TECHNOLOGY
is doing something about its quality, he
or she will be much slower to point the
finger of blame at the quarry,” says Saartjie
Duvenhage, chairperson of Aspasa’s
technical committee on
quality management.
The Glen Douglas laboratory is not the
biggest in the Afrimat group, which has
a state-of-the-art facility in the Western
Cape capable of doing the full battery of
tests. Yet its on-site laboratory is still at
the top end of the scale by South African
standards. This is an expense which many
independent quarries are unwilling to
make, says Duvenhage, “because they
don’t understand the value to the business
of a laboratory and in fact often think it’s a
waste of time and money.”
Glen Douglas mitigates the risk of
customer disputes by sending out regular
reports of its aggregate quality to its
customers, which engenders confidence.
Duvenhage says there is a
misconception in the industry that
quarries have to have a facility equivalent
to that of Gen Douglas, or none at all.
“Though it is more efficient and
practical to test aggregate with appropriate
equipment, the reality is that gradings
can be done manually for the cost of a
sequence of sieves and a good balance.
The major challenge is to persuade
quarries that they can still test in the
absence of an expensive laboratory on site.
Without one, they rather don’t do
any testing.”
There is no statutory requirement to
have a laboratory, or to do testing, but its
absence creates a problem when there are
quality disputes with clients. In addition,
major customers like SANRAL have
higher than average specifications and an
internal requirement for rigorous testing.
Boitumelo Mothobi, laboratory
analyst at Afrimat Glen Douglas, says if
he needs to do more detailed tests than
his laboratory is specified for, he sends
a sample to one of the local ISO 17025
accredited-labs, as Afrimat’s own Western
Cape facility is too far. Mothobi says they
also regularly send out a couple of samples
a year for external testing.
Successful QA is founded on
communication
“Successful quality control is really
founded on communication,” says
Duvenhage. The most basic test that
needs to be performed on-site is a grading
analysis. This tells the mine that it is
producing the aggregate size that it says
it is selling. The sample is put through a
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An on-site laboratory is more efficient, but the basic tests can nonetheless be done manually.
series of sieves of decreasing mesh sizes,
which can be done by hand. The only
thing that requires electricity for this test
is the balance.
“We look at the percentage of material
that is retained on each sieve and calculate
the cumulative percentage retained and
the cumulative percentage passing. This
is plotted on a graph and has to match
the requirement of the customer, and
also the agreed specifications of standard
SANS 1083, which is the requirement
for concrete aggregates,” says Mothobi.
abrasion resistance – but the basic test is
for size. Duvenhage says the ideal is one
test for every 500t, but sometimes this is
impractical and could be highly disruptive
to manpower (on some mines this may
require four or five tests a day).
She says the way to get around this
demanding requirement is to establish a
history of consistency by regular testing
and by supplementing that testing with
highly experienced staff in whom there
is confidence they would visually pick up
any variation in quality. Glen Douglas
“This leads to a costly dispute between quarry and
customer – and only if the quarry has a consistent
testing history will the odds be in its favour.”
SANS 1083 describes the lower and upper
envelope limit of each aggregate size. If a
client requires 20mm stone, then SANS
1083 sets the parameters for that. In line
with SANS 1083, a quarry and a customer
may agree on a product that falls outside
of the SANS 1083 envelope.
“A quarry cannot consistently claim
it is producing a certain size, unless it is
doing tests. This is why it is important
to have a laboratory – even if that lab
is under a tree.” There are many other
tests to measure characteristics such as
flakiness, water absorption, strength,
has employees who have been on staff for
20 years or more – one has been there 45
years – and has official testing records
going back many years. They have the
experience to recognise problems. If a
problem has been identified visually, it
is always followed up by a laboratory
analysis.
Mothobi points out that just as
important as testing is the amount of
attention paid to the quality and extent of
communication between operations and
the laboratory. “When anything changes
at the plant, such as a change in sieve
QUARRY SA | JANUARY/FEBRUARY 2019_23