Construction World October 2015

Asphalt

Asphalt gets progressively greener

Asphalt pavement is 100% recyclable and reusable, with recycled asphalt (RA) milled out of the surface layers of an existing asphalt paved road and then crushed, screened and combined with virgin asphalt mixes for new surfacing applications. RA is added to hot or warm mix asphalt in different quantities depending on the engineering design of the project and the capability of the manufacturing plant. Mobile plant Much Asphalt’s new Amman mobile plant, which was acquired in 2015 and brings its fleet of mobiles to four, is also capable of handling 40% RA. This unit is already in full production on a N1 contract near Bloemfontein. According to Much regional manager Francois van der Spuy, the capability of this plant was a major factor in securing the contract between Glen Lyon and Sydenham. “When we acquired the new mobile plant we were expecting SANRAL (the South African National Roads Agency Limited) to specify more 40% RA work and it has paid off for us in this case,” he said. The new plant will supply 240 000 tonnes of bitumen treated base (BTB) with A-P1 binder, 40% RA, rejuvenator and adhesion enhancer; 38 500 tonnes of ULM surfacing; and 2 000 tonnes of medium wearing course with 20% RA, rejuvenator and adhesion enhancer. The first trial was produced on 18 May 2015 with a target to average more than 900 tonnes per day. Financial savings There is a strong case for higher percentages of RA Much Asphalt has upgraded all but two of its 17 static plants in South Africa to include recycled asphalt in new asphalt mixes. These plants can now incorporate between 10% and more than 50% recycled asphalt. The two plants not enabled for recycling are located in remote areas where recycled asphalt is not freely available.

in new asphalt mixes as the aggregates and bitumen used in the production of asphalt are non-renewable and increasingly rare resources. The ongoing shortage of bitumen in South Africa necessitates expensive long distance hauling when local supply is unavailable. Reclaiming asphalt offers financial savings in material costs, energy costs and total job costs. In addition to saving the cost and carbon emissions involved in extracting and transporting aggregates and bitumen, the reuse of milled asphalt saves on waste and landfill space. Adding to the benefits of recycling is the fact that mixes with RA have shown similar performance to conventional mixes. According to Herman Marais, plant and technical director at Much Asphalt, high percentages of RA were used in new asphalt internationally in the early 80s. Some premature failures dulled its popularity and for several years RA was not used at all, and then only in lower pavement layers. The benefits inherent in the high quality aggregate used in asphalt and the valuable contribution that the recycled binder can make to the new asphalt were overlooked, says Marais. But advances in mix designs resulted in renewed use of RA some 10 years ago and SANRAL specifies RA content to be included in many major asphalt projects today, he adds. While there is still resistance to the use of RA in some quarters, he believes it is critical to make responsible reuse of resources to reduce our impact on the environment. Product consistency “However we need to be careful not to go to extremes without the proper knowledge and technology. It would not benefit the asphalt industry or the drive to sustainability to have a disastrous failure of a high RA mix. I don’t foresee extremely high RA contents (above 40%) being employed on remote projects unless RA is freely available and may go to waste.” The recycled material should be properly crushed and screened and Much has invested in several crushing and screening plants around the country for this purpose. The need to crush and screen into separate fractions to ensure a consistent product becomes increasingly important as the RA content of the mix is increased. Marais warns that it is important to reduce the moisture content of the RA before it is recycled as high moisture content decreases the rate of production. A 1% increase in moisture content can increase the fuel consumption required to heat the RA by 10%.

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