Sabrina Bradshaw

Hydration and Cation Exchange during Subgrade Hydration and Effect on Hydraulic Conductivity of Geosynthetic Clay Liners

AbstractExperiments were conducted to evaluate cation exchange during hydration of geosynthetic clay liners (GCLs) used in composite hydraulic barriers and the effect on their hydraulic conductivity. GCLs arranged in a composite barrier configuration were hydrated by contact with moist compacted subgrades (two clays, one silt, and one sand) under a confining stress of 10 kPa for 30 days to 1 year. No measurable exchange occurred in GCLs hydrated for 30 days. For hydration periods longer than 30 days, the exchange increased as the duration of hydration increased. The exchange during subgrade hydration had no measurable effect on the hydraulic conductivity to deionized (DI) water. However, if the GCL was desiccated after hydration, the hydraulic conductivity increased more than 1,000-fold. Dissolution of calcite within the bentonite during permeation with DI water also induced the replacement of sodium by calcium; however, this additional exchange had no measurable effect on the hydraulic conductivity to DI...

Effect of Municipal Solid Waste Leachate on Hydraulic Conductivity and Exchange Complex of Geosynthetic Clay Liners

AbstractTests were conducted to assess how permeation with synthetic and real municipal solid waste (MSW) leachate affects the hydraulic conductivity and exchange complex of geosynthetic clay liners (GCLs). GCLs were arranged in a composite barrier configuration for hydration on moist compacted subgrades for 30 or 90 days. After hydration, the geomembrane and subgrade soil were removed and the GCLs were permeated with typical and strong synthetic and real MSW leachates at different confining stresses for 342 to 1,281 days (4.9 to 148.9 pore volumes of flow). For most tests, hydraulic and chemical termination criteria were met (referred to as equilibrium), and in many cases the tests were conducted long after these criteria were achieved. Hydraulic conductivity of the GCLs increased no more than 5.6 times the hydraulic conductivity to deionized water (DIW), even though more than 80% of the sodium (Na) in the bentonite was replaced by other cations [predominantly calcium (Ca) and magnesium (Mg)]. Very long ...

pH-Dependent Leaching of Trace Elements from Recycled Concrete Aggregate

Recycled concrete aggregate (RCA) has excellent mechanical properties and is often used as base course in pavement construction. However, highly alkaline leachate from RCA has been observed in laboratory studies. The associated high-pH leaching patterns can be of concern, especially when compared to the neutral pH environment observed in actual road sections using RCA as base course. In this study, the pH-dependent leaching concentrations of trace elements copper (Cu) and zinc (Zn) and the oxyanion chromium (Cr) were investigated on unfractionated RCA samples and fractionated RCA samples (i.e., fine particles 0.075 mm, and gravel-sized particles 4.75 mm). A pH-buffering plateau was observed between pH 4.9 and 7.0 in the acid neutralization capacity curve. Cu and Zn showed the highest levels of leaching at pH≅2, and the lowest leaching at pH>7.5. Cr showed the lowest level of leaching between pH 5.0 and 6.5, and higher leaching concentrations towards the acid and alkali directions. The fine particles tended to leach more Cu and Zn than sand- and gravel-sized particles at 2

Hydraulic Conductivity of Geosynthetic Clay Liners to Recirculated Municipal Solid Waste Leachates

AbstractTests were conducted to assess how permeation with actual recirculated leachate from municipal solid waste (MSW) landfills affects the hydraulic conductivity and exchange complex of geosynthetic clay liners (GCLs). Long-term hydraulic conductivity tests were conducted (∼1 to 5  years) on GCL specimens with conventional sodium bentonite using seven recirculated MSW leachates and one conventional (nonrecirculated) MSW leachate as permeant liquids. Effects of stress and temperature were also assessed. Hydraulic termination criteria were achieved for all tests, and chemical termination criteria were achieved for nearly all. The long-term hydraulic conductivity of the GCL specimens to recirculated leachates (1.0–2.0×1011  m/s) was slightly less than the long-term hydraulic conductivity to the conventional leachate (2.0×10−11  m/s). Furthermore, the ratio of the hydraulic conductivity to recirculated MSW leachate to the hydraulic conductivity to DI water for GCL specimens (1.4–2.9) fell within the range...

Quantifying the Benefits of Using Flue Gas Desulfurization Gypsum in Sustainable Wallboard Production

A suite of high-As, high-C fly ashes from a university-based stoker-fired coal boiler were analyzed by a number of techniques, including high-resolution transmission electron microscopy (HR-TEM), time-of-flight secondary ion mass spectrometry (TOF-SIMS), X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscopy (FE-SEM). The sooty carbon is in the form of nano balls with the major fullerenes at C~60~^+^, C~70~^+^, and C~80~^+^, with species at C~2~ increments from C~56~^+^ to C~78~^+^. Arsenic and Hg, among other metals, are found in association with the fullerenes, but, with our techniques, it is not possible to determine if the metals are encapsulated by the fullerenes or attached to the side of the structure. TOF-SIMS studies suggest an association of As with the Al-Si glass; an association of Pb with oxides, sulfates, and carbon; Hg with carbon; Se in elemental form with carbon; and Cr in a variety of forms, including nano carbons, Fe sulfates and oxides, glass, and Cr-oxyhydroxides.

