness of cement, Tests for physical properties – Different grades
of cements-Supplementary cementitious materials: Fly ash, GGBS, Silica fume, Rice
husk ash, Calcinated ash (Basic properties and their contribution to concrete strength).
Admixtures: Mineral and Chemical admixtures
Unit-II
S.No Long Answer Questions CO PO BTL Marks
1 How are the aggregates classified, explain? 2,3 1,2,8 I 7
2
What is bulking of sand & alkali aggregate
reaction? 2,3 1,2,8 I 7
3 Explain about Bond Strength of aggregates 2,3 1,2,8 II,V 7
4
Explain about mechanical properties of
aggregates 2,3 1,2,8 II,V 7
5
Explain about the Physical properties of
6
Explain about the Deleterious substance in
7
Explain in brief about the Soundness of
8
Explain about the Thermal properties of
9
Explain about the Sieve analysis process
performed on aggregates 2,3 1,2,8 II,V 7
10
Explain about the Fineness modulus performed
on aggregates 2,3 1,2,8 II,V 7
11
Explain about the Grading of fine and coarse
aggregates as per relevant IS code Explain
about the Maximum aggregate size
2,3 1,2,8 II,V 7
12
Explain about the Chemical composition of
Portland Cement 2,3 1,2,8 II,V 7
13
Explain about the Hydration of Portland
Cement 2,3 1,2,8 II,V 7
14 Explain about the Structure of hydrated cement 2,3 1,2,8 II,V 7
15
Explain about the Setting of cement, Fineness
of cement 2,3 1,2,8 II,V 7
16 Explain about the Different grades of cements 2,3 1,2,8 II,V 7
17
What is meant by fineness modulus of
aggregate and soundness of aggregate 2,3 1,2,8 I 7
18
Explain in brief about Physical properties of
aggregate 2,3 1,2,8 II,V 7

2
19
Explain the manufacturing process involved in
Wet process of cement? 2,3 1,2,8 II,V 7
20
Illustrate about the different physical tests
conducted on the ordinary Portland cement? 2,3 1,2,8 II 7
21
List the different types of cements and explain
them in brief. 2,3 1,2,8 I,IV 7
22
Summarize short note on Supplementary
Cementitious materials. 2,3 1,2,8 II 7
23
Distinguish b/w Mineral and Chemical
admixtures 2,3 1,2,8 IV 7
24 Explain about Fly ash, GGBS 2,3 1,2,8 II,V 7
25 Explain about Silica fume, Rice husk ash 2,3 1,2,8 II,V 7
26 Explain about Calcinated ash & GGBS 2,3 1,2,8 II,V 7
27
Explain about the Basic properties of
Supplementary cementitious materials and
their contribution to concrete strength.
2,3 1,2,8 II,V 7
Aggregates
INTRODUCTION
Aggregates are the materials basically used as filler with binding material in
the production of mortar and concrete. They are derived from igneous, sedimentary
and metamorphic rocks or manufactured from blast furnace slag, etc. Aggregates
form the body of the concrete, reduce the shrinkage and effect economy.
They occupy 70-80 per cent of the volume and have considerable influence on
the properties of the concrete. It is therefore significantly important to obtain right
type and quality of aggregates at site. They should be clean, hard, strong, durable
and graded in size to achieve utmost economy from the paste.
Earlier aggregates were considered to be chemically inert but the latest
research has revealed that some of them are chemically active and also that certain
types exhibit chemical bond at the interface of aggregates and cement paste. To
increase the bulk density of concrete aggregates are used in two markedly different
sizes—the bigger ones known to be coarse aggregate (grit) and the smaller one’s fine
aggregate (sand).
The coarse aggregate form the main matrix of concrete and the fine
aggregate from the filler matrix between the coarse aggregate.
CLASSIFICATIONOF AGGREGATES
On the Basis of Geological Origin
The aggregates may be classified into natural aggregates and artificial aggregates.
Natural Aggregates:

3
These are obtained by crushing from quarries of igneous, sedimentary or
metamorphic rocks. Gravels and sand reduced to their present size by the natural
agencies also fall in this category. The most widely used aggregate are from igneous
origin. Aggregates obtained from pits or dredged from river, creek or sea are most
often not clean enough or well graded to suit the quality requirement. They therefore
require sieving and washing before they can be used in concrete.
Artificial Aggregates:
Broken bricks, blast furnace slag and synthetic aggregates are artificial
aggregates. Broken bricks known as brick bats are suitable for mass concreting, for
example, in foundation bases. They are not used for reinforced concrete works. Blast
furnace slag aggregate is obtained from slow cooling of the slag followed by crushing.
The dense and strong particles as obtained are used for making precast concrete
products. The sp. gr. of these range between 2–2.8 and bulk density 1120–1300
kg/m3. The blast furnace slag aggregate has good fire resisting properties but are
responsible for corrosion of reinforcement due to sulphur content of slag. Synthetic
aggregates are produced by thermally processed materials such as expanded clay
and shale used for making light weight concrete.
On the Basis of Size
According to size aggregates are classified as coarse aggregate, fine aggregate and
all-in- aggregate.
Coarse Aggregate
Aggregate retained on 4.75 mm sieve are identified as coarse. They are
obtained by natural disintegration or by artificial crushing of rocks. The maximum
size of aggregate can be 80 mm. The size is governed by the thickness of section,
spacing of reinforcement, clear cover, mixing, handling and placing methods. For
economy the maximum size should be as large as possible but not more than one-
fourth of the minimum thickness of the member. For reinforced sections the
maximum size should be at least 5 mm less than the clear spacing between the
reinforcement and also at least 5 mm less than the clear cover. Aggregate more than
20 mm size are seldom used for reinforced cement concrete structural members.
All-in-aggregate
Naturally available aggregates of different fractions of fine and coarse sizes
are known as all-in-aggregate. The deficiency of any particular fraction can be
corrected for use in the mix but they are not recommended for quality concrete.
Graded Aggregate

4
Aggregate most of which passes through a particular size of sieve are known
as graded aggregate. For example, a graded aggregate of nominal size 20 mm means
an aggregate most of which passes IS sieve 20 mm.
Fine Aggregate
Aggregate passing through 4.75 mm sieve is defined as fine. They may be
natural sand—deposited by rivers, crushed stone sand—obtained by crushing
stones and crushed gravel sand. The smallest size of fine aggregate (sand) is 0.06
mm. Depending upon the particle size, fine aggregates are described as fine, medium
and coarse sands. On the basis of particle size distribution, the fine aggregates are
classed into four zones; the grading zones being progressively finer from grading
zone I to grading zone IV (IS: 383).
On the Basis of Shape
Aggregates are classified as rounded, irregular, angular, and flaky.
Rounded Aggregates
These are generally obtained from river or sea shore and produce minimum
voids (about 32 per cent) in the concrete. They have minimum ratio of surface area
to the volume, and the cement paste required is minimum. Poor interlocking bond
makes it unsuitable for high strength concrete and pavements.
Irregular Aggregates
They have voids about 36 per cent and require more cement paste as
compared to rounded aggregate. Because of irregularity in shape, they develop good
bond and are suitable for making ordinary concrete.
Angular Aggregates
They have sharp, angular and rough particles having maximum voids (about
40 per cent). Angular aggregate provides very good bond than the earlier two, are
most suitable for high strength concrete and pavements; the requirement of cement
paste is relatively more.

5
Flaky Aggregates
These are sometimes wrongly called as elongated aggregate. However, both of
these influence the concrete properties adversely. The least lateral dimension of flaky
aggregate (thickness) should be less than 0.6 times the mean dimension. For
example, the mean sieve size for an aggregate piece passing through 50 mm and
retained on 40 mm sieve is (50 + 40)/2 = 45.0 mm. If the least lateral dimension is
less than 0.6 × 45 = 27.0 mm, the aggregate is classified as flaky. Elongated
aggregate is those aggregate whose length is 1.8 times its mean dimension. Flaky
aggregate generally orients in one plane with water and air voids underneath. They
adversely affect durability and are restricted to maximum of 15 per cent.
Based on Unit Weight
Aggregates are classified as normal-weight, heavy-weight and light-weight aggregate
depending on weight and specific gravity as given in Table 6.1
Based on Texture
Based on Texture Aggregates can be classified into
1. Smooth Surface Texture Aggregate
2. Rough Surface Texture Aggregate

6
Smooth Surface Texture Aggregate
These aggregate categories are generally hard, dense and fine-grained
aggregates are smooth textured. These aggregates have lesser surface area because
of lesser irregularities. When these aggregates are employed, lesser amount of
cement is necessary for the lubrication purpose.
With there is increase in surface smoothness, the contact area also decreases.
This means a highly polished particle will have less bonding area with the matrix.
Due to less water requirement, these produce high compressive strength but with
poor bonding and interlocking.
Rough Textures Aggregate
Rough textured aggregate has higher strength in tension. These help in
developing bond strength in tension. These will develop lower compressive strength.
Effect of the sources on the quality of aggregate
The aggregates used in concrete may be derived from the following three sources
1.Igneous rocks
2.Sedimentary rocks
3.Metamorphic rocks.
The effect of these sources on the quality of aggregate are explained as follows.
1.Igneous Rocks

7
The igneous rocks are generally very hard. dense, tough and have a
complicated structure. Due to these properties, they render the aggregate with
several important qualities such as strength. hardness, toughness. specific gravity
and durability. The one disadvantage of using an igneous rock is due to its high
chemical activity to react with the alkalis present in the cement, resulting in the
increased bond strength, which increases the formation of cracks.
2.Sedimentary Rocks
Aggregates made of sedimentary rocks are obtained by quarrying. Depending
upon the cementing material and the compaction pressure induced during the
formation, the aggregate quality obtained from the sedimentary rock changes. The
general sedimentary rocks used as aggregates are limestone and siliceous sand
stones, as they possess high compressive or crushing strength (10 m N/m2 - 200 m
N/m2) and satisficing hardness (2-4 mosh).
3.Metamorphic Rocks
Metamorphic rocks are derived due to the atmospheric action like temperature
and pressure on the igneous rocks. They are generally considered to have the same
properties as that of aggregates made from igneous rocks. Metamorphic rocks,
especially quartzite and gneiss are used as aggregates and are proved to be
acceptable, but in general, they are not excessively used. They are provided to be
economical and hence can be used for budget construction.
As a conclusion, the aggregate having the least cost with desired quality
should be adopted.
Characteristics of Aggregates
The properties to be considered while selecting aggregate for concrete are
strength, particle shape, specific gravity, bulk density, voids, porosity, moisture
content and bulking.
Strength
The strength should be at least equal to that of the concrete. Rocks commonly
used as aggregates have a compressive strength much higher than the usual range
of concrete strength. A typical stress-strain curve for aggregate is shown in Fig. 6.1.

8
The test conducted for strength evaluation are crushing test, impact-test and
ten per cent fines test. Of these the first one is the most reliable. Generally, the
specifications prescribe 45 per cent for aggregate used for concrete other than
wearing surface and 30 per cent for concrete for wearing surfaces, such as runways,
roads etc. limit for the crushing value. The toughness of aggregate is measured by
impact test. The impact value should not exceed 30 per cent for wearing surface and
45 per cent for remaining concretes. Hardness of aggregate is tested by abrasion
test. The abrasion value is restricted to 30 per cent for wearing surfaces and 50 per
cent for concrete for other purposes.
Stiffness
The modulus of elasticity of concrete is approximately equal to the weighted
average of the moduli of the cement paste and the aggregate, as such the modulus
of the coarse aggregate has an important influence on the stiffness of concrete. A
high value reduces the dimensional changes due to creep and shrinkage of cement
paste, but at the cost of higher internal stresses. In concrete that is to be subjected
to wide variations of temperature and humidity, internal cracking is reduced by the
use of a more compressible aggregate, but in practice this effect is rarely of sufficient
importance to determine the choice of aggregate.
Bond Strength
Due to difference between the coefficients of thermal expansion of paste and
aggregate and to the shrinkage of cement paste during hardening, concrete is in a
state of internal stress even if no external forces are present. It is reported that the
stresses are likely to be greatest at the paste-aggregate interfaces where minute
cracks exist, even in concrete that has never been loaded. Under increasing external

9
load, these cracks spread along the interfaces before extending into the paste or
aggregate particles.
The strength of the bond between aggregate and cement paste thus has an
important influence on the strength of concrete. There is no standard test for bond
but it is known that the rougher the surface texture of the particles, the better the
bond. The role of particle shape is less well understood; the greater specific surface
of angular particles should enable greater adhesive force to be developed, but the
angular shape probably causes more severe concentrations of internal stress.
Shape and Texture
The shape influences the properties of fresh concrete more than when it has
hardened. Rounded aggregate is highly workable but yield low strength concrete.
Same is the case with irregular shaped aggregate. Flaky aggregate requires more
cement paste, produce maximum voids and are not desirable. Angular shape is the
best. Crushed and uncrushed aggregates generally give essentially the same
strength for the same cement content. The shape and surface texture of fine
aggregate govern its void ratio and significantly affect the water requirement.
Specific Gravity
The specific gravity of most of the natural aggregates lies between 2.6-2.7.
The specific gravity and porosity of aggregates greatly influence the strength and
absorption of concrete. Specific gravity of aggregates generally is indicative of its
quality. A low specific gravity may indicate high porosity and therefore poor
durability and low strength. The concrete density will greatly depend on specific
gravity.
Bulk Density
The bulk density of aggregate depends upon their packing, the particles
shape and size, the grading and the moisture content. For coarse aggregate a higher
bulk density is an indication of fewer voids to be filled by sand and cement.
Void Ratio
If the voids in the concrete are more the strength will be low.
Porosity
The entrapped air bubbles in the rocks during their formation lead to minute
holes or cavities known as pores. The porosity of rocks is generally less than 20 per
cent; the concrete becomes permeable and ultimately affects the bond between

10
aggregate and cement paste, resistance to freezing and thawing of concrete and
resistance to abrasion of aggregate. The porous aggregate absorbs more moisture,
resulting in loss of workability of concrete at a much faster rate.
Moisture Content
The surface moisture expressed as a percentage of the weight of the saturated
surface dry aggregate is known as moisture content. A high moisture content
increases the effective water/cement ratio to an appreciable extent and may render
the concrete week.
Bulking
The increase in the volume of a given mass of fine aggregate caused by the
presence of water is known as bulking. The water forms a film over the fine aggregate
particles, exerts force of surface tension and pushes them apart increasing the
volume.
The extent of bulking depends upon the percentage of moisture present in the
sand and its fineness. With ordinary sand bulking varies from 15-30 percent. It
increases with moisture content up to a certain point (4-6%), reaches maximum, the
film of water on the sand surface breaks, and then it starts decreasing. Figure 6.2
shows the bulking of sand with moisture content.
In preparing concrete mixes if sand is measured by volume and no allowance
is made for bulking, the moist sand will occupy considerably larger volume than that
prepared by the dry sand and consequently the mix will be richer. This will cause,
less quantity of concrete per bag of cement. For example, if the bulking of sand is
10% and if mix ratio is 1:2:4, the actual volume of sand used will be 1.1 × 2 =2.2
instead of 2 per unit volume of cement. If this correction is not applied the actual
dry sand in the concrete will be (1 / 1.1) * 2 = 1.82, instead of 2 per unit volume of
cement. The mix proportion then would be 1:1.82:4 rather than 1: 2: 4. Which

11
indicates lesser production of concrete. Also, there will be chances of segregation,
honeycombing and reduced yield of concrete.
Bulking of sand can be determined, in field, by filling a container of known
volume (A) with damp sand in the manner in which the mixer hopper will be filled.
The height of sand in the container is measured. The sand is then taken out of
container carefully, ensuring no sand is lost during this transaction. The sand is
then either dried and filled back into the gauge box, or the container is filled with
water and the damp sand is poured in to displace the water. Whichever method is
adopted, the new depth of aggregate in the container gives the unbulked volume (B).
Then percentage bulking expressed as
A percentage of the dry volume =
Fineness Modulus
It is a numerical index of fineness, giving some idea about the mean size of
the particles in the aggregates. The fineness modulus (F.M.) varies between 2.0 and
3.5 for fine aggregate, between 5.5 and 8.0 for coarse aggregate, and from 3.5 to 6.5
for all-in aggregate. Aggregate, whose F.M. is required, is placed on a standard set
of sieves (80, 63, 40, 20, 12.5, 10, 4.75, 2.36, 1.18 mm and 600, 300, 150 _m) and
the set vibrated.
The material retained on each sieve after sieving represent the fraction of
aggregate coarser than the sieve in question but finer than the sieve above. The sum
of the cumulative percentages retained on the sieves divided by 100 gives the F.M.
A fineness modulus of 3.0 can be interpreted to mean that the third sieve i.e., 600
_m is the average size. The test procedure is given IS: 2386 (Part I).
The object of finding F.M. is to grade the given aggregate for the required
strength and workability of concrete mix with minimum cement. Higher F.M.
aggregate result in harsh concrete mixes and lower F.M. result in uneconomical
concrete mixes.
Deleterious Materials and Organic Impurities
Substances such as organic matters, clay, shale, coal, iron pyrites, etc. which
are weak, soft, fine or may have harmful physical or chemical effects on the
aggregates are considered to be deleterious. They affect the properties of concrete in
green as well as in hardened state and are undesirable. They may be classified as
those interfering with the process of hydration, i.e., organic matters, coatings such
as clay, etc. affecting the development of bond between aggregate and the cement
paste, and, unsound particles which are weak or bring about chemical reaction

12
between aggregate and cement paste. The surface coated impurities in aggregate can
be removed by adequate washing. However, chemically-bonded stable coating which
cannot be so removed may increase shrinkage cracks. The salts present in the sea-
shore sand should be washed out otherwise efflorescence is caused afterwards.
Mica, if present in sand, reduces the strength of concrete. Iron pyrites and sulphides
produce surface staining and pop-outs.
Soundness
Soundness is defined as the ability of aggregate to resist changes in volume
as a result of changes in physical conditions. The conditions affecting this property
are freezing and thawing, temperature changes, and alternate wetting and drying.
Porous and weak aggregates containing undesirable extraneous matter undergo
excessive volume changes under favourable conditions.
The freeze-thaw resistance of aggregate is related to its porosity, absorption,
and pore structure. This may cause local scaling to surface cracking consequently
leading to impaired appearance and sometimes structural failure. Aggregates may
also be chemically unstable. Some of the aggregate with certain chemical
constituents react with alkalis in cement which may cause abnormal expansion and
map cracking of concrete.
Alkali-Aggregate Reaction
What is ASR?
Visual symptoms
 network of cracks
 Closed or spalled joints
 Relative displacement
 cracking of concrete from alkali silica reactivity
The aggregates were considered to be inert material till 1940. Considerable
trouble has been experienced through extensive pop-outs and cracking in a fairly
close pattern, of concrete work to become plainly visible the effects can often be
observed in petrographic thin sections of the concrete within a few months. The
phenomenon is accompanied by extensive expansion and may lead in bad cases to
complete disruption and disintegration of the concrete and is known as alkali-
aggregate reaction or sometimes concrete cancer.

