Periodic Reporting for period 1 - W2WGCO2 (Waste to Worth: A green solution for waste concrete powder and incinerator bottom ash reinforced by CO2 capturing in concrete)
Période du rapport: 2023-05-01 au 2025-10-31
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.
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.
This study aims to develop a novel low-carbon binder by reducing cement and freshwater consumption. The project was carried out in the following phases:
Phase I: Evaluating the efficacy of concrete washout water and seawater in wet carbonation of waste concrete powder
This phase investigated the feasibility of utilizing concrete washout water (CWW) and seawater (SWW) in the wet carbonation of waste concrete powder (WCP), with a particular focus on the effect of temperature. The experimental program examined how temperature (20 °C, 45 °C, 60 °C) influenced the carbonation degree, the growth rate of carbonate crystals, and the polymerization of silicates in carbonated WCP. The CO2 sequestration and reaction products of carbonated WCP were characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The results indicated that the main carbonation products are calcite, decalcified tobermorite-like C-S-H gel and amorphous silica gel. Elevated temperatures accelerated the carbonation rate, and a carbonation degree comparable to that achieved in distilled water was reached after 60 min. Moreover, the pozzolanic reactivity of WCP was enhanced after carbonation. The findings of this study are expected to not only promote sustainable wastewater management in the concrete industry but also contribute to the practical implementation of carbonation technology in industrial applications.
Phase II: Turning biomass waste into sustainable supplementary cementitious materials
In this phase, innovative methods were developed to incorporate biochar as a sustainable green binder. For this purpose, biochar was first surface-treated using an innovative solution, and subsequently, biochar-cement paste mixtures were prepared with replacement levels of 2-20%. The workability, setting time, and compressive strength of the blended pastes were evaluated, and their microstructural characteristics were analyzed using advanced characterization techniques. This pre-treatment method effectively increased the cement replacement ratio by biochar from 4% (as reported in existing literature) to 10% in construction materials without compromising 28-day compressive strength, while also reducing global CO2 emissions by 10% to over 20%.
Phase III: Development of low-carbon binders from carbonated WCP, calcined clay, and biochar
After carbonating WCP and pre-treating biochar, low-carbon binders containing 20-50% of cement were developed using carbonated WCP, treated biochar, and low-grade calcined kaolinite clay. The effects of biochar content on the fluidity and mechanical properties were systematically investigated. The hydration mechanism of the 7- and 28-day binders was comprehensively characterized using TGA, XRD, FTIR, SEM, and TAM-air calorimetry. Compared to a mixture with 50% cement, partial replacement of cement with up to 8% biochar increased compressive strength and then slightly decreased it. Nevertheless, it was possible to produce binders with a minimum strength of 32.5 MPa, even with 20% cement.
Phase I: Evaluating the efficacy of concrete washout water and seawater in wet carbonation of waste concrete powder
This phase investigated the feasibility of utilizing concrete washout water (CWW) and seawater (SWW) in the wet carbonation of waste concrete powder (WCP), with a particular focus on the effect of temperature. The experimental program examined how temperature (20 °C, 45 °C, 60 °C) influenced the carbonation degree, the growth rate of carbonate crystals, and the polymerization of silicates in carbonated WCP. The CO2 sequestration and reaction products of carbonated WCP were characterized using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The results indicated that the main carbonation products are calcite, decalcified tobermorite-like C-S-H gel and amorphous silica gel. Elevated temperatures accelerated the carbonation rate, and a carbonation degree comparable to that achieved in distilled water was reached after 60 min. Moreover, the pozzolanic reactivity of WCP was enhanced after carbonation. The findings of this study are expected to not only promote sustainable wastewater management in the concrete industry but also contribute to the practical implementation of carbonation technology in industrial applications.
Phase II: Turning biomass waste into sustainable supplementary cementitious materials
In this phase, innovative methods were developed to incorporate biochar as a sustainable green binder. For this purpose, biochar was first surface-treated using an innovative solution, and subsequently, biochar-cement paste mixtures were prepared with replacement levels of 2-20%. The workability, setting time, and compressive strength of the blended pastes were evaluated, and their microstructural characteristics were analyzed using advanced characterization techniques. This pre-treatment method effectively increased the cement replacement ratio by biochar from 4% (as reported in existing literature) to 10% in construction materials without compromising 28-day compressive strength, while also reducing global CO2 emissions by 10% to over 20%.
Phase III: Development of low-carbon binders from carbonated WCP, calcined clay, and biochar
After carbonating WCP and pre-treating biochar, low-carbon binders containing 20-50% of cement were developed using carbonated WCP, treated biochar, and low-grade calcined kaolinite clay. The effects of biochar content on the fluidity and mechanical properties were systematically investigated. The hydration mechanism of the 7- and 28-day binders was comprehensively characterized using TGA, XRD, FTIR, SEM, and TAM-air calorimetry. Compared to a mixture with 50% cement, partial replacement of cement with up to 8% biochar increased compressive strength and then slightly decreased it. Nevertheless, it was possible to produce binders with a minimum strength of 32.5 MPa, even with 20% cement.
W2WGCO2 goes beyond the state of the art thanks to multiple results:
1) Wet carbonation is a promising method for recycling waste concrete powder (WCP) while permanently sequestering CO2. However, the large amount of fresh water required in wet carbonation challenges its practical implementation. Hence, using concrete washout water (CWW) and seawater as alternative carbonation media not only reduces freshwater consumption but also addresses the challenge of managing the large volume of CWW generated in ready-mixed concrete plants. This approach also enhances the feasibility of implementing the carbonation process in real-world applications.
