TECHNOLOGY
These samples are then mixed to prepare
the laboratory sample.
The method for representative sampling
is described in TMH5, which is also
currently under review.
“We sometimes see sample problems
where samples are taken directly from a
truck. During transport, segregation can
occur and by the time the truck arrives
at the site all the fine material will have
fallen to the bottom with all the course
material at the top. If you take a sample
from the bottom you will only get a
disproportionately high percentage of
fine material – similarly if you sample
only from the top. Similar segregation
occurs in a silo, where the fine material
congregates at the centre and the coarse
material to the sides,” says Duvenhage.
Due to the challenges with sampling,
Glen Douglas is strict when it comes
to allowing others to take a sample.
Customers must make an appointment to
take a sample and do it with a laboratory
member present who either extracts
the sample himself or monitors the
customer’s sampling method. The sample
is then split with Glen Douglas testing
one half, and the customer’s chosen
laboratory the other. “When we do that,
our product is never out-of-spec,” says
Mothobi. The results are generally close
– and once that has been done once or
twice, customers will rarely question our
results again, he adds.
Industrial applications also require
regular chemical analysis of materials.
Drill samples are then taken before
blasting.
Mothobi explains that the bench is
drilled and samples taken for testing
before commencing blasting, so they
know beforehand the silica content
before proceeding. Different sections of
the quarry have different silica content
and there can be contamination in
between – hence the need for testing
before proceeding with blasting. The
laboratory has a dust-free room for the
XRF analysis, to ensure the most
optimal working environment.
www.quarryonline.co.za
Boitumelo Mothobi, laboratory analyst at Afrimat Glen Douglas.
Testing is not just for the use of
customers, but often gives early warning
of operational issues such as a hole in a
sieve, as evidenced by bigger aggregates
than expected coming through. It
will become quickly evident from the
graphical plot of the grading.
The material grading is as much
dependent on human and machine
activity as on the raw material, and
therefore grading analysis has to be done
regularly to pick up errors.
Future training / tech needs
Barry Pearce of Learning Matters etc
says, “There is currently a big drive to
implement an official qualification for
the testers who produce the results in
the civil engineering laboratories be
they commercial laboratories, primary
(quarries) or secondary (concrete or
asphalt) material producers. The main
aim is to credit them with some form of
official competence in testing as well as
to place value towards the vital function
they provide in ensuring that quality
product conforming to the specifications
is supplied to the clients’ base.”
New technology has been developing
in tandem with skills: Xcentric Crusher,
for instance, has managed to achieve
profitable production levels for improved
crusher buckets, says Pieter van der
Merwe, MD of Xcentric Ripper SA. “The
increase in production per hour, with
long maintenance intervals (lubrication
200 hours), and a powerful heart that
provides the necessary reliability to
work with it constantly, makes out of the
Xcentric Crusher a machine that will turn
profitable your stone crushing or recycling
materials processes.
“This is possible thanks to the patent-
pending technology that applies a
high inertia power train, circular jaw
movement, as well as a new and easy
antiestagnation plate, which prevents large
shredding pieces from getting stuck in
the bucket´s mouth, not allowing them to
enter the crushing jaws. The granulometry
adjustment is easy and intuitive, which
enables a quick variation,” says Van der
Merwe.
QUARRY SA | JANUARY/FEBRUARY 2019_25