13
The trouble is due to reaction between silica in aggregate and alkalis in the
cement. In some cases, alkalis, mainly from the cement supplemented by alkalis in
the aggregate, react with carbonates in the aggregate to produce similar result. The
types of rocks which contain reactive constituents include traps, andesites,
rhyolites, siliceous limestone and certain types of sandstones. The reactive
components may be in the form of opals, cherts, chalcedony, volcanic glass
(excepting basaltic glasses), zeolites, and tridymite.
Harmful Reactive Substances
Some potentially harmful reactive minerals, rocks, and synthetic materials
Several of the rocks listed react very slowly and may not show evidence of any
harmful degree of reactivity until the concrete is 20 years old
Only certain sources of these materials have shown reactivity
Controlling of ASR
Non-reactive aggregates
Supplementary cementing materials or blended cements
Limit alkali loading
Lithium based admixtures
Limestone sweetening (30 % replacement reactive aggregates with crushed
limestone)
Fine Aggregate

14
Sand (> 0.07 mm) is used as a fine aggregate in mortar and concrete. It is a
granular form of silica. Sand used for mix design is known as standard sand (IS:
650). In India Ennore Sand is standard sand and in U.K. it is Leighton-Burrard
Sand. The standard sand should be obtained from Ennore, Tamil Nadu. It should
be quartz, light grey or whitish variety and should be free from silt. It should (100%)
pass through 2-mm IS sieve and should be (100%) retained on 90- micron IS sieve
with the following distribution,
Particle Size Per cent
Smaller than 2 mm and greater than 1 mm 33.33
Smaller than 1 mm and greater than 500 micron 33.33
Smaller than 500 microns but greater than 90 micron 33.33
Sand used in mortars for construction purposes should possess at least 85
per cent of the strength of standard sand mortars of like proportions and
consistency.
Importance of Sand in construction
The important functions of sand are,
1. It does not aim to develop any cracks in the mortar on drying.
2. It decreases the shrinkage of the binding material.
3.It helps to make mortars of any strength by different proportion of sand with
the binding material.
Sources of Sand:
Sand particles consist of small grains of silica (Si02). It is formed by the
decomposition of sand stones due to various effects of weather. The following are the
natural sources of sand.
a. Pit Sand:
This sand is found as deposits in soil and it is obtained by forming pits to a depth
of about 1m to 2m from ground level.
Pit sand consists of sharp angular grains, which are free from salts for making
mortar, clean pit sand free from organic and clay should only be used.
b. Rive Sand:
This sand is obtained from beds of rivers.
River sand consists of fine rounded grains.
Colour of river sand is almost white. As the river sand is usually available in clean
condition, it is widely used for all purposes.
c. Sea Sand:

15
This sand is obtained from sea shores. Sea sand consists of rounded grains
in light brown colour. Sea sand consists of salts which attract the moisture from the
atmosphere and causes dampness, efflorescence and disintegration of work. Due to
all such reasons, sea sand is not recommendable for engineering works. However,
be used as a local material after being thoroughly washed to remove the salts.
Disadvantages of Sea Sand
1.The sea sand causes efflorescence on walls.
2.As the sea sand is graded uniformly. it will give only less strength to the cement
mortar
3.The sea sand has much difficulty in drying and does not allow for saluting.
4.It is less durable.
5.It causes a lot of expensive damages in a short period of time.
6.It is very difficult to have a tine aggregate material in the quarry regions.
7.This sand is incapable for construction where walls are loaded continuously in a
shorter duration.
Replacing of natural sand with artificial sand
The increase in usage of natural sand in construction activities makes difficulty
to buy. Natural sand is expensive, which effects the effective construction work. By
excavating sand from river bed, the water level in the rivers is reduced. Therefore, to
overcome this problem the natural sand is replaced by fine aggregates. These fine
aggregates are obtained by crushing rock aggregates.
Characteristics of sand:
1. It should be chemically inert
2. It should be clean and coarse. It should be free from organic matter.
3. It should contain sharp, angular and durable grains.
4. It should not contain salts, which attract the moisture from atmosphere.
5. It should be well graded (i.e.) should contain particles of various sizes in suitable
proportions.
Classification
Sand may be classified on the basis of source, mineralogical composition, size
of the particles and particle size distribution. Depending upon the source sand may
be classed as
Natural Sand—resulting from natural disintegration of rocks or deposited by
streams;
Crushed Stone Sand—produced by crushing hard stones and,
Crushed Gravel Sand—produced by crushing natural gravel.

16
Based on mineralogical composition, sand is divided into quartz, felspar and
carbonaceous varieties.
Depending upon its size sand is classified as
Coarse Sand—Fineness Modulus (F.M.) 2.90-3.20;
Medium Sand—F.M.: 2.60-2.90 And;
Fine Sand—F.M.: 2.20-2.60.
Based on particle size distribution fine aggregate have been divided in four grades
from grading zone I to grading zone IV as given in Table 6.2.
Functions of Sand
The functions of sand are to achieve economy by its use as adulterant in
mortar, prevent shrinkage and development of cracks in mortar, furnish strength to
mortar against crushing and allow carbon dioxide from the atmosphere to penetrate
the fat lime mortars necessary for its air hardening.
Effect of Gradation
The grading of fine aggregate has a great influence on workability of mortar.
Very fine sand and very coarse sand have been found to be unsatisfactory for making
mortar and concrete. Very fine sand results in a poor mortar and is uneconomical,
whereas very coarse sand produces a harsh mix affecting workability. When well
graded (consisting of particles of different sizes) the voids are minimised.
Effect of Impurities
The impurities such as clay, dust and organic materials are harmful for
mortar and concrete and in any case should not exceed 4 per cent. Of this clay is
most harmful since it coats individual sand particles and prevents their bonding
with cement consequently diminishing the strength of mortar which is further
reduced by the enhanced water requirement of mortar. The clay and dust impurities
can be removed by careful washing. Addition of finely ground clay to clean coarse
sand may improve its grading and reduce voids. Hence, a lean mortar deficient in
fines may be improved both in density and workability by addition of small

17
percentages of such clays. The organic matters, shell and vegetables injure the
hardening properties of the cement reducing the strength and durability.
Effect by Entraining Air in Concrete
The quantity of fine aggregate required for making concrete mix can be
reduced by entraining air.
Coarse Aggregate
These may be uncrushed, crushed or partially crushed gravel or stone most
of which is retained on 4.75 mm IS sieve. They should be hard, strong, dense,
durable, clear and free from veins and adherent coatings; and free from injurious
amounts of disintegrated pieces, alkali, organic matter and other deleterious
substances. Flaky, scoriaceous and elongated aggregate should be avoided.
Functions
The functions of coarse aggregate are almost same as that of fine aggregate.
Cinder Aggregates
They are well-burnt furnace residue obtained from furnaces using coal as fuel
and are used for making lime concrete. They should be clean and free from clay,
dirt, wood ash or other deleterious matter. They are classed as A, B and C. Class A
is recommended for general purposes, class B for interior work not exposed to damp
conditions, and class C for precast blocks.
Sulphate content should not exceed 1 per cent when expressed as sulphur
trioxide and loss on ignition 10 per cent for class A, 20 per cent for class B, 25 per
cent for class C.
Average grading is as under:
Sieve No. Percentage passing
10 mm 10
4.75 mm 80
2.36 mm 60
1.18 mm 40
600 micron 30
300 micron 25
150 micron 16
Broken Brick Coarse Aggregate
They are prepared from well-burnt or over-burnt broken bricks free from
under-burnt particles, soil and salt and are used in lime concrete.
Water absorption after 24 hours on immersion in water should not exceed 25
per cent and water soluble matter should not exceed 1 per cent. Aggregate impact
value should not exceed 50 per cent.

18
Grading is as under:
Sieve No. (mm) Percentage passing (by weight)
80 100
40 95-100
20 45-75
4.75
Crushed Sand
All along in India, we have been using natural sand. The volume of concrete
manufactured in India has not been much, when compared to some advanced
countries. The infrastructure development such as express highway projects, power
projects and industrial developments have started now.
Availability of natural sand is getting depleted and also it is becoming costly.
Concrete industry now will have to go for crushed sand or what is called
manufactured sand.
Advantages of natural sand is that the particles are cubical or rounded with
smooth surface texture. The grading of natural F.A. is not always ideal. It depends
on place to place.
Barmac Rock-On-Rock VSI Crusher.
Being cubical, rounded and smooth textured it gives good workability. So far,
crushed sand has not been used much in India for the reason that ordinarily
crushed sand is flaky, badly graded rough textured and hence they result in
production of harsh concrete for the given design parameters.

19
We have been also not using superplasticizer widely in our concreting
operations to improve the workability of harsh mix. For the last about 4–5 years the
old methods of manufacturing ordinary crushed sand have been replaced by modern
crushers specially designed for producing, cubical, comparatively smooth textured,
well graded sand, good enough to replace natural sand.
Dust is a nuisance and technically undesirable in both coarse aggregate and
more so in fine aggregate. Maximum permissible particles of size finer than 75μ is
15% in fine aggregate and 3% in coarse aggregate. There is provision available in
these equipment’s to control and seal the dust.
In one of the high-rise building sites in western suburb of Mumbai, M 60
concrete was specified. The required slump could not be achieved by natural sand
with the given parameter of mix design. But with the use of manufactured sand with
proper shape, surface texture, desirable grading to minimise void content, a highly
workable mix with the given parameter of mix design, was achieved.
The following is the grading pattern of a sample collected from a sand crushing plant
on a particular date and time at Pune-Mumbai Road Project:
Table 3.17. Grading Pattern of Crushed Sand (Typical)
Testing of Aggregates
The size, shape, grading of aggregate and their surface moisture affect directly
the workability and strength of concrete whereas soundness, alkali-aggregate
reaction and presence of deleterious substances adversely affect the soundness and
durability of concrete. The following tests are conducted to ensure satisfactory
performance of aggregate.
Standard Grading Curve
The grading patterns of aggregate can be shown in tables or charts.
Expressing grading limits by means of a chart gives a good pictorial view. The
comparison of grading pattern of a number of samples can be made at one glance.

20
For this reason, often grading of aggregates is shown by means of grading curves.
One of the most commonly referred practical grading curves are those produced by
Road Research Laboratory (U.K.).
On the basis of large number of experiments in connection with bringing out
mix design procedure, Road Research Laboratory has prepared a set of type grading
curve for all-in aggregates graded down from 20 mm and 40 mm. They are shown in
figure 3.4 and Fig 3.5 respectively. Similar curves for aggregate with maximum size
of 10 mm and downward have been prepared by McIntosh and Erntory. It is shown
in Fig. 3.6. Fig. 3.7 shows the desirable grading limit for 80 mm aggregate.
Four curves are shown for each maximum size of aggregate except 80 mm
size. From values of percentage passing, it can be seen that the lowest curve i.e.,
curve No. 1 is the coarsest grading and curve No. 4 at the top represents the finest
grading. Between the curves No. 1 to 4 there are three zones: A, B, C. In practice the
coarse and fine aggregates are supplied separately. Knowing their gradation, it will
be possible to mix them up to get type grading conforming to any one of the four
grading curves.

21

22

23
Grading of Aggregates
Aggregate comprises about 55 per cent of the volume of mortar and about 85
per cent volume of mass concrete. Mortar contains aggregate of size of 4.75 mm and
concrete contains aggregate up to a maximum size of 150 mm.
Thus, it is not surprising that the way particles of aggregate fit together in the
mix, as influenced by the gradation, shape, and surface texture, has an important
effect on the workability and finishing characteristic of fresh concrete, consequently
on the properties of hardened concrete. Volumes have been written on the effects of
the aggregate grading on the properties of concrete and many so called “ideal”
grading curves have been proposed.
In spite of this extensive study, we still do not have a clear picture of the
influence of different types of aggregates on the plastic properties of concrete. It has
been this much understood that there is nothing like “ideal” aggregate grading,
because satisfactory concrete can be made with various aggregate gradings within
certain limits.
It is well known that the strength of concrete is dependent upon water/cement
ratio provided the concrete is workable. In this statement, the qualifying clause
“provided the concrete is workable” assumes full importance. One of the most
important factors for producing workable concrete is good gradation of aggregates.
Good grading implies that a sample of aggregates contains all standard
fractions of aggregate in required proportion such that the sample contains
minimum voids. A sample of the well graded aggregate containing minimum voids
will require minimum paste to fill up the voids in the aggregates

24
Sieve Analysis
This is the name given to the operation of dividing a sample of aggregate into
various fractions each consisting of particles of the same size. The sieve analysis is
conducted to determine the particle size distribution in a sample of aggregate, which
we call gradation.
A convenient system of expressing the gradation of aggregate is one which the
consecutive sieve openings are constantly doubled, such as 10 mm, 20 mm, 40 mm
etc. Under such a system, employing a logarithmic scale, lines can be spaced at
equal intervals to represent the successive sizes.
The aggregates used for making concrete are normally of the maximum size
80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 600-micron, 300 micron and
150 microns. The aggregate fraction from 80 mm to 4.75 mm are termed as coarse
aggregate and those fraction from 4.75 mm to 150 microns are termed as fine
aggregate. The size 4.75 mm is a common fraction appearing both in coarse
aggregate and fine aggregate (C.A. and F.A.).
Grading pattern of a sample of C.A. or F.A. is assessed by sieving a sample
successively through all the sieves mounted one over the other in order of size, with
larger sieve on the top. The material retained on each sieve after shaking, represents
the fraction of aggregate coarser than the sieve in question and finer than the sieve
above. Sieving can be done either manually or mechanically.
Fig. Set of Sieves assembled for conducting Sieve analysis.

25
Fig. Set of Sieves
In the manual operation the sieve is shaken giving movements in all possible
direction to give chance to all particles for passing through the sieve. Operation
should be continued till such time that almost no particle is passing through.
Mechanical devices are actually designed to give motion in all possible direction, and
as such, it is more systematic and efficient than hand sieving.
For assessing the gradation by sieve analysis, the quantity of materials to be
taken on the sieve is given Table 3.8.
From the sieve analysis the particle size distribution in a sample of aggregate
is found out. In this connection a term known as “Fineness Modulus” (F.M.) is being
used. F.M. is a ready index of coarseness or fineness of the material. Fineness
modulus is an empirical factor obtained by adding the cumulative percentages of
aggregate retained on each of the standard sieves ranging from 80 mm to 150 micron
and dividing this sum by an arbitrary number 100. The larger the figure, the course

26
is the material. Table No. 3.9 shows the typical example of the sieve analysis,
conducted on a sample of coarse aggregate and fine aggregate to find out the fineness
modulus.
Many a time, fine aggregates are designated as coarse sand, medium sand and
fine sand. These classifications do not give any precise meaning. What the supplier
terms as fine sand may be really medium or even coarse sand. To avoid this
ambiguity fineness modulus could be used as a yard stick to indicate the fineness
of sand.
The following limits may be taken as guidance:
Fine sand: Fineness Modulus: 2.2 - 2.6
Medium sand: F.M.: 2.6 - 2.9
Coarse sand: F.M.: 2.9 - 3.2
A sand having a fineness modulus more than 3.2 will be unsuitable for
making satisfactory concrete.
Particle Size Distribution Test
This test is primarily used to determine the grading of materials proposed for
use as aggregates or being used as aggregates. The results are used to determine
compliance with the particle size distribution with applicable specification
requirements and to provide necessary data for the control of the production of
various aggregate products and mixtures containing aggregates.
Sampling
Sample the aggregate in accordance with test procedure described above
Procedure
a) If the test sample has not been subjected to testing using method 7.1 (material
finer than the 75-micron test sieve by washing), dry it to constant mass at a
temperature of 100ºC plus or minus 5ºC and determine the mass of it to the nearest
0.1% of the total original dry sample mass.
b) Select the sieve sizes suitable to furnish the information required by the
specification covering the material to be tested.
Nest the sieves in order of decreasing opening size from top to bottom and
place the sample, or portion of a sample if it is to be sieved in more than one
increment, on the top sieve.
Agitate the sieves by hand or by mechanical means for a sufficient period,
established by trial or checked by measurement on the actual sample, to meet the
criteria for adequacy of sieving described in the note below.

27
Note
Adequacy of sieving criteria: Sieve for a sufficient period and in such manner that,
after completion, not more than 0.5% by mass of the total sample passes any sieve
during 1 minute of continuous hand sieving performed as follows:
Hold the individual sieve, provided with a snug-fitting pan and cover, in a
slightly inclined position in one hand. Strike the side of the sieve sharply and with
an upward motion against the heel of the other hand at the rate of about 150 times
per minute, turn the sieve about one-sixth of a revolution at intervals of about 25
strokes.
In determining sufficiency of sieving for sizes larger than the 4.75 mm sieve,
limit the material on the sieve to a single layer of particles. If the size of the mounted
testing sieves makes the described sieving motion impractical, use 200mm diameter
sieves to verify the sufficiency of sieving.
c) Limit the quantity of material on a given sieve so that all particles have opportunity
to reach the sieve opening a number of times during the sieving operation. For sieves
with opening smaller than 4.75 mm the mass retained on any sieve at the completion
of the sieving operation shall not exceed 6 kg/m2, equivalent to 4 g/in2 of sieving
surface. For sieves with opening 4.75 mm and larger, the mass in kg/m2 of sieving
surface shall not exceed the product of (2.5) x (sieve opening in millimetres).
d) Determine the mass of each size increment by weighing to the nearest 0.1% of the
total original dry sample mass. The total mass of the material after sieving should
be checked closely with original mass of sample placed on the sieves. If the amounts
differ dry more than 0.3%, based on the original dry sample mass, the results should
not be used for acceptance purposes.
e) If the sample had previously been tested add the amount finer than the 75-micron
sieve determined by that method to the mass passing the 75-micron sieve by dry
sieving of the same sample in this method.
Calculation
Calculate percentages passing, total percentages retained, or percentages in
various size fractions to the nearest 0.1% on the basis of the total mass of the initial
dry sample.
Report
The report shall include the following information:
a) Total percentage of material passing each sieve.
b) Total percentage of material retained on each sieve.
c) Report percentages to the nearest whole number, except if the percentage passing
the 75-micron sieve is less than 10%, it shall be reported to the nearest 0.1%.

28
Sample of fine aggregate, coarse aggregate or all-in-aggregate, as required to
be tested, are taken in sufficient quantities. The minimum weight of sample for the
test should be as follows.

29
FINENESS MODULUS OF FINE AGGREGATE AND COARSE AGGREGATE
Aim:
To determine the fineness of modulus of fine aggregate and coarse aggregate.
Apparatus:
Indian standard test sieves set, weighting balance, sieves shaker pan, tray.
Theory:
Fineness modulus is a numerical index used to know the mean size of particle
in the total Quantity of aggregate. Fineness modulus is to grade the given aggregate
for most economical mix and workability with less assumption of cement lower FM
gives uneconomical mix and higher FM gives harsh mix. It is defined the average
cumulative % retained by 100 was known as fineness modulus.

30
Fineness modulus is generally used to get an idea of how coarse or fine the
aggregate is. More fineness modulus value indicates that the aggregate is coarser
and small value of fineness modulus indicates that the aggregate is finer.
Procedure:
For Fine Aggregates
 Arrange the test services with larger openings at top and smaller openings at
bottom and finally below all keep a pan
 Take 1 kg of sand in to a tray and break the lumps, if any in case of fine aggregate
and 1kg of samples in the case of coarse aggregate and mixed aggregate.
 Sieve the aggregate using the appropriate sieves (10mm, 4.75 mm, 2.36 mm, 1.18
mm, 600-micron, 300 micron & 150 micron)
 Keep the sample in the top sieve and keep the total set in the top sieve and keep
the total Set in the shaker. Continue sieving for a period not less than 10 minutes.
 Weigh the material retained on each sieve property.
 Record the weight of aggregate retained on each sieve.
 Calculate the cumulative weight of aggregate retained on each sieve.
 Calculate the cumulative percentage of aggregate retained.
 Add the cumulative weight of aggregate retained and divide the sum by 100. This
value is termed as fineness modulus.
Calculations:
1. Cumulative % of weight retained = Cumulative weight of retained / Sample weight
× 100
2. % of weight Passing = (100 – Cumulative % of weight retained)
3. Fineness modulus = (Summation of cumulative % of weight retained up to 150
microns) / 100
Value of fineness Modulus of Sand
Type of Sand Fineness Modulus
Fine sand 2.2 – 2.6
Medium Sand 2.6 – 2.9
Coarse Sand 2.9 – 3.2
Observations:
Weight of sample for fine aggregates = 2000 gms

31
S.no. IS sieve size Wt.
retained
Gm
Cumulative
weight of
retained
(gm)
Cumulative
% of weight
retained
(For
Calculating
Fineness
Modulus)
% of weight
Passing (For
Grading or
Particle Size
Distribution)
1. 10 mm 0 0 0 100
2. 4.75 mm 25.07 25.07 1.2535 98.75
3. 2.36 mm 55.780 80.85 4.0425 94.7075
4. 1.18 mm 350.00 430.85 21.5425 73.165
5. 600 μ 945 1375.85 68.79 4.375
6. 300 μ 545 1920.85 96.04 0
7. 150 μ 60 1980.85 99.04 0
8. Pan 0
Summation of Cumulative % of weight retained 290.711
Sl.no IS SIEVE
WT.
RET.
CUM.
WT.
% CUM. WT.
RET.
%
PASS.
1 10 0 0 0 100
2 4.75 20 20 4 96
3 2.36 55 75 15 85
4 1.18 40 115 23 77
5 600 80 195 39 61
6 300 190 385 77 23
7 150 85 470 94 6
8 75 30 500 100 0
Wt. of Sample 500
F.M = (SUM OF % CUM. WT. RET. TILL 150
MICRONS ) / 100
SUM OF % CUM. WT. RET. TILL 150 MICRONS 252
F.M 2.52
For E.g.:
Fineness modulus of fine aggregate is 2.75. It means the average value of
aggregate is in between the 2nd sieve and 3rd sieve. It means the average aggregate
size is in between 0.3mm to 0.6mm as shown in below figure.

