Michael Bleby
28 August 2008
Johannesburg — IN PREPARATION for the expected start in early 2010 of regular flights of the A380, the world's largest passenger aircraft, airports operator Acsa is strengthening and widening runways and taxiways.
At Johannesburg's OR Tambo Airport, the 3,4km-long secondary runway has been strengthened. In the three years to June, 12km of taxiways were also upgraded. The major taxiway was doubled in width from 30m to 60m and the central 30m-wide strip was strengthened to increase its load-bearing capacity.
The taxiways consumed about 300000 tons of aggregate -- the dolomite, chlorite and quartzite stones that provide bulk in road surface material. Just over half of this, about 180000 tons, contained recycled asphalt pavement, or RAP in the industry jargon, and a further 80000 tons of recycled material was used as sub-base material in the road shoulders, for a total saving of about R15m.
Compared with a total project cost close to R300m, the saving from recycling is small. Still in its infancy in SA but widely used overseas, asphalt recycling is something the industry's leaders are keen to push. And while numerous obstacles lie in their way, the current inflationary environment seems to be their best ally in getting the message across.
"It makes a lot of economic sense to recycle. The environmental thing also makes sense. What we're trying to do in SA is say we need to use this material optimally, to reduce reliance on virgin materials," says Trevor Distin, CEO of the South African Bitumen Association , an industry group.
Asphalt, the substance that seals and strengthens roads, is made by heating aggregate with bitumen, an oil derivative, to hold it together. Soaring oil costs, along with increased demand for construction materials in the local economy, have seen the bitumen price double over the past two years to more than R6000 a ton. Over the same period, the price of aggregate has risen to about R130 a ton from as low as R80, says Herman Marais, the company's director of materials technology at Benoni-based Much Asphalt, the country's largest supplier.
The main benefit from recycling old asphalt comes from the saving in aggregate costs, although some of the old bitumen binder can be re-used as well.
In the US, Distin says, 80% of the asphalt that comes out of pavements -- about 80-million tons a year -- is re-used. More asphalt is recycled than glass or paper each year. In Europe, the volume recycled is close to 50%. In SA, by contrast, the industry is struggling to overcome a widespread perception that recycled asphalt is second-rate.
RAP is not a new practice. Rather, it is an old one that has had a bad experience in the past. In the 1980s there was a big drive to recycle asphalt, but with very high mixes of recycled material. The taxiways at ORT have about 15% RAP in them, which is such a low proportion that it has no structural effect on the material. Last time around, however, the proportions used reached as high as 70%. Many of the asphalts failed prematurely and the memories of that time provide a large hurdle to its acceptance now.
Much Asphalt, a unit of construction company Murray & Roberts, has for the past two years been offering a discount for buying RAP to boost demand.
"It's not much," says Marais. "We just look at the cost saving there is in re-using aggregate and bitumen and taking a little bit back for ourselves for the risk".
RAP can safely be used in higher proportions than it is most of the time in SA, says Derick Pretorius, a director with Cape Town-based Arcus Gibb, an engineering consultancy. Resurfacing work done at Hachiya Airport in Japan used RAP mixes of up to 40%.
The problem is that SA lacks the experience to get the mixtures right at higher levels, he says.
There are also cost considerations. The price difference between virgin aggregate and RAP in the US is much greater than in SA, Pretorius says, which encourages recycling in that country.
Higher transport costs also stand in the way. Because RAP must be returned to a mill to be heated and mixed with the fresh aggregate mix -- the technology does not exist in SA for the necessary onsite milling and asphalt production -- old asphalt has to be transported from the site to a mill, milled at 160° C and then returned. The break-even distance is about 40km, Pretorius says. Any further than that and RAP ceases to offer a price benefit.
But costs are rising. Other industries such as construction devour the same stone as the road makers and for them it is cheaper. Concrete, for example, doesn't require the same precise stone sizes as asphalt, which needs stones to be ground to specific sizes for different types of road.
"Compared with the rest of the industry, the asphalt sector is taking relatively small quantities (of aggregate) in construction," says Pieter Molenaar, a pavement principal specialist with Johannesburg-based engineering firm Stewart Scott International. "So if the producers of aggregate say 'If you want specific quality of stone there's a premium in price to be paid', this is now where the asphalt producers start thinking, is it possible to start using RAP? Isn't that a suitable alternative?"
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