Improving the chloride binding capacity of alkali activated slag by calcium and aluminum enriched minerals

Abstract

In this paper, a modified alkali activated slag with improved chloride binding capacity is proposed by introducing calcium and aluminum enriched phases in the binding system. The Ca and Al phases are added in order to promote the formation of AFm type phases in alkali activated system and then transformed into Friedel's salt (Fs) when in contact with chloride. The effects of calcium and alumina type on phase composition, chloride binding behavior, mechanical property of modified alkali activated slag binders are discussed. The results show that the addition of Ca and Al enriched minerals effectively improve the chloride binding capacity of the binder up to 44.4%. The combination of calcium hydroxide and metakaolin shows the highest binding efficiency, followed by calcium nitrite and cement. Metakaolin exhibits better modification on chloride binding capacity than nano alumina. The incorporation of Ca and Al enriched minerals together successfully promotes the formation of AFm type phases (Mc and AFm-NO2) in alkali activated system, while the addition of metakaolin increases the reaction degree and the mean chain length of C-(A)-S-H gels, contributing to the chloride binding capacity. The mechanical properties of alkali activated slag are also improved by adding calcium hydroxide, cement, and alumina enriched minerals, while calcium nitrite exhibits a slight negative effect.