Performance evaluation of geopolymer grout materials derived from high-volume circulating fluidized bed fly ash and ground granulated blast furnace slag

Circulating fluidized bed fly ash (CFBFA) is a significant byproduct of power plants and has attracted considerable attention due to its potential as a low-cost geopolymer precursor. However, unstable components in CFBFA, such as sulfur trioxide (SO3) and free lime (f-CaO), can lead to volumetric expansion, which limits its widespread application in cementitious materials. To address this issue, this study effectively combines CFBFA with ground granulated blast furnace slag (GGBS) to develop an environmentally friendly micro-expansive geopolymer subgrade grouting material. This approach enhances the utilization of CFBFA in cementitious applications. The research demonstrates that the utilization rate of CFBFA in the geopolymer grouting material can reach 70 %, and the material meets the subgrade grouting specifications for fluidity, setting time, and compressive strength. The developed grout material exhibits micro-expansive behavior that significantly improves repaired subgrade performance. Furthermore, freeze-thaw cycle test results confirm the durability of the grouting material, indicating that micro-expansion has a negligible effect on its durability. Additionally, X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) analyses were conducted to investigate the composition and microstructure of the grouting material with varying CFBFA dosages. These analyses reveal the performance evolution mechanisms of the grouting material, providing valuable insights into its preparation. Based on the experimental results, it is recommended to use a CFBFA content of 65-70 %, a GGBS content of 30-35 %, a 1.0 M alkaline activator at 35 % dosage, and a water-to-solid ratio of 0.65 to prepare high-performance subgrade grouting materials with microexpansive properties and excellent durability. Therefore, this paper introduces a novel method for producing geopolymer subgrade grouting materials using CFBFA and GGBS, offering a new perspective on the wide application of CFBFA in cementitious materials and contributing to the reduction of its environmental impact.