Concrete and cement are often unfairly blamed for unacceptably high carbon dioxide emissions, says Bryan Perrie, managing director of The Concrete Institute.
Perrie says the current average worldwide consumption of concrete is about a ton per year for every living person but, despite this extensive use, the global cement industry still accounts for only about 5% of man-made carbon dioxide emissions.
“Approximately 40% of this comes from burning coal and 60% from the calcination of limestone. It should also be remembered that structures are not constructed out of cement but from concrete – of which cement is but one ingredient,” he says.
The average international level of carbon dioxide emissions is about 1000 kg per ton of pure cement. “This value is being reduced by new technology and the use of alternative fuels in cement kilns, including the burning of waste tyres,” says Perrie.
“The primary method of significantly reducing the emissions is to lower the clinker factor in cement by the use of extenders such as blast furnace slag, fly ash, limestone and other similar materials which would end up in landfills if they were not used by the cement and concrete industry. Another industry contribution towards sustainability is the sourcing of synthetic gypsum from industrial by-products from the fertiliser and sulphuric acid industries.”
Perrie says when selecting aggregates for sustainable concrete production, it is important not to choose the cheapest sand as this may result in more expensive concrete with a significantly higher carbon dioxide footprint. The use of recycled concrete as an aggregate will further reduce the carbon dioxide emissions of concrete while simultaneously preserving natural resources and eliminating the need for dumping old concrete at landfill sites.
“Although the proportion of admixtures in a concrete mix is relatively small, recent developments in admixture technology now allow admixtures to be used to control important properties of concrete, such as workability, pumpability, durability, aesthetics and cost-effectiveness. Consequently, admixtures can have a major positive effect on sustainability,” he explains.
Concrete readymix plants are also engaged in environmental preservation practices such as recycling wash and waste water, saving costs and reducing consumption of precious water resources.
“Concrete has an excellent ecological profile compared to other construction materials and its social contribution cannot be overestimated. It is the second most used resource in the world after water, and contributes significantly to our standard of living – from the houses we live in, the schools and universities we attend, the offices we work in, the infrastructure of water reticulation and sewers, the dams that hold our water, to the roads that make transport for all our needs possible.”
Perrie believes using concrete “makes environmental sense” because properties such as economy, thermal mass, fire resistance and watertightness all add to the sustainability of concrete in the built environment. “Concrete structures have optimal energy performance with associated positive effects on whole-life energy usage,” he concludes.