The Elevated Temperature Performance Of Basalt Fiber Reinforced Polymer Composites

Fiber reinforced polymer(FRP) composites have excellent corrosion resistance and exhibit comparable/improved material properties than traditional construction materials. In recent years, FRPs are widely used as reinforcements in enhancing bridges and other infrastructures. Service life of such structures are complex and undoubtedly involve long time exposure to unpredictable weather conditions. Research on the performance of FRP and their enhanced structures at extreme conditions(such as temperature/fire) is the foundation for high performance FRP and such reinforced structure’s economic design. It is also important for many engineering practices so as to get the desired properties, both performance and safety, and thus gather great scientific significance.Basalt fiber is a new type of green, inorganic material with good mechanical properties. With the continuous development of economy and scientific quest for high performance materials, basalt fiber will certainly play an important role in practical applications. In this paper, the elevated temperature performance study of basalt fiber and BFRP have been explored. An attempt has been done in order to have a comprehensive and in-depth understanding of the temperature resistance behavior of basalt fiber and to provide data and theoretical support for its further development and practical application.The main contents and conclusions of the dissertation are given as follows:Firstly, the degradation of the basalt fiber and BFRP plates at elevated temperatures and after thermal aging were studied. At elevated temperature, basalt fiber tensile performance is decreased and the discreteness increased as the temperature ranged from room temperature to 200°C. The interlaminar shear strength degradation is more obvious, especially as the temperature exceeding the glass transition temperature of the material. The interlaminar shear strength retention rate is only 7.8% at 200°C. At the same time, the tensile properties of the BFRP showed a sharp degradation and the representative volume element model was used to predict the tensile strength of BFRP at elevated temperature. The specimens were thermally aged at 200°C and after 4 hours the mechanical properties of basalt fiber and BFRP showed no obvious change. Compared with glass fiber and GFRP plates, basalt fiber and BFRP plates showed excellent temperature resistance.Secondly, the effects of thermal aging on the water uptake behavior of BFRP plates were studied. The specimens were immersed in distilled water or alkaline solution after thermally aged at 135°C or 300°C for 4 hours. Thermal aging caused the BFRP internal resin matrix to degrade and the porosity was increased. As internal pore connectivity in the immersion environment, the water uptake and the diffusion coefficient of BFRP increased greatly. Theoretical water absorption and diffusion coefficient of BFRP along and perpendicular to the fiber direction was calculated and was compared with the water absorption and diffusion coefficient of pure resin matrix. The results showed that thermal aging led to change in the path of BFRP water absorption and diffusion and established that the interface between fiber and resin on the water absorption and diffusion of BFRP should be considered. The diffusion activation energy of BFRP was calculated based on Arrhenius theory.Thirdly, the effects of thermal aging on the long-term mechanical properties of basalt fiber and BFRP were investigated. The specimens were immersed in distilled water or alkaline solution separately after thermally aged at 135°C or 300°C for 4 hours. Thermal aging changed the short-distance order of the basalt fibers, and the tensile strength decreased by 32.8% for the specimen thermally aged at 300°C. The-Si-O-Si- bonds was destroyed by the hydroxyl ion in alkaline solution and the tensile strength tend to zero after one month immersion. BFRP surface was oxidized, and the tensile property had no obvious change. The interlaminar shear strength decreased obviously. Ester bond gradually disappeared as the immersion time increased. Tensile strength prediction was performed based on the activation energy theory of Arrhenius.Fourthly, the combined effects of elevated temperature and sustained loading on BFRP and BFRP-concrete interface were studied. The testing of BFRP was performed from room temperature upto 160°C with sustained load set as 35% fu, 50% fu and 65% fu respectively. Under the combined effects of load and temperature internal stress redistribution in BFRP occurred. The tensile property of BFRP at elevated temperature decreased obviously after four hours of processing. The higher the exposure temperature and sustained load level, more significant performance degradation was observed. For the specimen under 35% fu and 50% fu treated at 160°C, the tensile strength reduced by 20.0% and 41.8% at 160°C and the tensile strength reduced by 8.2% and 29.0% at room temperature respectively. A prediction method for the loaded BFRP tensile strength at elevated temperature was proposed based on the test results and theoretical analysis. BFRP-concrete interface was tested under temperature(room temperature to 60°C) and sustained load(35% fu). The load was transferred gradually from BFRP to the adhesive layer. The ultimate interface load was increased by 31.2% and 20.2% as temperature rising to 40°C and 60°C, respectively.