Preparation and characterization of non-sintering lightweight aggregate containing dredged sediment, fly ash and calcium carbide slag

• Novel lightweight aggregate (LWA) prepared via co-disposal of multiphase solid waste. • Calcium carbide slag balanced the contradiction of high-strength and low-density. • Beneficial minerals and “alveolate” structure explain the excellent performances of LWA. Transforming dredged sediment (DS) into building materials represents a highly promising recycling approach. However, the low hydration reactivity of DS poses a significant challenge during its utilization, particularly in non-sintered processes. To address this issue, the present study investigated the activation of DS through conditioning with various solid wastes - fly ash (FA) and calcium carbide slag (CCS) -and successfully developed a novel type of non-sintered lightweight aggregate (LWA). The optimal dry mixture was formulated by blending 33.32% DS, 19.77% FA, 16.57% CCS, and 3.39% metakaolin (MK), which were activated with 26.26% alkali activator (comprising waterglass, modulus 3.27, and 6 M NaOH) and 0.68% pore former (H₂O₂). This yielded the optimal LWA (HCSCA) with a maximum cylinder compressive strength of 8.75 MPa and a minimum bulk density of 622 kg/m 3 . Interactions significantly affected properties: Alkali concentration interacting with H 2 O 2 impacted cylinder strength. CCS dose interacting with alkali concentration/ H 2 O 2 influenced both cylinder strength and bulk density. The final hydration products of HCSCA were C-S-H gels and mineral phases (lawsonite, gismondine). These mineral distributions balanced strength and density of HCSCA. C-S-H gels in HCSCA exhibited an "alveolate" skeleton structure with high polymerization and stability. HCSCA possessed a mesoporous structure featuring small, scattered pores (average size = 32.28 nm).