Effect of silica fume on efflorescence formation and alkali leaching of alkali-activated slag

Abstract Alkali-activated cements (AACs) produced from industrial by-products have attracted great attention as an alternative to Portland cement, mainly because of the reduction of carbon dioxide emission and low energy consumption. However, AACs often suffer from severe efflorescence when subjected to humid environments because of their high soluble alkali content. This study reports the effect of silica fume on alkali leaching and efflorescence formation of alkali-activated slag. Specimens were prepared from ground granulated blast-furnace slag (BFS) and silica fume, where sodium hydroxide and sodium silicate solution were employed as activator solutions. Sample produced from 100% BFS exhibited the fastest efflorescence formation and alkali leaching rate. Incorporating silica fume into alkali-activated slag reduced the mobility of alkali, resulting in the decrease of efflorescence formation. However, almost all sodium can be leached out from the samples after immersion in water for 28 d, indicating the weak bond of sodium in the gel.