BUILDING MATERIALS AND THEIR PROPERTIES FOR CONSTRUCTIONS
- 1. BUILDING MATERIALS & PROPERTIES
- 2. 1. AGGREGATE: Aggregates are the important constituents of the concrete which give body to the concrete and also reduce shrinkage. Aggregates occupy 70 to 80 % of total volume of concrete. So, we can say that one should know definitely about the aggregates in depth to study more about concrete. Classification of Aggregates as per Shape and Size: Aggregates are classified based on so many considerations, but here we are going to discuss about their shape and size classifications in detail. i) Classification of Aggregates Based on Shape: We know that aggregate is derived from naturally occurring rocks by blasting or crushing etc., so, it is difficult to attain required shape of aggregate. But, the shape of aggregate will affect the workability of concrete. So, we should take care about the shape of aggregate. This care is not only applicable to parent rock but also to the crushing machine used. Aggregates are classified according to shape into the following types Rounded aggregates Irregular or partly rounded aggregates Angular aggregates Flaky aggregates Elongated aggregates Flaky and elongated aggregates Rounded Aggregate: The rounded aggregates are completely shaped by attrition (the resistance of a granular material to wear) and available in the form of seashore gravel. Rounded aggregates result in the minimum percentage of voids (32 – 33%) hence gives more workability. They require a lesser amount of water-cement ratio. They are not considered for high-strength concrete because of poor interlocking behavior and weak bond strength. Irregular Aggregates: The irregular or partly rounded aggregates are partly shaped by attrition and these are available in the form of pit sands and gravel. Irregular aggregates may result 35- 37% of voids. These will give lesser workability when compared to rounded aggregates. The bond strength is slightly higher than rounded aggregates but not as required for high strength concrete. Angular Aggregates: The angular aggregates consist well defined edges formed at the intersection of roughly planar surfaces and these are obtained by crushing the rocks. Angular aggregates result maximum percentage of voids (38-45%) hence gives less workability. They give 10-20% more compressive strength due to development of stronger aggregate-mortar bond. So, these are useful in high strength concrete manufacturing.
- 3. Flaky Aggregates: When the aggregate thickness is small when compared with width and length of that aggregate it is said to be flaky aggregate, or on the other, when the least dimension of aggregate is less than the 60% of its mean dimension then it is said to be flaky aggregate. Elongated Aggregates: When the length of aggregate is larger than the other two dimensions then it is called elongated aggregate or the length of aggregate is greater than 180% of its mean dimension. Flaky and Elongated Aggregates: When the aggregate length is larger than its width and width is larger than its thickness then it is said to be flaky and elongated aggregates. The above 3 types of aggregates are not suitable for concrete mixing. These are generally obtained from the poorly crushed rocks. ii) Classification of Aggregates Based on Size: Aggregates are available in nature in different sizes. The size of aggregate used may be related to the mix proportions, type of work etc. The size distribution of aggregates is called grading of aggregates. Following are the classification of aggregates based on size: Aggregates are classified into 2 types according to size Fine aggregate Coarse aggregate Fine Aggregate: When the aggregate is sieved through a 4.75mm sieve, the aggregate passed through it called fine aggregate. Natural sand is generally used as fine aggregate, silt and clay also come under this category. The soft deposit consisting of sand, silt, and clay is termed as loam. The purpose of the fine aggregate is to fill the voids in the coarse aggregate and to act as a workability agent. Coarse Aggregate: When the aggregate is sieved through 4.75mm sieve, the aggregate retained is called coarse aggregate. Gravel, cobble and boulders come under this category. The maximum size aggregate used may be dependent upon some conditions. In general, 40mm size aggregate used for normal strengths, and 20mm size is used for high strength concrete. The size range of various coarse aggregates given below. 1.1 Physical Prosperities of Aggregate: 1.1.1 Grading: Grading is the particle-size distribution of an aggregate as determined by a sieve analysis using wire mesh sieves with square openings. As per IS:2386(Part-1): Fine aggregate: 6 standard sieves with openings from 150 μm to 4.75 mm. (150 μm, 300 μm, 600 μm, 1.18mm, 2.36mm, 4.75mm)
