Improvement of Dredged Sediments : A laboratory study on dredged sediments with different types of binders

Abstract: tabilization and solidification (S/S) technique have been the most frequently used method for dredgedsediment improvement in Sweden and worldwide. As dredging activities are essential for safe navigationof ships and vessels that may processes harmful substances or organic pollutants to causecontamination of the surrounding environment. Stabilization/solidification technology has beenidentified as the most beneficial handling strategy for contaminated dredged sediments and treatedstabilized materials can be used in civil engineering applications (e.g. backfill or embankment). This (S/S)technique is the easiest way of improving high water content dredged sediments using different types ofbinders. During the stabilization process, dredged sediments are mixed with commonly used binders,such as Portland cement, fly ash and ground granulated blast furnace slag (Merit 5000). Nowadays,supplementary cementitous materials such as (fly ash and blast furnace slag) are being used increasinglyconsidering long term strength development of stabilized dredged materials instead of using morecement. Generally, cement hydration is a complex chemical-reactions. By addition of supplementarycementitious materials, it becomes more complex because of cement hydration and pozzolanicreactions. The overall objective of this thesis work is to improve the understanding of compressibilityand strength behavior of stabilized dredged materials. To achieve these objectives, a series ofunconfined compressive strength tests and consolidation tests were performed on stabilized dredgedmaterials (SDM) with different types and mixing ratios of binders. These lab tests have been focused onthe compressibility and strength properties of stabilized materials. The UCS test determines the amountof binders and curing time needed to achieve the required shear strength of SDM. The outcomes of thisthesis work show that the stabilized dredged sediments constitute of binder mixing ratio (Cement:Flyash:Merit 5000 as a proportion of 10:10:5) which is 25% of the total fresh dredged sediments can’tsustain any superstructure or surcharge load but it can only be used as backfill materials on site.Whereas, stabilized dredged material with binder mixing ratio (Cement:Fly ash:Merit 5000 as aproportion of 20:20:10) which is 50% of the total fresh dredged Sediment becomes stiff after 28 dayscuring and becomes very stiff after 91 days curing. It becomes obvious that the unconfined compressivestrength of SDM increases with higher amount of binders and longer curing time. The pozzolanicreaction continues after 28 days curing period. The presence of supplementary cementitous materials(fly ash, blast furnace slag and merit 5000) can improve the ductility of stabilized dredged materials(SDM) in the post-peak strength degradation zone without changing the unconfined compressivestrength. It is also obvious from the test results that the UCS values of stabilized dredged materialsincrease with decreasing moisture content/increasing bulk density. The consolidation properties of SDMare greatly influenced by the binder mixing ratio, curing time and preloading weight. Due to preloadingweight, the deformation in stabilized dredge sediments is irreversible because of cementation andpozzolanic effects. Considering both curing time and binder ratio, compression index (Cc) and swellingindex (Cs) values for SDM with binder ratio (20:20:10) have been lowered approximately by 75% and67%, respectively than SDM with binder ratio (10:10:5). After 91 days curing of SDM with binder ratio(20:20:10), the maximum value of tangent modulus is estimated about 9624 kPa which indicates thatthe superstructure can be erected on stabilized dredged materials. It is also concluded that physicochemicalvariables control the consolidation behavior of stabilized dredge materials (SDM) as thecoefficient of consolidation (Cv) value decreases with increasing consolidation pressure.