32
For Coarse Aggregates
 Arrange the test services with larger openings at top and smaller openings at
bottom and finally below all keep a pan
 Take 1 kg of sand in to a tray and break the lumps, if any in case of fine aggregate
and 1kg of samples in the case of coarse aggregate and mixed aggregate.
 Sieve the aggregate using the appropriate sieves (80 mm, 40 mm, 20 mm, 10 mm,
4.75 mm, 2.36 mm, 1.18 mm, 600-micron, 300 micron & 150 micron)
 Keep the sample in the top sieve and keep the total set in the top sieve and keep
the total Set in the shaker. Continue sieving for a period not less than 10 minutes.
 Weigh the material retained on each sieve property.
 Record the weight of aggregate retained on each sieve.
 Calculate the cumulative weight of aggregate retained on each sieve.
 Calculate the cumulative percentage of aggregate retained.
 Add the cumulative weight of aggregate retained and divide the sum by 100. This
value is termed as fineness modulus
Limits of Fineness Modulus for Coarse Aggregates
Fineness modulus of coarse aggregate varies from 5.5 to 8.0. And for all in
aggregates or combined aggregates fineness modulus varies from 3.5 to 6.5. Range
of fineness modulus for aggregate of different maximum sized aggregates is given
below.
Maximum size of
coarse aggregate
Fineness
modulus range
19mm 6.0 – 6.9
37.5mm 6.9 – 7.5
75mm 7.5 – 8.0
150mm 8.0 – 8.5
For E.g.:

33
If Fineness modulus of C.A obtained is 7.17 it means, the average size of
particle of given coarse aggregate sample is in between 7th and 8th sieves, that is
between 9.5mm to 19mm.
Calculations:
1. Cumulative % of weight retained = Cumulative weight of retained / Sample weight
× 100
2. % of weight Passing = (100 – Cumulative % of weight retained)
Fineness modulus = (Summation of cumulative % of weight retained up to 150
microns) / 100
Precautions:
 Sample should be taken by quartering.
 Careful sieving must be done to prevent any spilling of aggregate
Observations:
Weight of sample for coarse aggregates = 5000 gms
S.no. IS sieve size Wt. retained
Gm
Cumulative
weight of
retained (gm)
Cumulative
% of weight
retained
% of weight
Passing
1 63 mm 0 0 0 100
2 50 mm 0 0 0 100
3 40 mm 0 0 0 100
4 31.5 mm 0 0 0 100
5 25 mm 870 870 17.4 82.6
6 16 mm 2850 3720 74.4 25.6
7 12.5 mm 610 4330 86.6 13.4
8 10 mm 530 4860 97.2 2.8
9 6.3 mm 120 4980 99.6 0.4
10 Pan
Summation of Cumulative % of weight retained 3752
Graph:
Draw a graph between IS sieve size (in log scale) and %passing.
Result:

34
Fineness modulus of fine aggregate = 2.9
Fineness modulus of coarse aggregate= 3.752
REFERENCE:
IS: 383 – 1970
Limits of Fineness Modulus of Sand
Maximum size of aggregate
Fineness modulus
Minimum
Maximum
Fine Aggregate 2 3.5
Coarse aggregate 20mm 6 6.9
Coarse aggregate 40mm 6.9 7.5
Coarse aggregate 75mm 7.5 8.0
The air-dried sample is placed on a set of specific sieves with largest size on
the top. The set of sieves is shaked for 2 minutes. Arrangement of sieve for different
types of aggregate is as follows.
A curve is plotted with sieve sizes on abscissa on a graph (Fig. 6.3) and
percentage of aggregate passing as ordinate. From this graph relative number of
various sizes of aggregate can be readily compared.

35
Gap grading
So far, we discussed the grading pattern of aggregates in which all particle
size is present in certain proportion in a sample of aggregate. Such pattern of particle
size distribution is also referred to as continuous grading.
Originally in the theory of continuous grading, it was assumed that the voids
present in the higher size of the aggregate are filled up by the next lower size of
aggregate, and similarly, voids created by the lower size are filled up by one size
lower than those particles and so on.
It was realised later that the voids created by a particular fraction are too small
to accommodate the very next lower size. The next lower size being itself bigger than
the size of the voids, it will create what is known as “particle size interference”, which
prevents the large aggregates compacting to their maximum density.
It has been seen that the size of voids existing between a particular size of
aggregate is of the order of 2 or 3 size lower than that fraction. In other words, the
void size existing between 40 mm aggregate is of the size equal to 10 mm or possibly
4.75 mm or the size of voids occurring when 20 mm aggregate is used will be in the
order of say 1.18 mm or so.
Therefore, along with 20 mm aggregate, only when 1.18 mm aggregate size is
used, the sample will contain least voids and concrete requires least matrix. The
following advantages are claimed for gap graded concrete:
(i) Sand required will be of the order of about 26 per cent as against about 40 per
cent in the case of continuous grading.
(ii) Specific surface area of the gap graded aggregate will be low, because of high
percentage of C.A. and low percentage of F.A.
(iii) Requires less cement and lower water/cement ratio.
(iv) Because of point contact between C.A. to C.A. and also on account of lower
cement and matrix content, the drying shrinkage is reduced.

36
It was also observed that gap graded concrete needs close supervision, as it
shows greater proneness to segregation and change in the anticipated workability.
In spite of many claims of the superior properties of gap graded concrete, this
method of grading has not become more popular than conventional continuous
grading.
Flakiness Index and Elongation Index Test (IS: 2386 (Part I))
Because of large number of flaky particles in the coarse aggregate more voids
are formed in the concrete consequently more mortar is required to fill the voids,
resulting in uneconomy. Also, durability of concrete will be affected. For flakiness
index (F.I) and elongation index (E.I) sufficient quantity of aggregate is taken so as
to provide at least 200 pieces of any fraction to be tested. The sample is sieved
through I.S. sieves as given in Table 6.3.
Table 6.3 Dimensions of Thickness and length Gauges
Determination of Flakiness Index
The flakiness index of aggregate is the percentage by weight of particles in it
whose least dimension (thickness) is less than three-fifths of their mean dimension.
The test is not applicable to sizes smaller than 6.3 mm. This test is conducted by
using a metal thickness gauge, of the description shown in Fig.

37
A sufficient quantity of aggregate is taken such that a minimum number of
200 pieces of any fraction can be tested. Each fraction is gauged in turn for thickness
on the metal gauge. The total amount passing in the gauge is weighed to an accuracy
of 0.1 per cent of the weight of the samples taken.
The flakiness index is taken as the total weight of the material passing
the various thickness gauges expressed as a percentage of the total weight of
the sample taken.
Table 3.18 shows the standard dimensions of thickness and length gauges.

38
F.I = (Weight of aggregate passing through the slot of the thickness gauge /
Total weight of sample) x 100
Test for Determination of Elongation Index
The elongation index on an aggregate is the percentage by weight of particles
whose greatest dimension (length) is greater than 1.8 times their mean dimension.
The elongation index is not applicable to sizes smaller than 6.3 mm. This test is
conducted by using metal length gauge of the description shown in Fig.
A sufficient quantity of aggregate is taken to provide a minimum number of
200 pieces of any fraction to be tested. Each fraction shall be gauged individually
for length on the metal gauge. The gauge length used shall be that specified in
column of 4 of Table 3.18 for the appropriate size of material. The total amount
retained by the gauge length shall be weighed to an accuracy of at least 0.1 per cent
of the weight of the test samples taken.
The elongation index is the total weight of the material retained on the
various length gauges expressed as a percentage of the total weight of the
sample gauged.
The presence of elongated particles in excess of 10 to 15 per cent is generally
considered undesirable, but no recognised limits are laid down.

39
E.I = (Weight of the aggregate retained on length gauge/ Total weight of
aggregate) x 100
Indian standard explains only the method of calculating both Flakiness Index
and Elongation Index. But the specifications do not specify the limits. British
Standard BS 882 of 1992 limits the flakiness index of the coarse aggregate to 50 for
natural gravel and to 40 for crushed coarse aggregate. However, for wearing surfaces
a lower values of flakiness index are required.
Estimation of organic impurities in sand
Sand is tested, for organic impurities, as delivered and without drying. A 350-
ml graduated glass bottle is filled to the 75-mlmark with 3 per cent solution of
sodium hydroxide in water. The sand is added gradually until the volume measured
by the sand layer is 125 ml. The volume is made up to 200 ml by adding more
solution. The bottle is stoppered and shaken vigorously and then allowed to stand
for 24 hours. If the colour of the liquid above the sand is darker than the standard
solution, prepared a fresh, the following test should be made. 2.5 ml of 2 per cent
solution of tannic acid in 10 per cent alcohol is added to <)7.5 ml of a 3 per cent
sodium hydroxide solution. It is placed in a 350 ml bottle and is shaken vigorously
and allowed to stand for 24 hours. The colour of this is compared with the solution
above the sand.
Specific Gravity and Water Absorption Test (IS: 2386 (Part III))
Aggregate Larger than 10 mm:
A sample of 2000 g of aggregate is used for conducting the test. Aggregate
which has been artificially heated should not normally be used. The sample is
thoroughly washed to remove finer particles and dust, drained and then placed in

40
the wire basket and immersed in distilled water at a temperature between 22-32°e
with a cover of at least 50 mm of water above the top of the basket.
Immediately after immersion the interrupted air is removed from the sample
by lifting the basket containing it 25 mm above the base of the tank and allowing it
to drop 25 times at the rate of about one drop per second. The basket and aggregate
are kept completely immersed during the operation and for ,1 period of 24 ± 1/2
hours afterwards. The basket and the sample are jolted and weighed in water (weight
A1)' These are then removed from the water and allowed to drain for a few minutes,
after which the aggregate is gently emptied from the basket on to one of the dry
clothes. and the empty basket is returned to the water, jolted 25 times and weighed
in water (weight A1)'
The aggregate placed on the dry cloth are gently surface dried with the cloth,
and are completely surface dried. The aggregate art' then weighed (weight B). The
aggregate is there after placed in an oven at a temperature of 100-11oDe and
maintained at this temperature for 24 ± 1/2 hours. It is then removed from the oven,
cooled in the air-tight container and weighed (weight C). The computations are as
under the weight in g of the saturated surface dry aggregate in air the weight in g of
oven-dried aggregate in air
Aggregate Between 40 mm and 10 mm:
A sample of about 1000 g of the aggregate is screened on a 10 mm sieve,
thoroughly washed to remove fine particles of dust, and immersed in distilled water
in a glass vessel at a temperature of 22 to 32°C for 24 ± 1/2 hours. Soon after
immersion and again at the end of the soaking period, air entrapped in or bubbles
on the surface of the aggregate should be removed by gentle agitation. The vessel is
over filled by adding distilled water, dried on the outside and weighed (weight A).
The vessel is then emptied and the aggregate allowed to drain and later refilled
with distilled water. It is dried on the outside and weighed (weight B). The aggregate
is placed on a dry cloth and gently surface dried with the cloth. The aggregate is

41
weighed (weight C) after the surface is completely dried. The aggregate is then placed
in oven at a temperature of 100 to 110°C for 24 ± 1/2 hours and thereafter cooled
in air tight container and weighed (weight D)
Aggregate Smaller than 10 mm:
A Pycnometer shown in Fig. 6.6 is used for determining specific gravity. A
sample about 1000 g for 10 mm to 4.75 mm or 500 g if finer than 4.75 mm, is placed
in the tray and covered with distilled water at a temperature of 22-32°C. Soon after
immersion, air entrapped in or bubbles on the surface of the aggregate are removed
by gentle agitation with a rod. The sample is kept immersed for 24 ± 1/2 hours.
The water is then carefully drained from the sample through a filter paper,
any material retained being returned to the sample. The aggregate including any
solid matter retained on the filter paper should be exposed to a gentle current of
warm air to evaporate surface moisture and stirred at frequent intervals to ensure
uniform drying until no free surface moisture can be seen and the material just
attains a free-running condition. The saturated and surface dry sample is weighted
(weight A).
The aggregate is then placed in the pycnometer which is filled with distilled
water. The pycnometer is dried on the outside and weighed (weight B). The contents
of the pycnometer are emptied into the tray. The pycnometer is refilled with distilled

42
water to same level as before, dried on the outside and weighed (weight C). The water
is then carefully drained from the sample by decantation through a filter paper and
any material retained is returned to the sample. The sample is placed in the oven at
a temperature of 100 to 110°C for 24 ± 1/2 hours, during which period it should be
stirred occasionally to facilitate drying. It is then cooled in the air-tight container
and weighed (weight D).
Where A = weight in g of saturated surface-dry sample
B = weight in g of pycnometer or gas jar containing sample and filled with distilled
water
C = weight in g of pycnometer or gas jar filled with distilled water only
D = weight in g of oven-dried sample
Determination of Bulk Density and Voids (IS: 2386 (Part III))
The bulk density, measured in kilograms per litre is affected by several factors,
including the amount of moisture present and the amount of effort introduced in
filling the measure. This is laboratory test intended for comparing properties of
different aggregates. It is not generally suitable for use as a basis for quoting mix
design conversion factors.
The test is carried out on dry material when determining the voids, but when
bulking tests are required material with a given percentage of moisture may be used.
The measure is filled with thoroughly mixed aggregate to about one-third and
tamped with 25 strokes of the rounded end of the tamping rod. A further similar
quantity of aggregate is added with a further tamping of 25 times and the surplus
aggregate is struck off, using the tamping rod as a straight edge. The net weight of
the aggregate in the measure is determined and the bulk density is calculated.

43
The measure is then filled to overflowing by means of a shovel or scoop, the
aggregate being discharged from a height not exceeding 50 mm above the top of the
measure. The surface of the aggregate is then levelled with a straight edge. The net
weight of the aggregate in the measure is determined and the bulk density is
calculated.
The percentage of voids are calculated as follows:
where GS = specific gravity of the aggregate
γ = bulk density in kg/litre
Necessary adjustment for bulking of fine aggregate (Field method)
I Method:
Sufficient quantity of the sand is put loosely into a container until it is about
two third full. The sand is levelled off and a steel rule is pushed vertically down
through the sand at the middle to the bottom and the height is measured (say h
mm). The sand is transferred into another container. The first container is half filled

44
with water and about half the sand is put back and rammed with a steel rod (about
6 mm in diameter) so that its volume is reduced to a minimum. Then the remainder
of the sand is added and rammed in the same way. The depth is measured at the
middle with the steel rule (say h1 mm). The percentage of bulking of the sand due to
moisture is calculated from the formula:
II Method:
The damp sand (consolidated by shaking) is poured in a 250 ml measuring
cylinder up to the 200 ml mark. Then the cylinder is filled with water and the sand
is stirred well. The sand surface will be found to be below its original level. Supposing
the surface is at the mark y ml, the percentage of bulking of the sand due to moisture
is calculated as:
Crushing Value Test (IS: 2386 (Part IV))
The material for the test should consist of aggregate passing 12.5 mm sieve
and retained on 10 mm sieve. For other sizes, the materials are separated on the
appropriate sieves given in Table 6.6.
Table 6.6 Details of Aggregate Crushing Test for Non-standard Sizes of
Aggregate
About 6500 g of natural aggregate is required to provide samples for the 150
mm cylinder, or about 1000 g for the 75 mm cylinder. The aggregate is tested in a
surface-dry condition. The weight of material comprising the test sample is
determined (weight A).

45
The cylinder of the test apparatus is positioned on the base-plate and the test
sample is added in thirds, each being subjected to 25 strokes from the tamping rod.
The surface of the aggregate is carefully levelled and the plunger is inserted so that
it rests horizontally on this surface. The apparatus, with the test sample and plunger
in position is then placed between the platens of the testing machine and loaded at
a uniform rate as possible, so that the total load is reached in 10 minutes. The total
load should be 400 kN.
The load is released and the whole of the material is removed from the
cylinder and sieved on a 2.36 mm sieve for the standard test, or on the appropriate
sieve given in Table 6.5. The fraction passing the sieve is weighed. The ratio of the
weight of fines formed to the total sample weight in each test is expressed as a
percentage, recorded to the first decimal place:
Where B = weight of fraction passing the appropriate sieve
A = weight of surface-dry sample
Aggregate Impact Value Test (IS:2386 (Part IV))
The aggregate impact value gives a relative measure of the resistance of an
aggregate to sudden shock or impact, which in some aggregate differs from its
resistance to a slow compressive load. The test sample consists of aggregate the
whole of which passes a 12.5 mm sieve and is retained on a 10 mm sieve. The
aggregate comprising the test sample is dried in an oven for a period of four hours
at a temperature of 100-110°C and cooled.

46
The measure is filled about one-third full with the aggregate and tamped with
25 strokes of the rounded end of the tamping rod. A further similar quantity of
aggregate is added and a further tamping of 25 strokes is given. The measure is
finally filled to overflowing, tamped 25 times and the surplus aggregate is struck off,
using the tamping rod as a straight-edge. The net weight of aggregate in the measure
is determined to the nearest gram (weight A).
A cup, 102 mm internal diameter and 50 mm deep, is fixed firmly in position
on the base of the machine and the whole of the sample is placed in it and compacted
by a single tamping of 25 strokes of the tamping rod. The hammer is raised until its
lower face is 380 mm above the upper surface of the aggregate in the cup, and
allowed to fall freely on to the aggregate. The test sample is subjected to a total of 15
such blows each being delivered at an interval of not less than one second.
The crushed aggregate is then removed from the cup and the whole of it is
sieved on 2.36 mm IS sieve until no further significant amount passes in one minute.
The fraction passing the sieve is weighed to an accuracy of 0.1 g (weight B). The
fraction retained on the sieve is also weighed (weight C) and, if the total weight (B +
C) is less than the initial weight (A) by more than one gram, the result is discarded
and a fresh test made. Two tests are made. The ratio of the weight of fines formed to
the total sample weight in each test are expressed
as a percentage, recorded to the first decimal place:

47
Where B = weight of fraction passing 2.36 mm sieve
A = weight of oven-dried sample
Aggregate Abrasion Value Test (IS: 2386 (Part IV))
The abrasion value of coarse aggregate may be determined by either Deval
Machine or by Los Angeles machine.
Using Los Angeles Machine
The abrasive charge consists of cast iron spheres or steel spheres
approximately 48 mm in diameter and each weighing between 390 and 445 g. The
test sample consists of clean aggregate dried in an oven at 105 -110°C to
substantially constant weight. The test sample and the abrasive charge is placed in
the Los Angeles abrasion testing machine and the machine is rotated at a speed of
20 to 33 rev/min. For gradings A, B, C and D, the machine is rotated for 500
revolutions; for gradings E, F and G, it is rotated for 1000 revolutions.

