Mechanical Enhancement and Microstructural Analysis of Dredged Sediment Treated with Waste Shredded Tire and Fly Ash

This research investigated the stabilization of high-water-content dredged clay using waste shredded tires (WST) and fly ash (FA). A comprehensive suite of laboratory experiments inclusive of direct shear (DS) and unconfined compressive strength (UCS) tests, along with scanning electron microscope (SEM) analyses, was carried out to assess the influence of varying WST and FA proportions and curing durations on the mechanical behavior of the treated dredged clay. The experimental results indicated higher WST content in the range of 0% to 50% with 20% FA content, as well as longer curing times, led to significant increases in shear strength. For instance, peak shear stress increased by up to 66.9% at a normal stress of 200 kPa following a 7-day curing period. Notably, cohesion (c) and internal friction angle (φ) exhibited an increase with WST content, nearly doubling from 15.0 kPa to 28.0 kPa and increasing from 22° to 34°, respectively. The UCS test results indicated that the combination of WST and FA substantially enhanced the UCS (qu), achieving an increase of 581.3% relative to the untreated clay when treated with 35% WST and 20% FA after 28 days of curing. A quantitative expression of qu was developed as a function of WST content and curing time, which can be used to effectively predict the qu of WST- and FA-treated Zhenjiang dredged clay at a given WST content (0% to 50%) and curing time (3 h to 28 days) under the same initial water content of 41.4% and FA content of 20%. SEM images confirm that WST forms a bridging framework, while FA fills voids with cementitious compounds. This study highlights the potential for using WST and FA in engineering applications as a sustainable and effective solution for stabilizing soft, high-water-content clay.