Cement is a primary material in concrete as well as mortars, blocks, and plaster. It’s the glue that holds buildings and structures together. Most cement produced today is Ordinary Portland Cement (OPC) made by combining cement clinker, gypsum, and supplementary cementitious material (SCM).
The manufacture of 1kg of OPC releases between 0.7 and 1kg of carbon dioxide. Most of the emissions are assigned to the production of clinker. 50-60% of these emissions come from the calcination of the limestone, and most of the remainder from combustion of fossil fuels necessary to achieve the required kiln temperatures. As a result of this carbon dioxide release, cement production is responsible for around 7-8% of global CO2 emissions – and demand for cement will continue to increase with population growth up to 2050. Addressing these emissions will be critical if the world is to meet its climate goals.
Policy is Driving Change
Governments have implemented policies which should encourage emissions abatement. For instance, the EU Emissions Trading Scheme requires cement producers to buy permits to emit CO2 when exceeding their free allocations. Emitters can sell credits when under their allowance. However, free allowances to emit will be phased out with implementation of the Carbon Border Adjustment Mechanism which should promote emissions reduction (if the carbon price is high enough). In the U.S., the Biden Administration’s Buy Clean Task Force will now prioritize the use of low carbon concrete (among other materials) in nearly all public construction projects. This will be supported by direct investment into decarbonisation.
Industry also has reduction goals. The industry association, Dansk Beton (Denmark), has a goal to reduce 50% emissions by 2030 and several leading cement producers including Heidelberg, Holcim and Cemex have set targets to address their emissions and are planning to implement changes with increasingly robust standards, namely the Science Based Targets initiative.
Innovation is Addressing Abatement Challenges in the Cement Industry
The cement industry faces some difficult challenges when it comes to reducing emissions. Generally, new production processes with lower emissions tend to have higher production costs; while margins for producers are too slim to absorb these costs. Further, industry has significant capital sunk into the current production process and is slow to change.
Mature approaches to mitigation include clinker substitution, and to a lesser extent, carbon capture. Both face their own unique challenges. The use of alternative fuels such as tires, household, and commercial waste, is relatively commonplace. The approach displaces fossil fuel usage but unlocks carbon in these wastes.
Process Innovation, Carbon Capture and Use
Carbon capture involves separation of CO2 from other gases in flue gases, typically so it can be stored underground. This capture and storage approach attracts additional cost and is often constrained by the availability of CO2 transport and storage infrastructure. The cost of capture is falling as innovators such as Carbon Clean and Svante deploy technologies economically at smaller scales. Further, novel calciner configurations can enable the separation of process and fuel emissions while also enabling electrification or the use of alternative fuels. Leilac is currently engaged in deploying technology to capture around 100,000 tpa of CO2 in Hanover Germany, with construction commencing in 2023.
The use of carbon in fuels, chemicals, building materials and other products can address some of the challenges of capture and storage. For example, CarbonCure and Carbicrete use CO2 in the concrete curing process. The injected CO2 reacts with the concrete mix and becomes a calcium carbonate increasing the concrete’s compressive strength and improving its performance. Concrete4Change uses the same principle but through the application of carbon containing admixtures.
Synhelion is one of many companies looking to use captured carbon in the production of fuels or chemicals. Synhelion uses concentrated solar energy to turn CO2 and water into syngas. Synhelion raised $24M from CEMEX and others in December 2022 and is currently constructing an industrial plant to produce sustainable fuels using solar heat (and captured carbon). The start-up also connected its solar receiver with a CEMEX clinker production process to produce solar clinker (without use of fossil fuels).
Clinker Substitution and Supplementary Cementitious Materials
Clinker substitution involves the use of increasing amounts of SCM in place of clinker. These cements are already produced at scale by companies such as Ecocem, and can significantly reduce the emissions, depending on the rate of substitution. The approach can be constrained by prescriptive standards (which require minimum clinker ratios) and may be constrained by future availability of supplementary cementitious materials (common SCMs include fly ash from the coal-fired plants or blast furnace slag from the steel industry).
Innovators are increasingly raising funds to scale the use of alternative supplementary cementitious materials. Terra CO2 raised $46M in June 2022 to accelerate the commercialization of Terra’s OPUS cementitious materials made from a variety of local feedstocks and waste products. Meanwhile, Carbon Upcycling is piloting technology which will utilize its carbon utilization process to activate post-consumer coloured glass fines, sequestering CO2 emissions and producing high-performance SCMs.
Alternative Cements, Feedstocks, and Integrated Processes
A significant reduction in emissions can be achieved by using alternative feedstocks or processes which avoid the requirement to calcify limestone in clinker production. In many cases, the materials used as SCM can also be used as binding materials (when activated). This is a focus of many producers of SCM and other innovators including CemVision and Betolar. Another innovator, Brimstone Energy plans to produce Portland cement from calcium silicate rock. The process can be carbon negative because it produces magnesium compounds as a waste product which can be used to absorb carbon dioxide.
Significant reductions can also be achieved with the application of ‘bio-cement’ where organisms break down limestone, which is reconstituted in an end product e.g., bio-concrete. Several innovators have raised funding in the past year to develop bio-cements (or bio-concrete). BioMason raised $65M, Prometheus Materials raised $8M, and newly formed BioZeroc raised $450K in a pre-seed round.
Innovation Across the Value Chain
Ultimately, innovation can help significantly reduce emissions of the cement industry, but it will require funding to scale and bring down costs, and a focus on performance-based standards can help enable market access for alternative cements. We can also expect further innovation across the value chain: Mineralisation of CO2 in aggregates can lock away large amounts of CO2, production facilities can benefit from software solutions which optimise production processes and blends, and concrete 3D printing can help optimise installation.