Cement and carbon emissions

Because of its low cost, its ease of use and relative robustness to misuse, its versatility, and its local availability, concrete is by far the most widely used building material in the world today. Intrinsically, concrete has a very low energy and carbon footprint compared to most other materials. However, the volume of Portland cement required for concrete construction makes the cement industry a large emitter of CO2. The International Energy Agency recently proposed a global CO2 reduction plan. This plan has three main elements: long term CO2 targets, a sectorial approach based on the lowest cost to society, and technology roadmaps that demonstrate the means to achieve the CO2 reductions. For the cement industry, this plan calls for a reduction in CO2 emissions from 2 Gt in 2007 to 1.55 Gt in 2050, while over the same period cement production is projected to increase by about 50 %. The authors of the cement industry roadmap point out that the extrapolation of existing technologies (fuel efficiency, alternative fuels and biomass, and clinker substitution) will only take us half the way towards these goals. According to the roadmap, the industry will have to rely on costly and unproven carbon capture and storage technologies for the other half of the required reduction. This will result in significant additional costs for society. Most of the CO2 footprint of cement is due to the decarbonation of limestone during the clinkering process. Designing new clinkers that require less limestone is one means to significantly reduce the CO2 footprint of cement and concrete. A new class of clinkers described in this paper can reduce CO2 emissions by 20 to 30 % when compared to the manufacture of traditional PC Clinker.