Characterizing Cracking Potential of Cementitious Mixtures Based on Shrinkage and Humidity Drop Rate

Abstract

Tensile stress develops as early as upon final setting in concrete if shrinkage deformation due to thermal or hygral changes is restrained either externally or internally. Quantifying such stress and the associated cracking potential in concrete members is a difficult task due to many factors involved, such as creep and stress relaxation, tensile strength development, and the combined thermal and hygral effects. In this study, the early-age tensile stress development and cracking potential were investigated on cement paste and concrete with and without slag cement for different water-cementitious material ratios (w/cm). A method is proposed for evaluating early-age cracking potential based on experimental results and numerical simulations. It was found that cracking potential is closely related to the shrinkage rate rather than the shrinkage magnitude, confirming the findings of other studies. A unique relationship was found to exist between the shrinkage rate and cracking time for the cement paste studied. The cracking time was expressed as a function of the relative humidity (RH) drop rate and the aggregate content of a concrete mixture based on a relationship between mixture shrinkage and RH established previously. It was found that a high RH drop rate increases cracking potential. Concrete containing an aggregate content of 50% or less is highly sensitive to cracking, and thus is crucial for the cracking potential of the outer layer of concrete exposed to the environment without appropriate curing. This study proposes a new methodology for evaluating cracking potential, which has implications for mitigating early-age cracking in concrete members.