Modern Quarrying Q3 2022

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. Optimising efficiency 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 Sterley. “This leads to cost savings as up to 120 000 tonnes of rock is blasted at the same time. The quarry also has wide benches which allow space for bigger blasts.” In addition Villa Liza, the closest community, is 2 km from the quarry. The only structures that are relatively close are 88 kVA Eskom transformer which is located about 260 m from the pit and the quarry’ office which is about 500 m from the area where blasting takes place. This potential risk has been mitigated by innovation in blast designs. “The better you blast the less you have to crush,” explains Sterley. “Our blasting achieves increased fragmentation which leads to easier rock removal, increased truck capacity and less wear and tear on crushing equipment,” says Sterley. “The biggest challenge is sales demand. It is a cut throat market. Road projects are scarce and there are many competitors. In addition, we still have certain customers needing certain products. We are making a basket of products and cannot close taps to make a single product,” says Du Preez. “Because of the demand for 10 mm stone in the asphalt market, the tertiary plant used to run 24 hours a day, the secondary plant operated in two shifts of 9 hours each per day and the primary plant has always been a single shift. The current climate has forced us to play around and be flexible with what plant is operational and when. While we need to maintain our agreed stock levels, we cannot just run the plant. This is a challenge,” concludes Du Preez. l

AT THE QUARRY FACE

Villa Liza, the closest community, is 2 km from the quarry.

In order to produce the various products for the road building industry, a washing process is needed to meet the requirements and specifications of the saleable products

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 sizes 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 are pumped via the under ground 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

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