Effect of Progressive Substitution of Cement and Lime by Powdered Shells Used as a Curing Agent for Dredged Soil in a Port Area

This study aimed to address the challenges of solid waste utilization,cost reduction,and carbon reduction in the treatment of deep-dredged soil at Xuwei Port in Lianyungang city of China.Past research in this area was limited.Therefore,a curing agent made from powdered shells was used to solidify the dredged soil in situ.We employed laboratory orthogonal tests to investigate the physical and mechanical properties of the powdered shell-based curing agent.Data was collected by conducting experiments to assess the role of powdered shells in the curing process and to determine the optimal ratios of powdered shells to solidified soil for different purposes.The development of strength in solidified soil was studied in both seawater and pure water conditions.The study revealed that the strength of the solidified soil was influenced by the substitution rate of powdered shells and their interaction with cement.Higher cement content had a positive effect on strength.For high-strength solidified soil,the recommended ratio of wet soil:cement:lime:powdered shells were 100:16:4:4,while for low-strength solidified soil,the recommended ratio was 100:5.4:2.4:0.6.Seawater,under appropriate conditions,improved short-term strength by promoting the formation of expansive ettringite minerals that contributed to cementation and precipitation.These findings suggest that the combination of cement and powdered shells is synergistic,positively affecting the strength of solidified soil.The recommended ratios provide practical guidance for achieving desired strength levels while considering factors such as cost and carbon emissions.The role of seawater in enhancing short-term strength through crystal formation is noteworthy and can be advantageous for certain applications.In conclusion,this research demonstrates the potential of using a powdered shell-based curing agent for solidifying dredged soil in an environmentally friendly and cost-effective manner.The recommended ratios for different strength requirements offer valuable insights for practical applications in the field of soil treatment,contributing to sustainable and efficient solutions for soil management.

Coupling effect of cement-stabilization and biopolymer-modification on the mechanical behavior of dredged sediment

Nowadays,biopolymer stabilization as a promising eco-friendly approach in soft ground improvement has attracted wide attentions.However,the feasibility of using biopolymer as a green additive of cementstabilized dredged sediment(CDS)with high water content is still unknown.In this study,guar gum(GG)and xanthan gum(XG)were adopted as typical biopolymers,and a series of unconfined compressive strength(UCS),splitting tensile strength(STS)and scanning electron microscopy(SEM)tests were performed to evaluate the mechanical and microstructural properties of XG-and GG-modified CDSs considering several factors including biopolymer modification,binderesoil ratio and wateresolid ratio.Furthermore,the micro-mechanisms revealing the evolutions of mechanical properties of biopolymermodified CDS were analyzed.The results indicate that the addition of XG can effectively improve the strength of CDS,while the GG has a side effect.The XG content of 9%was recommended,which can improve the 7 d-and 28 d-UCSs by 196%and 51.8%,together with the 7 d-and 28 d-STSs by 118.3%and 42.2%,respectively.Increasing the binderesoil ratio or decreasing the wateresolid ratio significantly improved the strength gaining but aggravated the brittleness characteristics of CDS.Adding XG to CDS contributed to the formation of microstructure with more compactness and higher cementation degrees of ordinary Portland cement(OPC)-XG-stabilized DS(CXDS).The micro-mechanism models revealing the interactions of multiple media including OPC cementation,biopolymer film bonding and bridging effects inside CXDS were proposed.The key findings confirm the feasibility of XG modification as a green and high-efficiency mean for improving the mechanical properties of CDS.

Dredged marine soil stabilization using magnesia cement augmented with biochar/slag

Dredged marine soils(DMS)have poor engineering properties,which limit their usage in construction projects.This research examines the application of reactive magnesia(rMgO)containing supplementary cementitious materials(SCMs)to stabilize DMS under ambient and carbon dioxide(CO_(2))curing conditions.Several proprietary experimental tests were conducted to investigate the stabilized DMS.Furthermore,the carbonation-induced mineralogical,thermal,and microstructural properties change of the samples were explored.The findings show that the compressive strength of the stabilized DMS fulfilled the 7-d requirement(0.7-2.1 MPa)for pavement and building foundations.Replacing rMgO with SCMs such as biochar or ground granulated blast-furnace slag(GGBS)altered the engineering properties and particle packing of the stabilized soils,thus influencing their performances.Biochar increased the porosity of the samples,facilitating higher CO_(2) uptake and improved ductility,while GGBS decreased porosity and increased the dry density of the samples,resulting in higher strength.The addition of SCMs also enhanced the water retention capacity and modified the pH of the samples.Microstructural analysis revealed that the hydrated magnesium carbonates precipitated in the carbonated samples provided better cementation effects than brucite formed during rMgO hydration.Moreover,incorporating SCMs reduced the overall global warming potential and energy demand of the rMgO-based systems.The biochar mixes demonstrated lower toxicity and energy consumption.Ultimately,the rMgO and biochar blend can serve as an environmentally friendly additive for soft soil stabilization and permanent fixation of significant amounts of CO_(2) in soils through mineral carbonation,potentially reducing environmental pollution while meeting urbanization needs.

