Research On The Electrochemical Mechanism Of Concrete Steel Corrosion

All kinds of building was used too long,because of durability of the concrete, and it needlong time to study on corrosion of steel reinforcement in concrete, it hard to acquiringspecimens, so rapid electrochemical corrosion is often used. And study on the process of thecorrosion mechanism can be simulated the reinforced concrete corrosion and improvementaccuracy of prediction durability of concrete. This paper study on CRB550steel embedded inconcrete, then rate of corrosion of rebar in concrete was measuring by Tafel and Open circuitpotential method, and concentration of the chloride ion of surface was measuring by silver/silver chloride electrode in concrete. Finally corrosion mechanism was study by theory ofchloride ion diffusion and theory electrochemical corrosion.(1) When the chlorine ion and voltage was changed, specimens were tested by Tafelmethod after28days maintenance. Then corrosion rate was calculated. The corrosion rate ofthe reinforced concrete in0～5h increase with time gradually, and reach maximum in15～20h. The corrosion rate increases with the quality of chloride ion fraction increased, under anexternal2V DC voltage, and mass fraction of NaCl was5%, the corrosion rate is maximum83.89mm/a. In four different voltage, the corrosion rate of the most significant influenceunder3V DC voltage.(2) There are a clear sag in Tafel curve after reinforced concrete in corrosion for8h,when voltage is2V DC. It shows that corrosion current increase suddenly, The concentrationof chlorine ion accumulated ceaselessly in concrete reinforcement, and reinforcementcorrosion rate became faster, because chloride ions plays a catalytic role in steel corrosion.Then the surface of rebar corrosion occurred a little. The higher concentration of chlorine ionenvironment is, the faster corrosion rate become.(3) From circulation current-voltage curve, corrosion product of concrete reinforcementwas Fe(OH)₂,when voltage is2V DC voltage and mass fraction of chlorine ion is5.5%or7.5%.Then corrosion product of concrete reinforcement was Fe(OH)₃, when voltage is4V DCvoltage and mass fraction of chlorine ion is5.5%or7.5%.(4) The voltage of Ag/AgCl electrode put on the surface of the concrete steel become high with the corrosion of the concrete increase gradually. It indicate when concrete reinforced iscorrosion under voltage role, the speed of diffusion of chlorine ion to rebar surface increase.Surface of concrete happen carbonization, when mass fraction of chlorine is higherconcentration. Then internal OH-through the pore move to the concrete surface layer, and pHreduce lower.