Hydraulic Conductivity of Geosynthetic Clay Liners to Synthetic Coal Combustion Product Leachates

Experiments were conducted to evaluate whether coal combustion product (CCP) leachates adversely affect the hydraulic conductivity of geosynthetic clay liners (GCLs). Chemical properties of CCP leachates were compiled based on a nationwide survey of CCP disposal facilities. Five synthetic leachates were selected from this database to represent a range of conditions encountered in CCP disposal facilities: typical CCP leachate, strongly divalent cation fly ash leachate, flue gas desulfurization (FGD) residual leachate, high ionic strength ash leachate, and trona ash leachate. Five GCLs were tested: two conventional Na-bentonite GCLs, two polymer-modified bentonite GCLs, and one bentonite polymer composite (BPC). Hydraulic conductivity tests were conducted on non-prehydrated GCLs using flexible-wall permeameters. GCLs with Na-bentonite had high hydraulic conductivity (>10 m/s) to trona leachate, whereas the hydraulic conductivity of GCLs with polymer-modified bentonite was variable, ranging from 10 to 10 m/s. For the typical CCP, high ionic strength, FGD, and strongly divalent cation leachates, GCLs with Na-bentonite had moderate to high hydraulic conductivity (10 to 10 m/s). GCLs with polymer-modified bentonite had lower hydraulic conductivity (10 to 10 9 m/s) to FGD and strongly divalent cation leachates, and a wide range of hydraulic conductivities to high ionic strength leachate (10 to 10 m/s). All of the GCLs had low hydraulic conductivity (<10 m/s) to DI water. GCLs with BPC had very low hydraulic conductivity (< 10 m/s) to all leachates.

Using Foundry Sand in Green Infrastructure Construction

Foundry sand is a high-quality uniform silica sand that is used to make molds and cores for ferrous and nonferrous metal castings. The metal casting industry annually uses an estimated 100 million tons of foundry sand for production. Over time, foundry sands physically degrade until they are no longer suitable for molds. Consequently, 9 to 10 million tons of sand is discarded each year. However, the discarded foundry sands have remarkably consistent composition and are generally considered a higher quality material than typical bank run or natural sands used in construction. Currently, an estimated 28% of discarded foundry sand is reused, primarily in construction-related applications, while the remaining sand is disposed of in landfills (American Foundry Society 2007). Recycling of foundry sand can save energy, reduce the need to mine virgin materials, and may reduce costs for both producers and end users. Use of foundry sand as a fine aggregate in construction applications offers project managers the ability to enhance green sustainable construction by reducing their carbon footprint, while also qualifying for LEED credits. The U. S. Environmental Protection Agency (EPA) recently estimated that at the current recycling level 20,000 tons of CO2 emissions are prevented while 200 billion BTUs of energy are saved (US EPA 2008). Support for increased reuse of foundry sand has brought together the U.S. EPA, the Federal Highway Administration, the U. S. Department of Agriculture, the Recycled Materials Resource Center (RMRC), state environmental agencies, the foundry industry and end users to develop the tools and resources needed to increase foundry sand recycling to 50% by 2015. This paper provides a comprehensive overview of the engineering and construction properties of foundry sand for use in Portland cement concrete, hot mix asphalt, road subbase layers, embankments, and flowable fill. Recent studies addressing environmental concerns of using foundry sand as a construction material are reviewed. With the goal of advancing use of foundry sand in construction application, references to resources and tools, such as web-based training and a foundry locator map module, are made available.

Trace Element Leaching From Recycled Pavement Materials Stabilized With Fly Ash

Percolation rates and concentrations of trace elements are presented from leachate collected in pan lysimeters installed beneath roadway sections where fly ash was used to stabilize subgrade or base course. Data from control sections are also presented. Percolation rates from the base of a pavement profile vary seasonally in response to seasonal variations in meteorological conditions. Percolation rates typically range between 0.1-0.5 mm/d, with the average percolation rate falling between 0.1-0.2 mm/d depending on site conditions. Concentrations of six elements (B, Cd, Cr, Cu, Mo, and Zn) in leachate from roadway sections stabilized with fly ash have been elevated compared to concentrations from control sections at all field sites with control sections. Four elements from fly-ash-stabilized materials have been elevated in concentration relative to control section at some sites (As, B, Cd, Cr, and Mo) and have also exceeded MCLs. Both B and Mo persistently exceed MCLs. In contrast, concentrations of Cd and Cr have only exceeded MCLs in the first samples collected (PVF < 0.25), and then have remained well below MCLs.