The effect of activators on the dissolution characteristics and occurrence state of aluminum of alkali-activated metakaolin: Fid-Bau Portal

The effect of activators on the dissolution characteristics and occurrence state of aluminum of alkali-activated metakaolin

Deng, Gao / He, Yongjia / Lu, Linnu / Hu, Shuguang

Abstract

Highlights • The effect of different activators on the dissolution characteristics of aluminum in metakaolin (MK) is discussed. • The distribution and occurrence state of aluminum in hydration products strongly depend on the type of activators. • The sulfate accelerates the dissolution of Al ions from MK. • In MK-CH system, the formation of stratlingite is more favored than that of C-A-S-H.

Abstract The aluminum plays an important role in the alkali-activated metakaolin (MK) cements. In this paper, the effect of activators on the dissolution characteristics and occurrence state of aluminum of alkali-activated MK has been investigated. Three kinds of MK pastes (MK-calcium hydroxide (CH), MK-CH-gypsum and MK-CH-gypsum-sodium sulfate) cured at 50 °C are prepared. For MK-CH pastes, the results show that most of Al enters into the structure of stratlingite and C-A-S-H. The Al in stratlingite exists in the form of Al (IV) and Al (VI), the Al in C-A-S-H exists in the form of Al (IV). The formation of stratlingite is more favored than that of C-A-S-H. However, for MK-CH-gypsum and MK-CH-gypsum-sodium sulfate pastes, most of Al enters into the structure of C-A-S-H, AFm and ettringite. The Al in C-A-S-H exists in the form of Al (IV), the Al in AFm and ettringite exists in the form of Al (VI). Furthermore, the increase of sulfate concentration leads to an increase in mean chain length of C-A-S-H and a decrease in Al(IV)/Si of C-A-S-H. The dissolution characteristics and occurrence state of aluminum of alkali-activated metakaolin is affected by the type of activators.