The rapid expansion of urbanization and industrial activities has significantly increased the demolition, repair, and renovation of buildings and infrastructure, leading to the generation of massive quantities of Construction and Demolition Waste (CDW). As the largest waste stream in the EU, CDW accounts for over one-third of the total waste produced annually. While often regarded as a burden, CDW can be transformed into valuable resources through innovative methods such as alkali-activation and geopolymer technology. This study explores the use of unsorted CDW from residential buildings as a solid precursor for developing new alkali-activated materials. Several reactive systems, including alkaline solutions of sodium hydroxides and silicates at various concentrations, were explored, to achieve effective material consolidation. Additionally, metakaolin (MK), a well-known high-reactive precursor in geopolymer production, was tested in combination with CDW at different ratios to enhance the geopolymerization process. Results showed that a CDW/MK weight ratio of 60/40 and sodium silicate as alkaline activator allowed the production of a well-reacted and cohesive material, with a bulk density of 1.35 g/cm3, a monomodal mesoporosity with a modal pore size of 0.0214 μm (open porosity ∼42 vol%), and a compressive strength of 25 MPa. These characteristics are similar to those of properly reacted metakaolin-based geopolymers. Thermal characterization was performed up to 1000 °C showing that the material can exhibit thermal stability up to 650 °C. Above that temperature a shrinkage due to viscous flow occurred, followed by an expansion over 750 °C with the formation of macropores and dense struts. Based on these findings, the developed CDW-based geopolymer demonstrates significant potential for green building applications, particularly in environments requiring structural consistency and strength under medium-to-high temperatures, thus contributing to more sustainable construction practices. Within this scenario, macroporous CDW-based geopolymers were prepared via direct foaming using H2O2 as blowing agent to obtain lightweight material with low density, that could offer potential applications in insulation and other high-value sectors. This study was carried out within the MICS (Made in Italy – Circular and Sustainable) Extended Partnership and received funding from the European Union Next-Generation EU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) – MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.3 – D.D. 1551.11-10-2022, PE00000004). Authors also acknowledge the Emilia-Romagna Region for financial support through the project “ReWINDS - Recycling of Waste Into New Demonstrated Sustainable Solutions” (funded under the call of the Emilia-Romagna ERDF Regional Program 2021-2027, Action 1.1.2 - CUP: E27G22000290007, PG/2023/311857).
Valorization of unsorted construction and demolition waste through geopolymerization
Francesca Servadei
;Annalisa Natali Murri;Elena Landi;Valentina Medri;Elettra Papa
2025
Abstract
The rapid expansion of urbanization and industrial activities has significantly increased the demolition, repair, and renovation of buildings and infrastructure, leading to the generation of massive quantities of Construction and Demolition Waste (CDW). As the largest waste stream in the EU, CDW accounts for over one-third of the total waste produced annually. While often regarded as a burden, CDW can be transformed into valuable resources through innovative methods such as alkali-activation and geopolymer technology. This study explores the use of unsorted CDW from residential buildings as a solid precursor for developing new alkali-activated materials. Several reactive systems, including alkaline solutions of sodium hydroxides and silicates at various concentrations, were explored, to achieve effective material consolidation. Additionally, metakaolin (MK), a well-known high-reactive precursor in geopolymer production, was tested in combination with CDW at different ratios to enhance the geopolymerization process. Results showed that a CDW/MK weight ratio of 60/40 and sodium silicate as alkaline activator allowed the production of a well-reacted and cohesive material, with a bulk density of 1.35 g/cm3, a monomodal mesoporosity with a modal pore size of 0.0214 μm (open porosity ∼42 vol%), and a compressive strength of 25 MPa. These characteristics are similar to those of properly reacted metakaolin-based geopolymers. Thermal characterization was performed up to 1000 °C showing that the material can exhibit thermal stability up to 650 °C. Above that temperature a shrinkage due to viscous flow occurred, followed by an expansion over 750 °C with the formation of macropores and dense struts. Based on these findings, the developed CDW-based geopolymer demonstrates significant potential for green building applications, particularly in environments requiring structural consistency and strength under medium-to-high temperatures, thus contributing to more sustainable construction practices. Within this scenario, macroporous CDW-based geopolymers were prepared via direct foaming using H2O2 as blowing agent to obtain lightweight material with low density, that could offer potential applications in insulation and other high-value sectors. This study was carried out within the MICS (Made in Italy – Circular and Sustainable) Extended Partnership and received funding from the European Union Next-Generation EU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) – MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.3 – D.D. 1551.11-10-2022, PE00000004). Authors also acknowledge the Emilia-Romagna Region for financial support through the project “ReWINDS - Recycling of Waste Into New Demonstrated Sustainable Solutions” (funded under the call of the Emilia-Romagna ERDF Regional Program 2021-2027, Action 1.1.2 - CUP: E27G22000290007, PG/2023/311857).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
