Towards Sustainable Stabilization: Sodium Carbonate Tunning the Strength Development of Dredged Sediments Stabilized with Alkali- activated Ground Granulated Blast-furnace Slag

Abstract

Chemical stabilization of dredged sediments presents a promising solution for the reutilization of dredged waste in engineering fills. To promote decarbonization efforts, the use of low-carbon binders, such as alkali-activated ground granulated blast furnace slag (GGBS), emerges as a viable alternative to ordinary Portland cement. Dredged sediments commonly exhibit high water contents (e.g., exceeding 100%), which can compromise the efficacy of alkali-activated GGBS binders in enhancing the strength of these sediments. It has been demonstrated that sodium carbonate (Na2CO3) can potentially accelerate the strength development of alkali-activated GGBS-stabilized sediments. However, the mechanisms on how Na2CO3 influences the strength development of such stabilized sediments remain unclear. This knowledge gap impedes the establishment of a robust scientific foundation for optimizing the mixing design of alkali-activated GGBS binders to effectively stabilize dredged sediments. This study investigates the effects of varying Na2CO3 contents on the strength development of alkali-activated GGBS-stabilized sediments characterized by high water contents. To reveal the mechanisms underlying the effects of Na2CO3 on the strength development of GGBS-stabilized sediments, the reaction products and the pore structures of stabilized sediments are examined by using X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and mercury intrusion porosimetry techniques. The optimal content of Na2CO3 for attaining the highest 28-day compressive strength of stabilized sediments is determined to be 0.2% by weight. Below this optimal content, the strength of stabilized sediments increases with Na2CO3 content. However, surpassing this optimal content, the increase in Na2CO3 content results in a decrease in the strength of stabilized sediments. The addition of Na2CO3 additive into alkali-activated GGBS-stabilized sediments induces changes in the interactions between clay minerals and reaction products, thereby altering the pore size distribution within the sediments. These modifications in the pore size distribution results in the observed impacts of different Na2CO3 contents on the strength development of stabilized sediments. The revealed mechanisms can provide a scientific basis to optimize the alkali-activated GGBS binders used for the sustainable stabilization of dredged sediments.