Concrete is used worldwide and the footprint of its production constitute up to 8% of global
CO2 emissions. The recycling of end-of-life concrete structures becomes interesting both economically and environmentally. The fine fraction (<125 mm) is however a problematic waste, and here is investigated if this fraction that contains hydrated cement can be reused after reactivation.
In a study performed at VUB the characterization of mortars was done for mixtures of fresh cement and dehydrated concrete powder. In order to have a composition as close as possible to ordinary portland cement (OPC), it was necessary to dehydrate the recycled concrete at 550 °C. After dehydration, two different fractions were sieved (Ø<63 mm and Ø<125 mm ) to look at the impact of particle size distribution on the composition and properties of the concrete. To do that, simultaneous thermogravimetry-differential scanning calorimetry studies were carried out, along with XRD and SEM-EDX.
These analyses pointed out a higher concentration of silica in the coarser fraction, and a higher concentration of cementitious material in the finer fraction. Isothermal calorimetry of the hydration process showed no noticeable differences between OPC and OPC with 10% recycled cement .
Finally, mortars were casted with 90 % OPC and 10 % of the recycled cement fraction to compare with pure OPC based mortars. Mechanical tests and resonalysis showed that, after 7 days, the addition of 10 % of recycled cement into the OPC had a negligible or even positive impact on the mechanical properties of concrete.
These results give good hopes that the use of recycled material in cement powder could appear both environmentally friendly and economically more sustainable.