Eco-efficient recycling of engineering muck for manufacturing low-carbon geopolymers assessed through LCA: Exploring the impact of synthesis parameters of the performance

Abstract The construction industry's excessive reliance on cement has led to significant environmental concerns. With the push towards global low-carbon and sustainable development goals, there is an urgent need to find building materials that can replace cement. In this study, engineering muck (EM) produced by foundation pit engineering in subtropical area was used as raw material. The properties of EM were activated by pre-treatment methods to prepare low-carbon geopolymers. This study investigated the effects of synthesis parameters (SiO2/Na2O ratio and liquid-solid ratio) on the performance of the alkaline activated EM-based geopolymers. The results showed that the geopolymer with a SiO2/Na2O ratio of 1.5 achieved the highest compressive strength of 40 MPa in 7 days, exhibiting the densest structure and fewest cracks. In addition to also having the smallest pore sizes and highest thermal stability, indicating optimal pore structure for minimizing evaporation. This study showed that increasing the liquid-solid ratio refined the pore structure, but increased carbonate formation and mass loss at elevated temperatures. Moreover, a life cycle assessment (LCA) was used to compare the cradle-to-gate environmental impacts of the EM-based geopolymers and cement concretes, including global warming and acidification. The LCA demonstrated the CO2 and SO2 emissions of EM-based geopolymers were reduced by 4–26% and 8–19%, respectively, compared to concrete. This study suggests the use of alkaline activation technology to transform the EM into the geopolymers should be expected to become a substitute for concrete, providing a new type of green building material for the geotechnical engineering.