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MASTER TECHNICAL COACHING CENTER, , INTRODUCTION, CONCRETE, concrete, in construction, structural material consisting of a hard, chemically inert particulate, substance, known as aggregate (usually sand and gravel), that is bonded together, by cement and water., Components of Concrete, 1. Cement, 2. Sand, 3. Aggregate, 4. water, 5. Admixtures, Uses of Concrete, The major uses of concrete are1. Concrete Dams, The characteristics of concrete such as high strength and unit weight make it a more suitable, material for the construction of dams. Dams are used to store water and produce electricity., The loads imposed on the dam due to water pressure are very intense which makes concrete, as a suitable material for dam construction., , DIR - ER BHOOPESH SHARMA, , 1

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MASTER TECHNICAL COACHING CENTER, , 2. Residential Buildings, The construction of small buildings, villas, and even high-rise buildings are done using, concrete with traditional or modern form-work as a method of construction of the skeleton, from foundations to the slabs and of course columns and beams., , 3. Commercial Buildings, The use of concrete in commercial buildings makes it safer than using most other construction, materials. It is mostly more economic than steel buildings and requires less maintenance. It, is easy to control the heat transfer from inside to outside and vice versa which reduces the, energy consumed., , 4. Roads or Driveways, Concrete streets, pavements, and driveways are more durable and stronger than asphalt, roadways. The long-lasting service time and the less maintenance required for concrete, roads make it the first choice of material for the construction of roads and driveways., , DIR - ER BHOOPESH SHARMA, , 2

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MASTER TECHNICAL COACHING CENTER, , 5. Marine Construction, Concrete has had extensive use as a construction material for seawalls, jetties, groins,, breakwaters, bulkheads, and other structures exposed to seawater. The performance record, has generally been good., , 6. Culverts and Sewers, Sewers and underground construction works need strong and durable building materials and, concrete is the ideal one. Culverts, piers, foundation, abutments are constructed using, special concrete mix., , DIR - ER BHOOPESH SHARMA, , 3

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MASTER TECHNICAL COACHING CENTER, , 7. Foundations, The foundation of high-rise or low-rise buildings is usually constructed using reinforced, cement concrete, as it is durable and has a huge load-carrying capacity., , 8. Fences, The development in the precast concrete industry has improved the industry of concrete, fences. It is faster to produce and install the fence elements using precast than the traditional, method of concrete fence construction. Moreover, it is beautiful and more attractive., , 9. Concrete Bridges, Reinforced concrete strength, durability, ductility, weather resistance, fire resistance, and, long-lasting life cycle makes the concrete the best solution for constructing the bridges. Prestressed concrete, post-stressed concrete, self compacted concrete are different types of, concrete that may apply in bridges construction., DIR - ER BHOOPESH SHARMA, , 4

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MASTER TECHNICAL COACHING CENTER, , 1., 2., 3., 4., 5., 6., 7., , 1., 2., 3., 4., 5., 6., , Advantages of Concrete, The following are the advantages of concrete:, Availability of concrete ingredients easily., Easy handling and moulding of concrete into any shape., Easy transportation from the place of mixing to place of casting before initial set takes, place., Ability to pump/spray to fill into cracks and lining of tunnels., When reinforced, all types of the structures are made possible from an ordinary lintel, to massive fly overs, Monolithic character gives better appearance and much i rigidity to the structure., The property of concrete to possess high compressive strength, makes a concrete, structure more economical than that of steel structure., , Disadvantages of Concrete, The following are the disadvantages of concrete:, Due to low tensile strength, concrete is required to be reinforced to avoid cracks., In long structures expansion joints are required to be provided if there is large, temperature variance in the area., Construction joints are provided to avoid cracks due to drying shrinkage and moisture expansion., Soluble salts in concrete cause efflorescence if moisture reacts with them., Concrete made with ordinary Portland cement, gets integrated in the presence of, alkalies, sulfates etc., Sustained loads develop creep in structures, , What Is Fresh Concrete?, , DIR - ER BHOOPESH SHARMA, , 5

