Long-term performance of basalt fiber reinforced composite under coupled effects of alkalinity and freeze-thaw cycles

Basalt fiber (BF), a kind of natural fiber produced from the melt of basalt stones, has been regarded as a promising material in the manufacture of fiber reinforced composites considering the balance between mechanical properties and economical/environmental costs compared with other non-renewable/petroleum materials. Moreover, the BFRP composites are capable to fabricate the energy harvesting devices in marine engineering when piezoelectric nanocomposites and piezoelectric polymer matrix are adopted to collect offshore renewable energy. However, the long-term performance of BFRP in concrete alkaline and seawater environments has not been comprehensively understood yet, and the lack of knowledge on the performance of BFRP reinforcement under coupled alkalinity and freeze-thaw cycles prevents further application of composite structures in the frigid areas. In order to address the above questions, experimental investigations were carried out in this study with respect to the mechanical properties and deterioration mechanism of BFRP reinforcement under dynamic alkaline environment affected by seawater and temperature as well as under coupled alkaline and freeze-thaw cycles. The results showed that the strength retention of BFRP bars encapsulated in seawater-sea sand concrete and immersed in seawater is higher than that in distilled water, and as the erosion time increases and the temperature rises, severe resin damage occurs inside BFRP bars, and the weakening of connections between fibers and matrix becomes a significant cause of the decrease in tensile performance. Moreover, it is found that the long-term performance of BFRP under coupled alkaline and freeze-thaw cycles is affected by deterioration of resin at the surface, while the majority of internal fibers are free from attack by corrosive agents. These findings will provide a scientific basis for the reliable performance evaluation and further development of high performance and durable multifunctional BFRP materials in marine engineering.