High temperature-resistance modification of the magnesium phosphate inorganic adhesive and its bond properties between CFRP sheets and concrete

The carbon fibre reinforced polymer (CFRP)-strengthened concrete structures are faced with the great threat of fire due to the vulnerability of the epoxy organic adhesive to high temperature. The traditional epoxy organic adhesives are thus urgently needed to be replaced by the alternatives with high-temperature resistance. This paper explored the feasibility of using magnesium phosphate inorganic adhesive (MPIA) to serve as the bonding material for the CFRP-strengthened concrete structures. To this end, the high-temperature resistance modification of MPIA was conducted through the addition of glass powder (GP) in this study. The effects of the GP content ranging from 0% to 15% on the temperature development, mechanical property degradation, phase evolution and microstructural characteristics of the MPIA after exposure to different temperatures were investigated. The results showed that the glass powder could effectively fill the pores caused by the decomposition of the hydration products and the cracks caused by the shrinkage of MPIA matrix at elevated temperatures, which improved the microstructure of MPIA significantly and thus alleviated its strength degradation under high temperature. In terms of the mechanical properties, the MPIA with 10% GP (hereinafter referred to as TRMPIA) yielded the best high-temperature resistance. In addition, the interfacial bond property test after high temperature was also conducted on the concrete members strengthened with the CFRP sheets pasted by TRMPIA, and the test results were also compared with the specimens with epoxy served as the bonding material. The results showed that even after exposure to 600°C, the in-plane shear strength of TRMPIA still remained 14.0% of that at room temperature, while the bond strength of epoxy had been completely lost, which highlighted the advantage of high-temperature resistance of the modified MPIA served as the bonding material of CFRP-strengthened concrete structures.