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MASTER TECHNICAL COACHING CENTER, , When concrete is its plastic state, it is known as fresh concrete. Fresh concrete can, be easily molded to a durable structural member. It can be prepared on the spot and may, give a wide range of properties from easily available raw materials., Properties of Fresh Concrete, , , Workability., , , , Temperature., , , , Water Cement Ratio., , , , Segregation., , , , Bleeding., , , , Plastic shrinkage., , , , Setting Time., , , , Hydration., , 1. Workability of Fresh Concrete, The, diverse, requirements, of transportability,, compatibility,, mobility,, stability, mixability, playability, and finish ability of fresh concrete mentioned above are, collectively referred., To as workability. The workability of fresh concrete is thus a composite property. It is, difficult to define precisely all the aspects of the workability in a single definition., IS 6461 (Part-VII)-1973 defines workability as that Property of freshly mixed mortar or, concrete that determines the ease and homogeneity by which it could be mixed, placed,, compacted, and completed., 2. Temperature of Fresh Concrete, Concrete is not recommended to be placed at a temperature above 40°C without proper, precautions, as laid down in IS:7861 (part -1)., Special problems are encountered in the preparation, placement, and curing of concrete in, hot weather. The First 24 to 72 hours after placing fresh concrete are of extreme, importance., , DIR - ER BHOOPESH SHARMA, , 6

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MASTER TECHNICAL COACHING CENTER, , In this period, hydration of concrete occurs, which is a chemical process in which concrete, gains its strength., If the temperature of concrete is not controlled and it goes beyond maximum range during, hydration, then stresses are produced, and cracks are formed in concrete., Also, if the temperature falls below the minimum temperature, then concrete takes a, large time to set, and the hydration process slows down., It is necessary to understand here that concrete can be done at any temperature unless the, temperature is controlled., 3. Water Cement Ratio (w/c) of Fresh Concrete, It is the ratio of cement and water utilized in the preparation of concrete. The quantity of water, used at mixing concrete is very important., If the percentage of water used is less, then there will not be a sufficient quantity of water, to hydrate cement. It will result in weak and porous concrete., Therefore, the usual tendency is to use too much water that gives a more workable mix, but, it doesn’t give sound concrete. Too much water results in the segregation of, aggregates and gives porous concrete of low strength and low density., A certain minimum proportion of water is necessary to hydrate the cement completely. To, create the concrete sufficiently workable to be placed in position, some more water is needed., So long as the concrete is sufficiently workable, for the way of placing used, its strength, depends on the proportion of water to the cement in the mix., The water-cement ratio shouldn’t be allowed to exceed the specified limits for various, types of concrete and should usually be kept as low as the methods of placing will, allow., Abrahams, as a result of a large number of experiments, states that “with given materials, and conditions of the test, the ratio of the quantity of mixing water into the quantity of, cement alone determines the potency of concrete as long as the mix is of workable, plasticity.“, , DIR - ER BHOOPESH SHARMA, , 7

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8, , MASTER TECHNICAL COACHING CENTER, , This is known as water-cement ratio law. According to this law, the strength of concrete won’t, increase by simply increasing the quantity of cement unless the water-cement ratio is, reduced., Water-Cement Ratio Table, , IS 10262, , Minimum, Cement, Content, , W/C, Ratio, , Minimum, Cement, Content, , W/C Ratio, , Grade, , Mild, , 220, , 0.60, , 300, , 0.55, , M20, , Moderate, , 240, , 0.60, , M15, , 300, , 0.50, , M25, , Severe, , 250, , 0.50, , M20, , 320, , 0.45, , M30, , Very, Severe, , 260, , 0.45, , M20, , 340, , 0.45, , M35, , Extreme, , 280, , 0.40, , M25, , 360, , 0.40, , M40, , Grade, , 4. Segregation of Fresh Concrete, , Segregation is usually caused by excessive vibration of cement. The different materials that, make up the concrete mix have different weights, so while the concrete is in a liquid state,, there is a tendency for heavier materials to settle to the bottom, and the lighter slurry, to rise to the top., Isolation means the separation of newly designed solid ingredients from each other in a nonuniform mixture., , DIR - ER BHOOPESH SHARMA

