Effect of calcined street sweeping sediment on the mechanical and rheological properties of fly ash–slag geopolymers

Developing sustainable and high-performance binders is a major challenge for the construction sector. This study investigates the effect of calcined urban sediments on the mechanical and rheological properties of one-part geopolymers based on fly ash, ground granulated blast furnace slag (GGBS), and sodium metasilicate pentahydrate. Sediments collected from Mitry-Mory (France) were used as partial substitutes for fly ash at replacement levels of 9%, 18%, and 30%.Construction sector. This study investigates the effect of calcined urban sediments on the mechanical and rheological properties of one-part geopolymers based on fly ash, ground granulated blast furnace slag (GGBS), and sodium metasilicate pentahydrate. Sediments collected from Mitry-Mory (France) were used as partial substitutes for fly ash at replacement levels of 9%, 18%, and 30%.Comprehensive microstructural and chemical analyses, including XRD, FTIR, TGA, and mercury intrusion porosimetry (MIP), were performed to correlate reaction mechanisms with performance evolution. Results show that incorporating calcined sediments (SED) significantly enhances compressive and flexural strengths, mainly due to the formation of C–A–S–H, N–A–S–H, and hydrotalcite gels that densify the matrix and reduce porosity. Rheological measurements using a Bingham model revealed a rise in dynamic yield stress and plastic viscosity with sediment content, while bleeding tests demonstrated improved stability and water retention. The optimal balance between workability and stability was achieved for mixtures containing 9–18% sediments, whereas higher contents increased stiffness in the fresh state.These results illustrate the dual functionality of calcined sediments, both as reactive precursors and as rheology-modifying agents, thus opening up a circular and sustainable pathway for the production of environmentally friendly geopolymer materials. This work provides new insights into sediment induced geopolymerization and its potential for large scale implement in low carbon construction.