Analysis of Thermal and Mechanical Parameters of the BFRP Bars

Abstract

Fibre-Reinforced Polymer (FRP) reinforcement bars are gaining interest in terms of using them as an internal reinforcement in concrete construction parts due to their high tensile strength, corrosion resistance, low weight, and electrical indifference. Nevertheless, low elasticity and difficulties related to a high reduction in mechanical properties at even slightly elevated temperatures seem to limit this potential, due to existing fire safety requirements for buildings. Basalt FRP, which is the subject of this experimental study, is a relatively new type of non-metallic bars, and their environmental friendliness has been underlined in previous studies. The aim of this study is to determine the mechanical properties of BFRP bars, such as tensile and compressive strength and elasticity modulus, at normal and elevated temperatures up to 200 °C. The medium values of compressive strength at room temperature were in the range of 441.2–466.8 MPa, and it was significantly lower than the tensile strength (930.5–1121.3 MPa). Additionally, low values of elasticity modulus, especially when comparing to steel bars (typically about 210 GPa), were found in both compression (mean values: 31.0–38.4 GPa) and tension (mean values: 43.3–44.6 GPa). Low elasticity modulus may lead to difficulties with excessive deflections and crack widths, when designing bent elements with such reinforcement. Moreover, reduced mechanical properties at compression should not be neglected when designing compressed parts. Additionally, the phase change parameters, e.g., glass transition temperature, have been determined by means of DMA method, and the glass transition temperature was found to be equal to 107.5 °C.