Evaluation of the self-healing capacity of concrete with low-cost macro-capsules

This study focuses on the evaluation of the efficiency of a low-cost macrocapsule, using commercially available pharmaceutical capsules with specific modifications, for self-healing concrete. The macrocapsules were developed by the Belgian Building Research Institute in a previous study. The healing agent is a resin based on alkyd-urethane, a low-cost commercial product, which was selected for its compatibility with concrete and shell, and also for the following reasons: resin release, adhesion to concrete, and reduction in capillary water absorption. After their manufacturing, the macrocapsules were carefully integrated within the concrete mix at 5 volume-%, and cubes and slabs for compressive and impact tests were cast. Small beams 160 x 40 x 40 mm3 containing each three capsules (placed 15 mm above the bottom surface) were tested for flexural strength and capillary water absorption. The effect of self-healing was evaluated by sorptivity test for two different crack mouth opening displacements of 0.5 mm and 0.9 mm. In both cases, the cracks were partially or completely healed, and the mechanical properties of the macrocapsule specimens were quite the same as the reference specimens. This demonstrates that the modified low-cost macrocapsules are sufficient to heal large cracks without losing the concrete mechanical properties.