The effect of commercial superplasticizers on Cl⁻ ion partitioning in OPC mortar and its implications for the corrosion of steel embedded in concrete

The concentrations of soluble Cl⁻ ions and commercial superplasticizers in ordinary Portland cement mortar have been determined from pore fluid extractions. Samples were cured at 40°C for up to 180 days. During the curing the superplasticizer levels fall to around 10% of their initial concentrations within 90 days. Chloride ions react weakly with the cement; however, the addition of superplasticizer produces a marked decrease in Cl ion concentrations in pore fluid, suggesting that chlorination of the superplasticizer (or its degradation products) is occurring, accompanied by precipitation or adsorption of the organic admixture by cement hydration products. Partial chloride removal from the aqueous phase is accompanied by a decrease in the corrosion rates of embedded mild steel, suggesting that chemical factors within superplasticized cement paste may play a useful role in controlling chloride-induced corrosion.