With the passage of time after mixing ingredients of concrete with water, workability of concrete starts shrinking. This happens because of fluidity loss from the concrete. Fluidity is the amount of available water in concrete that is being utilized in hydration of cement compounds for the sake of bonding.
When hydration of cement compounds C3S and C3A occurs than water within a concrete gets absorbed by these compounds and now the least amount of water will remain for workable concrete. If the temperature at the site varies, then some amount of water also lost due to evaporation.
Effect On Slump
As the time further proceeds, loss in slump value of concrete becomes effective. Slump indicates how much concrete is workable? And hence slump value is almost directly related to the time passes. When time further proceeds slump loss will show almost linear behavior.
Slump loss increases likewise with the increase of temperature and it also start reducing if increasing any ingredient in concrete more than the required amount. Generally with the increase in cement contents then, then there is a decrease in the required amount of water and hence again it effects workability of freshly laid concrete.
If there is an extra addition i.e. Chemical admixtures that has some distinct functions. For example admixtures that are mostly used are set accelerators, set retarders, water reducing admixtures, etc. Then every isolated admixture has its own effect on the properties of concrete.
Workability of concrete is almost dependent on the amount extra available water in the concrete. For good workable concrete, calculate the concrete mix proportion and add that much amount of water in the concrete during batching.
So that after every loss, there is still enough water available within concrete that will be enough for hydration and workability of concrete. So if the least amount of extra water is available, then in the same manner available mixing time will be less and vice versa.