Stabilization-solidification of High Water Content Dredged Sediments_R1 Strength, Compressibility and Durability Evaluations

University dissertation from Luleå tekniska universitet

Abstract: Dredging activities at ports and harbors are inevitable for safe navigation of ships and vessels. The outcomes of dredging activities are huge volumes of dredged materials, which can range from very fine and contaminated sediments to sands and gravels. The coarse sands and gravels can be directly used in civil engineering applications. The fine dredged sediments (DS) are usually associated with high water content, low shear strength, high compressibility and presence of contaminants. However, these unfavorable properties do not exclude the suitability of fined dredged sediments for use in geotechnical applications. Stabilization-solidification technology provides a comprehensive treatment method for improving strength, reducing the compressibility and mobilizing the contaminants to be less mobile. These properties make the stabilized dredged material (SDM) suitable for use in civil engineering applications. Successful stabilization–solidification of the DS and the performance of the SDM depend on stabilization methods and materials. Process stabilization-solidification (PSS) is convenient technology for amending high water content DS with binders. The use of composite binders for stabilization–solidification of the DS is increasing due to increased artificial pozzolanas that can be used as supplementary cementitious materials (SCM). Primary binders such as cement can be supplemented with SCM (e.g. fly ash and ground granulated blast furnace slag). Cement hydration is a complex process with a complex series of unknown chemical reactions. The hydration of cement incorporating SCM is more complicated due to the co–existence of cement hydration and the pozzolanic reactions of the SCM. The fabric of dredged sediments formed under different physicochemical environments affects the reactivity of binders. The physicochemical interactions between binders and the DS that influence the strength, compressibility and durability of high water content stabilized dredged sediment are examined and presented in this thesis. The findings of this study show that the use of fly ash (FA) and ground granulated blast furnace slag (GGBS) delays strength development of composite binder (CB)-treated DS. Irrespective of the amounts of CB, the improved strength depends on the amount of cement in the blend. The unconfined compressive strength (UCS) increases with increasing cement quantity. Three phases of hydration mechanisms determine the compressibility behaviour of the SDM during curing. These are induction phase (IP), nucleation and crystallization phase (NCP), and hardening phase (HP). The durability of the SDM under repetitive freeze-thaw cycling on UCS and hydraulic conductivity (HC) depends on initially achieved UCS relative to HC prior to the f-t cycling and time of testing after f-t cycles. The HC of specimens with low UCS value increased with number of f-t cycles. The UCS showed decreased value up to 80% when specimens were tested directly after thaw period and decreased values of 14% when specimens were tested at the end of extended thaw period. The HC of specimens with high UCS value remained almost the same. These samples experienced permanent loss in the UCS values irrespective of time of testing. Considering healing potential on the SDM with reduced strength, increased hydraulic conductivity causes increased rate of dissipation of excess pore pressure, reduced undrained conditions, and improved strength (enhanced outcome). Irrespective of f-t method, detrimental effects of the freezing action on the UCS are greater under semi-closed than open freezing conditions

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