Effect of precursor element composition on compressive strength of alkali-activated dredged sediment

Abstract

The disposal of dredged sediment (DS) is a major challenge in urban construction projects, which is expected to be solved by alkali activation. For a long time, the lack of precise understanding regarding the precursor composition and reaction mechanisms has hindered the development of higher-strength alkali-activated dredged sediment (ADS) materials. This study investigates the impact of adjusting the element composition of the solid precursor (SP) on the uniaxial compressive strength (UCS) of ADS. Orthogonal analysis, as well as XRD, FTIR, Raman, and SEM methods, were utilized to examine the effects. The findings demonstrate that the molar ratio n(Ca)/n(Si) of the SP significantly influences the UCS of ADS, particularly during the mid-to-late stages of curing (≥7 days). Moreover, the polymerization degree of the product C(A)SH serves as a vital link between the macroscopic strength of the ADS samples and the microscopic elemental composition of the SP. The high content of Ca2+ and OH-, as well as the coordination of silicon-oxygen and aluminum-oxygen units, will promote the polymerization reaction in the system and form more CASH and CSH gels. Furthermore, as the polymerization degree of C(A)SH decreases, the pore composition and distribution in the sample become more complex, ultimately resulting in the deterioration of the macro-mechanical properties. These findings offer valuable insights for the solidification and comprehensive utilization of DS.