Innovative Application of Self-healing Technology to Masonry: A Proof of Concept

Cracks are one of the most common expressions of damage in masonry structures. Aside from aesthetic issues, they can compromise the overall behaviour of the structure; therefore, they are undesirable and need to be repaired. The repointing technique is traditionally implemented in this context, especially in historical masonry. Nevertheless, future damage is not prevented and may arise again, thus requiring renewed repointing interventions. The paper describes a preliminary study conducted at Delft University of Technology to investigate the applicability of the innovative self-healing technology to enable an automatic repair of masonry cracks. A bacteria-based self-healing mortar, developed to repair existing concrete structures, was implemented to explore the capacity of couplets to recover their original strength and aesthetic aspect after multiple damaging events. Specimens built with calcium-silicate and clay bricks were subjected to subsequent cracking cycles using a crack-mouth-opening-displacement controlled bond-wrench test. Experimental results showed that self-repair, in terms of strength restoration and aesthetic filling of cracks, occurs even after multiple cracking cycles when the self-healing mortar is used with both types of bricks, optimizing the autogenous healing of cement-based mortars. In this context, the healing effectiveness tended to decrease as the crack width and the number of cycles increased. The effectiveness varied also according to the types of brick and healing environment used, e.g. under humid conditions (RH ~ 95%), 50% vs 80% of the original capacity was regained in fully separated couplets made respectively with clay and calcium-silicate bricks. This outcome provides the ground to delineate the remaining testing campaign.