Types of Non-structural Cracks in Concrete

After placing concrete, water may rise to the top of the mix, settling the aggregates.

If reinforcements within the concrete obstruct this natural settlement, plastic settlement cracks develop above the reinforcements. Increasing the top cover can mitigate these cracks.

Water evaporation from concrete's top surface induces tensile stresses in the top layers when restrained from contraction, resulting in diagonal or random patterns of plastic shrinkage cracks.

Preventing water evaporation from concrete reduces these cracks.

Drying shrinkage in externally restrained concrete develops tensile stresses at the concrete's surface, resulting in surface cracks.

Movement joints are provided to minimize these cracks.

The dissipation of heat of hydration from concrete surfaces leads to surface cooling.

If the subsequent contraction of the concrete's top surface is restrained by its interior, tensile stresses are induced on the concrete surface, developing early thermal cracks.

Insulating concrete minimizes the occurrence of these cracks.

Lastly, over-trowelling rich concrete mixes accumulate the cement paste on the surface, which, upon drying, causes discontinuous hairline surface cracks known as crazing.