Matching Items (70)

Effect of Polymer Modification and Aging Level on Pull-Off Tensile Strength of Arizona Asphalt Binders By Esai Ponce Undergraduate Honors Thesis Submitted to

Description

Asphalt pavements deteriorate over time and are subjected to various distresses like rutting, fatigue cracking, stripping, raveling, etc. In this study, an experiment to indirectly assess aggregate stripping was completed in order to evaluate the effect of type of binder,

Asphalt pavements deteriorate over time and are subjected to various distresses like rutting, fatigue cracking, stripping, raveling, etc. In this study, an experiment to indirectly assess aggregate stripping was completed in order to evaluate the effect of type of binder, and aging on the binder-aggregate bond under dry conditioning. The asphalts used in the study are commonly used in the state of Arizona, which included both non-polymer modified and polymer modified asphalts. The phenomenon of stripping was simulated using the Bitumen Bond Strength Test (BBS) and evaluated for Arizona binders. The BBS test is a simple test that measures the "pull-off" tensile strength of the bond between asphalt and the aggregate. Polymer modified binders were found to have lower pull-off strength in comparison to the non-modified or neat binder which were found to possess greater pull-off strength, but lower elasticity, causing the failure to become brittle and spontaneous. However, when aged binder was used, the bond strength expectedly reduced for non-polymer modified asphalts but surprisingly increased for polymer modified asphalts. Both un-aged neat and polymer modified binders were observed to have a cohesive failure whereas only the aged polymer modified binders failed in cohesion. The aged non-polymer modified binders were seen to have an adhesive failure.

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2018-05

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Environmental Impacts of Reflective Materials: Is High Albedo a 'Silver Bullet' for Mitigating Urban Heat Island?

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Studies on urban heat island (UHI) have been more than a century after the phenomenon was first discovered in the early 1800s. UHI emerges as the source of many urban environmental problems and exacerbates the living environment in cities. Under

Studies on urban heat island (UHI) have been more than a century after the phenomenon was first discovered in the early 1800s. UHI emerges as the source of many urban environmental problems and exacerbates the living environment in cities. Under the challenges of increasing urbanization and future climate changes, there is a pressing need for sustainable adaptation/mitigation strategies for UHI effects, one popular option being the use of reflective materials. While it is introduced as an effective method to reduce temperature and energy consumption in cities, its impacts on environmental sustainability and large-scale non-local effect are inadequately explored. This paper provides a synthetic overview of potential environmental impacts of reflective materials at a variety of scales, ranging from energy load on a single building to regional hydroclimate. The review shows that mitigation potential of reflective materials depends on a set of factors, including building characteristics, urban environment, meteorological and geographical conditions, to name a few. Precaution needs to be exercised by city planners and policy makers for large-scale deployment of reflective materials before their environmental impacts, especially on regional hydroclimates, are better understood. In general, it is recommended that optimal strategy for UHI needs to be determined on a city-by-city basis, rather than adopting a “one-solution-fits-all” strategy.

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2015-07-01

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Mechanical and Thermal Properties of Copper Slag Concrete

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In this investigation, copper slag was used as a coarse aggregate in four different mixes of concrete, consisting of 0%, 25%, 50%, and 100% copper slag by volume. Locally available Salt river aggregate was used as a control, and mixes

