Bora Cetin

Experimental and numerical analysis of metal leaching from fly ash-amended highway bases.

A study was conducted to evaluate the leaching potential of unpaved road materials (URM) mixed with lime activated high carbon fly ashes and to evaluate groundwater impacts of barium, boron, copper, and zinc leaching. This objective was met by a combination of batch water leach tests, column leach tests, and computer modeling. The laboratory tests were conducted on soil alone, fly ash alone, and URM-fly ash-lime kiln dust mixtures. The results indicated that an increase in fly ash and lime content has significant effects on leaching behavior of heavy metals from URM-fly ash mixture. An increase in fly ash content and a decrease in lime content promoted leaching of Ba, B and Cu whereas Zn leaching was primarily affected by the fly ash content. Numerically predicted field metal concentrations were significantly lower than the peak metal concentrations obtained in laboratory column leach tests, and field concentrations decreased with time and distance due to dispersion in soil vadose zone.

Trace Metal Leaching from Embankment Soils Amended with High-Carbon Fly Ash

AbstractThe use of fly ash in highway applications as a stabilizing agent and soil amendment for embankments has become very common owing to its economical advantages. However, fly ash may contain toxic constituents that may pose environmental risk if they leach through the soil and reach groundwater. A series of water leach tests (WLTs), toxicity characteristic leaching procedure (TCLP) tests, and column leach tests (CLTs) were conducted to define the leaching of aluminum, arsenic, chromium, and zinc from a self-cementitious fly ash and four different off-spec high-carbon ashes. Laboratory results indicated that an increase in fly ash contents generally yields an increase in pH and leached metal concentrations regardless of the type of fly ash and metals. Furthermore, it was determined that there were significant differences in the leached metal concentrations measured in the three different laboratory tests, i.e., CCLT>CTCLP>CWLT. Analyses conducted using a numerical groundwater model indicated that pre...

Leaching characteristics of toxic constituents from coal fly ash mixed soils under the influence of pH.

Leaching behaviors of Arsenic (As), Barium (Ba), Calcium (Ca), Cadmium (Cd), Magnesium (Mg), Selenium (Se), and Strontium (Sr) from soil alone, coal fly ash alone, and soil-coal fly ash mixtures, were studied at a pH range of 2-14 via pH-dependent leaching tests. Seven different types of soils and coal fly ashes were tested. Results of this study indicated that Ca, Cd, Mg, and Sr showed cationic leaching pattern while As and Se generally follows an oxyanionic leaching pattern. On the other hand, leaching of Ba presented amphoteric-like leaching pattern but less pH-dependent. In spite of different types and composition of soil and coal fly ash investigated, the study reveals the similarity in leaching behavior as a function of pH for a given element from soil, coal fly ash, and soil-coal fly ash mixtures. The similarity is most likely due to similar controlling mechanisms (e.g., solubility, sorption, and solid-solution formation) and similar controlling factors (e.g., leachate pH and redox conditions). This offers the opportunity to transfer knowledge of coal fly ash that has been extensively characterized and studied to soil stabilized with coal fly ash. It is speculated that unburned carbon in off-specification coal fly ashes may provide sorption sites for Cd resulting in a reduction in concentration of these elements in leachate from soil-coal fly ash mixture. Class C fly ash provides sufficient CaO to initiate the pozzolanic reaction yielding hydrated cement products that oxyanions, including As and Se, can be incorporated into.

Utilization of sepiolite materials as a bottom liner material in solid waste landfills.

Landfill bottom liners are generally constructed with natural clay soils due to their high strength and low hydraulic conductivity characteristics. However, in recent years it is increasingly difficult to find locally available clay soils that satisfy the required engineering properties. Fine grained soils such as sepiolite and zeolite may be used as alternative materials in the constructions of landfill bottom liners. A study was conducted to investigate the feasibility of using natural clay rich in kaolinite, sepiolite, zeolite, and their mixtures as a bottom liner material. Unconfined compression tests, swell tests, hydraulic conductivity tests, batch and column adsorption tests were performed on each type of soil and sepiolite-zeolite mixtures. The results of the current study indicate that sepiolite is the dominant material that affects both the geomechanical and geoenvironmental properties of these alternative liners. An increase in sepiolite content in the sepiolite-zeolite mixtures increased the strength, swelling potential and metal adsorption capacities of the soil mixtures. Moreover, hydraulic conductivity of the mixtures decreased significantly with the addition of sepiolite. The utilization of sepiolite-zeolite materials as a bottom liner material allowed for thinner liners with some reduction in construction costs compared to use of a kaolinite-rich clay.

Preventing Swelling and Decreasing Alkalinity of Steel Slags Used in Highway Infrastructures

Steel slag is a byproduct of iron and steel production by the metallurgical industries. Annually, 21 million tons of steel slags are produced in the United States, and most of this slag is landfilled. Landfilling represents significant economic loss and uses valuable land space. Although steel slag has great potential for use in highway applications, especially as a granular highway base or subbase material, it has not been used extensively because of its high swelling potential and alkalinity. Swelling potential deteriorates the structural stability of highways, and high alkalinity poses an environmental challenge. This study seeks a methodology that promotes the use of steel slags in highway base and subbase layers by minimizing these two main disadvantages. Two treatment methods were used. In the first method, steel slag material was coated with bituminous material. In the second method, the slag was mixed with water treatment residuals at various percentages by weight. The mixtures prepared in this study were subjected to accelerated swelling tests and batch water leach tests. Results of the swelling tests indicated that the addition of both water treatment residuals and bituminous material into steel slag decreased the swelling rate significantly. Furthermore, bituminous-coated mixtures did not exhibit any swelling. These two methods also decreased the effluent pH of steel slag from 12.3 to 11.65 (bitumen-coated slag) and 9.8 (slag mixed with water treatment residuals). The batch test results did not satisfy the pH 8.5 limit regulated by the Maryland Department of Environment for placement of industrial byproducts in highways.

