There are good opportunities to reduce emissions from cement production, which now amount to some 7 per cent of global carbon dioxide emissions.
A previously published discussion paper advocated for opportunities to eliminate emissions from cement, which now amount to some 7 per cent of global CO2 emissions. Here follows a short summary of the discussion paper. The core process to produce cement drives out CO₂ from the limestone (a carbonate) to create cement clinker. CO2 is also produced from fossil fuels that are used to heat the limestone.
One thing that has not cut emissions is CCS. Though widely hyped since at least 2007, by Cembureau and others, there is still no cement plant in the world that uses CCS. Heidelberg Cement aims to capture 0.4 million tons per year at its Norcem plant in Norway by 2024, 0.4 per cent of the cement emissions in the ETS.
An alternative policy to CCS might be that Portland cement1 has to go the same way as other forms of fossilised carbon; just stop using them.
Research for alternative binders – the cements that glue sand and pebbles together to make concrete – is not pursued with enough vigour. When promising research is produced, it is not implemented.
The reason is simple. The current cement producers want to do what they do: mine limestone at their quarries, burn limestone in their kilns, mill it into the grades the construction industry is familiar with and transport the cement to more or less the same customers as now.
Change is always difficult. For a cement quarry/kiln/harbour it means scrapping existing capital and investing in something completely different somewhere else.
Magnesium cement or geopolymers could replace Portland cement for many applications, but this would require new quarries with new machinery, and new marketing channels.
The cement industry is resistant to change. It can resist because it is oligopolistic, with Holcim and Heidelberg near-monopolies in many parts of Europe.
There are many different alternatives to carbon-emitting cement, for example:
- Less cement per volume of concrete, as so much cement is not needed everywhere
- Less concrete through better design
- Other binders for concrete: fly-ash, slag, volcanic ash, crushed lava, rice husk and barley husk ashes, silica fume, crushed limestone (not burnt, not CO₂-emitting), and clay-based geopolymers . Some of them are already used extensively. The remaining potential is still big. Volcanic cement use “is abundant in certain locations and is extensively used as an addition to Portland cement” in Italy, China and Greece . Some of the alternative binders have a negative cost according to a McKinsey report .
- The IPCC WG3 report says that calcinated clay and limestone alone have a 40–50 per cent GHG reduction potential at near-zero cost, and that this could take place “today”. Calcinated clay is a very common mineral.
- The IPCC also says that “magnesium or ultramafic cements” may cut GHG to negative by 2040, but at unknown cost. Ultramafic means minerals with high alkalinity.
- Better aggregates, i.e. the sand and pebbles that the cement binds together. If aggregates are “multi-sized and well dispersed”, less cement is needed. The IPCC WG3 says this can cut emissions by up to 75 per cent at near-zero cost, and can be done “today”.
- A concrete building reabsorbs some CO₂ during its lifetime, and this is often used as a climate selling point by the cement industry. It is presently not credited against emissions in the IPCC guidelines. Industry-sponsored research has asked the IPCC to “update” its guidelines in this respect, but the world will not be saved by creative accounting.
- Alternative reinforcement for reinforced concrete: by using ceramics, glass polymer (plastic) fibres, stainless steel, or even graphene. If a lower pH can be accepted (as those materials do not rust, less cement is needed. If the carbon-intensive iron rebars are replaced with such fibres it would reduce emissions significantly.
- Other materials can replace concrete, some for niche applications in buildings, others more generally: wood, brick, stone (e.g. granite, for foundations), glass, steel, foam glass (for foundations), aerogel, MgO boards, and asphalt.
Wood alone could substitute for concrete and steel as building materials and “could provide a technical mitigation potential of 0.78–1.73 Gt CO₂” per year in a study quoted by the IPCC. Obviously, the availability of wood is limited, but there is some potential. The International Code Council now allows for construction of wood buildings up to 18 storeys tall.
Fredrik Lundberg
1 Portland cement is the most common type of cement.
Link to discussion paper: https://www.airclim.org/sites/default/files/documents/strengthening-eu-c... p15ff
