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MASTER TECHNICAL COACHING CENTER, , INGREDIENTS, OF, CONCRETE, , DIR - ER BHOOPESH SHARMA, , 1

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MASTER TECHNICAL COACHING CENTER, , Physical Properties of Cement, Different blends of cement used in construction are characterized by their physical properties., Some key parameters control the quality of cement. The physical properties of good cement, are based on:, 1) Fineness of cement, 2) Soundness, 3) Consistency, 4) Strength, 5) Setting time, 6) Heat of hydration, 7) Loss of ignition, 8) Bulk density, 9) Specific gravity (Relative density), , 1) Fineness of Cement, The size of the particles of the cement is its fineness. The required fineness of good cement is, achieved through grinding the clinker in the last step of cement production process. As, hydration rate of cement is directly related to the cement particle size, fineness of cement is, very important., , 2) Soundness of Cement, Soundness refers to the ability of cement to not shrink upon hardening. Good quality cement, retains its volume after setting without delayed expansion, which is caused by excessive free, lime and magnesia., 3) Consistency of Cement, The ability of cement paste to flow is consistency., It is measured by Vicat Test., In Vicat Test Cement paste of normal consistency is taken in the Vicat Apparatus. The plunger, of the apparatus is brought down to touch the top surface of the cement. The plunger will, penetrate the cement up to a certain depth depending on the consistency. A cement is said to, have a normal consistency when the plunger penetrates 10¡À1 mm., , 4) Strength of Cement, Three types of strength of cement are measured compressive, tensile and flexural. Various, factors affect the strength such as water-cement ratio, cement-fine aggregate ratio, curing, conditions, size and shape of a specimen, the manner of molding and mixing, loading, conditions and age., DIR - ER BHOOPESH SHARMA, , 2

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MASTER TECHNICAL COACHING CENTER, , Compressive Strength: It is the most common strength test. A test specimen (50mm) is taken, and subjected to a compressive load until failure. The loading sequence must be within 20, seconds and 80 seconds., , Tensile strength: Though this test used to be common during the early years of cement, production, now it does not offer any useful information about the properties of cement., , Flexural strength: This is actually a measure of tensile strength in bending. The test is, performed in a 40 x40 x 160 mm cement mortar beam, which is loaded at its center point until, failure., , 5) Setting Time of Cement, Cement sets and hardens when water is added. This setting time can vary depending on, multiple factors, such as fineness of cement, cement-water ratio, chemical content, and, admixtures. Cement used in construction should have an initial setting time that is not too low, and a final setting time not too high. Hence, two setting times are measured:, , Initial set: When the paste begins to stiffen noticeably (typically occurs within 30-45 minutes), Final set: When the cement hardens, being able to sustain some load (occurs below 10 hours), 6) Heat of Hydration, When water is added to cement, the reaction that takes place is called hydration. Hydration, generates heat, which can affect the quality of the cement and also be beneficial in maintaining, curing temperature during cold weather., On the other hand, when heat generation is high, especially in large structures, it may cause, undesired stress., The heat of hydration is affected most by C3S and C3A present in cement, and also by watercement ratio, fineness and curing temperature., The heat of hydration of Portland cement is calculated by determining the difference between, the dry and the partially hydrated cement (obtained by comparing these at 7th and 28th days)., , 7) Bulk density, When cement is mixed with water, the water replaces areas where there would normally be, air. Because of that, the bulk density of cement is not very important. Cement has a varying, range of density depending on the cement composition percentage. The density of cement may, be anywhere from 62 to 78 pounds per cubic foot., , 8) Specific Gravity (Relative Density), Specific gravity is generally used in mixture proportioning calculations. Portland cement has a, specific gravity of 3.15, but other types of cement (for example, portland-blast-furnace-slag, and portland-pozzolan cement) may have specific gravities of about 2.90., , DIR - ER BHOOPESH SHARMA, , 3

