Advanced shape memory alloy fibers designed to enhance crack closure and re-centring performance in cement-based composites

Crack-closing and re-centring attributes were observed in cementitious composites utilising segmented pseudoelastic shape memory alloy fibres (S-PSMAFs) developed in this study. S-PSMAFs, produced via laboratory deep drawing, displayed notable strain recovery capacity during detwinning and martensite phases in direct cyclic tensile tests. Cementitious composites incorporating S-PSMAFs at 0.5%, 0.75%, and 1.0% dosages underwent testing in static and cyclic flexure using both unnotched and notched beams. Results were compared with steel fibre (SF) reinforced specimens. Digital image correlation (DIC) provided full-field strain maps and crack propagation data. The cyclic testing allowed assessment of crack-closing and re-centring behaviour at varying deflections post-cracking and at ultimate limit state deflections. S-PSMAF-reinforced composites maintained a crack-closure ratio between 52% and 60% even at larger crack sizes (e.g., 3 mm). Re-centring ratios ranged from 80% to 55%, dependent on the imposed displacement amplitude of cycles. In contrast, SF-reinforced beams lacked effective crack-closing or re-centring behaviour, with both ratios decreasing drastically to about 10% over cycles. Additionally, S-PSMAF-reinforced composites exhibited higher flexural toughness, ductility, force reduction performance factor, greater energy dissipation, and smaller crack sizes compared to their SFreinforced counterparts.