Experimental research on the performance of acid - activated geopolymer and its application in dredged soil stabilization

Abstract

A series of geopolymers were synthesized by employing phosphoric acid (PA) as activator to activate low-calcium fly ash (FA) and metakaolin(MK), and geopolymer mortar was prepared using PA-activated FA-MK geopolymer and dredged soil. The PA-activated low-calcium FA geopolymer typically exhibited low compressive strength. Incorporating MK introduced reactive aluminum, which enhanced the compressive strength of the geopolymer. This strength improvement was further amplified as the M:F ratio (MK:FA ratio) increased. Under a certain M:F ratio, there existed an optimum H₃PO₄/Al₂O₃ molar ratio that maximized the compressive strength of geopolymer. A positive correlation was observed between the M:F ratio and the optimum H₃PO₄/Al₂O₃ molar ratio, with the latter exhibiting a gradual increase from 0.56 (M:F ratio = 0:1) to 0.64 (M:F ratio = 0.4:0.6) and ultimately 0.86 (M:F ratio= 1:0). The compressive and flexural strengths of the geopolymer mortar were significantly affected by the geopolymer/soil ratio and the PA concentration. When the actual PA concentration in geopolymer mortar approached the optimum PA concentration for the geopolymer paste, the mortar achieved its best mechanical properties. The stabilization of dredged soil using PA-activated geopolymer demonstrates significant sustainability benefits, while their cost-effectiveness and mechanical performance require further optimization. This research provides new approaches and data support for the reuse of low-calcium FA and dredged soil.