This paper aims to develop geopolymer concrete (GPC) with flash-calcined soils cured under ambient conditions. Flash calcination is a heat thermal technique used to eliminate pollutants and organic content in excavated soils and allow them to be used in cementitious formulations. To develop GPC, the materials used in the development of the GP precursor binder should be rich in silicon (Si) and Aluminum (Al) that can react with alkaline silicates to yield Si-O-Al bonds that would form cementitious materials. The GP precursor binder is composed of Metakaolin (MK), flash-calcined soils, and granulated blast furnace slag (GBFS). The thermally treated soils are flash-calcined dredged sediments (FCS) and flash-calcined excavated clays (FCC) while potassium silicate is used as the alkaline reagent. This study aims to use the materials above to develop GPC cured under ambient conditions with high strength, good durability, and microstructure properties. Seven formulations are done to evaluate the effect of replacing MK with either FCS or FCC and GBFS on the mechanical compressive strength, water absorption, and freeze-thaw test. The findings reveal that using only metakaolin (MK0) in the formulation yielded the highest compressive strength. These results align with the porosity test outcomes, which show correlations between micropore and macropore percentages. Analysis of the durability freeze-thaw test suggests that as the proportion of macropores increases, formulations incorporating FCS and FCC exhibit improved resistance to extreme temperatures. Conversely, an increase in GBFS content leads to a finer microstructure and reduced resistance. Water absorption testing indicates that formulations with FCS and FCC display favorable sorptivity coefficients compared to MK0, with increased GBFS content enhancing durability. SEM/EDS and calorimetry tests were conducted to investigate the impact of substituting FCS and FCC for MK within the geopolymer matrix.

Sulphoaluminate cement (SAC) is considered a low-carbon and energy-saving cementitious material, compared with ordinary Portland cement. However, the stabilization efficiency and improvement measures of SAC for dredged sediment (DS) are still unclear. This study used SAC as stabilizer for DS with high water content, and nanoparticles including nano-SiO2 (NS), nano-MgO (NM) and nanoAl2O3 (NA) were incorporated as nano-modifiers. Unconfined compressive strength (UCS) tests were carried out to evaluate the strength development of SAC-stabilized DS (SDS) and nano-modified SDS considering multiple influencing factors. Furthermore, the micro- mechanisms characterizing the strength development of SDS and nano-modified SDS were clarified and discussed based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. The results present that increasing SAC content or decreasing water content can obviously enhance the strength gaining of SDS, while the strength reduction also occurred. Incorporating suitable nanoparticles could significantly improve the strength gaining and simultaneously avoid the strength reduction of SDS. The optimum content of single NS, NM and NA was respectively 4 %, 6 % and 6 %. Composite nanoparticles containing two types of nanoparticles also exhibit positive effect on the strength gaining of SDS, and the optimum mass ratios of NS-NM, NS-NA and NM-NA were respectively 3:7, 1:9 and 5:5. By comparison, adding 6 % NA to SDS achieved the highest strength gaining. The hydration product ettringite was mainly responsible for the strength development of SDS and nano-modified SDS, and incorporating nanoparticles especially NA contributed to the formation of a tighter structure with stronger cementation inside nano-modified SDS. A conceptual model was proposed to characterize the micro-mechanism of strength development in nano-modified SDS. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The efficiency of alkali-activated ground granulated blast furnace slag in stabilizing dredged sediments with high water contents is suboptimal because the activators become diluted. To improve stabilization efficiency, additives such as nano-CaCO3 are proposed. However, some of the proposed additives may not be practical owing to their high costs. This study experimentally investigates the addition of Na2CO3 for the stabilization of dredged sediment with high water contents (i.e., 100%) using Ca(OH)2-activated slag. Experimental results show the optimal content of Na2CO3 to obtain the highest 28-day unconfined compressive strength of stabilized sediments is 0.2% gravimetrically. Below the optimal content, the strength increases with Na2CO3 content. Above the optimal content, a decrease in strength is observed. By examining the reaction products and microstructure of the stabilized dredged sediments, it is observed that the coupling mechanism of cation exchange and calcite precipitation promotes the development of finer capillary pores, leading to a reduction in interpore connectivity and lower structural heterogeneity of the fine capillary pores. Experimental evidence from this study broadens the practical applications of sustainable soil stabilization using additives.

