Browsing by Subject "Thermal properties"
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Item Controlling Thermal Properties of Asphalt Concrete and its Multifunctional Applications(2014-08-10) Shi, XijunControlling infrastructure temperature, especially flexible pavement, has attracted attention in both industrial and academic societies because: 1) material properties of asphalt, and corresponding structural responses and distresses are temperature dependent and 2) pavement surface temperature directly relates to various environmental or safety problems. This study investigates the feasibility of mitigating the temperature-related problems of civil infrastructures (especially asphalt pavement) by controlling thermal properties of the construction materials. To change thermal properties of asphalt concrete, expanded polypropylene (EPP) pellet and graphite were selected as the additives and mixed into asphalt concrete. Experimental tests are classified into two categories: 1) physical and thermal characterizations of raw materials including Scanning Electron Microscope and heat susceptibility tests, and 2) mechanical and thermal properties of the modified asphalt mixtures via indirect tensile test and hot disk test, respectively. The heat susceptibility test results show that use of EPP as an aggregate replacement is a better choice than the use of the melted-EPP as a binder modifier because it has a good heat susceptibility and is hard to melt at the HMA working temperature. The mechanical performances and thermal properties evaluation results show that by replacing the aggregate with EPP to have 18% by volume of total mixture, the indirect tensile strength was reduced by 17%, and the thermal conductivity and volumetric heat capacity decreased by 32% and 27%, respectively. By adding 4.8 vol. % of graphite, the indirect tensile strength decreased by 20%, and an increase of 43% in thermal conductivity was obtained. To simulate the effect of the thermally modified asphalt mixtures on the surface temperature of pavements and bridges, a series of heat transfer analysis were conducted using the finite difference heat transfer model. In addition, a case study of a building using EPP modified cement concrete was carried out to investigate the benefits of EPP modified concrete as a wall insulation. From the simulation results, it is concluded that adding graphite into asphalt mixture mitigates the urban heat island effect during summer by dropping the maximum surface temperatures of both pavement and bridge (3.1?C and 1.9?C, respectively, with 4.8% graphite), and the graphite modified asphalt concrete can reduce the use of deicing agents during winter by increasing the minimum surface temperature by 0.5?C for pavement and 0.2?C for bridge. On the other hand, adding EPP increases maximum surface temperature by 0.8?C for pavement and 1.0?C for bridge during winter, which show the potential for snow and ice removal application. In addition, the simulation shows that the EPP modified concrete can serve as a wall insulator.Item Laser flash analyzer studies on reactive materials for thermal property analysis(2011-05) Gordon, Amanda R.; Pantoya, Michelle; Berg, Jordan M.; Chaudhuri, JharnaThis study experimentally examined thermal properties of reactive materials that are a composite of fuel and oxidizer particles. Thermal diffusivity and heat capacity were measured using a laser pulse method while thermal conductivity was calculated from these measurements. The effects of fuel particle size, oxidizer, and initial temperature on thermal properties were studied. Three reactive materials were selected: aluminum (Al) with iron (III) oxide (Fe2O3); Al with Teflon (C2F4); and Al with titanium (IV) oxide (TiO2). The experimental measurements were performed using a Laser Flash Analyzer (LFA) then compared with calculations based on weighted averages of each component in the composite. Experimental results were examined and uncertainty levels were estimated to be relatively high: 7.66% for diffusivity, 18.23% for heat capacity, and 22.7% for conductivity. For this reason, the experimental and calculated values do not vary significantly for heat capacity. However, it was determined that the weighted average approach is not appropriate for either thermal diffusivity or conductivity. The Al particle size was varied from nanometer to micron with no observed effect in diffusivity, heat capacity, and conductivity. Elevating the initial temperature of the sample was shown to decrease diffusivity, and increase heat capacity for all formulations. Iron oxide has a significantly higher thermal diffusivity which contributes to higher thermal conductivity. Heat capacity was unaffected by the oxidizer chosen.