Thumb Rule for Curing Water Requirement:
1 bag of cement = 50 kg cement – requires maximum 12 litres of water during the entire curing cycle.
Evolution of Concrete Curing
Few decades ago, sand was an easily available and unregulated resource. Hence it was considered as a free material. But as the sector developed and the demand-supply mechanisms started evolving, the government started regulating sand mining and formalized the sector through licensing which resulted in a formalized cost structure.
Similarly, till the last decade, water was an easily available and unregulated resource. But as the sector evolved and the use increased by folds accompanied by water crisis induced by global warming, governments in many countries have started introducing regulatory policies to limit the usage and subsequently reduce wastage.
Curing was an often-ignored process until the advent of high strength concrete and speedy project plans with faster slab cycles. Although the construction technology has evolved rapidly, there has been barely any innovation in concrete curing.
Currently, the widely used methods such as ponding and sprinkling have no regulation on the amount of water and result in huge amounts of water loss. Since the run-off water contains minute concrete particles, it also results in ground water pollution through percolation. Today, given the water crisis and uncertain rainfall in arid regions, water wastage and ground water pollution are important issues to be addressed by the construction industry.
The water requirement in concrete curing is dependent on the cement content, which is in turn subject to the grade – mix design of concrete. The water-cement ratio decides the quantity of water which needs to be added to during the mixing process of cement, sand, aggregate with water to form concrete. This is the actual amount of water required to react with the cement particles to induce strength.
Owing to practical reasons such as slump of concrete, excess water cannot be added during the mixing process. Instead the water needs to be supplied consistently during the initial days of concrete strength gain. At this time, the unreacted cement particles require additional water for the settlement reaction to induce strength. Moreover, the water supplied during curing also compensates for moisture loss.
Image Source: flickr User astrid westvang