In July, Heidelberg Materials switched on the first continuous-mode enforced carbonation reactor at its Górazdze cement plant in Poland, developed under the EU’s Carbon4Minerals project. The new facility applies the company’s patented ReConcrete process to recycled concrete paste (RCP), mineralising CO2 from the kiln flue gas and converting the RCP into a reactive supplementary cementitious material (SCM). Crucially, the gas is used directly, without purification or separation.
Inside the ReConcrete process
The ReConcrete process begins with demolition concrete, which is processed at Heidelberg’s Katowice facility to recover aggregates and, most importantly, the hydrated cement paste fraction. This RCP is a fine powder with a high calcium silicate hydrate content. Under enforced carbonation, the material is exposed to kiln exhaust gases inside a sealed rotary drum. Moisture and temperature are carefully controlled to maximise the chemical reaction.
As CO2 from the flue gas reacts with the RCP, it forms stable calcium carbonate crystals while simultaneously altering the microstructure of the paste. This has two key outcomes. First, the CO2 is permanently mineralised in the RCP, locking it away. Second, the carbonation reactivates the material, increasing its pozzolanic properties so it behaves like an effective SCM.
Figures released by the Carbon4Minerals consortium suggest that for every tonne of RCP processed, around 100–150kg of CO2 can be chemically bound in the material. More significantly, when that carbonated RCP is used as an SCM, it allows clinker substitution that avoids a further 750–850kg of CO2 emissions. The combined impact is close to 1t of CO2 avoided per tonne of RCP processed — a number that, if achieved at scale, would be highly material to the industry’s carbon balance.
Scaling the pilot
At Górazdze, the enforced carbonation reactor has been designed to operate continuously rather than in small experimental batches. Christian Pfeiffer supplied the pilot line, which features a rotary reaction drum and a bag filter system engineered for airtight operation. Throughput is around 1.5tph of RCP — modest in the context of cement production but significant for demonstrating continuous industrial operation.
The next step is optimisation: fine-tuning moisture levels, residence times and gas flows to maximise carbonation efficiency, and running durability tests on the resulting SCM. Long-term consistency is crucial, since demolition waste streams vary in composition. For rollout, Heidelberg and its partners will need to ensure reliable selective separation of concrete waste, robust quality assurance, and standards recognition so the carbonated RCP can be used without question in certified mixes. This requires coordination between demolition contractors, recyclers and cement producers — an approach already highlighted in Carbon4Minerals research, which stresses the importance of separation facilities like Katowice as the link between demolition sites and cement kilns.
Accounting and regulatory hurdles
A further challenge lies in how mineralised CO2 is treated under carbon accounting frameworks. The EU Emissions Trading System and Intergovernmental Panel on Climate Change (IPCC) methodologies have traditionally recognised geological storage as “permanent,” but uptake through carbonation of construction materials is newer ground.
While the IPCC’s 2019 Refinement accepts that permanent carbonation of alkaline materials can be a valid storage pathway, harmonised verification methods are not yet in place. European standardisation bodies such as CEN/TC 350 are working on rules to measure and account for CO2 uptake in concrete, but until those are finalised, producers may struggle to claim full credit for the carbon stored in products like ReConcrete. Closing that gap will be essential for widescale adoption.
From pilot to rollout
Scaling up will also mean overcoming logistical hurdles. Units at 1.5tph show technical feasibility, but to influence European emissions targets the process must be replicated at much larger volumes and in multiple locations. This will involve new investment in demolition sorting, transport, processing, and integration with existing cement plants. Local loops will matter: having RCP separation and kilns in the same region reduces transport costs and helps create a genuinely circular economy.
Despite the obstacles, the Górazdze demonstration shows enforced carbonation is leaving the laboratory and entering industrial practice. It provides a more practical, bolt-on technology than full CCS, with the added value of a saleable product.
