Our 2050 Roadmap - The 5C Approach: Carbonation

In addition to reducing emissions, carbon neutrality can also be reached through greenhouse gas emissions removal through carbon sinks, as recognised in the European Climate Neutrality Law. Cement and concrete have here a key role to play through a process called re-carbonation, which effectively transforms European cities into carbon sinks.

Re-carbonation is the process whereby concrete re-absorbs some of the CO2 that was released during clinker production. It is a process that occurs naturally in all concrete structures, permanently trapping the CO₂. Thanks to recarbonation, cities effectively act as carbon sinks, allowing further reduction of emissions in the full cement and concrete value chain.

How can we reduce emissions from re-carbonation?

Re-carbonation in the built environment

In the built environment, re-carbonation occurs naturally in all concrete infrastructure. According to research by IVL¹, 23% of process CO₂ emissions of cement used, is being captured annually which equates to a 8% saving of total CO₂ emissions for the cement manufactured.

Enhanced re-carbonation of recycled concrete

Re-carbonation increases after demolition of a concrete building. The recycled concrete aggregates have a higher surface area and can absorb more easily CO₂ within the concrete paste (cement, water and sand) from the ambient air. Initial research has shown this can be accelerated by using the exhaust gases from a cement kiln which have a higher CO₂ content and are also at a higher temperature increasing the CO₂ captured up to 50% of process CO₂ emissions². Separating the aggregates from the recycled concrete and grinding the cement paste also enables higher CO₂ capture with the added advantage that the resulting material can be used as a clinker replacement in cement or as an additive in concrete.

Carbonation of natural minerals

Natural minerals such as olivine and basalt when crushed can also be re-carbonated when exposed to air or kiln exhaust gases. Up to 20% process CO₂ emissions can be absorbed. Once carbonated these materials can be used as clinker substitutes.³

[1] IVL Research Paper
[2] Fastcarb Research
[3] Reco2de Research

How can policy support this transformation?

Re-carbonation has a significant, untapped potential

Concrete absorbs CO₂ during its lifetime – the EU should fully use this untapped potential. The re-carbonation of built concrete products over their life cycle should be recognised in CO₂ emissions accounting, carbon footprint methodologies, and CO₂ certification removal schemes.

Innovation in action

Some examples of research projects aiming to reduce CO₂ emissions

Fastcarb

Uses a reaction chamber in which exhaust gases from the kiln pass over crushed recycled concrete resulting in up to 50% CO₂ capture within the concrete paste.

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