Investigation On The Effects Of Rainwater Flow Rate And Pre-stress On Electrochemical Anti-corrosion Of Stay Cable Steel Wires

Impressed current cathodic protection(ICCP)is considered an effective method for reducing the corrosion of structures,but little research on ICCP technique for high-strength steel wires in bridge cables has been studied because the atmospheric environment in which the steel wires are located can barely provide electrolyte solutions for the ICCP system.However,rainwater accumulates on the cable surface and forms rivulets under rainfall conditions,and such rainwater rivulets can be used as electrolyte solutions for the ICCP system of high-strength steel wires.On this basis,this thesis investigated the ICCP method of stay cable high-strength steel wires under rainfall environment.The effects of rainwater flow rate and pre-stress level on the cathodic protection efficiency of stay cable high-strength steel wires under different protection current densities were investigated respectively,and the corrosion damage of steel wires with different pre-stress levels and protection current densities was monitored through acoustic emission(AE)technique.The main works of this thesis are listed as follows.The effects of rainwater flow rates and protection current densities on the corrosion rate of stay cable high-strength steel wires were investigated.Weight loss and electrochemical measurements were used to characterize the corrosion rate.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)were used to analyze the microscopic morphology of corroded steel wires and the chemical composition of corrosion products,respectively.Results showed that in comparison with unprotected steel wires,the surface of steel wires with ICCP was flatter,the number and size of corrosion pits were significantly reduced,and the corrosion rate was significantly reduced.Thus,ICCP played a protective effect throughout the test period;however,the protection efficiency was slightly different under different flow rates.The steel wires were effectively protected at any protective current density under the flow rate of 0.7mL/min,but were not effectively protected when the protection current density reached60 mA/m~2 under the flow rates of 7 mL/min and 14 mL/min.The effects of pre-stress levels and current densities on the cathodic protection efficiency and mechanical properties of stay cable high-strength steel wires were investigated.Corrosion morphologies of steel wires were used to qualitatively characterize the corrosion degree.Weight loss measurement was used to quantitatively characterize the corrosion rate.Open circuit potential(OCP)and instant-off potential(IOP)were employed to evaluate the efficiency of ICCP.The static tensile tests were carried out to investigate the mechanical properties of steel wires with different corrosion levels.Results showed that the corrosion rate of steel wires increased with pre-stress level,and the greater the pre-stress,the higher the probability of steel wire corrosion.The application of ICCP reduced the accumulation of the rust layer of steel wires and the number and size of corrosion pits,and the efficiency of ICCP increased with the increase of the protection current density.When the protection current density was constant,there was no significant difference in the IOP value of steel wires with different pre-stress levels,and all steel wires to which ICCP was applied were effectively protected in the later periods of the test and were not in the state of overprotection.Different pre-stress levels had almost no effect on the mechanical properties of the corroded steel wires,and ICCP improved the ductility of the steel wires higher than the strength.A method of employing AE technique to monitor the corrosion degree of stay cable high-strength steel wires in simulated marine atmospheric rainwater environment was proposed.The variation characteristics of AE parameters of corroded steel wires under various pre-stress levels and protection current density conditions were studied.The AE monitoring results were compared with traditional weight loss and electrochemical measurement results.Results showed that the variation of cumulative ringing count curve and cumulative signal strength curve with test time were consistent with weight loss and OCP measurements and could reflect the evolution process of corrosion damage.According to the AE intensity analysis(IA)results,the corrosion level of steel wires was divided no corrosion,slight corrosion,medium corrosion and severe corrosion.Steel wires without ICCP were basically in the medium corrosion and severe corrosion levels,while steel wires with ICCP were basically in the no corrosion and slight corrosion levels.