By Dr Paula Carey, Co-founder and Technical Director
Until recently, the carbonation of the cement in concrete has been considered as an issue. Hydrated and un-hydrated cement within concrete carbonates slowly in the atmosphere. Initially, this is an advantage as it helps seal the outer surface of the concrete and reduces the pH levels. However, the carbonation front can then progress into the concrete, the rate of which, is dependent on the quality of the concrete and the climatic conditions. Eventually the carbonation front can reach the steel reinforcements reducing the passivation of the steel.
However, nowadays this process is looked on more positively as, a proportion of the CO2 generated during the calcination of the limestone and clay to manufacture cement is reabsorbed into the concrete, during its lifetime.
Carbonation and Carbon Capture
The manufacture of cement is responsible for at least 7% of global CO2 emissions and the cement industry is making significant commitments to reduce its impact on the environment, including Net Zero production by 2050.
The carbonation of industrial residues has great potential as a carbon capture and utilisation (CCU) solution. As it is naturally an exothermic process, it does not require the large amounts of renewable energy to convert the CO2 into marketable products that permanently store captured CO2. Residues that can be carbonated include by-products from the manufacture of cement and the crushed concrete resulting from demolition of concrete buildings.
In managed conditions, carbonation can be used to manufacture carbon negative aggregate, from residues produced in cement production and captured carbon. The aggregate can be used in concrete reducing its carbon footprint of concrete. By using aggregate manufactured through controlled carbonation, the need for natural aggregate is replaced and the carbon footprint of any construction project reduces.
Although carbonation has received a bad reputation in the cement industry in previous years, it is evident that the natural process, when controlled and managed, has the potentially to address some of the sector’s largest challenges. With NetZero targets and ambitions to transition to a more sustainable industry, carbonation CCU solutions provide a real solution.