Engineering and Construction

Plastic shrinkage cracking is defined as the cracking of the surface of concrete that develops in freshly mixed concrete soon after it has been placed and while it is still being finished. Because the concrete is still plastic, this type of shrinkage cracking is termed plastic shrinkage to distinguish it from drying shrinkage described in the previous sections. Plastic shrinkage cracking is most often associated with climate conditions, such as high temperatures, low humidity, and high winds that result in rapid evaporation of moisture from the concrete surface. Especially in the desert areas of the southwestern United States, the water may be quickly drawn from the concrete resulting in plastic shrinkage.

Plastic shrinkage cracks develop because of the tensile stresses generated in the concrete due to the evaporating water. The concrete cracks often form in distinct patterns of short and irregular cracks. The lengths are generally from a few inches to a few feet in length with spacing similar to crack lengths. For a discussion of the measures to prevent plastic shrinkage cracking, see Design and Control of Concrete Mixtures (PCA, 1994).