Building Materials and Concrete Technology Unit 3

NRI INSTITUTE OF TECHNOLOGY DEPARTMENT OF CIVIL ENGINEERING
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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 III
Fresh Concrete-Manufacture of concrete – Mixing and vibration of concrete,
Workability – Segregation and bleeding – Factors affecting workability, Measurement
of workability by different tests, Effect of time and temperature on workability –
Quality of mixing water, Ready mix concrete, Shotcrete

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Concrete: Manufacturing Process
A good quality concrete is essentially a homogeneous mixture of cement,
coarse and fine aggregates and water which consolidates into a hard mass due to
chemical action between the cement and water. Each of the four constituents has a
specific function. The coarser aggregate acts as a filler. The fine aggregate fills up

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the voids between the paste and the coarse aggregate. The cement in conjunction
with water acts as a binder. The mobility of the mixture is aided by the cement paste,
fines and nowadays, increasingly by the use of admixtures.
Most of the properties of the hardened concrete depend on the care
exercised at every stage of the manufacture of concrete. A rational proportioning of
the ingredients of concrete is the essence of the mix design. However, it may not
guarantee of having achieved the objective of the quality concrete work.
The aim of quality control is to ensure the production of concrete of uniform strength
from batch to batch. This requires some rules to be followed in the various stages of
concrete production and are discussed as follows. The stages of concrete production
are:
 Batching of materials
 Mixing
 Transportation
 Placing
 Compaction and
 Finishing of concrete
 Curing of concrete and methods of curing.

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Batching
Batching is the process of measuring concrete mix ingredients by either mass
or volume and introducing them into the mixer.
To produce concrete of uniform quality, the ingredients must be measured
accurately for each batch.
 Volume batching
 Weight batching
Volume batching:-
• This method is generally adopted for small jobs .
• Gauge boxes are used for measuring the fine and coarse aggregate.
• The volume of gauge box is equal to the volume of one bag of cement.
• Volume batching is not a good method for proportioning the material because
of the difficulty it offers to measure granular material in terms of volume.

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• Volume of moist sand in a loose condition weighs much less than the same
volume of dry compacted sand. The amount of solid granular material in a
cubic metre is an indefinite quantity.
• Because of this, for quality concrete material have to be measured by weight
only.
• However, for unimportant concrete or for any small job, concrete may be
batched by volume.
• Cement is always measured by weight. It is never measured in volume.
Generally, for each batch mix, one bag of cement is used. The volume of one
bag of cement is taken as thirty five (35) liters.
• Gauge boxes are used for measuring the fine and coarse aggregates. The
typical sketch of a gauge box is shown in Figure 6.12. The volume of the box
is made equal to the volume of one bag of cement i.e., 35 liters or multiple
thereof.
• Gauge bow are also called as FARMAS
• They can be made of timbers or steel.
• They are made generally deep and narrow
• Bottomless gauge boxes are generally avoided.
• While filling the gauge boxes the material should be filled loosely, no
compaction is allowed.
The gauge boxes are made comparatively deeper with narrow surface rather
than shallow with wider surface to facilitate easy estimation of top level. Sometimes
bottomless gauge-boxes are used.
This should be avoided. Correction to the effect of bulking should be made to
cater for bulking of fine aggregate, when the fine aggregate is moist and volume
batching is adopted.
Gauge boxes are generally called “Farmas”. They can be made of timber or
steel plates. Often in India volume batching is adopted even for large concreting

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operations. In a major site it is recommended to have the following gauge boxes at
site to cater for change in Mix Design or bulking of sand. The volume of each gauge
box is clearly marked with paint on the external surface.
Water is measured either in kg. or liters as may be convenient. In this case, the two
units are same, as the density of water is one kg. per liter.
The quantity of water required is a product of water/cement ratio and the
weight of cement;
for a example,
if the water/cement ratio of 0.5 is specified,
the quantity of mixing water required per bag of cement is
0.5 x 50.00 = 25 kg. or 25 liters.
The quantity is, of coarse, inclusive of any surface moisture
present in the aggregate.

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Weigh Batching:-
• Batching by weight is more preferable to volume batching ,as it is more
accurate and leads to more uniform proportioning.
• It does not have uncertainties associated with bulking.
 It’s equipment falls into 3 general categories :
I. Manual,
II. Semi automatic,
III. Fully automatic.
Weigh Batching:
Strictly speaking, weigh batching is the correct method of measuring the
materials. For important concrete, invariably, weigh batching system should be
adopted. Use of weight system in batching, facilitates accuracy, flexibility and
simplicity. Different types of weigh batchers are available, The particular type to be
used, depends upon the nature of the job.
Large weigh batching plants have automatic weighing equipment. The use of
this automatic equipment for batching is one of sophistication and requires qualified
and experienced engineers. In this, further complication will come to adjust water
content to cater for the moisture content in the aggregate.

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In smaller works, the weighing arrangement consists of two weighing buckets,
each connected through a system of levers to spring-loaded dials which indicate the
load. The weighing buckets are mounted on a central spindle about which they
rotate.
Thus, one can be loaded while the other is being discharged into the mixer
skip. A simple spring balance or the common platform weighing machines also can
be used for small jobs.
On large work sites, the weigh bucket type of weighing equipment's are used.
This fed from a large overhead storage hopper and it discharges by gravity, straight
into the mixer.
The weighing is done through a lever-arm system and two interlinked beams
and jockey weights. The required quantity of say, coarse aggregate is weighed,
having only the lower beam in operation. After balancing, by turning the smaller
lever, to the left of the beam, the two beams are interlinked and the fine aggregate
is added until they both balance.
The final balance is indicated by the pointer on the scale to the right of the
beams. Discharge is through the swivel gate at the bottom.
Automatic batching plants are available in small or large capacity. In this, the
operator has only to press one or two buttons to put into motion the weighing of all
the different ingredients.
Aggregate weighing machines require regular attention if they are to maintain
their accuracy. Check calibrations should always be made by adding weights in the
hopper equal to the full weight of the aggregate in the batch. The error found is
adjusted from time to time.
In small jobs, cement is often not weighed; it is added in bags assuming the
weight of the bag as 50 kg.
In reality, though the cement bag is made of 50 kg. at the factory, due to
transportation, handling at a number of places, it loses some cement, particularly,
when jute bags are used. In fact, the weight of a cement bag at the site is
considerably less. Sometimes, the loss of weight becomes more than 5 kg.
The above condition is one of the sources of error in volume batching and also
in weigh batching, when the cement is not actually weighed. But in important major
concreting jobs, cement is also actually weighed and the exact proportion as
designed is maintained.
Measurement of Water:
When weigh batching is adopted, the measurement of water must be done
accurately. Addition of water by graduated bucket in terms of liters will not be
accurate enough for the reason of spillage of water etc. It is usual to have the water

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measured in a horizontal tank or vertical tank fitted to the mixer. These tanks are
filled up after every batch.
The filling is so designed to have a control to admit any desired quantity of
water. Sometimes, water meters are fitted in the main water supply to the mixer
from which the exact quantity of water can be let into the mixer.
In modern batching plants sophisticated automatic microprocessor-controlled
weigh batching arrangements, not only accurately measures the constituent
materials, but also the moisture content of aggregates.
Moisture content is automatically measured by sensor probes and corrective
action is taken to deduct that much quantity of water contained in sand from the
total quantity of water. A number of such sophisticated batching plants are working
in our country for the last 10 years.
Cans for Measuring Water
MIXING of Concrete: -
The mixing should be ensured that the mass becomes homogeneous, uniform in
colour and consistency.
Methods of Mixing:
1.Hands (using hand shovels)
2.Stationary Mixers
3.Ready mix concrete
Hand Mixing: -
Mixing by hands using ordinary tools like, hand shovels etc. This type of mixing is
done for less output of concrete.

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Hand mixing is practised for small scale unimportant concrete works. As the
mixing cannot be thorough and efficient, it is desirable to add 10 per cent more
cement to cater for the inferior concrete produced by this method.
Hand mixing should be done over an impervious concrete or brick floor of
sufficiently large size to take one bag of cement. Spread out the measured quantity
of coarse aggregate and fine aggregate in alternate layers. Pour the cement on the
top of it, and mix them dry by shovel, turning the mixture over and over again until
uniformity of colour is achieved.
This uniform mixture is spread out in thickness of about 20 cm. Water is
taken in a water-can fitted with a rose-head and sprinkled over the mixture and
simultaneously turned over. This operation is continued till such time a good
uniform, homogeneous concrete is obtained. It is of particular importance to see that
the water is not poured but it is only sprinkled. Water in small quantity should be
added towards the end of the mixing to get the just required consistency.
At that stage, even a small quantity of water makes difference.
PROCEDURE:-
 Measured quantity of sand is spread evenly on platform.
 Spread the measured quantity of cement on this sand and mix it till the color of
concrete mixture is uniform.
 Spread the measured quantity of coarse aggregate on the platform with sand and
cement. Now spread the mixture of cement and sand on the stack of aggregate and
mix it at least 3 times.
 Add 3 quarters of total quantity of water required and turn the material towards
the center with spades.
STATIONARY MIXERS:-
Concrete is sometime mixed at jobsite in a stationary mixer having a size of 9 cubic
meter . These mixers may be of :
Tilting type

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Non-Tilting type
Tilting type mixer:-
It consist a conical drum which rotates on an inclinable axis.
It has only one opening.
The drum charged directly and discharged by tilting and reversing the drum.
NON TILTING TYPE MIXER:-
The mixing drum is cylindrical in shape and revolves two – horizontal axis.
It has opening on both sides.
The ingredients are charged in from one opening.
For discharging concrete chute is introducing to other opening by operating a lever.

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Normally, a batch of concrete is made with ingredients corresponding to 50 kg
cement. If one has a choice for indenting a mixer, one should ask for such a capacity
mixer that should hold all the materials for one bag of cement. This of course,
depends on the proportion of the mix.
For example, for 1 : 2 : 4 mix, the ideal mixer is of 200 litres capacity, whereas
if the ratio is 1 : 3 : 6, the requirement will be of 280 litres capacity to facilitate one
bag mix. Mixer of 200 litres capacity is insufficient for 1 : 3 : 6 mix and also mixer
of 280 litres is too big, hence uneconomical for 1 : 2 : 4 concrete.
To get better efficiency, the sequence of charging the loading skip is as under:
Firstly, about half the quantity of coarse aggregate is placed in the skip over which
about half the quantity of fine aggregate is poured.

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On that, the full quantity of cement i.e., one bag is poured over which the
remaining portion of coarse aggregate and fine aggregate is deposited in sequence.
This prevents spilling of cement, while discharging into the drum and also this
prevents the blowing away of cement in windy weather.
Before the loaded skip is discharged to the drum, about 25 per cent of the
total quantity of water required for mixing, is introduced into the mixer drum to wet
the drum and to prevent any cement sticking to the blades or at the bottom of the
drum.
Immediately, on discharging the dry material into the drum, the remaining 75
per cent of water is added to the drum. If the mixer has got an arrangement for
independent feeding of water, it is desirable that the remaining 75 per cent of water
is admitted simultaneously along with the other materials.
The time is counted from the moment all the materials, particularly, the
complete quantity of water is fed into the drum.
When plasticizer or superplasticizer is used, the usual procedure could be adopted
except that about one litre of water is held back.
Calculated quantity of plasticizer or superplasticizer is mixed with that one litre of
water and the same is added to the mixer drum after about one minute of mixing.
It is desirable that concrete is mixed little longer (say ½ minute more) so that
the plasticizing effect is fully achieved by proper dispersion.
When plasticizers are used, generally one has to do number of trials in the
laboratory for arriving at proper dosage and required slump. Small scale laboratory
mixers are inefficient and do not mix the ingredients properly. Plasticizer in small
quantity do not get properly dispersed with cement particles. To improve the
situations, the following sequence may be adopted.
Procedure for Utilizing Plasticizer for obtaining better and consistent results.
 Firstly, add all the water except about half a litre.
 Add cement and then add sand.
 Make an intimate mortar mix.
 Dilute calculated quantity of plasticizer with the remaining half a litre of water
and pour it into the drum.
 Rotate the drum for another half a minute, so that plasticizer gets well mixed with
cement mortar and then add both the fractions (20 mm and 10 mm) of coarse
aggregate.
 This procedure is found to give better and consistent results.
Mixing Time:

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Concrete mixers are generally designed to run at a speed of 15 to 20
revolutions per minute. For proper mixing, it is seen that about 25 to 30 revolutions
are required in a well designed mixer. In the site, the normal tendency is to speed
up the outturn of concrete by reducing the mixing time. This results in poor quality
of concrete.
On the other hand, if the concrete is mixed for a comparatively longer time, it
is uneconomical from the point of view of rate of production of concrete and fuel
consumption. Therefore, it is of importance to mix the concrete for such a duration
which will accrue optimum benefit.
It is seen from the experiments that the quality of concrete in terms of
compressive strength will increase with the increase in the time of mixing, but for
mixing time beyond two minutes, the improvement in compressive strength is not
very significant. Fig. shows the effect of mixing time on strength of concrete.
Concrete mixer is not a simple apparatus. Lot of considerations have gone as
input in the design of the mixer drum:
 The shape of drum
 The number of blades
 Inclination of blades with respect to drum surface
 The length of blades
 The depth of blades
 The space between the drum and the blades
 The space between metal strips of blades and speed of rotation etc., are important
to give uniform mixing quality and optimum time of mixing.
Generally mixing time is related to the capacity of mixer. The mixing time
varies between 1½ to 2½ minutes. Bigger the capacity of the drum more is the
mixing time.

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However, modern high speed pan mixer used in RMC, mixes the concrete in
about 15 to 30 secs. One cubic meter capacity high speed Pan Mixer takes only
about 2 minutes for batching and mixing.
The batching plant takes about 12 minutes to load a transit mixer of 6 m3
capacity.
Modern ready mixed concrete plant
Sometimes, at a site of work concrete may not be discharged from the drum
and concrete may be kept rotating in the drum for long time, as for instance when
some quarrel or dispute takes place with the workers, or when unanticipated repair
or modification is required to be done on the formwork and reinforcement.
Long-time mixing of concrete will generally result in increase of compressive
strength of concrete within limits.
Due to mixing over long periods, the effective water/cement ratio gets reduced,
owing to the absorption of water by aggregate and evaporation.
It is also possible that the increase in strength may be due to the improvement
in workability on account of excess of fines, resulting from the abrasion and attrition
of coarse aggregate in the mix, and from the coarse aggregates themselves becoming
rounded.
The above may not be true in all conditions and in all cases.
Sometimes, the evaporation of water and formation of excess fines may reduce
the workability and hence bring about reduction in strength. The excess of fine may
also cause greater shrinkage.
Retempering of Concrete

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Often long hauls are involved in the following situation-delivery of concrete
from central mixing plant, in road construction, in constructing lengthy tunnels, in
transportation of concrete by manual labour in hilly terrain.
Loss of workability and undue stiffening of concrete may take place at the time
of placing on actual work site.
Engineers at site, many a time, reject the concrete partially set and unduly
stiffened due to the time elapsed between mixing and placing.
Mixed concrete is a costly material and it can not be wasted without any
regard to cost. It is required to see whether such a stiffened concrete could be used
on work without undue harm.
The process of remixing of concrete, if necessary, with addition of just the
required quantity of water is known as “Retempering of Concrete”.
Sometimes, a small quantity of extra cement is also added while retempering.
Many specifications do not permit retempering. I.S. 457 – 1957 did not permit
retempering of partially hardened concrete or mortar requiring renewed mixing, with
or without addition of cement, aggregate or water.
However, many research workers are of the view that retempering with the
addition of a small quantity of water may be permitted to obtain the desired slump
provided the designed water/ cement ratio is not exceeded.
They caution that the production of concrete of excessive slump or adding water in
excess of designed water cement ratio to compensate for slump loss resulting from
delays in delivery or placing should be prohibited.
It is seen from the investigations, retempering of concrete which is too wet a
mix, at a delay of about one hour or so showed an increase in compressive strength
of 2 to 15 per cent.
Retempering at further delay resulted in loss of strength.
However, this loss of strength is smaller than would be expected from the
consideration of the total water/cement ratio i.e., the initial water cement ratio plus
water added for retempering to bring the mix back into the initial degree of
workability.
Maintenance of Mixer
Concrete mixers are often used continuously without stopping for several
hours for continuous mixing and placing. It is of utmost importance that a mixer
should not stop in between concreting operation. For this reason, concrete mixer
must be kept well maintained.
Mixer is placed at the site on a firm and levelled platform. The drum and
blades must be kept absolutely clean at the end of concreting operation. The drum
must be kept in the tilting position or kept covered when not in use to prevent the

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collection of rain water. The skip is operated carefully and it must rest on proper
cushion such as sand bags.
AGITATORTRUCKS:-
A vehicle carrying a drum or agitator body, in which freshly mixed concrete
can be conveyed from the point of mixing to that of placing, the drum being rotated
continuously to agitate the contents.
Advantages:
Operate usually from central mixing plants.
Watch for:
Timing of deliveries should suit job organization. Concrete crew
and equipment must be ready onsite to handle concrete.
Used for:
Transporting concrete for all uses according the need.
NON-AGITATINGTRUCKS:-
Used for:
Transport concrete on short hauls(small distance) over smooth roadways.
Advantages:
Cost of non- agitating equipment is lower than that of truck agitators or mixers.
Watch for:
Slump should be limited.
Possibility of segregation.
Height upon discharge is needed.