This study investigates the sustainable use of seabed dredged sediments and water treatment sludges as construction materials using combined dewatering and cement stabilization techniques. Dredged sediments and water treatment sludges, typically considered waste, were evaluated for their suitability in construction through a series of dewatering and stabilization processes. Dewatering significantly reduced the initial moisture content, while cement stabilization improved the mechanical properties, including strength and stiffness. The unconfined compressive strength (UCS), shear modulus, and microstructural changes were evaluated using various analytical techniques, including unconfined compression testing, free-free resonance testing, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The results show a direct correlation between reduced w/c ratios and increased UCS, confirming the potential of treated sludge as a subbase layer for roads and landfill liners. A chemical analysis revealed the formation of calcium silicate hydrate (CSH) and ettringite, which are critical for strength enhancement. This approach not only mitigates the environmental issues associated with sludge disposal but also supports sustainable construction practices by reusing waste materials. This study concludes that cement-stabilized dredged sediments and water treatment sludges provide an environmentally friendly and effective alternative for use in civil engineering projects.

Due to the high water content and poor compressive strength, dredged sediment cannot be recycled directly. Alkali-activated industrial wastes can serve as an alternative to cement for stabilizing sediment, offering the benefits of lower costs and reduced carbon emissions. However, pure chemical stabilization often shows limited effectiveness in treating sediments with high water content. This study develops a mixed binder including incinerated sewage sludge ash (ISSA) and ground granulated blast-furnace slag (GGBS) to stabilize Hong Kong marine deposit (HKMD) together with vacuum preloading. The research evaluates the new binder's effectiveness in treating HKMD with water content up to 200% and compares the performance with and without vacuum preloading. The results demonstrate that ISSA and GGBS can be used as cement alternatives to stabilize dredged sediment, and the composite stabilization method (VP-CSM) significantly outperforms the pure chemical stabilization method (CSM). The strength and stiffness of VP-CSM increase at least five times compared to CSM. Additionally, the treated HKMD exhibits a larger elastic range than pure clay and a smaller stiffness degradation rate than cemented clay. The treated HKMD exhibits cross-anisotropy in stiffness, which is caused by the anisotropic microstructural fabric and is further enhanced by vacuum preloading. The coupling effect of vacuum preloading and chemical solidification includes two main aspects: (1) vacuum preloading reduces the water content of the dredged sediment, which lowers the water-cement ratio and densifies the soil; (2) the solidification reaction increases the permeability coefficient of the mud in the early stage, thereby accelerating the efficiency of vacuum preloading.

To prevent the transmission of airborne infectious diseases (SARS, H1N1, COVID-19, and influenza), the use of disposable surgical face masks has increased dramatically in the past few years. To mitigate the environmental consequences associated with mask waste, implementing circular economy strategies with the reuse of mask waste is a sustainable method. This study explores an innovative way to reuse mask fiber (MF) with dredged sediment waste together as road construction materials. First, the MF was introduced into cement-treated/ untreated dredged marine sediment mixtures with different content and lengths. Then, a variety of laboratory tests were carried out to explore the basic physical and chemical characterization of raw materials and the development of mechanical properties of mixtures. In addition, the intrinsic mechanism of MF inclusion on cement-treated sediments was analyzed by scanning electron microscope (SEM) test. The results show that the inclusion of MF significantly improves the unconfined compression strength (UCS) and splitting tensile strength (STS) of both treated and untreated specimens. The highest UCS and STS values are at the condition with an MF content of 0.25%, a length of MF of 2 cm, and a curing time of 28 days. The combined strength increase caused by cement-MF together inclusion is much greater than the strength increase caused by either of them separately. It was also found that the elastic modulus (E50) decreased with the inclusion of MF. Furthermore, the addition of MF changes the brittle behavior of the specimens, which also improves the ductility and residual strength of the specimens. The SEM analysis demonstrates the microstructure of MF and MF-reinforced specimens. The creation of a stable and interconnected microstructure is largely attributed to the bridging impact of MF and the binding effect of hydration products, which significantly improves the mechanical behavior of specimens. The MFreinforced cement-treated sediment could be an innovative, environmentally friendly, and economical material for road construction.