Influence of laboratory compaction method on mechanical and hydraulic characteristics of unbound granular base materials

Unbound aggregate materials are commonly used in highway bases due to their satisfactory mechanical strength and permeability. Compaction is the most important procedure in highway base construction, thus it is imperative to determine the best compaction method that does not significantly alter the gradation of the aggregates during construction. A laboratory study was undertaken to evaluate the vibratory and impact compaction methods on resilient modulus, bearing capacity, permanent deformation, and hydraulic conductivity characteristics of several aggregates. The results indicated that impact compaction increases fines content of aggregates, resulting in reduced permanent deformation and hydraulic conductivity. Impact compaction usually provides higher resilient modulus and increases the linearity of the resilient modulus curves as compared with vibratory compaction.

Drainage and Mechanical Behavior of Highway Base Materials

AbstractThe mechanical and drainage properties of graded aggregate base (GAB) materials used in mechanistic pavement design are the level one inputs. Several highway agencies need an evaluation of the stiffness and drainage characteristics of GAB stone delivered at highly variable gradations to construction sites. To fulfill the current need, the mechanical and drainage properties of seven GAB materials with varying petrography and physical properties were evaluated in the laboratory and field. The resilient modulus and hydraulic conductivity test results obtained in the laboratory were compared with the field measurements. The summary resilient moduli at optimum moisture content (OMC) were generally lower than those at OMC–2%; however, permanent deformations increased with the addition of moisture content. The correlation between the mean laboratory and field stiffness/modulus values was fair to acceptable (R2=0.65 to 0.94), and additional measurements may yield a stronger correlation. An increase in bas...

Freeze–Thaw Performance of Fly Ash–Stabilized Materials and Recycled Pavement Materials

AbstractA comprehensive research was conducted to study the performance of a variety of stabilized geomaterials against the freeze–thaw (F–T) cycling process. Also included were unstabilized recycl...

Development of a Test Procedure for Freeze-Thaw Durability of Geomaterials Stabilized With Fly Ash

The objective of this research was to develop a freeze-thaw cycling test procedure and to investigate how the volume, moisture content, resilient modulus (Mr), and unconfined compressive strength (qu) of geomaterials, including soils and recycled materials, stabilized with fly ash change after freeze-thaw cycling. Three different types of materials (fine-grained and coarse-grained soils and recycled pavement materials) and five different fly ashes were used at different percentages (10, 12, 14, and 20 % by dry weight). Both one-dimensional and three-dimensional freezing of the specimens were considered. Freezing in three-dimensional was faster in terms of completing the freeze-thaw cycling and provided very similar results to the ones prepared in one-dimensional. Thus, three-dimensional freezing was adopted in this study without access to water (i.e., closed system). The results of this study indicated that the volume of all soil-fly ash mixtures tended to increase after freeze-thaw cycling; however, the volume change was not significant. Resilient modulus tests were conducted on all unstabilized materials, as well as on their mixtures with fly ash, while qu tests were conducted only on fine-grained soil and their fly ash mixtures. The Mr of all mixtures with one exception decreased by an average of 28.5 % when specimens were subjected to freeze-thaw cycling. The drop in the Mr of the specimens leveled off after 5 freeze-thaw cycles. A general trend of higher Mr of materials stabilized with fly ash (from 3 to 168 %), even after freeze-thaw cycles compared to unstabilized material was observed. In general, a reduction in unconfined compressive strength (qu) after freeze-thaw cycles up to 70 % was obtained. However, results showed that qu of stabilized soils that were subjected to freeze-thaw cycles were still higher (from 6 to 157 %) than the qu of unstabilized soils.

Effects of extraction methods and factors on leaching of metals from recycled concrete aggregates

Leaching of metals (calcium (Ca), chromium (Cr), copper, (Cu), iron (Fe), and zinc (Zn)) of recycled concrete aggregates (RCAs) were investigated with four different leachate extraction methods (batch water leach tests (WLTs), toxicity leaching procedure test (TCLP), synthetic precipitation leaching procedure test (SPLP), and pH-dependent leach tests). WLTs were also used to perform a parametric study to evaluate factors including (i) effects of reaction time, (ii) atmosphere, (iii) liquid-to-solid (L/S) ratio, and (iv) particle size of RCA. The results from WLTs showed that reaction time and exposure to atmosphere had impact on leaching behavior of metals. An increase in L/S ratio decreased the effluent pH and all metal concentrations. Particle size of the RCA had impact on some metals but not all. Comparison of the leached concentrations of metals from select RCA samples with WLT method to leached concentrations from TCLP and SPLP methods revealed significant differences. For the same RCA samples, the highest metal concentrations were obtained with TCLP method, followed by WLT and SPLP methods. However, in all tests, the concentrations of all four (Cr, Cu, Fe, and Zn) metals were below the regulatory limits determined by EPA MCLs in all tests with few exceptions. pH-dependent batch water leach tests revealed that leaching pattern for Ca is more cationic whereas for other metals showed more amphoteric. The results obtained from the pH-dependent tests were evaluated with geochemical modeling (MINTEQA2) to estimate the governing leaching mechanisms for different metals. The results indicated that the releases of the elements were solubility-controlled except Cr.