Microstructure and mechanical properties of activated high-alumina ferronickel slag with carbide slag and alkaline salts

Abstract

Alkali-activated materials have several remarkable advantages over Portland cement particularly in carbon emission and energy consumption. However, less work has focus on the feasibility of preparing geopolymers from high-alumina ferronickel slag (AFS) with alkaline salts as activators. This article reports the microstructure and mechanical properties of activated high-alumina ferronickel slag (AAFS) with a combination of carbide slag (CS) and Na2CO3 (SC) or Na2SO4 (SS). Results indicate that the AAFS pastes properties are affected by concentration (Na2O equivalent) and nature of activator. The hydration of high-alumina ferronickel slag (FNS) is accelerated as the Na2O equivalent increases from 0.5% to 3% regardless of alkaline salt type, while the early age hydration will be restricted when Na2O equivalent is higher than 3%. The pH of pore solution in SS-activated series is lower than that of SC-activated series. As such, SC-activated FNS pastes have higher exothermic heat in the initial hydration period than SS dosed specimens. Although SC-activated pastes have more gel products and smaller critical pore diameter, the SS-activated specimens can achieve higher compressive strength due to compact interfacial transition zone and reasonable hydration products composition.