Engineers are working on yet another way to deliver more energy and cut carbon dioxide emissions. The latest trick: use the waste from biofuel production to make a stronger, greener concrete.
Biofuel is rapidly becoming big business: as demand rises, farmers are gathering up wheat and rice straw and the leaves and stalks of maize – known in the US as corn stover – as the raw material for bioethanol to drive the next generation of tractors, buses and cars.
Concrete, too, is global big business: the world uses seven billion cubic metres of the stuff every year, and every tonne of cement – an essential part of the mixture - made by traditional processes means another tonne of CO2 dumped in the atmosphere. The manufacture of Portland cement contributes an estimated 5% of global CO2 emissions.
So Feraidon Ataie, a civil engineer from Afghanistan, now studying at the University of Kansas, has been working with colleagues on ways to close the loop. They are using byproducts of biofuel production to take the place of at least some of the cement in a concrete mix.
This stuff would normally be wasted. Biofuel made from corn or grain leaves a residue that can be turned into cattle feed. But biofuel from the cellulose waste – from wood chips, straw and so on – leaves a residue high in a woody substance, lignin, that usually has to be burned or buried.
When the Kansas team added 20% lignin waste to their cement, the subsequent chemical reaction delivered a concrete more than 30% stronger.
More than half of the human race now lives in cities: building materials are increasingly in demand and concrete long ago became the most used industrial material, after water.
The Kansas team is not the only one working on ways to reduce the impact of cement on the greenhouse gas emissions tally, and limit global warming.
A Canadian team is experimenting with ways to produce a concrete that will actually absorb CO2 emitted from factory flues. A Californian power station has tried bubbling CO2 exhausts through seawater to make a calcium carbonate product that could substitute for Portland cement. Manufacturers have launched a“sustainable cement initiative” to try to reduce emissions wherever possible.
But the catch is that concrete is not something that can be recycled. Every new road, new building or new bridge requires new cement. The Kansas engineers think they may have a contribution to make, just by adding the waste from bioethanol.
“If you use this in concrete to increase strength and quality, then you add value to this byproduct rather than just landfilling it”, said Ataie. “If you add value to the byproduct, then it is a positive factor for the industry. It can help reduce the cost of bioethanol production.”