Axial mechanical and environmental properties of CFRP-confined coal gangue sand concrete

To improve the mechanical properties of coal gangue sand (GS) concrete, carbon fiber reinforced plastics (CFRP) was used to confine the concrete. In this paper, the effects of the coal gangue sand replacement rates (r_GS), core concrete strength grade, and the number of CFRP layers (p) on the axial compressive mechanical properties of CFRP-confined coal gangue sand (CCGS) concrete were investigated experimentally. The experimental results showed that r_GS had a small impact on the failure mode of the CCGS concrete, which was the explosive failure. The ultimate bearing capacity (N_{u, e}) of the CCGS concrete decreased (maximum is 8.4 %) and increased (maximum is 134.1 %) respectively, as the r_GS and p increased. With the increase of the r_GS, the peak longitudinal strain of the CCGS concrete increases. The more the number of the CFRP layers, the better the lateral confined effect on the CCGS concrete. The r_GS has no significant effect on the circumferential strain efficiency coefficient, which is approximately 0.67. The highest utilization efficiency of the CFRP is 2 layers. Through finite element analysis, CFRP contributes the most to the ultimate bearing capacity of the CCGS concrete, increasing by 21.9 %, while GFRP contributes the least by 10.5 %. Increasing the cross-sectional dimensions will increase the N_{u, e}, but will not enhance the axial compressive strength of the confined core GS concrete. The design methods of the ultimate bearing capacity and constitutive model of the CCGS concrete were proposed and validated. A full-range load prediction analysis showed that increasing r_GS can improve the confinement effect of the CCGS concrete. Finally, through carbon emission calculation analysis, it was recommended to increase the number of CFRP layers while ensuring the large-scale consumption of coal gangue from the perspective of the social and economic benefits.