Effect of white mud on carbonation resistance of alkali activated slag

Abstract

White mud (WM) is a solid waste produced in the process of papermaking and it remains to be effectively utilized. It contains a large amount of CaCO3 and residual alkali metal ions. This paper aims to explore the effect of WM on carbonation resistance of alkali activated slag. The changes in mechanical properties and microstructure of alkali activated white mud/slag (AAWS) after natural carbonation and accelerated carbonation were analyzed. The results indicate that the mechanisms of natural carbonation and accelerated carbonation are different. The carbonation depth achieved in 90 days of natural carbonation can be reached in just 14 days of accelerated carbonation. Samples with 15 wt% WM blended possesses the smallest carbonation depth and the highest compressive strength. WM can effectively mitigate the natural carbonation of AAWS by dissolving Mg2+ and Ca2+. Mg2+ can migrate to increase the solubility of calcite, promote the generation of hydrotalcite to absorb carbon dioxide, and reduce the carbonation degree. Ca2+ will migrate after the carbonation and decalcification of the gel product and reduce the decalcification sensitivity. This study offers a sustainable approach for improving the carbonation resistance of AAWS.