In this investigation, copper slag was used as a coarse aggregate in four different mixes of concrete, consisting of 0%, 25%, 50%, and 100% copper slag by volume. Locally available Salt river aggregate was used as a control, and mixes were tested for density, strength, thermal conductivity, specific heat capacity, and thermal diffusivity. Density was shown to increase with increasing copper slag content, increasing an average of 2298 kg/m^3, 2522 kg/m^3, and 2652 kg/m^3 in the 25%, 50%, and 100% mixes. This represents a 15% increase in density from 0% to 100%. Compressive strength testing indicated that the presence of copper slag in concrete provides no definitive strength benefit over Salt River aggregate. This result was expected, as concrete's strength is primarily derived from the cement matrix and not the aggregate. Thermal conductivity showed a decreasing trend with increasing copper slag content. Th control mix had an average conductivity of 0.660 W/m*K, and the 25%, 50%, and 100% mixes had conductivities of 0.649 W/m*K, 0.647 W/m*K, and 0.519 W/m*K, respectively. This represents 21% drop in thermal conductivity over the control. This result was also expected, as materials formed at higher temperatures, like copper slag, tend to have lower thermal conductivities. Specific heat capacity testing yielded results that were statistically indeterminate, though unlike strength testing this arose from inaccurate assumptions made during testing. This also prevented accurate thermal diffusivity results, as diffusivity is a function of density, thermal conductivity, and specific heat capacity. However, given the trends of the first two parameters, it is plausible to say that diffusivity in copper slag concrete would be lower than that of the control ix. All of these results were plugged into ASU's Pavement Temperature Model to see what effect they had in mitigating the UHI effect.

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2012-05

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Impact of Material Properties and Urban Geometry on Urban Heat Island Effect

Description

Utilizing an urban canopy model (UCM) developed by Zhihua Wang, Ph.D. for a research study conducted for the National Asphalt Pavement Association (NAPA), several scenarios were run in order to determine the impact on the mitigation of the urban heat

Utilizing an urban canopy model (UCM) developed by Zhihua Wang, Ph.D. for a research study conducted for the National Asphalt Pavement Association (NAPA), several scenarios were run in order to determine the impact on the mitigation of the urban heat island (UHI) effect. These scenarios included various roof albedo, wall albedo, ground albedo, a combination of all three albedos, roof emissivity, wall emissivity, ground emissivity, a combination of all three emissivities, and normalized building height as independent variables. Dependent variables included canyon air temperature, effective ground temperature, effective roof temperature, effective wall temperature, and sensible heat flux. It was found that emissivity does play a part in reducing the different dependent variables; however, typically emissivity values are already within a preferred range that not much can be done with them. Normalized building height has a minor impact but the impact that it does have upon the different variables is lessened with lower values of the normalized building height. Increasing the wall albedo decreased the canyon air temperature and the effective wall temperature the most compared to the other variables when considering expenses. An increase in roof albedo reduced effective roof temperature and sensible heat flux the most when taking into consideration the cost of changing the albedo of the surface. Larger values of ground albedo helped to reduce the effective ground temperature more than the other variables considered when a budget is necessary.

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Date Created
2015-05

Forecasting Changes in Urban Heat Island in the US Southwest

Description

Recent developments in computational software and public accessibility of gridded climatological data have enabled researchers to study Urban Heat Island (UHI) effects more systematically and at a higher spatial resolution. Previous studies have analyzed UHI and identified significant contributors at

Recent developments in computational software and public accessibility of gridded climatological data have enabled researchers to study Urban Heat Island (UHI) effects more systematically and at a higher spatial resolution. Previous studies have analyzed UHI and identified significant contributors at the regional level for cities, within the topology of urban canyons, and for different construction materials.

In UHIs, air is heated by the convective energy transfer from land surface materials and anthropogenic activities. Convection is dependent upon the temperature of the surface, temperature of the air, wind speed, and relative humidity. At the same time, air temperature is also influenced by greenhouse gases (GHG) in the atmosphere. Climatologists project a 1-5°C increase in near-surface air temperature over the next several decades, and 1-4°C specifically for Los Angeles and Maricopa during summertime due to GHG effects. With higher ambient air temperatures, we seek to understand how convection will change in cities and to what ends.

In this paper we develop a spatially explicit methodology for quantifying UHI by estimating the daily convection thermal energy transfer from land to air using publicly-available gridded climatological data, and we estimate how much additional energy will be retained due to lack of convective cooling in scenarios of higher ambient air temperature.

