High-temperature mechanical properties of basalt fiber-reinforced concrete after salt spray erosion

To investigate the durability performance of basalt fiber-reinforced concrete (BFRC) subjected to the coupled effects of salt spray erosion and fire-induced high temperatures, this study systematically conducted combined exposure tests with salt spray durations (0, 30, 90, and 180 days) and elevated temperatures (20, 200, 400, 600, and 800 °C). The influence of fiber volume fractions (0%, 0.05%, 0.10%, and 0.15%) on the degradation patterns of bond strength and mechanical property of BFRC was investigated. Combined with microscopic characterization techniques, the microstructural evolution mechanism of BFRC under coupled damage conditions were revealed. The bond strength exhibited a non-monotonic trend with salt spray erosion time, with a reduction of 34.79% after 180 days of erosion. Specimens with a basalt fiber content of 0.15% demonstrated the most significant improvement in bond performance within the 200–400 °C range; however, the reinforcing effect of basalt fiber became largely ineffective at 800 °C. When the temperature was elevated to 400 °C, the bond strength at 180 days of salt spray erosion was 55.8%, 43.0%, and 16.0% lower than that of specimens with erosion durations of 0, 30, and 90 days, respectively. TG analysis revealed three characteristic weight-loss stages of BFRC at approximately 450 °C, 630 °C, and 820 °C. Finally, based on a combined theoretical and experimental approach, an interfacial analysis model was established. The calculation formulas applicable to both pre-cracking and post-cracking stages were derived. The predictions of the proposed theoretical model agree well with the experimental results, with relative errors within ±20%. The research findings provide theoretical support and engineering references for the evaluation of bond performance of reinforced concrete structures under complex environments.