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MASTER TECHNICAL COACHING CENTER, , More specifically, it implies the separation of coarse aggregates from the mortar in which they, are composed due to differences in the size, density, shape, and other properties of, the material., Due to the separation, the hive is made into concrete, and it basically affects the strength, of the concrete and its porosity., During concrete work, isolation in concrete can occur on-site, and this affects the, durability of your structures. In fine concrete, all the ingredients are properly distributed, and form a homogeneous mixture., If a concrete sample exhibits a tendency to separate coarse aggregates from the rest of, the material, it indicates the separation in the concrete., 5. Bleeding of Fresh Concrete, , Bleeding in concrete is sometimes referred to as water gain. This is a special form of, separation, in which some water from the concrete flows to the surface of the concrete, with, the lowest specific gravity among all concrete components., Excessive bleeding is seen in thin members such as roof slabs or road slabs, and when the, concrete is placed in sunny weather., Prevention of bleeding in concrete, , , Bleeding can be reduced with appropriate proportions and uniform and complete, mixing., , , , Bleeding is reduced by the use of finely divided pozzolanic materials, making a, long way to cross the water., , , , The air-penetrating agent is very effective for reducing blood., , DIR - ER BHOOPESH SHARMA, , 9

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MASTER TECHNICAL COACHING CENTER, , , Bleeding can be reduced by the use of fine cement or cement with low alkali, content., , 6. Plastic Shrinkage of Fresh Concrete, , If water is removed from the concrete before it sets, the volume of the concrete is, reduced by the amount of water removed. This volume reduction is known as plastic, shrinkage., This is the shrinkage that the fresh concrete undergoes until it sets completely., Water may be removed from the plastic concrete by evaporation or by being absorbed by dry, surfaces such as soil or old concrete or by the dry wooden formwork., 7. Setting Time of Fresh Concrete, When concrete changes its state from fresh to hardened then this process is called, setting. And the time required to complete this process is known as Setting Time of, Concrete., Setting time depends on the type of cement and it can be increase or decrease by adding, admixture in concrete., 8. Hydration In Fresh Concrete, When cement comes in contact with water, a chemical reaction begins. This reaction, is known as hydration., If the mixing water dries out too rapidly before the cement has fully hydrated, the curing, process will stop, and the concrete will not harden to its intended strength., , DIR - ER BHOOPESH SHARMA, , 10

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MASTER TECHNICAL COACHING CENTER, , Hydration occurs more rapidly at higher air temperatures. Hydration itself also generates, heat. This heat of hydration can be helpful during cold-weather construction but harmful, during hot-weather construction., Properties of Concrete in Hardened State, A hardened concrete must possess the following, properties., , , Strength is defined as the resistance of a hardened concrete to rupture under, different loadings and is accordingly designated in different ways i.e., tensile, strength, compressive strength, flexural strength, etc. A good quality concrete in, hardened state must possess the desired crushing strength., , , , Durability is defined as the period of time up to which concrete in hardened state, withstands the weathering effects satisfactorily. This property is mainly affected, by water cement ratio. A good quality concrete in hardened state must be durable., , , , The impermeability of hardened concrete may be defined as the property to resistentry of water. This property is achieved by using extra quantity of cement in, concrete mix. A concrete in hardened state must be impermeable., , , , Elasticity. Though hardened concrete is a brittle / material, it is desired that it should, possess adequate elasticity., , , , Shrinkage. A hardened concrete should experience least shrinkage. This property is, guided by water cement ratio. Shrinkage is less if the water cement ratio is less., , , , Thermal expansion. A hardened concrete should possess least coefficien t of, expansion., , DIR - ER BHOOPESH SHARMA, , 11