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Evaluation of the effects of aging on asphalt rubber

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Oxidative aging is an important factor in the long term performance of asphalt pavements. Oxidation and the associated stiffening can lead to cracking, which in turn can lead to the functional and structural failure of the pavement system. Therefore, a

Oxidative aging is an important factor in the long term performance of asphalt pavements. Oxidation and the associated stiffening can lead to cracking, which in turn can lead to the functional and structural failure of the pavement system. Therefore, a greater understanding of the nature of oxidative aging in asphalt pavements can potentially be of great importance in estimating the performance of a pavement before it is constructed. Of particular interest are the effects of aging on asphalt rubber pavements, due to the fact that, as a newer technology, few asphalt rubber pavement sections have been evaluated for their full service life. This study endeavors to shed some light on this topic. This study includes three experimental programs on the aging of asphalt rubber binders and mixtures. The first phase addresses aging in asphalt rubber binders and their virgin bases. The binders were subjected to various aging conditions and then tested for viscosity. The change in viscosity was analyzed and it was found that asphalt rubber binders exhibited less long term aging. The second phase looks at aging in a laboratory environment, including both a comparison of accelerated oxidative aging techniques and aging effects that occur during long term storage. Dynamic modulus was used as a tool to assess the aging of the tested materials. It was found that aging materials in a compacted state is ideal, while aging in a loose state is unrealistic. Results not only showed a clear distinction in aged versus unaged material but also showed that the effects of aging on AR mixes is highly dependant on temperature; lower temperatures induce relatively minor stiffening while higher temperatures promote much more significant aging effects. The third experimental program is a field study that builds upon a previous study of pavement test sections. Field pavement samples were taken and tested after being in service for 7 years and tested for dynamic modulus and beam fatigue. As with the laboratory aging, the dynamic modulus samples show less stiffening at low temperatures and more at higher temperatures. Beam fatigue testing showed not only stiffening but also a brittle behavior.

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2010

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Estimations of reductions in household vehicle miles traveled under scenarios of shifts in vehicle type choice

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Vehicle type choice is a significant determinant of fuel consumption and energy sustainability; larger, heavier vehicles consume more fuel, and expel twice as many pollutants, than their smaller, lighter counterparts. Over the course of the past few decades, vehicle type

Vehicle type choice is a significant determinant of fuel consumption and energy sustainability; larger, heavier vehicles consume more fuel, and expel twice as many pollutants, than their smaller, lighter counterparts. Over the course of the past few decades, vehicle type choice has seen a vast shift, due to many households making more trips in larger vehicles with lower fuel economy. During the 1990s, SUVs were the fastest growing segment of the automotive industry, comprising 7% of the total light vehicle market in 1990, and 25% in 2005. More recently, due to rising oil prices, greater awareness to environmental sensitivity, the desire to reduce dependence on foreign oil, and the availability of new vehicle technologies, many households are considering the use of newer vehicles with better fuel economy, such as hybrids and electric vehicles, over the use of the SUV or low fuel economy vehicles they may already own. The goal of this research is to examine how vehicle miles traveled, fuel consumption and emissions may be reduced through shifts in vehicle type choice behavior. Using the 2009 National Household Travel Survey data it is possible to develop a model to estimate household travel demand and total fuel consumption. If given a vehicle choice shift scenario, using the model it would be possible to calculate the potential fuel consumption savings that would result from such a shift. In this way, it is possible to estimate fuel consumption reductions that would take place under a wide variety of scenarios.

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2013

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Effect of roundabouts on accident rate and severity in Arizona

Description

This study examines the outcomes of roundabouts in the State of Arizona. Two types of roundabouts are introduced in this study, single-lane roundabouts and double-lane roundabouts. A total of 17 roundabouts across Arizona were chosen upon several selection criteria and

