Abstract
Historically, ring tests have been performed to determine the time for concrete or mortar specimens to crack under restrained shrinkage. When the concrete or mortar ring deforms due to shrinkage, the steel ring restrains the material and tensile stresses are induced. Stress development cannot be monitored for test setups in which the degree of restraint is so high that no measurable deformation occurs in the steel as the material shrinks. Such test setups have provided qualitative evaluations and have not enabled a simple procedure to be established to routinely quantify the restrained shrinkage characteristics of the materials. In this study, an instrumented ring setup is used to quantify the restrained shrinkage behavior of concrete and mortar. The setup provides a high degree of restraint while still allowing sufficient strain in the steel as the material shrinks.
It is shown with the ring setup that the cracking potential of concrete or mortar under restrained shrinkage can be classified on the basis of either how long it takes the material to crack or the rate of stress development in the material. The testing and analysis procedure provides a rational basis for assessing the relative performance of concrete or mortar mixtures when subjected to shrinkage under restraint. A simple procedure is also developed for a preliminary assessment of cracking potential using standard values of drying shrinkage and modulus of elasticity obtained at seven days after initiation of drying.
