Soft subgrades’ stabilization by using various fly ashes

This publication presents the results of research involving different types of self-cementing fly ashes (without any other activators) for the stabilization of four different types of soft subgrades from various road sites in Wisconsin, USA. The strength approaches were applied to estimate the optimum mixture design and to determine the thickness of the stabilized layer. The stabilized soil samples were prepared by mixing fly ash at different contents at varying water contents. The performance of fly ash stabilized subbase depends both on the specific source of fly ash and the engineering properties of soils. It is suggested that the performance analysis of fly ash should be based upon the laboratory tests such as index properties, compaction, unconfined compressive strength and CBR tests of a specific site. This is suggested rather than using the study of the physical properties and chemical composition of fly ash and soil. As disclosed in the literature, the strength gain due to stabilization depends mainly upon three factors; ash content, molding water content and compaction delay. The samples were subjected to unconfined compression strength and California bearing ratio (CBR) tests after 7 days curing time to develop water content–strength relationship. To evaluate the impact of compaction delay that commonly occurs in the field during construction, the sets of samples were compacted 2 h later after mixing with water. The unconfined compression strength and CBR tests were performed and used to determine the thickness of the stabilized layer in pavement design. All of these factors were taken into account throughout this research.     

Electro and Baromembrane Methods of Petrochemical Enterprises' Wastewater Treatment

The paper focuses on the development of production methods for new ion‐exchange membranes on the basis of ED‐20 industrial epoxide resin, resorcinol diglycidyl ether (RDGE), vinyl ether of monoethanolamine (VEMEA), and different di‐ and polyamines (polyethylenepolyamine (PEPA), polyethyleneimine (PEI), and hexamethylenediamine (HMDA)) in the presence of polyvinyl chloride (PVC) as a thermoplastic polymer binder. With the purpose to establish optimum conditions for synthesis of interpolymer membranes, the influence of reactants' concentration, of the temperature, of the nature and the quantity of the solvent, and of the process duration, was studied. It was found that when the VEMEA content in the reaction mixture is increased, the static exchange capacity (SEC) of the membrane increases in the presence of: PEI in the range of 1.2 to 4.7 mEq/L; PEPA: 1.0 to 4.0 mEq/L; and, HMDA: 1.4 to 5.2 mEq/L. It was shown that the optimum synthesis conditions are heating the reaction mixture to 60 °C to 70 °C for six to seven hours with constant stirring. For increasing the basicity of membranes, N‐alkylation was carried out using known alkylating agents (methyl iodide, dimethyl sulfate, and epichlorohydrin (ECH)). The primary electrochemical and physic‐mechanic properties of the obtained membranes were studied on pilot electrodialysis cells. The process flow diagram of the electrodialysis plant, as well as the engineering design documentation thereof were developed, and a pilot electrodialysis plant was constructed. The maximum production capacity of the pilot plant was 600 L/hr with a 30 percent desalinization rate. To increase the desalinization rate up to 75 percent, circulation of the solution and a decrease of production capacity was suggested. For meeting the treated water requirements in terms of salt content, a partial recirculation mode was introduced. In the course of the studies conducted, a process flow diagram was developed, and an experimental installation and a pilot reverse osmosis plant were fabricated for phenol and ammonium nitrogen purification. The pilot plant was tested using process condensate from the Pavlodar Petrochemical Plant. It was found that prior oxidation of the condensate with ozone in alkali medium resulted in phenol purification up to 85 percent and ammonium nitrogen up to 93 percent. ©2015 Wiley Periodicals, Inc.     

Life cycle based risk assessment of recycled materials in roadway construction

This paper uses a life-cycle assessment (LCA) framework to characterize comparative environmental impacts from the use of virgin aggregate and recycled materials in roadway construction. To evaluate site-specific human toxicity potential (HTP) in a more robust manner, metals release data from a demonstration site were combined with an unsaturated contaminant transport model to predict long-term impacts to groundwater. The LCA determined that there were reduced energy and water consumption, air emissions, Pb, Hg and hazardous waste generation and non-cancer HTP when bottom ash was used in lieu of virgin crushed rock. Conversely, using bottom ash instead of virgin crushed rock increased the cancer HTP risk due to potential leachate generation by the bottom ash. At this scale of analysis, the trade-offs are clearly between the cancer HTP (higher for bottom ash) and all of the other impacts listed above (lower for bottom ash). The site-specific analysis predicted that the contaminants (Cd, Cr, Se and Ag for this study) transported from the bottom ash to the groundwater resulted in very low unsaturated zone contaminant concentrations over a 200 year period due to retardation in the vadose zone. The level of contaminants predicted to reach the groundwater after 200 years was significantly less than groundwater maximum contaminant levels (MCL) set by the US Environmental Protection Agency for drinking water. Results of the site-specific contaminant release estimates vary depending on numerous site and material specific factors. However, the combination of the LCA and the site specific analysis can provide an appropriate context for decision making. Trade-offs are inherent in making decisions about recycled versus virgin material use, and regulatory frameworks should recognize and explicitly acknowledge these trade-offs in decision processes.     

A review of aqueous-phase VOC transport in modern landfill liners

Leachates from municipal solid waste (MSW) and hazardous waste landfills contain a wide range of volatile organic compounds (VOCs) in addition to inorganic compounds. VOCs have been shown to migrate and contaminate the surrounding environment and impair the use of groundwater. Therefore, the effectiveness of modern landfill liner systems to minimize migration of VOCs is of concern. Most modern landfills employ a composite liner consisting of a geomembrane overlying a compacted clay liner or a geosynthetic clay liner. The geomembrane is often believed to be the primary barrier to contaminant transport. However, for VOCs, the clay component usually controls the rate of transport since VOCs are shown to diffuse through geomembrane at appreciable rates. Additionally, analyses have shown that transport of volatile organic compounds (VOCs) generally is more critical than transport of inorganic compounds (e.g., toxic heavy metals), even though VOCs are often found at lower concentrations in leachates. Therefore, the effectiveness of modern landfill liner systems to minimize migration of VOCs and transport of VOCs through clay liners and modeling of transport through composite liners merit scrutiny. This paper presents a review of recent research by the author and others on these topics. A systematic and comprehensive approach to determine mass transport parameters for transport of VOCs in liquid phase through compacted clay liners, geosynthetic clay liners (GCLs), and geomembranes has enabled to develop realistic models to predict mass flux of VOCs through modern composite liners and provide a quantitative basis to evaluate potential for transport of dissolved VOCs and the equivalency of different composite liners.