Chemo-mechanical properties of alkali-activated slag/fly ash paste incorporating white mud

Abstract

White mud (WM) is a waste solid from paper industry. It mainly contains calcium carbonate and residual alkali metal ions (e.g., K+, Na+ and Mg2+). The aim of the study was to test the feasibility of incorporation white mud into a blended slag/fly ash alkali activated binder system. Blends of slag and fly ash was used as the precursor and WM was used as the filling material. Pastes with 0%, 10%, 20%, 30%, 40% and 50% WM were prepared for the investigation. It was found that the compressive strength decreases with the WM content increasing. Nevertheless, the paste containing 50% percent of WM is still comparable with Portland cement 42.5. Besides, XRD, TGA, FTIR, SEM/EDX tests were performed. The results indicated that the main reaction product of AASFW is a C-(N)-A-S-H type gel, and the formation of hydrotalcite is promoted as the increment of white mud replacement. In the end, nanoindentation reveals that the addition of WM leads to the histogram of both elastic modulus and hardness shifts towards lowers values. This supports the observation at meso-scale. It is expected that the current study provides an insight into the alkali activated slag/fly ash/white mud binder material and offers a sustainable solution for effective utilization of WM.