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TRUCK-MIXED CONCRETE
Used for:
Intermittent (periodic) production of concrete at jobsite, or small quantities.
Advantages:
Combined materials transporter and batching and mixing system.
One- man operation.
Transporting Concrete
Concrete can be transported by a variety of methods and equipment's. The
precaution to be taken while transporting concrete is that the homogeneity obtained
at the time of mixing should be maintained while being transported to the final place
of deposition. The methods adopted for transportation of concrete are:
(a) Mortar Pan (g) Skip and Hoist
(b) Wheel Barrow, Hand Cart (h) Transit Mixer
(c) Crane, Bucket and Rope way (i ) Pump and Pipe Line
(d ) Truck Mixer and Dumpers ( j ) Helicopter.
(e) Belt Conveyors
(f ) Chute
Mortar Pan:

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Use of mortar pan for transporation of concrete is one of the common methods
adopted in this country. It is labour intensive. In this case, concrete is carried in
small quantities.
While this method nullifies the segregation to some extent, particularly in
thick members, it suffers from the disadvantage that this method exposes
greater surface area of concrete for drying conditions.
Mortar Pan
Use of mortar pan for transporation of concrete is one of the common methods
adopted in this country. It is labour intensive. In this case, concrete is carried in
small quantities. While this method nullifies the segregation to some extent,
particularly in thick members, it suffers from the disadvantage that this method
exposes greater surface area of concrete for drying conditions.
This results in greater loss of water, particularly, in hot weather concreting
and under conditions of low humidity. It is to be noted that the mortar pans must
be wetted to start with and it must be kept clean during the entire operation of
concreting.
Mortar pan method of conveyance of concrete can be adopted for concreting
at the ground level, below or above the ground level without much difficulties.
Wheelbarrows and Buggies:
 Wheel barrows are normally used for transporting concrete to be placed at
ground level.
 This method is employed for hauling concrete for comparatively longer
distance as in the case of concrete road construction.
 If concrete is conveyed by wheel barrow over a long distance, on rough
ground, it is likely that the concrete gets segregated due to vibration.
 The capacity of wheelbarrows varies from 70 to 80 litres.
 Suitable for concrete road construction where concrete is deposited at
or below mixer level.

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Belt Conveyors:
Belt conveyors have very limited applications in concrete construction. The
principal objection is the tendency of the concrete to segregate on steep inclines, at
transfer points or change of direction, and at the points where the belt passes over
the rollers.
Belt Conveyors
Another disadvantage is that the concrete is exposed over long stretches which
causes drying and stiffening particularly, in hot, dry and windy weather.
Segregation also takes place due to the vibration of rubber belt. It is necessary
that the concrete should be remixed at the end of delivery before placing on the final
position.

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Modern Belt Conveyors can have adjustable reach, travelling diverter and
variable speed both forward and reverse. Conveyors can place large volumes of
concrete quickly where access is limited.
There are portable belt conveyors used for short distances or lifts. The end
discharge arrangements must be such as to prevent segregation and remove all the
mortar on the return of belt. In adverse weather conditions (hot and windy) long
reaches of belt must be covered.
Cranes and Buckets and Rope way:
Used for Work above ground level , Buckets use with Cranes, cableways, and
helicopters.
A crane and bucket is one of the right equipment for transporting concrete
above ground level.
Crane can handle concrete in high rise construction projects and are
becoming a familiar site in big cities.
Cranes are fast and versatile to move concrete horizontally as well as vertically along
the boom and allows the placement of concrete at the exact point.
Cranes carry skips or buckets containing concrete. Skips have discharge door at
the bottom, whereas buckets are tilted for emptying.
For a medium scale job the bucket capacity may be 0.5 m3.

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Truck Mixer and Dumpers
For large concrete works particularly for concrete to be placed at ground level,
trucks and dumpers or ordinary open steel-body tipping lorries can be used.
As they can travel to any part of the work, they have much advantage over the
jubilee wagons, which require rail tracks.
Dumpers are of usually 2 to 3 cubic metre capacity, whereas the capacity of
truck may be 4 cubic metre or more.

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Chute:
Chutes are generally provided for transporting concrete from ground level to
a lower level. The sections of chute should be made of or lined with metal and all
runs shall have approximately the same slope, not flatter than 1 vertical to 2 1/2
horizontal. The lay-out is made in such a way that the concrete will slide evenly in
a compact mass without any separation or segregation.
The required consistency of the concrete should not be changed in order to
facilitate chuting. If it becomes necessary to change the consistency the concrete
mix will be completely redesigned. This is not a good method of transporting
concrete.
However, it is adopted, when movement of labour cannot be allowed due to
lack of space or for fear of disturbance to reinforcement or other arrangements
already incorporated. (Electrical conduits or switch boards etc.,).

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Skip and Hoist:
This is one of the widely adopted methods for transporting concrete vertically
up for multistorey building construction. Employing mortar pan with the staging
and human ladder for transporting concrete is not normally possible for more than
3 or 4 storeyed building constructions. For laying concrete in taller structures, chain
hoist or platform hoist or skip hoist is adopted.
At the ground level, mixer directly feeds the skip and the skip travels up over
rails upto the level where concrete is required. At that point, the skip discharges the
concrete automatically or on manual operation. The quality of concrete i.e. the
freedom from segregation will depend upon the extent of travel and rolling over the
rails.
If the concrete has travelled a considerable height, it is necessary that
concrete on discharge is required to be turned over before being placed finally.
Transit Mixer

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Transit mixer is one of the most popular equipments for transporting concrete
over a long distance particularly in Ready Mixed Concrete plant (RMC). In India,
today (2000 AD) there are about 35 RMC plants and a number of central batching
plants are working. It is a fair estimate that there are over 600 transit mixers in
operation in India.
They are truck mounted having a capacity of 4 to 7 m3. There are two
variations. In one, mixed concrete is transported to the site by keeping it agitated all
along at a speed varying between 2 to 6 revolutions per minute. In the other category,
the concrete is batched at the central batching plant and mixing is done in the truck
mixer either in transit or immediately prior to discharging the concrete at site.
Transit-mixing permits longer haul and is less vulnerable in case of delay.
The truck mixer the speed of rotating of drum is between 4–16 revolution per minute.
 Used for transporting the concrete over long distance particularly in RMC
plant
With the development of twin fin process mixer, the transit mixers have become
more efficient in mixing. In these mixers, in addition to the outer spirals, have two
opposed inner spirals. The outer spirals convey the mix materials towards the
bottom of the drum, while the opposed mixing spirals push the mix towards the feed
opening. The repeated counter current mixing process is taking place within the
mixer drum.
Sometimes a small concrete pump is also mounted on the truck carrying
transit mixer. This pump, pumps the concrete discharged from transit mixer.
Currently we have placer boom also as part of the truck carrying transit mixer and
concrete pump and with their help concrete is transported, pumped and placed into
the formwork of a structure easily.
As per estimate made by CM Doordi, the cost of transportation of concrete by
transit mixer varies between Rs 160 to 180 per cubic metre.
Pumps and Pipeline

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Conveying concrete from central discharge point to formwork.
Pumping of concrete is universally accepted as one of the main methods of
concrete transportation and placing. Adoption of pumping is increasing
throughout the world as pumps become more reliable and also the concrete mixes
that enable the concrete to be pumped are also better understood.
Concrete Pumps:
In the past a simple two-stroke mechanical pump consisted of a receiving
hopper, an inlet and an outlet valve, a piston and a cylinder. The pump was powered
by a diesel engine.
The pumping action starts with the suction stroke drawing concrete into the
cylinder as the piston moves backwards. During this operation the outlet value is

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closed. On the forward stroke, the inlet valve closes and the outlet valve opens to
allow concrete to be pushed into the delivery pipe.
Fig. Direct Acting Concrete Pump
The modern concrete pump is a sophisticated, reliable and robust machine. The
modern concrete pump still operates on the same principles but with lot of
improvements and refinements in the whole operations.
During 1963, squeeze type pump was developed in U.S.A.
In this concrete placed in a collecting hopper is fed by rotating blades into a flexible
pipe connected to the pumping chamber, which is under a vacuum of about 600
mm of mercury.
The vacuum ensures that, except when being squeezed by roller, the pipe shape
remains cylindrical and thus permits a continuous flow of concrete.
Two rotating rollers progressively squeeze the flexible pipes and thus move the
concrete into the delivery pipe.

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Fig. shows the action of squeeze pump
The hydraulic piston pump is the most widely used modern pump. Specification
differ but concept of working of modern pump is the same as it was for original
mechanically driven pumps. A pump consists of three parts, a concrete receiving
happer, a valve system and a power transmission system.
There are three main types of concrete pump. They are mobile, trailor or static
and screed or mortar pump.
Capabilities of Concrete Pump:
Concrete has been pumped to a height over 400 m and a horizontal distance
of over 2000 m. This requires selected high pressure pump and special attention to
concrete mix design.
Pumpable Concrete :
A concrete which can be pushed through a pipeline is called a pumpable
concrete. It is made in such a manner that its friction at the inner wall of the pipeline

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does not become very high and that it does not wedge while flowing through the
pipeline. A clear understanding of what happens to concrete when it is pumped
through pipeline is fundamental to any study of concrete pumping.
Pumpable concrete emerging from a pipeline flows in the form of a plug which
is separated from the pipe wall by a thin lubricating layer consisting of cement paste.
The water in the paste is hydraulically linked with the interparticle water layer in
the plug.
Fig. shows the concrete flow under pressure.
Design Considerations for Pumpable Concrete:
The mix is proportioned in such a way that it is able to bind all the constituent
materials together under pressure from the pump and thereby avoiding segregation
and bleeding. The mix must also facilitate the radial movement of sufficient grout to
maintain the lubricating film initially placed on the pipeline wall.
The mix should also be able to deform while flowing through bends. There are
two main reasons why blockages occur and that the plug of concrete will not move:
 Water is being forced out of the mix creating bleeding and blockage by
jamming, or
 There is too much frictional resistance due to the nature of the ingredients of
the mix.
Choosing the Correct Pump
 For choosing the correct pump one must know the following factors
 " Length of horizontal pipe
 " Length of vertical pipe
 " Number of bends
 " Diameter of pipeline
 " Length of flexible hose
 " Changes in line diameter
 " Slump of Concrete.

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Common Problems in Pumping Concrete:
The most common problem in pumping concrete is blockage. If concrete fails
to emerge at the end of pipeline, if pump is mechanically sound, it would mean that
there is blockage somewhere in the system. This will be indicated by an increase in
the pressure shown on the pressure gauge.
Most blockages occur at tapered sections at the pump end.
Blockages take place generally due to the unsuitability of concrete mix,
pipeline and joint deficiencies and operator’s error or careless use of hose end. It has
been already discussed regarding the quality of pumpable concrete.
A concrete of right consistency which forms a concrete plug surrounded by
lubricating slurry formed inside the wall of pipeline with right amount of water, well
proportioned, homogeneously mixed concrete can only be pumped. It can be rightly
said that a pumpable concrete is a good concrete.
 Sometimes, high temperature, use of admixtures, particularly,
accelerating admixtures and use of high grade cement may cause blockages.
Chances of blockage are more if continuous pumping is not done.
 A pipeline which is not well cleaned after the previous operation,
uncleaned, worn-out hoses, too many and too sharp bends, use of worn out
joints are also other reasons for blockages.
 Operators must realise and use sufficient quantity of lubricating grout
to cover the complete length of pipeline before pumping of concrete. The hose
must be well lubricated.
 Extreme care should be taken in handling the flexible rubber end hose.
Careless bending can cause blockages.
Clearing Blockages:
 A minor blockage may be cleared by forward and reverse pumping.
 Excess pressure should not be blindly exerted. If may make the problem
worse.
 Sometime shortening the pipeline will reduce pressure and on restarting
pumping the blockage gets cleared off.
 Tapping the pipeline with hammer and observing the sound one can often
locate a blockage.
 Blockage could be cleared by rodding or by using sponge ball pushed by
compressed air or water at high pressure.
Placing of concrete

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The process of depositing concrete in its required position is termed as placing.
Concrete should be placed in systematic manner to get optimum results.
Precautions: -
Placing concrete within earth mould
 Concrete is invariable as foundation bed below the walls and columns before
placing concrete
 All loose earth must be removed.
 Roots of trees must be cut.
 If surface is dry, it should be made damp.
 If it is too wet or rain soaked the water, then slush must be removed
(Example: Foundation concrete for a wall or column).
Placing concrete in layers with in timber or steel shutter :-
This can be used in the following cases
 Dam construction
 Construction of concrete abutments
 Raft for a high rise building
 The thickness of layers depend on
 Method of compaction
 Size of vibrator
 Frequency of vibrator used
It is good for laying 15 to 30 cm thick layer of concrete, for mass concrete it
may vary from 35 to 45 cm. It’s better to leave the top of the layer rough so that
succeeding layer can have the good bond.
(example: Foundation concrete for a wall or column).
Placing concrete within large earth mould or timber plank formwork:
(example: Road slab and Airfield slab).
Placing concrete with in usual form work:-
 Adopted for column ,beam and floors rules that should be followed while
placing the concrete.
 Check the reinforcements are correctly tied and placed.
 Mould releasing agent should be applied.
 The concrete must be placed carefully with a small quantity at a time so that
they will not block the entry of subsequent concrete.
 (example: Foundation concrete for a wall or column).
Placing concrete under water:-
Concrete having cement content at least 450kg/m3 and a slump of 10 to
17.5cm can be placed underwater.

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Precautions To Be Taken For Placing Of Concrete On-Site:
 For the construction of road slabs, airfield slabs and ground floor slabs in
buildings, concrete is placed in bays.
 The ground surface on which the concrete is placed must be free from loose
earth, pool of water and other organic matters like grass, roots, leaves etc.
 The earth must be properly compacted and made sufficiently damp to prevent
the absorption of water from concrete.
 If this is not done, the bottom portion of concrete is likely to become weak.
 Sometimes, to prevent absorption of moisture from concrete, by the large
surface of earth, in case of thin road slabs, use of polyethylene film is used in
between concrete and ground.
 Concrete is laid in alternative bays giving enough scope for the concrete to
undergo sufficient shrinkage.
 Provisions for contraction joints and dummy joints are given.
 It must be remembered that the concrete must be dumped and not poured. It
is also to be ensured that concrete must be placed in just required thickness.
 The practice of placing concrete in a heap at one place and then dragging it
should be avoided.
 When concrete is laid in great thickness, as in the case of concrete raft for a
high rise building or in the construction of concrete pier or abutment or in the
construction of mass concrete dam, concrete is placed in layers.
The thickness of layers depends upon the mode of compaction. In reinforced
concrete, it is a good practice to place concrete in layers of about 15 to 30 cm thick
and in mass concrete, the thickness of layer may vary anything between 35 to 45
cm.
Several such layers may be placed in succession to form one lift, provided they
follow one another quickly enough to avoid cold joints. The thickness of layer is
limited by the method of compaction and size and frequency of vibrator used.
Before placing the concrete, the surface of the previous lift is cleaned
thoroughly with water jet and scrubbing by wire brush. In case of dam, even sand
blasting is also adopted.
The old surface is sometimes hacked and made rough by removing all the
laitance and loose material. The surface is wetted. Sometimes, a neat cement slurry
or a very thin layer of rich mortar with fine sand is dashed against the old surface,
and then the fresh concrete is placed.
The whole operation must be progressed and arranged in such a way that,
cold joints are avoided as far as possible. When concrete is laid in layers, it is better

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to leave the top of the layer rough, so that the succeeding layer can have a good
bond with the previous layer.
Where the concrete is subjected to horizontal thrust, bond bars, bond rails or bond
stones are provided to obtain a good bond between the successive layers. Of course,
such arrangements are required for placing mass concrete in layers, but not for
reinforced concrete.
Certain good rules should be observed while placing concrete within the
formwork, as in the case of beams and columns.
 Firstly, it must be checked that the reinforcement is correctly tied, placed and
is having appropriate cover.
 The joints between planks, plywood's or sheets must be properly and
effectively plugged so that matrix will not escape when the concrete is vibrated.
 The inside of the formwork should be applied with mould releasing agents for
easy stripping. Such purpose made mould releasing agents are separately
available for steel or timber shuttering.
Good rules should be observed while placing concrete within the formwork, as
in the case of beams and columns.
 The reinforcement should be clean and free from oil.
 Where reinforcement is placed in a congested manner, the concrete must be
placed very carefully, in small quantity at a time so that it does not block the
entry of subsequent concrete. The above situation often takes place in heavily
reinforced concrete columns with close lateral ties, at the junction of column
and beam and in deep beams.
 Generally, difficulties are experienced for placing concrete in the column.
 Often concrete is required to be poured from a greater height. (Height of
pouring concrete should not exceed 1.5 m)
 When the concrete is poured from a height, against reinforcement and lateral
ties, it is likely to segregate or block the space to prevent further entry of
concrete.
 To avoid this, concrete is directed by tremie, drop chute or by any other means
to direct the concrete within the reinforcement and ties.
Form work:
Form work shall be designed and constructed so as to remain sufficiently rigid
during placing and compaction of concrete. The joints are plugged to prevent the
loss of slurry from concrete.

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Stripping Time:
Formwork should not be removed until the concrete has developed a strength
of at least twice the stress to which concrete may be subjected at the time of removal
of formwork.
In special circumstances the strength development of concrete can be
assessed by placing companion cubes near the structure and curing the same in the
manner simulating curing conditions of structures.
In normal circumstances, where ambient temperature does not fall below 15°C
and where ordinary Portland cement is used and adequate curing is done.
Following striking period can be considered sufficient as per IS 456 of 2000.
Methods of Placing Underwater Concreting:-
 Bottom dump method
 Bagged method
 Tremie
 Grouted aggregate
 Concrete pump
Bottom dump method
In the bottom dump bucket concrete is taken through the water in a water-tight box
or bucket and on reaching the final place of deposition the bottom is made to open
by some mechanism and the whole concrete is dumped slowly.
This method will not give a satisfactory result as certain amount of washing
away of cement is bound to occur.

