Effects of mineral admixtures and lime on disintegration of alkali-activated slag exposed to 50 °C

• Alkali activated pastes (AAS) lose strength after exposure to 50 °C.
• The strength loss can be prevented by addition of silica fume (SF).
• SF performed better than fly ash (FA) in reducing strength loss.
• FA can effectively reduce strength loss when AAS were cured at 60 °C.
• Addition of lime leads to high strength loss of AAS after exposure to 50 °C.

Alkali-activated slag can totally disintegrate when exposed to 50 °C. This paper presents a study of possible solutions to avoid this disintegration by using silica fume (SF) and fly ash (FA) to partially replace slag. It was found that partial replacement of slag with SF significantly reduces strength loss. A mixture of 50% slag 50% SF (cured at 25 and 60 °C) showed no strength loss after the exposure. In comparison, a 55% drop of strength was observed in a mixture of 50% slag 50% FA (cured at 25 °C) after the same exposure. However, the strength loss of this mixture was reduced by 50% when cured at 60 °C. The presence of lime in AAS pastes increases the degree of strength loss after the exposure. The mechanisms for the above strength results are discussed in terms of hydration products and microcracking.