Efficient stabilization of dredged sludge with high water content using an improved bio-carbonation of reactive magnesia cement method

This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.

Experimental Research on the Dewatering of Dredged Sediment from Dianchi Lake

[Objective] The technological parameter suitable for the dewatering of dredged sediment from Dianchi Lake was studied.[Method] By means of the treatment method of sewage sludge in sewage treatment plant,flocculants including FeCl3,Al2(SO4)3 and PAM were taken as dewatering agents which were added in dredged sediment.[Result] The results showed that Al2(SO4)3 had better dewatering effect than FeCl3 and PAM,and the optimum dosing quantity of Al2(SO4)3 in dredged sediment was 170 mg/L,in addition,the water quality of supernatant met the first class B standard of GB18918-2002 and could be directly discharged to nature water without pollution.[Conclusion] The study could provide a simple and feasible way for the rapid dewatering of dredged sediment from Dianchi Lake,which would be convenient for the disposal and resource utilization of dredged sediment.

Comparison of Remolded Shear Strength with Intrinsic Strength Line for Dredged Deposits

Chandler proposed the intrinsic strength line to correlate the undrained shear strength of samples one-dimensionally consolidated from slurry with the void index proposed by Burland. The undrained shear strength on the intrinsic strength line is different from the remolded undrained shear strength that is an important parameter for design and construction of land reclamation. The void index is used in this study for normalizing the remolded strength behavior of dredged deposits. A quantitative relationship between remolded undrained shear strength and void index is established based on extensive data of dredged deposits available from sources of literature. Furthermore, the normalized remolded undrained shear strength is compared with intrinsic strength line. The comparison result indicates that the ratio of undrained shear strength on the intrinsic strength line over remolded undrained shear strength increases with an increase in applied consolidated stress.

High-efficiency stabilization of dredged sediment using nano-modified and chemical-activated binary cement

High-efficiency disposal of dredged sediment(DS)has become an imperative geo-environmental engineering issue due to the limited landfilling space and severe environmental burdens.This study firstly developed a novel high-efficiency nano-modified and chemical-activated binary cement(NBC),which was composed of binary cement(BC)consisting ordinary Portland cement(OPC)and ground granulated blast-furnace slag(GGBS),chemical-activator and nano-modifier.The effects of chemical-activation and nano-modification on the strength development of BC-stabilized DS(BCDS),and the optimum mix of NBC were respectively achieved via a series of unconfined compressive strength and orthogonal tests.Then,the high-efficiency and economic applicability of NBC in DS stabilization were evaluated by comparing with OPC.Furthermore,the microstructure and mineral composition evolutions inside NBCstabilized DS(NDS)were explored by conducting X-ray diffraction(XRD)and scanning electron microscopy(SEM)tests.The results show that both chemical-activation and nano-modification could effectively improve the strength gain of BCDS,and compared with single chemical-activator and nanomodifier,the composite chemical-activators and nano-modifiers exhibited better performances.Based on BC with OPC/GGBS mass ratio of 1:1,both anhydrous sodium metasilicate/anhydrous sodium sulfate(SM/SS)and nano-SiO_(2)/nano-MgO(NS/NM)with mass ratio of 1:9 were respectively determined to be optimum chemical-activator and nano-modifier.The optimum mass ratio of BC,SM/SS and NS/NM was 20:2:1,i.e.the optimum mix of NBC.Compared with OPC,NBC exhibited higher stabilization efficiency and better economic applicability.The generation of calcium silicate hydrate(CSH),calcium aluminate hydrate(CAH)and ettringite contributed to the formation of dense cemented soil matrix inside NDS,and a conceptual micro-mechanism model characterizing the strength development under the coupling action of chemical-activation and nano-modification was proposed.

