<p>Rock grouting involves injecting grout material into a rock mass to reduce its permeability and increase its strength. A critical aspect of grout design is determining the water/cement ratio, which primarily governs the flowability and viscosity of the cement grout. This paper examines the influence of the water/cement ratio on grout flow in a single rough-walled rock fracture using computational fluid dynamics (CFD) simulations. To better understand the grout flow within a rough-walled fracture, the fracture's roughness is modeled as a simplified sinusoidal geometry. The study identifies four distinct flow regimes of cement slurry in a rough-walled fracture. As the Reynolds number increases, the flow transitions through the following regimes: (1) yield stress-dominated flow, (2) laminar flow, (3) laminar flow with recirculation zones, and (4) non-linear flow. Under the same pressure conditions, cement slurry with a higher water/cement ratio flows more rapidly due to its lower cohesion, making it more prone to transitioning into the non-linear flow regime. Furthermore, the study reveals that, as the fracture roughness increases, the transition to the next flow regime occurs at a lower Reynolds number. The findings suggest that, in the presence of recirculation zones, there is a risk of insufficient sealing between the asperities of rough-walled fractures. This highlights the need to optimize the water/cement ratio and injection pressure, based on the fracture morphology, in order to achieve the effective sealing of these rough-walled fractures.</p>