We have been researching the carbonation process for over 25 years and in particular, how Accelerated Carbonation Technology (ACT) can produce carbon negative aggregates for the construction industry.
By using captured CO2, ACT can treat contaminated soils and hazardous industrial thermal residues, including cement bypass dust. With cement, CO2 reacts with calcium silicates in the presence of water before they have the chance to hydrate, forming calcium carbonate and a de-calcified silicate. This reaction reduces the pH of the system, so the formation of carbonate both chemically and physically binds heavy metal contamination.
By controlling the carbonation process, it is possible to engineer the optimum end-product, currently a granular solid with many valuable applications, including aggregates for construction and agricultural fertiliser.
The aggregate produced is carbon negative, lightweight (< 1200 kg/m³ – 30% less than natural comparators), water absorbent, has high insulation and hygric (moisture) properties, and the grading and colouring can be controlled.
Carbon negative aggregates have already been successfully manufactured from cement residues and can be repurposed in a number of applications such as ready-mix concrete, aggregate blocks, fertiliser/soil improver, pipe bedding and road construction. Hence, paving the way to Net Zero.
Many industrial thermal residues, such as steel slags, fly ash, incinerator bottom ash, red mud from aluminium processing, as well as cement by-pass dusts, also contain calcium silicates as well as calcium oxides, which will rapidly react with CO2 if the conditions are controlled.