PERFORMANCE TESTING OF SELF-HEALING CAPSULES IN EARLY-AGE CEMENTITIOUS MATERIAL

Abstract

Concrete cracks are inevitable due to chemical reactions and volume changes, as well as to environmental actions and mechanical loadings. Without proper repair, these cracks allow gases, liquids, and other deleterious materials to propagate into the concrete core. As a result, healing or sealing the cracks is pivotal to mitigate the occurrence of such deterioration. Encapsulation-based autonomous self-healing has been widely investigated as a solution; however, the efficacy of this technique is highly influenced by the performance of the capsules to protect the healing agents during concrete mixing and placing, while still triggering their release when young concrete cracks. Therefore, the objective of this study is to evaluate the performance of the self-healing capsules during concrete mixing and after hardening when the concrete undergoes volume changes due to hydration and drying. The initial stage of this research study was intended for reviewing the related literature to address the discontinuities and inconsistencies in the performance evaluation of self-healing cementitious materials. The following phases focused on testing the performance of self-healing capsules in early-age cementitious material employing fracture mechanics and finite elements techniques. The first phase focused on investigating the effectiveness of capsules in self-healing concrete at early-age providing insights into the design requirement for the success of the capsules. The second phase aimed at evaluating the performance of the self-healing capsules during concrete mixing. The correlations between the capsules’ shell properties, concrete rheological properties, capsules’ external forces, and capsule survival rate during concrete mixing were investigated. In the last phase, the performance of concrete containing self-healing capsules subjected to autogenous and drying shrinkage at an early-age was evaluated by numerically simulated ASTM C1581 restrained shrinkage test. The study accounted for the time-dependent concrete’s mechanical properties, and the capsule’s geometrical and mechanical properties. The results of this research provided in depth understanding of the performance evaluation of self-healing capsules in cementitious material during concrete mixing and after hardening. The developed models investigated the parameters that may contribute to the performance of the self-healing capsules, which can assist in manufacturing and designing of the capsules prior to their use in self-healing cementitious material applications.