Viscoelastic Shrinkage Stress in Soil-Cement Base

Engineers generally consider cracking in soil-cement bases to be caused by stresses induced by shrinkage and ambient temperature. When the shrinkage is assumed to be proportional to the moisture loss, the shrinkage strain is estimated by employing the diffusion equation. Expressions for shrinkage stresses are derived by postulating that the material obeys a linear viscoelastic stress strain relation (when subjected to deviatoric stress) and using the theory of thin plates. Tensile shrinkage stresses on the exposed surface attain maximum value during the early stages of drying (40 hr. to 100 hr.) depending upon restraint condition) and then decrease comparatively rapidly. Theoretically, shrinkage stress is highly localized on the exposed surface and decreases shrply with depth. As localized stresses exceed the tensile strength of soil-cement, the surface of the slab will crack or flow under stress. The effects of various parameters on the shrinkage stresses, and in turn on cracking of the soil-cement bases, are considered.