Characteristics of grouting coal rock under different water–cement ratios: Analysis of microscopic pore parameters and macroscopic mechanical properties

Grouting technology has evolved into a pivotal technique for ensuring the structural stability of rock mass engineering. To develop cement-based grouting materials tailored to complex rock mass engineering and enhance their stability and solidification-strengthening efficiency, this study systematically investigated the effect of w/c on slurry performance using ordinary Portland cement as the base material. Core properties, including setting time and compressive strength, were tested, coupled with microstructural characterization via x-ray photoelectron spectroscopy and low-temperature N2 adsorption. As the w/c ratio increases from 0.5:1 to 0.7:1, the initial setting time extends from 4 h 12 min 35 s to 6 h 13 min 12 s, the final setting time prolongs from 6 h 05 min 16 s to 11 h 12 min 44 s, and the elastic modulus decreases from 1.23 to 0.49 GPa. The results show that the optimized slurry with a w/c of 0.6:1 exhibits superior stability and curing strength, balanced elastic modulus and ductility, and a 109.42% higher uniaxial compressive strength than the raw rock sample. Microscopic analysis reveals that the high alkaline hydrolysis surface precipitation coupling mechanism forms a stable heterogeneous interface, rendering the slurry microstructure denser and more uniform with effectively filled pores. All tests were performed in triplicate, and the average values are reported. This study provides a grouting parameter optimization method suitable for complex rock stratum conditions, with significant engineering practicality and application value.