Net Zero Cement

Material Efficiency: Making efficient use of cement and cement products through avoiding the habitual overengineering and waste of material that has become commonplace in contemporary construction is an important pathway to reducing emissions overall from the industry. There are a lack of incentives to rationalize the use of cement as the material is viewed as low cost and the associated emissions from its production are not priced-in to its use. One of the key material efficiency measures from a GHG point of view is better concrete making to minimize pore space between aggregates, which minimizes the amount of cement required to hold them together – this is achieved through multi sized aggregates and better mixing. Material efficiency measures in construction could achieve reductions in cement demand by up to 26% by 2050.

Material Substitution in Portland Cement Clinker (PCC): Ordinary Portland Cement (OPC) is typically 95% clinker. Useful grades of cement can be produced with less clinker (and thus lower emissions overall) by substituting clinker for materials such as fly ash, silica fume, or slag cement. Collectively these substitutes are termed Supplementary Cementitious Materials (SCMs) and produce blended cements that have lower emissions than a “pure” Portland cement. Depending on the application, SCMs can theoretically make up as much as 30-50% of a blended cement by weight, but in practice limited available quantities of SCM materials (which are often waste products from other industrial processes) has meant that to date it is more typical to find concentrations of around 20-30%. Blended cements are in widespread use today. A promising future SCM source is naturally occurring clay. The use of calcinated clay (particularly kaolinite), paired 2:1 with ground limestone, could potentially free up a huge source of SCMs (enabling a push towards 50% substitution of clinker in cement). Calcinated clay cements are at the early commercialization stage of development and available in a limited number of markets.

Material Substitution using Alternative Binders: Various research efforts are underway to completely replace the clinker type used in Portland cement with alternative chemistries that offer similar engineering and technical properties Some of the most promising, in order of technological maturity, include alkali-activated binders, also known as “geopolymers” (early commercialization stage), the carbonation of calcium silicates (technology demonstration stage), and magnesium based cements (early laboratory stage work). In theory, the complete replacement of Portland cement clinker (PCC) would eliminate the release of CO2 to the atmosphere that comes from the calcination reaction stage of cement production, leaving only the emissions from process energy inputs (if any). However, because existing markets and supply chains, as well as construction standards and building codes, are typically based around Portland Cement Clinker (PCC), alternative cement types may face an uphill struggle for rapid adoption.

Fuel Switching to Low or Zero Carbon Alternatives for Kiln Heat: Multiple pathways exist for reducing emissions from clinker production through the substitution of fossil fuels used to achieve high temperatures in the kiln. In order of technological maturity, from the most to the least developed, the options include, waste derived fuels and biomass, which are already widely commercially deployed, heating kilns with solar thermal energy (full prototypes at scale exist), direct electric heating (early prototypes exist), and the partial use of hydrogen (laboratory scale concept). In the European Union the substitution of fossil fuels with waste and forestry residues is already commonplace and makes up around 40% of the energy input to a typical cement kiln. Fuel switching to zero carbon fuels would eliminate the emissions associated with providing process heat energy at the cement plant.

Capturing Emissions: A variety of emissions capture techniques exist to take the flue gasses produced during the cement manufacturing process and prevent their release to the atmosphere. The captured CO2 can then be compressed, transported, and stored in geological formations such as depleted oil and gas fields or deep saline aquifers, or used to manufacture products. The most mature carbon capture technologies for use in the cement industry are chemical adsorption and calcium looping (pre-commercial demonstration) for full CO2 capture of CO2.

Electrochemical Pathways to Cement Production: Two novel approaches exist for the calcination of calcium carbonate at low temperatures. Electrochemical decarbonisation of calcium carbonate uses electrolysis to create lime, with the main byproducts being hydrogen, oxygen and CO2 (in a concentrated waste gas that is easy to capture). This potentially opens the door to a largely electrified pathway for production of a drop-in replacement for Portland cement using decarbonized grid electricity. Another promising approach is the chemical decarbonisation of calcium carbonate. Two groups have currently begun work in this area. The first uses a sodium hydroxide at ambient temperature and pressures, a reaction that produces lime while simultaneously achieving near total (95%) capture of the CO2 in a solid form (sodium carbonate, also known as washing soda). The second group, who have formed a company around their technology, Brimstone Energy, uses chemical decomposition of calcium silicate to produce both lime for cement and magnesium byproducts that are claimed to naturally reattach free CO2 from the air. Electrochemical cement production is currently still at the laboratory test scale