Concrete is the second most used material on the planet after water and its production accounts for over 5% of world carbon emissions. As the world becomes ever more urban we need to find ways to decarbonise concrete.
Concrete production and use has increased about 400% since 1970, and now runs at about 20 billion tons per year. Traditional approaches to concrete production produce nearly one ton of carbon for every ton of concrete, although the net release is lower. Put another way, the net release of CO2 per cubic meter of concrete – ca 3900 lbs of concrete - is about 400lbs CO2: that is equivalent to running a home computer for a year; using 16 US gallons of petrol for a car; or using a microwave oven for a year.
The world’s population is now more than 50% urban; 70% by 2050. Given the huge growth of cities which that shift will represent, reducing construction-related carbon emissions is a priority. China currently accounts for 37% of world concrete production and India 6% - much of it in old fashioned plant. A 10% reduction in concrete related carbon emissions in the USA, which accounts for about 5% of the world total, could achieve one fifth of Kyoto targets in the US.
Help is at hand, from a combination of policy requirements and research.
Research at MIT has established that the nano-scale structure of concrete provides its strength, rather than the material per se.* The researchers hope to use the ‘genomic code’ of materials to find alternatives which require lower carbon emissions in production. Magnesium is one option, which has the added benefit of being a waste product which producers need to pay to dispose of.
Novacem, using research from Imperial College, is examining the use of magnesium oxide which is widely available worldwide, as an alternative to Portland cement. It needs temperatures of only 650o C making carbon emissions of 0.5 tons per ton of cement.
Calera in California is exploring a process which requires no heating, and is similar to that used by coral to secrete calcium carbonate. The process may mean that each ton of cement stores two fifths of a ton of CO2.
Masdar city in Abu Dhabi has set up a partnership with Al Falah to supply readymade concrete that has 30% lower emissions, in line with the city’s aims of sustainability.
Elsewhere, fly ash from coal fired power stations and slag from blast furnaces replace a proportion of the Portland cement thus not only reducing the carbon emission of the concrete per se, but also providing reuse opportunities for toxic waste. Structures such as the new bridge in Minneapolis and the building housing the Environmental Protection Agency already use this material; California requires a 15-35% fly ash content for roads.
Another MIT project is looking at concrete which lasts for 1000s of years, requiring less rebuilding and maintenance, thus reducing its lifespan carbon footprint.
In the UK, a zero energy building mandate has been imposed on new homes – by 2016 and new commercial structures by 2019, and is focusing minds; similar concepts are under discussion in the USA. Given that building efficiency has changed little since the early 20th century, even more radical solutions and targets will be needed – and not just for new buildings.