- 4. Coarse aggregate: 5 sieves with openings from 4.75mm to 80mm. (4.75mm, 10mm, 12.5mm, 20mm, 40mm) Grain size distribution for concrete mixes that will provide a dense strong mixture. Ensure that the voids between the larger particles are filled with medium particles. The remaining voids are filled with still smaller particles until the smallest voids are filled with a small amount of fines. Grading Limits for Fine Aggregates: (Based on Clause 4.3 of IS: 383 - 1970) IS Sieve Designation Percentage Passing Grading Zone I Grading Zone II Grading Zone III Grading Zone IV 10 mm 100 100 100 100 4.75 mm 90 – 100 90 – 100 90 – 100 95 – 100 2.36 mm 60 – 95 75 – 100 85 – 100 95 – 100 1.18 mm 30 – 70 55 – 90 75 – 100 90 – 100 600 microns 15 – 34 35 – 59 60 – 79 80 – 100 300 microns 5 – 20 8 – 30 12 – 40 15 – 50 150 microns 0 – 10 0 – 10 0 – 10 0 – 15 1.1.2 Fineness Modulus: The results of aggregate sieve analysis is expressed by a number called Fineness Modulus. Obtained by adding the sum of the cumulative percentages by mass of a sample aggregate retained on each of a specified series of sieves and dividing the sum by 100. The following limits may be taken as guidance: Fine sand: Fineness Modulus: 2.2 - 2.6 Medium sand: F.M.: 2.6 - 2.9 Coarse sand: F.M.: 2.9 - 3.2 A sand having a fineness modulus more than 3.2 will be unsuitable for making satisfactory concrete. 1.1.3 Flakiness Index: The flakiness index of aggregate is the percentage by weight of particles in it whose least dimension (thickness) is less than three-fifths of their mean dimension. The test is not applicable to sizes smaller than 6.3 mm. The flakiness index is taken as the total weight of the material passing the various thickness gauges expressed as a percentage of the total weight of the sample taken.
- 5. The below table shows the standard dimensions of thickness and length gauges. The flakiness index of aggregate is the percentage by weight of particles in it whose least dimension (thickness) is less than three-fifths of their mean dimension. 1.1.4 Elongation Index: The elongation index on an aggregate is the percentage by weight of particles whose greatest dimension (length) is greater than 1.8 times their mean dimension. The elongation index is not applicable to sizes smaller than 6.3 mm. The elongation index is the total weight of the material retained on the various length gauges expressed as a percentage of the total weight of the sample gauged. The presence of elongated particles in excess of 10 to 15 per cent is generally considered undesirable, but no recognized limits are laid down. 1.2 Mechanical Properties of Aggregate Property # 1. Toughness: Property # 2. Hardness: Property # 3. Specific Gravity: Property # 4. Porosity and Absorption of Water by Aggregate: Property # 5. Bulking of Sand: 1.2.1 Toughness: It is defined as the resistance of aggregate to failure by impact. The impact 1.2.2 Hardness: It is defined as the resistance to wear by abrasion, and the aggregate abrasion value is defined as the percentage loss in weight on abrasion. Deval Attrition Test: This test has been covered by IS 2386 Part (IV)-1963. In this test particles of known weight are subjected to wear in an iron cylinder rotated 10,000 (ten thousand) times at the rate of 30 to 33 revolutions per minute. After the specified revolution of the cylinder the material is taken out and sieved on 1.7 mm sieve and the percentage of material finer than 1.7mm is determined. This percentage is taken as the attrition value of the aggregate. The attrition value of about 7 to 8 usually is considered as permissible. Dorry Abrasion Test: This test has not been covered by Indian standard specifications. In this test a cylindrical specimen having its diameter and height of 25 cm is subjected to abrasion against a rotating metal disk sprinkled with quartz sand. The loss in weight of the cylinder after 1000 (one thousand) revolutions is determined. Then the hardness of rock sample is expressed by an empirical relation as follows: Hardness or sample = 20 – Loss in weight in grams/3 For good rock this value should not be less the 17. The rock having this value of 14 is considered poor.
