Thermomechanical Response of Basalt Fiber–Reinforced Polymer Rods and Constitutive Model Development

Basalt fiber–reinforced polymer (BFRP) composites have recently been introduced in civil engineering applications, yet research on their behavior at elevated temperatures remains limited. A comprehensive understanding of BFRP behavior is crucial for practical and cost-effective fire-safety design applications. This study investigates the performance of basalt fiber–reinforced polymer rods at elevated temperatures. Tension tests were conducted at temperatures up to 450°C, and the changes in mechanical properties were assessed. The findings indicated that the BFRP rods exhibited marginal degradation in mechanical properties at temperatures below 300°C, retained 58% of their tensile strength at 400°C, and lost all tensile strength at 450°C. Scanning electron microscopy analyses revealed fiber discreteness and resin decomposition at high temperatures. Additionally, a semiempirical constitutive law was developed to correlate the mechanical properties of the BFRP rods with the exposure temperature. The proposed model is novel and flexible and demonstrates good applicability to existing literature data sets within the investigated range of material properties. This model can predict the thermomechanical behavior of fiber-reinforced polymer bars using fundamental parameters typically known during manufacturing, potentially eliminating the need for elevated temperature testing.