Fabrication of one-part geopolymer from coal gasification slag via alkali fusion and component additive: Effect of different alkali-to-slag ratios

This research aims to explore using coal gasification slag (slag) to synthesize one-part geopolymer by alkali fusion and component additive. The effect of various alkali-to-slag (A/S) ratios on the synthetic one-part geopolymer was studied. The reaction products were analyzed using XRD, FTIR, TG-DTG, SEM, and XPS. The dissolution test, reaction degree experiment, and alkalinity of the pore structure were conducted to study the reaction process of the one-part geopolymer. The results demonstrated that the dissolution amount of Si and Al elements in the fusion product increased with the A/S ratio, and the fusion product with a high A/S ratio possessed high activity. In addition, as the A/S ratio was raised, the compressive strength of geopolymers increased initially before falling off, and geopolymer with an alkali-to-slag ratio of 1.2 (G-1.2) exhibited the highest compressive strength of 26.52 MPa. SEM images showed that geopolymers with a high A/S ratio had a relatively less porous matrix. Furthermore, the reaction degree of geopolymers and dissolution amount of the fusion product was raised as the A/S ratio increased, demonstrating that the fusion product was the primary reactant to provide active Si and Al species for geopolymerization. Moreover, the geopolymer with a low A/S ratio had a low reaction degree, and the slag additive could not be dissolved efficiently. The high A/S ratio of fusion product produced more Q4(mAl) structure in geopolymers, which reflected a relatively complete geopolymerization reaction. Additionally, a high A/S ratio improved the reactivity of the fusion product and led to the consumption of newly formed products in geopolymer, which destroyed the microstructure of geopolymer. An appropriate A/S ratio in the fusion product ensured the integrity of the geopolymer structure. The obtained results provide a new idea for the utilization of slag via alkali fusion and component additive method.