Curing is a process of maintaining suitable moisture level and temperature in the concrete for a definite period of time. The curing is the most important process to promote the hydration of cement in the concrete, which is a long term process and requires adequate water and proper temperature. With these two elements are in place, the hydration will continue and this will result in continues development in concrete strength. Concrete that deprived curing in early stages will dry off and stops gaining designed strength. There are many reports supporting this statement, and there are also evident that insufficient curing will only give 50 percent of the expected strength. Concrete that is cured for only three days will gain about 60 percent of the final strength, while the one cured for 7 days is expected to achieve about 80 percent of the strength. Therefore it is important to cure concrete continuously to achieve maximum strength. However, one have to bear in mind that by giving lesser curing duration, you are not killing or destroying the un-hydrated portion for your concrete. Once you resume the curing the strength gain will starts to resume again.
Water is most commonly used element to cure concrete, as water is needed to promote cement hydration. However, besides water temperature also plays an important role in strength development. An increase in temperature will increase the rate of hydration in concrete. Temperatures below 10 degree Celsius are not recommended for hydration and shall be avoided, especially at early ages as this would retard the strength development. High temperatures at early ages shall be avoided, as this would create other problems. Cement by itself will produce heat due to hydration, and if further heat is added with the external temperature; this would result in early thermal cracking due to rapid setting.
In reality concrete strength is not the only properties needed to make sure the stability or the integrity of any particular structure. However, it has been worldwide practice to select or specify concrete based on its strength. Therefore, it is important to make sure the concrete specified for any particular construction achieve its designed minimum strength within specified age. Normally, concrete strength is specified based on 28-days strength. In order to achieve the full strength at 28-days, the concrete shall be cured for a period of at least 28 days. Besides strength development, sufficient curing will also improve other properties of the concrete, such as durability, water tightness due to improved hydration product, volume stability, and etc.
In follow-up article on concrete curing, I will discuss more types of curing that normally used in concrete curing.