2) W2WGCO2 introduced an innovative treatment method that increased the viable cement replacement level of biochar from 4% (in previous attempts) to 10%. By providing affordable and eco-friendly alternatives such as WCP and biochar, this project addresses the shortage of conventional supplementary cementitious materials (e.g. fly ash and slag) in the future while supporting the industry in meeting future environmental regulations. Expanding the use of biochar as a partial cement substitute could increase the share of the low-carbon concrete market from 6% to at least 10%.
3) W2WGCO2 can significantly mitigate the environmental impacts of the cement and concrete industry by capturing CO2 in WCP and partially replacing cement with alternative materials. In addition, it helps conserve natural resources and improves the management of solid waste and wastewater, thereby reducing landfill use.
Therefore, W2WGCO2 manages to advance the state of the art in producing green concrete, not only in terms of environmental sustainability but also by creating economic opportunities, reducing construction costs, promoting resource efficiency, and supporting the development of a low-carbon construction sector. The project assists both the construction industry and the governmental sector in reducing CO2 emissions and promoting sustainable practices to meet the net-zero goal in Norway and EU by 2050. Construction companies can integrate W2WGCO2 methods into their practices to develop low-carbon cement-based products and green concrete. The proposed low-carbon binders can be utilized in various concrete applications, including ready-mix concrete, concrete blocks, and precast elements, as well as in construction projects such as buildings, roads, bridges, and infrastructure. Additionally, cement manufacturers can adopt this method to produce eco-friendly cement, meeting the growing demand for sustainable construction materials. Furthermore, by incorporating WCP and biochar in the cement, the project engages renewable energy companies (which produce biochar during the biomass pyrolysis process) and the waste management industries, creating additional socio-economic benefits.
In total, W2WGCO2 provides significant environmental benefits by addressing the cement industry’s 8-10% contribution to global CO2 emissions, aligning with four UN Sustainable Development Goals: SDG 13 (Climate Action) by reducing CO2 emissions by over 50% through development of low-carbon composite binders (with 50-80% cement replacement); SDG 9 (Industry, Innovation, and Infrastructure) by promoting sustainable industrialization with low-carbon materials; SDG 11 (Sustainable Cities and Communities) by creating greener urban environments; and SDG 12 (Responsible Consumption and Production) by using WCP and biochar as cement substitutes and CWW and seawater as alternative water sources.
1) Wet carbonation is a promising method for recycling waste concrete powder (WCP) while permanently sequestering CO2. However, the large amount of fresh water required in wet carbonation challenges its practical implementation. Hence, using concrete washout water (CWW) and seawater as alternative carbonation media not only reduces freshwater consumption but also addresses the challenge of managing the large volume of CWW generated in ready-mixed concrete plants. This approach also enhances the feasibility of implementing the carbonation process in real-world applications.
2) W2WGCO2 introduced an innovative treatment method that increased the viable cement replacement level of biochar from 4% (in previous attempts) to 10%. By providing affordable and eco-friendly alternatives such as WCP and biochar, this project addresses the shortage of conventional supplementary cementitious materials (e.g. fly ash and slag) in the future while supporting the industry in meeting future environmental regulations. Expanding the use of biochar as a partial cement substitute could increase the share of the low-carbon concrete market from 6% to at least 10%.
3) W2WGCO2 can significantly mitigate the environmental impacts of the cement and concrete industry by capturing CO2 in WCP and partially replacing cement with alternative materials. In addition, it helps conserve natural resources and improves the management of solid waste and wastewater, thereby reducing landfill use.
Therefore, W2WGCO2 manages to advance the state of the art in producing green concrete, not only in terms of environmental sustainability but also by creating economic opportunities, reducing construction costs, promoting resource efficiency, and supporting the development of a low-carbon construction sector. The project assists both the construction industry and the governmental sector in reducing CO2 emissions and promoting sustainable practices to meet the net-zero goal in Norway and EU by 2050. Construction companies can integrate W2WGCO2 methods into their practices to develop low-carbon cement-based products and green concrete. The proposed low-carbon binders can be utilized in various concrete applications, including ready-mix concrete, concrete blocks, and precast elements, as well as in construction projects such as buildings, roads, bridges, and infrastructure. Additionally, cement manufacturers can adopt this method to produce eco-friendly cement, meeting the growing demand for sustainable construction materials. Furthermore, by incorporating WCP and biochar in the cement, the project engages renewable energy companies (which produce biochar during the biomass pyrolysis process) and the waste management industries, creating additional socio-economic benefits.
In total, W2WGCO2 provides significant environmental benefits by addressing the cement industry’s 8-10% contribution to global CO2 emissions, aligning with four UN Sustainable Development Goals: SDG 13 (Climate Action) by reducing CO2 emissions by over 50% through development of low-carbon composite binders (with 50-80% cement replacement); SDG 9 (Industry, Innovation, and Infrastructure) by promoting sustainable industrialization with low-carbon materials; SDG 11 (Sustainable Cities and Communities) by creating greener urban environments; and SDG 12 (Responsible Consumption and Production) by using WCP and biochar as cement substitutes and CWW and seawater as alternative water sources.