Mechanical characterisation and bond performance of sustainable B-TRM systems for masonry

Textile-reinforced mortar (TRM) systems are a promising solution for repairing and strengthening existing structures because of their ease of installation, reversibility, fire resistance and vapour permeability, which make them particularly compatible with masonry substrates. Growing interest in reducing the environmental impact of construction materials has promoted the development of cement-free alkali-activated matrices as potential alternatives to conventional binders. However, limited information is available on one-part alkali-activated slag (AAS) mortars specifically developed for TRM systems, particularly regarding their combined tensile, bond and durability performance on different masonry substrates. This study presents the first results of a comprehensive experimental investigation on a sustainable basalt (B)-TRM system incorporating a one-part AAS mortar activated by a hybrid solid system of sodium metasilicate, sodium carbonate and calcium hydroxide. The proposed mortar was systematically compared with a commercial natural hydraulic lime (NHL)-based mortar reinforced with the same coated basalt textile. The experimental programme included direct tensile tests on dry textiles and TRM composites, as well as direct single-lap shear (DSLS) tests on clay-brick and yellow-tuff masonry substrates. In addition, selected specimens incorporating the NHL-based mortar were subjected to a freeze–thaw conditioning protocol to provide a preliminary assessment of durability. Both systems exhibited similar tensile and bond failure mechanisms, predominantly involving basalt-fibre rupture; in the DSLS tests, fibre rupture was in some cases accompanied by transverse matrix cracking. Compared with the NHL-based system, the AAS-based TRM showed an approximately 17% lower average tensile strength, while maintaining satisfactory mechanical performance. In the bond tests, the AAS system achieved an efficiency factor close to 100% on yellow-tuff masonry and approximately 84% on clay-brick masonry, highlighting the influence of substrate characteristics on stress transfer. Freeze–thaw conditioning did not produce a systematic reduction in either tensile or bond strength, although it affected the stress–strain and stress–slip responses of the NHL-based systems. Overall, the proposed one-part AAS mortar proved to be a promising cement-free matrix for B-TRM applications, providing satisfactory tensile and bond performance while expanding current knowledge on the influence of matrix chemistry, substrate type and environmental conditioning. These findings support the development of lower-impact strengthening solutions for masonry structures and provide a basis for future long-term durability investigations.