48
The machine is so driven and so counter-balanced as to maintain a
substantially uniform peripheral speed. If an angle is used as the shelf, the machine
is rotated in such a direction that the charge is caught on the outside surface of the
angle. At the completion of the test, the material is discharged from the machine
and a preliminary separation of the sample made on a sieve coarser than the 1.70
mm. The finer portion is then sieved on a 1.70 mm sieve. The material coarser than
the 1.70 mm sieve is washed, dried in an oven at 105 -110°C to a substantially
constant weight, and accurately weighed to the nearest gram. The difference between
the original and the final weights of the test sample expressed as a percentage of the
original weight of the test sample gives the percentage of wear.
CEMENT

49
Definition
A cement is any substance which binds together other materials by a
combination of chemical processes known collectively as setting. Cements are dry
powders and should not be confused with concretes or mortars, but they are an
important constituent of both of these materials.
Cement act as the 'glue' that gives strength to structures. Mortar is a mixture
of cement and sand whereas concrete also includes rough aggregates. Cement is a
powdered material with water forms a paste that hardens slowly. It has an important
property that when mixed with water a chemical reaction (hydration) takes place.
Cement in its broadest term means any substance which acts as a binding
agent for materials natural cement (Roman Cement) is obtained by burning and
crushing the stones containing clay, carbonates of lime and some amount of
carbonate of magnesia. The clay content in such stones is about 20 to 40 percent.
Natural cement resembles very closely eminent hydraulic lime. It is not strong as
artificial cement, so it has limited use in practice.
Artificial cement is obtained by burning at very high temperature a mixture of
calcareous and argillaceous materials in correct proportion. Calcined product is
known as clinker. A small quantity of gypsum is added to clinker and it is then
pulverized into very fine powder is known as cement. Cement was invented by a
mason Joseph Aspdin of Leeds in England in 1824. The common variety of artificial
cement is known as normal setting cement or ordinary cement or Portland cement.
History of Cement

50
1. The cementitious properties of lime in mortars and concrete have been known
since early historic times. The Romans used lime concretes and developed pozzolanic
cements of lime and certain volcanic earths.
2. Lime mortars and concretes continued to be used in the middle Ages.
3. 1824, Joseph Aspdin from Leeds city - England, produced a powder made from
the calcined mixture of limestone and clay.
4. He called it "Portland Cement", because when it hardened it produced a material
similar to stones from the quarries near Portland Island in UK.
The ordinary Portland cement has been classified as 33 Grade (IS269:1989),
43 Grade (IS 8112:1989), and 53 Grade (IS 12669-1987). The physical requirements
of all these three types of cement are almost same except for compressive strength
and are as follows:
Sl. No
Physical Method Grade
requirement of Testing 33 43 53
1
Fineness Blaine's air
(Sp. Surface permissibility 225 225 225
in (m2/kg)
2
Soundness Le-Chatelier 10mm 10mm 10mm
apparatus
Autoclave 0.80% 0.80% 0.80%
3
Setting Time Vicat apparatus
Initial(min) 30 30 30
Final(max) 600 600 600
4
Compressive strength
(MPa) not <
72 ± 1 hr 16 23 27
168 ± 2 hr 22 33 37
672 ± 4 hr 33 43 53
IS:10262 has classified the OPC grade-wise from A to F
based on 28 day
compressive strength as follows.
Category Strength (Mpa)
A 32.5 to 37.5
B 37.5 to 42.5
C 42.5 to 47.5
D 47.5 to 52.5
E 52.5 to 57.5

51
F 57.5 to 62.5
Accordingly, the 33, 43 and 53 grades of cement correspond to categories A,
C and E, respectively. However, most of the 43-grade cements available in the
market fall in category D and that 53-grade cements in category F.
Raw Materials of Portland Cement
1. Calcareous rocks such as limestone, marl, chalk.
2. Argillaceous rocks (silica and alumina) such as in clay and shale.
Portland cement production must contain, in proper form and proportions of lime,
silica and alumina.
Properties of Cement- Physical & Chemical
Cement, a popular binding material, is a very important civil engineering
material. This article concerns the physical and chemical properties of cement, as
well as the methods to test cement properties.
Properties of Cement
Physical Properties of Cement
Different blends of cement used in construction are characterized by their physical
properties. Some key parameters control the quality of cement. The physical
properties of good cement are based on:
 Fineness of cement
 Soundness
 Consistency
 Strength
 Setting time
 Heat of hydration
 Loss of ignition
 Bulk density
 Specific gravity (Relative density)
These physical properties are discussed in details in the following segment. Also,
you will find the test names associated with these physical properties.
Fineness of Cement
The size of the particles of the cement is its fineness. The required fineness of
good cement is achieved through grinding the clinker in the last step of cement
production process. As hydration rate of cement is directly related to the cement
particle size, fineness of cement is very important.
Soundness of Cement

52
Soundness refers to the ability of cement to not shrink upon hardening. Good
quality cement retains its volume after setting without delayed expansion, which is
caused by excessive free lime and magnesia.
Tests:
Unsoundness of cement may appear after several years, so tests for ensuring
soundness must be able to determine that potential.
Le Chatelier Test
This method, done by using Le Chatelier Apparatus, tests the expansion of
cement due to lime. Cement paste (normal consistency) is taken between glass slides
and submerged in water for 24 hours at 20+1°C. It is taken out to measure the
distance between the indicators and then returned under water, brought to boil in
25-30 mins and boiled for an hour. After cooling the device, the distance between
indicator points is measured again. In a good quality cement, the distance should
not exceed 10 mm.
Autoclave Test
Cement paste (of normal consistency) is placed in an autoclave (high-pressure
steam vessel) and slowly brought to 2.03 MPa, and then kept there for 3 hours. The
change in length of the specimen (after gradually bringing the autoclave to room
temperature and pressure) is measured and expressed in percentage. The
requirement for good quality cement is a maximum of 0.80% autoclave expansion.
Consistency of Cement
The ability of cement paste to flow is consistency.
It is measured by Vicat Test.
In Vicat Test Cement paste of normal consistency is taken in the Vicat
Apparatus. The plunger of the apparatus is brought down to touch the top surface
of the cement. The plunger will penetrate the cement up to a certain depth depending
on the consistency. A cement is said to have a normal consistency when the plunger
penetrates 10±1 mm.
Strength of Cement
Three types of strength of cement are measured – compressive, tensile and
flexural. Various factors affect the strength, such as water-cement ratio, cement-
fine aggregate ratio, curing conditions, size and shape of a specimen, the manner of
moulding and mixing, loading conditions and age. While testing the strength, the
following should be considered:
Cement mortar strength and cement concrete strength are not directly related.
Cement strength is merely a quality control measure.
The tests of strength are performed on cement mortar mix, not on cement paste.

53
Cement gains strength over time, so the specific time of performing the test should
be mentioned.
Compressive Strength
It is the most common strength test. A test specimen (50mm) is taken and subjected
to a compressive load until failure. The loading sequence must be within 20 seconds
and 80 seconds.
Tensile strength
Though this test used to be common during the early years of cement production,
now it does not offer any useful information about the properties of cement.
Flexural strength
This is actually a measure of tensile strength in bending. The test is performed in a
40 x40 x 160 mm cement mortar beam, which is loaded at its centre point until
failure.
Setting Time of Cement
Cement sets and hardens when water is added. This setting time can vary depending
on multiple factors, such as fineness of cement, cement-water ratio, chemical
content, and admixtures. Cement used in construction should have an initial setting
time that is not too low and a final setting time not too high. Hence, two setting times
are measured:
Initial set:
When the paste begins to stiffen noticeably (typically occurs within 30-45
minutes)
Final set:
When the cement hardens, being able to sustain some load (occurs below 10
hours) Again, setting time can also be an indicator of hydration rate.
Heat of Hydration
When water is added to cement, the reaction that takes place is called hydration.
Hydration generates heat, which can affect the quality of the cement and also be
beneficial in maintaining curing temperature during cold weather. On the other
hand, when heat generation is high, especially in large structures, it may cause
undesired stress. The heat of hydration is affected most by C3S and C3A present in
cement, and also by water-cement ratio, fineness and curing temperature. The heat
of hydration of Portland cement is calculated by determining the difference between
the dry and the partially hydrated cement (obtained by comparing these at 7th and
28th days).
Loss of Ignition

54
Heating a cement sample at 900 - 1000°C (that is, until a constant weight is
obtained) causes weight loss. This loss of weight upon heating is calculated as loss
of ignition. Improper and prolonged storage or adulteration during transport or
transfer may lead to pre-hydration and carbonation, both of which might be
indicated by increased loss of ignition.
Bulk density
When cement is mixed with water, the water replaces areas where there would
normally be air. Because of that, the bulk density of cement is not very important.
Cement has a varying range of density depending on the cement composition
percentage. The density of cement may be anywhere from 62 to 78 pounds per cubic
foot.
Specific Gravity (Relative Density)
Specific gravity is generally used in mixture proportioning calculations.
Portland cement has a specific gravity of 3.15, but other types of cement (for
example, Portland-blast-furnace-slag and Portland-pozzolan cement) may have
specific gravities of about 2.90.
Chemical Properties of Cement
The raw materials for cement production are limestone (calcium), sand or clay
(silicon), bauxite (aluminium) and iron ore, and may include shells, chalk, marl,
shale, clay, blast furnace slag, slate. Chemical analysis of cement raw materials
provides insight into the chemical properties of cement.
Tricalcium aluminate (C3A)
Low content of C3A makes the cement sulphate-resistant. Gypsum reduces the
hydration of C3A, which liberates a lot of heat in the early stages of hydration. C3A
does not provide any more than a little amount of strength.
Type I cement: contains up to 3.5% SO3 (in cement having more than 8% C3A)
Type II cement: contains up to 3% SO3 (in cement having less than 8% C3A)
Tricalcium silicate (C3S)
C3S causes rapid hydration as well as hardening and is responsible for the cement’s
early strength gain an initial setting.
Dicalcium silicate (C2S)
As opposed to tricalcium silicate, which helps early strength gain, dicalcium silicate
in cement helps the strength gain after one week.
Tetracalcium Alumino Ferrite (C4AF)
Ferrite is a fluxing agent. It reduces the melting temperature of the raw
materials in the kiln from 3,000°F to 2,600°F. Though it hydrates rapidly, it does
not contribute much to the strength of the cement.

55
Magnesia (MgO)
The manufacturing process of Portland cement uses magnesia as a raw
material in dry process plants. An excess amount of magnesia may make the cement
unsound and expansive, but a little amount of it can add strength to the cement.
Production of MgO-based cement also causes less CO2 emission. All cement is
limited to a content of 6% MgO.
Sulphur trioxide (Anhydrous Sulphide) SO3
Sulphur trioxide in excess amount can make cement unsound.
Iron oxide/ Ferric oxide
Aside from adding strength and hardness, iron oxide or ferric oxide is mainly
responsible for the colour of the cement.
Alkalis
The amounts of potassium oxide (K2O) and sodium oxide (Na2O) determine
the alkali content of the cement. Cement containing large amounts of alkali can
cause some difficulty in regulating the setting time of cement. Low alkali cement,
when used with calcium chloride in concrete, can cause discoloration. In slag-lime
cement, ground granulated blast furnace slag is not hydraulic on its own but is
"activated" by addition of alkalis. There is an optional limit in total alkali content of
0.60%, calculated by the equation Na2O + 0.658 K2O.
Free lime
Free lime, which is sometimes present in cement, may cause expansion.
Silica fumes
Silica fume is added to cement concrete in order to improve a variety of
properties, especially compressive strength, abrasion resistance and bond strength.
Though setting time is prolonged by the addition of silica fume, it can grant
exceptionally high strength. Hence, Portland cement containing 5-20% silica fume
is usually produced for Portland cement projects that require high strength.
Alumina
Cement containing high alumina has the ability to withstand frigid
temperatures since alumina is chemical-resistant. It also quickens the setting but
weakens the cement.
3.1 Ingredients – Functions
Ordinary Portland cement contains two basic ingredients, namely argillaceous
and calcareous. In argillaceous materials, clay predominates and in calcareous
materials, calcium carbonate predominates. Good ordinary cement contains
following ingredients.
1. Lime (CaO) ………. 62%

56
2. silica (Sio2) ………. 22%
3. Alumina (Al2 o3) ………. 5%
4. Calcium sulphate (CaSo4) ………. 4%
5. Iron Oxide (Fe2 O3) ………. 3%
6. Magnesia (MgO) ………. 2%
7. Sulphur ………. 1%
8. Alkalis ………. 1%
Functions of Ingredients:
1. Lime: Lime is the important ingredient of cement and its proportion is to be
maintained carefully. Lime in excess makes the cement unsound and causes the
cement to expand and disintegrate. On the other hand, if lime is in deficiency the
strength of the cement is decreased and it causes cement to set quickly
2. Silica: This also an important ingredient of cement and it gives or imparts quick
setting property to imparts strength to cement.
3.Alumina: This ingredient imparts quick setting properly to cement. Express
alumina weakens the cement.
4. Calcium Sulphate: This ingredient is in the form of gypsum and its function is
to increase the initial setting time of cement.
5. Magnesia: The small amount of this ingredient imparts hardness and colour to
cement.
6. Sulphur: A very small amount of sulphur is useful in making sound cement. If it
is in excess, it causes the cement to become unsound.
7. Alkalis: Most of the alkalis present in raw material are carried away by the flue
gases during heating and only small quantity will be left. If they are in excess in
cement, efflorescence is caused.
The oxide composition of ordinary PC

57
A Typical Chemical Composition of Ordinary Portland Cement (OPC)
Composition of Cement Clinker
The various constituents combine in burning and form cement clinker. The
compounds formed in the burning process have the properties of setting and
hardening in the presence of water. They are known as Bogue compounds after the
name of Bogue who identified them. Le-Chatelier and Tornebohm have referred these
compounds as Alite (C3S), Belite (C2S), Celite (C3A) and Felite (C4AF). The following
Bogue compounds are formed during clinkering process.
The principal mineral Formula Name Symbol
compounds in Portland cement
1. Tricalcium silicate - 3CaO.SiO2 - Alite - C3S
2. Dicalcium silicate - 2CaO.SiO2 – Belite - C2S
3. Tricalcium aluminate - 3CaO.Al2O3 - Celite - C3A
4. Tetracalcium alumino ferrite - 4CaO.Al2O3.Fe2O3 - Felite - C4AF
The properties of Portland cement vary markedly with the proportions of the
above four compounds, reflecting substantial difference between their individual
behaviour.
Tricalcium silicate
It is supposed to be the best cementing material and is well burnt cement. It
is about 25-50% (normally about 40 per cent) of cement. It renders the clinker easier
to grind, increases resistance to freezing and thawing, hydrates rapidly generating
high heat and develops an early hardness and strength.
However, raising of C3S content beyond the specified limits increases the heat
of hydration and solubility of cement in water. The hydrolysis of C3S is mainly

58
responsible for 7-day strength and hardness. The rate of hydrolysis of C3S and the
character of gel developed are the main causes of the hardness and early strength
of cement paste. The heat of hydration is 500 J/g.
Dicalcium silicate
It is about 25-40% (normally about 32 per cent) of cement. It hydrates and
hardens slowly and takes long time to add to the strength (after a year or more). It
imparts resistance to chemical attack. Raising of C2S content renders clinker harder
to grind, reduces early strength, decreases resistance to freezing and thawing at
early ages and decreases heat of hydration.
The hydrolysis of C2S proceeds slowly. At early ages, less than a month, C2S
has little influence on strength and hardness. While after one year, its contribution
to the strength and hardness is proportionately almost equal to C3S. The heat of
hydration is 260 J/g.
Tricalcium aluminate
It is about 5-11% (normally about 10.5 per cent) of cement. It rapidly reacts
with water and is responsible for flash set of finely grounded clinker. The rapidity of
action is regulated by the addition of 2-3% of gypsum at the time of grinding cement.
Tricalcium aluminate is responsible for the initial set, high heat of hydration and
has greater tendency to volume changes causing cracking.
Raising the C3A content reduces the setting time, weakens resistance to
sulphate attack and lowers the ultimate strength, heat of hydration and contraction
during air hardening. The heat of hydration of 865 J/g.
Tetracalcium alumino ferrite
It is about 8–14% (normally about 9 per cent) of cement. It is responsible for
flash set but generates less heat. It has poorest cementing value. Raising the C4AF
content reduces the strength slightly. The heat of hydration is 420 J/g.
Calculation of Compound Composition of Portland Cement
Bogue developed a method for calculating the compound composition from
the oxide analysis of a cement. This method is based upon cooling of the clinker at
such rate that equilibrium is maintained. Although equilibrium does not usually
obtain in commercial operations, valuable information can be derived from such
calculations. Cement and hydration of Portland cement can be schematically
represented as below:

59
Hydration of cement
The chemical reaction between cement and water is known as hydration of
cement. The reaction takes place between the active components of cement (C4AF,
C3A, C3S and C2S) and water. The factors responsible for the physical properties of
concrete are the extent of hydration of cement and the resultant microstructure of
the hydrated cement.
When the cement comes in contact with water, the hydration products start
depositing on the outer periphery of the nucleus of hydrated cement. This reaction
proceeds slowly for 2-5 hours and is called induction or dormant period.
As the hydration proceeds, the deposit of hydration products on the original
cement grain makes the diffusion of water to unhydrated nucleus more and more
difficult, consequently reducing the rate of hydration with time. At any stage of
hydration, the cement paste consists of gel (a fine-grained product of hydration
having large surface area collectively), the unreacted cement, calcium hydroxide,
water and some minor compounds.
The crystals of the various resulting compounds gradually fill the space
originally occupied by water, resulting in the stiffening of the mass and subsequent
development of the strength. The reactions of the compounds and their products are
as follows:

60
C3S + H2O → C–S–H* + Ca (OH)2
C2S + H2O → C–S–H + Ca (OH)2 H* is H2O
C3A + H2O → C3AH6 S is SO3
C3A + H2O + CaSO4 → CA C S H12
(Calcium sulpho-aluminate)
C4AF + H2O → C3AH6 + CFH
The product C–S–H gel represents the calcium silicate hydrate also known as
tobermorite gel which is the gel structure. The hydrated crystals are extremely small,
fibrous, platey or tubular in shape varying from less than 2 mm to 10 mm or more.
The C–S–H phase makes up 50–60% of the volume of solids in a completely hydrated
Portland cement paste and is, therefore, the most important in determining the
properties of the paste. The proposed surface area for C–S– H is of the order of 100–
700 m2/g and the solid-to-solid distance being about 18 Å. The Ca (OH)2 liberated
during the silicate phase crystallizes in the available free space.
The calcium hydroxide crystals also known as portlandite consists of 20-25%
volume of the solids in the hydrated paste. These have lower surface area and their
strength contributing potential is limited. The gel must be saturated with water if
hydration is to continue. The calcium hydroxide crystals formed in the process
dissolve in water providing hydroxyl (OH–) ions, which are important for the
protection of reinforcement in concrete. As hydration proceeds, the two crystal types
become more heavily interlocked increasing the strength, though the main
cementing action is provided by the gel which occupies two-thirds of the total mass
of hydrate.

61
Heat of Hydration
The reaction of cement with water is exothermic. The reaction liberates a
considerable quantity of heat. This liberation of heat is called heat of hydration. This
is clearly seen if freshly mixed cement is put in a vacuum flask and the temperature
of the mass is read at intervals.
The study and control of the heat of hydration becomes important in the
construction of concrete dams and other mass concrete constructions. It has been
observed that the temperature in the interior of large mass concrete is 50°C above
the original temperature of the concrete mass at the time of placing and this high
temperature is found to persist for a prolonged period. Fig 1.2 shows the pattern of
liberation of heat from setting cement1.4 and during early hardening period.
On mixing cement with water, a rapid heat evolution, lasting a few minutes,
occurs. This heat evolution is probably due to the reaction of solution of aluminates
and sulphate (ascending peak A). This initial heat evolution ceases quickly when the
solubility of aluminate is depressed by gypsum. (descending peak A). Next heat
evolution is on account of formation of ettringite and also may be due to the reaction
of C3S (ascending peak B). Refer Fig. 1.2.
Different compounds hydrate at different rates and liberate different
quantities of heat. Fig. 1.3 shows the rate of hydration of pure compounds. Since
retarders are added to control the flash setting properties of C3A, actually the early
heat of hydration is mainly contributed from the hydration of C3S. Fineness of
cement also influences the rate of development of heat but not the total heat. The
total quantity of heat generated in the complete hydration will depend upon the
relative quantities of the major compounds present in a cement.
Analysis of heat of hydration data of large number of cements, Verbec and
Foster1.5 computed heat evolution of four major compounds of cement. Table 1.7.
shows the heats of hydration of four compounds.

