Influence of liquid-to-solid ratios on properties and microstructure of coal gasification slag-based one-part geopolymer

Limited studies have been conducted on the synthesis of one-part geopolymer involving coal gasification slag by alkali fusion and component additive method (AFCAM). The ratio of liquid-to-solid (L/S) is the key aspect that has a major impact on the one-part geopolymer's compressive strength (UCS). Our research aims to determine how different L/S ratios affect the microstructure and characteristics of one-part geopolymers. MIP analysis and hydration heat test were conducted to analyze the influence caused by different L/S ratios. The results showed that as the L/S ratio increased, the UCS of geopolymers decreased, and the setting time of fresh slurry increased steadily. Additionally, geopolymer with 0.25 as an L/S ratio (G-L/S-0.25) achieved a higher UCS at 48.31 MPa, whereas the total setting time was more than 23 hours. The low L/S ratio produced more gel pores and less total porosity in the geopolymer matrix, which improved the UCS. Moreover, lower porosity suggested that the geopolymer sample had higher compactness and a better internal structure. It is found that the dissolution of the fusion product released heat in the first hour, and no coal gasification slag dissolution heat was detected after one hour. This suggested coal gasification slag showed low reactivity as the additive and was embedded in the geopolymer matrix after 28-day curing. The tested results showed that G-L/S-0.25 had a greater reaction degree. This study illustrated the effects of the L/S ratio on one-part geopolymer and provided a new thought to enhance the UCS of coal gasification slag-based geopolymer.