BENEFICIATION
Professional chemist Cyril Attwell from ARC Innovations is one of South Africa’s biggest
proponents of low- and no-cement concrete.
hybrid material to increase the strength
and durability of concrete while reducing
the environmental and economic costs.
Strengths of up to 52MPa at 28 days have
been achieved on certain sites using ARC
technology and zero cement, with the
optimisation of the crystal lattice through
mineral synergy increasing the strengths
beyond what is considered normal.
“Now if you look at the environmental
impact of cement, the 344 000 tonnes in the
original estimate would have required about
4.5km by 3.5km of rainforest to be alive for
40 years to counteract the CO 2 produced to
make it. By applying ARC technology and
extension to reduce the amount of cement
used in the concrete, we were able to reduce
that to 2.5km by 3.5km — a basic saving of
2km by 3.5km of rainforest that would need
to be alive for 40 years to counteract the CO 2 .
And this without impacting the strength.
“In fact, during the project we were
experiencing temperatures of down to
-6°C overnight, and usually cement stops
dissolving at 5°C. However, because of the
ARC technology we were able to withstand
the temperatures going down to -6°C and still
strip the next morning and move those 50
26 _ QUARRY SA | SEPTEMBER 2017
tonne precast elements at 16 hours because
of the strength we achieved. We didn’t have
to apply steam, which would have chased up
the carbon footprint even more.”
After the Gautrain project, Attwell and his
team moved on to the Portside skyscraper
— Cape Town’s tallest building, and also its
greenest. “The original specification for
the project allowed for 30% substitution of
cement, but we ended up substituting up to
85% with slag waste,” he explains. And from
there, to 102 Rivonia in Johannesburg. “For
102 Rivonia, we used 60% substitution, but
this time with Ulula ash rather than slag
waste. And that was up to 80MPa concrete
as well, achieved at ambient temperature
with no steam curing or anything like that
to increase the carbon footprint.”
Then came the groundbreaker: Transnet’s
City Deep Container Terminal upgrade:
the first commercial application of 100%
cement replacement in South Africa.
Transnet’s City Deep
Container Terminal
In September 2013, Murray & Roberts
was involved with Transnet’s City Deep
Container Terminal upgrade. “What made
the project unique,” explains Attwell,
“was that there was zero cement used in
the concrete, and 40ℓ (4%) of commercial
activator — only 20ℓ of silicate — was used
instead of the standard 200–300ℓ (20–30%),
resulting in an approximate 92.7% reduction
in the carbon footprint compared to a
standard 45MPa concrete.” And this was
without compromising the strength.
“We achieved a 50MPa concrete, which
went up to 75MPa after one year,” says
Attwell. “We’re actually monitoring it
on a yearly basis — coring it, checking
the strength and durability, and making
sure that it is getting stronger and not
deteriorating, because there’s very little
history on this material.”
The specifications for the project called
for a maximum substitution of 30% with ash.
Murray & Roberts proposed a reverse: 30%
cement and 70% ash, the highest substitution
ever done in South Africa at that time. Using
the data from the extensive testing the
concrete had undergone — five to 10 times
the amount of testing standard concrete
undergoes, including some tests that normal
concrete never sees because of the need for a