Matching Items (5)
Description
In recent years, an increase of environmental temperature in urban areas has raised many concerns. These areas are subjected to higher temperature compared to the rural surrounding areas. Modification of land surface and the use of materials such as concrete and/or asphalt are the main factors influencing the surface energy balance and therefore the environmental temperature in the urban areas. Engineered materials have relatively higher solar energy absorption and tend to trap a relatively higher incoming solar radiation. They also possess a higher heat storage capacity that allows them to retain heat during the day and then slowly release it back into the atmosphere as the sun goes down. This phenomenon is known as the Urban Heat Island (UHI) effect and causes an increase in the urban air temperature. Many researchers believe that albedo is the key pavement affecting the urban heat island. However, this research has shown that the problem is more complex and that solar reflectivity may not be the only important factor to evaluate the ability of a pavement to mitigate UHI. The main objective of this study was to analyze and research the influence of pavement materials on the near surface air temperature. In order to accomplish this effort, test sections consisting of Hot Mix Asphalt (HMA), Porous Hot Mix asphalt (PHMA), Portland Cement Concrete (PCC), Pervious Portland Cement Concrete (PPCC), artificial turf, and landscape gravels were constructed in the Phoenix, Arizona area. Air temperature, albedo, wind speed, solar radiation, and wind direction were recorded, analyzed and compared above each pavement material type. The results showed that there was no significant difference in the air temperature at 3-feet and above, regardless of the type of the pavement. Near surface pavement temperatures were also measured and modeled. The results indicated that for the UHI analysis, it is important to consider the interaction between pavement structure, material properties, and environmental factors. Overall, this study demonstrated the complexity of evaluating pavement structures for UHI mitigation; it provided great insight on the effects of material types and properties on surface temperatures and near surface air temperature.
ContributorsPourshams-Manzouri, Tina (Author) / Kaloush, Kamil (Thesis advisor) / Wang, Zhihua (Thesis advisor) / Zapata, Claudia E. (Committee member) / Mamlouk, Michael (Committee member) / Arizona State University (Publisher)
Created2013
Description
Early-age cracks in fresh concrete occur mainly due to high rate of surface evaporation and restraint offered by the contracting solid phase. Available test methods that simulate severe drying conditions, however, were not originally designed to focus on evaporation and transport characteristics of the liquid-gas phases in a hydrating cementitious microstructure. Therefore, these tests lack accurate measurement of the drying rate and data interpretation based on the principles of transport properties is limited. A vacuum-based test method capable of simulating early-age cracks in 2-D cement paste is developed which continuously monitors the weight loss and changes to the surface characteristics. 2-D crack evolution is documented using time-lapse photography. Effects of sample size, w/c ratio, initial curing and fiber content are studied. In the subsequent analysis, the cement paste phase is considered as a porous medium and moisture transport is described based on surface mass transfer and internal moisture transport characteristics. Results indicate that drying occurs in two stages: constant drying rate period (stage I), followed by a falling drying rate period (stage II). Vapor diffusion in stage I and unsaturated flow within porous medium in stage II determine the overall rate of evaporation. The mass loss results are analyzed using diffusion-based models. Results show that moisture diffusivity in stage I is higher than its value in stage II by more than one order of magnitude. The drying model is used in conjunction with a shrinkage model to predict the development of capillary pressures. Similar approach is implemented in drying restrained ring specimens to predict 1-D crack width development. An analytical approach relates diffusion, shrinkage, creep, tensile and fracture properties to interpret the experimental data. Evaporation potential is introduced based on the boundary layer concept, mass transfer, and a driving force consisting of the concentration gradient. Effect of wind velocity is reflected on Reynolds number which affects the boundary layer on sample surface. This parameter along with Schmidt and Sherwood numbers are used for prediction of mass transfer coefficient. Concentration gradient is shown to be a strong function of temperature and relative humidity and used to predict the evaporation potential. Results of modeling efforts are compared with a variety of test results reported in the literature. Diffusivity data and results of 1-D and 2-D image analyses indicate significant effects of fibers on controlling early-age cracks. Presented models are capable of predicting evaporation rates and moisture flow through hydrating cement-based materials during early-age drying and shrinkage conditions.
