Valorization of saline dredged sludge by low-carbon geopolymer production: Salt content impact, mechanisms, and carbon emissions

• Geopolymers derived from saline dredged sludge (DS) were developed. • Complete efflorescence resistance at ≤2% salt content. • Compressive strength reduced as salt content increased. • Mechanisms of salt content effect on geopolymer properties were disclosed. • The valorization of DS via geopolymer production demonstrates low-carbon benefits. This study demonstrates a green and low-carbon approach for valorizing saline dredged sludge (DS) by producing geopolymers from DS combined with fly ash (FA) and ground granulated blast furnace slag (GGBS), activated by an alkaline activator. Systematically investigating salt content effects (0-8%), the DS-FA/GGBS geopolymers exhibit complete efflorescence resistance at ≤ 2% salt content but suffer significant compressive strength reduction.The compressive strength decreases from 14.5 ± 1.4 MPa to 12.7 ± 0.7 MPa by 12.4% at 2% salt content and escalates to a 45% reduction at 8% salt content. The deterioration mechanisms are deciphered: excessive salt levels caused NaCl oversaturation and crystallization due to evaporation, causing physical damage. Additionally, excessive sodium ions increase the Si-O-Na/Si-O-T bond ratio from 0.46 to 2.13, shortening polymer chains and weakening the matrix. Environmentally, the carbon footprint ranges from 212.7 to 239.4 kg CO 2 -eq/m 3 , demonstrating a 40% reduction compared to cement-based solidification (392.0 kg CO 2 -eq/m 3 ). These findings provide quantifiable evidence for saline DS geopolymers as a sustainable alternative in coastal engineering.