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Bagged method
In some situations, dry or semi-dry mixture of cement, fine and coarse
aggregate are filled in cement bags and such bagged concrete is deposited on the
bed below the water. This method also does not give satisfactory concrete, as the
concrete mass will be full of voids interspersed with the putrescible (liable to decay)
gunny bags.
The satisfactory method of placing concrete under water is by the use of tremie
pipe.
The word “tremie” is derived from the French word “hopper”.
Tremie Method

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A tremie pipe is a pipe having a diameter of about 20 cm capable of easy
coupling for increase or decrease of length. A funnel is fitted to the top end to
facilitate pouring of concrete. The bottom end is closed with a plug or thick
polyethylene sheet or such other material and taken below the water and made to
rest at the point where the concrete is going to be placed.
Since the end is blocked, no water will have entered the pipe. The concrete
having a very high slump of about 15 to 20 cm is poured into the funnel. When the
whole length of pipe is filled up with the concrete, the tremie pipe is lifted up and a
slight jerk is given by a winch and pully arrangement. When the pipe is raised and
given a jerk, due
to the weight of concrete, the bottom plug falls and the concrete gets discharged.
Placing Concrete Underwater: -
Method Used:
Tremie
Advantages:
Can be used to funnel concrete down through the water into the structure.
Watch for:
Discharge end always has to be buried in fresh concrete to ensure seal
between water and concrete

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Particular care must be taken at this stage to see that the end of the tremie
pipe remains inside the concrete, so that no water enters into the pipe from the
bottom. In other words, the tremie pipe remains plugged at the lower end by
concrete.
Again concrete is poured over the funnel and when the whole length of the
tremie pipe is filled with concrete, the pipe is again slightly lifted and given slight
jerk. Care is taken all the time to keep the lower end of the tremie pipe well embedded
in the wet concrete.
The concrete in the tremie pipe gets discharged. In this way, concrete work is
progressed without stopping till the concrete level comes above the water level.
This method if executed properly, has the advantage that the concrete does
not get affected by water except the top layer. The top layer is scrubbed or cut off to
remove the affected concrete at the end of the whole operation.
During the course of concreting, no pumping of water should be permitted. If
simultaneous pumping is done, it may suck the cement particles. Under water
concreting need not be compacted, as concrete gets automatically compacted by the
hydrostatic pressure of water.

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Secondly, the concrete is of such consistency that it does not normally require
compaction. One of the disadvantages of under water concreting in this method is
that a high water/cement ratio is required for high consistency which reduces the
strength of concrete. But at present, with the use of superplasticizer, it is not a
constraint.
A concrete with as low a w/c ratio as 0.3 or even less can be placed by tremie
method.
Grouted aggregate Method
Another method, not so commonly employed to place concrete below water is the
grouting process of prepacked aggregate.
 Coarse aggregate is dumped to assume full dimension of the concrete mass.
Cement mortar grout is injected through pipes, which extend up to the bottom
of the aggregate bed.
 The pipes are slowly withdrawn, as the grouting progresses.
 The grout forces the water out from the interstices and occupies the space.
 For plugging the well foundation this method is often adopted.
Concrete Pump
Concrete also can be placed under water by the use of pipes and concrete
pumps. The pipeline is plugged at one end and lowered until it rests at the bottom.
Pumping is then started.
When the pipe is completely filled, the plug is forced out, the concrete
surrounding the lower end of the pipe seals the pipe. The pumping is done against
the pressure of the plug at the lower end.

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When the pumping effort required is too great to overcome the pressure, the
pipe is withdrawn and the operation is repeated. This process is repeated until
concrete reaches the level above water.
Slip-Form Technique
There are special methods of placement of concrete using slip-form technique.
Slip forming can be done both for vertical construction or horizontal construction.
Slip-forming of vertical construction is a proven method of concrete construction
generally adopted for tall structures. In this method, concrete is continuously
placed, compacted and formwork is pulled up by number of hydraulic Jacks, giving
reaction, against jack rods or main reinforcements.
The rate of slipping the formwork will vary depending upon the temperature
and strength development of concrete to withstand without the support of formwork.
In India number of tall structures like chimneys and silos have been built by this
technique.

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Although this method of construction is suitable for uniform shaped
structures it was adopted for the core construction of stock exchange building at
Bombay having irregular shape and number of openings. The core of 380 feet tall
structure was completed in about 38 days. The formwork was slipped at the rate of
about 12.5 cm per hour.
The horizontal slip-form construction is rather a new technique in India. It is
adopted for road pavement construction. For the first time the slip-form paving
method was adopted in Delhi-Mathura concrete Road construction during mid
1990’s.
The slip-form pavers were used by many contracting firms in the construction
of Mumbai- Pune six lane express highway. The state-of the art method of slip form
pavement construction has come to India in a big way.
Slip-form paver is a major equipment, capable of spreading the concrete dumped in
front of the machine by tippers or dumpers, compacting the concrete through
number of powerful internal needle vibrators and double beam surface vibrators.
The paver carries out the smooth finishing operation to the highest accuracy and
then texture the surface with nylon brush operating across the lane.
The equipment also drops the tie bar at the predetermined interval and push
them through and places them at the predetermined depth and recompact the

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concrete to cover up the gap that are created by the dowel bars. Generally no
bleeding takes place because of the stiff consistency of the concrete (2 cm slump)
that is designed for placing by slip-form paver.
If at all any little bleeding water is there, upon its disappearance, membrane
forming curing compound is sprayed on to the textured surface of concrete.
All the above operations are continuously carried out and the slip-form paver crawls
continuously on tracked wheel, guided by laser control. Proper alignment to cater
for straight line, or curve of any degree with calculated super elevation, or upward
or downward gradients are controlled by laser application.
Computerized laser control is the backbone of this state-of- the art slip-form
paver equipment. The speed of construction i.e., the speed of continuous movement
of paver is around 1 meter per minute and in a day of 16 hours working, this
equipment can complete about one km of one lane road of width 3.75 m and depth
35 cm.
In the Mumbai-Pune express highway construction, they have used two types
of paving equipment's namely wirtgen SP 500 and CMI. They are used for lane by
lane construction. Whereas in Europe and the other advanced countries, slip-form
pavers capable of completing two or three lanes in one operation are used.
To feed such a paver, large quantity of concrete of uniform quality is required. In
India today, the capacity of batching is a limitation. In Europe continuous batching
plants which can supply consistent quality of concrete at a rate of 150 to 250 m3/hr
are available.
This rate will make it possible to supply extra wide slip-form paver.
Sophistication in road construction has just started in India. With the experience
gained, we will be able to produce large quantities of manufactured fine and coarse
aggregate of right quality needed for high rate of production of concrete to meet the
requirement of multi lane slip-form paver.
Placing high quality concrete by slip-form technique for a width of 8.5 m
Compaction of Concrete

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Compaction of concrete is the process adopted for expelling the entrapped air
from the concrete. In the process of mixing, transporting and placing of concrete air
is likely to get entrapped in the concrete. The lower the workability, higher is the
amount of air entrapped.
Purpose:
• To remove entrapped air bubbles in concrete
• To achieve high density
• To improve strength and durability
• To eliminate honey comb and other defects.
In other words, stiff concrete mix has high percentage of entrapped air and,
therefore , would need higher compacting efforts than high workable mixes. If this
air is not removed fully, the concrete loses strength considerably. Fig. 6.23 shows
the relationship between loss of strength and air voids left due to lack of compaction.
It can be seen from the figure that 5 per cent voids reduce the strength of cocrete by
about 30 per cent and 10 per cent voids redduce the strength by over 50 per cent.
Therefore, it is imperative that 100 per cent compaction of concrete is one of
the most important aim to be kept in mind in good concrete-making practices. It
must be borne in mind that 100 per cent compaction is important not only from the
point of view of strength, but also from the point of durability.
In recent time, durability becomes more important than strength. Insufficient
compaction increases the permeability of concrete resulting in easy entry for
aggressive chemicals in solutin, which attack concrete and reinforcement to reduce
the durabilityof concrete. Therefore, 100 per cent compaction of concrete is of
paramount importance.
In order to achieve full compaction and maximum density, with reasonable
compacting efforts available at site, it is necessary to use a mix with adequate
workability. It is also of common knowledge that the mix should not be too wet for
easy compaction which also reduces the strength of concrete.

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For maximum strength, driest possible concrete should be compacted 100 per
cent. The overall economy demands 100 per cent compaction with a reasonable
compacting efforts available in the field.
Importance of Compaction
• Air voids increase concrete's permeability. That in turn reduces its
durability.
• If the concrete is not dense and impermeable, it will not be watertight. It will
be less able to withstand aggressive liquids.
• Moisture and air are more likely to penetrate to the reinforcement causing it
to rust.
• Proper compaction also ensures that the formwork is completely filled
i.e. there are no pockets of honeycombed material and that the required finish is
obtained on vertical surfaces

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The following methods are adopted for compacting the concrete:
(a) Hand Compaction
(i ) Rodding (ii ) Ramming (iii ) Tamping
(b) Compaction by Vibration
(i ) Internal vibrator (Needle vibrator)
(ii ) Formwork vibrator (External vibrator) (iii ) Table vibrator
(iv ) Platform vibrator
(v ) Surface vibrator (Screed vibrator)
(vi ) Vibratory Roller.
(c ) Compaction by Pressure and Jolting
(d) Compaction by Spinning.
Hand Compaction:
Hand compaction of concrete is adopted in case of unimportant concrete work
of small magnitude. Sometimes, this method is also applied in such situation, where
a large quantity of reinforcement is used, which cannot be normally compacted by
mechanical means. Hand compaction consists of rodding, ramming or tamping.
When hand compaction is adopted, the consistency of concrete is maintained
at a higher level. The thickness of the layer of concrete is limited to about 15 to 20
cm.
Rodding

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It is nothing but poking the concrete with about 2 metre long, 16 mm diameter
rod to pack the concrete between the reinforcement and sharp corners and edges.
Rodding is done continuously over the complete area to effectively pack the concrete
and drive away entrapped air. Sometimes, instead of iron rod, bamboos or cane is
also used for rodding purpose.
Ramming
It should be done with care. Light ramming can be permitted in unreinforced
foundation concrete or in ground floor construction. Ramming should not be
permitted in case of reinforced concrete or in the upper floor construction, where
concrete is placed in the formwork supported on struts.
If ramming is adopted in the above case the position of the reinforcement may
be disturbed or the formwork may fail, particularly, if steel rammer is used.
Tamping
It is one of the usual methods adopted in compacting roof or floor slab or road
pavements where the thickness of concrete is comparatively less and the surface to
be finished smooth and level.
Tamping consists of beating the top surface by wooden cross beam of section
about 10 x 10 cm. Since the tamping bar is sufficiently long it not only compacts,
but also levels the top surface across the entire width.

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Compaction by Vibration:
It is pointed out that the compaction by hand, if properly carried out on
concrete with sufficient workability, gives satisfactory results, but the strength of
the hand compacted concrete will be necessarily low because of higher water cement
ratio required for full compaction.
Where high strength is required, it is necessary that stiff concrete, with low
water/cement ratio be used.
To compact such concrete, mechanically operated vibratory equipment, must
be used. The vibrated concrete with low water/cement ratio will have many
advantages over the hand compacted concrete with higher water/cement ratio.
The modern high frequency vibrators make it possible to place economically
concrete which is impracticable to place by hand. A concrete with about 4 cm slump
can be placed and compacted fully in a closely spaced reinforced concrete work,
whereas, for hand compaction, much higher consistency say about 12 cm slump
may be required.
The action of vibration is to set the particles of fresh concrete in motion,
reducing the friction between them and affecting a temporary liquefaction of
concrete which enables easy settlement. While vibration itself does not affect the

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strength of concrete which is controlled by the water/cement ratio, it permits the
use of less water.
Concrete of higher strength and better quality can, therefore, be made with a
given cement factor with less mixing water.
Double Beam Screed Board Vibrator
Where only a given strength is required, it can be obtained with leaner mixes
than possible with hand compaction, making the process economical. Vibration,
therefore, permits improvement in the quality of concrete and in economy.
Compaction of concrete by vibration has almost completely revolutionised the
concept of concrete technology, making possible the use of low slump stiff mixes for
production of high quality concrete with required strength and impermeability.
The use of vibration may be essential for the production of good concrete
where the congestion of the reinforcement or the inaccessibility of the concrete in
the formwork is such that hand compaction methods are not practicable.
Vibration may also be necessary if the available aggregates are of such poor
shape and texture which would produce a concrete of poor workability unless large
amount of water and cement is used.
In normal circumstances, vibration is often adopted to improve the
compaction and consequently improve the durability of structures.
In this way, vibration can, under suitable conditions, produce better quality concrete
than by hand compaction.
Lower cement content and lower water-cement ratio can produce equally
strong concrete more economically than by hand compaction.
Although vibration properly applied is a great step forward in the production of
quality concrete, it is more often employed as a method of placing ordinary concrete
easily than as a method for obtaining high grade concrete at an economical cost.
All the potential advantages of vibration can be fully realised only if proper
control is exercised in the design and manufacture of concrete and certain rules are
observed regarding the proper use of different types of vibrators.
Internal Vibrator:
Of all the vibrators, the internal vibrator is most commonly used. This is also
called, “Needle Vibrator”, “Immersion Vibrator”, or “Poker Vibrator”. This essentially
consists of a power unit, a flexible shaft and a needle (head (poker)) . The power unit

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may be electrically driven or operated by petrol engine or air compressor. The
vibrations are caused by eccentric weights attached to the shaft or the motor or to
the rotor of a vibrating element.
Electromagnet, pulsating equipment is also available. The frequency of
vibration varies upto 12,000 cycles of vibration per minute. The needle diameter
varies from 20 mm to 75 mm and its length varies from 25 cm to 90 cm.
The bigger needle is used in the construction of mass concrete dam.
Sometimes, arrangements are available such that the needle can be replaced by a
blade of approximately the same length. This blade facilitates vibration of members,
where, due to the congested reinforcement, the needle would not go in, but this blade
can effectively vibrate.
They are portable and can be shifted from place to place very easily during
concreting operation. They can also be used in difficult positions and situations.
Formwork Vibrator (External Vibrator):
Formwork vibrators are used for concreting columns, thin walls or in the
casting of precast units. The machine is clamped on to the external wall surface of
the formwork. The vibration is given to the formwork so that the concrete in the
vicinity of the shutter gets vibrated. This method of vibrating concrete is particularly
useful and adopted where reinforcement, lateral ties and spacers interfere too much
with the internal vibrator.

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Use of formwork vibrator will produce a good finish to the concrete surface. Since
the vibration is given to the concrete indirectly through the formwork, they consume
more power and the efficiency of external vibrator is lower than the efficiency of
internal vibrator.
Table Vibrator:
This is the special case of formwork vibrator, where the vibrator is clamped to
the table. or table is mounted on springs which are vibrated transferring the
vibration to the table.
They are commonly used for vibrating concrete cubes. Any article kept on the
table gets vibrated. This is adopted mostly in the laboratories and in making small
but precise prefabricated R.C.C. members.

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Vibrating Table
Platform Vibrator:
Platform vibrator is nothing but a table vibrator, but it is larger in size. This
is used in the manufacture of large prefabricated concrete elements such as electric
poles, railway sleepers, prefabricated roofing elements etc.
Sometimes, the platform vibrator is also coupled with jerking or shock giving
arrangements such that a through compaction is given to the concrete.
Surface Vibrator:
Surface vibrators are sometimes knows as, “Screed Board Vibrators”. A small
vibrator placed on the screed board gives an effective method of compacting and
levelling of thin concrete members, such as floor slabs, roof slabs and road surface.
Mostly, floor slabs and roof slabs are so thin that internal vibrator or any other
type of vibrator cannot be easily employed. In such cases, the surface vibrator can
be effectively used. In general, surface vibrators are not effective beyond about 15
cm. In the modern construction practices like vaccum dewatering technique, or slip-
form paving technique, the use of screed board vibrator are common feature. In the
above situations double beam screed board vibrators are often used.
Vibratory screeds
• Used to consolidate concrete in floors and other flat works
• Concrete should not have slump more than 75 mm ( 3 inch ).
• For slump greater than 75 mm, accumulation of fine aggregates and mortar
will occur
• They should not applied after concrete has been sufficiently
consolidated.

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• Vibratory screeds are used for consolidating non reinforced slabs or light
reinforced slabs
• Combination of internal vibrators and surface vibrators are used for
reinforced slabs.
• Vibratory rollers , electric hammer , and trowels are some other surface
vibrators
• A vibratory roller is used for consolidating thin slabs.
• Electric hammer is used for compacting test cubes.
Compaction by Pressure and Jolting:

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This is one of the effective methods of compacting very dry concrete. This
method is often used for compacting hollow blocks, cavity blocks and solid concrete
blocks. The stiff concrete is vibrated, pressed and also given jolts.
With the combined action of the jolts vibrations and pressure, the stiff
concrete gets compacted to a dense form to give good strength and volume stability.
By employing great pressure, a concrete of very low water cement ratio can be
compacted to yield very high strength.
Compaction by Spinning:
Spinning is one of the recent methods of compaction of concrete. This method
of compaction is adopted for the fabrication of concrete pipes. The plastic concrete
when spun at a very high speed, gets well compacted by centrifugal force.
Patented products such a “Hume Pipes”, “spun pipes” are compacted by spinning
process.

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Vibratory Roller:
One of the recent developments of compacting very dry and lean concrete is
the use of Vibratory Roller. Such concrete is known as Roller Compacted Concrete.

