Alkali-activated reactive powder concrete with recycled and industrial steel fibres

This paper experimentally investigates the influence of type, content, and geometry of steel fibre on the mechanical properties of ambient-cured alkali-activated reactive powder concrete (AARPC). The study examines compressive strength, splitting tensile strength, flexural strength, modulus of elasticity, and stress–strain behaviour under compression. Two types of steel fibre were used: industrial steel fibre (IF) with 6 mm long and 0.2 mm in diameter, and waste steel fibre (WF) recovered from discarded tyres, with lengths ranging from 5 to 40 mm and diameters from 0.1 to 0.35 mm. The fibres were incorporated into AARPC mixtures at volume fractions of 1%, 2%, 3%, and 4%. In addition, hybrid fibre systems (HF), comprising a combination of IF and WF, were also studied. Test results indicate that the addition of IF and WF of 3–4% significantly influenced the flowability of AARPC. The inclusion of 3% HF yielded the highest increase in compressive strength, splitting tensile strength, flexural strength, modulus of elasticity, peak stress, and the corresponding strain. Moreover, toughness increased by 232% with HF and by 164.8% with WF. Finally, WF has been found promising to fully or partially replace IF in AARPC.