Carbon-free cement thanks to hydrogen?

Hydrogen is envisaged both to decarbonize the heat necessary for the design of cement and to recover the heat and CO2 resulting from it. These options would be combined with CO2 capture to produce a carbon-neutral cement. However, this idea is challenged by other interesting solutions for several low-carbon cements.

This article is a part of our dossier on hydrogen, innovation and ecology and more precisely its part of practical uses.

The construction industry is one of the most polluting sectors and one of the big reasons for this is cement. Its production alone is responsible for 7 to 8% of global greenhouse gas emissions. One of the main reasons for this terrible environmental impact is on the one hand a very important need for heat and on the other hand the very nature of the reaction: carbon is extracted from the limestone rock. The opposite of what should be done for the environment in short…

At the same time, it is a crucial production. Cement forms concrete when mixed with water, sand and gravel. This material, multiplying the possibilities of construction, has triggered an architectural revolution and, even if wooden constructions are making progress, it is hard to see consumption reducing soon. Decarbonizing cement production is therefore one of the most important challenges of the ecological transition.

We will start by going back to the production of cement today, before studying how hydrogen would make it possible to decarbonize it and what are the competing technologies. Along with steel production, this is one of the main non-electrifiable processes that hydrogen could help decarbonize.

Cement production: massive carbon dioxide emissions

Resistance and fluidity: a revolutionary material

Cement plays the role of “hydraulic binder“: mixed with sand and gravel, it gives concrete. In 1817, Louis Vicat discovered the theory of hydraulicity, which paved the way for the invention of cement as we know it, Portland cement, in 1824 by the British Joseph Aspdin. Louis Vicat also discovered clinker, a constituent element of slow cement and which will allow the development of Portland cement (rq: now we are talking about portland standard CEM).

Its mechanical, physical and chemical properties have triggered an unprecedented architectural revolution: it is liquid and endowed, once dry, with considerable resistance. Works that were unthinkable even a few years before have multiplied thanks to these new materials. Buildings with improbable shapes appeared, but also prefabricated buildings which provided housing for many workers.

Manufacturing cement in a nutshell

The cement path begins at the quarry: it is necessary to extract the limestone (80%) and the clay (20%) which are the main components. We will then grind them, reduce them to powder, to form what manufacturers call “flour”. It is placed in a circuit of “cyclone” pipes which leads it to a very powerful furnace. The material goes against the direction of hot air exceeding 900°C which will partially calcine it during its journey (we speak of “limestone calcination”). It will then be burned at 1450°C (usually using fossil fuels such as gas or coal) in a rotary kiln to form the “clinker“. Then it is brutally cooled, materials are added to it, the main ones being slag, from the reduction of iron in blast furnaces producing steel, pozzolan, cilice smoke or fly ash.

The final composition will determine its classification and use. There are different types of concrete. CEM-I includes >95% clinker and can be used for very demanding uses, such as slabs, floors or walls. The CEM-II includes 65% clinker and is suitable for structural work. CEM-III contains 5-64% clinker and the balance blast-furnace slag, hence its name “blast-furnace cement”. It can be found in large structures, such as the pillars of a bridge.

The chemical reaction of clinker production

What interests us here is on the one hand the calcination of the limestone (CaCO3 => CaO +‡ CO2). In fact, the carbon is removed from the limestone so that, recomposing itself with the silica and the alumina of the clay (SiO2–Al2O3), it makes tricalcium silicate or alite (Ca3SiO5, 50 to 65%), dicalcium silicate or belite (Ca2SiO4, 15-20%), tricalcium aluminate or aliminate (Ca3Al2O6, 5-15%) and tetracalcium ferro-aluminate or ferrite (Ca4Al2Fe2O10, 5-10%). (Wikipedia)

In addition to the energy consumption to produce the heat (generally between 3.3 and 4MJ/kg of clinker, JRC 2010 p.48), CO2 is therefore released chemically. Not great… In total, one tonne of clinker directly emits 535 kg of CO2 from limestone calcination and an average of 330 kg for heat production. (Kumar Chatterjee 2018, p.168) If we extend this analysis to the entire manufacturing life cycle, the carbon footprint of cement becomes even heavier: we must include GHG emissions from ore extraction and transport of these gigantic masses. Vasilakis (2001) estimates them at 141 kg of additional CO2.

Carbon-free cement thanks to hydrogen?

In general, decarbonizing cement production seems to be an important concern for the cement industry. Thus, the Vicat group has announced that it wants to achieve carbon neutrality by 2050. Lafarge (Holcim) announces that 55% of its R&D projects are devoted to carbon and that it wants to reduce net CO2 emissions per tonne of cement to 550kg in 2022 and 475kg in 2030.

Using hydrogen to decarbonize heat

Hydrogen is envisaged to replace fossil fuels (coal, gas) for the creation of heat necessary for heating the furnace. It was already possible to substitute part of the fuels with biofuels, but the bulk remained fossil energy. Hydrogen would make it possible to do without it completely. Obviously, the problem of its production would have to be solved: it is currently mainly derived from the steam reforming of methane or the gasification of coal. For these hypotheses to be viable, the hydrogen would have to come from low-carbon processes, such as electrolysis of water (with low-carbon energy) or pyrogasification.

However, this path is not simple: the hydrogen flame does not have the same properties as the methane flame and, if the desired effect can be achieved by coupling H2 to biofuels or biomass.

