Role of Chloride Ion and Cation Type Accompanied by Sulfate Ion on Durability Performance of Concrete in Conjoint Chloride–Sulfate Environment

Abstract

This work assessed the durability performance of concrete made with ordinary portland cement (OPC), portland pozzolana cement (PPC), OPC +20% fly ash, and OPC +30% fly ash subjected to sulfate-only and to conjoint chloride–sulfate environments. Results indicated that the degree of surface deterioration of the concrete was mitigated in concrete specimens kept in conjoint chloride–sulfate solutions compared with those kept in sulfate-only solutions. Reduction of compressive strength of concrete decreased with the increase of NaCl concentration in conjoint chloride–sulfate solutions. Blended cement concretes had better immunity to sodium sulfate attack, whereas OPC concrete had better immunity to magnesium sulfate attack. In the presence of sulfate and conjoint chloride–sulfate ions, the formation of various compounds in concrete which produce variations in concrete compressive strength was corroborated by the results of XRD and FESEM analyses. Reduction of the compressive strength of concrete in exposure solutions decreased in the order MgSO4>Na2SO4>NaCl+MgSO4>NaCl+Na2SO4.