 Properties of Mass Concrete, Myself Chetanji Kunapuri, Assistant Professor, Department of Civil Engineering, World Change to Technology, Solapur. These are the learning outcomes. Student will be able to describe the properties of mass concrete after this session. Let's see the introduction. Mass concrete is the concrete having considerable dimension that may get affected by thermal behavior of concrete. This is the first logical understanding of this concrete. Mass concrete means concreting of the dams, concreting of massive columns, thick foundations, large bridges, piers, retaining walls. So, all types of structures concreting is called as mass concreting. Now, in the design of the dam, strength of the concrete is not having that much importance. The most important thing in that is the concreting, extent of the concreting and because of that whatever heat is generated because of heat of hydration, how to control that that is the major issue. Now, if a certain amount of heat is generated, how to absorb such heat so that heat inside the body of concrete is minimized. This is one more aspect for important aspect in mass concrete. Now, mass concrete is basically concrete with higher proportion of CA and lesser cement content. This is the practical aspect of mass concrete. Generally, large size aggregates are preferred for mass concrete. So, the surface area of aggregate that can be reduced by larger size of aggregates and because of that the cement content have to have to automatically reduce it. Now, let us see what are the materials for mass concrete. Falling materials can be preferred. Now, Portland cement with low heat of hydration. So, whenever this type of cement with low heat of hydration is used mass concrete means definitely the extent of the concrete is big cement content is also use of the cement is also more and use of the cement means evolution of the heat of hydration is more. So, minimum amount of heat should be there for that purpose this type of cement can be used and one more aspect is the economy can also be achieved. Next is pozzolana or pozzolanas can shall be added into the concrete. So, basically fly ash it will help to reduce the heat of hydration pure cementitious cement particle cement material will reduce definitely it will directly reduce the heat of hydration. So, fly ash the pozzolana which is a very fine material. So, which improves the workability also and it delay the strength gain also. So, heat of hydration and strength gaining these are related to each other. Next is the aggregates. In case of large beams and columns 20 to 30 mm size is suitable for dams, barrages, wears 40 mm aggregates can be used. Now, one ratio is suggested here fine aggregate to total aggregate ratio means in total aggregate the fine aggregate content it must be near about 25%. Now, regarding this mixing water quantity of mixing water must be very low so that it you can give only 0 to 50 slump even 0 slump is also admissible. Now, admixture water reducing type of admixture, retarding admixture is preferred means what the setting time is delayed and according to that the heat of hydration will not be very fast in early age. Now, coolants how this can be done why this is because of the temperature control is required and that can it must be maintained 5 to 20 degree celsius that is why this coolants are required. Addition of finely chipped ice instead of water can be used or it is useful so that the temperature of concrete we can keep constant. Aggregate should be kept damp this is one method so which will reduce the temperature also. Next is cast concrete should be cured with cold water so for curing sprayed water with the spray with cold water that is be more useful for keeping the temperature low. Now, let us see what are the properties of mass concrete. The properties of mass concrete are the same that of normal concrete but some of these are discussed below which are important for mass concrete. First is workability. Now, optimum workability term is used, optimum workability means whatever workability minimum required for concreting that much we can keep here. Uniformity of the workability means low cement content that will can be assured by uniformity of the workability. Non-uniformity in the workability it is difficult in mixing and placing and compaction. In mass concreting water cement ratio is always high cement content is low but the uniformity of workability and uniformity of cement content that is that will give us or this will facilitate us mixing placing and compaction. Regarding this slump slump must be always low but it depends on the dimensions of the members. What type of member we are casting whether it is beams columns or any other members. Spacing of reinforcement method of placing and consolidation these things are important and these will decide the slump value. Now, next property of the concrete is the durability and this durability depends upon the mix design, workmanship, placing and curing. So, mix design that is the origin that is the proportioning, workmanship that is the how the laborers are carrying out the concreting and what is the practice then the placing and curing that is also important. This mix the durability basically depends upon the property of the materials or ingredients which are used for the mass concrete. Selection of the material is also important means most important is the chemical resistance of the concrete. The concrete must be having some chemical resistance because mass concrete is used in these types of structures like dams, barrages. So, weathering durability is important, entrainment of minute air bubbles into the concrete that will assure your weathering and durability. So, small whites are generated because of this air entrainment of air bubbles. Now, air entrain concrete or air entrain mass concrete we can say this will give you resistance to prison throw, thaw and wetting and drying actions. Now, in severe condition severe aggressive condition for the concrete means the sulphate attack if it is possible then sulphate resistant cement must be used in mass concrete. Any concrete exposed to sulphate should be air entrained air entrained means whites are generated and water attack sulphic attack is there that sulphate for that a sulphate attack air entrainment is important. Next is when the mass concrete is used for dam site type of structure water tightness is the important property and it should concrete should be impermeable and to achieve this first is good quality aggregate shall be used, low water cement ratio shall be used, good consolidation during the placing, proper curing and use of pozzolana these things will give you water tight concrete. Most important thing is in that is the use of pozzolana. One thing is that the cement content is low water cement ratio is low in that case concreting with the optimum workability is a difficult job and that too with the water tight property. So, in that case use of pozzolana that will help us to give water tight concrete as well as the concrete with optimum workability. Now, next property is actually strength and for this strength one figure is shown here which will explain your relation between 28 days concrete of strength and water cement ratio. Now, if you for the strength in case of mass concrete strength issue that that parameter is actually very low but with low water cement ratio with low cement content achieving the strength is also important task. So, it is very economical to add pozzolana in the concrete if the pozzolanic material like fly ash if this that is added into the concrete it is very fine. So, it will improve the workability as well as it will increase the strength also. Now, the pozzolanic material is having little cementing value but it react with calcium hydroxide to form cementitious compounds. So, while when the water is added in the fresh state the pozzolanic material will help you to improve the workability because it is having very little cementing strength or cementing value and whenever it reacts with the calcium hydroxide it forms the cementitious compound after your fresh state. Now, see this above reaction contributes to ultimate strength and water tightness of the concrete. So, ultimate strength after the entire hydration process of the concrete and water tightness that that is assured by pozzolanic matter and but really that will give you good strength also and it increases the plasticity and workability of the concrete. Now, for that purpose let us see this graph on x axis water cement ratios are given on y axis 28 day concrete strength is given in MPa. Now, you can see here this is particularly for mass concrete for 0.6 water cement ratio you can see here the strength is in between 15 to 20 lower strength range is specified I think this is 17 to 18 MPa and here above it is near about 24 MPa. So, the 0.6 water cement ratio for mass concrete that will give you the range of 18 to 24 Newton per mm square approximately that strength. So, for different water cement ratio the strength is given here the range we can use for our mixed designs. Now, table one is given recommended maximum water cement ratio for mass concrete and now you can see here the types of structures and location of the concrete is specified here and the maximum water cement ratio by weight for severe climate for mild climate these water cement ratios are specified. Now, the location of the concrete type of concrete according to this climatic condition we can select one of the water cement ratio from this and expected strength we can take from this graph. Now, this is the question for you what is the maximum water cement ratio for the concrete continues to submerged in water for mild climate these are the options pause the video think of that observe the earlier slide and give the answer the answer is 0.58 is the maximum water cement ratio these are the references thank you.