![]() Most of the water will eventually evaporate, causing shrinkage of the concrete slab. When concrete is mixed, more water than is needed for hydration is mixed with the dry components, such as sand, cement and an aggregate. The resulting differences in moisture content produce tensile stresses which are relieved by cracking of concrete near the surface. When this happens, surface concrete will dry more quickly than underlying concrete. Water may sometimes evaporate from the surface concrete faster than moisture can migrate from the underlying concrete to replace it. This condition produces tensile stresses which are relieved by cracking of concrete near the surface. The hot, expanding underlying concrete acts as a restraint to shrinkage of the cooling, shrinking surface concrete. Both of these conditions contribute to cooling and shrinking of the concrete near the surface. At the same time, concrete at the surface of the slab is exposed to air and loses water through evaporation. ![]() The chemical hydration process through which concrete hardens produces heat which causes concrete to expand. Temperature differences can contribute to the development of cracks. ![]() Factors Influencing Locations of Crack Development
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