- 6. 1.2.3 Porosity and Absorption of Water by Aggregate: All aggregates, particles have pores with in their body. The characteristics of these pores are very important in the study of the properties of aggregate. The porosity, permeability, and absorption of aggregates influence the resistance of concrete to freezing and thawing, bond strength between aggregate and cement paste, resistance to abrasion of concrete etc. The size of pores in the aggregate varies over a wide range, some being very large, which could be seen even with naked eye. The smallest pore of aggregate is generally larger than the gel pores in the cement paste, pores smaller than 4 microns are of special interest as they are believed to affect the durability of aggregates subjected to alternate freezing and thawing. Some of the pores are wholly within the body of the aggregate particles and some of them are open upto the surface of the particle. BRICKS AND MASONRY BLOCKS: BRICK: A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term brick denotes a block composed of dried clay, but is now also used informally to denote other chemically cured construction blocks. Bricks can be joined using mortar, adhesives or by interlocking them. In India, standard brick size is 190 mm x 90 mm x 90 mm as per the recommendation of BIS. With mortar thickness, the dimension of the brick becomes 200 mm x 100 mm x 100 mm which is also known as the nominal size of the modular brick. Block is a similar term referring to a rectangular building unit composed of similar materials, but is usually larger than a brick. Lightweight bricks (also called lightweight blocks) are made from expanded clay aggregate. In India, most commonly used, rectangular, standard size of solid concrete block is 4″(100 mm), 6″(150 mm) and 8″ (200 mm) thick CMU. 2.1 Types of Bricks: a) Classification of Bricks Based on Quality: First Class 1. Cement of lime mortar is used, 2. The surface and edges of bricks are sharp, 3. And the thickness of mortar joints doesn’t exceed 10mm Second Class 1. Ground moulded bricks are used, 2. Bricks are rough and shape is slightly irregular, 3. The thickness of mortar joint is 12 mm Third Class 1. Bricks are not hard, rough surface with distorted shape, 2. Used for temporary structures, 3. Used in places where rainfall is not heavy b) Classification of Bricks Based on Building Process:
- 7. 1. Common Bricks: These bricks are the most common bricks used. They don’t have any special features or requirements. They have low resistance, low quality, low compressive strength. They are usually used on the interior walls. 2. Engineering Bricks: These bricks are known for many reasons. They have high compressive strength and low absorption capacity. They are very strong and dense. They have good load bearing capacity, damp proof, and chemical resistance properties. They have a uniform red color. They are classified as Class A, class B, class C. Class A is the strongest but Class B is most used. They are used for mainly civil engineering works like sewers, manholes, ground works, retaining walls, damp proof courses, etc. MASONRY BLOCKS: Masonry block is an important component in construction and building materials in many parts of the world. Concrete block is made from Portland Cement, aggregates and water. It is also known as a concrete masonry unit (CMU). As a building material, concrete offers several attractive characteristics to designers and builders. Standard size of Brick—A solid or hollow manufactured masonry unit of either concrete, clay or stone. Concrete brick—A concrete hollow or solid unit smaller in size than a concrete block Concrete block—A hollow or solid concrete masonry unit. Larger in size than a concrete brick. Block walls have higher density as compared to brick constructions and hence they offer more soundproofing. Their efficient acoustic insulation is a big help if your home is constantly surrounded by noise that could keep you from getting a sound sleep. 2.2 Field Tests on Brick: A field test on bricks gives the idea about its basic quality based on its shape, size and colour at first observation without any big appliances. They are the very common and easiest way to check the quality of brick. Field tests of brick are very helpful on the site. Some very common tests of brick that is followed to find if brick is good at first observation are as follows: Shape and Size of Clay Bricks: The clay bricks should have a uniform rectangular plan surface, as per standard size and sharp straight edges. BSI recommends the standard size of brick is 190 mm x 90 mm x 90 mm and constructional size is 200 mm x 100 mm x 100 mm.