ContributorsBakhshi, Mehdi (Author) / Mobasher, Barzin (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Zapata, Claudia E. (Committee member) / Arizona State University (Publisher)
Created2011
Description
Numerous studies have examined the interplay of climate, tectonics, biota and erosion and found that these variables are intertwined in a complicated system of feedbacks and as a result, some of these factors are often oversimplified or simply neglected. To understand the interplay of these factors one must understand the processes that transport or inhibit transport of soil. This study uses the short-lived, fallout-derived, radionuclides 137Cs and 210Pb to identify soil transport processes and to quantify soil transport using the profile distribution model for 137Cs. Using five field sites in the San Gabriel Mountains of California, I address four questions: (1) Is there a process transition between high and low gradient slopes observable with short-lived isotopes? (2) Do convex hilltops reflect short-term equilibrium erosion rates? (3) Do linear transects of pits accurately characterize hillslope averaged erosion rates? and (4) What role does fire play on short-term soil transport and isotope distribution? I find no evidence supporting a process transition from low gradient to high gradient slopes but also find that significant spatial variability of erosion rates exist. This spatial variability is the result of sensitivity of the method to small scale variations in isotopes and indicates that small scale processes may dominate broader scale trends. I find that short-term erosion rates are not at equilibrium on a convex hilltop and suggest the possibility of a headward incision signal. Data from a post-fire landscape indicates that fires may create complications in 137Cs and 210Pb distribution that current models for erosion calculation do not account for. I also find that across all my field sites soil transport processes can be identified and quantified using short-lived isotopes and I suggest high resolution grid sampling be used instead of linear transects so that small scale variability can be averaged out.
ContributorsWalsh, Joseph Robert (Author) / Heimsath, Arjun M. (Thesis advisor) / Whipple, Kelin X. (Committee member) / Zapata, Claudia E. (Committee member) / Arizona State University (Publisher)
Created2011
Description
One of the most economical and viable methods of soil improvement is dynamic compaction. It is a simple process that uses the potential energy of a weight (8 tonne to 36 tonne) dropped from a height of about 1 m to 30 m, depending on the project requirement, on to the soil to be compacted hence densifying it. However, dynamic compaction can only be applied on soil deposits where the degree of saturation is low and the permeability of the soil mass is high to allow for good drainage. Using dynamic compaction on saturated soil is unsuitable because upon application of the energy, a part of the energy is transferred to the pore water. The technique also does not work very well on soils having a large content of fines because of the absence of good drainage. The current research aims to develop a new technology using biogenic gas production to desaturate saturated soils and extend the use of dynamic compaction as a ground improvement technique to saturated soils with higher fines content. To evaluate the feasibility of this technology an experimental program has been performed. Soil columns with varying soil types have been saturated with substrate solution, resulting in the formation of nitrogen gas and the change in soils volume and saturation have been recorded. Cyclic triaxial tests have been performed to evaluate the change in volume and saturation under elevated pressure conditions and evaluate the response of the desaturated soil specimens to dynamic loading. The experimental results showed that soil specimens treated with MIDP under low confinement conditions undergo substantial volume expansion. The amount of expansion is seen to be a factor of their pore size, which is directly related to their grain size. The smaller the grain size, smaller is the pore size and hence greater the volume expansion. Under higher confining pressure conditions, the expansion during gas formation is suppressed. However, no conclusive result about the effect of the desaturation of the soil using biogenic gas on its compactibility could be obtained from the cyclic triaxial tests.
ContributorsBorah, Devajani (Author) / van Paassen, Leon A. (Thesis advisor) / Kavazanjian, Edward (Committee member) / Zapata, Claudia E. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Enzyme-induced carbonate precipitation (EICP) is an emerging technology for ground improvement that cements soil with calcium carbonate to increase strength and stiffness. EICP-improved soil can be used to support new facilities or it can be injected under existing facilities to prevent excessive deformation. The limitations for commercial adoption of EICP are the cost and the lack of implementation at field-scale. This research demonstrated two ways to reduce the cost of EICP treatment at field-scale. The first was a modification to the EICP solution such that lower amounts of chemicals are needed to achieve target strengths. The second was to use a simple and inexpensive enzyme extraction method to produce the enzyme at a large-scale. This research also involved a two-stage scale-up process to create EICP biocemented soil columns using a permeation grouting technique. The first stage was at mid-scale where 0.6 m x 0.3 m-diameter EICP biocemented soil columns were created in boxes. This work confirmed that conventional permeation grouting equipment and methods are feasible for EICP soil treatment because the columns were found to have a uniform shape, the injection method was able to deliver the EICP solution to the edges of the treatment zone, and downhole geophysics was effectively used to measure the shear wave velocity of the biocemented soil mass. The field-scale stage was performed in the Test Pit facility at the Center for Bio-mediated and Bio-inspired Geotechnics' Soils Field Laboratory. Seven biocemented soil columns were created with diameters ranging from 0.3-1 m and heights ranging from 1-2.4 m. Effective implementation at this scale was confirmed through monitoring the injection process with embedded moisture sensors, evaluating the in situ strength improvement with downhole geophysics and load testing, and testing of the excavated columns to measure shear wave velocity, dimensions, carbonate content, and strength. Lastly, a hotspot life cycle assessment was performed which identified ways to reduce the environmental impacts of EICP by using alternative sourcing of inputs and extraction of byproducts. Overall, this research project demonstrates that EICP is a viable ground improvement technique by way of successfully producing field-scale biocemented soil columns.
ContributorsMartin, Kimberly Kathryn (Author) / Kavazanjian, Jr., Edward (Thesis advisor) / Zapata, Claudia E. (Committee member) / van Paassen, Leon (Committee member) / Arizona State University (Publisher)
Created2021