"The problem is, making concrete also pumps carbon dioxide into the atmosphere. Cement, a key ingredient in concrete, is the world's second-largest industrial CO2 emitter and is responsible for about seven per cent of carbon emissions globally and 1.4 per cent of Canada's.
But cutting down on those emissions is hard to do. Most of the carbon generated through cement making comes from the fundamental process of heating ground limestone (calcium carbonate), clay and sand at extremely high temperatures in a kiln until it forms small nodules called clinker, which is then ground into cement."
"Worldwide, cement manufacturing is a major source of greenhouse gas (GHG) emissions— cement production accounts for approximately 7% of GHGs globally. Among global industrial emissions, cement accounted for about 26% in 2019.Footnote 1 These emissions primarily come from the chemical process reactions needed to convert limestone into clinker, the precursor to cement, and from the fossil-fuel emissions generated to produce the high temperatures (approximately 1,450 degrees Celsius) required to achieve that process.
Likewise, cement production accounts for a significant share of Canada’s current GHG emissions. Facility-level reporting through Canada’s Greenhouse Gas Reporting Program listed 11.2 megatonnes (Mt) of carbon dioxide (CO2) in 2019 for the cement manufacturing industry. This represents about 1.5% of Canada’s emissions."
"The CO2 produced for the manufacture of structural concrete (using ~14% cement) is estimated at 410 kg/m3 (~180 kg/tonne @ density of 2.3 g/cm3) (reduced to 290 kg/m3 with 30% fly ash replacement of cement).[14] The CO2 emission from the concrete production is directly proportional to the cement content used in the concrete mix; 900 kg of CO2 are emitted for the fabrication of every ton of cement, accounting for 88% of the emissions associated with the average concrete mix.[15][16] Cement manufacture contributes greenhouse gases both directly through the production of carbon dioxide when calcium carbonate is thermally decomposed, producing lime and carbon dioxide,[17] and also through the use of energy, particularly from the combustion of fossil fuels."
"The production of clinker is the most energy-intensive process in the overall production of concrete. Clinker is an intermediate precursor to cement, and its production is a major source of CO2 in relation to cement. It is produced in a series of complex chemical reactions that ultimately transforms calcium carbonate in limestone to calcium oxides and calcium silicates. This process is responsible for more than 60% of the CO2 emissions from cement manufacturing. The remaining CO2 emissions, just under 40%, come largely from the energy combustion required to heat that process (other smaller sources of emissions include electricity use and on-site transportation and related equipment). Clinker is blended (and inter-ground) with different proportions of gypsum and unprocessed limestone to produce cement."
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