Non-ferrous metallurgical slags as SCMs - a study of reactivity and hydration mechanism of a pyro-metallurgical slag before and after heat treatment

A raw slag containing Zn and Pb and a heat-treated slag with lower Zn and Pb content from the same pyro-metallurgical recycling process were investigated as supplementary cementitious material for blended Portland cement. The reactivity of both slags was similar to the reactivity of siliceous fly ash. In blends with Portland cement, the slags started to react noticeably after 2 days of hydration. After 91 days the untreated slag showed a higher reaction degree than the heat-treated slag. However, the untreated slag retarded early Portland cement hydration due to the presence of Zn and Pb in the slag. The reaction of the slag altered the AFm phases in the system, and formation of a (Fe, Mg)-Al-layered double hydroxide was favoured in the blend with untreated slag. Further work related to leaching is suggested to ensure environmental safety when using such pyro-metallurgical slags as supplementary cementitious material.