Construction World April 2017

WASTE MANAGEMENT AND RECYCLING

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.

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

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

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.

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CONSTRUCTION WORLD APRIL 2017