High Early Strength Concrete and Its Cure Time

High early strength concrete is a new type of high-performance concrete that achieves the compressive strength at least one day after site-pouring. It is characterized by using a low water-to-cement ratio and/or increasing the admixture concentration.

The curing time of concrete depends on the mixture proportions, ambient weather and temperature, and hydration rate. Increasing the cement to water ratio will decrease the initial setting time, but may compromise long-term strength.

Temperature and moisture: The optimum temperature and moisture for concrete curing is dependent on the concrete mix design, size and shape of the concrete members, production facilities (in-situ or plant production) and economics. In general, the concrete can reach its final compressive strength in 7 days at most temperatures under normal conditions; however, it may take longer if a cold climate or heavy traffic is present.

Accelerating hydration: Addition of an accelerating admixture, such as calcium chloride standardized by ASTM D 98, can increase the rate of hydration and accelerate strength development. It is also important to maintain the presence of mixing water in the concrete during the early hardening period, by ponding or immersion, spraying (or fogging), and/or wet coverings.

Sealing: Preventing the loss of mixing water from the surface by sealing can increase the effectiveness of curing by retarding evaporation and maintaining the moisture content of the concrete. This can be achieved by impervious paper, plastic sheeting or by applying membrane-forming compounds.

The maturity method of monitoring the strength development of concrete is a good example of a technique that can be used to control concrete curing in real time. The maturity method is based on the principle that the time-temperature history of in-situ concrete can be monitored and compared with laboratory or field-cured specimens to determine the exact strength development at any given point during the construction process.