In Vietnam, the larger amount of municipal solid waste (MSW) is generated but the main treatment method still is landfilling. Currently, the incinerator is applied for MSW treatment. Previous researches showed that MSW bottom ash (MSWIBA) can be used as construction material such as roadbed and foundation layers. The direct shear test results showed that the friction angle of MSWIBA was from 38° to 55°, which was suitable for construction materials. However, in Vietnam, there is limited research about the mechanical properties of MSWIBA. Thus, this paper focuses on the effect of compaction ratio on the shear strength of MSWIBA by using large direct shear with a diameter of 300 mmx300 mm. The results showed that the internal friction angle for MSWIBA was about 31° and 44 ° for compaction ratio of 90 percent and 95 percent, respectively. In addition, cohesion was also quite high for two cases.

Road base layers play an important role in bearing, transmitting, and distributing part of the load to the underground. Unbound aggregates crushed from natural rock are the most popular materials used to construct the base layers of the pavements. However, nowadays the sources of natural materials have been increasingly exhausted and the pollution from construction and demolition waste (CDW) is a big problem in Vietnam. Therefore, the utilization of CDW for recycling is a crucial issue to reduce the generation amount of CDW and consumption of natural resources. With regards to the applicability of recycled concrete aggregates (RCA) to unbound roadbed materials, many studies have been done to investigate the effect of grading of particles on mechanical properties. However, the effect of other factors such as maximum particle size (Dmax) and fines content (Fc in wt.%; typically, with particle size less than 0.075 mm) have not been fully understood. In this study, concrete waste taken from a CDW landfill in Vietnam and was crushed and sieved to prepare graded RCA samples for a series of laboratory tests to characterize mechanical properties such as compaction, bearing capacity, and saturated hydraulic conductivity. The graded RCA samples with two different Dmax, 25 and 37.5 mm, and four different Fc values ranging from 0 to 20 %, were prepared. This study showed that maximum dry density (MDD) and CBR value of graded aggregates with Dmax = 25 and 37.5 mm reached the highest values at Fc = 5%. Except for the sample with Fc = 20 % and Dmax = 25 mm, the measured CBR values of tested samples satisfied the technical requirements of Vietnamese and Japanese standards. Besides, the particle breakage of aggregates and saturated hydraulic conductivity were highly controlled by Fc and both values decreased with increasing in Fc.

The Port of Savannah is located 18 miles inland from the Atlantic Ocean in the southeastern United States. Historically, 6 million cubic meters of river sediment is dredged from the Savannah River each year; however, the Savannah Harbor Expansion Project (SHEP) (Georgia, USA), which is proposed to accommodate post Panamax ships in the channel, will result in further increased dredge volume for disposal. Because dredge materials are currently disposed on land, this study was focused on identifying possible beneficial uses of dredge material in order to reduce the requirements for land disposal. A laboratory-based study was performed to assess the feasibility of large volume geotechnical use options for dredged sediments. Four samples were collected from the disposal facilities and characterized using physical, chemical and morphological analysis techniques, including grain size distribution, Atterberg limits test, specific gravity, scanning electron microscopy (SEM), laser diffraction particle size analysis (PSA), total organic carbon content (TOC), loss on ignition (LOI), and thermogravimetric analysis (TGA) analysis. The compactibility of the dredge was quantified using the standard Proctor test. Overall, characterization and compaction results demonstrated that the dredge material is viable for use as a nonstructural fill material, indicating that additional research and feasibility studies focused on specific beneficial use options is warranted. These results have important implications on the potential for beneficial use of the dredged sediment.

The purpose of this study is to investigate the effect of the length of the chemical fibers (CF) on the mechanical properties of slag mixed with CF. Furthermore, the effect of the difference between fibrous wood chips (FWC) and CF on mechanical properties is to be examined. In this study, a series of consolidated drained triaxial compression tests were conducted on a material mixed with steelmaking slag and FWC assuming under sieve residue or CF. The chemical fiber length and curing periods were changed in this study. As a result, it was found that 2% by volume of the CF mixture increased both the shear strength and the residual strength compared to the slag. However, their increases were up to the fiber length of 20 mm. When 5% by volume of FWC, the length of which was about 18.9 mm, were mixed to the slag, there were no increases observed in both the shear strength and the residual strength.

With the rapid promotion of city urbanization, the amount of municipal solid waste (MSW) is increasing.Incineration can significantly reduce the mass, volume and generate energy at the meanwhile, making it a mainstream approach for recycle of MSW. The process of incineration brings about various benefits, such as good capacity reduction, high quality reduction, effective removal of harmful components, and high efficiency of resource reuse. The utilization of MSWI bottom ash can achieve the purpose of energy conservation, emission reductio n and resource recycling. Recently, MSWI has been successfully recycled for many applications, especially in road construction. Many simulation studies have conducted it as substitutable material in subgrade layer, owing to the similarity to traditional mi neral aggregate. It is indispensable to develop a resistance as subgrade layer, and the purpose of this paper is to investigate the feasibility of MSWI bottom ash for practical application in subgrade layer. For this reason, an ABAQUS finite element simula tion model of pavement structure subjected to dynamic loads has been conducted.

