Pressure Filtration Resistance
Pressure filtration resistance has been a consideration of the high mobility grouting industry for decades. In recent years, the sanded grout and tremie concrete industries have discovered its importance and incorporated testing into their specifications. When grout or concrete is pressurized, water can be squeezed out, leaving hard filter-caked dry components behind. Pressure filtration is measured with a filter press. The API filter press is typically used for grout and the Bauer filter press is used for concrete. In curtain grouting, water is squeezed out at tight apertures causing incomplete void fill. In tremie concrete, hydrostatic pressure can lead to segregation, taking the form of bleed channels that migrate to the surface. Similar to water retention, in augercast piling (ACIP), grout at the bottom of the pile can experience significant pressure from pumping and the weight of the grout above, that can squeeze out mix water, leaving hard-packed filter cake that is impenetrable to reinforcing elements.