Flexural performance and crack closing capacity of double-hooked-end superelastic shape memory alloy fibre-reinforced concrete beams under cyclic loading using digital image correlation

Abstract

This study investigated the flexural response of hooked-end superelastic shape memory alloy (SMA) fibre-reinforced concrete beams under cyclic loading. The fibres were fabricated from heavily coldworked 1 mm diameter NiTi alloy followed by heat treatment at 350 °C for 40 min. Fibre volume fractions of 0.25 %, 0.5 %, 0.75 % and 1 % in normal strength (NS) concrete and 0.5 % and 1 % in high performance (HP) concrete were investigated. The fibre-reinforced prisms were tested under four-point bending. Digital image correlation (DIC) techniques were used to measure the cracking behaviour of the SMA FRC beams. The results demonstrated that increasing the volumetric ratio of the superelastic fibres as well as the compressive strength of the matrix led to higher flexural strength and toughness, deflection recovery, and crack closing performance. HP concrete matrix with 1 % SMA showed the highest toughening and displacement recovery performance, with a re-centering ratio of more than 55 % at L/140 mid-span displacement. An SMA fibre volume fraction between 0.75 % and 1 % in NS mixtures and at least 1 % in HP composites can be adopted for better flexural resistance.