Concrete Curing Rates and Their Strengths

Rate

• No predetermined mathematical relationship exists between rate of curing and concrete strength. Nonetheless, the process involves several important factors. Curing of concrete involves a chemical reaction between the water and the ingredients in the cement. Chemical reactions proceed more rapidly at higher temperatures, so curing also is more rapid in hot weather. The warmer weather, however, also causes moisture to evaporate more rapidly from the concrete's surface.

Water

• It's important to have a uniform temperature throughout the slab. Otherwise some parts will cure more rapidly than others, leading to cracking. It's also important to ensure the continuous presence of moisture. If the concrete is moistened at certain points in time and allowed to dry out again at others, it will not achieve its maximum strength because of the uneven rate of curing.

Curing Compounds

• Applying curing compounds can also affect the rate of curing and thereby improve the strength of the product. These compounds trap moisture in the surface of the concrete by creating a waxy layer on top. Since the curing reaction takes place more rapidly when more moisture is present, trapping the water in the concrete quickens the process. It also helps ensure more complete curing and thus a better end result.

Considerations

• In general, a higher rate of curing is desirable because it makes the whole process more rapid and contributes to a stronger product. The curing rate must be even and uniform throughout the slab or at least uniform to the fullest extent possible. Rapid curing in some places accompanied by slow curing in others may lead to problems. Covering the concrete in a layer of water or "ponding," applying wet coverings and sprinkling are other techniques that can help ensure sufficient moisture remains available.