Thermal Stresses of Concrete at Early Ages

Abstract

The cracking tendency of cast-in-place concrete at early ages under restrained conditions is a concern. In particular, in the building industry, in order to meet the construction speed requirements, external load (due to formwork removal and post-tensioning) is applied while concrete is hydrating, typically 1–4 days after concrete pour. Despite careful design, numerous failures have recently been reported in the industry during construction, prompting this investigation. The paper presents interim findings of a research program investigating the in situ thermal stresses at early ages. The intrinsic thermal stresses including the effects of creep and shrinkage associated with early age concrete were investigated. A degree of reaction–based approach was used to account the evolution of the material properties of concrete. The double power law (DPL) and an American Concrete Institute model were considered to account for the creep and shrinkage effects, respectively. Results show that the tensile strength at early age can be exceeded by the intrinsic thermal stresses.