This study examines the outcomes of roundabouts in the State of Arizona. Two types of roundabouts are introduced in this study, single-lane roundabouts and double-lane roundabouts. A total of 17 roundabouts across Arizona were chosen upon several selection criteria and according to the availability of data for roundabouts in Arizona. Government officials and local cities’ personnel were involved in this work in order to achieve the most accurate results possible. This thesis focused mainly on the impact of roundabouts on the accident rates, accident severities, and any specific trends that could have been found. Scottsdale, Sedona, Phoenix, Prescott, and Cottonwood are the cities that were involved in this study. As an overall result, both types of roundabouts showed improvements in decreasing the severity of accidents. Single-lane roundabouts had the advantage of largely reducing the overall rate of accidents by 18%, while double-lane roundabouts increased the accident rate by 62%. Although the number of fatalities was very small, both types of roundabouts were able to stop all fatalities during the analysis periods used in this study. Damage rates increased by 2% and 60% for single-lane and double-lane roundabouts, respectively. All levels of injury severities dropped by 44% and 16% for single-lane and double-lane roundabouts, respectively. Education and awareness levels of the public still need to be improved in order for people to be able to drive within the roundabouts safely.

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2016

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Crumb rubber modified crack sealants to improve performance

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Crack sealing is considered one of the least expensive and cost effective maintenance activity used on pavements. In some cases, crack sealing suffers from premature failure due to various material, environmental, and construction issues. A survey that was conducted as

Crack sealing is considered one of the least expensive and cost effective maintenance activity used on pavements. In some cases, crack sealing suffers from premature failure due to various material, environmental, and construction issues. A survey that was conducted as part of this study showed that the highest sealant failure year occurring on the second year. Therefore, any attempt to increase the sealants’ service life by addressing and improving the sealant properties and their resistance to failure will benefit the effectiveness of this treatment.

The goal behind this study was to evaluate the potential improvement in performance of hot applied sealant material commonly used in the Phoenix area, and evaluate the performance of using a neat binder modified with crumb rubber (at 5 and 10% by weight of binder) as a low-grade sealing material. The sealants was also modified with crumb rubber at 2.5, and 5% by weight fo the sealant. Six ASTM tests were conducted for the comparison. These tests are the Standard Penetration Test (SPT) and Cone Penetration Test (CPT), Resilience Test, Softening Point Test, Brookfield Viscometer Test, and Dynamic Shear Rheometer (DSR).

The results showed that adding only crumb rubber to a neat binder for its potential use as a crack sealant is inadequate to meet the specifications expected for sealants. However, the modification of the sealant with crumb rubber showed some benefits, such as increased elasticity and decreased temperature susceptibility. A crumb rubber content of 2.5% by weight of the sealant was recommended.

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2016

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Finite element analysis on the effects of elastomeric inclusions for abating heat transfer in steel reinforced concrete columns

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Concrete columns constitute the fundamental supports of buildings, bridges, and various other infrastructures, and their failure could lead to the collapse of the entire structure. As such, great effort goes into improving the fire resistance of such columns. In a

Concrete columns constitute the fundamental supports of buildings, bridges, and various other infrastructures, and their failure could lead to the collapse of the entire structure. As such, great effort goes into improving the fire resistance of such columns. In a time sensitive fire situation, a delay in the failure of critical load bearing structures can lead to an increase in time allowed for the evacuation of occupants, recovery of property, and access to the fire. Much work has been done in improving the structural performance of concrete including reducing column sizes and providing a safer structure. As a result, high-strength (HS) concrete has been developed to fulfill the needs of such improvements. HS concrete varies from normal-strength (NS) concrete in that it has a higher stiffness, lower permeability and larger durability. This, unfortunately, has resulted in poor performance under fire. The lower permeability allows for water vapor to build up causing HS concrete to suffer from explosive spalling under rapid heating. In addition, the coefficient of thermal expansion (CTE) of HS concrete is lower than that of NS concrete. In this study, the effects of introducing a region of crumb rubber concrete into a steel-reinforced concrete column were analyzed. The inclusion of crumb rubber concrete into a column will greatly increase the thermal resistivity of the overall column, leading to a reduction in core temperature as well as the rate at which the column is heated. Different cases were analyzed while varying the positioning of the crumb-rubber region to characterize the effect of position on the improvement of fire resistance. Computer simulated finite element analysis was used to calculate the temperature and strain distribution with time across the column's cross-sectional area with specific interest in the steel - concrete region. Of the several cases which were investigated, it was found that the improvement of time before failure ranged between 32 to 45 minutes.

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2011