62
Since the heat of hydration of cement is an additive property, it can be
predicted from an expression of the type H = aA + bB + cC + dD
Where H represents the heat of hydration, A, B, C, and Dare the percentage
contents of C3S, C2S, C3A and C4AF. and a, b, c and d are coefficients representing
the contribution of 1 per cent of the corresponding compound to the heat of
hydration. Normal cement generally produces 89-90 cal/g in 7 days and 90 to 100
cal/g in 28 days.
The hydration process is not an instantaneous one. The reaction is faster in
the early period and continues indefinitely at a decreasing rate. Complete hydration
cannot be obtained under a period of one year or more unless the cement is very
finely ground and reground with excess of water to expose fresh surfaces at intervals.
Otherwise, the product obtained shows unattacked cores of tricalcium silicate
surrounded by a layer of hydrated silicate, which being relatively impervious to
water, renders further attack slow. It has been observed that after 28 days of curing,
cement grains have been found to have hydrated to a depth of only 4μ. It has also
been observed that complete hydration under normal condition is possible only for
cement particles smaller than 50μ.

63
A grain of cement may contain many crystals of C3S or others. The largest
crystals of C3S or C2S are about 40μ. An average size would be 15-20μ. It is
probable that the C2S crystals present in the surface of a cement grain may get
hydrated and a more reactive compound like C3S lying in the interior of a cement
grain may not get hydrated.
The hydrated product of the cement compound in a grain of cement adheres
firmly to the unhydrated core in the grains of cement. That is to say unhydrated
cement left in a grain of cement will not reduce the strength of cement mortar or
concrete, as long as the products of hydration are well compacted. Abrams obtained
strength of the order of 280 MPa using mixes with a water/cement ratio as low as
0.08. Essentially, he has applied tremendous pressure to obtain proper compaction
of such a mixture.
Owing to such a low water/cement ratio, hydration must have been possible
only at the surface of cement grains, and a considerable portion of cement grains
must have remained in an unhydrated condition.
The present-day High-Performance concrete is made with water cement ratio
in the region of 0.25 in which case it is possible that a considerable portion of cement
grain remains unhydrated in the core. Only surface hydration takes place. The
unhydrated core of cement grain can be deemed to work as very fine aggregates in
the whole system.
Calcium Silicate Hydrates
During the course of reaction of C3S and C2S with water, calcium silicate
hydrate, abbreviated C-S-H and calcium hydroxide, Ca (OH)2 are formed. Calcium
silicate hydrates are the most important products. It is the essence that determines
the good properties of concrete.

64
It makes up 50-60 per cent of the volume of solids in a completely hydrated
cement paste. The fact that term C-S-H is hyphenated signifies that C-S-H is not a
well-defined compound. The morphology of C-S-H shows a poorly crystalline fibrous
mass. It was considered doubtful that the product of hydration of both C3S and C2S
results in the formation of the same hydrated compound. But later on, it was seen
that ultimately the hydrates of C3S and C2S will turn out to be the same. The
following are the approximate equations showing the reactions of C3S and C2S with
water.
However, the simple equations given above do not bring out the complexities
of the actual reactions. It can be seen that C3S produces a comparatively lesser
quantity of calcium silicate hydrates and more quantity of Ca (OH)2 than that formed
in the hydration of C2S. Ca (OH)2 is not a desirable product in the concrete mass,
it is soluble in water and gets leached out making the concrete porous, particularly
in hydraulic structures. Under such conditions it is useful to use cement with higher
percentage of C2S content.

65
C3S readily reacts with water and produces more heat of hydration. It is
responsible for early strength of concrete. A cement with more C3S content is better
for cold weather concreting. The quality and density of calcium silicate hydrate
formed out of C3S is slightly inferior to that formed by C2S. The early strength of
concrete is due to C3S. C2S hydrates rather slowly. It is responsible for the later
strength of concrete. It produces less heat of hydration. The calcium silicate hydrate
formed is rather dense and its specific surface is higher. In general, the quality of
the product of hydration of C2S is better than that produced in the hydration of
C3S. Fig 1.4 shows the development of strength of pure compounds.
Calcium Hydroxide
The other products of hydration of C3S and C2S is calcium hydroxide. In
contrast to the C-S-H, the calcium hydroxide is a compound with a distinctive
hexagonal prism morphology. It constitutes 20 to 25 per cent of the volume of solids
in the hydrated paste. The lack of durability of concrete, is on account of the presence
of calcium hydroxide. The calcium hydroxide also reacts with sulphates present in
soils or water to form calcium sulphate which further reacts with C3A and cause
deterioration of concrete. This is known as sulphate attack.
To reduce the quantity of Ca (OH)2 in concrete and to overcome its bad effects
by converting it into cementitious product is an advancement in concrete
technology. The use of blending materials such as fly ash, silica fume and such other
pozzolanic materials are the steps to overcome bad effect of Ca (OH)2 in concrete.
This aspect will be dealt in greater detail later.

66
Calcium Hydroxide
The only advantage is that Ca (OH)2, being alkaline in nature maintain pH
value around 13 in the concrete which resists the corrosion of reinforcements.
Structure of Hydrated Cement
To understand the behaviour of concrete, it is necessary to acquaint ourselves
with the structure of hydrated hardened cement paste. If the concrete is considered
as two-phase material, namely, the paste phase and the aggregate phase, the
understanding of the paste phase becomes more important as it influences the
behaviour of concrete to a much greater extent.
It will be discussed later that the strength, the permeability, the durability,
the drying shrinkage, the elastic properties, the creep and volume change properties
of concrete is greatly influenced by the paste structure. The aggregate phase though
important, has lesser influence on the properties of concrete than the paste phase.

67
Therefore, in our study to understand concrete, it is important that we have a
deep understanding of the structure of the hydrated hardened cement paste at a
phenomenological level.
Transition Zone
Concrete is generally considered as two-phase material i.e., paste phase and
aggregates phase. At macro level it is seen that aggregate particles are dispersed in
a matrix of cement paste. At the microscopic level, the complexities of the concrete
begin to show up, particularly in the vicinity of large aggregate particles.
This area can be considered as a third phase, the transition zone, which
represents the interfacial region between the particles of coarse aggregate and
hardened cement paste. Transition zone is generally a plane of weakness and,
therefore, has far greater influence on the mechanical behaviour of concrete.
Although transition zone is composed of same bulk cement paste, the quality
of paste in the transition zone is of poorer quality. Firstly, due to internal bleeding,
water accumulate below elongated, flaky and large pieces of aggregates. This reduces
the bond between paste and aggregate in general. If we go into little greater detail,
the size and concentration of crystalline compounds such as calcium hydroxide and
ettringite are also larger in the transition zone. Such a situation account for the
lower strength of transition zone than bulk cement pastes in concrete.
Measurements of heat evolved during the exothermic reactions also gives
valuable insight into the nature of hydration reactions. Since approximately 50% of
a total heat evolution occurs during the first 3 days of hydration, a continuous
record of the rate of heat liberation during this time is extremely useful in
understanding the degree of hydration and the resultant structure of the hardening
cement paste. Fig. 1.5 shows the composition of cement pastes at different stages of
hydration.

68
The mechanical properties of the hardened concrete depend more on the
physical structure of the products of hydration than on the chemical composition of
the cement. Mortar and concrete, shrinks and cracks, offers varying chemical
resistance to different situations, creeps in different magnitude, and in short,
exhibits complex behaviour under different conditions.
Even though it is difficult to explain the behaviour of concrete fully and
exactly, it is possible to explain the behaviour of concrete on better understanding
of the structure of the hardened cement paste. Just as it is necessary for doctors to
understand in great detail the anatomy of the human body to be able to diagnose
disease and treat the patient with medicine or surgery, it is necessary for concrete
technologists to fully understand the structure of hardened cement paste in great
detail to be able to appreciate and rectify the ills and defects of the concrete.
For simplicity’s sake we will consider only the structure of the paste phase.
Fresh cement paste is a plastic mass consisting of water and cement. With the lapse

69
of time, say one hour, the hardening paste consists of hydrates of various
compounds, unhydrated cement particles and water. With further lapse of time the
quantity of unhydrated cement left in the paste decreases and the hydrates of the
various compounds increase. Some of the mixing water is used up for chemical
reaction, and some water occupies the gel-pores and the remaining water remains
in the paste.
After a sufficiently long time (say a month) the hydrated paste can be
considered to be consisting of about 85 to 90% of hydrates of the various compounds
and 10 to 15 per cent of unhydrated cement. The mixing water is partly used up in
the chemical reactions. Part of it occupies the gel-pores and the remaining water
unwanted for hydration or for filling in the gel-pores causes capillary cavities.
These capillary cavities may have been fully filled with water or partly with
water or may be fully empty depending upon the age and the ambient temperature
and humidity conditions. Figure 1.6 (a) and (b) schematically depict the structure of
hydrated cement paste. The dark portion represents gel. The small gap within the
dark portion represents gel-pores and big space such as marked “c” represents
capillary cavities.1.6 Fig. 1.7 represents the microscopic schematic model of
structure of hardened cement paste.
Rate of Hydration
The reaction of compound C3A with water is very fast and is responsible for
flash setting of cement (stiffening without strength development) and thus it will
prevent the hydration of C3S and C2S. However, calcium sulphate (CaSO4) present
in the clinker dissolves immediately in water and forms insoluble calcium
sulphoaluminate. It deposits on the surface of C3A forming a colloidal membrane
and consequently retards the hydration of C3A. The amount of CaSO4 is adjusted
to leave a little excess of C3A to hydrate directly. This membrane in the process
breaks because of the pressure of the compounds formed during hydration and then
again C3A becomes active in the reaction.
The hardening of C3S can be said to be catalysed by C3A and C3S becomes
solely responsible for gain of strength up to 28 days by growth and interlocking of
C-S-H gel. The increase in strength at later age is due to hydration of C2S.
Water Requirement for Hydration
About an average 23 per cent (24 per cent C3S, 21 per cent C2S) of water by
weight of cement is required for complete hydration of Portland cement. This water
combines chemically with the cement compounds and is known as bound water.
Some quantity of water, about 15 per cent by weight of cement, is required to fill the
cement gel pores and is known as gel water.

70
Therefore, a total of 38 per cent of water by weight of cement is required to
complete the chemical reaction. The general belief that a water/cement ratio less
than 0.38 should not be used in concrete because for the process of hydration, the
gel pores should saturate – is not valid. This is because as even if excess water is
present, complete hydration of cement never takes place due to deposition of
hydration products. As a matter of fact, water/cement ratio less than 0.38 is very
common for high strength concretes. If excess water is present, it will lead to
capillary cavities.
Manufacture of Cement
Calcareous and argillaceous raw materials are used in the manufacture of
Portland cement. The calcareous materials used are cement rock, limestone, marl,
chalk and marine shell. The argillaceous materials consist of silicates of alumina in

71
the form of clay, shale, slate and blast furnace slag. From the above materials, others
like lime, silica, alumina, iron oxide and small quantities of other chemicals are
obtained. Cement can be manufactured either by dry process or wet process.
Dry Process
The dry process is adopted when the raw materials are quite hard. The process
is slow and the product is costly. Limestone and clay are ground to fine powder
separately and are mixed. Water is added to make a thick paste. The cakes of this
paste, which contain about 14 per cent of moisture, are dried and are charged into
rotary kiln (Fig. 5.3).
Fig. 5.3 Rotary Kiln
The product obtained after calcination in rotary kiln is called clinker. The
clinker is obtained as a result of incipient fusion and sintering at a temperature of
about 1400°- 1500°C. Because ferric oxide has lower melting point than the other
oxides, it acts as a flux. Aeration of cement clinker, which is commonly practised to
slake free lime, also causes an absorption of some moisture and carbon dioxide.
Absorption of moisture tends to decrease the setting whereas that of carbon dioxide
accelerates setting.
The clinker is cooled rapidly to preserve the metastable compounds and their
solid solutions — dispersion of one solid in another — which are made as the clinker
is heated. Clinker is then cooled and ground in tube mills (Fig. 5.4), where 2-3% of
gypsum is added.

72
Fig. 5.4 Rotary Kiln
Generally, cement is stored in bags of 50 kg. A flow diagram of dry process is
shown in Fig. 5.5. The purpose of adding gypsum is to coat the cement particles by
interfering with the process of hydration of the cement particles. This retard the
setting of cement.

73
Fig. 5.5 Flow Diagram of Cement Manufacture – Dry Process

74
Wet Process
The operations in the wet process of cement manufacture are mixing, burning
and grinding. The crushed raw materials are fed into ball mill (Fig. 5.6) and a little
water is added.
Fig 5.6 Ball Mill
On operating the ball mill, the steel balls in it pulverize the raw materials
which form a slurry with water. This slurry is passed to silos (storage tanks), where
the proportioning of the compounds is adjusted to ensure desired chemical
composition. The corrected slurry having about 40 per cent moisture content, is
then fed into rotary kiln (Fig. 5.4) where it loses moisture and forms into lumps or
nodules. These are finally burned at 1500-1600°C. The nodules change to clinker at
this temperature. Clinker is cooled and then ground in tube mills. While grinding
the clinker, about 3 per cent gypsum is added. The cement is then stored in silos
from where it is supplied. A flow diagram of manufacturing cement by wet process
is shown in Fig. 5.7.
Comparison of Wet and Dry Process:
The chief advantages of the wet process are the low cost of excavating and grinding
raw materials, the accurate control of composition and homogeneity of the slurry,
and the economical utilization of fuel through the elimination of separated drying
operations. On the other hand the longer kilns, essential in the wet process, cost
more and are less responsive to a variable clinker demand than the short kilns which
can be used in the dry process.

75
Fig. 5.7 Flow Diagram of Cement Manufacture – Wet Process

76
Types of Cement
Cements of unique characteristics for desired performance in a given
environment are being manufactured by changing the chemical composition of OPC
or by using additives, or by using different raw materials. Some of the cements
available in the market are as follows.
Rapid Hardening Portland Cement(IS: 8041)
It has high lime content and can be obtained by increasing the C3S content but is
normally obtained from OPC clinker by finer grinding (450 m2/kg). The basis of
application of rapid hardening cement (RHC) is hardening properties and heat
emission rather than setting rate. This permits addition of a little more gypsum
during manufacture to control the rate of setting. RHC attains same strength in one
day which an ordinary cement may attain in 3 days. However, it is subjected to large
shrinkage and water requirement for workability is more. The cost of rapid
hardening cement is about 10 per cent more than the ordinary cement. Concrete
made with RHC can be safely exposed to frost, since it matures more quickly.
Properties
Initial setting time 30 minutes (minimum)
Final setting time l0 hours (maximum)
1 day 16.0 N/mm2
3 day 27.5 N/mm2
Uses
It is suitable for repair of roads and bridges and when load is applied in a short
period of time.
High Alumina Cement(IS: 6452)
This is not a type of Portland cement and is manufactured by fusing 40 per
cent bauxite, 40 per cent lime, 15 per iron oxide with a little of ferric oxide and silica,
magnesia, etc. (Table 5.5) at a very high temperature. The alumina content should
not be less than 32%. The resultant product is ground finely. The main cement
ingredient is monocalcium aluminate CA which interacts with water and forms
dicalcium octahydrate hydroaluminate and aluminium oxide hydrate.
2(CaO.AL2O3.10H2O) + H2O = 2CaO.Al2O3.8H2O + 2Al(OH)2
The dicalcium hydroaluminate gel consolidates and the hydration products
crystallise. The rate of consolidation and crystallisation is high leading to a rapid
gain of strength. Since C3A is not present, the cement has good sulphate resistance.

77
Properties
It is not quick setting: initial setting time (minimum) is 30 minutes, even up to 2
hours. The final setting time should not exceed 600 minutes. It attains strength in
24 hours, high early strength, high heat of hydration and resistance to chemical
attack. Compressive strength after one day is 30.0 N/mm2 and after 3 days it is
35.0 N/mm2. After setting and hardening, there is no free hydrated lime as in the
case of ordinary Portland cement. The fineness of the cement should not be less
than 225 m2/kg. The cement should not have expansion more than 5 mm.
Uses
It is resistant to the action of fire, sea water, acidic water and sulphates and is used
as refractory concrete, in industries and is used widely for precasting. It should not
be used in places where temperature exceeds 18°C.
Supersulphated Portland Cement (IS: 6909)
It is manufactured by intergrinding or intimately blending a mixture of
granulated blast furnace slag not less than 70 per cent, calcium sulphate and small
quantity of 33 grade Portland cement. In this cement tricalcium aluminate which is
susceptible to sulphates is limited to less than 3.5 per cent. Sulphate resisting
cement may also be produced by the addition of extra iron oxide before firing; this
combines with alumina which would otherwise form C3A, instead forming C4AF
which is not affected by sulphates. It is used only in places with temperature below
40°C.
Water resistance of concretes from super sulphate Portland cements is higher
than that of common Portland cements because of the absence of free calcium oxide
hydrate. In super sulphate Portland cements the latter is bound by slag into calcium
hydro aluminates of low solubility and calcium hydro silicates of low basicity,
whereas concretes from Portland cement carry a large amount of free calcium oxide
hydrate which may wash out and thus weaken them.

78
Super sulphate Portland cement has satisfactory frost and air resistances, but
it is less resistant than concrete from Portland cement due to the fact that hydro
silicates of low basicity show greater tendency to deformation from humidity
fluctuations and resist the combined action of water and frost less effectively.
Properties
It has low heat of hydration and is resistant to chemical attacks and in particular
to sulphates. Compressive strength should be as follows:
72 ± 1 hour _ 15 N/mm2
168 ± 2 hours _ 22 N/mm2
672 ± 4 hours _ 30 N/mm2
It should have a fineness of 400 m2/kg. The expansion of cement is limited to
5 mm. The initial setting time of the cement should not be less than 30 minutes,
and the final setting time should not be more than 600 minutes.
Uses
Supersulphated Portland cement is used for similar purpose as common
Portland cement. But owing to its higher water-resisting property, it should be
preferred in hydraulic engineering installations and also in constructions intended
for service in moist media. RCC pipes in ground water, concrete structures in
sulphate bearing soils, sewers carrying industrial effluents, concrete exposed to
concentrated sulphates of weak mineral acids are some of the examples of this
cement. This cement should not be used in constructions exposed to frequent
freezing-and-thawing or moistening-and-drying conditions.
Sulphate Resisting Portland Cement (is: 12330)
In this cement the amount of tricalcium aluminate is restricted to on
acceptably low value (< 5). It should not be mistaken for super sulphated cement. It
is manufactured by grinding and intimately mixing together calcareous and
argillaceous and/ or other silica, alumina and iron oxide bearing materials. The
Materials are burnt to clinkering temperature. The resultant clinker is ground to
produce the cement. No material is added after burning except gypsum and not more
than one per cent of air-entraining agents are added.
Properties
The specific surface of the cement should not be less than 225 m2/kg. The
expansion of cement is limited to 10 mm and 0.8 per cent, when tested by Le-
chatelier method and autoclave test, respectively. The setting times are same as that
for ordinary Portland cement.
The compressive strength of the cubes should be as follows.

79
72 ± 1 hour _ 10 N/mm2
168 ± 2 hours _ 16 N/mm2
672 ± 4 hours _ 33 N/mm2
It should have a fineness of 400 m2/kg. The expansion of cement is limited to
5 mm. The initial setting line of the cement should not be less than 30 mm and the
final setting time should not be more than 600 mm.
Uses
This cement can be used as an alternative to order Portland cement or
Portland pozzolana cement or Portland slag cement under normal conditions. Its use
however is restricted where the prevailing temperature is below 40°C. Use of
sulphate resisting cement is particularly beneficial in conditions where the concrete
is exposed to the risk of deterioration due to sulphate attack; concrete in contact
with soils or ground waters containing excessive sulphate as well as concrete in sea
water or exposed directly to sea coast.
Portland Slag Cement (IS: 455)
It is manufactured either by intimately intergrinding a mixture of Portland
cement clinker and granulated slag with addition of gypsum or calcium sulphate, or
by an intimate and uniform blending of Portland cement and finely ground
granulated slag.
Slag is a non-metallic product consisting essentially of glass containing
silicates and aluminosilicates of lime and other bases, as in the case of blast-furnace
slag, which is developed simultaneously with iron in blast furnace or electric pig iron
furnace. Granulated slag is obtained by further processing the molten slag by rapid
chilling or quenching it with water or steam and air. The slag constituent in the
cement varies between 25 to 65 per cent.
Properties
The chemical requirements of Portland slag cement are same as that of 33
grade Portland cement. The specific surface of slag cement should not be less than
225 m2/kg. The expansion of the cement should not be more than 10 mm and 0.8
per cent when tested be Le Chatelier method and autoclave test, respectively. The
initial and final setting times and compressive strength requirements are same as
that for 33 grade ordinary Portland cement.
Uses
This cement can be used in all places where OPC is used. However, because
of its low heat of hydration it can also be used for mass concreting, e.g., dams,
foundations, etc.