A general framework of coupled biochemical-thermo-hydro-mechanical (THMBC) processes has been developed to analyze the complex phenomena in degradable soils, such as municipal solid and natural gas hydrate, whose solid skeleton can be decomposed by biological or chemical reactions. The frame contains the linear momentum equilibrium equation, the mass conservation equations for the liquid and gas phases, the energy conservation equation. The evaporation and condensation of water, and the dissolution of gas in water are considered in the mass conservation equation of the fluid. The biochemical reaction rate can be used to link the source and sink terms of the fluid with solid mass loss, meanwhile to give a quantitative description of changes in porosity and strain. The impact of the solid mass loss and the porosity change on the hydro-mechanical properties are involved. As a case study, a model describing the coupling process of landfilled MSW was proposed. In this model, the constitutive model considering the influence of degradation was used, and the degradation chemical formula of the degradable component was given. The results of a large-scale experiment were compared with numerical simulations.

The utilization of industrial byproducts, IBPs, for creating huge infrastructure projects (viz., land reclamation, rehabilitation of low-lying areas, backfilling of mines and construction of embankments, etc.), is being hypothesized to address the issues related with the sustainability. One of such IBPs are the bauxite residues, BRs, which get generated at alumina refineries; either in the slurry form or cakes coming out of the filter press, has been stacked at industrial premises, in the form of heaps or dumps. Ideally, the BRs can be utilized for the above-mentioned projects, provided they are suitably ‘ neutralized’ to bring down their pH. Though, at this stage, it appears to be a ‘ distant dream’, successful demonstration of such a philosophy would be a game-changer for the alumina refineries and the infrastructure sector, in general. In lieu of this, different techniques for neutralizing the BRs by using various chemicals, (sea)water, and bacteria have been adopted in the past. However, another interesting strategy to neutralize the magnanimous quantity of BRs stacked could be through purging CO2 that needs to be investigated in detail. With this in view, and to investigate the technical feasibility of CO2 purging in the BRs in their semi-solid state, a setup NeGaPur (connoting to the Neutralization by Gas Purging) that simulates BRs-gas interaction in the laboratory conditions has been adopted and its details are presented in this paper.

The application of micro-nano bubbles (MNBs) in water treatment technology has been gaining more and more attention recently. In order to investigate the effect of salinity and surfactant on mass transfer characteristics of oxygen MNBs, a series of laboratory experiments conducted on oxygen MNBs water with different salinities and surfactant concentrations. The test results showed that two ranges obtained for oxygen MNBs size and the main parts were 0.026-0.172 μm and 1.635-6.540 μm. With the salinity of 0 g/L, the peak value of dissolved oxygen (DO) in oxygen MNBs water was 44.13 mg/L and the saturation time of DO was 11400 min. But when the salinity was 3 g/L, the peak value of DO increased by 7.68% and the saturation time of DO was extended by 9.32%. When the salinity was between 0 g/L and 2 g/L, the mass transfer efficiency of oxygen MNBs was adversely affected by salinity. In addition, sodium dodecyl benzene sulfonate (SDBS) reduced the peak value of DO and extended the saturation time of DO by changing the interface potential of oxygen MNBs.

We developed and studied a simple and environmentally friendly soil solidification technique utilizing bio-mineralization or bio-cementation process. The microorganism used for this technique was baker’s dry yeast. To adjust the pH of the soil and promote mineralization, agricultural fertilizer was used. Sandy soil was solidified by mixing the materials, adding water, and letting them cure. In terms of reproducible results, it was possible to produce solidified bodies with the same strength as cement-improved soil. In our study, only environmentally friendly materials have been used. Therefore, this technique can be applied not only for ground improvement, but also for other various applications such as sandy soil utilization.

Microbiologically Induced Calcite Precipitation (MICP) has been proposed to improve the weak sandy soil ground via bio-augmentation or bio-stimulation. Compared with bio-augmentation, bio-stimulation approach has more advantages since indigenous microbes are more likely to survive and effectively generate MICP. This paper reports a preliminary experimental study of investigating the mechanism of bio-stimulation and shear strength behavior of bio-cemented carbonate sand via a series of column enrichment and soil direct shear tests. The carbonate sand was firstly treated by enrichment media containing nutrient solution and urea, and then treated by cementation solution containing urea and calcium chloride. After treatment, direct shear tests were conducted under four normal stress (25 kPa, 50 kPa, 100 kPa and 200 kPa). The results indicate that indigenous ureolytic bacteria can be enriched in soil effectively, and the shear strength can be improved significantly.