Modification of nanoparticles for the strength enhancing of cementstabilized dredged sludge

This paper investigates the effectiveness of nano-modification on the strength enhancement of cementstabilized dredged sludge(CDS).Three types of nanoparticles including nano-SiO2(NS),nano-Al2O3(NA)and nano-MgO(NM)were used as cement admixtures for dredged sludge stabilization.Effects of single nanoparticle content,mass ratio of composite nanoparticles and curing time on the strength development of CDS were evaluated via a series of unconfined compressive strength(UCS)tests.The pH evolutions of CDS caused by nanoparticles were also examined by a range of pH tests.Furthermore,micromechanisms reflecting the strength evolutions were analyzed by performing scanning electron microscopy(SEM)and X-ray diffraction(XRD)tests.The results indicated that adding nanoparticles can significantly improve the UCS of CDS.For single nano-modification,the optimum contents of NS,NA and NM were 4%e6%,6%and 8%,which can increase the 7-and 28-d UCSs of CDS by 38%and 50%,17%and 35%,65%and 67%,respectively.Compared with single nano-modification,composite nano-modifications were more effective in improving the strength gain of CDS.The optimum mass ratios of composite nanoparticles,namely NS/NA,NS/NM and NA/NM,were 9/1,3/7 and 3/7,respectively.Based on the strength growth rate,the composite nanoparticles with NS/NM of 3/7 were highly recommended.The addition of nanoparticles obviously affected the pH evolution of CDS,which was mainly determined by the difference of OHproduction and consumption inside nano-modified CDS.The microstructural analysis revealed that C-S-H and C-A-H gels are the main cementitious products,and the addition of nanoparticles can obviously contribute to a denser and more homogenous microstructure of CDS.

STUDY ON PREDICTION FOR TRANSPORT AND DIFFUSION OF DREDGED MATTER IN JIAOZHOU BAY, CHINA

The finite element method was used to simulate the currents of Jiaozhou Bay and the nearcoast areas, and then established the model of the transport and diffusion of suspended particulate matter there. The transport and diffusion of dredged matter near the discharging field were estimated; and the results were used to analyze the effects of the suspended particulate matter on the marine environment.

Mechanical properties of dredged soil reinforced by xanthan gum and fibers

Biopolymers have become popular in geotechnical engineering as they provide a carbon-neutral alternative for soil solidification.Xanthan gum(XG)and jute fiber(JF)were selected to solidify the Yellow River dredged soil.The mechanical behavior of solidified dredged soil(SDS)was investigated using a series of uniaxial compression and splitting tension tests at different XG and JF contents and fiber lengths.The results indicate that on the 28th day,the unconfined compressive strength(UCS)values of SDS samples reached 2.83 MPa and splitting tensile strength(STS)of 0.763 MPa at an XG content of 1.5%.When the JF content was greater than 0.9%,the STS of the SDS samples decreased.This is because that the large fiber content weakened the cementation ability of XG.The addition of JF can significantly increase the strain at peak strength of SDS samples.There is a linear relationship between the UCS and STS of the dredged soils solidified by XG and JF.Microanalysis shows that the strength of SDS samples was improved mainly via the cementation of XG itself and the network structure formed by JF with soil particles.The dredged soil reinforced by XG and JF shows better mechanical performance and has great potential for application.

An Experimental Study of the Physicochemical Properties of a Cement Matrix Containing Dredged Materials

Recently, the amount of dredged soil material (DM) has been rapidly increasing in Korea due to four major river maintenance projects and new harbor construction. DM waste is mostly dumped into the ocean, while only a small part of it has been utilized for coastal reclaiming, or as filling and backfilling material. This study carried out physical and chemical tests to map out a specific plan for utilizing DM in a mortar mixture. The compressive strength tests and microstructure analysis using XRD and SEM of cement mortar contained DM were performed as a replacement for fine aggregate or as a filler material of mortar matrix. The study measured the impact of contaminants contained in DM and how silt and clay influenced the compressive strength of the mortar.

A method of determining nonlinear large strain consolidation parameters of dredged clays

A method of obtaining the large strain consolidation parameters of dredged clays considering the influence of the initial water content is investigated in this study. According to the test results of remolded clays with high initial water contents reported by Hong et al. （2010）, a relationship between the void ratio （e） and effective stress （a3 is established. Furthermore, based on the available permeability data from the literature, a new relationship between the permeability coefficient （k） and the ratio （e/eL） of the void ratio to the void ratio at the liquid limit （eL） is proposed. The new proposed expression considering the initial water content improves the e-k equation established by Nagaraj et al. （1994）. Finally, the influence of the initial void ratio and effective stress on the large strain consolidation coefficient g（e） defined by Gibson et al. （1981） and k/（1 ＋e） in large strain analysis is discussed. The results show that, under a constant effective stress, the value of k/（1 ＋e） increases with the initial void ratio. The large strain consolidation coefficient shows the law of segmentation change, which decreases with the increase of the effective stress when the effective stress is less than the remolded yield stress, but increases rapidly with the effective stress when the effective stress is larger than the remolded yield stress.

