CONSTRUCTION • At the Khobab Wind Farm, a four-star eco-product label has been awarded for the low-cement concrete used to build the wind turbine bases achieved by substituting cement with ground granulated blast furnace slag (GGBFS) or fly ash from the steel works at Saldanha Bay. The average carbon footprint on the bases at the Khobab Wind Farm was 90.7kg.CO2/m³. The average carbon footprint for a standard 30MPa readymix concrete base is from 290 to 340kg.CO2/m³. Eco Standard also commended the use of recycled water in this application in the water scarce region. These projects represent a fraction of infrastructure in South Africa and the uptake of geopolymers has been slow while the country landfills hundreds of millions of tons of ash and slag to the detriment of the environment. The problem is an absence of national standards covering the use of geopolymers, and consulting engineers are reluctant to sign off on projects using materials that do not meet current national standards because of the high risk involved if the material fails.
One cubic metre of concrete has a carbon footprint of 350kg of CO2, making this staple material in the construction industry one of the biggest contributors to greenhouse gases in the world.
While we wait for standards to be adopted, this does not mean there is no more that can be done in South Africa. The opportunity for substitution of ingredients to make concrete, rather than cement/clinker, are where gains can be made. Here, cement replacement is becoming more common. This provides massive carbon offsets, significant cost benefits, options for using recycled water, landfill diversion benefits of problematic waste streams and associated negative environmental impacts, improved resistance to fire and aggressive chemicals, and a host of other benefits. We need to make changes to national standards, material specifications, as well as procurement and supply chain policies to drive the uptake of
The Portside Tower in Cape Town.
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Loeriesfontein Wind Farm is the first high-fatigue structure in the world that will be constructed with 100% cement replacement. alternative low-carbon alternatives to meet this country’s international obligations to driving a low-carbon economy through the Paris Climate Agreement and UNFCCC. The fact that South Africa has world-leading scientists in these fields means that we should be leading the race.
