For attaining the desired strength of your concrete, you know that you have to do proper curing to the concrete for the hydration of cement.
For a good cement hydration, you need to maintain proper water content on the surface of the concrete unit. After adding water, the evaporation is carried out throughout the curing period.
Curing of concrete is the method of maintaining the required amount of water content and temperature in a fresh concrete for a specific period of time.
The objective of water curing of concrete is to prevent the moisture loss from the concrete and attains a convenient temperature.
The water-cement ratio for cement hydration is 0.23 and 0.15 for filling the voids in the pores of the concrete. Therefore a total 0.38 water-cement ratio is required for proper water curing of concrete. But for the reason to overcome the extra evaporation loss, everybody may fix the water-cement ratio as 0.50.
The next thing that you need to take care after deciding water-cement ratio is curing period of concrete or you can say curing time.
What is the right time or period required for concrete curing process?
The period of curing concrete varies with environmental factors such as vapor pressure, wind, temperature, relative humidity etc..
If the wind is too high then evaporation rate will very high. Similarly, the evaporation will also increase with temperature and vapor pressure. The vapor pressure is taken between the atmosphere and concrete surface. If there is a large variation, the rate of evaporation will also high.
The American concrete institute recommends the minimum curing period time is the period corresponding to concrete achieving 70 percent of the characteristic compressive strength of concrete. The 70 percent of characteristic compressive strength achieves at its 7 days from casting of concrete. So a minimum curing period of 7 days should be done.
According to ACI, there are three stages of curing of concrete initial, intermediate and final.
Initial Curing of concrete
The initial curing is evaporation losses from bleeding water of concrete. You know that for every concrete construction, there will be a few amounts of bleeding water remains on the surface of the concrete.
The drying of concrete starts only after the evaporation loss of bleeding water. Initial curing is required to prevent the plastic shrinkage cracks of concrete
Intermediate curing in concrete
The next stage in curing is intermediate curing. The intermediate curing is occurring between the initial setting and final setting of concrete.
The final curing will be done only after the final setting of concrete. Final curing is done to prevent the loss of water content from the surface quickly.