Compressive behavior and models of FRP-confined coal gangue concrete after sulfate exposure and sustained high stress conditions

With advancements in fiber-reinforced polymer (FRP), FRP-confined coal gangue concrete (FCGC) has been explored as a potential supporting member for underground mines. Nevertheless, supporting structures face harsh conditions, including sulfate exposure and sustained load, which can severely impact the compressive performance of FCGC. Thus, the axial compressive test was performed on FCGC after sulfate exposure and sustained high stress conditions, taking inner concrete, FRP layer, stress-to-strength ratio, sulfate concentration and load duration time as variables. Results indicate that after sulfate exposure and sustained high stress conditions, the failure modes of FCGC also feature the FRP hoop rupture near the mid-height region, and the stress–strain curves also display a bilinear pattern, compared to the control specimens. The slope of the initial portion shows a slight increase due to the compactness of the inner concrete, while the second portion exhibits a degradation. The residual ratio of ultimate stress and strain ranges from 0.897–1.062, and 0.633–0.805, respectively, where the extent of degradation increases with higher sulfate concentration and stress-to-strength ratios. Besides, after sulfate exposure and sustained high stress conditions, the lateral strain of FCGC becomes larger if the axial strain is the same. Furthermore, the strength and strain models were modified incorporating the impact factors of load duration time, sulfate concentration, and stress-to-strength ratio.