Canadian Clay Products, Inc.
|Canada's Major Bentonite Producer|
Bentonite as a Sealant
Bentonite is a commercially available clay consisting mainly of the clay mineral Montmorillonite and occurs in two main forms in nature; namely a sodium variety and a calcium variety. The two varieties differ mainly in that sodium bentonite is known to swell to several times its original volume when contacted by water. Calcium bentonite on the other hand swells to a much lesser degree.
Bentonite is noted for its affinity for water and for tremendous swelling properties. It can be described as a bundled plate structure, the surface of which is populated by sodium ions. The addition of water causes the sodium ion to hydrate, generating a negative charge on the bentonite plate. Since like electric charges repel each other the platelets are moved apart causing a phenomena called "swelling". The rate of swelling depends upon the fineness, grade and how the bentonite is handled. All grades expand very slowly when water is poured on them, much faster when they are poured into water. Fine powdered bentonite grades absorb water slowly; intermediate and specially sized bentonite absorbs water more rapidly.
Bentonite absorbs nearly five times
its weight of water and at full saturation it occupies a volume of 12 to
15 times its dry bulk weight. On drying it shrinks to its original
volume. Swelling is reversible - it can be (wetted), swelled and
(dried), shrunk an infinite number of times if the water used is fairly
pure. This swelling is important, since the entire swollen mass - that
is clay and water -
Natural clays are generally
combinations of different types of clays in varying quantities. However,
most clays contain substantial
Bentonite however, can be used in a practical fashion when mixed with soils because:
product is shipped dry and applied as a dry granulated material and
hence is easily handled; and
Bentonite in contact with water
remains flexible at all times. It never becomes rigid, sets or cures. It
has existed underground in its present mineral form for many thousands
of years. Therefore, by retaining an axle grease type consistency, it is
not subject to tearing, ripping, cracking or any problems to which more
rigid systems are susceptible. The flexible expanding and self sealing
Clearly, this can be a hit and miss approach if you don't know where the seepage area is. But since the water seepage is moving toward the leaking area it will carry the bentonite with it. Pinpointing the exact spot of the problem is not necessary, but of course it is more economical if the general area seepage is known.
The bentonite can be scattered dry over the surface from a boat or blown by a gunite compressed air system over the surface of the water. In addition, a bentonite slurry can be pumped into the system either at the influent or over the surface of the water.
Bentonite can be admixed with soils with a high seepage, or permeability rate and thereby lowers the permeability, or seepage rate in direct proportion to the amount and type of bentonite added and the uniformity of blending.
How bentonite works:
Water cannot go through a grain of sand but by taking circuitous can easily find its way through the air voids in the soil. Beach sand containing 30% or more air spaces allows water to leak readily.
The same soil can be made impermeable with the BENTONITE. When trapped within the voids, BENTONITE swells in contact with water. While the swelling of the BENTONITE is restricted by the sand and gravel grains, the BENTONITE expands to fill the voids and forms a tough, leathery mineral mastic through which water cannot readily move.
A 2 to 3 inch seal of BENTONITE and soil is as impermeable as a 12 to 18 inch layer of packed native clay.
In the past native clays of variable quality have been assumed to be as effective means of containing the water from ground infiltration. However there are several problems:
variable quality of the natural clay.
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