Developing green and economical low-alkalinity seawater sea sand concrete via innovative processing underground sediment

Large-scale expansion of urban underground space has led to the accumulation of substantial sediment. Now the primary disposal approach involves long-distance transport followed by dumping in open areas or landfills, incurring excessive deposition and causing landslides. To tackle this concern, a novel processing scheme that transforms sediment into supplementary cementitious material is proposed for preparing sustainable seawater sea sand concrete (SWSSC). Notably, it is determined that this transformed sediment improves cement hydration and reduces cement dosage, achieving a 35% reduction in CO₂ emissions compared to traditional SWSSC with identical strength according to life cycle assessment. Furthermore, it offers the additional benefit of cost-effective. Microanalysis has demonstrated that the recycled sediment reacts with calcium hydroxide and produces secondary calcium-silicate-hydrate gel, contributing to the mechanical properties and decrease in alkalinity of SWSSC. A design model for SWSSC is proposed, focusing on alkalinity, mechanical strength, and environmental benefits. This proposed model enhances application of SWSSC in construction, catering to specialized marine engineering structures, like artificial islands, harbors and offshore structures. This study contributes to a large-scale processing strategy of sediment and provides an economical and green alternative construction material for sustainable infrastructures.