Chloride ion penetration frequently leads to steel corrosion and reduces the durability of reinforced concrete. Although previous studies have investigated the chloride ion permeability of some fiber concrete, the chloride ion permeability of the basalt fiber reinforced concrete (BFRC) has not been widely investigated. Considering that BFRC may be subjected to various exposure environments, this paper focused on exploring the chloride ion permeability of BFRC under the coupling effect of elevated temperatures and compression. Results demonstrated that the chloride ion content in concrete increased linearly with temperature. After exposure to different elevated temperatures, the chloride ion content in BFRC varied greatly with increasing stress. The compressive stress ratio threshold for the chloride ion penetration was measured. A calculation model of BFRC chloride ion diffusion coefficient under the coupling effect of elevated temperatures and mechanical damage (loading test) was proposed.

The early-age mechanical properties of ordinary concrete after a thermal cycle are investigated in this paper, to provide information on the residual safety of concrete structures after a fire occurred during the construction phase. The specimens are heated up to 150, 350 and 550 °C, from 3 to 28 days after casting, and tested in compression and in splitting tension after a rest period. The effects of curing period before heating, exposure temperature, cooling methods (in sprayed water or in air) and of the rest period prior to testing are investigated. The rest period after a thermal cycle performed at an early age brings in a marked recovery in terms of final residual compressive and tensile strengths. More than 50–60% of the loss may be recovered which is much lower than that documented in recent studies on fly-ash concrete. The lowest recovery is exhibited by the concretes exposed to high temperature at 7^th day. Extending the rest period increases the strength recovery. For the concrete heated at 3^rd, 7^th and 14^th day, cooling the specimens in sprayed water lead to larger strength recoveries than in air, both the strengths immediately after cooling and that after rest periods.

Concrete structures are vulnerable to fire-induced damage throughout their service life, with high-temperature exposure presenting a critical safety hazard. This study addresses the critical safety risks posed by fire-induced damage in concrete structures, particularly focusing on the distinct behavioral differences between early-age and mature concrete during both heating and cooling. To investigate these variations, concrete specimens cured for 3, 14, 28, 60, and 90 days were subjected to deformation tests and heated to target temperatures ranging from 100 to 800 °C. Key parameters, including compressive strength, mass loss, and linear expansion rate, were measured. The results show that the linear expansion rate and thermal expansion coefficient increased with temperature at all ages, with residual linear expansion rates at 800 °C ranging from 0.49% to 0.55%, decreasing slightly with age. While compressive strength was higher in older specimens at room temperature, it became similar across ages after exposure to high temperatures, especially above 500 °C. Notably, constant-temperature exposure significantly influenced the deformation behavior. These findings suggest that fire resistance assessments should account for concrete age and, more importantly, the effects of sustained high-temperature exposure, which critically alter deformation patterns and residual properties.

Traditional pseudo-static loading tests fail to capture the unique characteristics of special ground motions, limiting their ability to accurately evaluate the seismic performance of steel-reinforced concrete (SRC) columns. In this study, eight SRC columns were subjected to pseudo-static tests using far-field, near-field, and traditional loading protocols to investigate their structural response under different seismic scenarios. The results show that far-field loading, characterized by repeated large displacement cycles, leads to increased damage accumulation, reduced hysteresis curve fullness, greater bearing capacity loss, significant stiffness degradation, and diminished ductility and energy dissipation. In contrast, near-field loading—dominated by an initial extreme displacement—results in fewer but less developed cracks and a larger concrete crushed zone at failure. The severe initial damage under near-field loading causes a noticeable decline in stiffness and strength during subsequent cycles. During the second loading stage, both the peak load and post-peak deformation capacity are further reduced, significantly impairing the columns’ ability to resist additional seismic demands. These findings highlight the critical role of loading history in shaping the seismic behavior of SRC composite columns.

The bearing capacity of reinforced concrete (RC) beam will be weakened by fire. It is necessary to strengthen RC beams after fire. The carbon fiber mesh (CFM) can be used to reinforce RC beams. In this paper, RC beams were exposed to varying temperatures, followed by reinforcement with varying layers of CFM. The influence of the heating temperature and the number of CFM layers on the flexural performance of RC beams was investigated. The results indicated that the cracking loads of RC beams were 18.2, 16.4, 16.3, and 15.5 kN when the RC beams were subjected to room temperatures, 150, 350, and 550 °C. Compared to the unreinforced beams at room temperature, the cracking loads of the RC beams were reduced by 9.89%, 10.44%, and 14.84%. As the quantity of CFM reinforcement layers rises, so does the ultimate bearing capacity. For example, when the temperature was 150 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 20% and 31.76% compared to the reference beam. When the temperature was 350 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 19.51% and 28.04% compared to the RC beam without CFM. When the temperature was 550 °C, the ultimate loads of the beams with one and three layers of CFM were increased by 20% and 26.67% compared to the RC beam without CFM. Fire-damaged RC beams can be strengthened by one layer of CFM and mortar if the temperature was below 350 °C. Fire-damaged RC beams can be strengthened by three layers of CFM and mortar if the temperature was below 550 °C. The mechanical properties can be obviously enhanced.