The cement industry is one of the most polluting and carbon intense of all industries, producing three times the carbon emissions of the aviation industry. Its products are ubiquitous: the basis of foundations, roads, dams, and airport runways. Every phase of concrete spews massive amounts of CO2 into the atmosphere. The worst phase, however, is the manufacturing one, where half of the pollution comes from the energy to heat limestone to 1,500 degrees Celsius and the other half from the chemical process of breaking down the limestone into calcium oxide. To get the high temperatures required, coal is the preferred fuel.
One of the most straightforward ways to reduce emissions is to transition to cleaner-burning fuels. Some plants are using old tires, a great source of energy and one of the most effective ways of disposing of used tires. Even cleaner options are starting to be tried, namely, hydrogen-based fuels and electricity generated from wind and solar.
As suggested above, energy for high heat is only part of the concern. The other is the CO2 released during limestone’s chemical transformation into “clinkers,” chunks subsequently ground into powder to become Portland cement. For many years, the construction sector has been making substitutions for Portland cement in concrete mixes — the most prevalent being waste products like fly ash or rice husks. Consequently, industry-wide, the amount of clinkers has been reduced by about 30 percent since 1990.