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.