240ℓ and thereafter 250ℓ – meaning the
concrete strength is variable – a ready-mix
plant cannot use it because the plant will
lose credibility,” says Du Plessis. “With
recycled aggregates, consistent grading is
not something you can guarantee unless
you get your recycled material from one
reliable source.”
Therefore, to write a specification will
be challenging, while to adhere to it will
be even more challenging. The specs will
have to be even more strict than for natural
aggregates, because people will cut corners
in what they put in, adds Du Plessis. The
challenge, he says, is that the trade is
struggling to get approval for ordinary
natural aggregate samples. Each aggregate
has to go through vigorous testing worth
nearly R20 000 to ensure compliance to all
specifications as set out in SANS 1083. For
instance, for a major project like a power
station a supplier can expect hundreds
of thousands or up to a million rand of
testing throughout the project life to ensure
consistency and performance.
has been taking place for over a hundred
years and a number of techniques have been
developed and continue to be developed to
provide economically and environmentally
suitable methods to suit various projects
and locations. In South Africa, asphalt from
existing road pavements has been used
since the mid-1970s for the production
of millions of tonnes of recycled mix that
have the same performance characteristics
as hot mixed asphalt made with all virgin
materials.
Saied Solomons, CEO of the South
African Bitumen Association (Sabita), says
that recycled or reclaimed asphalt (RA)
refers to the portion of asphalt which, once
removed from an existing road surface, is
reclaimed and re-used for the purposes of
new road building, maintenance or repair.
RA typically consists of 95% high quality
aggregate and 5% of aged bitumen.
“Over time, road surfaces either
deteriorate or the road requires an upgrade
for other reasons, but these require the
existing road surface to be demolished or
“We have old mines in Secunda, Witbank and
Middelburg which have to be filled. We can pump self-
compacting or self-levelling concrete into the mines
to fill the cavities, and for this we can quite efficiently
use recycled aggregates because it’s cheaper, and in
the case of fly ash it would be free. In fact, some of the
mines will pay you to take it off their hands.”
Aggregate from a quarry is relatively
predictable because it comes from solid
rock in which one wouldn’t expect organic
material. In comparison, aggregate from
a recycling plant where everyone simply
dumps their concrete and rubble will
represent a wide variety of quality of
material from multiple sources. “We have
different specifications for aggregates from
different sources to be used in construction
– to guarantee consistency. With recycling
they’re all mixed together. There is definitely
a use for recycled aggregate, but not for
high-spec construction,” says Du Plessis.
Asphalt’s long history of
recycling
The reuse of road material across the globe
www.quarryonline.co.za
repaired. Although the road surface may
no longer function as a whole, the asphalt
component of the road surface can be
re-used and provides a valuable source
of material that can be reclaimed. It is
important to note that prior to reclamation
the asphalt is always tested to determine if
it is suitable for reclamation and there are
a number of standards which are used for
this,” says Solomons.
In the past few years this technology
has received much more attention
as the world puts more emphasis on
environmental conservation and carbon
footprint reduction. In addition, the costs
of building this type of infrastructure have
also increased and economic reasons are a
driver. The method is to accommodate over
90% of recycled asphalt producing materials
TECHNOLOGY
Kate Stubbs, director, Business Development
and Marketing from Interwaste.
at a low energy cost with an appropriate
design life.
Future trends
As an example of what the future holds,
Qatar has set itself a target to recycle 15%
of solid waste generated in the country
over the next four years, according to
the Qatar Second National Development
Strategy (NDS2). The state is making
significant efforts to increase the waste
recycling rate and promote environmental
awareness on reducing the quantity of
domestic solid waste.
The generation of total solid waste
(construction, domestic and others) on
the country increased from 8Mt in 2008
to 12Mt in 2013. As the infrastructure
works of the FIFA World Cup and
related demolition and rebuilding of
enterprises is nearing completion, the
generated amount of construction waste is
expected to decrease. A high proportion
of construction waste, especially cement,
brick and tile waste, is fully suitable for
crushing and recycling as a replacement of
gravel extracted from new quarries in some
lower applications.
Stubbs concludes, “It is critical that any
business going forward needs to incorporate
its environmental impact into its business
processes from cradle to grave. From the
sourcing of various raw materials, to the
production and final consumption or route
to market, companies need to understand
the generation of waste in each process
to ensure the long term commercial and
environmental viability of the business.”
QUARRY SA | NOVEMBER/DECEMBER 2018_27