Intermittent curing – Making the concrete dry for some time is called intermittent curing. Even the delayed application of curing will permit rapid drying of the surface and crazing. This occurs due to direct sunlight, low humidity, or drying winds. Improper curing – When the evaporation rate from the concrete surface is higher than the moisture gain from curing, the crazing cracks occur in concrete. They do not affect the structural integrity of concrete and rarely do they affect the durability or wear resistance. Often they are not readily visible until the surface has been wetted and it is beginning to dry out. Generally, crazing cracks develop at an early age and are apparent the day after placement or at least by the end of the first week. The irregular hexagonal areas enclosed by the cracks are typically no more than 40 mm across and may be as small as 20 mm in unusual instances. Crazing is caused by drying out of the concrete surface, so it is particularly common when the surface has been exposed during placement to low humidity, high air or concrete temperature, hot sun, or any combination of these. They are associated with early surface drying or cooling, causing the immediate surface to shrink differently than the underlying concrete. It is a result of conditions and curing methods at the point the concrete is laid or even the way it is finished. Crazing in concrete floors is the development of random cracks or fissures on the surface of concrete caused by shrinkage of the surface layer.
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