Climate change and environmental degradation pose an existential threat to Europe and the world. To overcome these challenges, the European Union (EU) has adopted a set of proposals under the European Green Deal (EGD) to align climate, energy, and taxation policies with the target of reducing net greenhouse gas emissions by at least 55% by 2030, compared to 1990 levels. The EGD also serves as a growth strategy that aims to transform the EU into a fair and prosperous society where there are no net emissions of greenhouse gases in 2050.
Among the sectors driving environmental degradation, the construction industry is a major contributor through resource depletion, CO2 emissions, and waste generation. Concrete, the most widely used man-made material worldwide, accounts for about 8-10% of global CO2 emissions, primarily from cement clinker production. Over the past decades, the use of supplementary cementitious materials (SCMs), such as granulated blast furnace slag (GGBS) and fly ashes (FA), has proven effective in reducing CO2 emission by up to 30–40% in the construction sector through partial replacement of cement in concrete. However, the availability of these traditional SCMs is steadily declining due to factors such as increased demand, higher steel recycling rates, reduced coal-fired power generation, and the shift toward renewable energy. The limited supply of high-quality SCMs therefore poses a significant barrier to scaling up green concrete production.
At the same time, construction and demolition waste is the largest waste stream in the EU, accounting for more than a third of all waste generated. A major fraction of this stream is waste concrete powder (WCP), whose volume continues to rise at the end of concrete’s life cycle, creating serious challenges for landfill management. Due to its high-water absorption and low reactivity, only a small portion of WCP generated in the EU is currently reused, with most ending up in landfills.
In this context, W2WGCO2 aims to explore the potential of reusing WCP and bottom ash from bioenergy facilities (carbon-rich biochar) as alternative materials to cement. Specifically, WCP is treated through CO2 capture, while biochar undergoes an innovative surface treatment. Subsequently, cementitious composites incorporating cement (20-50%), carbonated WCP, low-grade calcined kaolinite clay, and pre-treated biochar are developed, achieving binder strengths of 32.5-42.5 MPa.
The first objective of W2WGCO2 is to enhance the pozzolanic reactivity of WCP through wet carbonation in concrete washout water and seawater. This approach not only improves the cementitious properties of WCP and enables higher cement replacement levels in concrete but also reduces freshwater usage during carbonation, facilitating the large-scale implementation of wet carbonation processes.
The second objective of W2WGCO2 focuses on the surface treatment of biochar using an innovative solution, increasing its replacement level from 4% (as reported in existing literature) to 10%, while achieving comparable 28-day compressive strength to pure cement. The last objective is to develop composite binders with a minimum grade of 32.5 MPa, in which 50-80% cement is replaced by low-value solid residues such as WCP, calcined clay, and biochar. By achieving these objectives, W2WGCO2 will introduce new SCMs for low-carbon cement production while permanently capturing CO2, reducing resource depletion, and minimizing the waste volume in landfills.