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MASTER TECHNICAL COACHING CENTER, , Different Types Of Cement, 1. Ordinary Portland Cement (OPC), Ordinary Portland Cement also known as OPC is a type of cement that is manufactured and, used worldwide. It is widely used for all purposes including:, , , , , Concrete: When OPC is mixed with aggregates and water, it makes concrete, which is, widely used in the construction of buildings, Mortar: For joining masonry, Plaster: To give a perfect finish to the walls, , Cement companies in Malaysia offer OPC in three different grades, namely grades 33, 43, and, 53., Besides the aforementioned purposes, Ordinary Portland cement is also used to manufacture, grout, wall putty, solid concrete blocks, AAC blocks, and different types of cement., , 2. Portland Pozzolana Cement (PPC), To prepared PPC or Portland Pozzolana cement, you need to grind pozzolanic clinker with, Portland cement., PPC has a high resistance to different chemical assaults on concrete. It is widely used in, construction such as:, , , , , , , , Marine structures, Sewage works, Bridges, Piers, Dams, Mass concrete works, , 3. Rapid Hardening Cement, Cement suppliers in Malaysia also offer rapid Hardening cement. Rapid Hardening Cement is, made when finely grounded C3S is displayed in OPC with higher concrete., It is commonly used in rapid constructions like the construction pavement., , 4. Extra Rapid Hardening Cement, DIR - ER BHOOPESH SHARMA, , 4

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MASTER TECHNICAL COACHING CENTER, , As the name suggests, Extra rapid hardening cement gains strength quicker and it is obtained, by adding calcium chloride to rapid hardening cement., Extra rapid hardening cement is widely used in cold weather concreting, to set the cement fast., It is about 25% faster than that of rapid hardening cement by one or two days., , 5. Low Heat Cement, Cement manufacturers in Malaysia offers low heat cement that is prepared by keeping the, percentage of tricalcium aluminate below 6% and by increasing the proportion of C2S., This low heat cement is used in mass concrete construction like gravity dams. It is important to, know that it is less reactive and the initial setting time is greater than OPC., , 6. Sulphates Resisting Cement, This type of cement is manufactured to resist sulphate attack in concrete. It has a lower, percentage of Tricalcium aluminate., Sulphates resisting cement is used for constructions in contact with soil or groundwater having, more than 0.2% or 0.3% g/l sulphate salts respectively., It can also be used in concrete surfaces subjected to alternate wetting and drying like bridge, piers., , 7. Quick Setting Cement, Cement suppliers in Malaysia also offer quick setting cement which sets faster than OPC but the, strength remains the same. In this formula, the proportion of gypsum is reduced., Quick setting cement is used for constructions that need a quick setting, like underwater, structures and in cold and rainy weather conditions., , 8. Blast Furnace Slag Cement, This type of cement is manufactured by grinding the clinker with about 60% slag and it is, similar to Portland cement. It is used for constructions where economic considerations are, important., , DIR - ER BHOOPESH SHARMA, , 5

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MASTER TECHNICAL COACHING CENTER, , 9. High Alumina Cement, High alumina cement is obtained by mixing calcining bauxite and lime with clinker during the, manufacturing process of OPC., To be considered high alumina cement, the total amount of alumina content should be at least, 32%, and the ratio of the weight of alumina to lime should be kept between 0.85 to 1.30., The most common uses are in constructions that are subject to high temperatures like a, workshop, refractory, and foundries., , 10. White Cement, This type of cement is manufactured by using raw materials that are free from iron and oxide., White cement needs to have lime and clay in a higher proportion. It is similar to OPC but it is, more expensive., , What is an 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 Size and Shape, Aggregates are classified based on so many considerations, but here we are going to discuss, about their shape and size classifications in detail., 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, , DIR - ER BHOOPESH SHARMA, , 6

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MASTER TECHNICAL COACHING CENTER, , Rounded Aggregate, The rounded aggregates are completely shaped by attrition 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 behaviour 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, DIR - ER BHOOPESH SHARMA, , 7

