Microscopic mechanism and macroscopic response of sodium gluconate in regulating the performance of green and low-carbon ultra-fine cement grouting materials

To address the issues of rapid setting, insufficient fluidity, poor injectability and low utilization of solid waste in traditional sulphoaluminate cement (SAC) slurry, and to meet the requirements of deep roadway surrounding rock green grouting reinforcement engineering, a green and low-carbon ultrafine cement grouting material with high fluidity and controllable setting time was developed by ultrafine processing of SAC clinker, calcination modification of industrial by-product desulfurization gypsum and quicklime, and using sodium gluconate as a retarder. The effects of sodium gluconate dosage on the fluidity, setting time, volume expansion and mechanical strength of ultrafine sulphoaluminate cement grouting material (USCGM) were investigated by different characterization methods. The mechanical bearing performance of USCGM cemented crushed stone was evaluated based on sandstone aggregate grouting consolidation tests. The results show that the setting time and fluidity of USCGM slurry are positively correlated with the dosage of sodium gluconate. They increase with the increase of sodium gluconate dosage, while the volume expansion rate and compressive strength of the hardened samples increase first and then decrease. The comprehensive performance of USCGM is the best at 0.5% retarder, with the initial and final setting times of the blank control group extended by 27.51% and 59.23% respectively, and the fluidity increased by 10.81%. Although the early compressive strength (8 h, 1 d) slightly decrease, the compressive strength from 3 d to 28 d increase by 3.3% to 5.83%, achieving a comprehensive improvement in working performance and later mechanical strength development. XRD, SEM, FTIR and hydration heat characterization show that appropriate sodium gluconate helps to delay the early formation of AFt, regulates the morphology of AFt crystals, and optimizes the pore structure of the stone. It plays a triple coupling role of "chemical complexation retardation-physical adsorption water blocking- crystal regulation strengthening". The grouting reinforcement test shows that the peak load and corresponding slip of 0.5% sodium gluconate modified USCGM sandstone cemented specimen are increased by 14.21% and 18.5% respectively compared with the control group, indicating enhanced mechanical bearing capacity and plastic deformation ability.