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The development of underground space is an important trend for urban infrastructure in cities supporting socio-economic activities, while it also results in an enormous accumulation of sediment waste, which consumes vast land resources, causes serious environmental problems and endangers public safety. It is urgent to explore pathways of recycling sediment waste with low carbon impact for sustainable infrastructure. This study employed calcination and alkali activators to recycle sediment waste into geopolymer paste. The mechanical properties and working performance of recycled geopolymer paste were investigated and the underlying mechanism of this recycling scheme was revealed with microscale characterizations. Results showed that the compressive strength of recycled geopolymer paste could reach 50 MPa. The environmental impact of geopolymer paste and cement-based paste has been analyzed via life cycle assessment (LCA). Recycled geopolymer paste can save 310 kg CO 2 eq/t of carbon emissions, which is 39% lower than that of cement-based material. Moreover, the multi-criteria approach was adopted to evaluate geopolymer paste and cement paste considering mechanical properties, working performance, carbon emissions, energy consumption and cost, and geopolymer paste exhibits better overall performance. The findings inspire a construction waste management strategy and contribute to low-carbon construction materials for sustainable urban infrastructure. • Sediment waste is recycled into geopolymer paste via calcination and alkali activator. • The optimum mix ratio range of geopolymer paste with sediment waste is determined. • Mechanical and environmental performance of geopolymer paste has been studied. • A sustainable sediment waste management strategy and a low-carbon construction material is inspired. [ABSTRACT FROM AUTHOR]

Low-carbon emission mortar samples were prepared using reactivated cementitious materials (RCMs) produced by calcinating hydrated cement paste with adjusted Ca/Si ratios. Carbonation curing was employed to enhance the cementing capacity of the RCMs and to sequestrate CO 2. The compressive strength, phase assemblage, microstructure, and environmental impacts of the mortars were analyzed. According to the results, the mortar sample produced with the RCM with a 10% addition of silica fume during calcination attained the highest compressive strength (35.3 MPa) after water curing, while higher silica contents were unfavorable because the low-lime calcium silicates that formed have limited water reactivity. Carbonation curing significantly promoted reactions of the RCMs and, thus, the compressive strength of the mortars compared to water curing. The amorphous and metastable calcium carbonates contributed more to the densification of the microstructure than the calcite. From the life cycle assessment, the RCM mortars had a significantly lower impact on global warming potential compared to Portland cement mortars. [Display omitted] [ABSTRACT FROM AUTHOR]