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MASTER TECHNICAL COACHING CENTER, , 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., , 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 in 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., , DIR - ER BHOOPESH SHARMA, , 8

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9, , MASTER TECHNICAL COACHING CENTER, , 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., , 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., Fine aggregate, , Size variation, , Coarse Sand, , 2.0mm – 0.5mm, , Medium sand, , 0.5mm – 0.25mm, , Fine sand, , 0.25mm – 0.06mm, , Silt, , 0.06mm – 0.002mm, , Clay, , <0.002, , DIR - ER BHOOPESH SHARMA

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10, , MASTER TECHNICAL COACHING CENTER, , 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., Coarse aggregate, , Size, , Fine gravel, , 4mm – 8mm, , Medium gravel, , 8mm – 16mm, , Coarse gravel, , 16mm – 64mm, , Cobbles, , 64mm – 256mm, , Boulders, , >256mm, , Characteristics of Aggregates, Resistance to Freeze Thaw:, (Important in structures subjected to weathering) – The freeze thaw resistance of an aggregate, is related to its porosity absorption, and pore structure. Specifications require that resistance, to weathering be demonstrated by the magnesium sulfate test., Abrasion Resistance:, (Important in pavements, loading plat-forms, floors, etc.) Abrasion resistance is the ability to, withstand loads without excessive wear or deterioration of the aggregate., DIR - ER BHOOPESH SHARMA

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MASTER TECHNICAL COACHING CENTER, , Chemical Stability:, (Important to strength and durability of all types of structures) Aggregates must not be, reactive with cement alkalies. This reaction may cause abnormal expansion and mąp-cracking, of concrete., Particle Shape and Surface Texture:, (Important to the workability of fresh concrete) Rough textured or flat and elongated particles,, due to their high surface area, require more water to produce workable concrete than do, rounded or cubical aggregates., Grading:, (Important to the workability of fresh concrete) The grading or particle size distribution of an, aggregate is determined by sieve analysis., Specific Gravity (Density):, The specific gravity of an aggregate is the ratio of its weight to the weight of an equal volume of, water at a given temperature. Most normal weight aggregates have a specific gravity ranging, from 2.4 to 2.9. It is not a measure of aggregate quality. It is used for certain computations in a, mix design., Absorption and Surface Moisture:, The moisture conditions of aggregates are designated as:, Oven-Dry: Fully absorbent., Air-Dry: Dry at the surface but containing some interior moisture, thus somewhat absorbent., Saturated Surface-Dry: Neither absorbing water from, nor contributing water to the concrete, mix., Wet with free moisture: Containing an excess of moisture on the surface., Batch weights of materials must be adjusted for moisture conditions of the aggregates., Dry-rodded unit weight:, Dry-rodded unit weight is the mass (weight) of one cubic meter (foot) of dry coarse aggregate, that is compacted, by rodding in three equal layers, in a standard container. For any one, aggregate the dry-rodded unit weight varies with the size and gradation., BULKING OF SAND:-, , DIR - ER BHOOPESH SHARMA, , 11

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MASTER TECHNICAL COACHING CENTER, , Bulking in sand Occurs When dry sand interacts with the atmospheric moisture. Presence of, moisture content forms a thin layer around sand particles. This layer generates the force which, makes particles to move aside to each other. This results in the increase of the volume of sand., Excessive presence of moisture content in the sand makes concrete to less durable and lose its, strength. Remember, excessive presence of moisture content increase the workability of, concrete but loses its strength., As per IS2386-3 Bulking in Sand, Presence of 4% of moisture content in sand increases 25% of, its volume., % of Moisture content, , Percentage of Bulking with respect to volume, , 2%, , 15%, , 3%, , 20%, , 4%, , 25%, , 5%, , 30%, , DIR - ER BHOOPESH SHARMA, , 12