Properties of alkali-activated slag with addition of cation exchange material

The massive mobile alkali metal cations in alkali-activated slag (AAS) cements are significantly connected to the issues such as efflorescence, carbonation and potential alkali-aggregate reaction, and greatly restrict their extensive application and development. This paper attempts to use cation exchange materials to remove the freely moved alkali cations in AAS cements. Two representative cation exchange materials, vermiculite and 5A zeolite, were added at mass ratio of 5% and 10% to slag activated by sodium hydroxide. 5A zeolite showed a faster and stronger ions exchange capability to vermiculite in alkaline solution. However vermiculite immobilized more Na+ ions than 5A zeolite in AAS pastes, and the specimens with vermiculite displayed a higher compressive strength, attributed to generate more hydration products which were shown in XRD, TG-DSC and EDS tests, and formed a compact microstructure seen in SEM image. It is concluded that these two cation exchange materials could remarkably reduce the unrestrained alkali ions in the AAS cements, and the properties of AAS cements influenced by cation exchange materials are highly dependent on the category of the exchanged cations.