TECHNOLOGY
Saartjie Duvenhage, chairperson of Aspasa’s technical committee on quality management, at
Afrimat Glen Douglas in Henley-on-Klip.
sizes, the mine manager and supervisors
will notify us immediately to test a sample
to verify we are within the spec.”
This regular communication did not
occur overnight and took years to evolve,
he says. The fact that Mothobi has the
authority to stop operations is also unusual,
as laboratory staff typically do not have such
authority (one reason is that their reports
were historically habitually ignored).
A weakness of testing throughout
the industry has been that while the
laboratory tests and produces reports,
operations personnel do not take notice of
many quarries, only the mine manager
can halt production, but he has many
responsibilities and may not be readily
available, and so the mine will just
continue wastefully producing out-of-spec
material and worse, even incurring the
cost of transporting it. Hence, I believe the
laboratory manager should similarly have
this authority.”
Aspasa is currently involved with
Barry Pearce from Learning Matters etc
together with SANRAL, NLA-SA and
other aggregate users, in developing
a training programme for laboratory
“Regular testing which produces consistent results,
mitigates the risk of customer disputes when combined
with sending out regular reports of its aggregate quality
to its customers, which engenders confidence.”
them. When laboratory analysts have the
authority to stop production – testing is
taken a lot more seriously. The analyst will
only order such an unusual action if the
sample was out-of-spec.
Duvenhage says she lobbies for such
authority to become more widespread.
“On some quarries the material is loaded
directly onto a train. It is easy to load, but
very hard to unload if it later becomes
evident that the batch is out-of-spec. On
24_QUARRY SA| JANUARY/FEBRUARY 2019
analysts to standardise qualifications and
thereafter to strengthen their authority.
At the moment there is no formal
qualification for analysts. The proposed
qualification is at NQF level 4,
equivalent to Grade 12, with laboratory
manager at NQF5, which allows them
to register with ECSA. It is envisaged
that this will be undertaken using the
international standard SIO 17024 for the
deeming of personnel competence for a
particular vocational operation.
A quarry may test twice a day, and after
accumulating a year’s history of testing
it becomes apparent that the product is
entirely consistent. “If the trend of the
graphs is a consistent flat line, there’s no
point in continuing to test so frequently.
The testing frequency can be reduced
and supported by constant awareness
and visual review as to source changes
and alterations in operations. That is
something which comes from experience
and excellent communication – it cannot
be taught. This does not mean sampling
and testing can be done away with: it must
continue to be tested.”
But testing is only viable as an activity
to the extent it is cost effective. If testing
is to be done on a quarry ‘by the book’,
says Duvenhage, it might require as many
as 18 samples to be taken per shift, which
requires employing extra people.
Rules of sampling
Duvenhage says that one of the main
problems in disputes is the sampling
procedure.
“We are looking for a sample that
is representative of the load that
was delivered. If the sample is not
representative, the result will not be
accurate even though the test method
may be correct. For example, lighter fines
tend to gravitate to the bottom of a heap
and is not representative of the entire
batch. There is a specific methodology to
sampling, and the entire testing process
becomes tainted if this is not adhered to.
“Testing requires a sample which tells
us what is in the stockpile. The customer
does not want to know, for instance, what
is on the conveyor belt at a particular
moment in time (although this may be
important for the production manager).
Sometimes the operations on a quarry
push out finer and sometimes coarser
material, so we have to take enough
samples of finer and coarser material to
get a comprehensive idea of what is in
the stockpile. This is best achieved by a
mechanical sampler, but it is an expensive
proposition.
It can also be done manually, provided
it is done according to rules to ensure a
representative sample:
• a sample cannot be taken closer than
a metre to the ground, or there might
be some contamination
• you cannot take just one sample from
a single location on the stockpile, as
there is segregation of coarser and
finer material in the stockpile