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CONSTRUCTION WORLD
APRIL
2017
44
WASTE MANAGEMENT AND RECYCLING
According to Mohamed Docrat, production
superintendent at AfriSam’s Jukskei Quarry,
it is “in the nature of the game” that unused
concrete will be returned to their on-site
readymix facility on those occasions when
customers over-order or when there are
other factors that prevent the customer
from taking full delivery.
“We have had a readymix batching plant
on our quarry site for many years, and
have always faced the challenge of having
to accommodate the returned concrete
in a way that is safe and environmentally
acceptable,” says Docrat.
“The returned concrete comes in at any
time of the day or night; it can’t be left in the
mixers, of course, so it has to be dumped,
even after hours when there is not as much
supervision.”
He says that a number of solutions have
been tried over the years – some more
successful than others – including the
filling of mined out areas, the creation of
roadways and block making for separation
barriers in the quarry.
“One of the issues is the inconsistency
of the material being returned,” he says.
“Applications employing formwork, such as
block making, are often constructive, but
when the concrete arrives back as a ‘slush’,
it may not keep its shape in the formwork
and this can create other problems.”
Solution
Many of these ideas worked quite well in
terms of the purpose for which they were
designed, but they all came with associated,
and sometimes unpredictable, costs.
“Ideally we wanted a solution that could
pay for itself by generating a revenue
stream,” says Docrat. “So last year the
management team put their heads together
to come up with a way of generating a
saleable product from the waste.”
The solution focused on the idea of
adding the recycled concrete to the
quarry’s G5 product, as this was a product
category that was permitted to contain
material from multiple sources (unlike
products within the G1 classification,
which were single-source only).
Indeed, the process of breaking up the
returned concrete generates plenty of fines,
says Docrat, which is beneficial to the
product as the class specification for
G5 demands that it must comprise about
80% fines.
It was decided that returned material
would mainly be dumped in a specified area
at Jukskei Quarry some distance away from
the main quarry site.
“It was important to contain the returned
concrete, because it can run when it is wet,”
he says. “After enough drying time, we send
in an excavator-mounted hydraulic hammer
to break it up into sizes between about
250 mm and 400 mm. It is then loaded by
excavator into a dump truck, which hauls it
to a secondary stockpile.”
The plant operators, as well as the
load-haul operators, play an important
role in checking that the material is within
specification. For instance, the load-haul
operators must be selective in what they
bring to the stockpile, so that it can be
blended in the appropriate quantities
before crushing.
The blended material is then fed into
a jaw crusher, after which the crushed
material goes onto a production stockpile.
Here, a loader operator again blends, or
homogenises, the material before it is taken
by dump truck to a set-back stockpile,
where it is ready for sale.
“We add between 15% and 20% of
RECYCLING SOLUTION
concrete returns
After years of trying to responsibly resolve the headache of readymix
wastage and returns, AfriSam’s Jukskei Quarry in Midrand has made
a breakthrough that will see this unsightly and potentially problematic
material reused in its G5 sub-base product for road-building.
LEFT:
Mohamed Docrat, production superintendent at AfriSam's Jukskei Quarry showing some of the paving work done using recycled concrete.
RIGHT:
The return concrete has also been used around the readymix plant to pave large areas.