Pilot project measures potential of CO2 in recycled concrete


Zurich/Villigen AG – A scientific pilot project has demonstrated that concrete can reabsorb and permanently store up to 10 percent of the CO2 produced during its manufacture. In addition, concrete enriched with CO2 is stronger. This allows the proportion of cement in recycled concrete to be reduced.

A Pilot project led by the Swiss Federal Institute of Technology Zurich (ETH), in collaboration with experts from the Swiss Federal Laboratories for Materials Testing and Research (Empa), the Water Research Institute of the ETH Domain(Eawag), the Paul Scherrer Institute(PSI), and the companies Kästli Bau from Rubigen BE and neustark from Bern, along with 18 other partners, showed that concrete demolition granulate fumigated with CO2 can save around 15 percent of the greenhouse gas produced during its manufacture.

A total of 10 percent of this is achieved by the novel building materials, which have been enriched with carbonated concrete granules. Another 5 to 7 percent can be achieved because the CO2-enriched concrete granules make the cement compounds in recycled concrete stronger than normal concrete. This was the result of complex measurements carried out by Andreas Leemann of Empa’s Concrete & Asphalt department, among others: “A reactive phase, in other words, which is newly formed in the granules and produces a higher strength in the recycled concrete. This has already surprised us,” he is quoted as saying in a media release.

Further potential was also shown by the CO2 treatment of the so-called recycling water from water, cement and sand, which is produced during the cleaning of concrete trucks and mixing plants. One kilogram of it was able to bind the considerable amount of 120 grams of CO2 gas. Life cycle analyses have summed up that the carbonated material can reduce the net greenhouse effect by around 13 percent compared to concrete with conventional cement and no recycled material. For concrete with recycled material, the effect is still 9 percent.

The project leaders present the research results to the public at the so-called closing event. It will take place on December 6 at ETH’s Audi Max. ce/mm