- 8. Visual inspection: In this test bricks are closely inspected for its shape. The bricks of good quality should be uniform in shape and should have truly rectangular shape with sharp edges. Hardness of Clay Bricks: The clay bricks should be sufficiently hard when scratched by a finger-nail no impression should be left on the brick surface. Colour of Clay Bricks: The clay bricks should have a uniform deep red colour throughout. It indicates the uniformity of chemical composition and the quality of burning of the bricks. Texture and compactness of Clay Bricks: The surfaces should not be so smooth to cause skidding of mortar. The clay brick should have a pre-compact, homogeneous and uniform texture. A broken surface should be free form cracks, holes grits or lumps of lime. Soundness of Clay Bricks: When two clay bricks are stuck together, a metallic ringing sound should come. Structure: A brick is broken and its structure is examined. It should be homogeneous, compact and free from any defects such as holes, lumps etc. Thermal Conductivity of Clay Bricks: Generally, we are not conducting any test for thermal conductivity because the thermal conductivity of clay brick is low, i.e., it protects from heat. Basic Strength of Clay Bricks: When dropped flat on the hard ground from a height of about one meter, clay bricks should not break. 2.3 Laboratory Tests on Brick: Laboratory tests on brick determine the mechanical properties of brick and give a scientific
- 9. approach to ensure the quality of bricks. It is essential while purchasing the brick and examine the properties for the quality of construction. Followings brick tests are performed in the laboratory to determine the quality of brick. 1. Water Absorption of Bricks: 2. Compressive Strength of Brick: 3. Efflorescence: 4. Dimension tolerance: 2.3 Properties of Brick: The essential properties of bricks may be conveniently discussed under the following four headings: physical, mechanical, thermal and durability properties. (1) Physical Properties of Bricks:. (i) Shape: (ii) Size: (iii) Color. (iv) Density. (2) Mechanical Brick Properties. (i) Compressive Strength of Bricks: (ii) Flexure Strength: (3) Thermal Properties of Building Bricks: (4) Durability: CEMENT 4.1 TYPES OF CEMENT (Other cements) 1. Ordinary Portland Cement (OPC) 2. Portland Pozzolana Cement (PPC) 3. Rapid Hardening Cement 4. Quick setting cement 5. Low Heat Cement 6. Sulfates resisting cement 7. Blast Furnace Slag Cement 8. High Alumina Cement 9. White Cement 10. Colored cement 11. Air Entraining Cement
- 10. 60 to 67% Lime (CaO) 12. Expansive cement 13. Hydrographic cement 4.2 CHEMICAL PROPERTIES OF PORTLAND CEMENT ARE AS FOLLOWS: Silica (SiO2) 17 to 25% Alumina (Al2O3) 3 to 8% Iron oxide (Fe2O3) 0.5 to 6% Magnesia (MgO) 0.1 to 4% Sulphur trioxide (SO3) 1 to 3% Soda and/or Potash (Na2O+K2O) 0.5 to 1.3% Physical Properties of Ordinary Portland Cement Properties Values Specific Gravity 3.16 Normal Consistency 29% Initial Setting time 65min Final Setting time 275 min Fineness 330 kg/m2 Soundness 2.5mm Bulk Density 830-1650 kg/m3 BOGUES COMPOUNDS: When water is added to cement, it react with the ingredients of the cement chemically and results in the formation of complex chemical compounds terms as BOGUES compounds. 1. Tri-Calcium Aluminate (3CaO.Al2O3 or C3A)---------------------------8-12%
- 11. 2. Tetra Calcium Alumino Ferrate (4CaO.Al2O3.Fe2O3 or C4AF)-------6-10% 3. Tri-Calcium Silicate (3CaO.SiO2 or C3S)--------------------------------30-50% 4. Di-Calcium Silicate (2CaO.SiO2 or C2S)---------------------------------20-45% 1. Tri-Calcium Aluminate (3CaO.Al2O3 or C3A) 2. Tetra Calcium Alumino Ferrate (4CaO.Al2O3.Fe2O3 or C4AF) 3. Tri-Calcium Silicate (3CaO.SiO2 or C3S) .Di-Calcium Silicate (2CaO.SiO2 or C2S)