Prestress-Tuned Sliding and Interlocking in Nacre-Inspired Bowtie-block Masonry Walls for Damage-Tolerant Protection

Protective walls made of brittle cementitious materials often fail due to localized cracking, limited deformation capacity, and poor post-damage integrity under severe out-of-plane loading. Inspired by the sliding, frictional dissipation, interlocking, and bridging mechanisms that give mollusk-shell nacre its exceptional toughness, this study develops and experimentally validates a mortarless, post-tensioned biomimetic protective wall. The system is assembled from custom bowtie-shaped concrete blocks with 5° inclined seating surfaces and longitudinal high-strength steel wires, translating nacre's hierarchical brick-and-mortar architecture into a construction-scale structural form. Mechanical characterization of the blocks found mean compressive, tensile, in-plane flexural, and out-of-plane flexural strengths of 9.1, 1.2, 4.2, and 3.7 MPa, respectively. Three full-scale wall specimens were tested under out-of-plane static loading at stabilized prestress levels of 2.07, 3.51, and 6.21 kN per wire. Results show that wall performance is governed not by maximum prestress, but by prestress-tuned activation of inter-block sliding and progressive geometric locking. The optimized specimen, prestressed at 2.07 kN per wire, achieved a peak load of 43.2 kN, an ultimate central deflection of 90 mm, and a total energy dissipation of 12.8 kJ. Higher prestress increased initial stiffness but suppressed sliding, localized damage, and reduced energy absorption. The findings of this study provide structural-scale proof of concept for prestress-dependent, architecture-controlled damage tolerance, while also highlighting the potential lifecycle and maintainability benefits of mortarless modular assembly.