Durability design criteria for the hybrid carbon fibre reinforced polymer (CFRP)-reinforced geopolymer concrete bridges

This study proposes an innovative carbon fibre reinforced polymer composite-geopolymer concrete (CFRP-GPC) system to improve the durability and structural performance of existing deteriorated reinforced concrete (RC) bridges. A rigorous experimental program is designed to investigate the transport mechanism of corrosive agents such as acids and chloride in the constituents via mechanical and microstructural analysis and to develop diffusion models for CFRP-GPC systems considering synergistic effects of temperature and pH fluctuations. Experimental results show that tensile strength of CFRP and epoxy resin reduces by up to 25% and the failure of composite mainly occurs at the fibre-epoxy interface after exposure to acid. The compressive strength of geopolymer concrete decreases by 66% and 61.3% while the mass loss reduces by 5.3% and 3.7% for samples after exposure to the 10% and 32% hydrochloric acid solution, respectively. The diffusion coefficients of the constituent materials vary from 10-8 to 10-6 mm2/s whilst the diffusion rate within the CFRP is the lowest due to the presence of carbon fibres. Furthermore, a computational model is established to evaluate the performance of the proposed hybrid system in improving long term durability performance of a roadway geopolymer concrete bridge in Australia. The numerical results indicate that the proposed CFRP-confined GPC can substantially impede the acid diffusion into the bridge column, and reduce the level of diffusion and thereby improve the service-life. Parametric study shows that the diffusion rate in CFRP-GPC columns increases up to 58% and 394% for epoxy and CFRP when temperature elevates from 23 °C to 80 °C. In addition, elevation in the exposure temperature from 23 °C to 80 °C increases the mass loss to 22% and 25% under pH = 1 and 7. The findings of this research provide a framework for durability design of hybrid CFRP-GPC systems.