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sustainable construction world
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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
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%.
Asphalt
Asphalt
gets progressively
greener
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.