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This method of concrete construction originated from Japan and spread to
USA and other countries mainly for the construction of dams and pavements. Heavy
roller which vibrates while rolling is used for the compaction of dry lean concrete.
Such roller compacted concrete of grade M 10 has been successfully used as
base course, 15 cm thick, for the Delhi- Mathura highway and Mumbai-Pune
express highways.
General Points on Using Vibrators
Vibrators may be powered by any of the following units:
(a ) Electric motors either driving the vibrator through flexible shaft or situated in
the head of the vibrator.
(b) Internal combustion engine driving the vibrator needle through flexible shaft,
and
(c ) Compressed-air motor situated near the head of the vibrator.
Where reliable supplies of electricity is available the electric motor is generally
the most satisfactory and economical power unit. The speed is relatively constant,
and the cables supplying current are light and easily handled.
Small portable petrol engines are sometimes used for vibrating concrete. They
are more easily put out of action by site conditions. They are not so reliable as the
electric or compressed air motors. They should be located conveniently near the
work to be vibrated and should be properly secured to their base.
Compressed-air motors are generally quite suitable but pneumatic vibrators
are sometimes difficult to manipulate where the compressor cannot be placed
adjacent to the work such as on high scaffoldings or at depths below ground level
due to the heavy weight of air hoses.
Compressed-air vibrators give trouble especially in cold weather, by freezing
at exhaust unless alcohol is trickled into the air line or dry air is used. Glycol type
antifreeze agents tend to cause gumming of the vibrator valves. There is also a
tendency for moisture to collect in the motor, hence care should be taken to remove
the possible damage. The speed of both the petrol and compressed-air motors tend
to vary giving rise to variation in the compacting effect of the vibrator.
Further Instructions on use of Vibrators
Care shall be taken that the vibrating head does not come into contact with
hard objects like hardened concrete, steel and wood, as otherwise the impact may
damage the bearings.
The prime mover should as far as possible, be started only when head is raised
or resting on soft support.

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Similar precautions shall be observed while introducing or withdrawing the
vibrator in the concrete to be consolidated. When the space for introduction is
narrow, the vibrator should be switched on only after the vibrator head has been
introduced into the concrete.
Unnecessary sharp bends in the flexible shaft drive shall be avoided.
Vibrators conforming to the requirements of IS 2505-1963 (i.e., Specification
for concrete vibrators, immersion type) shall be used.
The size and characteristics of the vibrator suitable for a particular job vary
with the concrete mix design, quality and workability of concrete, placing conditions,
size and shape of the member and shall be selected depending upon various
requirements. Guidance regarding selection of a suitable vibrator may be obtained
from Table 6.7.
Correct design of concrete mix and an effective control in the manufacture of
concrete, right from the selection of constituent materials through its correct
proportioning to its placing, are essential to obtain maximum benefits of vibration.
For best results, the concrete to be vibrated shall be of the stiffest
possible consistency, generally within a range of 0.75 to 0.85 compacting
factor, provided the fine mortar in concrete shows at least a greasy wet appearance
when the vibrator is slowly withdrawn from the concrete and the material closes over
the space occupied by the vibrator needle leaving no pronounced hole.
The vibration of concrete of very high workability will not increase its
strength; it may on the contrary, cause segregation.
Formation of a watery grout on the surface of the concrete due to
vibration is an indication that the concrete is too softly made and unsuitable
for vibration; a close textured layer of viscous grout may, however, be allowed.
For vibrated concrete, the formwork shall be stronger than is necessary for
hand compacted concrete and greater care is exercised in its assembly. It must be
designed to take up increased pressure of concrete and pressure variations caused
in the neighbourhood of the vibrating head which may result in the excessive local
stress on the formwork.
More exact details on the possible pressures are not available and much
depends upon experience, judgement and the character of work. The joints of the
formwork shall be made and maintained tight and close enough to prevent the
squeezing out of grout or sucking in of air during vibration.
Absence of this precaution may cause honey-combing in the surface of
concrete, impairing the appearance and sometimes weakening the structure. The
amount of mortar leakage or the permissible gap between sheathing boards will

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depend on the desired final appearance of the work but normally gaps larger than
1.5 mm between the boards should not be permitted.
Sometimes even narrower joints may be objectionable from the point of view
of their effect on the surface appearance of certain structures. The number of joints
should be made as few as possible by making the shutter sections large. Applications
of mould releasing agents on the formwork, to prevent the adhesion on concrete
should be very thin as otherwise they may mix with the concrete under the effect of
vibration, and cause air entrainment and blow holes on the concrete surface.
The vibrator may be used vertically, horizontally or at an angle
depending upon the nature of the job. But needle vibrators should be immersed
in beams and other thick sections, vertically at regular intervals. The concrete to be
vibrated shall be placed in position in level layers of suitable thickness not greater
than the effective length of the vibrator needle.
The concrete at the surface must be distributed as horizontally as possible,
since the concrete flows in slopes while being vibrated and may segregate. The
vibration shall, therefore, not be done in the neighbourhood of slopes.
The internal vibrator should not be used to spread the concrete from the filling
as this can cause considerable segregation of concrete. It is advisable to deposit
concrete well in advance of the point of vibration. This prevents the concrete from
subsiding non-uniformly and thus prevents the formation of incipient plastic cracks.
When the concrete is being continuously deposited to an uniform depth along
a member, vibrator shall not be operated too near the free end of the advancing
concrete, usually not within 120 cm of it. Every effort must be made to keep the
surface of the previously placed layer of concrete alive so that the succeeding layer
can be bonded with it by the vibration process.
However, if due to unforeseen circumstances the concrete has hardened in
the underlying layer to such an extent that it cannot be penetrated by the vibrator
but is still fresh (just after initial set) unimposed bond can be achieved between the
top and underlying layers by systematically and thoroughly vibrating the new
concrete into contact with old.
Height of Concrete Layer
Concrete is placed in thin layers consistent with the method being used to
place and vibrate the concrete. Usually concrete shall be placed in a thickness not
more than 60 cm and on initial placing in thickness not more than 15 cm.
The superimposed load increasing with the height of the layer will favour the
action of the vibrator, but as it is also the path of air forced upwards, it may trap air

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rising up by vibration. Very deep layers (say more than 60 cm) should, therefore, be
avoided although the height of layer can also be one metre provided the vibrator
used is sufficiently powerful, as in dams.
Depth of Immersion of Vibrator
To be fully effective, the active part of the vibrator shall be completely
immersed in the concrete. Its compacting action can be usually assisted by
maintaining a head of concrete above the active part of the vibrator, the primary
object of which is to press down upon and confine the concrete in the zone of
influence of the vibrator.
The vibrator head shall be dipped through the filling which is to be
consolidated to a further depth of 10 to 20 cm in the lower layer which has already
been consolidated so that there is a good combination of various layers and the grout
in the lower layer is distributed in the new filling.
Spacing and Number of Insertion Positions
The points of insertion of the vibrator in the concrete shall be so spaced that
the range of action overlap to some extent and the freshly filled concrete is
sufficiently compacted everywhere. The range of action varies with the
characteristics of the vibrator and the composition and workability of concrete.
The range of action and the degree of compaction can be recognized from the
rising air bubbles and the formation of a thin shining film around the vibrating head.
With concrete of workability of 0.78 to 0.85 compacting factor, the
vibrator shall generally be operated at points 35 to 90 cm apart.
The specified spacing between the dipping positions shall be maintained
uniformly throughout the surface of concrete so that the concrete is uniformly
vibrated.
Speed of Insertion and Withdrawal of the Vibrating Head
The vibrating head shall be regularly and uniformly inserted in the concrete
so that it penetrates of its own accord and shall be withdrawn quite slowly whilst
still running so as to allow redistribution of concrete in its wake and allow the
concrete to flow back into the hole behind the vibrator.
The rate of withdrawal is determined by the rate at which the compaction in
the active zone is completed. Usually a speed of 3 cm/s gives sufficient consolidation
without undue strain on the operator. Further concrete is added as the vibrators are
withdrawn so as to maintain the head of the concrete until the lift of the concrete is
completed.

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Duration of Vibration
New filling shall be vibrated while the concrete is plastic, preferably within one
hour. The duration of vibration in each position of insertion is
dependent upon the height of the layer, the size and characteristics of the vibrator
and the workability of the concrete mix.
It is better to insert the vibrating head at a number of places than to
leave it for a long time in one place, as in the latter case, there is a tendency
for formation of mortar pocket at the point of insertion of the vibrator.
The vibrator head shall be kept in one position till the concrete within its
influence is completely consolidated which will be indicated by formation of circular
shaped cement grout on the surface of concrete, appearance of flattened glistening
surface and cessation of the rise of entrapped air.
Vibration shall be continued until the coarse aggregate particles have blended
into the surface but have not disappeared. The time required to effect complete
consolidation is readily judged by the experienced vibrator operator through the feel
of the vibrator, resumption of frequency of vibration after the short period of
dropping off of frequency when the vibrator is first inserted.
Doubt about the adequacy of vibration should always be resolved by further
vibration; well proportioned concrete of the correct consistency is not readily
susceptible to over-vibration.

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Vibrating Concrete at Junctions with Hardened Concrete
In cases where concrete has to be joined with rock or hardened concrete,
defects can occur owing to the layers nearest to the hardened concrete not being
sufficiently vibrated.
In such cases the procedure given below should be adopted:
 The hardened concrete surface should be prepared by hacking or roughening
and removing laitance, greasy matter and loose particles.
 The cleaned surface shall be wetted.
 A cement sand grout of proportion 1:1 and of creamy consistency is then
applied to the wet surface of the old concrete, and the fresh concrete vibrated
against it.
Vibrating the Reinforced Concrete
The reinforcement should be designed to leave sufficient space for the
vibrating head. Where possible, the reinforcement may be grouped so that the width
of groups of bars does not exceed 25 cm and a space of 7.5 cm exists between the
groups of bars to allow the vibrator to pass freely; the space between the bars in any
group may be reduced to two-thirds of the nominal size of coarse aggregate.
When the reinforcements lie very close to each other, greater care is taken in
vibrating so that no pockets or collections of grout are formed. Except where some
of the concrete has already set and provided that the reinforcement is adequately
supported and secured, the vibrator may be pressed against the reinforcement.
Vibrating near the Formwork
For obtaining a smooth close textured external surface, the concrete should
have a sufficient content of matrix. The vibrator head shall not be brought very near
the formwork as this may cause formation of water whirls (stagnations), especially
if the concrete containing too little of fine aggregate.
On the other hand, a close textured surface may not be obtained, if the
positions of insertion are too far away from the formwork. The most suitable distance
of the vibrator from the formwork is 10 to 20 cm. With the vibration done at the
correct depth and with sufficient grout rising up at the formwork, the outside surface
will generally have a close textured appearance.

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In the positions of formwork difficult to reach and in concrete walls less than
30 cm thick it is preferable to use vibrators of small size which can be brought to
the required place and which will not excessively strain the formwork.
Vibrating High Walls and Columns
While designing the formwork, reinforcement, as well as the division of layers
for high walls and columns, it should be kept in mind that with the usual driving
shaft lengths it is not possible to penetrate the vibrating head more than three
metres in the formwork.
In the case of higher walls and columns it is recommended to introduce
the shaft driven vibrating needle through a side opening into the formwork.
For use with high walls and columns, the flexible driving shaft can be brought
to a length of six to eight metres or even more by using adopter pieces. The motor-

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in-head type vibrators are more useful for the purpose in cases where a very long
current cable can be used for sinking the vibrator to a greater depth.
Over-Vibration
There is a possibility of over-vibration while trying to achieve thorough
vibration, but it is exceedingly unlikely in well proportioned mixes containing normal
weight aggregates.
Generally, with properly designed mixes, extended vibration will be only a
waste of effort without any particular harm to the concrete.
However, where the concrete is too workable for the conditions of placing, or
where the quantity of mortar is excess of the volume of voids in the coarse aggregate,
or where the grading of the aggregate is unsatisfactory, over-vibration will encourage
segregation, causing migration of the lighter and smaller constituents of the mix to
the surface, thereby producing layer of mortar or laitance on the surface, and
leakage of mortar through the defective joints in the formwork.
This may produce concrete with poor resistance to abrasion and attack by
various agencies, such as frost, or may result in planes of weakness where
successive lifts are being placed.
If over vibration occurs, it will be immediately evident to an experienced
vibrator operator or supervisor by a frothy appearance due to the accumulation
of many small air bubbles and the settlement of coarse aggregates beneath the
surface.
These results are more liable to occur when the concrete is too wet and the
proper correction will be to reduce the workability (not the vibration), until the
evidence of over-vibration disappears during the amount of vibration judged
necessary to consolidate the concrete and to eliminate air-bubble blemishes.
Re-vibration
Re-vibration is delayed vibration of concrete that has already been placed and
compacted. It may occur while placing successive layers of concrete, when vibrations
in the upper layer of fresh concrete are transmitted to the underlaying layer which
has partially hardened or may be done intentionally to achieve certain advantages.
Except in the case of exposed concrete and provided the concrete becomes
plastic under vibration, re-vibration is not harmful and may be beneficial.
By repeated vibration over a long period (repetition of vibration earliest after
one hour from the time of initial vibration), the quality of concrete can be improved
because it rearranges the aggregate particles and eliminates

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entrapped water from under the aggregate and reinforcing steel, with the
consequence of full contact between mortar and coarse aggregate or between steel
and mortar and thus produces stronger and watertight concrete.
Plastic shrinkage cracks as well as other disturbances like hollow space below
the reinforcement bars and below the coarse aggregate, can thereby be closed again
provided the concrete becomes soft again when the vibrator head in introduced.
Re-vibration of concrete results in improved compressive and bond strength,
reduction of honey-comb, release of water trapped under horizontal reinforcing bars
and removal of air and water pockets.
Re-vibration is most effective at the lapse of maximum time after the initial
vibration, provided the concrete is sufficiently plastic to allow the vibrator to sink of
its own weight into the concrete and make it momentarily plastic.
Vibration of Lightweight Concrete
In general, principles and recommended practices for consolidation of
concrete of normal weight hold good for concrete made with light weight aggregate,
provided certain precautions are observed.
There is always a tendency for light weight pieces of aggregate to rise to the
surface of fresh concrete, particularly under the action of over-vibration; and a fairly
stiff mix, with the minimum amount of vibration necessary to consolidate the
concrete in the forms without honey-comb is the best insurance against undesirable
segregation.
The rise of lightweight coarse aggregate particles to the surface, caused by
over-vibration resulting from too wet a mix makes finishing difficult if not
impossible.
Consequences of improper Compaction
There are various problems and defects that could arise when concrete is not
vibrated adequately.
• Honeycomb
• Excessive entrapped air voids
• Sand streaks
• Cold joints
• Placement lines
• Subsidence cracking

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Honeycomb in Concrete due to poor Compaction or Vibration
Cold Joints due to poor Compaction of Concrete
Excessive entrapped air voids:
Under vibration leaves a lot of entrapped air in concrete which reduces
strength
Sand streaks:
When heavy bleeding washes mortar then a harsh mixture left behind that
lacks workability. It is also caused by insufficient fine aggregates

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Placement lines:
These are dark lines between adjacent layers of concrete batches. it occurs
when vibrators did not penetrate through under lying layers.
Defects from over vibration
Segregation:
Heavier aggregates settle while lighter aggregates rise
Bleeding:
water comes out at surface due to excessive vibrations.
Form damages
 Over vibration may damage the formwork.
 Under vibration is more often a problem than over vibration
Workability

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It is a property of raw or fresh concrete mixture. In simple words, workability
means the ease of placement and workable concrete means the concrete which can
be placed and can be compacted easily without any segregation.
Workability is a vital property of concrete and related with compaction as well
as strength. The desired workability is not same for all types of concrete. More
workability is required for a thin inaccessible section or heavily reinforced section
rather than a mass concrete body. Hence, we can’t set a standard workability for all
casting works.
Compaction and workability are very close to each other. Workability can also
be defined as the amount of useful internal work necessary to produce full
compaction.
The property of concrete which determines the amount of useful internal work
necessary to produce complete compaction.
- IS 1199-1958
Workability is the property determining the effort required to manipulate a freshly
mixed quantity of concrete with minimum loss of homogeneity
- ASTM C 125-93
Workability is that property of freshly mixed concrete or mortar which
determines the ease and homogeneity with which it can be mixed, placed,
consolidated and finished
- American Concrete Institute (ACI) Standard 116R-90 (ACI 1990b
Reason for Different types of definition
A variety is seen between definitions of workability because it is not very
accurate scientific term like specific gravity or weight. All definitions are qualitative
in nature and personal viewpoint is reflected instead of scientific precision. There
are some other terms used to describe concrete as cohesiveness, consistency,

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flowability, mobility, pump-ability etc. These terms have their specific meaning but
they cannot be determined inaccurate number or unit.
Types of Workability of Concrete
Workability of concrete can be classified into following three types:
Unworkable Concrete:
An unworkable concrete also known as harsh concrete, is a concrete with a
very little amount of water. The hand mixing of such concrete is difficult. Such type
of concrete has high segregation of aggregates. and it is very difficult to maintain the
homogeneity of concrete mix.
Medium Workable concrete:
Medium workable concrete is used in most of the construction works. This
concrete is relatively easy to mix, transport, place, and compact without much
segregation and loss of homogeneity.
Highly Workable Concrete:
This type of concrete is very easy to mix, transport, place and compact. It is
used where effective compaction of concrete is not possible. The problem is that
there are high chances of segregation and loss of homogeneity in highly workable
concrete.

