Sodium silicate- impregnated perlite as self-healing agent for geopolymers: Comparison of autonomous and autogenous healing

In this study, expanded perlite, a lightweight aggregate, was used as a carrier for the self-healing agent, sodium silicate. The effectiveness of autogenous versus autonomous self-healing in repairing damage was evaluated under two healing conditions: water immersion (WH) and 100 % relative humidity at 60°C (100 %RH-60°C). Sodium silicate- impregnated perlite (SS-Perlite) was employed to promote autonomous healing. Microscopic examination after 28 d revealed limited surface crack closure under all conditions, suggesting that the rigid structure of the geopolymer restricted the penetration of the healing agent. Despite this, SS-Perlite significantly enhanced compressive strength recovery in WH and 100 %RH-60°C conditions, although full restoration was not achieved. Autonomous healing was more effective under the 100 %RH-60°C condition, where sodium silicate release facilitated reactions with unreacted geopolymer compounds. Water absorption tests demonstrated higher healing efficiency in samples with increased perlite content, particularly under WH conditions, while limited crack closure was observed under 100 %RH-60°C. FT-IR and XRD analyses confirmed that the crack-filling material was predominantly a secondary aluminosilicate compound. These results suggest that optimizing the SS-Perlite system and adjusting environmental exposure conditions could further improve the self-healing performance of geopolymer mortars.