 Welcome to the sessions, Properties of Lightweight Concrete. This is Chetanji Kunapuray, Assistant Professor of Department of Cell Engineering, Vulture and Institute of Technology. So, these are the learning outcomes. At the end of the session, student will be able to explain the concept of lightweight concrete, the properties of lightweight concrete. Let us see the introduction of lightweight concrete. Definition wise, lightweight concrete is produced by including large quantities of air in the aggregate in matrix or in between the matrix particles or combination of these processes. Even lightweight material can be used to produce the lightweight concrete and basically the major mass contributing material is the aggregate. So, if the unit weight is less than about 1000 kg per meter cube, that these types of aggregates are designated as lightweight aggregate. Now, why the density is less? This is only because of the cellular structure or highly porous microstructure of the aggregate. So, the lightweight is because of this reason only. Generally the density of normal concrete is 2200 to 2600 kg per meter cube, which leads to heavy self-weight of the structure elements. However, the density of lightweight concrete varies from 300 to 1850 kg per meter cube. So, from this, let us see what are the advantages of lightweight concrete. Now, if the density is reducing, definitely the self-weight of the structure elements will reduce. So, if the structure elements are lighter, then their dead load will reduce. So, reduction in the dead load of the structure, this is the first advantage. Then when the dead load will reduce, the section sizes will reduce, which facilitates the speedy construction of the building of the structures. Next thing is as the sections are reducing, structural sizes are reducing, which reduces the haulage and handling cost of material as well as sections as well as the entire construction activity. Next thing, major advantage of lightweight concrete is in case of weak soils and tall structures because in RCC structures or in the buildings, generally dead load is the major contributing load in the total load. So, because of a heavy dead load, the spread of the foundation is more or the size of the foundation will be big in weak soils and in case of tall structure, the spread is also more, size is also more. So, as dead load will reduce, the spread or size of the foundation will reduce, so the foundation cost will reduce. And last thing is reduction is the section size, reduction in the structure, reduction in the material as well as the speedy construction and all other further activities of the construction for these types of lightweight concrete structures. These activities also will become fast and less time consuming, which will give us the overall economy and that economy can be achieved all. Let us see what are the properties of lightweight concrete. Now, these are the following properties of lightweight concrete. First is the compressive strength and density of the concrete which are correlated to each other. Next, modulus of elasticity and the Poisson ratio which are elastic properties of the concrete. Next is water absorption and moisture content and creep shrinkage after hardened state, thermal expansion and conductivity. So, these are basically primary properties of the lightweight concrete. Now, the suitability of lightweight concrete depends on above desired properties. Now, let us see the first property that is the compressive strength and density of the concrete. Basically, this is the basic relationship in the concrete that is the relationship between compressive strength and density. So, as density will improve, the strength of the concrete will improve. In case of lightweight concrete, generally the strength is lower than that of the normal concrete. Why this is because you can see this graph which is giving you relationship or the plot of this graph is compressive strength versus density of the concrete. Now, the density of concrete affects its strength. This figure shows an increase in strength from 30 to 60 MPa when the density is improved from 1300 kg per meter cube, so you can see here. So, improvement in the density leads to increase in the strength that we can see here. You can see the relationship of compressive strength to density for different countries. So, this is Germany or the concrete which is produced in the Germany in that graph. You can see different countries USA, Germany, Switzerland, Great Britain, USSR, Russia. So, the relationship is explained here and the strength is doubled from 30 to 60 when the density is whereas, the density is 1.5 times of 1360 that is 1900 kg per meter cube. Now, let us see this modulus velocity and Poisson's ratio. For concrete of density 1500 to 2500 kg per meter cube and strength up to 35 MPa. So, ACI recommends this figure 2 and this equation for calculation of modulus of elasticity. You can see this equation that is E c is equal to W raise to 1.5 into 0.043 root f dash c and this will give you E c or elasticity in MPa. Where this f dash c is cylinder compressive strength of the concrete and this f dash c can be calculated from this expression that is 0.7 under 0.7 fck. You can see this graph on x axis compressive strength in MPa on y axis modulus of elasticity in MPa. This line representing normal weight concrete and this zone representing light weight concrete. These two lines are for sand light weight aggregate concrete in several times the sand is used to improve the density of the concrete so that why these lines are for that. Now, this is the range for all light weight concrete. Now, this graph explains relationship between modulus of elasticity and strength. The next parameter is Poisson's ratio mu. Mu is based on several tests carried out and it varies 0.15 to 0.25. Practically the mu value is 0.2 taken for light weight concrete. Now, my question for all of you is as per ACI what is the relationship between cylinder and cube compressive strength? These are the options for you A, B, C, D 0.5, 0.6, 0.7, 0.8. Now, write down the answer for this question pause the video. The answer is 0.7 so relationship between cylinder strength and cube strength is 0.7. Now, let us see absorption properties so water absorption and moisture content. Now, generally light weight concrete is produced by using light weight coarse aggregates and light weight coarse aggregates are having higher degree of absorption. This is only because of their cellular pattern as well as microstructure is highly porous. So, light weight coarse aggregates are absorbing more water it is these are having high degree of absorption. This absorption is in between 5 to 20 percent of the water which is really high. Normal weight aggregates deserves 2 percent of the absorption. Now, how it is a difficult this is for workability purpose we want water and whatever water content is given in our IS or in the references this water content is for the hydration process and if this much quantity of what is absorbed so workability will be the issue so evaluating the workability in the mix design is very difficult. Next is CRIP and shrinkage values of the CRIP and shrinkage are greater for light weight concrete when it is compared to the normal concrete. This is only because of the cause strength as strength increased CRIP becomes less. So, for ultra high strength light weight concrete the value of CRIP becomes same or equal for normal and light weight concrete. Now, next is thermal expansion and thermal conductivity. So, the thermal expansion in terms of coefficient of thermal expansion is given and it is less than normal concrete though so because basically thermal expansion is a function of component materials for the concrete. So, the range for thermal expansion is 8 to 12 into 10 is to minus 6 for light weight concrete whereas, it is 9 to 13 into 10 is to minus 6 for normal weight concrete. Not much difference is there, but difference is there. Now, light weight concrete from this parameter of the property wise it is very excellent it has excellent insulating property. So, expression is given here for thermal conductivity k is equal to 0.072 e raise to 0.00125 w where w is unit weight of the concrete in kg parameter cube and e value is 2.7182. If you substitute w here you will get k. Here one thing I want to explain here as density of concrete increases the thermal conductivity increases. So, thermal conductivity is better because only of reduced density or lower density. Now, these are the few recommendations related to the physical properties of concrete and which are shown in table 1 and 2. Table 1 is recommended as slumps table 2 is relationship between water cementation and compressive strength. This recommended slumps for 3 different types of constructions are given for beams and reinforced concrete it is in between 125 minimum is a 25 100 is maximum. For columns building columns 100 to 25 and for slabs 75 to 25 so, while designing the mix and the fresh property like slump we can select the value in between of these maximum minimum. Now, as a guideline for taking the water cement ratio this table we can refer this is approximate water cement ratio and here you can see for M 20 grid of concrete the for non air entrained concrete it is 0.68. Now, this is the table 3 which gives you approximate mixing water and air content requirement for different slumps and nominal maximum sizes of aggregate. I am emphasizing on this that is a non air entrained concrete and the water quantity for nominal aggregate size there are 3 sizes 10 15 20. For 20 it is 189 for 20 to 25 to 50 slump and 204 kg per meter for 75 to 100 these things we can use in our mix designs also. These are the references for the video thank you.