Modern Quarrying Q1 2019

ON PHOTO: AFRISAM EIKENHOF QUARRY Mines and processes andersite rock

T he andersite rock found at AfriSam’s Eikenhof quarry is one of the hardest and most abrasive aggregate materials you can find at any quarrying operation in the world. In the quarrying circles, granite is mostly regraded the toughest rock to crack, but its 340 MPa average strength is an easy crush compared with andersite. According to works manager, Yedwa Christopher Mgxekwa, the strength of the andersite rock at Eikenhof is between 400 and 600 MPa. The tough nature of the rock presents both challenges and opportunities for the quarry. On the downside, the highly- abrasive rock doesn’t have any mercy for the equipment that handles it. Therefore, equipment lifecycles are much shorter, while wearable components wear much faster than at any other operation. On the upside, the uniaxial compressive strength of the rock makes Eikenhof the supplier of choice for a wide range of customer groups, all the way from asphalt and concrete TURNING CHALLENGES INTO STEPPING STONES Mining and processing andersite rock – an extrusive rock intermediate in composition between rhyolite and basalt – is no walk in the park. Its high silica content makes it too abrasive and a nightmare for every piece of equipment that handles it. However, at Eikenhof quarry, AfriSam is riding on the rock’s most favourable property, the high uniaxial compressive strength, to produce highly sought after material for road construction and concrete production. Munesu Shoko was recently on site.

AT THE QUARRY FACE

producers, to lintel and tile manufacturers, among many others. In concrete production, for example, the compressive aggregate strength is an important factor that influences the selection of an aggregate supplier. Given that aggregate is commonly considered an inert filler, which accounts for 60 to 80% of the volume and 70 to 85% of the weight of concrete, aggregate strength plays a major role in the overall strength, workability and durability of concrete. Rising over challenges A major challenge on site is the tough nature of the rock, especially its processing. “Our andersite rock is very abrasive. It eats into anything that handles it,” says Mgxekwa. To give an idea, the maintenance team has to change crusher liners every two weeks across the different areas of the processing plant.

26

MODERN QUARRYING QUARTER 1 - 2019