Study on the curing mechanism of cemented backfill materials prepared from sodium sulfate modified coal gasification slag

In order to promote the resource utilization of coal gasification slag (CGS) solid waste, the use of modified coal gasification slag (MCGS) to replace the cement in the cemented backfill materials is an effective way to improve the utilization rate of CGS resources, reduce the backfill cost and reduce the environmental pollution of the cement industry. In this paper, the dosage of sodium sulfate (SS) in the MCGS cemented backfill materials (MCGS-CB) system composed of MCGS–cement–aeolian sand is optimized, and the curing mechanism of MCGS-CB under the action of SS is revealed. The results show that the addition of MCGS delays the early hydration reaction process, accelerates the consumption of sulfate in the system, and shows the phenomenon of sulfate deficiency; The pozzolanic reaction of MCGS increased the ratio of Al/Ca, Si/Ca, S/Ca and Na/Ca of hydration products, changed the structure of hydration products, promoted the formation of hydration products such as C-S(A)-H, C-N-S(A)-H and AFt, increased the density of matrix, reduced the pore volume of harmful pores, and increased the compressive strength. Under the action of SS, the hydration reaction process of the early MCGS-CB was accelerated, the time of the sulfate depletion (SD) point was delayed, and the reaction time of the MCGS was advanced; The consumption of Al and Si ions drives the dissolution of the aluminosilicate glass body in the MCGS, thereby further promoting the formation of hydration products such as C-S(A)-H, C-N-S(A)-H and AFt, and increasing its matrix compactness. About 4% SS has a good excitation effect on MCGS, and excessive SS addition will cause microcracks in MCGS-CB, resulting in a reduction in strength. The results of this study can provide theoretical guidance for the ratio design and field application of sulfate-coal gasification slag-cement cementation system.