Objective The filling of grouting materials plays a significant role in ensuring the performance of anchoring structures. This study aims to further enhance the fluidity of grouting materials, reduce their dry shrinkage in the curing process, and ensure complete filling. This will help improve the bonding property between the anchoring body and the rock and soil mass to be reinforced.

Methods Using cement as the primary material, as well as fly ash and metakaolin as admixtures, this study designed and prepared 20 groups of binary and ternary mixtures and one control group. Through tests of the fluidity, bleeding ratios, and mechanical strengths of these mixtures with different mix ratios, this study determined the impacts of metakaolin and fly ash on the performance of cement-based grouting materials. In combination with the X-ray diffraction (XRD) analysis and scanning electron microscopy , this study revealed the mechanisms underlying the regulation of metakaolin and fly ash for the performance of cement-based grouting materials. Finally, this study proposed the optimum mix ratio of grouting materials while considering the fluidity and filling ability of grouts, as well as the load-bearing capacity of the anchoring body.

Results and Conclusions  With the metakaolin and fly ash contents were controlled at approximately 6% and 15% to 20%, respectively, the resulting grout exhibited a reduced viscosity of 0.16 Pa·s and a reduced bleeding rate of 2% at γ = 100 s⁻¹ compared to pure cement grout. Furthermore, its compressive strength increased to approximately 30 MPa at day 7 and about 32.7 MPa at day 28. In this case, the cement-based grouting material delivered the optimal overall performance. The XRD and SEM analyses indicate that metakaolin and fly ash exhibited significant synergistic effects when mixed into the ternary mixtures, as evidenced by a faster hydration rate, a more even distribution of hydration products, and a denser microstructure. The results of this study provide a scientific basis for enhancing the performance of cement-based grouting materials by using metakaolin and fly ash as admixtures, offering a valuable reference for the design and applications of grouting materials in anchoring engineering.