Internal relative humidity and drying stress gradients in concrete

A moisture gradient develops as concrete dries, inducing a drying shrinkage stress gradient that can lead to early-age cracking in restrained concrete. A new internal relative humidity measurement system was used to quantify the moisture gradient in early-age concrete exposed to drying. A simple model was developed to estimate the stress gradient associated with drying in both free and fully restrained concrete specimens. The model predicts that the stresses in the surface layer of restrained concrete exceed the tensile strength of the material prior to complete specimen failure. Comparison of the model and experimental results indicate that the fully restrained specimens with the most severe drying stress gradients failed at the earliest ages.