Utilization of Dredged River Sediment in Preparing Autoclaved Aerated Concrete Blocks

In this study,the dredged river sediment,soft texture and fine particles,is mixed with other materials and transformed into eco-friendly autoclaved aerated concrete(hereinafter referred to as AAC)blocks.The results indicated the bricks produced under the conditions of 30%–34%dredged river sediment,24%cement,10%quick lime,30%fly ash,2%gypsum and 0.09%aluminum powder with 0.5 water to material ratio,2.2 MPa autoclave pressure and 6 h autoclave time,the average compressive strength of 4.5 MPa and average dry density of 716.56 kg/m³were obtained,the two parameters(strength&density)both met the requirement of national industry standard.At the same time,the contents of dredged river sediment,cement,lime,fly ash,gypsum and aluminum powder were 15%,48%,20%,15%,2%and 0.09%,respectively,and the non-AAC block made of 0.5 water to material ratio,the average compressive strength of 3.1 MPa and average dry density of 924.19 kg/m³were obtained,the two parameters(strength&density)also met the requirement of national industry standard.In addition,the AAC block’s phase composition and morphology were micro-analyzed by SEM and XRD,the main substances in AAC block were found to be tobermorite and CSH,Among them,the chemical bond between Si-O-Si and Al-O-Al is broken,Al-O-Si is regenerated,Al substituted tobermorite with better strength is formed,and the compressive strength of AAC is further improved.

Dispersal and Fate of Dredged Materials Disposed of in the Changjiang Estuary Determined by Use of An in Situ Rare Earth Element Tracer

To investigate the dispersal pattern and the fate of dredged materials disposed at a pre-selected disposal site, a field tracer experiment was conducted in the North Passage of the Changjiang Estuary during the 2005 flood season. Three tons of dredged materials were mixed with 2.792 kg of sodium hexachloroiridate （IV） hexahydrate （SHH）, which contained the rare earth element tracer iridum （Ir）. Sampling was conducted at pre-selected sections of the estuary on the second, third and fourth day after the release of dredged materials. All samples were evaluated by use of neutron activation analysis. The majority of the dredged material was dispersed nearly parallel to the navigation channel and deposited between the channel and the south dike. Only a small quantity of dredged materials entered or crossed the navigation channel, and the back silting ratio in the navigation channel was about 5%. The dredged materials also dispersed southeasterly beyond two dike heads.

NUMERICAL SIMULATION OF 3-D TURBULENT FLOWS OVER DREDGED TRENCHES

A 3- D free surface flow in open channels based on the Reynolds equations with the k-ε turbulence closure model is presented in this paper. Insted of the 'rigid lid' approximation, the solution of the free surface equation is implemented in the velocity-pressure iterative procedure on the basis of the conventional SIMPLE method. This model was used to compute the flow in rectangular channels with trenches dredged across the bottom. The velocity, eddy viscosity coefficient, turbulent shear stress, turbulent kinetic energy and elevation of the free surface can be obtained. The computed results are in good agreement with previous experimental data.

Research on the Solidification Mechanism Based on the Water Characteristic Curve of Solidified Dredged Sediment

The fractal model about water characteristics of solidified sediment was built according to the granular metric analysis curve of solidified dredged sediment, the measured value during the low-suction stage of the curing process was used for fitting parameters in the model to obtain the complete water characteristic curve of solidified dredged sediment. Then, the quantitative calculation model of capillary water, attached water, evaporated water and bound water was built by the water characteristic curve and from the view of quantitative angle, the paper analyzed the solidification mechanism of solidified dredged sediment. The result showed that： the model can realize the quantitative calculation about different tapes of water during the curing process, the evaporated water during the curing process mainly came from the capillary water, and the generated bound water during the curing reaction came from the attached water.

