once constructed is crucial to extend
the service life to the maximum. If
the application is to be done on a road
already constructed, the surface needs
to be hard-packed by compaction and
grading and must have as little residual
dust as possible before spraying to
assist DUSTAC penetrating the surface.
“Dustac is a green
product - Nontoxic, renewable
and environmentally
friendly. “
Properties and dilution
•• The initial and subsequent
rejuvenation applications of DUSTAC
are generally accomplished by
spraying a solution of the powder and
water onto the surface to be treated.
As the percentage of solid matter
in the solution affects the viscosity
or “thickness” of the solution, it
is necessary to dilute the liquid
DUSTAC to 10 to 30% solids. This is
necessary, as penetration into the soil
particles is affected by the “thickness”
of the solution and logically, the
finer the particles, the more difficult
penetration becomes. The converse is
true for coarsely graded soils where a
higher solids content application can
be used.
•• DUSTAC can be used as either –
* a powder supplied in bags, or
* a solution delivered by road
tanker.
•• To explain the terminology of solids in
solutions it is necessary to understand
that the specific gravity of a solution
increases as the solids content is
raised. Water has an SG of 1 and
therefore a litre of water weighs 1
kilogram. A DUSTAC solution of 5053% solids is the maximum effective
dilution as the viscosity or “thickness”
would increase handling problems
such as pump ability. Therefore the
liquid version is supplied at 50 to 53%
solid content, which is the optimum
in terms of transport costs. This liquid
DUSTAC has an SG of 1.267 which
implies that a litre would weigh 1.267
kilograms.
• To explain the effect of Specific
Gravity on the product application,
it should be considered that DUSTAC
liquid at 53% solids is 1.267 times
as heavy as water. Therefore the
recommended dosage is 1 litre per
square metre. The solid’s equivalent
is 1.267 x 0.53 (percentage solids
divided by 100) = 0.67 kg per m2.
• Logically, the application rate in lt/m2
will increase as the product is diluted
with water, but will still yield the mass
of solids as recommended. Assuming
a dilution of 20% solids, the equation
would be 1.267 x 0.20 = 0.25 kg
solids per m2. If the original factor of
0.67 is then divided by the 0.25 kg
of solids, this will equal = 2.68 lt/m2.
The SG describes the “thickness” or
viscosity of the product and obviously
affects the penetration of the liquid
into the soil. If the substrate is of
a clay nature (fine compacted silt)
the penetration will be minimal
with a “thick” or viscous solution
and therefore needs to be diluted
with water. The converse is true for
sandy or loosely packed soil where
a “thicker” or more viscous solution
is required. This is largely based
on experience or pre-application
trials. An added note which requires
mention is the fact that 20 to 53%
solutions increase in viscosity under
low temperature conditions and might
desIgn Namibia October - December 2013
39