Title: Modeling and Experimental Study of Thermal Management for Infrastructure Surface Materials
Description: The rapid growth of population and climate change has subjected our civil infrastructures to high load demands and fast aging or degradation over time. Temperature plays a key role in the performance of the aging infrastructure in form of thermal stress and cracking, temperature-induced material aging and degradation, temperature-dependent deformation, and softening. Thus, the importance of predicting the consequent behavior of the infrastructures under environmental conditions becomes imperative. This research characterizes three infrastructure surface materials, namely asphalt pavement, solar panels, and phase change materials (PCM), models the efficacy of modifiers and novel methods to improve their performance and uses these materials in the design and testing of thermal management systems for different applications. The connection between these materials is the thermal management in pavement overlays, which can be extended to other infrastructure surfaces. Asphalt pavement modified with recycled crumb rubber (CR) is a sustainable way to reuse the millions of tires that used to end in landfills.

However, the ultraviolet (UV) rays from the sun have been shown to adversely affect the asphalt’s performance in the long run. The severe photo-oxidation can cause changes in the volatile components of the asphalt and result in hardening, aging, and thermal cracks in it. The effect of UV rays on the rubber-modified asphalt may be even more complex due to the presence of crumb rubber particles and their chemical/physical incompatibility and changes in the glass transition. In order to examine these effects, a PG 64-22 is modified with two percentages of 16.6 wt.% and 20.0 wt.% crumb rubber. Results show the specific heat capacities increase with UV aging with 16.6% having the highest value. The addition of the rubber particles does not change the chemical composition of the binder as confirmed by the elemental analysis. However, after UV exposure, peaks associated with carbonyl and sulfoxide are observed, proving that the rubber-modified binder is subject to photo-oxidation as well. The 16.6. wt.% shows the best performance against aging with the lowest sulfoxide index and the highest aliphatic index.

Another advantage of adding crumb rubber particles is the formation of a matrix due to the crosslinking of the rubber particles with the binder after being heated, as approved by microscopic images. The carbon nanotubes (CNT) are used to modify the asphalt binder to improve its rheological characteristics while also enhancing the thermal conductivity of the mixture to facilitate the transfer of heat to the surface. In this study, two samples of 3% and 6% multi walled carbon nanotubes (MWCNTs) are prepared using a foaming technology. Foaming the asphalt via water lowers its viscosity and temperature resulting in the saving of the base material and consumed energy while increasing the coating of the aggregates. The results show the CNTs can improve the thermal conductivity of the foamed binder by almost 2X while not negatively affect its rheology. For the other end of the thermal management system, a new hydronic system is introduced for the building integrated photovoltaics and thermal (BIPVT) silicon module that acts for the dual objectives of collecting heat to be used for the thermal management of the pavement and controlling the surface temperature of the solar module itself for the optimal efficiency under different operating conditions.

The BIPVT panel with different flow rates of 100 to 600 ml/min were tested for the effectiveness of the cooling design. The results from experiments and simulations show that at 200 ml/min, an optimal balance for the performance of the panel is achieved to not only reduce the temperature of the panel from 88°C to 65°C, but also generate a partially heated water outlet of 37°C (compared with the 23°C inlet) that can be used for the hot water system of the building, or as the inlet feed to the hydronic cooling/heating pavement system. In addition, the BIPVT design proves to restore the power of the solar module by 24.6% at a 200 ml/min flow rate, as confirmed from the I-V curves. Finally, the feasibility study of converting the waste animal fat to a phase change material (PCM) is explored. In PCMs, the high latent heat characteristics are used to store or release energy during the phase change. The use of PCMs can significantly lower the temperature variation of buildings and the consequent energy use.

While most common PCMs are paraffin-based and too expensive for large scale applications, a bio-based and more economic alternative could be the key to its vast use in infrastructure systems. However, more research is needed to achieve an animal fat PCM with high latent heat values. In this study, characterizing the raw fat shows a ~20% saturated content. After hydrolysis, the saturated portion has been increased to 65%, but the improvement in the latent is not significant. However, after separation of the fatty acids by use of crystallization, the resulting fully saturated fatty acids (palmitic and stearic acids) show a 3.5X increase in the value of the latent heat, increasing it from ~55 J/g for free fatty acids to ~195 J/g for saturated fatty acids. The promising results of the high latent heat values make the current bio-based PCM a good alternative that needs to be further explored in the future to be used for applications in buildings and BIPVT panels. Overall, the results of this PhD study provide a comprehensive understanding of materials and systems for thermal management of asphalt pavements and enable the design and development of durable self-heated pavements, which can be immediately extended to other infrastructure applications such as wall panels, net-zero buildings, and solar panels.