Strengthening of concrete structures using carbon fibre reinforced polymers and cement-based adhesives

The research project conducted in this study concerns the investigation of the application of cement-based adhesives in CFRP strengthening of reinforced concrete members. The results demonstrate that mineral-based adhesives can provide the desired matrices for CFRP reinforcement. The literature review covers the background of CFRP application with conventional techniques. The bond characteristics of CFRP to concrete substrate, the flexural performance of retrofitted RC beams, and the failure modes at normal temperature are discussed. The guidelines for and numerical approaches to CFRP application are reviewed. Current studies of CFRP application at high temperature and related studies on the application of cement-based adhesive as bonding agent are investigated. The experimental work on the bond characteristics of CFRP material to concrete substrate using cement-based adhesive includes tests on single-lap shear. Results show that the cementitious adhesive can provide a reliable matrix for CFRP textiles to achieve certain bond stresses comparable to what can be achieved using conventional inorganic adhesives. The failure mode is debonding through the CFRP-mortar interface. The bond-slip relationship was extracted and later applied in finite element analysis. The experimental work on retrofitting of RC beams using cementitious adhesive showed that CFRP textile is the most compatible option with this new type of adhesive. The CFRP textile can improve the flexural ultimate strength of RC beams by 35%. The failure mode was intermediate debonding, similar to that achieved by using epoxy as reported in the research literature. A new type of anchorage was utilised for CFRP application using cementitious adhesive, which improved the ultimate capacity by 42%. The failure mode was concrete crushing on top, inferring that the full possible capacity of the beam was utilised. The experimental work pursued an investigation of flexural performance of retrofitted beams at high temperature. The results show that the retrofitted RC beam with cement-based adhesive had a considerable high temperature endurance compared to the specimens with epoxy. The failure temperature was 844°C. The proposed strengthening technique is therefore a reliable method for structures at high risk of fire exposure. The failure mode is intermediate debonding within a high moment region. Finite element analysis (FEA) was conducted to simulate and gain a better understating of the performance of retrofitted members. There was a good correlation between the empirical results and the FE analysis. Furthermore, FEA was used to simulate the performance of a retrofitted RC beam under fire, and to predict the fire endurance and failure mode of the beam.