Experimental investigation on application of 3D-printed auxetic cementitious composites to strengthen concrete block masonry

Unreinforced masonry (URM) is highly vulnerable to out-of-plane (OOP) flexural failure owing to its low tensile strength and limited strain capacity. Traditional external strengthening methods often face challenges such as debonding, localised stress distribution and poor crack control. As an alternative, Auxetic cementitious composites (ACC) comprising negative Poisson’s ratio auxetic meshes embedded in mortar can resolve these issues. To develop ACC, a 3D-printed re-entrant chiral auxetic (RCA) structure was employed as a reinforcing medium for hollow concrete block masonry. Block masonry prisms (three courses high) and wallettes (four courses high) with different mechanical strengths were built and rendered using these 3D-printed RCA meshes made of polylactic acid (PLA) and thermoplastic polyurethane (TPU). The prisms were rendered on both sides and tested under axial compression, while the wallettes were rendered on the tension side and subjected to flexural tests. Failure patterns, stress-strain and load-displacement responses, ductility and energy absorption characteristics were evaluated. The results indicated that ACC considerably improved mechanical performance. Both PLA and TPU based ACC composites made with high-strength mortar enhanced the masonry prisms’ compressive strength by 20%, ultimate strain capacity by 280%, and energy absorption by 300–350% compared to the unrendered masonry prism samples. In terms of flexural performance, both PLA and TPU based ACC rendered wallettes achieved a notable 1600% increase in flexural load capacity and enhanced ductility by 60%, while a 16,000% increase in energy absorption was observed compared to control wallettes. The ACC composites with TPU-RCA meshes exhibited the best overall performance under flexural testing. The specimens with ACC composite renders made with high-strength mortar demonstrated a more ductile failure mode by eliminating typical render debonding. In comparison with traditional strengthening systems, ACCs exhibited greater flexural efficiency along with moderate energy absorption characteristics. The results underscore the potential of ACC for improving masonry performance.