Performance optimization of superfine cement through composite modification using coal-based solid waste and modifiers

ObjectiveSuperfine cement-based grouting materials generally suffer from limitations including high bleeding rates, unfavourable rheological properties, poor stability, and strength retrogression. These issues can be mitigated by incorporating modifiers, which allows for the reutilization of coal-based solid waste while enhancing the performance of composite, superfine cement-based grouting materials. MethodsSuperfine cement-based grouting materials with different mixing ratios were prepared by using superfine cement as the basic material, fly ash (FA) and mineral fines (MFs) as primary admixtures, and modified bentonite, methyl cellulose ether (MCE), U-type expansive agent (UEA), and magnesium oxide (MgO) as modifiers. These grouting materials and pure superfine cement were examined using macroscopic performance analyses, including tests of grout rotational viscosity, compressive strength experiments, and groutability tests. In ccombination with microscopic analysis through scanning electron microscopy (SEM), this study systematically investigated the laws of impacts of different mixing schemes on the fluidity, stability, peak hydration temperature, and mechanical strength of composite grout. Results and ConclusionsVarious admixtures and their ratios exhibited significant nonlinear superimposition effects on the bleeding rate and stability of grout. Specifically, MCE enhanced the stability of grout but inhibited its mobility. The coal-based solid waste admixtures effectively reduced the peak hydration temperature of grout, with a maximum decrease of 48.6%. UEA and MCE delayed the onset of peak hydration temperature by 1−4 hours. In terms of mechanical properties, the bentonite-modified systems yielded superior 28-day compressive strength compared to MCE-modified systems. UEA outperformed MgO in shrinkage compensation and late-stage strength enhancement, while also mitigating the strength retrogression observed in the pure cement system. Grouting tests demonstrate that the mixing ratio scheme comprising 70% superfine cement, 20% FA, and 10% MFs, combined with 10% UEA and 5% bentonite, exhibited the optimal diffusion performance, bonding property, and cost efficiency. The results of this study can provide a reference for enhancing the performance of modified cement-based materials and promoting the high-value utilization of coal-based solid waste.