Concrete is the most common and widely used construction material in the world, with a consumption of approximately 1.5 tons per capita annually worldwide. This consumes 3000 million ton of cement, around 400 kg per capita. Sweden consumes around 250 kg of cement per capita.  The production of Portland cement consumes around 3500 MJ energy per ton. In addition, Portland cement production releases considerable amounts of CO2 when limestone is heated and calcinated. With 800 kg of CO2 per ton of cement around 5 % of the global release of CO2 comes from cement clinker production. About half of this comes from the limestone. Concrete, however, also binds CO2 when it is carbonated. In a geological time perspective, all concrete will carbonate and thus half of the released CO2 will be bound to carbonated concrete, which would reduce the environmental impact (Xi et al 2016). I reality the absorption is much less, and is related to the time interval of interest.  How fast CO2 will be absorbed depends on the type of concrete or cementitious material, site of the concrete, amount of CO2 in the environment and the environment as such, etc. It is also depending on the amount CO2 in the atmosphere and the temperature. In the end, to be able to calculate the uptake it is important to find out what happens with the concrete after demolition and if it is possible to increase the speed of carbonation.  This report mainly cover the mechanism and mode of carbonation to be able to get a better and more accurate understanding of how to calculate carbonation and CO2 uptake.  This project was funded by the Swedish Consortium for financing Basic research in the Concrete Field. The consortium members are: Cementa, Färdig Betong, Abetong, Swerock, Betongindustri and Strängbetong.