Introduction : Hydration is the process in which cement mixes with sand, gravel and water to harden and form the mixture we call concrete.
Sugar (yes, the white sugar used in households) behaves like a Retarding Admixture and reduces the rate of hydration reaction of cement.
Sugar is very effective, even in minute quantities. To such an extent that, an excess of sugar content in the concrete mix by weight of 0.2% will impede the hydration reaction completely. As a result, the concrete will never set, and collapse immediately once the shuttering is removed. This process is known as Killing of Set.
It is generally done in hot weather conditions to counter the hardening process due to high temp.
Sugar based soln’s are sometimes added to the mix when workers need to keep the mix moist.
The setting time increases with the increase in % of sugar up to 0.06%.
The delay in setting of concrete could be useful in preventing cold joints & in reducing early setting of cement in hot weather concreting.
Sugar when used in right proportions acts as retarder but when it is used in excess, it reverse the property i.e., becomes accelerator.
Sugar above 0.08% by wt of cement accelerated the setting time with nominal gain in initial strength.
So a careful using of sugar can be economical compared to chemical retarder products