The Challenge

Concrete manufacturing is a major contributor to global greenhouse gas emissions, accounting for approximately 6–8% of worldwide CO2 emissions. This stems largely from the energy-intensive process of heating limestone at very high temperatures during cement production, a key ingredient in concrete (IEA, 2023). With ongoing urbanisation and industrial growth, demand for concrete is expected to rise, intensifying its environmental impact.

Energy consumed during the day-to-day functioning and maintenance of buildings represents about 30% of global energy consumption. This increases to 34% when including the energy used to produce of cement, steel and aluminium in their construction (IEA, 2023). The construction sector also requires huge amounts of resources and accounts for about 50% of all extracted material (European Commission, 2018). These figures underscore the critical need for circular approaches that reduce resource use and emissions in construction.

The Circular Opportunity

Zurich’s Ultra Green Concrete (UGC) project, led by ETH Zurich, offers an innovative model for sustainable concrete production.

Cement production typically involves using around 95% clinker mixed with a small proportion of gypsum. The clinker is created by heating limestone and clay in kilns at roughly 1,450 °C, a process that inherently generates carbon dioxide through the breakdown of limestone (Ethz.ch, 2023).

The UGC project reduces reliance on clinker - the most carbon-intensive components in cement - by substituting it with alternative minerals such as calcined clay and limestone. This lowers the overall cement content and cuts CO₂ emissions in the concrete manufacturing process (Ethz.ch, 2023).

In parallel, the ETH Zurich ‘Airlements’ project utilises recyclable mineral foam to create 3D-printed formwork components, which further reduces the volume of concrete needed on site. The foam is made from recycled industrial waste formed together with foam and finished with a cement-free protective plaster which can be assembled into a two-meter-tall system for non-structural walls (Designboom, 2023). This combination of material innovation and smart construction techniques improves both resource efficiency and sustainability in building processes.

ETH Zurich’s approach also focuses on recycling demolition waste as input for fresh concrete production. By reusing up to 98% of recycled concrete in new builds, exemplified by and extension to Zurich’s main art gallery Kunsthaus Zurich, this approach avoids landfill disposal and conserves virgin raw materials (Bloomberg, 2021).

Climate and Resource Impact

These circular methods have yielded measurable emissions reductions. The UGC project has achieved nearly a 40% reduction in CO₂ emissions compared to traditional concrete mixes. Depending on the application, the project’s concrete can emit as little as 80–100 kg of CO₂ per cubic metre, compared with approximately 300 kg/m³ for conventional mixtures (ETH Zurich, 2023).

Additionally, by employing recyclable mineral foam formwork, UGC reduces concrete usage by up to 70%, further amplifying the environmental benefits (3D Printing Industry, 2025). The project has also saved an estimated 17,000 m³ of virgin materials and significantly reduced landfill requirements, aligning with circular economy principles of waste minimisation and resource conservation.

Replicability and Industry Innovation

Zurich’s success has inspired a growing movement among companies and cities worldwide to adopt circular concrete technologies. The UGC project aims to make high-performance, low-carbon concrete more accessible to the broader construction sector (ETH Zurich, 2023).

The UGC project serves as a practical model for sustainable manufacturing of construction materials. Ireland’s own manufacturing and construction industries can draw valuable lessons to support circularity, reduce emissions, and meet net-zero commitments through innovation in recycled concrete technologies and material efficiency.

Examples of emerging sustainable concrete innovations include:

• CarbonCure Technologies injects recycled CO₂ into fresh concrete, permanently mineralising the gas and lowering the carbon footprint while maintaining performance.

  
  

• Biomason uses microorganisms to ‘grow’ biocement, dramatically cutting emissions from cement production and producing certified biocement products in commercial-scale factories.

  
  

• Neustark captures carbon dioxide from industrial biogas plants, storing it safely within recycled concrete aggregates to create a long-lasting carbon sink and producing certified carbon credits.

These innovations demonstrate significant progress in transforming concrete from a major CO₂ emitter into a material aligned with circular economy and climate goals.