First of all I would like to tell you there is always some properties of any materials or mixtures which are neglected at the long run or does not have any significance after a specific period.
I think while referring plasticity of cement and concrete you are trying to know Plasticity of cement paste ( cement water mix) and Plasticity of fresh concrete mix (cement, fine aggregate, coarse aggregate and water). These properties are our concern only when the cement paste and concrete are in semi solid state ( when they are not in hardened state).
For Cement Paste plasticity is required to mould the paste into desired shape. We call it consistency of cement when it is not too hardened nor too flowable (flowable means fluid state which allows it to flow under gravity because of low viscosity). This consistency property helps us to make a workable (workability is the property by virtue of which a paste has greater degree of ease to work with). Hence this consistency incorporates plasticity in itself. It is defined in terms of water percentage added by weight of dry cement.
Now coming to plasticity of concrete. Again this is also required only when concrete is fresh ( means, concrete is in semi solid state and can be mould to any shape like shape of slab, beam, tappered beam, column etc). It is also referred with workability because the more important property of fresh concrete is to place it in desired shape. Later after final setting time concrete is going to be hardened anyway. So in the case of fresh concrete mix we account for workability which has plasticity incorporated in it. This workability is also calculated in terms of percentage of water added with respect to weight of dry cement (water content).
So you see plasticity is more of a physical property here. You will see in construction sites concreting of certain places like a large area slab takes 12–16 hours at a stretch and engineers sometimes need to stay overnight for concreting. Because if they leave the concrete in mid, it might be hardened (loose it's plasticity) and you cannot have a monolithic (continuous) structure which is dangerous sometimes.
Note: Plasticity is a very important property in case of soil. Because it never hardens (like concrete) and can flow at a particular water content depending on other conditions. So if you need to feel plasticity more, study the Index Properties of soil in the subject SOIL MECHANICS.
I think while referring plasticity of cement and concrete you are trying to know Plasticity of cement paste ( cement water mix) and Plasticity of fresh concrete mix (cement, fine aggregate, coarse aggregate and water). These properties are our concern only when the cement paste and concrete are in semi solid state ( when they are not in hardened state).
For Cement Paste plasticity is required to mould the paste into desired shape. We call it consistency of cement when it is not too hardened nor too flowable (flowable means fluid state which allows it to flow under gravity because of low viscosity). This consistency property helps us to make a workable (workability is the property by virtue of which a paste has greater degree of ease to work with). Hence this consistency incorporates plasticity in itself. It is defined in terms of water percentage added by weight of dry cement.
Now coming to plasticity of concrete. Again this is also required only when concrete is fresh ( means, concrete is in semi solid state and can be mould to any shape like shape of slab, beam, tappered beam, column etc). It is also referred with workability because the more important property of fresh concrete is to place it in desired shape. Later after final setting time concrete is going to be hardened anyway. So in the case of fresh concrete mix we account for workability which has plasticity incorporated in it. This workability is also calculated in terms of percentage of water added with respect to weight of dry cement (water content).
So you see plasticity is more of a physical property here. You will see in construction sites concreting of certain places like a large area slab takes 12–16 hours at a stretch and engineers sometimes need to stay overnight for concreting. Because if they leave the concrete in mid, it might be hardened (loose it's plasticity) and you cannot have a monolithic (continuous) structure which is dangerous sometimes.
Note: Plasticity is a very important property in case of soil. Because it never hardens (like concrete) and can flow at a particular water content depending on other conditions. So if you need to feel plasticity more, study the Index Properties of soil in the subject SOIL MECHANICS.
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