Study on the monotonic axial compression behavior of the GFRP confined autoclaved steel slag blocks compound concrete circular column

Steel slag, a major by-product of the steel industry, poses significant environmental and resource challenges. Using untreated steel slag in concrete will cause cracking due to the poor volume stability of steel slag. This study employed a novel autoclave modification procedure to produce high-quality steel slag. The autoclaved steel slag blocks (ASSBs) and normal concrete (NC) were mixed pouring into the GFRP tube to form the GFRP-confined autoclaved steel slag blocks compound concrete (GCASSBCC) circular column, enabling ASSBs large-scale and cost-effective utilization in concrete. Subsequently, the monotone axial compression test of the GCASSBCC circular column was conducted for the first time, with the mixing ratio of ASSBs and the number of GFRP sheet wrapping layers as variables. The test results indicate that the relationship between autoclave pressure and the minimum required autoclave time for achieving volume stability in steel slag follows a power function. After autoclaving, the free CaO and MgO in the steel slag undergo hydration to form Ca(OH)2 and Mg(OH)2, the contents decreasing from 3.75 % and 2.13 % to 0.18 % and 0.32 %, respectively. The compressive strength of concrete with 15 % and 30 % ASSBs is 6.27 % and 14.53 % lower than that of NC. The first portion of the stress-strain curve for GCASSBCC circular columns appears elonged, and the bearing capacity is comparable to that of the corresponding GFRP confined normal concrete (GCNC) circular columns. With the increased mixing ratio of ASSBs, the lateral expansion of confined specimens increases, and the ultimate strain decreases. Finally, a monotone axial compression stress-strain model for the GCASSBCC circular column incorporating the mixing ratio of ASSBs into analytic expression was developed, which can accurately reproduce the test stress-strain curves in detail. The proposed stress-strain model provides a reliable tool for engineers designing the GCASSBCC circular column.