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Workability
A theoretical water/cement ratio calculated from the considerations discussed
above is not going to give an ideal situation for maximum strength. Hundred per
cent compaction of concrete is an important parameter for contributing to the
maximum strength. Lack of compaction will result in air voids whose damaging
effect on strength and durability is equally or more predominant than the presence
of capillary cavities.
Desirable Workability for Construction
Desirable workability depends on two factors which are:
1.Section size, amount and spacing of reinforcement:
When a section is narrow, complicated, several narrow corners, inaccessible
parts; a highly workable concrete is desirable to obtain full compaction through a
reasonable amount of effort. When the section is crowded with steel reinforcement
and spacing of bars is relatively small, compaction can be difficult and hence highly
workable concrete is recommended in such cases. If there are no limitations of the

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critical section or heavy reinforcement, we can get a wide range of workability for
concrete casting.
2.Method of compaction:
If concrete is compacted manually, more workability is recommended because
hand compaction is not very much uniform and effective. If there is a scope of the
vibrator or machine compaction, we can choose workability from a wide range.
Strength of Concrete & Workability Relationship
The strength of concrete is the most important property for us. It depends on
density ratio or compaction and compaction depend on sufficient workability. Fresh
concrete must have a workability as compaction to maximum density is possible
with a reasonable amount of work.
But excessive workability can lessen compressive strength. From the graph,
we can see that compressive strength of concrete decreases with increase in w/c
ratio. An increase of w/c ratio indicates an increase of workability. Hence, the
strength of concrete inversely proportional to the workability and too much
workability should be avoided.
Figure: Compressive strength vs w/c ratio of concrete
Methods of Improving Workability of Concrete
To increase workability there are some ways like:
1. Increasing water/cement ratio
2. Using larger aggregate
3. Using well-rounded and smooth aggregate instead of irregular shape
4. Increasing the mixing time and mixing temperature
5. Using non-porous and saturated aggregate

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6. With addition of air-entraining mixtures
7. Adding appropriate admixtures
Factors Affecting the Workability of Concrete
The primary materials of concrete are cement, fine aggregates (sand), coarse
aggregates and water. Many times, admixtures are used in concrete to enhance its
properties. Therefore, properties of these materials and their content affect the
workability of concrete. Following are the general factors affecting concrete
workability:
1. Cement content of concrete
2. Water content of concrete
3. Mix proportions of concrete
4. Size of aggregates
5. Shape of aggregates
6. Grading of aggregates
7. Surface texture of aggregates
8. Use of admixtures in concrete
9. Use of supplementary cementitious materials

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Cement Content of Concrete
Cement content affects the workability of concrete in good measure. More the
quantity of cement, the more will be the paste available to coat the surface of
aggregates and fill the voids between them. This will help to reduce the friction
between aggregates and smooth movement of aggregates during mixing,
transporting, placing and compacting of concrete. Also, for a given water-cement
ratio, the increase in the cement content will also increase the water content per
unit volume of concrete increasing the workability of concrete. Thus, increase in
cement content of concrete also increases the workability of concrete.
Type and Composition of Cement
The effect of type of cement or characteristics of cement on the workability of
concrete. The cement with increase in fineness will require more water for same
workability than the comparatively less fine cement. The water demand increased
for cement with high Al2O3 or C2S contents.
Mix Proportions of Concrete
Mix proportion of concrete tells us the ratio of fine aggregates and coarse
aggregates w.r.t. cement quantity. This can also be called as the aggregate cement
ratio of concrete. The more cement is used, concrete becomes richer and aggregates
will have proper lubrications for easy mobility or flow of aggregates. The low quantity
of cement w.r.t. aggregates will make the less paste available for aggregates and
mobility of aggregates is restrained.
Water/Cement Ratio or Water Content in Concrete
Water/cement ratio is one of the most important factors which influence the
concrete workability. Generally, a water cement ratio of 0.45 to 0.6 is used for good
workable concrete without the use of any admixture. Higher the water/cement ratio,
higher will be the water content per volume of concrete and concrete will be more
workable. Higher water/cement ratio is generally used for manual concrete mixing
to make the mixing process easier. For machine mixing, the water/cement ratio can
be reduced.
These generalized method of using water content per volume of concrete is
used only for nominal mixes. For designed mix concrete, the strength and durability
of concrete is of utmost importance and hence water cement ratio is mentioned with
the design. Generally designed concrete uses low water/cement ratio so that desired
strength and durability of concrete can be achieved.
Water/Cement Ratio or Water Content in Concrete
Water/cement ratio is one of the most important factors which influence the
concrete workability. Generally, a water cement ratio of 0.45 to 0.6 is used for good

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workable concrete without the use of any admixture. Higher the water/cement ratio,
higher will be the water content per volume of concrete and concrete will be more
workable. Higher water/cement ratio is generally used for manual concrete mixing
to make the mixing process easier. For machine mixing, the water/cement ratio can
be reduced.
These generalized method of using water content per volume of concrete is
used only for nominal mixes. For designed mix concrete, the strength and durability
of concrete is of utmost importance and hence water cement ratio is mentioned with
the design. Generally designed concrete uses low water/cement ratio so that desired
strength and durability of concrete can be achieved.
Shape of Aggregate
The shape of aggregates affects the workability of concrete. It is easy to
understand that rounded aggregates will be easy to mix than elongated, angular and
flaky aggregates due to less frictional resistance.
The workability of rounded or cubical size aggregate is more than angular or
flaky aggregates. As angular or flaky aggregates give the concrete very harsh.
Due to the round size of aggregates, the frictional resistance between the
aggregates is greatly reduced. So, as well as possible the aggregates should not be
angular or flaky in the shape for getting more workable concrete.

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Other than that, the round aggregates also have less surface area compared
to elongated or irregular shaped aggregates. This will make less requirement of water
for same workability of concrete. This is why river sands are commonly preferred for
concrete as they are rounded in shape.
Grading of Aggregate
If aggregates are well graded, that means less will be the void content and
higher will be the workability, so as well as possible, the aggregate should be the
well-graded.
Grading of aggregates have the maximum effect on the workability of concrete.
A well graded aggregates have all sizes in required percentages. This helps in
reducing the voids in a given volume of aggregates.
The less volume of voids makes the cement paste available for aggregate
surfaces to provide better lubrication to the aggregates. With less volume of voids,
the aggregate particles slide past each other and less compacting effort is required

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for proper consolidation of aggregates. Thus, low water cement ratio is sufficient for
properly graded aggregates.
Surface Texture of Aggregates
Surface texture such as rough surface and smooth surface of aggregates
affects the workability of concrete in the same way as the shape of aggregates. With
rough texture of aggregates, the surface area is more than the aggregates of same
volume with smooth texture. Thus, concrete with smooth surfaces is more workable
than with rough textured aggregates.
If the surface of the aggregates is smooth or glassy texture, it will produce less
surface area and will give better workability.
The frictional resistance between the smooth particle is reduced and which
will produce higher workability. So, this is an important factor for workability.

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Admixtures
There are many types of admixtures used in concrete for enhancing its
properties. There are some workability enhancer admixtures such as plasticizers
and superplasticizers which increases the workability of concrete.
Admixture plays a vital role in improving the properties of concrete.
Superplasticizer and plasticizer much enhance the workability of concrete with a
low water-cement ratio. They are also known as water-reducing admixtures. They
help in reducing the quantity of water required for the same slump value.
Air entraining admixture also greatly increases the workability of concrete. It
helps in reducing friction between aggregates by creating number of air bubbles that
act as rollers between air particles.
Use of Supplementary Cementitious Materials
Supplementary cementitious materials are those which are used with cement
to modify the properties of fresh concrete. Fly ash, fibers, silica fume, slag cements
are used as supplementary cementitious materials. The use of fly ash in improves
the workability of concrete by reducing the water content required for same degree
of workability or slump value. The use of steel or synthetic fibers in concrete reduces
the workability of concrete as it makes the movement of aggregates harder by
reducing the lubricating effect of cement paste.
The workability of concrete is reduced and increased based on the quantity of
silica fume. The use of silica fume in concrete can improves workability when used
at low replacement rates, but can reduce workability when added at higher
replacement rates. Silica fume are used as pumping aid for concrete when used as

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2 to 3% by mass of cement. The use of slag cement also improves workability but its
effect depends on the characteristics of the concrete mixture in which it is used.
Fresh Concrete
• Measurement of workability using
 Slump cone test
 Compaction factor test
 Vee-Bee test
 Flow Test
 Kelly ball test
 K – Slump Test
Measurement of Workability
It is discussed earlier that workability of concrete is a complex property. Just
as it eludes all precise definition, it also eludes precise measurements. Numerous
attempts have been made by many research workers to quantitatively measure this
important and vital property of concrete. But none of these methods are satisfactory
for precisely measuring or expressing this property to bring out its full meaning.
Some of the tests, measure the parameters very close to workability and provide
useful information. The following tests are commonly employed to measure
workability.

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(a) Slump Test
(b) Compacting Factor Test
(c) Vee Bee Consistometer Test.
(d) Flow Test
(e) Kelly Ball Test
Slump test
It is a laboratory or at site test used to measure the consistency of concrete.
Slump test shows an indication of the uniformity of concrete in different batches.
The shape of the concrete slumps shows the information on the workability and
quality of concrete. The characteristics of concrete with respect to the tendency of
segregation can be also judged by making a few tamping or blows by tapping rod on
the base plate. This test continues using since 1922 due to the simplicity of
apparatus and simple procedure. The shape of the Slump cone shows the
workability of concrete.
Principle of Slump test
The slump value of concrete is just a principle of gravity flow of surface of the
concrete cone that indicates the amount of water added to it, which means how
much this concrete mix is in workable condition.
Standards for Slump test
US – standard
In the United States, this test is known as “Standard Test Method for Slump of
Hydraulic – Cement Concrete” and flow the code ASTM C143 OR (AASTO T119).
United Kingdom & Europe
The older standard for British was first (BS 1881–102). But now they use European
standards (BS EN 12350-2).
Indian Standard
Indian standard is: IS 1199-1959
Factors which influence the concrete slump test
• Material properties like chemistry, fineness, particle size distribution, moisture
content and temperature of cementitious materials.
• Size, texture, combined grading, cleanliness and moisture content of the aggregates,
• Chemical admixtures dosage, type, combination, interaction, sequence of addition
and its effectiveness.
• Air content of concrete.
• Concrete batching, mixing and transporting methods and equipment
• Temperature of the concrete

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• Sampling of concrete, slump-testing technique and the condition of test equipment
• The amount of free water in the concrete, and
• Time since mixing of concrete at the time of testing.
Apparatus for Slump test
Following apparatus are used in the slump test of concrete:
• Metallic mould in the shape of a frustum of cone having
 Bottom diameter 20 cm (8 in),
 Top diameter 10 cm (4 in) and
 Height 30 cm (12in).
• Steel tamping rod having 16 mm (5/8 in) diameter, 0.6 m (2 ft.) long with bullet end.
• Trowel
• Wire Brush
Figure: Apparatus for Slump Test

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Procedure of Slump test
 During Slump test following steps are followed:
 First of all, the internal surface of the mould is cleaned and free from moisture and
free from other old sets of concrete.
 Then place the mould on the smooth horizontal, rigid, and non-absorbant surface.
 The mould is then filled with fresh concrete in four layers with taping each layer
25 times by taping rod, and level the top surface with a trowel.
 Then the mould is slowly pulled in vertical and removed from concrete, so as not
to disturb the concrete cone.
 This free concrete deforms all the surface to subside due to the effect of gravity.
 That subsidence of concrete in the periphery is a SLUMP of concrete.
 The height difference between the height of subsidence concrete and mould cone
in mm is ‘slump value of concrete’.
Figure: Concrete Slump Test Procedure
Recorded slump value of a sample is = ……… mm
NOTE:
The above operation should be carried out at a place free from Vibrations or
shock and within a period of 2 minutes after sampling.
Precaution during test
 The internal surface of the mould should be cleaned and free from moisture.
 The base plate or surface should be free from vibrations or shocking.
 This test is done just after sampling nearly after 2 minutes.
Uses and Drawbacks of slump test
 This test does not give good results for very wet and dry concrete.
 Also, or stiff-mix, it is not sensitive.
 The table below shows the various values of slump with the workability of
concrete.

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Following chart shows the Slump Value of concrete for different Degree of workability
for various placing conditions:
1.True Slump – True slump is the only slump that can be measured in the
test. The measurement is taken between the top of the cone and the top of the
concrete after the cone has been removed as shown in figure-1.
2.Zero Slump – Zero slump is the indication of very low water-cement ratio,
which results in dry mixes. This type of concrete is generally used for road
construction.
3.Collapsed Slump – This is an indication that the water-cement ratio is too
high, i.e., concrete mix is too wet or it is a high workability mix, for which a slump
test is not appropriate.
4.Shear Slump – The shear slump indicates that the result is incomplete, and
concrete to be retested.
Degree of
workability
Placing Conditions Slump(mm)
Very Low
Binding concrete (member of concrete
by spreading, shallow sections,
Pavements using pavers (mixer with
spreading arrangements)
Compaction
factor 0.75 – 0.8
Low
Mass concrete, lightly reinforced
slab, beam, wall, column sections,
canal lining, strip footing (ling wall with
smaller width)
25 – 75
Medium
Heavily reinforced sections in slab,
beams, walls, columns. Slip formwork
(slope concrete), pumped concrete.
50-100
High Trench fill, in-situ piling 100-150
Very high
Tremie concrete (concreting in
water by using water tight pipe to pour
concrete.)
Flow test.

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Figure: Types of Concrete Slump Test Results
Modern Technology:
For fast testing, a new apparatus called ‘K-Slump Tester’ is developed. This
device can measure slump value within a minute after it is inserted into fresh
concrete. And it can also measure relative workability.
Why we use the compaction factor test?
Although there are other tests such as
Vee-Bee Consistometer Test, Flow Table Test, Kelly-Ball Test, this test is
suitable for low workability where the concrete needs to be compacted by an external
force.
The test performed as per IS code 1199, and it gives accurate results compared
to slump cone tests because low workability concrete may fail by doing slump tests.
Principles of Compaction Factor Test
The compaction factor test is performed to find out the workability of concrete
where the coarse aggregate size does not exceed 38mm.
The compaction factor test can be used in both field & lab based on the
circumstances

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Compacting Factor Test
The compacting factor test is designed primarily for use in the
laboratory but it can also be used in the field. It is more precise and sensitive
than the slump test and is particularly useful for concrete mixes of very low
workability as are normally used when concrete is to be compacted by
vibration. Such dry concrete is insensitive to slump test. The diagram of the
apparatus is shown in Figure. The essential dimensions of the hoppers and mould
and the distance between them are shown in Table.
The compacting factor test has been developed at the Road Research
Laboratory U.K. and it is claimed that it is one of the most efficient tests for
measuring the workability of concrete. This test works on the principle of
determining the degree of compaction achieved by a standard amount of work done
by allowing the concrete to fall through a standard height. The degree of compaction,
called the compacting factor is measured by the density ratio i.e., the ratio of the
density actually achieved in the test to density of same concrete fully compacted.

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Apparatus
• Compaction factor apparatus
• Trowels,
• Hand scoop (15.2 cm long),
• A rod of steel or other suitable material (1.6 cm diameter, 61 cm long rounded at
one end) and
• A balance.
• Sampling Concrete mix is prepared as per mix design in the laboratory.
Procedure of Compaction Factor Test on Concrete
 Place the concrete sample gently in the upper hopper to its brim using the hand
scoop and level it.
 Cover the cylinder.
 Open the trapdoor at the bottom of the upper hopper so that concrete fall into the
lower hopper.
 Push the concrete sticking on its sides gently with the road.

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 Open the trapdoor of the lower hopper and allow the concrete to fall into the cylinder
below.
 Cut of the excess of concrete above the top level of cylinder using trowels and level
it.
 Clean the outside of the cylinder.
 Weight the cylinder with concrete to the nearest 10 g.
 This weight is known as the weight of partially compacted concrete (W2).
 Empty the cylinder and then refill it with the same concrete mix in layers
approximately 5 cm deep, each layer being heavily rammed to obtain full
compaction.
 Level the top surface.
 Weigh the cylinder with fully compacted. This weight is known as the weight of fully
compacted concrete (W3).
 Find the weight of empty cylinder (W1).
Note:
The test is sufficiently sensitive to enable difference in workability arising from
the initial process in the hydration of cement to be measured.
Each test, therefore should be carried out at a constant time interval after the
mixing is completed, if strictly comparable results are to be obtained.
Convenient time for releasing the concrete from the upper hopper has been
found to be two minutes after the completion of mixing.
Calculation of Compaction Factor Value
The compaction factor is defined as the ratio of the weight of partially
compacted concrete to the weight of fully compacted concrete. It shall normally to
be stated to the nearest second decimal place.
Compaction Factor Formula
Compaction Factor (CF) =
(Partially compacted Concrete Weight) / (Fully compacted Concrete Weight)
Partially compacted concrete weight Wp = W2 – W1
Fully compacted Concrete Weight Wf = W3 – W1
Compaction factor CF = Wp/Wf
The compaction factor value should be between the range of 0.7 to 0.95.
Recommended compaction factor value is given below for different concrete
workability.

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Which one is the best test to determine the workability of concrete?
Slump test or compacting factor?
If accurate results are required then the compaction factor test is best, else do
the workability test by slump cone method because it is easy to do in the field.
Objective and Theory of Vee-Bee Test on Concrete
The main objective of Vee-Bee test is to determine the workability of the freshly
mixed concrete. The Vee-Bee test gives an indication about the mobility and the
compactibility aspect of the freshly mixed concrete. Vee-bee test carries out the
relative effort measurement to change the mass of the concrete from a definite shape
to the other.

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That is, as per the test, from the conical shape to the cylindrical shape by
undergoing vibration process. The measurement of the effort is done by time
measurement in seconds. The amount of work measured in seconds is called as
the remolding effort. The time required for the complete remolding is a measure of
the workability and is expressed in the Vee-Bee seconds.
The experiment is named after the developer V Bahrmer, of Sweden. The
method can be also applied for dry concrete. For concrete that have slump value
more than 50mm, the remolding activity will be so fast that the measurement of time
is not possible.
Apparatus for Vee-Bee test
The Vee-Bee test apparatus consist of a Vee-Bee consistometer as per IS: 119
– 1959, as shown in the figure.
The apparatus consists of
 A vibrating table which is supported and mounted on elastic supports.
 It also consists of a sheet metal slump cone
 A weighing balance
 Cylindrical container,
 A standard iron tamping rod and
 Trowels.