80
Low Heat Portland Cement (IS: 12600)
To limit the heat of hydration of low heat Portland cement (LHC), the
tricalcium aluminate component in cement is minimised and a high percentage of
dicalcium silicate and tetracalcium alumino ferrite is added. The heat of hydration
should not be more than 272 and 314 J/g at the end of 7 and 28 days respectively.
The rate of development of strength is slow but the ultimate strength is same as that
of OPC. To meet this requirement, specific surface of cement is increased to about
3200 cm2/g.
Properties
Less heat is evolved during setting low heat Portland cement. When tested by
Le Chatelier method and autoclave test the expansion should not be more than 10
mm and 0.8%, respectively. The minimum initial setting time should not be less
than 60 minutes, and the final setting should not be more than 600 minutes.
The compressive strength should be as follows.
72 ± 1 hour _ 10 N/mm2
168 ± 2 hours _ 16 N/mm2
672 ± 4 hours _ 35 N/mm2
Uses
It is most suitable for large mass concrete works such as dams, large raft
foundations, etc.
Portland Pozzolana Cement (IS: 1489 (Part 1))
It is manufactured by grinding Portland cement clinker and pozzolana (usually
fly ash 10-25% by mass of PPC) or by intimately and uniformly blending Portland
cement and fine pozzolana. Pozzolana (burnt clay, shale, or fly ash) has no
cementing value itself but has the property of combining with lime to produce a
stable lime-pozzolana compound which has definite cementitious properties. Free
lime present in the cement is thus removed.
Consequently, the resistance to chemical attack increases making it suitable
for marine works. The hardening of Portland pozzolana cement consists in hydration
of Portland cement clinker compounds and then in interaction of the pozzolana with
calcium hydroxide released during the hardening of clinker. At the same time,
calcium hydroxide is bound into a water-soluble calcium hydro silicate according to
the reaction
Ca (OH)2 + SiO2 + (n – 1) H2O = CaO.SiO2. nH2O

81
with the effect that pozzolana Portland cement acquires greater water-resisting
property than
ordinary Portland cement.
Properties
These have lower rate of development of strength but ultimate strength is
comparable with ordinary Portland cement.
Compressive Strength 72 ± 1 hr 16.0 N/mm2
168 ± 2 hrs 22.0 N/mm2
672 ± 4 hrs 33.0 N/mm2
The initial and the final setting times are 30 minutes (minimum) and 600 minutes
(maximum), respectively. The drying shrinkage should not be more than 0.15% and
the fineness should not be less than 300 m2/kg.
Uses
It has low heat evolution and is used in the places of mass concrete such as
dams and in places of high temperature.
Quick Setting Portland Cement
The quantity of gypsum is reduced and small percentage of aluminium
sulphate is added. It is ground much finer than ordinary Portland cement.
Properties
Initial setting time = 5 minutes
Final setting time = 30 minutes
Uses
It is used when concrete is to be laid under water or in running water.
Masonry Cement (IS 3466)
The Portland cement clinker is ground and mixed intimately with pozzolanic
material (fly ash or calcined clay), or non-pozzolanic (inert) materials (limestone,
conglomerate’s, dolomite, granulated slag) and waste materials (carbonated sludge,
mine tailings) and gypsum and air entraining plasticizer in suitable proportions. The
physical requirements of masonry cement are as follows.
1. Fineness: Residue on 45-micron IS Sieve, Max, Percent (by wet sieving) 15
2. Setting Time (by Vicat Apparatus):
(a) Initial, Min 90 min
(b) Final, Max 24 h
3. Soundness:
(a) Le-Chatelier expansion, Max 10 mm

82
(b) Autoclave expansion, Max 1 per cent
4. Compressive Strength: Average strength of not less than 3 mortar cubes of 50 mm
size, composed of 1 part masonry cement and 3 parts standard sand by volume, Min
7 days 2.5 MPa
28 days 5 MPa
5. Air Content: Air content of mortar composed of 1 part masonry cement and 3
parts standard sand by volume, Min = 6 per cent
6. Water Retention: Flow after suction of mortar composed of 1 part masonry cement
and 3 parts standard sand by volume, Min = 60 per cent of original flow
White and Coloured Portland Cement (IS: 8042)
It is manufactured from pure white chalk and clay free from iron oxide.
Greyish colour of cement is due to iron oxide. So, the iron oxide is reduced and
limited below 1 per cent. Coloured cements are made by adding 5 to 10 per cent
colouring pigments before grinding. These cements have same properties as that of
ordinary
Portland cement and are non-staining because of low number of soluble
alkalis. Sodium alumino fluoride is added during burning which acts as a catalyst
in place of iron.
Properties
Loss on ignition of white cement is nil. The compressive and transverse
strength of this cement is 90 per cent of that of 33 grade ordinary Portland cement.
Uses
These cements are used for making terrazzo flooring, face plaster of walls
(stucco), ornamental works, and casting stones.
Air Entraining Cement
Vinsol resin or vegetable fats and oils and fatty acids are ground with ordinary
cement. These materials have the property to entrain air in the form of fine tiny air
bubbles in concrete.
Properties
Minute voids are formed while setting of cement which increases resistance
against freezing and scaling action of salts. Air entrainment improves workability
and water/cement ratio can be reduced which in turn reduces shrinkage, etc.
Uses
Air entraining cements are used for the same purposes as that of OPC.

83
Calcium Chloride Content
It is also known as extra rapid hardening cement and is made by adding 2 per
cent of calcium chloride. Since it is deliquescent, it is stored under dry conditions
and should be consumed within a month of its dispatch from the factory.
Properties
The rate of strength development is accelerated; a higher percentage of
calcium chloride causes excessive shrinkage. Strength gained after 1 day is 25 per
cent more and after 7 days about 20 per cent more than the ordinary Portland
cement.
Uses
It is very suitable for cold weathers.
Water Repellent Cement (IS: 8043)
It is also called hydrophobic cement. A small number of hydrophobic
surfactants such as stearic acid, boric acid or oleic acid is mixed with the ordinary
Portland cement during grinding of clinker. These substances are added in amounts
of 0.1 to 0.5% of the weight of cement in terms of dry admixtures.
These acids form a thin (monomolecular) film around the cement particles
which prevent the entry of atmospheric moisture. The film breaks down when the
concrete is mixed, and the normal hydration takes place.
When concrete is being prepared, hydrophobic admixtures plasticize the mix
and contribute to the formation of uniformly distributed fine pores in concrete as it
hardens and thus enhance its frost resistance. Hydrophobic cement also features
greater water resistance and water permeability.
The specific surface of hydrophobic cement should not be less than 350
m2/kg. The average compressive strength should not be less than
72 ± 1 hour _ 15.69 N/mm2
168 ± 2 hours _ 21.57 N/mm2
672 ± 4 hours _ 30.40 N/mm2
The weak points of hydrophobic cement are its small strength gain during the
initial period because of the hydrophobic films on cement grains which prevent the
interaction with water, but its 28-day strength is equal to that of ordinary Portland
cement.
Uses
It is most suitable for basements and for making water tight concrete.

84
Water Proof Cement
It is manufactured by adding stearates of Ca and Al and gypsum treated with
tannic acid, etc. at the time of grinding.
Properties
It is resistant to penetration of water.
Uses
Water retaining structures like tanks, reservoirs, retaining walls, swimming
pools, bridge piers, etc.
Refractory Concrete
An important use of high alumina cement is for making refractory concrete to
withstand high temperatures in conjunction with aggregate having heat resisting
properties. It is interesting to note that high alumina cement concrete loses
considerable strength only when subjected to humid condition and high
temperature. Desiccated high alumina cement concrete on subjecting to the high
temperature will undergo a little amount of conversion and will still have a
satisfactory residual strength. On complete desiccation the resistance of alumina
cement to dry heat is so high that the concrete made with this cement is considered
as one of the refractory materials.
At a very high temperature alumina cement concrete exhibits good ceramic
bond instead of hydraulic bond as usual with other cement concrete. Crushed
firebrick is one of the most commonly used aggregates for making refractory concrete
with high alumina cement. Such concrete can withstand temperature up to about
1350°C. Refractory concrete for withstanding temperature up to 1600°C can be
produced by using aggregates such as sillimanite, carborundum, dead-burnt
magnesite. The refractory concrete is used for foundations of furnaces, coke ovens,
boiler settings. It is also used in fire pits, construction of electric furnaces, ordinary
furnaces and kilns. High alumina cement can be used for making refractory mortars.
Rediset Cement
Accelerating the setting and hardening of concrete by the use of admixtures
is a common knowledge. Calcium chloride, lignosulfonates, and cellulose products
form the base of some of admixtures. The limitations on the use of admixtures and
the factors influencing the end properties are also fairly well known.
High alumina cement, though good for early strengths, shows retrogression of
strength when exposed to hot and humid conditions. A new product was needed for

85
use in the precast concrete industry, for rapid repairs of concrete roads and
pavements, and slip-forming.
In brief, for all jobs where the time and strength relationship were important.
In the PCA laboratories of USA, investigations were conducted for developing a
cement which could yield high strengths in a matter of hours, without showing any
retrogression. Regset cement was the result of investigation. Associated Cement
Company of India have developed an equivalent cement by name “REDISET”
Cement.
Oil-Well Cement (IS 8229-1986)
Oil-wells are drilled through stratified sedimentary rocks through a great
depth in search of oil. It is likely that if oil is struck, oil or gas may escape through
the space between the steel casing and rock formation. Cement slurry is used to seal
off the annular space between steel casing and rock strata and also to seal off any
other fissures or cavities in the sedimentary rock layer.
The cement slurry has to be pumped into position, at considerable depth
where the prevailing temperature may be up to 175°C. The pressure required may
go up to 1300 kg/cm2. The slurry should remain sufficiently mobile to be able to
flow under these conditions for periods up to several hours and then hardened fairly
rapidly. It may also have to resist corrosive conditions from sulphur gases or waters
containing dissolved salts. The type of cement suitable for the above conditions is
known as Oil-well cement.
The desired properties of Oil-well cement can be obtained in two ways: by
adjusting the compound composition of cement or by adding retarders to ordinary
Portland cement. Many admixtures have been patented as retarders. The
commonest agents are starches or cellulose products or acids. These retarding
agents prevent quick setting and retains the slurry in mobile condition to facilitate
penetration to all fissures and cavities. Sometimes workability agents are also added
to this cement to increase the mobility.
IRS-T 40 Special Grade Cement
IRS-T-40 special grade cement is manufactured as per specification laid down
by ministry of Railways under IRST40: 1985. It is a very finely ground cement with
high C3S content designed to develop high early strength required for manufacture
of concrete sleeper for Indian Railways.

86
IRS-T 40 special grade cement was originally made for
manufacturing concrete sleeper for railway line.
This cement can also be used with advantage for other applications where
high early strength concrete is required. This cement can be used for prestressed
concrete elements, high rise buildings, high strength concrete.
Storage of Cement
Portland cement is kept in sacks of 0.035 m3 (50 kg) capacity for local use.
These are stored for short period of time in air tight room avoiding moisture and
dampness, at some distance from walls and at some height from floors. The stack
should be covered with suitable coverings to avoid circulation of air through the
stack and not more than ten bags should be stacked one over another.
Testing of Cement
Experience has shown that it is practically impossible to make large quantities
of cement without any variation in quality. To be sure, some mills working with raw
materials which run very uniformly and using the best of equipment and methods
of operation will have very few unsuccessful 'burns' in a year, whereas others will be
less fortunate.
Nevertheless, the consumer has little chance of ascertaining how his
particular consignment of cement was made; therefore, if he has under way a
construction of any importance, he ought to satisfy himself regarding the quality of
his purchase. He should test his cement not only to see that he gets what he has
paid for but also to forestall the possibility of a failure through the use of defective
material.
Testing of cement can be brought under two categories:
(a) Field testing
(b) Laboratory testing.

87
Field Testing
It is sufficient to subject the cement to field tests when it is used for minor works.
The following are the field tests:
(a) Open the bag and take a good look at the cement. There should not be any visible
lumps. The colour of the cement should normally be greenish grey.
(b) Thrust your hand into the cement bag. It must give you a cool feeling. There
should not be any lump inside.
(c) Take a pinch of cement and feel-between the fingers. It should give a smooth and
not a gritty feeling.
(d) Take a handful of cement and throw it on a bucket full of water, the particles
should float for some time before they sink.
(e) Take about 100 grams of cement and a small quantity of water and make a stiff
paste. From the stiff paste, pat a cake with sharp edges. Put it on a glass plate and
slowly take it under water in a bucket. See that the shape of the cake is not disturbed
while taking it down to the bottom of the bucket. After 24 hours the cake should
retain its original shape and at the same time it should also set and attain some
strength.
If a sample of cement satisfies the above field tests it may be concluded that
the cement is not bad. The above tests do not really indicate that the cement is really
good for important works. For using cement in important and major works it is
incumbent on the part of the user to test the cement in the laboratory to confirm the
requirements of the Indian Standard specifications with respect to its physical and
chemical properties. No doubt, such confirmations will have been done at the factory
laboratory before the production comes out from the factory. But the cement may
go bad during transportation and storage prior to its use in works. The following
tests are usually conducted in the laboratory.
(a) Fineness test. (b) Setting time test.
(c) Strength test. (d) Soundness test.
(e) Heat of hydration test. (f) Chemical composition test.
In engineering construction, the main qualifications demanded of a cement
are permanency of structure, strength, and a rate of setting suitable to the demands
of the work. To determine these qualifications, both physical and chemical tests are
made, the former, on account of importance, more often than the latter. As a result
of long experience, the physical tests which have come into general use in
determining the acceptability of cement are:
(1) soundness or constancy of volume,

88
(2) strength,
(3) time of set or activity, and
(4) fineness.
In order that the results of such tests made by different parties may accord as nearly
as possible, it is necessary that a standard method be rigidly adhered to and that
only experienced operators, who fully appreciate the necessity of eliminating
personal equation from all manipulations, be employed.
Physical Tests (IS: 4031)
Fineness Test
The degree of fineness of cement is the measure of the mean size of the grains
in it. There are three methods for testing fineness:
the sieve method—using 90-micron (9 No.) sieve,
the air permeability method— Nurse and Blains method and
the sedimentation method— Wagner turbidimeter method.
The last two methods measure the surface area, whereas the first measures grain
size. Since cement grains are finer than 90 microns, the sieve analysis method does
not represent true mean size of cement grains. Also, the tiny cement grains tend to
conglomerate into lumps resulting in distortion in the final grain size distribution
curves. Considering these demerits, fineness is generally expressed in terms of
specific area, which is the total surface area of the particles in unit weight of
material.
Conditions Affecting Fineness
The chemical composition and the degree of calcination influence the
hardness of the clinker and consequently the fineness to which the cement is
ground. Clinker, high in iron or silica, is apt to be hard and difficult to grind. The
same is true with a hard-burned clinker. Fineness is also influenced by the time of
grinding and the character of the pulverizing machinery. It has been found that
cement becomes finer with age provided it does not absorb too much moisture. This
is probably due to the decrepitation of the coarser grains resulting from the
hydration of the embedded lime particles.
Importance
Finer the cement, more is the strength since surface area for hydration will
be large. With increase in fineness, the early development of strength is enhanced
but the ultimate strength is not affected. An increase in the fineness of the cement
increases the cohesiveness of the concrete mix and thus reduces the amount of

89
water which separates to the top of a lift (bleeding), particularly while compacting
with vibrators.
However, if the cement is ground beyond a certain limit, its cementative
properties are affected due to the prehydration by atmospheric moisture. Finer
cement reacts more strongly in alkali reactive aggregate. Also, the water requirement
and workability will be more leading to higher drying shrinkage and cracking.
Sieve Method
A 100 g of cement sample is taken and air-set lumps, if any, in the sample are
broken with fingers. The sample is placed on a 90-micron sieve and continuously
sieved for 15 minutes. The residue should not exceed the limits specified below:
Type of cement Percentage of residue Specific surface (m2/kg) not<
by weight
1. Ordinary Portland Cement (OPC) 10 225
2. Rapid Hardening Cement (RHC) 5 325
3. Portland Pozzolana Cement (PPC) 5 300
Air Permeability Method
This method of test covers the procedure for determining the fineness of
cement as represented by specific surface expressed as total surface area in sq.
cm/gm. of cement. It is also expressed in m2/kg. Lea and Nurse Air Permeability
Apparatus is shown in Fig. below. This apparatus can be used for measuring the
specific surface of cement.

90
The principle is based on the relation between the flow of air through the
cement bed and the surface area of the particles comprising the cement bed.
From this the surface area per unit weight of the body material can be related
to the permeability of a bed of a given porosity. The cement bed in the permeability
cell is 1 cm. high and 2.5 cm. in diameter. Knowing the density of cement the weight
required to make a cement bed of porosity of 0.475 can be calculated. This quantity
of cement is placed in the permeability cell in a standard manner.
Slowly pass on air through the cement bed at a constant velocity. Adjust the
rate of air flow until the flowmeter shows a difference in level of 30-50 cm. Read
the difference in level (h1) of the manometer and the difference in level (h2) of the
flowmeter. Repeat these observations to ensure that steady conditions have been
obtained as shown by a constant value of h1/h2. Specific surface Sw is calculated
from the following formula:

91
Blaine Air Permeability Apparatus
It is used for determining the fineness of Portland Cement measures the
specific surface area of fine materials in square centimetres per gram of test sample.
By using this apparatus, a quantity of air is drawn through a bed of definite porosity.
The rate of airflow is determined by the pore volume in the bed, a function of the
size of particles.
Included Items:
 Blaine Air Permeability Apparatus w/ wood panel and base
 Stainless-steel test cell
 Plunger
 Perforated disk
 Calibrated U-tube manometer
 Rubber aspirator and bulb
 8oz bottle red spirit manometer fluid
 Filter paper
 Woodblock for test cell

92
Consistency Test
This is a test to estimate the quantity of mixing water to form a paste of normal
consistency defined as that percentage water requirement of the cement paste, the
viscosity of which will be such that the Vicar’s plunger penetrates up to a point 5 to
7 mm from the bottom of the Vicar’s mould.
Importance
The water requirement for various tests of cement depends on the normal
consistency of the cement, which itself depends upon the compound composition
and fineness of the cement.
Test Procedure
300 g of cement is mixed with 25 per cent water. The paste is filled in the
mould of Vicat’s apparatus (Fig. 5.9) and the surface of the filled paste is smoothened
and levelled. A square needle 10 mm x 10 mm attached to the plunger is then
lowered gently over the cement paste surface and is released quickly. The plunger
pierces the cement paste. The reading on the attached scale is recorded. When the
reading is 5-7 mm from the bottom of the mould, the amount of water added is
considered to be the correct percentage of water for normal consistency.

93
Fig. Vicat’s Apparatus
Determination of Initial and Final Setting Times
When water is added to cement, the resulting paste starts to stiffen and gain
strength and lose the consistency simultaneously. The term setting implies
solidification of the plastic cement paste. Initial and final setting times may be
regarded as the two stiffening states of the cement. The beginning of solidification,
called the initial set, marks the point in time when the paste has become
unworkable.
The time taken to solidify completely marks the final set, which should not be
too long in order to resume construction activity within a reasonable time after the
placement of concrete. Vicat’s apparatus used for the purpose is shown in Fig. 5.9.
The initial setting time may be defined as the time taken by the paste to stiffen to
such an extent that the Vicat’s needle is not permitted to move down through the
paste to within 5 ± 0.5 mm measured from the bottom of the mould.
The final setting time is the time after which the paste becomes so hard that
the angular attachment to the needle, under standard weight, fails to leave any mark
on the hardened concrete. Initial and final setting times are the rheological
properties of cement.

