Producing a ton of concrete emits about 0.9 ton of CO2, thus making concrete one of the heavyweights when it comes to CO2 emissions. The production of cement is currently estimated to amount for five percent of global CO2 emissions.
A forecast from the Danish Technological Institute predicts that the demand for cement will be doubled in 2050 compared to the need in 2010. If cement continues to be produced with the same methods as now, the increased need of cement will therefore produce a massive increase in CO2 emission.
Residual waste with great potential
At DTU Civil Engineering Professor Lisbeth M. Ottosen and Research Assistant Nina Marie Sigvardsen work on replacing a part of the cement in the production of concrete with wood ash. The preliminary tests have shown that there is a big difference in wood ashes from different plants, and thus their suitability as cement replacement. An example of a critical parameter is whether or not the ash is moistened in the plant. The latter appears to be the most suitable as replacement in the production of concrete.
“We consider ourselves as being ambassadors for the quality of building materials. This means that something must be gained for the environment as well as for the quality of building materials when we strive to develop something new. Both needs are met, if we replace a portion of cement in our concrete with wood ash.”
Today wood ash is categorised as residual waste without additional applications. However, there is a great potential in wood ash because it can be used as cement replacement in concrete production and thus help lower CO2 emissions from the concrete production.
“It is important to emphasise that we are not trying to make a new kind of dump site in our concrete. We consider ourselves as being ambassadors for the quality of building materials. This means that something must be gained for the environment as well as for the quality of building materials when we strive to develop something new. Both needs are met, if we replace a portion of cement in our concrete with wood ash,” explains Lisbeth M. Ottosen.
Reutilisation of wood ashes produces profit
To replace parts of the cement in concrete production will not only produce environmental benefits. If the power plants get rid of the inconvenience of depositing wood ash and instead get the opportunity to redeploy wood ash, the expense for production of new concrete will decrease considerably.
This means that both the industry and the environment can benefit greatly from the recycling potential in wood ash. However, this requires targeted research that strives to replace parts of the cement in concrete with wood ash.
“If we are to fully exploit the potential of replacing parts of the cement in concrete with wood ash it is necessary to know more about how the ashes should be treated in a more precise way. This applies both to the treatment at the power plants and later, when the ashes are mixed into the cement. That calls for increased cooperation with the industry so we can ensure that we plan the recycling process in the best way possible,” says Lisbeth M. Ottosen.