Lithium silicate as a healing agent in vascular networks for natural hydraulic lime mortars: a step towards cyclic self-healing systems for heritage materials

Built heritage is increasingly exposed to diverse and intense environmental stressors as a consequence of climate change. Consequently, historic masonry repair strategies must evolve to support a more resilient and long-lasting preservation approach. Drawing on biomimetic principles, recent innovations have introduced vascularisation techniques to enable autonomous crack repair in lime-based mortars, including targeted patching applications where localized material loss needs to be effectively restored. However, the effectiveness of these self-healing systems depends largely on the performance of the healing agents, particularly their long-term reactivity and compatibility with traditional materials. This study evaluated lithium silicate solutions, LS15 and LS20 (15 % and 20 % lithium wt. respectively) as healing agents in natural hydraulic lime mortars using simplified vascular networks. Samples were pre-cracked to a crack width of 0.1 mm and were allowed to heal over 14 days. Three-point bending tests were conducted to assess mechanical recovery at 14, 28, and 365 days, including up to three damage–healing cycles for long-term evaluation. No significant autogenous healing was observed in the control specimens. LS20 achieved maximum single-cycle strength and stiffness recovery of 187 % and 124 %, respectively, at early age. Over multiple cycles, in samples aged 1 year, LS15 showed greater consistency, reaching up to 68 % strength and 51 % stiffness recovery by the third cycle. These results demonstrate lithium silicate’s potential for repeatable, cyclic self-healing in heritage-compatible mortars. • Lithium silicates act as effective, heritage-compatible healing agents for NHL-mortars • LS15 shows better long-term cyclic healing; LS20 gives higher single-cycle recovery • Healing likely governed by matrix densification and secondary hydration processes