Construction World September 2022

The quarry is a big supplier to asphalt markets which it supplies with its sought-after products – especially 10 and 20 mm road stone.

primary, secondary and tertiary sites of the plant and a pipeline taking slime away from the plant to the pit. “We supply water to all the screens and cyclone. Including the dewatering screen, there are six screens across the primary, secondary and tertiary plant,” says Du Preez. In the primary section, rock is broken down from 600 mm to 85 mm fragmentation. “We have a secondary crusher in the primary section which crushes the stone down further before it goes onto the ISP. Our secondary crushing is the biggest process and it has the most conveyors and most screens. This where smaller products such as concrete stone and sand are produced.” The tertiary plant makes a coarse and a fine sand. The latter is used by the likes of Much Asphalt and the former by ready-mix customers. At the tertiary plant smaller sizer of aggregate, 6, 7, 10, 14 mm are produced while it also produces 20 road stone aggregate. Challenges Even though the facility is using its own water, there is no

getting away from using Eskom. “Because the water for the screens is pumped via the underground pipelines, the escalating electricity cost has been significant. Even with the lower demand for especially road building product resulting in us running at lower capacity, our electricity costs are still almost 50% more than before,” says Du Preez. In addition to the steep increases in electricity cost, the ongoing load shedding has been challenging from a scheduling, planning and especially time perspective. “If the load shedding schedule is not adhered, resulting in a power outage while under load and rock gets stuck in the jaw crusher, that machine can be non-functional for a day or two,” says Du Preez. Optimisingefficiency Rooikraal Quarry is fortunate that the depth from the overburden to competent rock is mere 0,5 m. The result is that development costs are very low, and planned drilling and blasting only has to happen once a month. “The fairly square shape of the shallow pit allows for big blasts,” says

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An aerial photo showing the close proximity of the dolerite and dolomite pits.

Rooikraal Quarry’s dolerite is crushed to produce an array of material sizes.

38 CONSTRUCTION WORLD SEPTEMBER 2022