Multiscale laboratory investigation of the mechanical and microstructural properties of dredged sediments stabilized with cement and fly ash

Abstract

The process of removing sediments from the bottom of dams generates large amounts of dredged sediments, which are considered waste. With stabilization, the dredged sediments can be reused as construction materials in civil engineering works. The aim of this paper is to present a multiscale laboratory investigation into the mechanical properties and microstructural characteristics of dredged sediments stabilized with Ordinary Portland cement (OPC) type I and fly ash (FA). The base sediment was high–plasticity silt. Mechanical tests were conducted to determine the unconfined compressive strength (UCS), splitting tensile strength (STS), wetting and drying (W–D) cycle number, free–free resonance (FFR) and resilient modulus (Mr). In addition to evaluating the mechanical properties, microstructural analyses were also conducted using X–ray diffraction XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) to understand the behavior of the dredged sediments stabilized with OPC and FA. The overall test results indicated that OPC and FA were effective at stabilizing the dredged sediment. An FA content of 10% was the most effective at improving the mechanical properties of the stabilized samples. Six W–D cycles were sufficient, as the strength of the six W–D cycles was very low. The ratios of seismic compression (E0) and shear modulus (G0) to UCS were 24 and 9, respectively, whereas the ratio Mr to UCS was 148. The Poisson's ratio (ν) values were distributed in the range of 0.317 to 0.381. Microstructural analyses showed that the combination of OPC and 10% FA provided suitable proportions of silicon dioxide and calcium hydroxide, resulting in the creation of a large quantity of calcium silicate hydrate during the pozzolanic reactions.