MODEL STUDY OF DREDGED CHANNEL SILTATION IN OFFSHORE OPEN WATER

Based on the model study, the siltation of dredged channel under the condition of clear water and sediment-water mixture in Lianyun Harbor, Jiangsu Province and the experimental method under complex hydrodynamic elements such as tides, winds, waves and tidal currents are studied. The regularities of the variation of the velocity in the dredged channel in clear water are discussed as well. A group of curves such as water depth, velocity and angle has been plotted as a guide to the selection of a proper direction for a dredged channel. The intensity of siltation and the rate of deposition in the condition of sediment-water mixture, and the relationship between the dimensions of the dredged channel and the deposition amount can be estimated.

Tensile strength behavior of cement-stabilized dredged sediment reinforced by polypropylene fiber

This study evaluated the feasibility of using polypropylene fiber(PF)as reinforcement in improving tensile strength behavior of cement-stabilized dredged sediment(CDS).The effects of cement content,water content,PF content and length on the tensile strength and stress–strain behavioral evolutions were evaluated by conducting splitting tensile strength tests.Furthermore,the micro-mechanisms characterizing the tensile strength behavior inside PF-reinforced CDS(CPFDS)were clarified via analyzing macro failure and microstructure images.The results indicate that the highest tensile strengths of 7,28,60,and 90 d CPFDS were reached at PF contents of 0.6%,1.0%,1.0%,and 1.0%,exhibiting values 5.96%,65.16%,34.10%,and 35.83%higher than those of CDS,respectively.Short,3 mm,PF of showed the best reinforcement efficiency.The CPFDS exhibited obvious tensile strain-hardening characteristic,and also had better ductility than CDS.The mix factor(C_(C)^(a)/C_(w)^(b))and time parameter(q_(t0)(t))of CDS,and the reinforcement index(k_(t-PF))of CPFDS were used to establish the tensile strength prediction models of CDS and CPFDS,considering multiple factors.The PF“bridge effect”and associated cementation-reinforcement coupling actions inside CPFDS were mainly responsible for tensile strength behavior improvement.The key findings contribute to the use of CPFDS as recycled engineering soils.

An integrated method for the rapid dewatering and solidification/stabilization of dredged contaminated sediment with a high water content

To more efficiently treat the dredged contaminated sediment(DCS)with a high water content,this study proposes an integrated method(called PHDVPSS)that uses the solidifying/stabilizing(S/S)agents and prefabricated horizontal drain(PHD)assisted by vacuum pressure(VP).Using this method,dewatering and solidification/stabilization can be carried out simultaneously such that the treatment time can be significantly shortened and the treatment efficacy can be significantly improved.A series of model tests was conducted to investigate the effectiveness of the proposed method.Experimental results indicated that the proposed PHDVPSS method showed superior performance compared to the conventional S/S method that uses Portland cement(PC)directly without prior dewatering.The 56-day unconfined compressive strength of DCS treated by the proposed method with GGBS-MgO as the binder is 12–17 times higher than that by the conventional S/S method.DCS treated by the PHDVPSS method exhibited continuous decrease in leaching concentration of Zn with increasing curing age.The reduction of Zn leachability is more obvious when using GGBS-MgO as the binder than when using PC,because GGBS-MgO increased the residual fraction and decreased the acid soluble fraction of Zn.The microstructure analysis reveals the formation of hydrotalcite in GGBS-MgO binder,which resulted in higher mechanical strength and higher Zn stabilization efficiency.

Consolidation behavior of Tianjin dredged clay using two air-booster vacuum preloading methods

This paper presents model tests(macro aspect)and microstructure tests(micro aspect)for investigating the consolidation behavior of Tianjin dredged clay using the prefabricated vertical drain air-booster vacuum preloading(PAVP)and tube air-booster vacuum preloading(TAVP)methods.The mechanism of air-booster vacuum preloading(AVP)using a spring-like system is explained.The main difference between these two methods is the air-boosting equipment.A new anticlogging air-booster prefabricated vertical drain(PVD)is used in the PAVP technique and a self-designed air-booster tube is used in the TAVP technique.In the model tests,a comparison of the variables that are monitored during reinforcement(vacuum pressure,surface settlement,water discharge,and pore-water pressure)and after reinforcement(water content,dry density,and vane shear strength)is conducted.The results indicate that the consolidation behavior of Tianjin dredged clay using the PAVP method is better than that using the TAVP method.PAVP more efficiently mitigates the issue of water-draining PVD clogging and significantly accelerates drainage consolidation.In addition,in the microstructure tests,a comparison of the variables that are monitored after reinforcement(via scanning electron microscopy(SEM)and mercury intrusion porosimetry(MIP))is conducted,and the results further explain the model test results.