Combined effect of coal chemical wastewater and PC on preparing of coal-to-liquids residue-based alkali activated materials

Aimed to achieve "waste control by waste" of coal-to-liquids (CTL) industry, coal gasification residue (CGR), the most typical CTL residue, and coal chemical wastewater (CCW) were used as aluminosilicate precursor and auxiliary activator respectively to prepare alkali activated materials (AAMs). CGR-based AAMs using a less concentrated NaOH solution than conventional, with CCW as mixing water were synthesized. The results showed that CCW benefited the compressive strength of CGR-based AAMs significantly, but demonstrating slight reduction over time. The combined effect of CCW and Portland cement (PC) supplied continuous increase of strength and eliminated the strength reduction with age. The mechanisms behind the improved performance of the AAMs due to the introduction of CCW and PC were discussed by XRD, FTIR, TG-DSC, MIP and ESEM. It was found that the increased alkali content due to the introduction of the CCW, supplied more extensive dissolution of active aluminosilicate and progressive geopolymerization of CGR. The coexistence of both N-A-S-H gel and C-A-S-H gel (originated from the introduced PC) in hardened AAM pastes reduced the proportion of pores larger than 100 nm to less than 30%, and provided denser structure.