Research On The Performance Degradation Of CFRCM-concrete Interface Caused By Impressed Current Cathodic Protection

The corrosion of steel bars caused by marine environment and the uncontrolled-use of sea sand are the main reasons for the deterioration of the durability of concrete structures in coastal areas.For the existing concrete structures polluted by chloride the corrosion of the steel bar leads to degradation of the mechanical properties of the structure.In order to solve this problem,this thesis simulates the chloride-polluted existing concrete elements in the coastal area?the specimen is mixed with 3%of NaCl solution?,and adopts Carbon Fiber Reinforced Cementitious Matrix?CFRCM?as anode material for Impressed Current Cathodic Protection?ICCP?system and prefabricated formwork for Structural Strengthening?SS?,which combine to the so-called ICCP-SS system.Researches and analyzes of the interfacial bond properties between CFRCM and concrete under the ICCP-SS system were proposed in this research.The success or failure of structural reinforcement depends on the bonding quality between the reinforcement material and the concrete.Using ICCP technology can protect the steel reinforcement in the concrete,but whether it will affect the interface between the reinforcement material and the concrete is also the content of this paper.Therefore,in this dissertation,under different charge densities and different cement-based materials,the tensile bonding test and double shear test were used to study the interfacial adhesion between carbon fiber reinforced cement-based composites and concrete.The main contents include:1.Conducting tensile bond tests of the interface between CFRCM and concrete.The influences of compositions?C1,C2,C3?,current densities?20mA/m²?60mA/m²?100mA/m²,abbreviate i20,i60,i100?,and protection durations?4 months,6 months,abbreviate t1,t2?on the interfacial bond strength between CFRCM and concrete elements were investigated.The results showed:?1?The average tensile strength of C1 and C2 series specimens is higher than the average tensile strength of C3 series specimens without fly ash and silica fume,indicating that the pozzolanic effect of fly ash and silica fume and the filling ability of micro-aggregates improved the Interface bond properties;?2?With the increase of charge density,the average tensile strength of C1 series specimens showed a certain decreasing trend,while that of C2 and C3 series specimens remained unchanged;?3?The observation of the surface of the anode interface by the SEM method revealed that the degradation of the bond strength of the C1 cement-based cement material added with short chopped carbon fiber was faster than that of the C2 and C3 without the short chopped carbon fiber;?4?Through EDS and XRD observations,it was found that under the driving of the applied current,the Ca²⁺in the anode area will be transferred to the cathode area,and as the charge density increases,the transfer amount also increases;?5?Through chloride titration experiments,it was also found that Cl^-in the concrete near the cathode and in the electric field will transfer to the anode area,and the amount of transfer will increase as the charge density increases.2.The double-shear test of interface between CFRCM and concrete was conducted.The effects of composition materials,densities,and protection durations?Consistent with the tensile bond tests?on the interfacial bond strength between CFRCM and concrete were also investigated.The results show;?1?The average shear strength of C1 and C2 specimens is higher than that of C3 specimens without fly ash and silica fume,indicating that the pozzolanic effect of the fly ash and silica fume and the filling ability of micro-aggregates improved the Interface bond properties;?2?With the increase of charge density,the average shear strength of C1 series specimens showed a certain decrease,while the C2 and C3 series specimens did not change;?3?With the increase of the charge density,the stiffness of the C1,C2,and C3 series specimens is basically unchanged;?4?The CFRP/cement paste interface was determined by the failure mode of the double shear test and the weak surface of the composite test piece was CFRP/cement paste.This was also demonstrated by measurement of the strain change of the specimen by DIC method.