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CONSTRUCTION WORLD
FEBRUARY
2015
PROJECTS AND CONTRACTS
which amounted to about 123 840 m
3
of the 144 000 m
3
concrete, which
would otherwise have been disposed of at landfill sites. The quantity
that was not recycled came from structural concrete with a high level of
rebarred material. However, the rebar was recovered for off-site scrap
metal processing.
The old pavement was crushed to a G5 material specification and
reused as base and sub-base quality material. Apart from the posi-
tive environmental benefit of reusing the old pavement, the use of a
great deal of virgin aggregate was prevented. It is estimated that about
R14-million would otherwise have had to be spent on the procurement
of new aggregate and on transport.
Placing geopolymer concrete is very similar to placing Portland
cement, meaning no additional training for workers or extra equip-
ment. In addition, recycled materials such as slag and fly ash can be
used to make geopolymer concrete, thereby reducing the carbon foot-
print of the material by 80% to 90%.
Murray & Roberts Infrastructure achieved 51 MPa in 28 days, with
compressive strengths up to 80 MPa at six months. Fifty MPa is equiv-
alent to the pressure exerted by the weight of 10 pockets of cement
concentrated on the point of a single finger. The carbon footprint of a
cubic metre of cement is 350 kg to 400 kg of carbon dioxide equivalent
per cubic metre, and 100 kg/m
3
for geo-polymer concrete. This means
geopolymer concrete reduces greenhouse gas emissions by 60% to 70%.
Specific deconstruction processes
Deconstruction processes were as specific as the construction process.
The demolition of the existing infrastructure and feeding of this
resource as a material stream into the crushing areas and reprocessed
stockpiles meant a clear understanding of the quantities scheduled
for the foundations upstream. Planners and engineers thus needed to
understand the rates of the demolition, earthworks and processing of
the G5 to ensure that none of these processes entailed any delay.
Environmental impact
The resource-intensive traditional way of making cement has seen
the industry rank among the top environmental offenders, leading to
increased calls for more sustainable solutions.
The concrete used on this project achieved a 63% to 70% replacement
of raw milled clinker with siliceous PFA, almost double the maximum
specified limit on most construction projects. Using this quantity of
PFA alters the concrete hydrate formed in such a way as to increase the
durability/service life of the elements.
In terms of concrete technology, the reliance on coal fired power
stations for the majority of electricity in South Africa in addition to the
large metal resources, mean that large quantities of PFA and slag mate-
rials are readily available. The efficient uptake of such waste by-prod-
ucts can assist in economic growth by slashing the cost of construction
and increasing the durability of the structures being built.
From a client perspective Transnet, which operates multiple sites
countrywide, can incorporate the possibility of the reuse of existing
infrastructure in future refurbishments, in order to produce new prod-
ucts of high quality and durability that are also environmentally sound.
Murray & Roberts Infrastructure, in conjunction with Transnet, can
therefore reference this project as a benchmark case study.
Health and safety
Murray & Roberts’ values of safety, integrity and accountability as well
as the group’s STOP.THINK.ACT 24/7 zero harm culture is embedded
in the Environmental Framework, which is divided into four environ-
mental programmes, forming part of the larger Integrated Management
System (IMS):
• Integrated waste management
• Emissions and pollutants minimisation in construction
• Sustainable material and resource management
• Energy efficiency through mass balancing
The Murray & Roberts’ Exco has endorsed the SHEQ policy and Environ-
mental Framework and requires performance reporting. Significantly,
as at the end of June 2014 the contract had been running LTI free
for 12 months.
Project information
• Project start date: September 2012
• Project end date: October 2014
• Client: Transnet Freight Rail
• Main contractor: Murray & Roberts Infrastructure
• Principal agent: Murray & Roberts Infrastructure
• Project manager: Transnet Capital Projects
• Consulting engineer: Transnet Capital Projects
• Project value: R230-million