Experimental study on microstructure and mechanical properties of basalt FRP bars

Steel reinforced concrete (RC) is the most widely used material for civil infrastructures such as buildings and bridges in the world. However, such material confronts severe threatens arising from the deterioration of steel reinforcement in concrete, which will greatly shorten the service life of RC structures, endanger the safety of dwellers, and is not conducive to the development of a sustainable world. Facing such serious challenges, researchers have been exploring corrosion-resistant and sustainable construction materials to substitute traditional steel reinforcement. Hence, basalt fibre reinforced polymer (BFRP) bars with superior chemical resistance are emerging as a promising reinforcing material to respond the challenge. However, BFRP rebar is yet to be comprehensively investigated to evaluate its feasibility and enhance its acceptance in the construction industry. In general, a superior construction material should meet requirements regarding both short-term and long-term performances, where outstanding short-term performance is the prerequisite for a material to be applicable. Thus, this project aims to assess the feasibility of BFRP as a reinforcing material in RC structures by investigating its short-term performances and connecting its manufacturing methods and industrial applications. Mechanical properties including tensile, compressive, and flexural strengths of BFRP bars are measured and compared with those of other commercially available BFRP bars to have an overall understanding of the contemporary BFRP industry. Moreover, the internal microstructures BFRP are investigated using SEM and XCT along with a series of image processing and analysis, based on which the relationship between microstructure and mechanical properties is explored. Furthermore, considering the application, this project estimates the bond behaviour of BFRP in concrete to assess general performance of BFRP reinforced concrete and provides related suggestions regarding manufacturing methods. Overall, BFRP rebar has outstanding short-term performances including mechanical properties, microstructures, and bond behaviours in concrete, which makes BFRP a promising alternative to steel reinforcement. However, engineering performances of BFRP rebar show significant variations, since the manufacturing methods in terms of the raw material selection, parameters throughout the manufacturing process and quality controls could be different from various manufacturers, meanwhile a knowledge framework for BFRP rebar production and application similar to that of steel is still missing, which make it difficult to have a systematic understanding and analysis on the BFRP rebar. Hence, the improvement of manufacturing methods is essential to achieve superior and consistent performances of BFRP rebar. Moreover, the durability of bars should also be explored to further verify long-term performances of BFRP as a superior construction material to combat challenges of structural deterioration towards shaping a sustainable world