Bentonite is an absorbent clay. Bentonite suspended in water forms a thinning material called bentonite slurry, which is used in the engineering industry. Bentonite slurry’s most significant property is its permeability, according to Geo-Solutions.com. Bentonite slurry has been used in the United States since the 1940s and increased in popularity in the 1970s.
Bentonite is used to make slurry walls. Slurry walls are used to build tunnels or foundations in areas with high ground water tables, where soft earth is too close to open water, according to RussellReid website. At the World Trade Center site, slurry walls were used to construct the bathtubs.
Bentonite Slurry Advantages
Bentonite slurry has the advantages in the geo-technical engineering industry of cost effectiveness, low permeability and resistance to contaminated groundwater. It is the most common evacuation fluid used for making a diaphragm wall, according to the Civil Engineering Portal website, Bentonite gel’s strength and viscosity allows for cutting, suspension and removal.
United States Environmental Protection Agency Requirements
The US EPA recommends the following properties for bentonite slurries, according to,
Integrated Publishing.com website. “Bentonite samples which exhibit the greatest lowing properties for bentonite slurries: viscosity swell and are the least affected by contaminants are greater than 40 sec, usually chosen for use in the remainder of the com-unit weight around 1,025 kg/m3 (65 pcf), pH between patibility testing. 7 and 10, and a bentonite content of 4 to 8 percent. USACE guide specification CEGS-02444 states that Viscosity API RP 13B-1 >40 sec >1025 kg/m3 Density >1025 kg/m, 64 pcf, filtrate loss
An abstract posted on Informaworld website, authored by Jeffery C. Evans, entitled,
‘Membrane Behavior of Soil-Bentonite Slurry Trench Cutoff Walls,’ 2008, reports encouraging results from investigation of the membrane behavior in bentonite-based soil-bentonite backfills used in cutoff walls for waste containment and site remediation. The results indicate that two model backfills, a natural clay with 89% fines and a mixture of clean sand with 5% by weight of dry sodium bentonite, act as semi-permeable membranes.
Disposal of Spent Bentonite
Bentonite is an environmental hazard that can pollute the water, according to NetReg.gov website. When using bentonite it should be contained within the working area and away from water sources or surface water drains. A construction site using bentonite slurry, should temporarily store spent bentonite in a bulk liquid tank for disposal, according to a RussellReid.com website. Then arrange with an approved disposal facility to vacuum and transport the spent bentonite for disposal.