Study On Durability Of CFRP-reinforced Concrete Bending Members Under Acid Rain Environment

Mechanical properties and durability of CFRP-reinforced concrete bending members are deteriorated due to the combined effect of Hi and SO42-in acid rain environment,which results in the significant economic loss.It has become a challenge for civil engineering.Under acid rain and second corrosion condition,the deterioration of durability of CFRP-reinforced concrete bending members results from the deterioration of physical and mechanical properties of concrete and Interfacial Transition Zone(ITZ)between coarse aggregate and mortar,the corrosion of reinforcing steel and the bond properties of CFRP-concrete interface,which need to be deeply considered for further research.This research is based on the recent study on durability of concrete exposed to acid rain,and funded by the National Natural Science Foundation of China(Grant No.51178069)and the Scholar Program of China Scholarship Council(No.201506570009).In this research,experimental investigation,theoretical analysis,numerical simulation and structure monitoring were carried out under micro-,meso-and macro-scale,to determine the deterioration mechanism of physical and mechanical properties of concrete and ITZ,corrosion state of reinforcing steel,bond properties of CFRP-concrete interface and flexural behavior of CFRP-reinforced concrete beams.The principal research work is listed as follow:1.A study on physical and mechanical properties of concrete and ITZ between coarse aggregate and mortar under acid rain environment.Based on SEM,DES and nanoindentation test,the deterioration mechanism of physical properties(microstructure,surface crack and elemental composition)and mechanical properties(hardness,stiffness and modulus of elasticity)of mortar and ITZ were analysed under micro-scale.The modified stress-strain relationship of mortar and ITZ under acid rain corrosion was proposed.Based on a concrete model with coarse aggrate,cement and ITZ,cracking,damage evolution and failure modes of concrete under acid rain were discussed under meso-scale.2.A study on corrosion state of reinforcing steel in concrete.Based on accelerated corrosion tests,unidirectional diffusion model of Cl-and structure monitoring methods,relationship between potential and corrosion rate of reinforcement,chloride diffusion depth,chloride ion concentration on specific location were determined under macro-scale.Experimental results were used to evaluate the corrosion state of reinforcing steel in engineering structure.Two corrosion monitoring methods of reinforcing steel in concrete(based on Fiber Bragg Grating and Carbon Nano Tube)were proposed.3.A study on bond properties of CFRP-concrete interface under acid rain environment.Based on single shear test and.cohesive traction-separation behavior,bond stress,slip and fracture energy of of CFRP-concrete interface exposed to acid rain were obtained,and the bond-slip relationship was proposed under macro-scale.Based on nanoindentation test,elemental composition and modulus of elasticity of epoxy resin adhesive-mortar interface were analysed under micro-scale.4.A study on flexural behavior of CFRP-reinforced concrete beams under acid rain environment and second corrosion condition.Based on four-point bending test,deterioration mechanism of flexural behavior(concrete strength,damage depth,frequency,strain distribution,load-deflection curces,ductility,cracking patterns,damage evolution and failure modes)of CFRP-reinforced concrete beams exposed to acid rain were analysed under macro-scale.The relationship between Acoustic Emission parameters(RA,AF and b-value)and cracking patterns were discussed.The relationship between fractal dimensions of cracks and flexural behavior of CFRP-reinforced concrete beams were founded.Deterioration mechanism of CFRP-reinforced concrete beams under second corrosion condition was analysed.