94
Importance
It is important to know the initial setting time, because of loss of useful
properties of cement if the cement mortar or concrete is placed in moulds after this
time. The importance of final setting time lies in the fact that the moulds can be
removed after this time. The former defines the limit of handling and the latter
defines the beginning of development of mechanical strength.
Conditions Affecting Setting Time
The factors influencing the setting properties of cement are its composition,
the percentage of retardant, degree of calcination, fineness of grinding, aeration
subsequent to grinding clinker, percentage of water used to make cement paste, the
temperature of the mixing water, cement and the atmosphere where the cement
paste is placed, and the amount of manipulation the paste receives.
The effect of lime, silica and alumina in controlling the set have been
discussed in Sec. 5.3. The effect of gypsum is to increase the setting time of freshly
ground cement. It is usually mixed with the clinker before final grinding, or just after
the clinker has received preliminary grinding. The addition of gypsum before
calcination causes it to decompose into lime and sulphur trioxide. Since the latter
is liberated in the kiln, there is resulting effect on the setting time.
Often, an underlimed cement becomes quick setting after seasoning. This can
be avoided by adding to the cement 1 or 2 per cent of hydrated lime or the fraction
of a per cent of Plaster of Paris. Setting time of cement is rapid with the increase in
the fineness of cement. When the mixing water used in testing cement paste is

95
increased by 1 per cent above that required for normal consistency, an increase of
about 30 minutes or more is observed in the initial or final set.
Cements stored in warm rooms will, in general, be quick setting than those
stored in cold places. Cold mixing water retards set while warm water accelerates it.
Cement exposed to thoroughly saturated atmosphere will set much more slowly than
those exposed to a dry atmosphere. If, however, a considerable proportion of moist
CO2 is present in the air, the setting time is found to reduce greatly. By lengthening
the time of mixing and by prolonged trowelling of the surface mortars, it is also
possible to considerably delay the setting time.
Test Procedure
A neat cement paste is prepared by gauging cement with 0.85 times the water
required to give a paste of standard consistency. The stop watch is started at the
instant water is added to the cement. The mould resting on a nonporous plate is
filled completely with cement paste and the surface of filled paste is levelled smooth
with the top of the mould. The test is conducted at room temperature of 27± 2°C.
The mould with the cement paste is placed in the Vicat’s apparatus as shown
in Fig. 5.9 and the needle is lowered gently in contact with the test block and is then
quickly released. The needle thus penetrates the test block and the reading on the
Vicat’s apparatus graduated scale is recorded. The procedure is repeated until the
needle fails to pierce the block by about 5 mm measured from the bottom of the
mould. The stop watch is pushed off and the time is recorded which gives the initial
setting time.
The cement is considered to be finally set when upon applying the needle
gently to the surface of test block, the needle makes an impression, but the
attachment fails to do so.
Soundness Test
It is essential that the cement concrete does not undergo large change in
volume after setting. This is ensured by limiting the quantities of free lime and
magnesia which slake slowly causing change in volume of cement (known as
unsound). Soundness of cement may be tested by Le- Chatelier method or by
autoclave method. For OPC, RHC, LHC and PPC it is limited to 10 mm, whereas for
HAC and SSC it should not exceed 5 mm.
Importance
It is a very important test to assure the quality of cement since an unsound cement
produces cracks, distortion and disintegration, ultimately leading to failure.
Conditions Affecting Soundness

96
The main cause for unsoundness in Portland cement is the hydration of the
uncombined lime encased within the cement particles. Exposed, finely ground, free
lime in small percentages, hydrates before the cement sets and produces no
injurious effect. The uncombined lime in cement is a result of either underburning
the clinker or of excess lime in the raw materials.
Freshly ground cement is often unsound due to the presence of uncombined
lime. Cement is thus allowed to aerate for two to three weeks, allowing the lime to
hydrate, to overcome unsoundness. Fine grinding of the raw material and clinker
help to produce a sound cement. By grinding fine, the raw materials, it is possible
to produce a homogeneous mixture before burning where the lime is uniformly
distributed. The coarse grains of cement may imprison minute particles of
uncombined lime which do not hydrate. These lime particles on hydration produces
disintegration.
Le-Chatelier Method
The apparatus is shown in Fig. The mould is placed on a glass sheet and is
filled with neat cement paste formed by gauging 100 g cement with 0.78 times the
water required to give a paste of standard consistency. The mould is covered with a
glass sheet and a small weight is placed on the covering glass sheet. The mould is
then submerged in the water at temperature of 27°+/- 2°C. After 24 hours, the
mould is taken out and the distance separating the indicator points is measured(a).
The mould is again submerged in water. The water is brought to boiling for 100 oC
and allowed to boil for 3 hours. The mould is removed from water and is cooled
down. The distance between the indicator points is measured again(b). The
difference (b – a) between the two measurements represents the unsoundness of
cement.

97
Determination of Strength
Cement hydrates when water is added to it and cohesion and solidity is
exhibited. It binds together the aggregates by adhesion. The strength of mortar and
concrete depends upon the type and nature of cement. So, it should develop a
minimum specified strength if it is to be used in structures. Cement is tested for
compressive and tensile strengths.
Conditions Affecting Strength
Cement is very strong at early ages if a high lime or high alumina content is
there. Gypsum and Plaster of Paris in small percentages also tend to increase the
strength slightly, but when present in quantities larger than 3 per cent, these
substances provide variable effects. The effect of the clinker compounds on strength
have already been discussed in Sec 5.4. In addition to the effect of composition, the
strength of cement is greatly influenced by the degree of burning, the fineness of
grinding, and the aeration it receives subsequent to final grinding. An under burnt
cement is likely to be deficient in strength
Compressive strength is the basic data required for mix design. By this test,
the quality and the quantity of concrete can be controlled and the degree of
adulteration can be checked.
Test Procedure
The test specimens are 70.6 mm cubes having face area of about 5000 sq.
mm. Large size specimen cubes cannot be made since cement shrinks and cracks
may develop. The temperature of water and test room should be 27°± 2°C. A mixture
of cement and standard sand in the proportion 1:3 by weight is mixed dry with a
trowel for one minute and then with water until the mixture is of uniform colour.
Three specimen cubes are prepared. The material for each cube is mixed separately.
The quantities of cement, standard sand and water are 185 g, 555 g and (P/4) + 3.5,
respectively where P = percentage of water required to produce a paste of standard
consistency.
The mould is filled completely with the cement paste and is placed on the
vibration table. Vibrations are imparted for about 2 minutes at a speed of 12000±400
per minute. The cubes are then removed from the moulds and submerged in clean
fresh water and are taken out just prior to testing in a compression testing machine.
Compressive strength is taken to be the average of the results of the three cubes.
The load is applied starting from zero at a rate of 35 N/sq. mm/minute. The
compressive strength is calculated from the crushing load divided by the average

98
area over which the load is applied. The result is expressed in N/mm2. The minimum
specified strength for some of the cements is given in Table 5.4.
Tensile strength
The tensile strength may be determined by Briquette test method or by split tensile
strength test.
Importance
The tensile strength of cement affords quicker indications of defects in the cement
than any other test. Also, the test is more conveniently made than the compressive
strength test. Moreover, since the flexural strength, is directly related to the tensile
strength this test is ideally fitted to give information both with regard to tensile and
compressive strengths when
the supply for material testing is small.
Briquette test method
A mixture of cement and sand is gauged in the proportion of 1:3 by weight.
The percentage of water to be used is calculated from the formula (P/5) + 2.5, where
P = percentage of water required to produce a paste of standard consistency. The
temperature of the water and the test room should be 27° ± 2°C. The mix is filled in
the moulds of the shape shown in Fig. 5.11.
After filling the mould, an additional heap of mix is placed on the mould and
is pushed down with the standard spatula, until the mixture is level with the top of
the mould. This operation is repeated on the other side of the mould also. The
briquettes in the mould are finished by smoothing the surface with the blade of a
trowel. They are then kept for 24 hours at a temperature of 27° ± 2°C and in an
atmosphere having 90 per cent humidity.
The briquettes are then kept in clean fresh water and are taken out before
testing. Six briquettes are tested and the average tensile strength is calculated. Load
is applied steadily and uniformly, starting from zero and increasing at the rate of 0.7
N/sq. mm of section in 12 seconds.

99
Ordinary Portland cement should have a tensile strength of not less than 2.0 N/mm2
after 3 days and not less than 2.5 N/mm2 after 7 days.
Specific Gravity Test
The specific gravity of hydraulic cement is obtained using Le-Chatelier flask shown
in Fig. 5.13.

100
Conditions Affecting Specific Gravity
Long seasoning is the chief cause of a low specific gravity in unadulterated
cement. This is because the freshly ground cement when exposed to air rapidly
absorbs moisture and carbon dioxide. Cements with high contents of iron oxide have
a higher specific gravity. The effect of fineness of grinding upon specific gravity is
slight. Very finely ground cements are likely to have lower specific gravities.
Test Procedure
The flask is filled with either kerosene free of water, or naphtha having a
specific gravity not less than 0.7313 to a point on the stem between zero and 1-ml
mark. The flask is immersed in a constant temperature water bath and the reading
is recorded. A weighed quantity of cement (about 64 g of Portland cement) is then
introduced in small amounts at the same temperature as that of the liquid. After
introducing all the cement, the stopper is placed in the flask and the flask rolled in
an inclined position, or gently whirled in a horizontal circle, so as to free the cement
from air until no further air bubbles rise to the surface of the liquid. The flask is
again immersed in the water-bath and the final reading is recorded. The difference
between the first and the final reading represents the volume of liquid displaced by
the weight of the cement used in the test.
Specific gravity = Weight of cement
Displaced volume of liquid in ml
Specific Gravity of Cement (Sc) is calculated by using following formula,
= {(W2 – W1) / ((W4 – W1) – (W3 – W2))} X Sk
Specific Gravity of Kerosene (Sk) = (W4 – W1)/ (W5 – W1)
Admixtures
What Is Admixture?

101
Admixtures are the special ingredients added during concrete mixing to
enhance the properties of fresh concrete. Admixtures are materials other than the
aggregate, water, and cement added to the concrete.
Different Types of Admixtures are added to the concrete mix are used to
upgrade the behaviour of concrete under different weather conditions.
Admixtures minimize the construction cost by altering the properties of
hardened concrete, ensure the quality of concrete during mixing, transporting,
placing, curing, and overcome certain emergencies during concrete operations.
Why is admixture used?
Over decades, attempts have been made to obtain concrete with certain
desired characteristics such as high compressive strength, high workability, and
high performance and durability parameters to meet the requirement of complexity
of modern structures.
The properties commonly modified are the heat of hydration, accelerate or
retard setting time, workability, water reduction, dispersion and air-entrainment,
impermeability and durability factors.
The major reasons for using admixtures are:
• To reduce the cost of concrete construction.
• To achieve certain properties in concrete more effectively than by other
means.
• To maintain the quality of concrete during the stages of mixing, transporting,
placing, and curing in ad-verse weather conditions.
• To overcome certain emergencies during concreting operations.
Types of Admixtures
Chemical admixtures –
Accelerators, Retarders, Water-reducing agents, Super plasticizers, Air entraining
agents etc.
Mineral admixtures –
Fly-ash, Blast-furnace slag, Silica fume and Rice husk Ash etc

102
Polymer Based
Functions of Admixtures in Concrete
Followings are the main purposes for which admixtures should be added in the
concrete mix:
 To increase or decrease the setting time of the fresh concrete mix.
 To make better or enhance the workability or flowability of concrete mix
which is the main property of the concrete.
 To maximize the strength and durability of the concrete.
 To reduce the heat of hydration.
 To lowers the segregation and bleeding which may occur during the placing
of concrete.
 To reduce the permeability of concrete.
 To achieve other desirable properties.

103
Each class of admixture is defined by its primary function. It may have one or more
secondary functions, however, and its use may affect, positively or negatively,
concrete properties other than those desired.
Types of Concrete Admixtures
Concrete admixtures are of different types and they are as follows:
1. Water Reducing Admixtures
2. Retarding Admixtures
3. Accelerating Admixtures
4. Air entraining concrete admixture
5. Pozzolanic Admixtures
6. Damp-proofing Admixtures
7. Gas forming Admixtures
8. Air detraining Admixtures
9. Alkali Aggregate Expansion Inhibiting Admixtures
10. Anti-washout Admixtures
11. Grouting Admixtures
12. Corrosion Inhibiting Admixtures
13. Bonding Admixtures
14. Fungicidal, Germicidal, Insecticidal Admixtures

104
15. Colouring Admixtures
1. Water Reducing Admixtures
Water reducing admixtures, the name itself defining that they are used to
minimize the water demand in a concrete mix. Workability is the important property
of concrete which is improved with the addition of water but if water is added more
than required the strength and durability properties of concrete gets affected.
In addition to increase in workability it also improves the strength of concrete,
good bond between concrete and steel, prevents cracking, segregation,
honeycombing, bleeding etc.
Water reducing admixtures are also called as plasticizers and these are
classified into three types namely plasticizers, mid-range plasticizers and super
plasticizers.
Water Reducing Admixtures
These admixtures are used for following purposes:
1. To achieve a higher strength by decreasing the water cement ratio at the same
workability as an admixture free mix.
2. To achieve the same workability by decreasing the cement content so as to reduce
the heat of hydration in mass concrete.
3. To increase the workability so as to ease placing in accessible locations
4. Water reduction more than 5% but less than 12%
5. The commonly used admixtures are Ligno-sulphonates and hydro carboxylic acid
salts.
6. Plasticizers are usually based on lignosulphonate, which is a natural polymer,
derived from wood processing in the paper industry.
Actions involved:

105
1. Dispersion:
Surface active agents alter the physic chemical forces at the interface. They
are adsorbed on the cement particles, giving them a negative charge, which leads to
repulsion between the particles.
Electrostatic forces are developed causing disintegration and the free water
become available for workability.
2. Lubrication:
As these agents are organic by nature, thus they lubricate the mix reducing the
friction and increasing the workability.
3. Retardation:
A thin layer is formed over the cement particles protecting them from hydration and
increasing the setting time. Most normal plasticizers give some retardation, 30–90
minutes
Fig 1: Water Reducing Admixture
Normal plasticizer reduces the water demand up to 10%, mid-range
plasticizers reduce the water demand up to 15% while super plasticizers reduce the
water demand up to 30%.
Calcium, sodium and ammonium lignosulphonates are commonly used
plasticizers. Some of the new generation super plasticizers are acrylic polymer
based, poly carboxylate, multi carboxylate ethers etc.
2. Retarding Admixtures
Retarding admixtures slow down the rate of hydration of cement in its initial
stage and increase the initial setting time of concrete. These are also called as

106
retarders and used especially in high temperature zones where concrete will set
quickly.
The quick setting in some situations may lead to discontinuities in structure,
poor bond between the surfaces, creates unnecessary voids in concrete etc.
Retarders are useful to eliminate this type of problems. Commonly used
retarding admixture is calcium sulphate or gypsum. Starch, cellulose products,
common sugar, salts of acids are some other retarders. Most of water reducing
admixtures are also acts as retarding admixtures and they are called as retarding
plasticizers.
Fig 2: Retarding Admixture (Gypsum)
3. Accelerating Admixtures
Accelerating admixtures are used to reduce the initial setting time of concrete.
They speed up the process of initial stage of hardening of concrete hence they are
also called as accelerators.
These accelerators also improves the strength of concrete in it early stage by
increasing the rate of hydration. Earlier hardening of concrete is useful in several
situations such as early removal of formwork, less period of curing, emergency repair
works, for constructions in low temperature regions etc.
Accelerating Admixture

107
Some of the accelerating admixtures are triethenolamine, calcium formate,
silica fume, calcium chloride, finely divided silica gel etc. Calcium chloride is the
cheap and commonly used accelerating admixture.
Fig 3: Accelerator (Silica Fume)
4. Air Entraining Concrete Admixture
Air entraining admixtures are one of the most important inventions in
concrete technology. Their primary function is to increase the durability of concrete
under freezing and thawing conditions.
When added to concrete mix, these admixtures will form millions of non-
coalescing air bubbles throughout the mix and improves the properties of concrete.
Air entrainment in concrete will also improve the workability of concrete,
prevents segregation and bleeding, lower the unit weight and modulus of elasticity
of concrete, improves the chemical resistance of concrete and reduction of cement
or sand or water content in concrete etc.
Air Entraining Admixture
Most used air entrainment admixtures are vinsol resin, darex, Teepol, Cheecol
etc. These admixtures are actually made of Natural wood resins, alkali salts, animal
and vegetable fats and oils etc.

108
Fig 4: Freezing and Thawing Effect on Concrete
5. Pozzolanic Admixtures
Pozzolanic admixtures are used to prepare dense concrete mix which is best
suitable for water retaining structures like dams, reservoirs etc. They also reduce
the heat of hydration and thermal shrinkage.
Best pozzolanic materials in optimum quantity gives best results and prevents
or reduces many risks such as alkali aggregate reaction, leaching, sulfate attack etc.
Pozzolanic materials used as admixtures are either natural or artificial.
Naturally occurring Pozzolanic materials are clay, shale, volcanic tuffs,
pumicite, etc. and artificial pozzolans available are fly ash, silica fume, blast furnace
slag, rice husk ash, surkhi etc.
Pozzolanic Admixture

109
Fig 5: Fly ash
6. Damp-proofing Admixtures
Damp proofing or water proofing admixtures are used to make the concrete
structure impermeable against water and to prevent dampness on concrete surface.
In addition to water proof property, they also acts like accelerators in early
stage of concrete hardening.
Damp-proofing Admixture
Damp proofing admixtures are available in liquid form, powder form, paste
form etc. The main constituents of these admixtures are aluminum sulfate, zinc
sulfate aluminum chloride, calcium chloride, silicate of soda etc. which are
chemically active pore fillers.

110
Fig 6: Dampness on Concrete Surface
7. Gas forming Admixtures
Aluminium powder, activated carbon, hydrogen peroxide are generally used
gas forming chemical admixtures. When gas forming admixtures are added, it reacts
with hydroxide obtained by the hydration of cement and forms minute bubbles of
hydrogen gas in the concrete.
The range of formation of bubbles in concrete is depends upon many factors
such as amount of admixture, chemical composition of cement, temperature,
fineness etc. The formed bubbles help the concrete to counteract the settlement and
bleeding problems.
Gas Forming Admixture

111
Fig 7: Activated Carbon Powder
Gas forming admixtures are also used to prepare light weight concrete. For
settlement and bleeding resistance purpose, small quantity of gas forming
admixtures which is generally 0.5 to 2% by weight of cement is used.
But for making light weight concrete larger quantity generally 100 grams per
bag of cement is recommended.
8. Air detraining Admixtures
Air-detraining Admixtures are used to remove the excess air from the concrete
voids. Sometimes, the aggregates may release the gas into concrete and air entrained
is more than required then this type of admixtures are useful.
Some of the mostly used air-detraining admixtures are tributyl phosphate,
silicones, water insoluble alcohols etc.
9. Alkali Aggregate Expansion Preventing Admixtures
Alkali aggregate expansion in concrete is happened by the reaction of alkali of
cement with the silica present in the aggregates. It forms a gel like substance and
cause volumetric expansion of concrete which may lead to cracking and
disintegration.
Use of pozzolanic admixtures will prevent the alkali-aggregate reaction and in
some cases air-entraining admixtures are also useful. Generally used admixtures to
reduce the risk of alkali aggregate reaction are aluminium powder and lithium salts.

