The Civil Engineering Contractor February 2018 | Page 27

INSIGHT
old factories and warehouses can
be converted into dwellings. The
quality of the concrete in structures
will determine its suitability for
reuse.”
He concedes, however, that
there are still some challenges
to be overcome in the quest for
using higher volumes of recycled
concrete. “There are potential
problems such as irregularity of
supply, contamination, and lack of
consistent quality, coupled with
the high cost of quality concrete
recovery, site sorting, noise, and
pollution resulting from recovery
and processing on site.
“But the benefits, particularly for
countries with shrinking economies,
far outweigh the challenges.
Architects and specifiers need to
increasingly consider the use of
recycled concrete when designing
new buildings,” he adds.
Hilton Cowie, technical manager
at Greenlite Insulated Concrete,
says that part of the challenge is
the conservative South African
construction industry mindset,
coupled with a “low-level labour
skills set”, adding, “with the
generation of skilled tradesmen
all but retired”. Additionally, he
says, there is generally “very poor
on-site management”. 
In terms of alternative building
technologies, Cowie believes that
South Africa is “far behind Europe
and US” and adds, “but the South
African construction industry is
starting to take alternative building
technology (ABT) seriously. I have
been using ABTs in South Africa for
the past 20 years and only now am I
starting to see a more ‘mainstream’
interest in ABTs,” he attests.
He says the company only uses
recycled polystyrene as aggregate
mixed with cement, water, and
their additives. “All our products are
Agrément SA and SABS approved
and fall under the ABT umbrella,” he
points out.
Commenting on the benefits of
green building, Cowie is candid in his
opinion: “The benefits of going ‘green’
are obvious in our day and age. We are
currently processing 25 tons of post-
consumer/waste polystyrene per
month; that is equivalent in volume
to filling an Olympic-size swimming
pool — every two months. That waste
would have been destined for landfill,”
he muses.
“We are busy with 300 emergency
housing units in Philippi at the
moment and, on this project alone,
we would have used 46 tons of waste
polystyrene to construct energy-
efficient houses when completed.
It’s a no-brainer!” he grins.
A second life for concrete
Because concrete has a huge
carbon
footprint,
discarded
concrete becomes a problem for
the environment, says University of
Notre Dame engineering professor
Yahya Kurama. “It’s very intens ive
in terms of its demands on energy,
water, land space, everything.”
Producing concrete accounts for
5% of the world’s annual human-
generated CO 2 emissions. In the US,
it — along with other demolished
building materials — takes up nearly
half of all landfill space.
To reduce such harm, the
construction sector has concentrated
on things like reducing new concrete
production and finding new uses for
concrete by-products.
In the US, while recycled
concrete is used in pavements and
roads, it is not used for load-
bearing structures. Kurama and his
team, along with scientists from
the University of Texas at Tyler and
New Mexico State University, set
out to determine whether it was
strong and durable enough to be
used to construct buildings.
“Currently, there’s a lot more
supply of recycled concrete
aggregates than demand,” he points
out. “What we are trying to do is
bring up the demand and at the
same time generate the engineering
background that these materials can
be used in a higher-level application.”
Kumara’s team is studying different
recycled aggregate combinations in
hopes of supplying that demand, and
are interested in two sources for
recycled concrete. The traditional
RCA, or recycled concrete,
is something that comes from a
demolished structure, such as a
bridge or a building. This means
that it has had the opportunity to
accumulate other materials — wood
chips, asphalt, brick — from the
construction site. However, no
one wants to have to sort that out,
because it’s an added cost.
The other, cleaner source, is
rejected material from a precast
concrete plant, which has no steel,
wood, or other construction debris
mixed in. In both cases, the material
is crushed down as aggregate and
mixed with fresh cement to make a
new product.
As strong as new
The team is testing both types of
recycled concrete to determine
durability and many other qualities:
life cycle costs, weight-bearing
abilities, statistical variabilities,
and properties of the aggregates.
Kurama says they are also working
out how they might engineer around
any differences between the recycled
materials and traditional concrete.
Using recycled material reduces
concrete’s environmental impact by
about half, from decreased water
usage and less mining, to decreased
transportation costs, because
materials are often on site or close
by. Analysis has shown that in some
instances, recycled concrete is
stronger than its natural counterpart.
“Nobody is going to see an
immediate effect of this,” Kurama
says of his work, “but if you
think about the impact of built
infrastructure 20 years, 30 years,
40 years, 50 years down the road,
this will have a big impact in terms
of reducing concrete’s impact on
our environment.”
That’s good news, because it is
expected that the world will need
4.4-billion metric tons of concrete a
year by 2050. nn
"The durability of concrete
structures is a key factor in their
suitability for reuse.”
Bryan Perrie – The Concrete Institute
CEC February 2018 - 25