Eco-sustainable design of seawater sea-sand slag-based geopolymer mortars incorporating ternary solid waste

Abstract

This study aimed to explore the feasibility of utilizing geopolymer as alternatives to Ordinary Portland Cement (OPC) in marine engineering. Eco-friendly seawater sea-sand slag-based geopolymer mortars (SS-SGMs) were prepared by blending seawater, sea-sand, Basalt Fibres (BF), Polypropylene Fibres (PPF), and ternary solid waste. The effects of activator modulus, alkaline content, water-to-binder ratio, and the volume fractions of BF and PPF on the mechanical performance, environmental impact, and cost of SS-SGMs were researched using the L₁₆(4)⁵ Taguchi orthogonal method. Three evaluation methods were used to assess the impact of the different factors. First, the influence of a single factor was analyzed using methods of range and variance analysis. Subsequently, three new evaluation metrics were proposed to consider the synergistic effects of mechanical performance, environment, and cost. Finally, a Gray-Technique of Ordering Preferences by Similarity to Ideal Solution (Gray-TOPSIS) model was established, and the influence weights of each factor were proposed, thereby determining the optimal solution in a multi-index evaluation system. The recommended optimal mix proportion for SS-SGMs was determined as follows: activator modulus of 1.0, alkaline content of 4%, water-to-binder ratio of 0.42, PPF volume fraction of 0.4%, and BF volume fraction of 0.3%. Compared to OPC with the same strength grade, SS-SGMs demonstrated similar costs, a reduction in carbon emissions by approximately 75–83%, a decrease in energy consumption by around 50–67%, and lower drying shrinkage than traditional geopolymer. Under the influence of seawater, the products of SS-SGMs were capable of forming chloride-ion adsorbing products like hydrotalcite and Brucite. Additionally, the formation of C₄AH₁₃ and ion clusters can enhance the matrix density, thereby improving the mechanical performance of SS-SGMs.