This is what the plant of the Hanson UK subsidiary of Heidelberg Cement in Ribblesdale (UK) successfully experimented with in October 2021. It successfully operated a furnace powered solely by green hydrogen, from biomass and glycerine co-produced by other industries. Everything would be carbon neutral. (press release from HeidelbergCement)

The Vicat group has announced that it will do without fossil fuels by 2024. There is also a partnership in Austria between Lafarge (cement manufacturer) and ThyssenKrupp (equipment manufacturer – electrolyzers)

Hydrogen to recover waste heat from clinker production

Another way to reduce GHG emissions from cement is to recover the waste heat produced. One of the ways to do this would be by combining it with high temperature electrolysis. The cement manufacturer Vicat has joined forces with the Atomic Energy Commission (CEA) to recover heat using high-temperature electrolysers developed by Genvia.

Hydrogen to recover CO2

The CO2 produced on site could be combined with H2 to produce methane or methanol.

This is the possibility explored by the Hynovi project led by the Vicat group. The cement manufacturer plans to capture 40% of the CO2 from a cement plant (Montalieu-Vercieu, 38) and combine it with the low-carbon hydrogen produced on site by the Hynamics electrolysers (330MW announced for 2025) to produce carbon-free methanol ( 200,000 tonnes per year announced, i.e. a quarter of France’s methanol consumption).

Lafarge – Holcim is trying, along the same lines, to recover the CO2 produced into green fuel in an experimental unit in Lägerdorf, Germany.

Hydrogen to reduce indirect emissions

The manufacture of cement mobilizes extremely heavy vehicles. These cannot be electrified with batteries: the latter would be too heavy. This is one of the advantages of hydrogen: it can (to go further, I refer you to our article on hydrogen mobility).

The Vicat group has, in this sense, experimented with the production of hydrogen on site. They plan to produce enough of it to supply 10 Nikola trucks, on the one hand thanks to alkaline electrolyzers supplied by Hynamics, the EDF subsidiary, and on the other hand thanks to the high-temperature electrolysis which we have just talk.

The necessary carbon capture

Obviously, using hydrogen to heat the cement does not solve the problem of GHG emissions from the limestone decalcification reaction itself. It would therefore be necessary to use carbon capture (CCUS) to capture the emissions in question.

LafargeHolcim allegedly has 20 CCUS projects in Europe, Canada and the US exploring in particular different avenues for storage / use.

One of the ways to improve it is Leilac technology (Low Emissions Intensity Lime And Cement). This would be based on the Calix “direct separation” technology, which would have been designed for the production of magnesite and has been fitted to a commercial-scale reactor since 2013. The difficulty of adaptation would lie in the heat, which is much higher in the case of cement, fumes. An experimental unit (LEILAC1) was built in Lixhe (Belgium) in 2019. The LEILAC2 project, starting in 2020 and funded to the tune of 16 million euros by the European program Horizon 2020, aims to separate (recover?) 20% of the emissions of a standard cement manufacturing plant. At the same time, the university will experiment with (potentially) low-carbon heat sources (electricity and alternative fuels).

Parentheses: some alternative cements

Beyond these innovations, it seems interesting to me to mention the alternatives to traditional cement. You have:

  • Cements (H-Iona, H-UKR, etc.) from Hoffmann Green Cement Technologies (HGCT) are produced cold, without cooking and without limestone, using co-products from industry (slag from blast furnaces, clays, phosphogypsum, etc.). ), which makes it possible to produce concrete comparable to traditional concrete. They announce a concrete several times less polluting Imagined in 2014 by Julien Blanchard and David Hoffmann, the company was listed on the stock market in 2019.
  • LafargeHolcim has developed a range of “ECOplanet” cements which would emit 30 to 90% less CO2 in 2020. Ecoplanet prime would emit ~50-60% less CO2, Ecoplanet max ~80-90% and Ecoplanet zero would be coupled with carbon compensation to reach 100%. The first Ecoplanet cement would have been available in 2021.
  • Ciments Calcia, a French subsidiary of HeidelbergCement, is also developing FastCarb (Accelerated Carbonation of Recycled Concrete Aggregates), which consists of using recycled concrete to absorb CO2.
  • Wood concrete. It would involve incorporating wood aggregates into the concrete recipe. This is what CCB greentech would offer with “TimberRoc“. This can also be combined with low carbon cements. This is what Capremib, a manufacturer of precast concrete, attempted to do with the HGCT solution in 2020.

Note that the use of slag from blast furnaces during iron reduction could be contradicted if this steelmaking process is replaced by the direct reduction of iron with hydrogen (DRI-EAF). This could interfere with solutions like H-Iona or Ecocem, which rely on it. The cement industry knows this well, Calcia has also recognized it:

But this type of recycling will decrease due to the transformation of the steel industry: the future is no longer in blast furnaces but in steel production combining pre-reduced iron ore (DRI) and electric arc furnace (EAF). This process significantly reduces CO2 emissions but its residues can no longer be used as such by the cement industry. This is why the “SAVE CO2” project seeks to develop new types of EAF slag that can be used as components of cement and concrete. These innovations aim to strengthen the circular economy and synergies between the steel and cement industries.

(in french)

Thus, there is a lot of research and innovation on the decarbonization of concrete. Will hydrogen come out as the most viable solution? It is uncertain.


  • Joint Research Centre, Institute for Prospective Technological Studies, Kourti, I., Delgado Sancho, L., Schorcht, F., et al., Best available techniques (BAT) reference document for the production of cement, lime and magnesium oxide : Industrial Emissions Directive 2010/75/EU (integrated pollution prevention and control), Publications Office, 2013,
  • Davis J.S. et al. (2018), « Net-zero emissions energy systems », Science • 29 Jun 2018 • Vol 360, Issue 6396 • DOI: 10.1126/science.aas9793
  • Vasilakis, N. (2001) Life Cycle Assessment and Exergy Analysis of Concrete, Diploma Thesis, LHTEE/AUTh, Thessaloniki, Greece. (cité dans Koroneos et al. 2005)
  • C’est pas sorcier -BETON : Les sorciers au pied du mur