Modern Quarrying

High quality dolerite aggregate from B&E International’s Howards Quarry at eMalahleni is keeping Much Asphalt’s nearby static plant well stocked to produce asphalt for the N4 highway project and developments as far as Nelspruit over 200 km east.

As one of Southern Africa’s largest commercial suppliers of hot and cold asphalt products, Much Asphalt keeps a close eye on standards and specifications of both its ingredients and final product, according to eMalahleni branch manager Gavin Roos.

Howards Quarry meets high standardsA loader in Much Asphalt’s stockyard blends dolerite aggregate from B&E International’s Howard quarry.

“The quality of stone we use is an important aspect of asphalt production, as it gives the road its strength,” says Roos. “Dolerite is particularly good for asphalt because it is a strong stone and doesn’t crush under weight, so it is able to withstand the heavy truck traffic that our highways must endure without deteriorating.”

Before making a choice of aggregate supply, Much Asphalt takes samples from source quarries and sends them for specialised laboratory testing.

“This allows us to establish that the key aspects like fraction sizes, aggregate crushing value (ACV) and moisture content are suitable for our use and is in line with Committee of Land Transport Officials (Colto) standards,” he says. “Permeability and adhesion properties are also important, as we must ensure that the bitumen is going to adhere fully to the stone, or this leads to stripping on the road where stones begin to come loose.”

At plant level, the focus is then on maintaining a consistent grading of the stone ensuring that every load that is delivered is up to standard. Howards Quarry trucks in supplies daily so that Much Asphalt always has substantial stockpiles; this helps in retaining a consistency of aggregate, which is blended on site by means of a payloader.

Good dolerite sources are being systematically depleted and quality aggregates produced from this igneous rock have become scarce, according to Howards Quarry manager Andre Kamfer. “The result is often that quality materials have to be hauled over ever-increasing distances, adding to the overall cost of a project. Fortunately in this case, the Much Asphalt facility at eMalahleni – one of 15 static plants that the company operates around South Africa – is just a few kilometres down the N4 highway from the quarry.”

B&E International – a member of the Raubex group of companies and a provider of integrated crushing, mining and processing solutions – has until recently been operating its Kusile Quarry in this area. Now at the end of its life, Kusile Quarry’s production has been replaced by Howards Quarry, which has an expected life of 25 years.

“Independent tests verify that this hard rock dolerite source is far superior to anything else found in the region,” says Kamfer. “This allows us to provide superior quality aggregates to asphalt plants, mines, readymix companies and other contractors in the area.”

Roos emphasises the need for continuous, daily testing at his on-site laboratory. After every 100 t of aggregate delivered, testing is done to determine sand equivalent, fines, grading and other factors that affect the ‘recipe’ for high quality asphalt.

“Based on our test results, we then make adjustments after bringing in different fraction sizes from a -4,75 mm dust up to a 28 mm stone,” he says. “Depending on the consistency of the stone, gradings and fines, we adjust our final mixture because the asphalt makes use of a combination of those fractions. The more consistent the stone received from the aggregate supplier, the better for us.”

The mix must result in a final grading that aligns with the company engineers’ specifications; on roadwork applications this will also be done in compliance with Colto standards. To ensure the accuracy of the on-site laboratory, its equipment is regularly checked against Much Asphalt’s SANAS-accredited main laboratory in Cape Town. The company’s regional laboratory in Benoni is also used for more technical tests on both aggregate and bitumen.

Recent infrastructure upgrades at the eMalahleni asphalt plant – which was initially adapted and enlarged from a mobile plant – has included an improved conveyor system and storage silos. The plant can also treat recycled asphalt in new asphalt mixes, incorporating between 10% and 20% recycled asphalt.

Howards Quarry produces the aggregate requirements for road building across the spectrum including sub-base, G2, G1, all concrete aggregates and the full range of seal and asphalt aggregates. It also generates railway ballast, gabion and dump rock aggregates, and crusher sands in - 7,0 mm and a -475 mm (super sand) fractions.

www.beinternational.co.za

Contact Modern Quarrying

Title: Editor
Name: Dale Kelly
Email: dalek@crown.co.za
Phone: 083 419 9162


Title: Advertising Manager
Name: Bennie Venter
Email: benniev@crown.co.za
Phone: (011) 622-4770
Fax: (011) 615-6108

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