Experimental study of rapid-setting cement-based slurry using in capsule expansion technology: Mechanical performance evolution and microstructure dependence

Rapid-setting cement-based slurry (RCS) is increasingly used in grouting applications requiring early strength development and rapid load transfer. However, the microstructural mechanisms governing the mechanical evolution of RCS, particularly when combined with capsule expansion technology (CET), remain insufficiently understood. This study investigates the relationship between mechanical properties and microstructure in RCS incorporating chemical additives and CET, using mechanical testing and multi-scale microstructural characterization at different curing ages. The results show that RCS undergoes rapid hardening within the first day and achieves a compressive strength of 10.48 MPa at 28d. The compressive strength increases by 215% during the first day due to accelerated hydration and pore filling. Between 14 and 28d, the elastic modulus stabilizes at 346 MPa, while the toughness index increases by a factor of 13.6, indicating enhanced crack resistance. The failure mode transitions from ductile to brittle, accompanied by notable microstructural densification. The micropore content increases from 29.7% to 78.4%, whereas mesopores and overall porosity decrease. These findings provide insights for optimizing rapid-setting grouting materials used in performance-critical engineering applications.