Effect of ultrafine process on microstructure and mechanical properties of sulphoaluminate cement grouting materials under high water-cement ratio

In order to solve the problems of poor permeability and low early strength of mineral cement grouting materials, and effectively control the large deformation of surrounding rock in deep roadway, an early-strength superfine cement grouting material was developed by using sulfate cement clinker, industrial by-product desulphurized gypsum and quick lime as raw materials with using calcination treatment and ultrafine processing technology. The effects of particle size on slurry properties, mechanical properties and microstructure of sulphoaluminate cement grouting materials (SCGM) with different water-cement ratios (0.8, 1.0, 1.2) were investigated by various testing methods. The result shows that with the decrease of water-cement ratio and particle size, the setting time of SCGM is obviously shortened, the bleeding rate is reduced, and the compressive strength is gradually improved. At the water-cement ratio of 0.8 and raw material particle size of 1.5 µm, the compressive strength of SCGM2 at 8 h and 7 d is 4.5 MPa and 14.6 MPa respectively, which is increased by 80.0% and 45.5% compared with control group (SCGM0). The initial setting time is as low as 3 min, with almost no bleeding phenomenon observed, and micro expansion achieved. TG-DTG, XRD, and FTIR analyses confirm that the main hydration products of SCGM are AFt, Calcite and C-S-H gel. Moreover, an increase in water-cement ratio leads to higher AFt content while decreasing particle size results in similar effects on AFt formation. Based on CEMDATA18 database, a thermodynamic model of sulphoaluminate cement verifies the evolution trend of hydration products for SCGM under different water-cement ratios. It confirms that increasing the water-cement ratio promotes the formation and growth of AFt. SEM analysis reveals that both water-cement ratio and particle size influence the morphology, composition, and structural compactness of hydration products for SCGM. At a water-cement ratio of 0.8, the interaction between hydration products in SCGM2 forms a dense three-dimensional network structure, which optimizes calculi structure development. It provides new insights for early strength ultrafine cement-based grouting materials.