The starting point, as Pierluigi Zerbino explained to an audience of businesses and academics, is disarmingly simple: “We asked ourselves: can the circular economy help to decarbonise the construction industry?” Behind that question, however, lies a concrete problem that European policymakers have been grappling with for years.
Brussels has already drawn up policy packages, action plans, and incentives based on the assumption that the circular economy can deliver specific benefits in the construction sector: reductions in emissions, material consumption, and decarbonisation costs. There is, however, a problem, explains Davide Aloini, professor at the University of Pisa: “To date, there are no validated models that enable a systematic and comprehensive assessment of the impact that the circular economy can have on reducing emissions within the European economic and industrial system.”
This is where CO2NSTRUCT comes in, a Horizon Europe project involving the Department of Energy, Systems, Territory and Construction Engineering (DESTEC) at the University of Pisa, which was presented on 25 June in the main lecture hall of the School of Engineering.
CO2NSTRUCT builds on TIMES, the model used by several European countries to support their national energy planning, and maintained by the European Commission’s Joint Research Centre in a dedicated version (JRC-EU-TIMES) to simulate the evolution of the energy system across the 27 EU Member States up to 2050. It is not a forecasting tool but a scenario tool: it does not predict what will happen, but explores what could happen if one or more variables are changed. The decision to start from an already validated model, rather than from a blank page, gives CO2NSTRUCT a level of credibility that a prototype built from scratch would not yet possess.
The problem is that TIMES, in its original form, was not designed to account for circularity. Zerbino explained this plainly during the same event in Pisa: “The TIMES model has some weaknesses for our purposes, even though it is fairly comprehensive for its original objectives: it does not include some supply chains relevant to construction, it assesses sectors in isolation, and it does not know what additional activities are required to implement circularity.”
In other words, there were three specific shortcomings: the model overlooked some raw material production chains relevant to construction; it did not link changes in demand from Europe’s building stock to the resulting need for materials and their production; and it could not quantify the economic and environmental costs, or the additional benefits (such as reduced demand for virgin raw materials), associated with activating a circular system.
Addressing these gaps required four years of work: a review of technical and scientific literature, mapping of European circular supply chains, field data collection with industry – a task carried out in particular by the University of Pisa – and the structured synthesis of this data into information useful to extend the capabilities of the TIMES model. At the Pisa event, the latest figures presented by engineer Giammarco Montalbano showed 180 circular practices identified in the literature across six material clusters (steel, cement, glass, brick, insulation materials and wood), 40 analysed in detail and 26 already incorporated into the model.
One of the supply chains examined by the project was flat glass, significant both for its economic importance and for its potential contribution to Europe’s green transition. From silica sand extraction to glass melting, every stage (energy, water, materials and emissions) is tracked to determine which steps can genuinely be avoided through recycling or reuse. Discussions with industrial stakeholders clearly show that, at present, flat glass can only be recycled “flat to flat”: producing new flat glass requires cullet from other flat glass products, rather than glass from bottles or packaging. Increasing, for example, the share of cullet from the current 30% to 50% by 2030 would require collection volumes that are difficult to envisage on an industrial scale.
The model is designed to help bring clarity and order when assessing the impacts of the circular economy. In an interview given in June, Zerbino was unequivocal: “We know that decarbonising the construction sector through the circular transition could represent an additional cost for individual stakeholders, but at a global system level it could deliver savings compared with alternative decarbonisation strategies.”
The preliminary results presented in Pisa give this idea an initial figure: the model has already identified eleven circular practices that are cost-effective compared with the reference scenario, and estimates that the circular economy could reduce the cost per tonne of CO₂ abated in the European construction sector, while also lowering the sector’s electricity demand by 2050.
The project acknowledges that knowledge gaps remain, for example in the wood supply chain, where 80% of European sawmills are micro or small enterprises that often do not even collect cost data. This uncertainty exists alongside an increasingly complex regulatory landscape: the EPBD Directive (EU) 2024/1275 will make the calculation of embodied carbon in construction materials mandatory for new buildings larger than 1,000 square metres from 2028, and for all buildings from 2030.
Aloini and Zerbino stress that the model remains a prototype, dependent on the availability of industrial data that are not always there. Yet the role the project aims to play was summed up by Zerbino in a single sentence at the end of the Pisa presentation: “Our model aims to become a tool to support this type of decision-making.” It is precisely the kind of tool that European circular economy policy has lacked for years.
Cover: photo by Envato