Determination of diffusion coefficient of chloride in concrete: an electrochemical impedance spectroscopic approach

For predicting the service life of concrete structures in marine environment, diffusion of chloride (D) is an important parameter. Electro-migration tests and ponding tests are two techniques conventionally adopted, however they are destructive in nature. EIS (Electrochemical impedance spectroscopy) being non-destructive appears a promising technique to arrive at ‘DR’ (D from EIS) in situ in structures. The DR of ordinary Portland cement concrete (OPC) was compared with that of Portland pozzolana cement concrete (PPC). The effect of curing on DR was analyzed. The splash zone condition was created by subjecting the specimens to alternate wetting and drying cycles. At the end of 28 days of curing, the DR of PPC concrete is only 66.7% of that obtained in OPC concrete. A linear correlation was established between DR and the porosity of the concrete. Due to pozzolanic reaction, the rate of pore refinement is faster in PPC concrete compared to OPC concrete. In M25-PPC concrete at the end of 28 days of curing, the pore size is decreased to 14.6% of that obtained at the end of 3 days of curing. The reduction of pore size by densification of pore structure due to pozzolanic reaction reduces the DR value in PPC concrete. In 30 MPa concrete the DR under wet cycle is 3 times higher than in dry cycle, which implied that corrosion is initiated 3 times faster in concrete exposed to the splash zone condition.