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The use of phase-change materials (PCMs) in asphalt mixture is expected to solve some problems related to asphalt-pavement temperature, such as rutting behaviors and urban heat island effect. This study mainly evaluated the thermal and mechanical properties of asphalt mixtures with and without various PCMs (PCM-L, PCM-Z) using laboratory performance tests. The experimental tests included thermal conductivity and diffusivity, volumetric heat capacity, indoor temperature changes versus time when heated or cooled, indirect tensile strength, high-temperature rutting, and low-temperature cracking. In addition, a hot disk thermal constants analyzer was used to measure the thermal constants of asphalt mixtures. The results showed that different PCMs had different effects on the thermal constants of asphalt mixtures. Compared with control sample, the sample with PCM-L showed a higher thermal conductivity, whereas the sample with PCM-Z had a lower thermal conductivity. Moreover, PCM-Z exhibited a more-significant phase-change adjusting-temperature effect on asphalt mixtures than PCM-L. However, the addition of PCM to asphalt mixtures resulted in a decreased indirect tensile strength and a weakened rutting resistance, but the effect of PCM-Z was smaller than that of PCM-L. In addition, the asphalt mixture with PCM-Z exhibited better cracking resistance than the mixture with PCM-L and control mixture. Therefore, it is recommended to use PCM-Z in asphalt mixtures to solve the problem of pavement at high temperatures.
Asphalt pavements feature good performance and relatively low construction and maintenance costs. However, the black color of asphalt binder implies that the sunlight is not reflected but absorbed, which raises the temperature of the asphalt pavement and impairs its long-term durability. Conventional cool pavement technologies reduce the surface temperature of roads regardless of season. These technologies, however, have detrimental negative impacts during the winter season. An innovative strategy presented in this dissertation is to use innovative thermochromic material to develop thermochromic asphalt binders with desirable solar reflectance, i.e., they reflect more solar energy at high temperature and reflect less solar energy at low temperature. Thermochromic materials are substances that can reversibly change their colors in response to temperature. Comparison measurements have found that the surface temperature of thermochromic asphalt binder is lower than that of the conventional asphalt binder with maximum decrease as high as 6.6 °C during typical summer day in the northeast U.S. (i.e. Cleveland, OH). This helps to improve its resistance to high temperature related performance degradation (such as rutting, fatigue, etc), and mitigate urban heat island effects. Besides the cooling effects, study showed that the surface temperature of thermochromic asphalt was higher than regular asphalt under low temperature. This means thermochromic asphalt can delay ice formation on the surface of road, which is an important potential benefit for road safety in cold regions. The thermal, optical, mechanical, pyrolytical, and chemical properties of the thermochromic asphalt binders were characterized. Superpave binder grading was assigned to the thermochromic binders. Experiments were also conducted to assess the performance of hot mix asphalt (HMA) with thermochromic asphalt binders. The results from the mechanical experiments indicated that thermochromic HMA can achieve satisfactory performance. The thermal performance of the thermochromic HMA was evaluated from long-term field exposure. The results indicated that the effectiveness of the thermochromic HMA could sustain after long term exposure. The dissertation conducted a study to gauge the potential of thermochromic asphalt concrete to improve the durability of the pavement, reduce the environmental impacts, and mitigate ice related safety issues on the road. This demonstrates innovation for development of sustainable and environmental benign infrastructure.
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.
The effect of minus No. 200-sized material (mineral filler) on the fundamental mechanical properties of hot-mix asphalt is not well understood. In the work reported in this paper a series of minus No. 200 (75 ?m) mineral fillers were used to prepare and characterize filler-asphalt mastics and hot-mix asphalt concrete. The mineral fillers were blends of dust of fracture and baghouse dust was sampled from seven sources. The gradation and the void-filling characteristics of the mineral fillers were determined. Mastics prepared with the fillers were characterized with viscosity measurements at 60°C (140°F) and dynamic mechanical properties, storage modulus, loss modulus, and tan delta, over a wide temperature range. Mixtures containing the mineral fillers were prepared using several different filler-asphalt ratios. Originally, the behavior of the mixes was to be evaluated with a fatigue test in which a test beam is supported on an elastic (lowmodulus rubber) foundation. This test method proved unacceptable because the failures that occurred were in shear rather than bending fatigue. As an alternative, the single-edge-notched-beam (SENB) fracture toughness test was used. With this procedure it was possible to determine the fracture toughness of the mixes as a function of temperature. The source of the mineral filler, as reflected by the properties of the mineral filler-asphalt mastics, was correlated with the fracture toughness properties of the mixes.
A computer program was developed at the University of Minnesota to predict asphalt concrete cooling times for road construction during adverse weather conditions. Cooling models require extensive experimental data on the thermal properties of hot-mix paving materials. A sensitivity analysis was performed to determine which thermal properties affect pavement cooling times significantly. The results indicated that more information on asphalt thermal conductivity and thermal diffusivity is required. Two suitable test methods for determining these properties at typical paving temperatures and densities were developed, and preliminary results for dense-graded and stone-matrix asphalt (SMA) mixes agreed well with values reported in the literature.
The objective of this investigation was to develop a model to predict on-board sound intensity (OBSI) on hot mix asphalt pavements using on-site and laboratory data. The data used included noise and physical property data collected on 25 asphalt-surfaced roadway test sections at the MnROAD pavement testing facility. These test sections were constructed mainly in 2007 and 2008 using a variety of materials, mixtures and layer thicknesses. A modeling approach called the mechanism decomposition approach was used to develop the models. In this approach, the contributions of different noise mechanisms to the overall noise level and to noise in certain frequency ranges are modeled separately then are combined to form the total noise spectrum. Ultimately, two nonlinear statistical models were developed that predict one-third octave band and overall sound intensity levels on asphalt-surfaced pavements. The models incorporate the pavement parameters that were found to have the most significant effects on tire-pavement noise including pavement macrotexture, air temperature, modulus of the pavement surface layer, and the combined effect of temperature and modulus. The models differ in the type of texture data used as an input parameter. The models have been found to predict the overall OBSI sound intensity level to within 1.5 dB and the onethird octave bands to within 2 dB for most of the pavements tested. Other metrics and evaluation of the model accuracy by cell, year, temperature and other factors are also reported. The models are provided in an Excel spreadsheet.