Study On Migration Characteristics Of Chloride Ion In Mortar Under The Action Of Stray Current

Stray current is abbreviated as "flow current",that is,the current outside the defined loop,mainly from rail transit such as urban subways.The stray current and chloride ions have a superposition effect on the reinforced concrete structure in the coastal environment,which can lead to accelerated degradation of the reinforced concrete structure and greatly shorten the safe service life of the infrastructure.In this paper,the basic properties of mortar and chloride ion migration characteristics under stray current are studied.The main research results are obtained as follows:(1)Reducing the water-cement ratio can significantly improve the resistance of the mortar to chloride ion penetration.When the fly ash or slag is replaced part of cement by the same amount,the chloride ion migration coefficient of the mortar can also be reduced.Moreover,with the increase of fly ash or slag content,the chloride ion migration coefficient of mortar decreases.(2)The chloride ion binding isotherm of the mortar shows nonlinear changes,which has a high fitting degree with Freundlich isotherm equation or Langmuir isotherm equation.However,under the action of electromigration,the chloride ion binding isotherm conforms to a linear relationship.(3)The stray chloride ion electromigration devices SC-RCM and SC-ASTM based on RCM and ASTM methods can be used to study the migration characteristics of chloride ions under stray current.The output spurious voltage and the measured spurious signal have similar frequency domain characteristics.The output spurious signal frequency domain interval is 0 ~ 0.1 Hz,mainly basing on low frequenvy.Comparing SC-RCM and SC-ASTM devices,it is appropriate to use a SC-RCM device with a larger capacity of sodium chloride solution tank.(4)The stray current has an accelerating effect on the migration of chloride ions,Which lead to close to direct current in the migration mode of chloride ions but lower the migration efficiency compared to the direct current.The chloride ion concentration in the solution pool,the non-zero mean value of the stray current,the voltage amplitude and the frequency all have a certain effect on the migration behavior of chloride ions in the mortar.(5)Based on the forward non-steady state electromigration formula,the chloride ion electromigration formula under stray current is constructed after dividing the spurious signal voltage equally and processing statistics of the time under effect of different voltages and the empirical value of the reduction coefficient K is obtained through the chloride ion electromigration test.