Enhancing coal gangue aggregates with fly ash-cement slurry: Synergistic effects of CO2 mineralization on physical and mechanical properties

Abstract

The application of coal gangue in construction materials faces challenges due to its inherent structural looseness, elevated porosity, and high carbon content. This study encapsulated coal gangue aggregates (CGAs) with a fly ash-cement slurry, varying the content of fly ash (0 %, 10 %, 20 %, and 30 %) and maintaining a water-to-cement ratio of 0.35. These aggregates were subjected to a curing process within an environment containing a CO2 concentration of 20 %, 0.1 MPa pressure, 70 % humidity, and a temperature of 20°C. The study delved into examining how the combination of fly ash-cement slurry encapsulation and CO2 mineralization impacts the physical properties and microstructure of CGAs, focusing on understanding the influence and mechanism behind the synergistic effects. Findings reveal that following the encapsulation process using a fly ash-cement slurry, CGAs exhibit a higher apparent density, a reduced crushing value, but a notable increase in water absorption rate. Notably, treatment with 10 % fly ash-cement slurry and CO2 mineralization increased the apparent density by 3.85 %, reduced the crushing value by 39.57 %, and limited the increase in water absorption rate to 9.9 %. Additionally, the elastic modulus of the enhanced aggregates rose by 12.73 %. This can be attributed to the formation of a significant quantity of C-S-H gel and CaCO3 products as a result of the interplay between the encapsulated fly ash-cement slurry and CO2 mineralization. This process effectively occupied the voids within the coal gangue. Consequently, CO2 mineralization enhanced the interfacial transition zone between the slurry and coal gangue, ultimately leading to improved coal gangue's mechanical performance.