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Fig. Consistometer Used in Vee-Bee Test of Concrete
Description of Apparatus
 The vibrating table as shown in figure-1 has a dimension of 380mm length and a
width of 260mm.
 At a height of 305mm, it is supported on a rubber shock absorber above the level of
floor.
 A vibrator is provided under the table. This vibrator is operated electrically.
 The whole mentioned assembly is mounted on a base as shown above which is in
turn resting on rubber supports three in number.
 The sheet metal slump cone mold has opening at both ends and is placed in a
cylindrical container as shown in figure.
 The cylinder container is mounted over the vibration table with the help of wing
nuts.
 The cone used in the arrangement have height equal to 300mm, the top and the
bottom diameters as 200 and 100mm respectively.
 Base consist of a swivel arm holder.
 There is another swivel arm that is fixed into it that consist of a funnel and a guide
sleeve.
 The detachment from the vibrating table is possible for the swivel arm.
 A graduated rod is fixed to the swivel arm through the guide sleeve. The graduated
rod has the provision for screwing the transparent disc.

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 The slump of the concrete cone is measured through the divisions on the scale
marked on the rod.
 A 20mm diameter standard iron tamping rod is used that have a length of 500mm.
Procedure of Vee-Bee Test on Concrete
The procedure for conducting the Vee-Bee test are as follows:
Step 1:
 Initially the sheet metal slump cone is placed inside the cylinder container that is
placed in the consistometer. The cone is filled with four layers of concrete.
 Each concrete layer is one fourth the height of the cone.
 Each layer after pouring is subjected to twenty-five tamping with the standard
tamping rod.
 The tamping is done with the rounded end of the rod.
 The strokes are distributed in uniform manner.
 This must be done in such a way theta the strokes conducted for the second and
the subsequent layers of concrete must penetrate the bottom layers.
 Once the final layer has been placed and compacted, the concrete is struck off to
make it in level with the help of a trowel. This makes the cone to be exactly filled.
Step 2:
 After the preparation of the concrete cone, the glass disc attached to the swivel arm
is moved and is placed on the top of the slump cone placed inside the cylindrical
container.
 The glass disc has to be placed such that it touches the top of the concrete level and
the reading is measured from the graduated rod.
Step 3:
 Now the cylindrical cone is removed immediately by raising the cone slowly in the
vertical direction.
 The transparent disc on the top of the concrete is placed down to the new position
and the reading is determined.
Step 4:
The difference in the values measured from step 3 and step 4 will give the slump.
Step 5:
 Now the electrical vibrator is switched on and at the same time we have to start the
stop watch.
 The concrete is allowed to spread out in the cylindrical container.
 Until the concrete is remolded the vibration is continued.
 This stage is when the surface of the concrete becomes horizontal and the concrete
surface completely adheres uniformly to the transparent disc.

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Step 6:
 The time required for complete remolding in seconds is recorded.
 This time in seconds gives us the measure of workability of the fresh concrete.
 This time is expressed in Vee-Bee’s seconds.
 Observation and Calculations in Vee-Bee Test
 Initial reading from the graduated rod, before unmolding (a) in mm
 The final reading on the graduated rod after removing the mold (b) in mm
 Slump = a – b in mm
 The time required for complete remolding in seconds
 Hence the consistency of the concrete is measured in ---------- vee-bee seconds.
Precautions Necessary in Vee-Bee Test
 The mold should be cleaned and free from moisture internally before adding the
concrete mix.
 While the strokes are applied over the layers, care must be taken to apply it
uniformly all throughout the layers.
 This helps in having the impact of the strokes in full depth.
 The removal of the slump cone should be lifted upward in such a way that the
concrete cone is not disturbed in any means.
 The vee-bee tests must be conducted at a distance away from any other source of
vibration than the vibration procedure provided in the test.
 When a state attains at which the transparent disc rider completely covers the
concrete and all the voids and cavities present in the concrete surface get
disappeared, the remolding of concrete is attained completely.
Vee-Bee Test Compared with Other Workability Tests
 The test procedure of Vee-Bee test carries out the similar procedure that a freshly
mixed concrete is subjected to in its actual state.
 This is an added advantage of Vee bee test when compared with other tests, the
slump test and the compaction factor test.
 The remolding completion is visually ascertained that can cause difficulty in
measuring the end-point and hence have the chances to have errors.
 This chance of error is more pronounced in the concrete mixes that have higher
workability.
 This mix thus has a lower value for Vee-Bee time. In the cases of concrete mixes that
have slump value greater than 125mm, the phenomenon of remolding is found to
be very quick and the time cannot be measured.
 This means that the Vee bee test is not suitable for measuring the mobility of
concrete of higher workability.

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 This higher workability comes in the range of slump value greater than 75mm.
 In some situations, this issue is overcome by making use of an automatic operating
device that records the movement time.
 Generally, the Vee-bee test is best suited for concrete mixes that have low or very
low value of workability.
 Among the three-workability test recommended by IS: 119 -1959 i.e., the slump test,
the compaction factor test, and the Vee-bee test, the slump test method is most
popular test to measure concrete workability.
 Table below shows the Vee-bee time in seconds for various workability as per
American Concrete Institute 211 (ACI Committee 211).

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Flow Test
This is a laboratory test, which gives an indication of the quality of concrete
with respect to consistency, cohesiveness and the proneness to segregation.
In this test, a standard mass of concrete is subjected to jolting. The spread or
the flow of the concrete is measured and this flow is related to workability.
Flow Table Apparatus
The BIS has recently introduced another new equipment for measuring flow
value of concrete.
This new flow table test is in the line with BS 1881 part 105 of 1984 and DIN
1048-part I. The apparatus and method of testing is described below.
 The flow table apparatus is to be constructed in accordance with Fig. (a) and (b)
Flow table top is constructed from a flat metal of minimum thickness 1.5 mm. The
top is in plan 700 mm x 700 mm. The center of the table is marked with a cross, the
lines which run paralleled to and out to the edges of the plate, and with a central
circle 200 mm in diameter.
 The front of the flow table top is provided with a lifting handle as shown in Fig. (b)
The total mass of the flow table top is about 16 ± 1 kg.
 The flow table top is hinged to a base frame using externally mounted hinges in such
a way that no aggregate can become trapped easily between the hinges or hinged
surfaces.
 The front of the base frame shall extend a minimum 120 mm beyond the flow table
top in order to provide a top board. An upper stop similar to that shown in Fig. (a)
is provided on each side of the table so that the lower front edge of the table can only
be lifted 40 ± 1 mm.
Fig. Flow Table Arrangement

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The lower front edge of the flow table top is provided with two hard rigid stops which
transfer the load to the base frame.
The base frame is so constructed that this load is then transferred directly to the
surface on which the flow table is placed so that there is minimal tendency for the
flow table top to bounce when allowed to fall.
Accessory Apparatus
Mould: The mould is made of metal readily not attacked by cement paste or liable
to rust and of minimum thickness 1.5 mm. The interior of the mould is smooth and
free from projections, such as protruding rivets, and is free from dents. The mould
shall be in the form of a hollow frustum of a cone having the internal dimensions as
shown in Fig. The base and the top are open and parallel to each other and at right
angles to the axis of the cone. The mould is provided with two metal foot pieces at
the bottom and two handles above them.
Tamping Bar: The tamping bar is made of a suitable hardwood and having
dimensions as shown in Fig.
Sampling: The sample of freshly mixed concrete is obtained.
Fig. Apparatus for Flow Table Test

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Procedure:
 The table is made level and properly supported. Before commencing the test, the
table-top and inner surface of the mould is wiped with a damp cloth.
 The slump cone is placed centrally on the table. The slump cone is filled with
concrete in two equal layers, each layer tamped lightly 10 times with the wooden
tamping bar. After filling the mould, the concrete is struck off flush with the upper
edge of the slump cone and the free area of the tabletop cleaned off.
 Half a minute after striking off the concrete, the cone is slowly raised vertically by
the handles. After this, the table-top raised by the handle and allowed to fall 15
times in 15 seconds.
 The concrete spreads itself out. The diameter of the concrete spread shall then be
measured in two directions, parallel to the table edges. The arithmetic mean of the
two diameters shall be the measurement of flow in millimeters.

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Kelly Ball Test
Kelly ball test is a simple field test which is very useful in determining
workability of concrete in real-time. It is justified that Kelly ball test performed faster
and provided accurate results with great precision than the slump test. But the only
disadvantage with the Kelly ball test that it requires a large amount of concrete when
compared with the slump test of concrete.
The test has been determined and invented by Kelly and hence known as
Kelly Ball Test or concrete ball test.
This has not been covered by Indian Standards Specification. The Kelly ball
test was earlier standardized as ASTM C360-92: “Standard Test Method for Ball
Penetration in Freshly Mixed Hydraulic Cement Concrete.” The ASTM standard was

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suspended in 1999 due to lack of use. The test has never been used widely outside
the United States (Bartos 1992). Indian Standards have not covered this test.
Apparatus of Kelly ball test:
Kelly ball test apparatus consists of a cylinder with one end having a
hemispherical shape of 15cm weighing 13.6kg and the other end is attached to a
graduated scale and handle. The whole arrangement is secured on a fixed stand.
The results have been specified by measuring the penetration made by the
hemisphere when freely placed on fresh concrete. The impression is measured by a
graduated scale immediately.
Fig: Kelly Ball
Procedure for Kelly ball test:
 Freshly mixed concrete (test sample) is poured into a container up to a depth of
20cm.

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 Once the container is filled with the concrete, the top surface is leveled and struck
off.
 The Kelly ball setup is kept on concrete as shown below by holding the handle of
hemisphere such that the frame touches the surface of the concrete.
 Ensure that the setup is kept at minimum 23cm away from the container ends.
(Place at the middle portion of the container)
 Now release the handle and allow the ball to penetrate through the concrete.
Fig. Placing of Kelly Ball in Concrete for Test
 Once the ball is released, the depth of penetration is immediately shown in the
graduate scale to the nearest 6mm.
 Note down the depth of penetration from the attached graduated scale.
 Repeat the same experiment for three times at different portions in the container
and average the value.
 The test can be performed in about 15 seconds and it gives much more consistent
results than Slump Test.
Formula for Kelly ball test: -
 The results of the Kelly ball test are correlated with the Slump test
 Average Value of the reading = Slump value
Advantages of Kelly ball test:
 The test results are more accurate when compared with the slump test.
 This test is a simple and instant which can perform on site.
 It doesn’t require lengthy calculation to find the workability of concrete.
Disadvantages of Kelly ball test:
 Kelly ball test is not suitable for larger size aggregates.
 The surface of the concrete should be leveled to test the concrete.
 This test is not recognized and used by Indian standards.
 Large aggregate can influence the results.

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K-Slump test
K Slump test is first covered by ASTM C 1362 and used to determine the workability
of concrete and degree of compaction of fresh concrete.
K slump test is an instant & direct test where slump value is evaluated
in one minute. It has a tester which is inserted in fresh concrete to measure the
slump value of concrete.
K slump test is also useful for finding the relative workability of concrete.
Apparatus of K Slump Test:
 The K slump tester is made with chrome plated steel, Aluminum, and plastic.
 The upper part is made of Plastic serves as a handle, and
 The lower part made of the chrome plated steel tube is used for testing.
The lower part of K slump tester:

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The round chrome plated steel is hollow and has an external dia of the 1.9cm
and internal diameter of 1.6cm.
The length of the tube is 25cm, and it also includes the solid cone at the
bottom which facilitates inserting the tube into the fresh concrete.
The lower part of the steel tube is also provided with two types of openings. 4
Rectangular slots of 5.1cm long and 0.8cm wide. 22 round holes of 0.64cm
Middle part of K Slump Tester
The disc floater of dia 6cm and thickness 0.24cm divides the tube into two
parts.
The disc is used to prevent the k slump tester from sinking into the fresh
concrete exceeding the preselected level.

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Upper part of K Slump tester
The upper part of K slump tester has a hollow plastic tube of dia 6cm, and
0.24cm thickness which is graduated with centimeter scale and the bottom portion
of tube has the aluminum cap 3 cm diameter and 2.25 cm long which has a little
hole and a screw that can be used to set and adjust the reference zero of the
apparatus.
The Hollow plastic rod can move freely inside the chrome plated tube through
the disc. The rod is also provided with the small pin which is used to support the
measuring tube at the beginning of the test.
Remember: both tubes are hollow.
Procedure of K Slump Test:
1. Wet the tester and clean it with a cloth.
2. Raise the plastic tube let it sit on the pin support.

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3. Take a container and pour some fresh concrete and level it.
4. Now insert the k slump tester vertically down until the disc floater rests at the
surface of the concrete. Do not rotate while inserting or removing the K slump tester.

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5. Wait for 60 seconds, lower the measuring rod slowly until it rests on the surface
of the concrete that has entered the tube and read the slump value directly on the
scale of the measuring rod.
6. Remove the tester from the fresh concrete vertically up don’t rotate or shake while
removing the rod from the concrete.
7. Due to the presence of holes at the bottom part of tester the concrete flows into
the K slump tester.
8. Again lower the measuring rod slowly till it touches the surface of the concrete
retained in the tube and read workability directly on the scale of the measuring rod.

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SEGREGATION AND BLEEDING IN CONCRETE
Segregation
Segregation can be defined as the separation of the constituent materials of
concrete. A good concrete is one in which all the ingredients are properly distributed
to make a homogeneous mixture. If a sample of concrete exhibits a tendency for

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separation of say, coarse aggregate from the rest of the ingredients, then, that
sample is said to be showing the tendency for segregation. Such concrete is not only
going to be weak; lack of homogeneity is also going to induce all undesirable
properties in the hardened concrete.
There are considerable differences in the sizes and specific gravities of the
constituent ingredients of concrete. Therefore, it is natural that the materials show
a tendency to fall apart.
Segregation may be of three types —
Firstly,
The coarse aggregate separating out or settling down from the rest of the matrix,
Secondly,
The paste or matrix separating away from coarse aggregate and
Thirdly,
Water separating out from the rest of the material being a material of lowest specific
gravity.
A well-made concrete, taking into consideration various parameters such as
grading, size, shape and surface texture of aggregate with optimum quantity of
waters makes a cohesive mix. Such concrete will not exhibit any tendency for
segregation. The cohesive and fatty characteristics of matrix do not allow the
aggregate to fall apart, at the same time, the matrix itself is sufficiently contained by
the aggregate. Similarly, water also does not find it easy to move out freely from the
rest of the ingredients.
The conditions favorable for segregation are, as discussed from the above
 The badly proportioned mix where sufficient matrix is not there to bind and contain
the aggregates. Insufficiently mixed concrete with excess water content shows a
higher tendency for segregation.
 Dropping of concrete from heights as in the case of placing concrete in column
concreting will result in segregation.
 When concrete is discharged from a badly designed mixer, or from a mixer with worn
out blades, concrete shows a tendency for segregation.
 Conveyance of concrete by conveyor belts, wheel barrow, long distance haul by
dumper, long lift by skip and hoist are the other situations promoting segregation of
concrete.

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 Vibration of concrete is one of the important methods of compaction. It should
be remembered that only comparatively dry mix should be vibrated. It too wet a mix
is excessively vibrated; it is likely that the concrete gets segregated. It should also
be remembered that vibration is continued just for required time for optimum
results. If the vibration is continued for a long time, particularly, in too wet a mix, it
is likely to result in segregation of concrete due to settlement of coarse aggregate in
matrix.
 In the recent time we use concrete with very high slump particularly in RMC.
The slump value required at the batching point may be in the order of 150 mm and
at the pumping point the slump may be around 100 mm. At both these points cubes
are cast. One has to take care to compact the cube mould with these high slump
concrete. If sufficient care and understanding of concrete is not exercised, the
concrete in the cube mould may get segregated and show low strength. Similarly,
care must be taken in the compaction of such concrete in actual structures to avoid
segregation.
 While finishing concrete floors or pavement, with a view to achieve a smooth
surface, masons are likely to work too much with the trowel, float or tamping rule
immediately on placing concrete. This immediate working on the concrete on
placing, without any time interval, is likely to press the coarse aggregate down,
which results in the movement of excess of matrix or paste to the surface.
Segregation caused on this account, impairs the homogeneity and
serviceability of concrete. The excess mortar at the top cause’s plastic shrinkage
cracks.
 From the foregoing discussion, it can be gathered that the tendency for
segregation can be remedied by correctly proportioning the mix, by proper handling,
transporting, placing, compacting and finishing.
 At any stage, if segregation is observed, remixing for a short time would make
the concrete again homogeneous. As mentioned earlier, a cohesive mix would reduce
the tendency for segregation. For this reason, use of certain workability agents and
pozzolanic materials greatly help in reducing segregation. The use of air-entraining
agent appreciably reduces segregation.
 Segregation is difficult to measure quantitatively, but it can be easily observed
at the time of concreting operation. The pattern of subsidence of concrete in slump
test or the pattern of spread in the flow test gives a fair idea of the quality of concrete
with respect to segregation.

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Bleeding
Bleeding is sometimes referred as water gain. It is a particular form of
segregation, in which some of the water from the concrete comes out to the surface
of the concrete, being of the lowest specific gravity among all the ingredients of
concrete. Bleeding is predominantly observed in a highly wet mix, badly
proportioned and insufficiently mixed concrete. In thin members like roof slab or
road slabs and when concrete is placed in sunny weather show excessive bleeding.
Due to bleeding, water comes up and accumulates at the surface. Sometimes,
along with this water, certain quantity of cement also comes to the surface. When
the surface is worked up with the trowel and floats, the aggregate goes down and
the cement and water come up to the top surface. This formation of cement paste at
the surface is known as “Laitance”.

