Effect of sulphate exposure on mortar consisting of ferronickel slag aggregate and supplementary cementitious materials

The present study evaluates the effect of sulphate attack on mortar samples consisting of different proportions of ferronickel slag (FNS) aggregate and supplementary cementitious materials (SCM) such as fly ash and ground FNS (GFNS). The physical and chemical changes occurred in mortar specimens after exposure to 5% sodium sulphate solution were investigated. The test results showed no significant effect of using different percentages of FNS aggregate on sulphate attack of the specimens. Higher expansion and strength loss with visible surface cracking were noticed in the specimens using no SCM. Specimens using fly ash or GFNS as SCM exhibited low expansion and only marginal strength losses. This improvement against sulphate resistance by fly ash and GFNS was due to their pozzolanic activity that improved the microstructure and prevention of ettringite formation, which was confirmed by scanning electron microscopic (SEM) images and energy dispersive spectroscopy (EDS). Therefore, the use of FNS aggregate did not have any negative effect on the sulphate resistance of mortar specimens. The use of GFNS improved sulphate resistance by pozzolanic reaction similar to that of fly ash.