Use of coal bottom ash for the production of sodium silicate solution in metakaolin-based geopolymers concerning environmental load reduction

This research proposes applying coal bottom ash (CBA) to metakaolin-based geopolymers. The conventional CBA mixing method in geopolymers degrades the compressive strength of the geopolymers mainly because of the low reactivity of CBA. To minimize the strength degradation and maximize the available CBA content in geopolymers, the CBA was treated with an alkaline solution and then mixed with metakaolin. A sodium hydroxide solution with 10 and 12 M concentrations, a water-to-solid ratio of 0.50, and curing at ambient temperature were used for all geopolymer composites. If replaced with CBA up to 15% of the total weight of the geopolymer, the proposed method can not only yield a higher compressive strength than the conventional mixing method by providing external silicon from the CBA, but it can also show compressive strength similar to a typical geopolymer without CBA. The properties observed by XRD, FT-IR, SEM/EDS, and MIP disclose the reasons for the proposed method accommodating a larger amount of CBA.