The concrete curing process comprises an interaction between Portland cement and water, which aids in the regulated release of heat from the concrete. Moisture is lost too rapidly without curing, and there isn't enough water for the crystals to form, resulting in weaker concrete. Curing also causes alkalinity in the concrete, which helps prevent acid stains from resurfacing down the road. Concrete cures even without human intervention if the right conditions are met. The two main factors that affect the rate at which concrete cures are temperature and relative humidity. Concrete sets when water loses its ability to remain in a liquid state at a certain temperature. This happens when the average annual temperature of an area where the concrete is placed exceeds 90 degrees F. If the temperature drops below 40 degrees F, the concrete cannot cure properly. Concrete must be able to absorb moisture from the air for it to cure. This is called "moisture-retaining capacity." Concrete with high levels of aggregate, such as gravel or rock, can retain more moisture than smooth concrete made with fine particles. Therefore, the surface of a stone patio will dry out faster than the surface of another type of patio. If you want the concrete to retain more moisture, add coarse aggregate or turf grass to the mix. In addition, concrete continues to cure even after it has set.