Effect of limestone powder addition on threshold chloride concentration for steel corrosion in reinforced concrete

The effects of limestone replacement fraction, limestone specific surface area and water-to-binder (W/B) ratio on the threshold chloride concentration (TCC) for steel corrosion were evaluated. XRD and SEM analyses were conducted to examine the crystalline phases and microstructure of limestone-blended cement paste, respectively. The influence of pH value of concrete pore solution on the chloride binding capability was also investigated. The results demonstrate that the chloride threshold decreases as the limestone content or the W/B ratio increases, while limestone fineness shows negligible effect. XRD analyses indicate that addition of limestone inhibits the transformation from ettringite (AFt) to monosulfate (AFm), which exhibits superior chemical binding capability for chloride ions. SEM analyses suggest that addition of 15 wt% limestone contribute to a denser microstructure. Reduction in the pH value of pore solution compromises the chloride binding capability of concrete.