The experiment utilized a composite cementitious system comprising ordinary Portland cement and fast-hardening sulfoaluminate cement, with crushed limestone serving as the fine aggregate. A full machine-made sand grout was prepared using this system. Silica fume, fly ash, and stone powder were employed as mineral admixtures to investigate their impact on the flowability, compressive strength, and vertical expansion rate of the full machine-made sand grout. Additionally, SEM electron microscopy was used to analyze the microscopic mechanisms of the full machine-made sand grout. Research findings indicate that the concurrent use of mineral admixtures is advantageous in enhancing both the flowability and mechanical properties of the grout while also improving the transition zone between the grout and aggregate. The optimal dosage of mineral admixtures obtained through orthogonal experimentation is 5% silica fume, 6% fly ash, and 8% slag.