Behaviour of steel-fibre-reinforced recycled concrete-filled square steel tubular short columns under axial compressive load

Abstract

Recycled concrete technology is a viable solution to construction and demolition waste issues. This study introduces a series of axial compressive tests on steel-fibre-reinforced recycled concrete-filled square steel tubular (SFRACFST) short columns. The test results exhibit that as the replacement percentage of recycled coarse aggregates (Rp) increases, the ultimate compressive strength (Nu) of the specimens with 4 mm of tube thickness (Ts) slightly increases from 1558.901 to 1702.952 kN. In contrast, the corresponding peak-longitudinal displacement (Δu) decreases from 3.055 to 2.101 mm, and the maximum reduction in post-peak load attains 32.15%. However, the use of steel fibres improves the mechanical behaviour of the specimens, especially in ductility. For instance, compared to the specimen C40-T4-R100-ST0.0, the Δu of the specimens with a higher volume fraction of steel fibres (Vsf) significantly increases by 33.93% (from 2.101 to 2.814 mm), and the maximum reduction in post-peak load decreases from 30.18 to 25.31%. This is because the anchoring and bridging effects of fibres effectively retard the macrocrack expansion within the core concrete. In addition, a formula is proposed to predict the Nu of square SFRACFST short columns under the axial compressive load.