It is during the production of clinker, the main component of cement, when most CO2 emissions associated with cement occur. The majority of these emissions are unavoidable, as they result from the chemical reaction that occurs when the raw material (limestone) calcinates into clinker in the kiln. Replacing the clinker in our final cement products with alternative mineral components such as pozzolan, slag or fly ash reduces the carbon intensity of the cement. A significant portion of these constituents come from waste or byproducts recovered from other industries. While we aim to further reduce our clinker factor, the limited availability of mineral components in some markets, or the absence of specific product properties in others, act as limiting factors. In markets where these factors are favorable, our replacement rates have reached 50 percent.
Another key way to reduce the carbon intensity of our cement production is to use pretreated waste and low-carbon fuels. These serve as a replacement for fossil fuels that provide the energy needed to operate a cement kiln. In some of our operations, we have been able to meet 90 percent of our energy requirements with alternative fuels, but we also acknowledge our potential to increase this rate significantly in the coming years.
Cement production is an energy-intensive process. Energy costs and security of supply are key business drivers. Improving our energy efficiency reduces the carbon intensity of our products and lowers our production costs.We have reduced our energy consumption per tonne of clinker to 3,518 megajoules in 2018 (1990: 4,532 megajoules), among the lowest rates in the sector. Since 1990, we have increased our cement production by around 79 percent, while our annual energy consumption has increased by just 18 percent.
