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Barrier and cutoff walls: originally conceived for a one phase self-hardening slurry cutoff wall construction
method, IMPERMIX® because of its intrinsic properties of very low permeability and chemical compatibility with most
contaminants quickly served other techniques that can create barriers without trenching like deep soil mixing walls,
jet grouted barriers and vibrated beam thin walls.
When hydraulic conductivity reaches as low as E-10 cm/sec and below, a practical limit is achieved
in terms of testing laboratory capabilities. The great affinity of slag cement for water causes the cured slurry to
continue hydrating while it is permeated. IMPERMIX® exhibits what we call a threshold hydraulic gradient below
which no flow by advection will occur and the barrier becomes totally impermeable. Molecular diffusion is the only
means of chemical transport through the barrier at this point and limit conditions then determine how much
chemical may escape the containment. All things being equal, IMPERMIX®'s tortuosity is so complex that the
coefficient of molecular diffusion to salt can be 10 to 50 times lower than of a typical clay liner or
soil-bentonite slurry wall.
The conventional definition of porosity as per ASTM does not apply to self-hardening slurries,
in the same way as it does not apply to sodium silicate gel. You cannot define a wet material's physical properties
by destroying it by fire. Cured IMPERMIX® should be seen as a mineral gel of extremely low porosity in its natural
condition, hence its very low permeability. Since the actual "pore volume" is unknown, compatibility tests have to
be run differently:
a) conventional hydraulic conductivity tests, some time run at gradients of 100 or 200 limit themselves to
establish a trend of decreasing permeability under the permeant, after establishing a base line with tap water.
b) IMPERMIX samples are prepared using the worst site water sample as the mixing water. And testing them as per a).
This is the proof positive test.
c) An other test, which is akin to a molecular diffusion test, by which a sample base line permeability is measured
with tap water as permeant and subsequently immerged in a bath of contaminated water for a period of months.
And then retested for hydraulic conductivity again with tap water. Given that sorbtion and molecular diffusion
occurs from the outside toward the sample's center, chances are that the porosity has decreased and the permeability
has therefore also decreased, if measurable.
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