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In such a case, the top surface of slabs and pavements will not have good
wearing quality. This laitance formed on roads produces dust in summer and mud
in rainy season. Owing to the fact that the top surface has a higher content of water
and is also devoid of aggregate matter; it also develops higher shrinkage cracks. If
laitance is formed on a particular lift, a plane of weakness would form and the bond
with the next lift would be poor. This could be avoided by removing the laitance fully
before the next lift is poured.
Example of external bleeding
Water while traversing from bottom to top, makes continuous channels. If the
water cement ratio used is more than 0.7, the bleeding channels will remain
continuous and unsegmented by the development of gel. This continuous bleeding
channels are often responsible for causing permeability of the concrete structures.
While the mixing water is in the process of coming up, it may be intercepted
by aggregates. The bleeding water is likely to accumulate below the aggregate. This
accumulation of water creates water voids and reduces the bond between the
aggregates and the paste. The above aspect is more pronounced in the case of flaky
aggregate.
Similarly, the water that accumulates below the reinforcing bars, particularly
below the cranked bars, reduces the bond between the reinforcement and the
concrete. The poor bond between the aggregate and the paste or the reinforcement
and the paste due to bleeding can be remedied by revibration of concrete. The
formation of laitance and the consequent bad effect can be reduced by delayed
finishing operations.
Bleeding rate increases with time up to about one hour or so and thereafter
the rate decreases but continues more or less till the final setting time of cement.
Bleeding is an inherent phenomenon in concrete. All the same, it can be
reduced by proper proportioning and uniform and complete mixing. Use of
finely divided pozzolanic materials reduces bleeding by creating a longer path

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for the water to traverse. It has been already discussed that the use of air-
entraining agent is very effective in reducing the bleeding.
It is also reported that the bleeding can be reduced by the use of finer cement
or cement with low alkali content. Rich mixes are less susceptible to bleeding than
lean mixes.
The bleeding is not completely harmful if the rate of evaporation of water from
the surface is equal to the rate of bleeding. Removal of water, after it had played its
role in providing workability, from the body of concrete by way of bleeding will do
good to the concrete.
Early bleeding when the concrete mass is fully plastic, may not cause much
harm, because concrete being in a fully plastic condition at that stage, will get
subsided and compacted. It is the delayed bleeding, when the concrete has lost its
plasticity, that causes undue harm to the concrete. Controlled revibration may be
adopted to overcome the bad effect of bleeding.
Bleeding presents a very serious problem when Slip Form Paver is used for
construction of concrete pavements. If two much of bleeding water accumulates on
the surface of pavement slab, the bleeding water flows out over the unsupported
sides which causes collapsing of sides.
Bleeding becomes a major consideration in such situations. In the pavement
construction finishing is done by texturing or brooming. Bleeding water delays the
texturing and application of curing compounds.

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Method of Test for Bleeding of Concrete
 This method covers determination of relative quantity of mixing water that will bleed
from a sample of freshly mixed concrete.
 A cylindrical container of approximately 0.01 m3 capacity, having an inside diameter
of 250 mm and inside height of 280 mm is used.
 A tamping bar similar to the one used for slump test is used. A pipette for drawing
off free water from the surface, a graduated jar of 100 cm3 capacity is required for
test.
 A sample of freshly mixed concrete is obtained. The concrete is filled in 50 mm layer
for a depth of 250 ± 3 mm (5 layers) and each layer is tamped by giving strokes, and
the top surface is made smooth by troweling.
 The test specimen is weighed and the weight of the concrete is noted. Knowing the
total water content in 1 m3 of concrete quantity of water in the cylindrical container
is also calculated.
 The cylindrical container is kept in a level surface free from vibration at a
temperature of 27°C ± 2°C. it is covered with a lid.
 Water accumulated at the top is drawn by means of pipette at 10 minutes interval
for the first 40 minutes and at 30 minutes interval subsequently till bleeding ceases.
 To facilitate collection of bleeding water the container may be slightly tilted.
 All the bleeding water collected in a jar.
Effect of time and temperature on workability
Time
Fresh concrete stiffens with time and loss workability though it is not exactly
settling or getting strength at all. After mixing concrete, some water is absorbed by

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aggregate, some may be lost by evaporation and some may be spent for initial
chemical reactions. The loss in workability by time depends on various factors like:
Initial workability: if initial workability is high, slump loss will be greater
Property of cement: if alkali content is high and sulfate content is low, sump loss
will be greater
Moisture content of aggregate: dry aggregate will absorb more water and workability
will decrease
With the passage of time after mixing ingredients of concrete with water,
workability of concrete starts shrinking. This happens because of fluidity loss from
the concrete. Fluidity is the amount of available water in concrete that is being
utilized in hydration of cement compounds for the sake of bonding.
When hydration of cement compounds C3S and C3A occurs than water within
a concrete gets absorbed by these compounds and now the least amount of water
will remain for workable concrete. If the temperature at the site varies, then some
amount of water also lost due to evaporation.
EFFECT ON SLUMP
As the time further proceeds, loss in slump value of concrete becomes
effective. Slump indicates how much concrete is workable. And hence slump value
is almost directly related to the time passes. When time further proceeds slump loss
will show almost linear behavior.
Slump loss increases likewise with the increase of temperature and it also
start reducing if increasing any ingredient in concrete more than the required
amount. Generally with the increase in cement contents then, then there is a
decrease in the required amount of water and hence again it effects workability of
freshly laid concrete.
If there is an extra addition i.e. Chemical admixtures that has some distinct
functions. For example admixtures that are mostly used are set accelerators, set
retarders, water reducing admixtures, etc. Then every isolated admixture has its
own effect on the properties of concrete.
CONCLUSION
Workability of concrete is almost dependent on the amount extra available water in
the concrete. For good workable concrete, calculate the concrete mix proportion and
add that much amount of water in the concrete during batching.
Temperature

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High temperature reduces workability and increases slump loss. Slump loss
is less influenced by temperature in stiff mixes because this type of mix is less
affected by a change in water content.
When fresh concrete is laid at the site then proper curing of concrete is
required, because structures are exposed to the environment and in these conditions
if there is no such an arrangement against the environment, then there are many
factors that affect the workability of concrete and temperature is One of them.
Temperature, almost in every aspect has negative effects on the properties of
concrete and same is the case with the workability of fresh concrete.
When temperature increases, then in the same proportion workability of fresh
concrete decreases. The reason that stands behind is “ when temperature increases
then evaporation rate also increases due to that hydration rate decreases and hence,
concrete will gain strength earlier “. Due to fast hydration of concrete, a hardening
comes in concrete and that decreases the workability of fresh concrete. Therefore,
In return manipulation of concrete become very difficult.
EFFECT ON FLOWABILITY OF CONCRETE
When temperature increases then fluid viscosity increases too and that
phenomenon affects the flow ability of fresh concrete. Flow ability of concrete starts
reducing and hence, as a result concrete workability decrease. And when workability
of concrete decreases, then due to the less flow ability of a fluid, voids within the
mass of concrete develops more.
This is because deeper air voids in concrete only fill, if freshly mixed fluid has
the ability to move deeper inside the small opening in the concrete. As in the present
case due to higher temperature, viscosity of fluid increases and that viscous of fluid
resists the movement of fluid.
Now In case when empty voids left in the concrete, then number of weak points
rise in concrete and that became the reason of a reduction in the strength of
concrete.
CONCLUSION
It indicates that the temperature has a negative effect on the workability of concrete
as well as strength up to some extent. Temperature decreases the setting time by
increasing hydration rate and that increase the early age strength of the concrete.
Quality of Mixing Water

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Water
It is an important ingredient of concrete as it actively participates in the
chemical reaction with cement. Since it helps to form the strength giving cement gel,
the quantity and quality of water is required to be looked into very carefully. It has
been discussed enough in chapter 1 about the quantity of mixing water but so far,
the quality of water has not been discussed. In practice, very often great control on
properties of cement and aggregate is exercised, but the control on the quality of
water is often neglected. Since quality of water affects the strength, it is necessary
for us to go into the purity and quality of water.
Qualities of Water
A popular yard-stick to the suitability of water for mixing concrete is that, if
water is fit for drinking it is fit for making concrete. This does not appear to be a
true statement for all conditions. Some waters containing a small amount of sugar
would be suitable for drinking but not for mixing concrete and conversely water
suitable for making concrete may not necessarily be fit for drinking. Some
specifications require that if the water is not obtained from source that has proved
satisfactory, the strength of concrete or mortar made with questionable water should
be compared with similar concrete or mortar made with pure water.
Some specification also accept water for making concrete if the pH value of
water lies between 6 and 8 and the water is free from organic matter. Instead of
depending upon pH value and other chemical composition, the best course to find
out whether a particular source of water is suitable for concrete making or not, is to
make concrete with this water and compare its 7 days’ and 28 days’ strength with
companion cubes made with distilled water. If the compressive strength is up to 90
per cent, the source of water may be accepted. This criteria may be safely adopted
in places like coastal area of marshy area or in other places where the available
water is brackish in nature and of doubtful quality. However, it is logical to know
what harm the impurities in water do to the concrete and what degree of impurity
is permissible is mixing concrete and curing concrete.

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Underground water is sometime found unsuitable for mixing or even for
curing concrete. The quality of underground water is to be checked.
Carbonates and bi-carbonates of sodium and potassium effect the setting time
of cement. While sodium carbonate may cause quick setting, the bi-carbonates may
either accelerate or retard the setting. The other higher concentrations of these salts
will materially reduce the concrete strength. If some of these salts exceeds 1,000
ppm, tests for setting time and 28 days strength should be carried out. In lower
concentrations they may be accepted. Brackish water contains chlorides and
sulphates. When chloride does not exceed 10,000 ppm and sulphate does not exceed
3,000 ppm the water is harmless, but water with even higher salt content has been
used satisfactorily.
Salts of Manganese, Tin, Zinc, Copper and Lead cause a marked reduction in
strength of concrete. Sodium iodate, sodium phosphate, and sodium borate reduce
the initial strength of concrete to an extra-ordinarily high degree. Another salt that
is detrimental to concrete is sodium sulphide and even a sulphide content of 100
ppm warrants testing. Silts and suspended particles are undesirable as they
interfere with setting, hardening and bond characteristics. A turbidity limit of 2,000
ppm has been suggested. Table 4.1 shows the tolerable concentration of some
impurities in mixing water.
The initial setting time of the test block made with a cement and the water
proposed to be used shall not differ by ±30 minutes from the initial setting time of
the test block made with same cement and distilled water.

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The following guidelines should also be taken into consideration regarding the
quality of water.
(a) To neutralize 100 ml sample of water using phenophthaline as an indicator, it
should not require more than 5 ml of 0.02 normal NaOH.
(b) To neutralise 100 ml of sample of water, using mixed indicator, it should not
require more than 25 ml of 0.02 normal H2So4.
(c) Permissible limits for solids are as given below in table 4.2.

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Algae in mixing water may cause a marked reduction in strength of concrete
either by combining with cement to reduce the bond or by causing large amount of
air entrainment in concrete. Algae which are present on the surface of the aggregate
have the same effect as in that of mixing water.
Use of Sea Water for Mixing Concrete
Sea water has a salinity of about 3.5 per cent. In that about 78% is sodium
chloride and 15% is chloride and sulphate of magnesium. Sea water also contain
small quantities of sodium and potassium salts. This can react with reactive
aggregates in the same manner as alkalis in cement. Therefore, sea water should
not be used even for PCC if aggregates are known to be potentially alkali reactive. It
is reported that the use of sea water for mixing concrete does not appreciably reduce
the strength of concrete although it may lead to corrosion of reinforcement in certain
cases.
Research workers are unanimous in their opinion, that sea water can be used
in un-reinforced concrete or mass concrete. Sea water slightly accelerates the early
strength of concrete. But it reduces the 28 days strength of concrete by about 10 to
15 per cent. However, this loss of strength could be made up by redesigning the mix.
Water containing large quantities of chlorides in sea water may cause efflorescence
and persistent dampness. When the appearance of concrete is important sea water
may be avoided. The use of sea water is also not advisable for plastering purpose
which is subsequently going to be painted.

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Sea water is not to be used for prestressed concrete or for reinforced
concrete.
If unavoidable, it could be used for plain cement concrete (PCC).
Divergent opinion exists on the question of corrosion of reinforcement due to
the use of sea water. Some research workers cautioned about the risk of corrosion
of reinforcement particularly in tropical climatic regions, whereas some research
workers did not find the risk of corrosion due to the use of sea water. Experiments
have shown that corrosion of reinforcement occurred when concrete was made with
pure water and immersed in pure water when the concrete was comparatively
porous, whereas, no corrosion of reinforcement was found when sea water was used
for mixing and the specimen was immersed in salt water when the concrete was
dense and enough cover to the reinforcement was given. From this it could be
inferred that the factor for corrosion is not the use of sea water or the quality of
water where the concrete is placed.
The factors effecting corrosion is permeability of concrete and lack of cover.
However, since these factors cannot be adequately taken care of always at the site
of work, it may be wise that sea water be avoided for making reinforced concrete.
For economical or other passing reasons, if sea water cannot be avoided for making
reinforced concrete, particular precautions should be taken to make the concrete
dense by using low water/cement ratio coupled with vibration and to give an
adequate cover of at least 7.5 cm.
The use of sea water must be avoided in prestressed concrete work because
of stress corrosion and undue loss of cross section of small diameter wires. The
latest Indian standard IS 456 of 2000 prohibits the use of Sea Water for mixing and

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curing of reinforced concrete and prestressed concrete work. This specification
permits the use of Sea Water for mixing and curing of plain cement concrete (PCC)
under unavoidable situation. It is pertinent at this point to consider the suitability
of water for curing. Water that contains impurities which caused staining, is
objectionable for curing concrete members whose look is important. The most
common cause of staining is usually high concentration of iron or organic matter in
the water. Water that contains more than 0.08 ppm. of iron may be avoided for
curing if the appearance of concrete is important. Similarly, the use of sea water
may also be avoided in such cases. In other cases, the water, normally fit for mixing
can also be used for curing.
Ready Mixed Concrete (RMC)
Ready Mixed Concrete is a tailor – made concrete that is manufactured in a factory or within a
batching plant based on the standard required specifications. The prepared concrete mix is then
taken to the work site within transit mixers mounted over a truck.
This type of concrete guarantee higher durability and sustainability. As the work is
carried out by an expert supplier, the mixture formed is precise and of higher quality. Special
concrete mixtures too can be made efficiently by this concrete manufacturing method.
INTRODUCTION
 Ready-mix concrete (RMC) is a ready-to-use material, with predetermined mixture of
Cement, sand, aggregates and water.
 The Idea of Ready Mix Concrete (RMC) was first introduced by Architect Jurgen Heinrich
Magens, he got his patent of RMC in Germany in 1903.
 In 1907, he discovered that the available time for transportation could be prolonged not
only by cooling fresh concrete but also by vibrating it during transportation.
 The first concrete mixed off site and delivered to a construction site was effectively done
in Baltimore, united states in 1913, just before the first world war. The first concept of
transit mixer was also born in 1926 in the united states.

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 In 1939, the first rmc plant was installed in united kingdom and in 1933. Between
the years 1950 and 1980 considerable growth of rmc took place in the US.
 In India rmc was first initially was used in 1950. During the construction sites of
dams like Bhakra Nangal, koyna.
The increasing availability of special transport vehicles, supplied by the new and fast growing
automobile industry, played a positive role in the development of RMC industry.
OBJECTIVES:
 Better quality concrete is produced.
 Elimination of storage space for basic materials at site.
 Elimination of Procurement / Hiring of plant and machinery.
 Wastage of basic materials is avoided.
MATERIALS REQUIRED FOR RMC
1. AGGREGATE :
Aggregates are the important constituents in concrete.They give body to the concrete,
reduce shrinkage and effect economy.The mere fact that the aggregates occupy 70-80 per cent
of the volume of concrete.
Aggregates are divided into two categories from the consideration of size
 Coarse aggregate
 Fine aggregate
The size of the aggregate bigger than 4.75 mm is considered as coarse aggregate and
Aggregate whose size is 4.75 mm and less is considered as fine aggregate.
2. CEMENT

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Cement is a binder material which sets and hardens independently, and can bind other
materials together.
Cement is made up of four main compounds,
 Dicalcium Silicate (2CaO SiO2),
 Tricalcium silicate (3CaO SiO2),
 Tricalcium acuminate (3CaO Al2O3),
 Tetra-calcium aluminoferrite (4CaO Al2O3 Fe2O3).
These compounds are designated as C2S, C3S,C3A, and C4AF.
where C stands for calcium oxide (lime), S for silica and A for alumina, and F for iron
oxide.
Small amounts of uncombined lime and magnesia also are present, along with alkalis
and minor amounts of other elements.
3. ADMIXTURE:
 Air-entraining admixtures (mainly used in concrete exposed to freezing)
 Water-reducing admixtures, plasticizers (reduce the dosage of water while maintaining
the workability)
 Retarding admixtures (mainly used in hot weather to retard the reaction of hydration)
 Accelerating admixtures (mainly used in cold weather to accelerate the reaction of
hydration)
 Super plasticizer or high range water-reducer (significantly reduce the dosage of water
while maintaining the workability)
 Miscellaneous admixtures such as corrosion inhibiting, shrinkage reducing, coloring,
pumping etc.
 FLY ASH:
 Fly ash is a by-product from coal-fired electricity generating power plants.
 The fly ash is generally used in the concrete in the following ways.
 As partial replace for cement.
 As partial replacement for sand.
 As simultaneous replacement for both cement and sand.

