Effect of long-term carbonation on strength and permeability of magnesia-coal based solid waste backfill materials

Evaluating the long-term safe operation of storage facilities requires a vital index investigating the performance change of storage backfill materials due to prolonged carbonation. For the first time, this study employed multiple indices to characterize the basic properties of storage backfill under carbonation over two years. The results show that long-term hydration positively influences concrete properties and promotes the development of harmless holes smaller than 20 nm in backfill materials. However, this study also revealed that carbonation for up to two years adversely affects backfill material properties. The carbonation progresses slowly, with a maximum carbonation depth reaching 147 mm. Compared to long-term hydration, the backfill subjected to carbonation curing for two years showed significant disadvantages regarding strength characteristics, permeability, pH levels and pore structure. Specifically, the uniaxial compressive strength decreased from 11.015 MPa to 8.583 MPa. The internal axial permeability of the sample was 0.945 md, and the internal permeability was 0.109 md. The pH of the sample dropped significantly from 12.8 to 6.8, and its porosity increased from 15.67 % to 29.30 %. Carbon sequestration and utilization is a hot topic, and the results of this study should arouse attention to the application of CO₂ in the concrete and mine backfill field and provide an essential reference for further research on long-term performance changes of carbonation.