Purpose Straw fiber (SF) is a natural and environmentally friendly material, which has great potential in improving the hydro-mechanical behavior of cemented dredge sediment. However, the treatment mechanisms and optimum application dosage of SF in cemented sediment at high water content are unclear. This study investigates the effect of SF on the shear strength and permeability of cemented sediment at high water content (3 times the liquid limit). Methods Various SF contents (0%, 0.3%, 0.5%, 1%, 3%, 5%, 8% and 12% by mass) and curing ages (3, 7, 14, 28, 60, 90, 180 days) were considered to improve cemented dredged sediment. The effectiveness of the improvement was evaluated through unconfined compression and permeability tests. Results The test results show that there is an optimum SF content of 0.5%, below which the unconfined compression strength (q(u)) of SF-reinforced cemented sediment (SFCS) increased with SF content. Beyond this point, q(u) decreased with SF content. The brittleness index (I-b), which indicates the ductility behavior, increased with SF content across the entire SF range (0-12%). When SF addition was relatively low (< 0.5%), pore filling and bridge effects increased the interface force between SF and sediment particles, resulting in positive effects on the improvement of SFCS strength. However, when SF content exceeded 0.5%, the higher organic matter from SF could suppress pozzolanic reaction, leading to weaker cemented bonding between sediment particles and hence lower sediment strength. Conclusion This study suggests that 0.5% SF should be applied in cemented dredged sediment at high water content to optimize its strength.

Generally, high-water-content of dredged sediment (DS) tends to suffer from inferior mechanical properties and obvious shrinkage after solidification, so finding solutions to this issue is helpful for promoting the recovery and recycling of DS. In this paper, in reference to natural gypsum (NG), phosphogypsum (PG) was incorporated into DS solidified with alkali-activated slag (AAS) system. The effect of PG (0 %-20 %) on the hydration process (0-168 h), mechanical properties (3 d, 7 d and 28 d) and autogenous shrinkage (0-7 d) of DS solidified with AAS was investigated. It is found that the addition of PG not only induces the generation of ettringite to compensate for shrinkage, but also accelerates the formation of C-A-S-H by providing active calcium to promote stiffness to resist shrinkage. This results in a reduction of autogenous shrinkage by 74.3 % and an increase of compressive strength by 28.5% when PG dosage is 15%. Compared with NG, the difference in 28d-compressive strength of PG group is not more than 7.34 % under equivalent dosages. The dissolved SO4 2-from PG could be adsorbed on CA-S-H and preserved in pore solution in the form of Na2SO4. The decrease in S/Si from 0.31 to 0.09 indicates stored SO42- could be released back into system to promote the further generation of ettringite. To obtain superior mechanical properties and volume stability, appropriate PG dosage is 10 %-15 %. Compared with the control group, it increases the content of ettringite and amorphous phase by 2.4 %-4.6 % and 3.3 %-3.7 %, respectively. This research not only provides theoretical support for DS solidified with AAS to realize efficient utilization of solid waste resources (i.e., DS, PG and slag), but also gives a new insight into solidification of other high-watercontent system, such as backfill mining, grouting materials and treatment of soft soil foundations.

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, binder-soil ratio and water-solid 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 binder-soil ratio or decreasing the water-solid 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. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Natural clay is the most common material used for the veneer cover soil in solid waste landfill because of its good impermeability and mechanical stability. However, it is often difficult to obtain in the arid regions of northern China and an alternative material is urgently needed. This study utilized polyanionic cellulose (PAC) to modify the dredged sediment from the Yellow River (DSYR) to replace the clay used as the veneer cover soil in solid waste landfills. Some engineering properties of PAC-modified dredged sediment (PMDS), including compaction, permeability, shear strength, and drying shrinkage, were investigated by considering the factors of PAC dosage and compaction degree (CD). Microscopic tests were conducted to analyze the improvement mechanism of DSYR engineering properties by PAC modification. The results indicated that the hydraulic conductivity of PMDS decreased obviously with the PAC dosage or compaction degree. The addition of PAC significantly improved the shear strength of DSYR, along with an increase in cohesion but a decrease in the internal friction angle. During drying, there was no apparent horizontal displacement for PMDS, and the vertical displacement was less than 0.17 mm. Microscopic tests revealed that the dosage of PAC and compaction degree mainly affected the contact and pore distribution characteristics between soil particles, thereby changing the impermeability and mechanical properties of DSYR.