The effectiveness of using some natural and/or synthetic fibers such as bamboo, jute, steel fibers, polyester fibers, etc. in the soil improvement techniques has been recognized by many researchers. In addition, eco-friendly soil improvement techniques using biomineralization by microorganisms have attracted attention in recent years. This technique improves the mechanical properties of soil by precipitating calcium carbonate between soil particles and adhering the particles. In the current study, the author investigated an effectiveness of using waste paper fiber to suppress liquefaction and a self-healing process based biomineralization by microorganisms. As a result of solidification tests based on column approach, it was revealed that many calcium carbonate minerals are generated on the surface of waste paper fibers and between sand particles, and uniaxial strength is improved.

In the past decades, efforts have been made to substitute Ordinary Portland Cement (OPC) by developing novel cement materials using industrial byproducts such as Alkali-Activated Slag (AAS), in which Granular Ground Blast Furnace Slag (GGBS) is a popular one. So far, numerous studies on AAS show that its superiority in high early strength, resistance to sulfate attack compared with OPC. Besides, different chemicals, fiber, and additives have been amended with the AAS, trying to achieve more engineering application. Biochar is an additive produced from the anerobic pyrolysis of biowastes such as leaves, which can effectively reduce the carbon dioxide emission from the decaying of biowastes. When biochar is added to AAS system, the high interior surface area will increase water capacity, cation exchange capacity and surface sorption capacity to achieve a better hydration degree. Currently, the engineering properties of the biochar-enhanced AAS stabilized soils have not yet been investigated. In this study, the admixture of GGBS, hydrated lime and biochar is applied to stabilize the local coral sand for the purpose of coastal erosion control. The unconfined compression test, pH, water content, microstructural of the biochar-enhanced AAS stabilized coral sand are measured and observed. The results show that with the addition of biochar in AAS system, an optimum content for biochar can make the stabilized soil display better ductility without compromising its strength.

The mixture of clayey soil and steelmaking slag has the property of solidification, where the mixture is consolidated as it solidifies. This study examines the effects of the consolidation of the mixture owing to overburden pressure during curing on properties of its shear strength. A unconfined compression test and a consolidated-undrained triaxial compression test (CU test) were performed on specimens that had been cured while applying an overburden pressure to clayey soil mixed with steelmaking slag. The results of the unconfined compression test revealed that the relationship between overburden pressure and qu at the same duration of curing was linear, and both the slope and intercept of the primary equation increased with the duration of curing. The CU test showed that an overburden pressure of 50 kN/m2 during curing increased the value of qmax by 2.7 times when the mixture was cured under atmospheric pressure for 28 days. In addition, regardless of the presence of overburden pressure during curing, as solidification progressed, a peak appeared in the q–p' plane beyond q/p'= 3.

Excavated rock and sediment in which arsenic release naturally occurs is necessary to be treated with an appropriate technique such as chemical immobilization. The physical condition such as particle size ratio of rock to the immobilization material possibly enhances/suppresses the effects of arsenic immobilization because arsenic should be contacted and reacted with the immobilization material in the rock pores for the immobilization. This study prepared the up-flow column percolation test using the excavated rocks with the different particle sizes and immobilization material with constant particle size to determine a suitable ratio of the diameter of the average particle size in the rock samples to that in the immobilization material. The column percolation test showed that the contribution of arsenic immobilization by the immobilization material was higher in the larger particle size of excavated rock while the arsenic retention capacity of excavated rock was high in the smaller particle size. The arsenic concentrations in the leaching water were the lowest and the percentage of arsenic retained during the column percolation test was the highest in the particle size of 1.0–2.0 mm of excavated rock. Based on these results, this study suggests that the suitable particle size ratio of excavated rock to the immobilization material was 2 to 10.

A significant amount of foam shield tunneling surplus excavation soil, which contain a foaming agent and a blow off inhibitor, has been produced on shield tunneling construction. To utilize the surplus soil effectively for reclamation of harbor areas, engineering properties of the mixture of the surplus soil and steelmaking slag, which is an industrial byproduct in steel manufacturing, have been studied. Issues regarding the putting of the mixture in water was studied in this study. Two types of water putting ways were investigated through small-sized laboratory model experiments. One way was to put from the bottom of a water tank; the other was to put from the water surface. Effects of the ways for configuration of the sedimented mixture, bearing capacity of the mixture and segregation of the mixtures were studied by the experiments. Results show that the configuration of the sedimented mixture and the steepest gradient are not affected by the putting ways. The maximum and average bearing capacities of the ground surface were larger when the mixture was put from the water tank bottom. The water turbidity was smaller when the mixture was put from the water tank bottom.