Mustafa Dayioglu, Master of Science (Graduated in 2015)

Research Title:Improving the Engineering Properties of Expansive Belle Fourche Clay by Using Chemical Additives

Expansive soil problems are frequently observed in the northern plains (North Dakota and South Dakota, Montana, Wyoming and Colorado) and southwest states (Texas and Arizona) of the United States and billions of dollars are spent each year for repairing structures (Wyoming Office of Homeland Security 2014). Repair costs of the structural damages due to the expansive soil problems are usually much more expensive than the cost to stabilize the soil prior to construction. Different techniques have been used to mitigate the volumetric instability of soils such as changing the applied compaction energy and moisture content, pre-wetting expansive soils before the construction, building moisture barriers and waterproof membrane. In addition to those methods, another widely used technique is mixing the soil with chemical additives such as cement, fly ash and lime. The main objective of this study is to improve the engineering properties (strength and swelling pressure) of Belle Fourche clay, which is obtained from Belle Fourche Shale that is one of the most common expansive shales in South Dakota (Brandner 2009), to provide adequate foundation for pavements. To achieve this goal, the locally available Belle Fourche Shale was mixed with 3 different chemical additives: class C fly ash, class F fly ash and lime. A number of tests were conducted on Belle Fourche clay as well as mixtures of Belle Fourche clay with class C and class F fly ashes and lime. Swelling pressure and unconfined compression strength of the soil and mixtures were measured. In addition, the impacts of curing period, chemical additive type and content on the engineering properties of Belle Fourche clay were investigated. Lastly, the effect of freeze and thaw (F-T) cycles on the swelling pressure and strength of specimens was studied.

MERRA Brian Ruppelt, Master of Science (Graduated in 2014)

Research Title: Performance of Different Climate Data Sources in Mechanistic-Empirical Pavement Distress Analyses

Accuracy and reliability of the input data are critical in the MEPDG approach for predicting pavement performance. Climatic factors affect the behavior of all layers in the pavement system and have a direct influence on several deterioration processes including thermal cracking, frost heave and thaw weakening, rutting, (Mills et al. 2007; Johanneck and Khazanovic, 2010; Meagher et al. 2012). It is known that climate is a crucial parameter that must be taken into account during the design of pavements. However, there have been concerns about the reliability and accuracy of the climate data provided with the MEPDG software.

To address this need, our research team used a new and spatially comprehensive weather data source for MEPDG software in addition to data available from ground-based weather stations. NASA’s Modern-Era Retrospective Analysis for Research and Applications (MERRA) product can be used to provide hourly climatic data for MEPDG analysis. MERRA is a global climate reanalysis product that combines computed model fields with ground-, ocean-, atmospheric-, and satellite-based observations. The purpose of this research project was to identify the best climate sources to use in MEPDG pavement performance predictions. The results of this study showed that MERRA is as reliable as ground-based weather stations for critical weather data. In addition, MERRA has several advantages over currently available ground-based weather sources: denser, more uniform, and broader spatial coverage; better temporal frequency and continuity; excellent data consistency and quality.

Stephanie Jones Stephanie Jones, Master of Science, (Graduated in 2014)

Research Title: Evaluation of Potential Applications of Recycled Concrete Aggregate and Fly Ash for Acid Mine Drainage Remediation

When feasible it is of best practice to prevent the formation of acid mine drainage (AMD) using source control measures such as sealing or flooding of underground mines, solidification of mine tailings, and disposal of mine wastes in sealed waste heaps.  Unfortunately, these treatment methods can be extremely costly, requiring continuous chemical input and large volumes of virgin material, such as lime (CaO) and limestone (CaCO3).  In an effort to reduce the high costs of AMD treatment, interest has developed in various applications of low-cost waste products, such as fly ash and recycled concrete aggregate (RCA), for AMD remediation.  Both RCA and fly ash are highly alkaline, exhibiting unique binding properties that could make them effective alternatives to costly, lime and limestone treatment.

The objective of this study, through laboratory testing and analysis, was to evaluate the low-cost construction waste products, recycled concrete aggregate and fly ash, as remediation materials for AMD treatment.  Column Leach Tests (CLTs) were conducted to assess the impact of fly ash and RCA on pH, electrical conductivity, alkalinity, oxidation reduction potential (Eh); and concentrations of Ca, Cu, Cr, Fe, Mg, Mn, and Zn in AMD. Following the CLTs, additional analytical methods were conducted to better understand the treatment process on a molecular basis.  X-ray fluorescence spectroscopy (XRF) was used to evaluate the impact of oxide, alkalinity, and unburned carbon content of the remediation materials on their capacity to sorb metals from AMD.  In addition, Geochemist’s Workbench was employed to create a geochemical model to better understand changes in aqueous speciation of AMD caused by treatment.

LewisAA Janile O. Bestgen, Master of Science (Graduated in 2014)

Research Title: Environmental Suitability Recycled Concrete Aggregates Used in Highway Base Layers

The use of recycle materials in pavement systems in lieu of natural aggregates has been an interest for some time. Crushed waste concrete, termed recycled concrete aggregate (RCA), is  considered as an alternative material to be used in roadway construction.  Using recycled materials increases the sustainability of the project because the environmental and economic impacts associated from mining and processing of natural aggregates are minimized and/or eliminated.  This also diverts concrete waste streams from landfills, saving valuable space. Recycled concrete aggregate use is widespread in many countries but it is shown that RCA materials have potential to leach metals. The objective of this study was to understand the impact of atmospheric exposure time, reaction time, L:S ratio, particle size and pH on the leaching behavior of the selected metals (Ca, Cr, Cu, Fe and Zn) and to identify the leaching controlling mechanisms of metals, and also to compare the concentration levels obtained from the Batch Water Leach tests (WLT) against the concentration levels obtained from Synthetic Precipitation Leaching Procedure tests (SPLPs), and Toxicity Leaching Procedure tests (TCLP), which were selected to simulate the exposure of RCA to potentially more acidic water environment.