112
Alkali Aggregate Expansion
Fig 8: Effect of Alkali Aggregate Reaction on Concrete
10. Anti-washout Admixtures
Anti-washout admixtures are used in concrete especially for under water
concrete structure. It protect the concrete mix from being washed out under water
pressure. It improves the cohesiveness of concrete.
This type of admixtures are prepared from natural or synthetic rubbers,
cellulose based thickeners etc.
Anti-washing Admixtures

113
Fig 9: Underwater Concreting
11. Grouting Admixtures
Grouting admixtures are added to grout materials to improve the grout
properties according to the requirement of grout. Sometimes, there is a need of quick
set grout and sometimes there is a need of slow set grout to spread into deep cracks
or fissures.
Hence, different admixtures are used as grout admixtures based on situation.
Accelerators like calcium chloride, triethanolamine etc. are used as grout
admixtures when the grout is to be set rapidly.
Similarly retarders like mucic acid, gypsum etc. are used to slow down the
setting time of grout. Gas forming admixtures like aluminum powder is added to
grout material to counteract the settle of foundations.
In these admixtures, the accelerators like calcium chloride, triethanolamine,
etc. are used when the grout is to be set rapidly. Similarly, retarders like mucic acid,
gypsum, etc. are used to slow down the setting time of grout.
Grouting Admixtures

114
Fig 10: Grouting
12. Corrosion Preventing Admixtures
Corrosion of steel in reinforced concrete structure is general and it is severe
when the structure is exposed to saline water, industrial fumes, chlorides etc. To
prevent or to slow down the process of corrosion preventing admixtures are used.
Some of the corrosion preventing admixtures used in reinforced concrete are
sodium benzoate, sodium nitrate, sodium nitrite etc.
Fig 11: Corrosion of Steel in Concrete

115
Corrosion Preventing Admixture
13. Bonding Admixtures
Bonding admixtures are used to create a bond between old and fresh concrete
surfaces. In general, if fresh concrete is poured over a hardened concrete surface,
there is a chance of failure of fresh concrete surface due to weak bond with old
surface.
To make the bond stronger, bonding admixtures are added to cement or
mortar grout which is applied on the concrete surface just before placing fresh
concrete.
This type of admixtures are used for pavement overlays, screed over roof
provision, repair works etc. Bonding admixtures are water emulsions and they are
made from natural rubber, synthetic rubbers, polymers like poly vinyl chloride,
polyvinyl acetate etc.
Fig 12: Concrete Pavement Overlay

116
Bonding admixtures
14. Fungicidal, Germicidal, Insecticidal Admixtures
To prevent the growth of bacteria, germs, fungus on hardened concrete
structures, it is recommended that the mix should have fungicidal, germicidal and
insecticidal properties. These properties can be developed by adding admixtures like
polyhalogenated phenols, copper compounds and dieledren emulsions etc.
Fig 13: Concrete affected by Fungi
15. Coloring Admixtures
Coloring admixtures are the pigments which produce color in the finished
concrete. The admixtures used to produce color should not affect the concrete
strength.
Generally coloring admixtures are added to cement in a ball mill, then colored
cement can be obtained which can be used for making colored concrete. Some of the
coloring admixtures and their resultant colors are tabulated below.
Table 1: Coloring Admixtures and their Resultant Colors
Admixture Color obtained
Iron or Red oxide Red

117
Hydroxides of iron Yellow
Barium manganite and Ultramarine Blue
Chromium oxide and chromium
hydroxide
Green
Ferrous oxide Purple
Carbon black Black
Manganese black , Raw umber Brown
Fig 14: Colored Concrete
Color Admixtures
Advantages of Admixture
Admixture Benefits are given below,
 Admixtures in concrete can accelerate the setting time.
 Some admixtures have enzymes that work as an anti-bacterial agent.
 Admixtures added in concrete can reduce the initial strength but increase the
strength of concrete.
 They help in lowering the heat of hydration and reduce the chances of thermal
cracking in concrete.

118
 It improves concrete resistance against the freeze-melting effect on concrete.
 It cut off cement quantity requirement in concrete and which makes concrete
economical.
 Improve practicality of concrete.
 Admixtures provide early initial strength in concrete.
Disadvantages of Admixture
The disadvantages of admixtures as given below,
 CaCl2 high added in concrete can increase the risk of corrosion of steel – not
allowed in reinforced concrete.
 Some admixtures are more expensive and less effective.
 It can increase drying shrinkage in concrete.
 They provide less resistance to sulfate attacks.
Pozzolanic materials are:
• Siliceous or siliceous-aluminous materials,
• Little or no cementitious value,
• In finely divided form and in the presence of moisture,
Chemically react with calcium hydroxide liberated on hydration, at ordinary
temperature, to form compounds, possessing cementitious properties.
They are also known as POZZOLANIC materials.
Improves many qualities of concrete, such as:
• Lower the heat of hydration and thermal shrinkage;
• Increase the water tightness;
• Reduce the alkali-aggregate reaction;
• Improve resistance to attack by sulphate soils and sea water;
• Improve extensibility;
• Lower susceptibility to dissolution and leaching;
• Improve workability;
• Lower costs.

119
Fly ash is finely divided residue resulting from the combustion of powdered
coal and transported by the flue gases and collected by “Electrostatic Precipitator”.

120
Figure 2. Schematic layout of a coal-fired electrical generating station
In the production of fly ash, coal is first pulverized in grinding mills before
being blown with air into the burning zone of the boiler. In this zone the coal
combusts producing heat with tempertures reaching approximately 1500°C
(2700°F).
At this temperature the non-combustible inorganic minerals (such as quartz,
calcite, gypsum, pyrite, feldspar and clay minerals) melt in the furnace and fuse
together as tiny molten droplets. These droplets are carried from the combustion
chamber of a furnace by exhaust or flue gases.
Once free of the burning zone, the droplets cool to form spherical glassy
particles called fly ash (Figure 3). The fly ash is collected from the exhaust gases by
mechanical and electrostatic precipitators. Fly ash is the most widely used
pozzolanic material all over the world.
(Figure 3)

121
Type of Fly Ash as per American Society for Testing and Materials (ASTM C618)
Class F
 It contain particles covered in a kind of melted glass.
 This greatly reduces the risk of expansion due to sulfate attack, which may occur
in fertilized soils or near coastal areas.
 It is generally low-calcium and has a carbon content less than 5 percent but
sometimes as high as 10 percent.
 It is used at dosages of 15 to 25 percent by mass of cementitious material.
Class C
 It is also resistant to expansion from chemical attack.
 It has a higher percentage of calcium oxide than Class F and is more commonly
used for structural concrete.
 It is typically composed of high-calcium fly ashes with a carbon content of less
than 2 percent.
 Currently, more than 50 percent of the concrete placed in the U.S. contains fly
ash.
 it is used at dosages of 15 to 40 percent by mass of cementitious material.

122
Type of Fly Ash as per IS Codes (IS 3812-1981)
Grade I
 This grade of Fly ash is derived from bituminous coal having fractions
SiO2+Al2O3+Fe2O3 greater than 70 %.
Grade II
 This grade of Fly ash derived from lignite coal having fractions SiO2+Al2O3+Fe2O3
greater than 50 %.
Type of Fly Ash based on boiler operations
Low temperature(LT) fly ash
 It is produced when the combustion temperature is below 900o C
High temperature(HT) fly ash
 It is generated out of combustion temperature below 1000o C
Amount used
• Up to 35% by mass of cement (According to IS: 456 – 2000) & minimum shall not
be less than 15%.
Results - effects
• Reduction of water demand for desired slump. With the reduction of unit water
content, bleeding and drying shrinkage will also be reduced.
 fly ash is not highly reactive, the heat of hydration can be reduced through
replacement of part of the cement with fly ash.
Mechanism of Fly Ash
 The chemistry of hydration of Portland cement is that about 50% of Portland
cement is composed of the primary mineral tri-calcium silicate, which on hydration
forms calcium silicate hydrate and calcium hydroxide.

123
Hydration reaction of Portland cement and fly ash Portland cement
 If we have Portland cement, and the fly ash is the pozzolana, it can be represented
by silica because non-crystalline silica glass is the principal constituent of fly ash.
 The silica combines with the calcium hydroxide released on hydration of Portland
cement.
 Calcium hydroxide in hydrated Portland cement does not do anything for strength,
so therefore we use it up with reactive silica.
 Slowly and gradually it forms additional calcium silicate hydrate which is a binder,
and which fills up the space, and gives us impermeability and more and more
strength.
Chemical Composition
The chemical composition of fly ash depends upon the type of coal used and the
methods used for combustion of coal.

124
HVFAC is a concrete where excess of 35%of fly-ash is used as replacement
Use of fly ash is because of many factors such as:
a) Abundance of fly ash
b) Fly ashes from major TPP(Trans-Pacific Partnership) are of very high quality i.e.
quality of fly ash.
c) Economic factor i.e. Cost of fly ash with in 200 km from a TPP is as low as 10%
to 20% of the cost of cement.
d) Environmental factors i.e. reduction in CO2 emission.
Effects of Fly Ash on Hardened Concrete
• contributes to the strength of concrete due to its pozzolanic reactivity.
• continued pozzolanic reactivity concrete develops greater strength at later age not
at initial stage.
• contributes to making the texture of concrete dense, resulting in decrease of water
permeability and gas permeability.

125
Used at
• Many high-rise buildings
• Industrial structures
• Water front structures
• Concrete roads
• Roller compacted concrete dams
High volume Fly Ash has been used in the Barker Hall Project, University of
California at Berkeley for the construction of shear walls.

126
In India, fly ash was used for the first time in the construction of Rihand Irrigation
Project, Uttar Pradesh in 1962, replacing cement up to about 15 per cent
Applications
 It can be used as prime material in many cement-based products.
 It can be used in Portland cement concrete pavement or PCC pavement.
 fly ash provides economic benefits in construction projects.
 It is used as embankment and mine fill, and it has increasingly gained acceptance
by the Federal Highway Administration.
 The amount of fine aggregate in the concrete mix must be reduced to accommodate
the additional volume of the fly ash.
Benefits
 Cost-effective.
 environmentally friendly and it reduces CO2 emissions.
 It requires less water and it have Great workability

127
 High strength gains, depending on use.
 Can be used as an admixture.
 non-shrink material.
 Produces dense concrete with a smooth surface and sharp detail.
 Reduces crack problems, permeability, and bleeding.
 Reduces heat of hydration.
 Allows for a lower water-cement ratio for similar slumps when compared to no-fly-
ash mixes.
Disadvantages
 Slower strength gain
 Seasonal limitation
 Increased need for air-entraining admixtures
 Increase of salt scaling produced by higher proportions of fly ash
Silica Fume
1.fine micro-crystalline silica produced in electric arc furnaces as a by-product.
2. Very fine non-crystalline silica produced in electric arc furnaces as a by-product.
It is a product resulting from reduction of high
purity quartz with coal in an electric arc furnace in the manufacture of silicon or
ferrosilicon alloy.
1. Micro silica is initially produced as an ultrafine undensified powder
2. At least 85% SiO2 content
3. Mean particle size between 0.1 and 0.2 micron
4. Minimum specific surface area is 15,000 m2/kg
5. Spherical particle shape
Silica Fume
Silica fume, also referred to as micro silica or condensed silica fume, is
another material that is used as an artificial pozzolanic admixture. It is a product
resulting from reduction of high purity quartz with coal in an electric arc furnace in
the manufacture of silicon or ferrosilicon alloy. Silica fume rises as an oxidized
vapour. It cools, condenses and is collected in cloth bags.

128
It is further processed to remove impurities and to control particle size.
Condensed silica fume is essentially silicon dioxide (more than 90%) in
noncrystalline form. Since it is an airborne material like fly ash, it has spherical
shape. It is extremely fine with particle size less than 1 micron and with an average
diameter of about 0.1 micron, about 100 times smaller than average cement
particles. Silica fume has specific surface area of about 20,000 m2/kg, as against
230 to 300 m2/kg.
Silica fume as an admixture in concrete has opened up one more chapter on
the advancement in concrete technology. The use of silica fume in conjunction
with superplasticizer has been the backbone of modern High-performance
concrete.

129
The transition zone is a thin layer between the bulk hydrated cement paste
and the aggregate particles in concrete. This zone is the weakest component in
concrete, and it is also the most permeable area.
Silica fume plays a significant role in the transition zone through both its
physical and chemical effects.
a) Behaviour of Cement particles with water
b) Behaviour of Cement particle + Super Plasticizer + water
c) Behaviour of Cement + water + Superplasticizer + Micro silica

130
Micro silica is available in the following forms:
1. Undensified forms with bulk density of 200–300 kg/m3
2. Densified forms with bulk density of 500–600 kg/m3
3. Micro-pelletised forms with bulk density of 600–800 kg/m3
4. Slurry forms with density 1400 kg/m3
5. Admixtures and Construction Chemicals.
6. Slurry is produced by mixing undensified micro silica powder and water in equal
proportions by weight.
Slurry is the easiest and most practical way to introduce micro silica into the
concrete mix.
7. Surface area 15–20 m2/g.
8. Standard grade slurry pH value 4.7, specific gravity 1.3 to 1.4, dry content of
micro silica 48 to 52%.

131
Pozzolanic Action of Silica fume
Micro silica is much more reactive than fly ash or any other natural pozzolana.
The reactivity of a pozzolana can be quantified by measuring the amount of Ca (OH)2
in the cement paste at different times.
In one case, 15% of micro silica reduced the Ca (OH)2 of two samples of cement
from 24% to 12% at 90 days and from 25% to 11% in 180 days. Most research
workers agree that the C – S – H formed by the reaction between micro silica and Ca
(OH)2 appears dense and amorphous.
Effect of Silica fume on fresh concrete
The increase in water demand of concrete containing micro silica will be about 1%
for every 1% of cement substituted.
lead to lower slump but more cohesive mix.
make the fresh concrete sticky in nature and hard to handle.
large reduction in bleeding and concrete with micro silica could be handled and
transported without segregation.
to plastic shrinkage cracking and, therefore, sheet or mat curing should be
considered.
produces more heat of hydration at the initial stage of hydration.
the total generation of heat will be less than that of reference concrete.
Effect of Silica fume on hardened concrete
1. Modulus of elasticity of micro silica concrete is less.
2. Improvement in durability of concrete.

132
3. Resistance against frost damage.
4. Addition of silica fume in small quantities actually increases the expansion.
5. Conserve cement
6. Produce ultra-high strength concrete of the order of 70 to 120 Mpa.
7. Increase early strength of fly concrete.
8. Control alkali-aggregate reaction.
9. Reduce sulphate attack & chloride associated corrosion.
BLAST FURNACE SLAG
Blast-furnace slag is a non-metallic product consisting essentially of silicates and
aluminates of calcium and other bases.
The molten slag is rapidly chilled by quenching in water to form a glassy sand like
granulated material.
The granulated material when further ground to less than 45 microns will have
specific surface of about 400 to 600 m2/ kg (Blaine).

133
In India, we produce about 7.8 million tons of blast furnace slag. All the blast
furnace slags are granulated by quenching the molten slag by high power water jet,
making 100% glassy slag granules of 0.4 mm size. The blast furnace slag is mainly
used in India for manufacturing slag cement.
There are two methods for making Blast Furnace Slag Cement. In the first
method blast furnace slag is interground with cement clinker along with gypsum. In

134
the second method blast furnace slag is separately ground and then mixed with the
cement.
Clinker is hydraulically more active than slag. It follows then that slag should
be ground finer than clinker, in order to fully develop its hydraulic potential.
However, since slag is much harder and difficult to grind compared to clinker, it is
ground relatively coarser during the process of inter-grinding. This leads to waste of
hydraulic potential of slag. Not only that the inter-grinding seriously restricts the
flexibility to optimize slag level for different uses.
The hydraulic potential of both the constituents – clinker and slag can be fully
exploited if they are ground separately. The level of fineness can be controlled with
respect to activity, which will result in energy saving. The present trend is towards
separate grinding of slag and clinker to different levels.
The clinker and gypsum are generally ground to the fineness of less than 3000
cm2 /g (Blaine) and slag is ground to the level of 3000–4000 cm2/g (Blaine) and
stored separately.
They are blended after weigh batching, using paddle wheel blenders, or
pneumatic blenders. Pneumatic blenders give better homogeneity when compared
to mechanical blenders.
Effects of Blast-furnace slag on fresh concrete
 Reduces the unit water content necessary to obtain the same slump.
 Water used for mixing is not immediately lost, as the surface hydration of slag is
slightly slower than that of cement.
 Reduction of bleeding.
Effects of Blast-furnace slag on hardened concrete
Reduced heat of hydration
Refinement of pore structures
Reduced permeabilities to the external agencies
Increased resistance to chemical attack.

135
Fig. Reduction in Water Content
Blast furnace slag, although is an industrial by-product, exhibits good
cementitious properties with little further processing. It permits very high
replacement of cement and extends many advantages over conventional cement
concrete.
At present in India, it is used for blended cement, rather than as cement
admixture. In large projects with central batching plant and in RMC this cement
substitute material could be used as useful mineral admixture and save cement to
the extent of 60 to 80 per cent.
Rice Husk Ash
It is obtained by
• Burning rice husk in a controlled manner without causing environmental
pollution.
• Material of future as mineral additives

136
Amount used
• 10% by weight of cement.
• It greatly enhances the workability and impermeability of concrete
It contains
• Amorphous silica (90% SiO2) in very high proportion when burnt in controlled
manner.
• 5% carbon.
• 2% K2O.
•The specific surface of RHA is between 40 – 100 m2/g.
India produces about 122 million ton of paddy every year. Each ton of paddy
producers about 40 kg of RHA. There is a good potential to make use of RHA as a
valuable pozzolanic material to give almost the same properties as that of micro
silica.
In U.S.A., highly pozzolanic rice husk ash is patented under trade name Agro-
silica and is marketed. Agro-silica exhibit super pozzolanic property when used in
small quantity i.e., 10% by weight of cement and it greatly enhances the workability
and impermeability of concrete.
It is a material of future as concrete admixtures.
Effects of Rice Husk Ash
Reduces susceptible to acid attack and improves resistance to chloride
penetration.

137
Reduces large pores and porosity resulting very low permeability.
Reduces the free lime present in the cement paste.
Decreases the permeability of the system.
Improves overall resistance to CO2 attack.
Enhances resistance to corrosion of steel in concrete.
Reducing micro cracking and improving freeze-thaw resistance.
Improves capillary suction and accelerated chloride diffusivity.
METAKAOLIN
Considerable research has been done on natural pozzolans, namely on
thermally activated ordinary clay and kaolinitic clay. These unpurified materials
have often been called “Metakaolin”.
Although it showed certain amount of pozzolanic properties, they are not
highly reactive.
• Highly reactive metakaolin is made by water processing to remove unreactive
impurities to make100% reactive pozzolana.
• Such a product, white or cream in colour, purified, thermally activated is called
High Reactive Metakaolin (HRM).
High reactive metakaolin shows high pozzolanic reactivity and reduction in Ca
(OH)2 even as early as one day. It is also observed that the cement paste undergoes
distinct densification.
The improvement offered by this densification includes an increase in strength
and decrease in permeability.
The high reactive metakaolin is having the potential to compete with silica
fume.

138
High reactive metakaolin by trade name “Metacem” is being manufactured
and marketed in India by speciality Minerals Division, Head office at Arundeep
Complex, Race Course, South Baroda 390 007.
• the synergy of cement and metakaolin tends to reduce the pore size to about a
tenth of the diameter within the first days. This is valid to a replacement until the
20% level and about 27% water in which most of the Portlandite formed will have
reacted to form additional CSH* or CSAH** phases.
• Through the formation of these phases the pores will be filled by additional binding
material.
Due to the lower pores diameter the water uptake is reduced.
• The total pore volume depends on the w/b ratio***. With very high porosity the
advantages of metakaolin replacement will decrease.
Effects of Metakaolin
• High reactive metakaolin shows high pozzolanic reactivity and reduction in
Ca (OH)2 even as early as one day.
• The cement paste undergoes distinct densification.
• Densification includes an increase in strength and decrease in permeability.
Use of Metakaolin
• The high reactive metakaolin is having the potential to compete with silica fume.

139

Building Materials and Concrete Technology Unit 2

More Related Content

What's hot (20)

Similar to Building Materials and Concrete Technology Unit 2 (20)

Recently uploaded (20)

Building Materials and Concrete Technology Unit 2