Cement recarbonation refers to the process where part of the CO2 emitted during the cement production is re-absorbed by concrete in use through carbonation. Carbonation is a slow process that occurs in concrete where lime (calcium hydroxide) in the cement reacts with carbon dioxide from the air and forms calcium carbonate. At the end of their useful life, buildings and infrastructure (reinforced concrete structures) are demolished. If the concrete is then crushed, its exposed surface area increases and this increases the recarbonation rate. The amount of recarbonation is even greater if stockpiles of crushed concrete are left exposed to the air prior to reuse. In order to benefit from the CO2 trapping potential, crushed concrete should be exposed to atmospheric CO2 for a period of several months before its reuse (e.g. as road underlay). This needs to be taken into account in the way construction waste is dealt with.
- Studies have shown that up to 25% of the originally emitted CO2 during the cement manufacturing can be reabsorbed, when proper recycling practices are applied;
- To optimize the CO2 uptake at the end of life of a construction work, it is essential to ensure that proper construction and demolition waste sorting and concrete recycling practices are in place;
- To understand the full potential of recarbonation, fundamental research should be supported;
- Based on the outcome of research, an innovative set of policies on the treatment of crushed concrete building waste would enable recarbonation to reach its full potential.