Pressure Filtration, From Grouts to Concrete-PPT Presentation

PPT Presentation

Pdf Summary

The presentation explains how pressure filtration affects grout and tremie-concrete performance in deep foundations. Under pressure, porous soil or a small opening can draw water from a mix, concentrating cement and aggregate. This can form a filter cake, create bleed channels and pockets, cause segregation, or prematurely harden material. The risk increases with depth and pressure, and is especially significant for lean, sanded grouts used in applications such as ACIP piles and void filling. Even saturated soil can take up mix water when grout pressure exceeds pore pressure; above the water table, capillary forces can also draw water into soil.<br /><br />Pressure-filtration testing provides a practical way to assess stability. The API Filter Press test applies 100 psi to a grout sample and records filtrate volume, cake thickness, and time. Its pressure filtration coefficient (Kpf) relates filtrate volume to initial sample volume and elapsed time. A high Kpf indicates greater water loss and potential instability; a low value indicates better resistance to segregation. Static bleed tests should be used alongside filtration tests, since very unstable grout may block the filtrate tube and produce misleading results.<br /><br />For tremie concrete, the Bauer Filter Press uses a larger sample, 5 bar pressure, and a fixed five-minute test. Filtration loss can indicate total bleeding potential, while bleed rate and static segregation tests help assess concrete stability over the period before hardening.<br /><br />The presentation also describes water-retentive admixtures and other mix adjustments that can reduce filtration and bleeding. Filtration tests are fast and useful in laboratory or field settings for mix development and material acceptance, and can flag concerns about water loss, segregation, and pumping. However, results should be interpreted with complementary tests and an understanding of project conditions.

Keywords

pressure filtration

grout stability

tremie concrete

deep foundations

filter cake

bleeding

segregation

API Filter Press

Bauer Filter Press

water-retentive admixtures