Shrinkage compensation of alkali-activated slag concrete and microstructural analysis

The shrinkage compensating of alkali activated slag (AAS) concrete with an expanding admixture (EA) composed of anhydrite and quick lime as the expanding source is investigated. The effects of the expanding admixture on the compressive strength and volumetric change of the AAS concrete are tested, followed by microstructural analysis of the hardened AAS pastes. The test results have shown that the EA is effective for compensating the shrinkage of AAS concrete. Ettringite is not formed in the AAS paste. Formation of the calcium hydroxide in the AAS paste is the main expanding source. Adding EA into the AAS concrete can increase its early age compressive strength, but lowers slightly the late age compressive strength.