Optimization of Mix Proportions for Type IV Cement-Based Grouting Materials Using Orthogonal Experimental Design

This study systematically investigates the effects of water-to-binder ratio, total binder content, silica fume content, and fly ash content on the fluidity and compressive strength of Type IV cement-based grouting materials. An L₁₆(4⁴) orthogonal experimental design was adopted to evaluate the influence of these four factors on initial and 30 min slump flow, as well as 1-day, 3-day, and 28-day compressive strength. The range analysis results indicate that silica fume content exerts the most significant effect on initial slump flow, while the water-to-binder ratio predominantly governs the 30 min slump flow and early-age compressive strength, such as at 1 day and 3 days. The total binder content is identified as the key factor influencing the 28-day compressive strength. Furthermore, supplementary tests on the combined incorporation of fly ash and silica fume reveal that silica fume enhances early-age strength but reduces fluidity, whereas fly ash improves fluidity but promotes later-age strength development, with an optimal substitution range for both admixtures. Microstructural analyses including XRD and SEM and hydration heat tests further elucidate the underlying mechanisms, demonstrating that the effects of the two admixtures optimize the hydration process and microstructure densification. Based on the comprehensive evaluation, the optimal mix proportion was determined as A₃B₂C₄D₂, corresponding to a water-to-binder ratio of 0.31, a fly ash content of 15%, a total binder content of 690 kg/m³, and a silica fume content of 8.5%. This optimized formulation achieves a balanced performance in both workability and strength development.