A. Cement is the key ingredient in concrete that helps to achieve desired properties in concrete including strength and durability. The cement used in majority of concrete applications is portland cement, and manufacturing portland cement results significant amount of CO₂ emissions. This in fact directly contributes to the global CO₂ emissions related to concrete manufacturing (about 8% of the total global CO₂).
Portland cement is manufactured from raw materials, typically limestone and clay that combine at high temperatures, approximately 2640°F (1450°C) to form calcium silicates that provide the binding properties of cement. Approximately 40 % of the CO₂ emitted during pyroprocess is due to fuel combustion, with the remaining 60 % driven off of the limestone during calcination. It is generally estimated that producing 1 ton (900 kg) of portland cement produces 1 ton of CO₂. However, the cement manufacture industry has been very active and innovative over the last few decades to reduce carbon footprints, and therefore, these general estimates may be higher than correct values.
References: ACI PRC-130-19; SCG1; ITG-10R; ITG-10.1R-18; E3-13