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Bentonite 3

The document discusses the preparation and properties of bentonite slurry used in concrete construction. It states that bentonite slurry viscosity should be low to allow easy pumping over long distances and removal of suspended particles, but must have enough gel strength to prevent settling if pumping is interrupted. When preparing bentonite slurry, fresh water and proper mixing techniques are important to fully hydrate the bentonite and avoid clumping. The amount of bentonite powder added depends on the desired slurry properties.

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85 views1 page

Bentonite 3

The document discusses the preparation and properties of bentonite slurry used in concrete construction. It states that bentonite slurry viscosity should be low to allow easy pumping over long distances and removal of suspended particles, but must have enough gel strength to prevent settling if pumping is interrupted. When preparing bentonite slurry, fresh water and proper mixing techniques are important to fully hydrate the bentonite and avoid clumping. The amount of bentonite powder added depends on the desired slurry properties.

Uploaded by

visanu
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© © All Rights Reserved
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contaminated slurry with fresh or reconditioned slurry before the concrete is placed.

Sometimes there can be a build-up of fine silt and clay particles in the slurry which cannot
be removed by conventional desanding or desilting equipment. A practical upper limit has
therefore to be set on the density of the slurry, after which it is considered to be unsuitable
for re-use.

4.1.5 Cleaning

Suspended soil particles can be removed from a slurry more easily if the slurry has a low
viscosity. Desanding becomes increasingly difficult as the viscosity of the slurry
increases, and also as the amount of suspended solids increases.

4.1.6 Pumping

Pumping bentonite slurry over distances of several hundred metres can become difficult
and inefficient if the viscosity of the slurry is too high or the slurry contains a large amount
of suspended solids. The slurry should have low viscosity to minimise the energy required
for pumping but should have sufficient gel strength to prevent soil particles from settling
out in the delivery lines if pumping is interrupted.

5 PREPARATION OF BENTONITE SLURRY

When a bentonite slurry is being prepared, the objective is to achieve maximum hydration
of the bentonite. Potable quality fresh water from a mains supply should be used in the
mixing process to achieve the best results. If there is any doubt about the quality of the
water, a chemical analysis should be carried out to determine its suitability or the need for
chemical treatment before use.

Salt water should not be used in the preparation of bentonite slurry because there is no
simple chemical treatment available to remove the sodium chloride.

The presence of calcium or magnesium in fresh water will inhibit dispersion of the
bentonite powder, but it is a relatively simple matter to treat these chemically before the
water is used. Calcium can be removed by soda ash (sodium carbonate) which precipitates
out the calcium as calcium carbonate. Care must be taken not to over-treat the water, since
this will provide an excess of carbonate ions which will hinder hydration. Magnesium can
be treated with caustic soda (sodium hydroxide) which can also be used to provide some
alkalinity to assist in dispersing the bentonite when it is mixed.

Bentonite slurry can be prepared either in batches or in a continuous process, depending on


the type of equipment used. The bentonite powder must be added to the mixing water
gradually in order to ensure that all the particles are wetted and do not clump into partially
hydrated balls. Typically, the bentonite powder is added through a simple venturi hopper
or directly into a high shear mixer. The mixing equipment must generate sufficient shear
to ensure that all the individual bentonite particles are dispersed in the mixing water. The
quantity of bentonite powder to be added to the mixing water depends on the quality of the

9
© Federation of Piling Specialists – January 2006 (2nd edition)
(first published April 2000)

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