Experimental Research on Axial Compressive Performance of Reinforced Concrete Columns Strengthened with CFRP Sheets Bonded by Magnesium Phosphate Inorganic Adhesive

To investigate the feasibility of replacing traditional epoxy resin with magnesium phosphate inorganic adhesive （MPIA） for carbon fiber reinforced polymer （CFRP） sheet-strengthened reinforced concrete （RC） columns， axial compression tests were conducted on eleven RC square columns. The experimental variables included adhesive type， the number of CFRP sheet layers， and the amount of transverse reinforcement， in order to evaluate load–vertical strain curves， transverse strain development， and the displacement ductility factor. The study examined the damage evolution and failure mechanisms of the CFRP sheet-strengthened columns， revealed the synergistic mechanism between the CFRP sheets and MPIA， and analyzed the enhancement effect of MPIA-bonded CFRP sheets on axial compressive performance. Test results indicated that both MPIA and epoxy resin effectively confined the core concrete， with MPIA-strengthened columns exhibiting a greater improvement in bearing capacity. In addition， CFRP sheet-strengthened specimens using MPIA exhibited lower ductility than those using epoxy resin， but performed better than other inorganic adhesive systems. Furthermore， based on design codes and literature research， this study modified existing predictive models and proposed a method for calculating the axial compressive capacity of CFRP sheet-strengthened RC square columns using MPIA as the adhesive.