Performance of capsules in self-healing early-age concrete due to restrained shrinkage

Performance of capsules in concrete was evaluated numerically using a simulated ASTM C1581 restrained shrinkage test and experimentally measured concrete shrinkage strain data to determine their effectiveness in healing cracks in early-age concrete. The model accounts for the concrete’s time-dependent mechanical properties, and the capsule’s geometrical and mechanical properties, and depth. A finite element model was developed to simulate the concrete volume change due to autogenous and drying shrinkage and the corresponding state of stress, and fracture mechanics to trace crack initiation and propagation in a restrained shrinkage ring. The performance of capsules in self-healing early-age concrete was found to depend on the capsules’ geometry, the stiffness ratio of concrete-to-capsule, and bond strength-to-rupture strength ratio of concrete-to-capsule. Results reveal that corresponding ratios of concrete effective stiffness and bond strength at 28 days to the stiffness and rupture strength of the capsules provide a threshold limit after which capsules debond in self-healing early-age concrete.