Solidification of nitrate solutions with alkali-activated slag and slag-metakaolin cements

Abstract

© 2014 Elsevier B.V. All rights reserved. The solidification of nitrate solutions with alkali-activated slag (AASC) and slag-metakaolin cements (AASMC) and the resulting setting times, compressive strengths, dimensional stability, water resistance, hydration products, microstructures, and macroporous network structures were evaluated. The influences of the alkali activator concentration, mineral composition of metakaolin, ratio of slag to slag + metakaolin, and concentration of NaNO3 on the cement performance were all evaluated in detail. The compressive strength of cemented nitrate solutions with AASC and AASMC aged for 28 days was from 13.4 to 42 MPa depending on the NaNO3 concentration. X-ray diffractometer, differential thermal analyzer, and electron microscope analyses suggested that NaNO3 crystallizes in cementitious matrices without reacting with the hydration products of AASC and AASMC. X-ray microtomography showed that the solidified NaNO3 solution with a salt concentration of 700 g/l and AASC had a denser microstructure without shrinkage microcracks, a smaller macropore volume, and smaller macropore sizes than hardened AASC-based paste mixed with water.