Filtration of cement-based grouts measured using a long slot

• We manufactured a long slot with a defined constriction of 75 μm.
• We used it to examine filtration of three cement based grouts with d95 = 12–30 μm.
• Filtration occurred at the constriction for all grouts independently of grain size.
• Filtration of grouts was also tested with short slot and penetrability meter.
• Poorer penetrability was measured with the other equipment.

Penetrability of cement-based grout is an important issue when sealing the rock around tunnels and measurement of this property of the grout is needed for designing the grouting process and the development of grout. This paper investigates plug-building or the filtration process in a long slot where a slot constriction is placed relatively far from both the “borehole” and the end of the slot. In this slot, a certain shear stress develops before and after a constriction, which may influence plug-building at the constriction. This method is also compared with short slot and penetrability meter. The smallest groutable fracture for all three measured grouts is reasonably close to 75 μm. Measurements using the long slot showed better penetrability results compared to the short slot and the penetrability meter. The short slot is more practical and gives reasonably good results. The penetrability meter underestimates the penetrability of the grouts.