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WATER :
The pH value of water should be in between 6.0 and 8.0 according to IS 456-2000.
RIcE HUSk / HULL ASH (RHA)
 Today, rice is grown and harvested on every continent except Antarctica.
 The majority of all rice is produced in India, China, Japan, Indonesia, Thailand, Burma,
and Bangladesh. Asian farmers’ accounts for 92- percent of the world's total rice
production.
 More than 550 million tons of rice is produced annually around the globe.
 That rice husk are used in RMC to increase the strength.
EQUIPMENTS REQUIRED:
Storage of materials - Silos, containers and bins
Batching arrangement
Measuring and recording equipment
Mixing equipment
Control systems
Electrical, hydraulic and pneumatic drives
Conveying systems (belt / screw conveyors)

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Silos
Aggregate Feeding Belt Conveyors
Manual Batching plant
In case of manual batching all weighing and batching of concrete are done manually. It is used
for small jobs.

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Semiautomatic Batching Plant
• In it, the aggregate bin gates are opened by manually operated switches and gates are
closed automatically when the material has been delivered.
• Contains interlock which prevents charging and discharging.
Automatic Batching Plant:-
Fully automatic:-
• In it, the material are electrically activates by a single switch and complete
autographic record are made of the weight of each material.
• The batching plant comprises 2,3,4 or 6 compartment bins of several capacities.
• Over the conveyer belt ,the weigh batchers and discharging are provided below the bins.
MIXING PROCESS:
Thorough mixing of the materials is essential for the production of uniform concrete. The
mixing should ensure that the mass becomes homogeneous, uniform in color and consistency.

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Types of Ready Mixed Concrete
There are three types of ready mix concrete (RMC) depending upon the mixing of the
various ingredients as given below:
 Transit mixed concrete
 Shrink mixed concrete
 Central mixed concrete
1. Transit mixed concrete
It is also called dry batched concrete because all the basic ingredients including water
are charged directly into the truck mixer. The mixer drum is revolved fast at charging speed
during the loading of the material and after that it continues rotating at a normal agitating
speed. In this type of ready mix concrete, also three types of variations are possible as given
below:
Concrete mixed at job site
While being transported towards the destination, the drum is revolved at a slow or
agitating speed of 2 rpm, but after reaching the site just before discharging the material, it is
revolved at maximum speed of 12 to 15 rpm for nearly 70 to 100 revolution for ensuring
homogeneous mixing.
Concrete mixed in transit
The drum speed is kept medium during the transit time, i.e. approximately 8 rpm for about 70
revolutions. After 70 revolutions, it is slowed down to agitating speed of 2 rpm till discharging
the concrete.
Concrete mixed in the yard
The drum is turned at high-speed of 12 to 15 rpm for about 50 revolutions in the yard
itself. The concrete is then agitated slowly during transit time.
2. Shrink mixed concrete
The concrete is partially mixed in the plant mixer and then balance mixing is done in the
truck mounted drum mixer during transit time. The amount of mixing in transit mixer depends
upon the extent of mixing done in the central mixing plant. Tests should be conducted to
establish the requirement of mixing the drum mixer.
3. Central-mixed concrete
It is also called central batching plant where the concrete is thoroughly mixed before
loading into the truck mixer. Sometimes the plant is also referred as wet-batch or pre-mix plants.
While transporting the concrete, the truck mixer acts as agitator only. Sometimes, when
workability requirement is low or the lead is less, non-agitating units or dump trucks can also
be used.

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Flow Chart of Manufacturing Process Of Concrete At RMC Plant
MIXING PROCESS
TRANSIT MIXED (OR "TRUCK- MIXED") CONCRETE:
 While ready mixed concrete can be delivered to the point of placement the overwhelming
majority of it is brought to the construction site in truck-mounted, rotating drum mixers.
 Truck mixers have a revolving drum with the axis inclined to the horizontal.
 Inside the shell of the mixer drum are a pair of blades or fins that wrap in a helical
(spiral) configuration from the head to the opening of the drum.
 The concrete is loaded and mixed, it is normally hauled to the job site with the drum
turning at a speed of less than 2 rpm.

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TRANSIT MIXER
NEEDS TO BE SPECIFIED BY CONSUMER FOR RMC
 Characteristic strength or grade (N/mm2)
 Target workability or slump in mm required at site
 Exposure conditions for durability requirements
 Maximum water to cement ratio
 Minimum cement content
 Maximum aggregate size
 Type of cement
 Mineral admixture and its proportion (Kg/m3)
CHECKS BY CONSUMER BEFORE ORDERING THE RMC
Calibrations of all measuring devices and their accuracy.
Mode of operation of plant should preferably be fully automatic and not manual.
Quality of materials proposed to be used.
Adequacy of quantity of materials used.
INSPECTION OF CONSUMER
Advantages of Ready Mixed Concrete
 Quality concrete is obtained as a ready-mix concrete mix plant make use of sophisticated
equipment and consistent methods.

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 There is strict control over the testing of materials, process parameters and continuous
monitoring of key practices during the manufacture.
 Poor control on the input materials, batching and mixing methods in the case of site mix
concrete is solved in a ready-mix concrete method.
 Speed in the construction practices followed in ready mix concrete plant is followed
continuously by having mechanized operations.
 The output obtained from a site mix concrete plant using a 8/12 mixer is 4 to 5 metric
cubes per hour which is 30-60 metric cubes per hour in a ready mix concrete plant.
 Better handling and proper mixing practice will help to reduce the consumption of cement
by 10 – 12%.
 Use of admixtures and other cementitious materials will help to reduce the amount of
cement.
 The concrete mixed is used with high versatility. It is placed by following best concrete
placing methods.
 Cement is saved and the dust caused is reduced as ready mix concrete make use of bulk
concrete instead of bags of cement.
 Cement saving will conserve the energy and the resources.
 Less consumption result in less production of cement hence less environmental pollution.
 More durable structure is obtained thus increasing the service life and saving the life
cycle costs.
 Ready mix concrete manufacture have less dependency on human labours hence the
chances of human errors is reduced.
 This will also reduce the dependency on intensive labours.
 Small or large quantities of concrete as per the specification is delivered timely at the site.
 This demands no space for storing the raw materials at site. There is no delay due to
sitebased batching plant erection/ dismantling; no equipment to hire; no depreciation of
costs.
 Petrol and diesel consumed is less thus noise and air pollution is reduced.
Disadvantages of Ready Mixed Concrete
 The transit time from the time of preparation of concrete to the delivery site, will result
in loss of workability. This will demand for additional water or admixtures to maintain
the workability as per the specification.
 At site, the QA/QC engineer are supposed to check the workability through slump test
before using it for construction.
 Traffic during the transit of concrete can result in setting of concrete. This will hence
require addition of admixtures to delay the setting period. But unexpected traffic is a
great problem.
 The formwork and placing arrangement must be prepared in advance in large area as the
concrete can be bought in larger amounts.
CONCLUSION:
The concrete quality produced in RMC plant is highly consistent with low deviation order.
It provides a high degree of overall strength of hardened concrete and the performance of the
structure at a later date.

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RMC operations are highly mechanized and fully controlled through electronic controls and
hence reduce the probability of errors in various operations.
INTRODUCTION
Shotcreting has proved to be the best method for construction of curved
surfaces
Domes are now much easier to construct with the advent of with this shotcrete
technology.
Tunnel linings are also becoming easy technology.
This technical paper includes the concept of shotcrete and how it differs from
conventional concrete.
It also enumerates the different types of process involved in shotcreting.
DEFINITION OF SHOTCRETE
Shotcrete is a mortar or high-performance concrete conveyed through a hose
and pneumatically projected at high velocity onto a backing surface. applied mixture
of cement, aggregate, and water conveyed through a hose and projected at high
velocity onto the application surface.
It is the force of this spraying action that leads to compaction of the concrete
or mortar which then forms layers of concrete to the required thickness.
Shotcreting has been an acceptable way of placing cementitious material in a
variety of applications.
This mechanism reduces the rebound waste that occurs through the
shotcreting process and these fibres also resist plastic shrinkage and cracking
through their ability to enhance the early-stage tensile strength of concrete.
Shotcrete is today an all-inclusive term that describes spraying concrete or mortar
with either a dry or wet mix process.
Gunite is a trademarked name that is incorrectly used to describe the dry-mix
shotcrete process
Shotcrete emerged as the only acceptable industry term to correctly describe
"pneumatically applied concrete “.
HISTORY

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Shotcrete, then known as gunite (/ gunite/), was invented in 1907 by
American taxidermi Akeley to repair the crumbling facade of the Field Columbian
Museum in Chicago (the old Palace of Fine Arts from the World's
Columbian Exposition.
He used the method of blowing dry material out of a hose with compressed
air, injecting water at the nozzle as it was released. In 1911, he was granted a patent
for his inventions, the "cement gun", the equipment used, and "gunite", the material
that was produced.
There is no evidence that Akeley ever used sprayable concrete in his taxidermy
work, as is sometimes suggested. F. Trubee Davison covered this
and other Akeley inventions in a special issue of Natural History magazine [
Until the 1950s when the wet-mix process was devised, only the dry-mix
process was used. In the 1960s,
The alternative method for gunning by the dry method was devised with the
development of the rotary gun, with an open hopper that could be fed continuously.
Shotcrete is also a viable means and method for placing structural concrete.
SHOTCRETE MATERIALS (SAME AS CONCRETE)
• Portland Cement
• Water
• Sand
• Admixtures / Fibres
Difference: ???
• Applied via Compressed Air
SHOTCRETE, HIGH PERFORMANCE PRODUCT CONSISTING OF …
NOVEL SHOTCRETE MATERIALS
 POLYMER MODIFICATION
 POZZOLANIC ADMIXTURES
 FIBER REINFORCEMENT

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 LOW VELOCITY SHOTCRETE
 STEEL FIBRE REINFORCED MICRO SILICA SHOTCRETE
EQUIPMENTS USED IN SHOTCRETE
 Batching and mixing equipment
 Admixture dispensers
 Air COMPRESSOR
 Nozzles
 Shotcrete accelerator
SHOTCRETE VERSUS CONVENTIONAL CONCRETE
Unlike conventional concrete, which is first placed and then compacted in
second operation
shotcrete undergoes placement and compaction at the same time due to the
force with which it is projected from the nozzle.
Shotcrete is more dense, homogeneous, strong, and waterproof than is
possible to obtain by any other process.
Shotcrete is not placed or contained by forms. It can be impacted onto any
type or shape of surface, including vertical or overhead areas.
WORKING OF DRY PROCESS PROCEEDS AS PER
THE FOLLOWING STEPS:
Step1: Pre blended, dry or semi-dampened materials are placed into
shotcrete equipment and metered into a hose.
Step2: Compressed air conveys materials at high velocity to the nozzle
where the water is added.
Step3: Then the material is consolidated on receiving surface by high
impact velocity
The dry process can be used for any shotcreting applications from the
smallest patching and sealing works to largest projects.
The maximum production achievable with dry process equipment ranges
from 10-12 yards per hour of dry mix depending on the conditions.
Most applications have production rates of 2-6 cubic yards per hour of mix.
Advantages of Dry process:
Easy start up, shutdown and clean up.
Control of materials is on site.
Nozzle man can be up to 1000ft horizontally or 500ft vertically from the gun.

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DEFINITION OF WETMIX SHOTCRETE
Shotcrete in which all of the ingredients, except accelerator, are mixed before
introduction into the delivery hose.
SHOTCRETE (WET MIX)
Accelerator, if used, is added to the shotcrete mixture at the nozzle in
such a way that the quantity can be properly regulated and monitored

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WORKING OF WET PROCESS PROCEEDS AS PER THE FOLLOWING STEPS:
Step 1: Wet material is pumped to the nozzle where compressed air is
introduced to
Step2: All ingredients, including water, are thoroughly mixed and introduced
into the shotcrete equipment provide high velocity for placement and consolidation
of the material onto the receiving surface.
Step 3: Mostly wet-process shotcreting is done with premixed mortar or small
aggregate concrete.
The mix design and consistency of supply are very important in order to provide a
mix with the workability or plasticity to be pumped through a small-diameter hose.
Sand gradation is same as for the dry process and for coarse aggregate mixes;
20-30 percent of 20mm aggregate is added. Cement content will vary according to
agg.
However, most mixes contain approximately 700 pounds or more of cement.
Advantages of Wet process:
Little or no formwork is required.
Cost effective method for placing concrete.
Ideal for irregular surface applications
Allows for easier material handling in areas with difficult access
APPLICATION OF SHOTCRETE
v Support of underground openings in tunnel, mines, drainage.
v Rock slope stabilization and support for excavated foundations, often in
conjunction with rock and soil anchor systems.
v Channel linings, protection of bridge abutments and stabilization of debris-flow
prone creeks.
v Rehabilitation of reinforced concrete structures such as bridges, chemical
processing and handling plants.
v Rehabilitation of deteriorated marine structures such as bulkheads, piers, sea
v Piers / Docks
v Ditches
v Retaining Walls
v Scope Stabilization
Typical Use of Shotcrete

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Use of Shotcrete
Infrastructure rehabilitation
– Bridges, parking structures, subway tunnels etc.
Infrastructure rehabilitation
– Dams and hydraulic structures (water reservoirs, canals, spillways, locks,
creek stabilization, etc.)

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– Marine structures (piers, wharves, sea walls, light stations, berth faces,
dry docks, etc.)
ADVANTAGES
v Little or no framework is required.
v Cost effective method for placing concrete.
v Ideal for irregular surfaces application.
v Allows for easier material handling in areas with difficult access.
v Easy start up, shutdown and clean up.
v an increase in load bearing capacity due to redistribution of stresses.
v Excellent corrosion resistance
v Highway and railroad tunnels
v Mining operations
v Slope stabilization
v Building foundations
v Concrete repair & restoration
v Parking garages
v Housing

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DISADVANTAGES
v Rain may wash out the cement leaving a sandy surface, or it may saturate the
shotcrete and cause sloughing or sagging
v Strong wind will separate the material between the nozzle and the point of deposit,
reducing the strength
v It requires skilled and experienced labours.
v A greater degree of geotechnical knowledge is required
v Improperly applied shotcrete may create conditions much worse than the
untreated condition
CONCLUSION
v the use of Shotcrete to build new concrete structures as well as to restore and
repair existing structures is well known and documented and it is perhaps the most
diverse method available for concrete construction.
v the use of this innovative technology is increasing day by day and procedures for
its proper performance are well developed and high-quality work is regularly
obtained.
v Shotcrete is a viable option for doing superstructure repair (unformed) and
substructure repair (unformed) if done strictly according to specifications and best
practices.
v It is a good substitute for the manual lay-up method for vertical and overhead
applications using rapid set mortar.
What is Guniting
u the guniting is the most effective process of repairing concrete work which has
been damaged due to inferior work or other reasons. It is also used for providing an
impervious layer.
u the gunite is a mixture of cement and sand, the usual proportion being 1:3. A
cement gun is used to deposit this mixture on the concrete surface under a pressure
of about 20 to 30 N/cm2.
Key points: -
u Gunite is also known as shotcrete or pneumatically applied mortar.

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u It can be used on vertical and overhead, as well as on horizontal surfaces and is
particularly useful for restoring surfaces spalled due to corrosion of reinforcement.
u Gunite is a mixture of Portland cement, sand and water, shot into the
place by compressed air.
u Guniting is basically used in swimming pool, dams, tanks, etc.
Mixture:
u A cement-sand mixture in the ratio of 1:2 or 1:3 depending upon the requirement,
is applied at high pressure over the surface with the help of specialized equipment.
u Guniting is extensively used to rehalibate concrete bridges, dams, spillways,
buildings, etc.
Mixture for guniting being made.
WHAT IS THE PROCEDURE OF GUNITING?

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u the cement is mixed with slightly moist sand and then necessary water is added
as the mixture comes out from the cement gun. A regulating valve is provided to
regulate the quantity of water.
u the surface to be treated is cleaned and washed. The nozzle of gun is generally
kept at a distance of about 750 mm to 850 mm from the surface to be treated and
the velocity of nozzle varies from 120 to 160 m/sec.
u Sand and cement are mixed dry in a mixing chamber, and the dry mixture along
a pipe or hose to a nozzle, where it is forcibly projected on to the surface to be coated.
u the flow of water at the nozzle can be controlled to give a mix of desired stiffness,
which will adhere to the surface against which it is projected.
Spraying of concrete
u There are two different methods of spraying:
- Dry process spraying
- Wet process spraying
u Dry process spraying is the process in which the mixture of damp sand and cement
is passed through the delivery hose to the nozzle and the water is mixed at that time.
u Water cement ratio should be between 0.33 and 0.50
u This process is often used for repair work.

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u It is because of its fast application process and restoration of structural strength
at early stage
u the performance characteristics of dry sprayed concrete are they have good
density and high strength.
u It has very good bond to a suitable substance.
u These advantages make it more variable than conventional concrete as wet process
sprayed concrete.
Quality finish
u Distance of spraying should be about 0.6m to 1.5m from treatment surface.
u Angle of spraying should as far as possible perpendicular to treatment surface.
u Formed in successively from top down without gaps or slumps.
u Freshly gunite surface should be protected from rain or strong sunlight.
u Wet slope surface should be allowed to dry by covering with tarpaulin for a few
days before guniting to ensure good bonding between gunite and slope surface,
WHAT ARE THE ADVANTAGES OF GUNITING?
Following are the advantages of guniting

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u the high compressive strength is obtained. Strength of about 56 to 70 N/mm2 at
28 days is generally obtained.
u the high impermeability is achieved.
u the repairs are carried out in any situation in a short time

Building Materials and Concrete Technology Unit 3

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Building Materials and Concrete Technology Unit 3