Holcim and Canary Wharf unveil net-negative concrete using biochar, marking a seismic shift in sustainable construction

A consortium led by Holcim UK and Canary Wharf Group has demonstrated a concrete mix that its backers say achieves net zero , and even net-negative , lifecycle emissions by embedding biochar made from local waste into structural pours across live London projects. According to ESG News, full-scale trials at Canary Wharf produced a projected net global warming potential of -14 kgCO₂e per cubic metre after optimisation, turning conventional thinking about concrete’s carbon role on its head.

The programme combined contractors and engineering consultancies including O’Halloran O’Brien, Arup, Ramboll, B&GE, Thornton Tomasetti, Walsh Associates and Robert Bird Group with academic partners from Queen’s University Belfast and the University of Cambridge. Trial pours began in April 2025 and continued through to large raft slabs in September at Bank Street and a theatre slab at Wood Wharf, allowing assessment under real construction conditions rather than in the laboratory. ESG News reports the initial biochar mixes delivered up to an 80 percent reduction in net Global Warming Potential versus standard CEM I concretes, with an intermediate result of 69 kgCO₂e/m³ before further optimisation reached negative values.

At the heart of the innovation is biochar produced from coppiced hardwood and spent coffee grounds collected from Canary Wharf’s retail outlets. The process locks biogenic carbon into a stable, charcoal-like material that is then incorporated into the concrete matrix, effectively converting built elements into long-term carbon stores. Holcim’s own materials note that adding biochar can permanently sequester carbon and that its low-carbon concrete range can reduce embodied emissions by up to 70 percent while retaining required mechanical properties.

Holcim’s product development lead, Jasen Gauld, framed the trials as a demonstration for market adoption: “The aim of these trials was to show that next-generation concrete mixes can perform as well as, or better than, standard concretes – giving contractors and the wider supply chain confidence to adopt them and embedding circular thinking into the buildings we help create. “By optimising the biochar-coffee mix, we have achieved net zero concrete – a Holcim first – while maintaining strength, durability, and circularity. Where increased binder might otherwise have been needed, our products can remove that requirement, reducing overall embodied carbon. At the same time, the carbon in the biochar is locked into the concrete, allowing buildings to fulfill a new role as long-term carbon stores, keeping CO₂ safely out of the atmosphere. This demonstrates that high-performance, low-carbon, circular materials are ready for real-world use.”

Canary Wharf Group’s role as both client and delivery partner allowed rapid on-site validation. Jonathan Ly, Director of Structures at CWG, said: “This collaboration represents a pivotal moment for the real estate sector’s transition to net zero. As both developer and main contractor, CWG occupies a unique position in the industry where we can validate next-generation materials on live projects at pace, allowing us to build the market confidence that low-carbon concrete needs to become mainstream. “Achieving net-zero concrete with our biochar-coffee mix demonstrates that circular economy principles aren’t just aspirational, they can deliver measurable environmental and commercial value. By transforming spent coffee grounds from our own retailers into a construction material that sequesters carbon, we’re proving that sustainable development can be both ambitious and practical.”

The trials also explored alternative low-carbon binders and admixtures. ESG News and Holcim materials reference mixes using graphene that halved emissions while improving strength and durability, and comparisons against blends containing ECOCEM ACT were used for benchmarking. Holcim additionally showcased biochar concrete internationally at the 2025 Architecture Biennale in Venice alongside architect Alejandro Aravena and ELEMENTAL, applying the technology in a full-scale Basic Services Unit prototype that used 100 percent recycled aggregates, according to a Holcim media release and coverage in Concrete Connect.

Partners plan two years of post-placement monitoring , led by project contributors including Skanska, Arup and Queen’s University Belfast , to produce the verification data that regulators, clients and investors will require before such mixes can be accepted at scale. Industry commentary in Resource Media highlights the September 2025 pour that delivered the -14 kgCO₂e/m³ projection but stresses that long-term durability, standardised testing protocols for biogenic carbon accounting and supply-chain scaling for feedstocks remain gating factors for broader procurement.

For investors and procurement teams focused on industrial decarbonisation, the trials indicate a route where emissions reductions and carbon removal converge via circular feedstocks. If monitoring confirms durability and the accounting holds up under scrutiny, net-zero or net-negative concretes could change embodied-carbon calculations for major infrastructure pipelines and alter asset-level climate risk assessments. Regulators tightening embodied-carbon disclosure in Europe and beyond will be watching the verification process closely, and developers with in-house project pipelines such as Canary Wharf may accelerate commercialisation by acting as early adopters and validators.

The Canary Wharf programme, Holcim’s biennale demonstration and the Whale on the Wharf sculpture , which used the biochar mix for underwater counterweights and was reported to cut embodied carbon by two thirds , together create multiple real-world proof points. Nonetheless, widespread adoption will depend on standardised measurement, clear treatment of biogenic carbon in building codes and secure, sustainable collection channels for organic waste feedstocks. The next 24 months of monitoring and independent review will therefore be decisive in determining whether biochar-enhanced concrete can move from pioneering projects to procurement mainstream.