Over the past century, an increase in anthropogenic CO₂ emissions has caused atmospheric CO₂ concentrations to rise. Cement production accounts for around 8% of global anthropogenic CO₂ emissions. As well as the CO₂ emissions associated with concrete production, another critical challenge lies in the scarcity of primary raw materials such as sand and gravel. The most promising application was using RCF as a partial substitute for Portland cement, leveraging its potential pozzolanic properties.

The research focused on a representative sample of RCF obtained from the Renewi Westpoort concrete recycling plant. Its physical, chemical and mineralogical properties were characterised using various measurement techniques, including X-ray fluorescence (XRF), thermogravimetric analysis (TGA), selective dissolution and X-ray diffraction (XRD). The theoretical carbonation potential was determined using thermodynamic modelling and verified using the Steinour formula. Experimental carbonation tests were conducted at laboratory scale under controlled conditions, focusing on moist and wet carbonation methods.

The oxide content of the RCF, collected over a period of more than one year, showed a maximum variation of 2.03 for SiO₂, indicating that the chemical composition of the samples was highly consistent. TGA combined with MS revealed that the concrete had significantly carbonised over its lifetime, with an estimated carbon uptake of 8.76%, equivalent to a calcium carbonate content of 19.9%. Based on the thermodynamic model, the theoretical carbonation potential was found to be 14.0 g/100 g RCF.

For wet carbonation, the maximum carbon uptake was found to be 8.48 g/100 g RCF after 120 minutes of carbonation, which equated to a degree of carbonation of 60.6%. Wet carbonation had the highest carbonation rate, with 85.6% of the carbonation occurring within the first 10 minutes. Based on thermogravimetric analysis (TGA) and X-ray diffraction (XRD), calcite was the main reaction product, in accordance with thermodynamic modelling. Furthermore, Fourier transform infrared spectroscopy (FTIR) revealed the progressive polymerisation of silica tetrahedra, indicating the formation of silica gel.

The wet carbonation experiment was found to cause an increase in portlandite consumption during the R3 test. Following wet carbonation treatment, portlandite consumption increased to 26.5%. Comparing the heat release of cRCF with RCF showed that there was greater reactivity during the acceleration period. The strength activity index (SAI) was 94.5%, comparable to the performance of ordinary Portland cement (OPC). This suggests that cRCF, sourced from demolition sites, is a viable SCM.