The Influence of Environmental Conditions on the Performance of Self-Healing Mortars for Masonry Repair

Abstract

The preservation of historic masonry structures requires durable repair techniques that minimize intervention while maintaining the original appearance. In this context, bio-based self-healing mortars present a promising solution, yet their application in masonry remains underexplored. Previous research demonstrated the potential of a poly-lactic acid (PLA)-based agent to heal cracks in masonry with cement-based mortars, restoring both bond strength and aesthetics. However, when extended to more porous cement–lime mortars and clay bricks, new challenges emerged. Leaching, likely resulting from interactions between the mortar’s porosity and the healing environment, underscored the need for further investigation. To this purpose, the study investigates clay brick couplets built with two mortar compositions of increasing lime content, exposed to two different healing environments. Specifically, a PLA-based healing agent was incorporated into cement–lime mortars with lime/cement ratios of 1.0 and 3.33 by volume. Each mortar was used both plain and with 10% of the healing agent (by binder volume) to build the specimens. After pre-cracking through bond wrench testing, the couplets were left to heal for 60 days under either high humidity or wet–dry cycle conditions. The results highlight the critical influence of the healing environment on overall performance. While wet–dry cycles proved ineffective in this case, humid conditions enabled partial recovery of flexural bond strength, with values reaching up to 15% in samples containing the healing agent and higher lime content. Visual inspection confirmed complete crack closure, supporting the aesthetic—and potentially watertightness—restoration. Additionally, reference samples with higher lime content also exhibited minor strength recovery, likely due to the migration of free lime and its reaction within the crack. These advancements underscore the potential of bio-based self-healing mortars for masonry repair and establish a foundation for further research.