Self-Healing of Aged Concrete Containing Crystalline Admixture and Expansive Agent under Repeated Loading

While self-healing concrete has been increasingly studied this past decade, research on the self-healing of a crack after repeated loading is still scarce. Studying this topic is of utmost importance because structures in practice are subjected to repeated damage, causing a variety of crack openings. Hence, this paper presents an evaluation of the self-healing properties of aged concrete containing a combination of crystalline admixture (CA) and expansive agent (CSA), and submitted to repeated loading. Pre-cracked at 218 days old by means of a three-point bending test, the prisms were reloaded every three weeks and healed in wet/dry cycles in between. After two loadings, they were reloaded a third time until failure. Two types of reloading procedures were carried out: (1) reloading to the same residual crack width; and (2) reloading with increasing crack width. Self-healing was assessed with water permeability measures before and after each reloading, macroscopic observations of the cracks, and mechanical recovery. The results showed that two phenomena occurred with opposite effects: damage versus healing. The magnitude of both processes depends on the reloading procedure. When reloading to the same crack width, the damage effect was lower than the healing effect, indicating that the healing products provided sealing even after repeated loading. When reloading with an increasing crack width, the damage effect was greater than the healing effect, but the healing rates were higher than reloading to a constant crack width, because of the creation of new fresh crack surfaces that healed faster. In any case, multiple damage slows down healing but the self-healing process continues. This confirms the long-term healing potential of cracked structures made of, or repaired with, self-healing concrete.