Keikhaei Dehdezi, Pejman
Enhancing pavements for thermal applications.
PhD thesis, University of Nottingham.
Renewable energy combined with energy efficiency can offer a viable and influential solution to minimise the harmful consequences of both fossil fuel depletion and increases in the cost of power generation. However, in most cases renewable energy technologies require high initial investments that may deter potential users. Pavement Energy Systems (PES) potentially offer a low-cost solution to sustainable and clean energy generation by utilising the thermo-physical properties and design features of new/existing pavement infrastructure. Within the PES, fluid-filled pipes are buried in the pavement at varying depths and transfer heat to and from the surrounding material, for application as a solar energy collector and/or thermal storage media. The fluid in the pipes can absorb/reject heat to the pavement and deliver useful energy to nearby buildings as well as benefiting the pavement structure and
pavement users (in terms of reduced rutting, winter road maintenance, etc.). A significant advantage of such systems is that the pipes can be installed within pavements that are
already needed for structural reasons and need not to be installed as single-function elements, as do conventional thermal utilisation systems.
In this project, the effect of pavement materials and layer design optimisations on the performance of PES was investigated both theoretically and experimentally. The thermo-physical properties and load-bearing performance of concrete and asphalt pavements, consisting of conventional and unconventional components, were determined. In addition, pseudo 3D transient explicit finite-difference software was developed for modelling and performance analysis of the PES under various operating conditions and configurations. This software is capable of predicting the outlet fluid temperature and temperature distributions within the pavement structure. Furthermore, large-scale physical models of the PES were designed and constructed to compare the performance of the thermally modified pavement structures with those of conventional ones and also to validate the model. The physical model consisted of copper pipes embedded in pavements which were irradiated (causing surface heating) using halogen lamps.
The results of thermo-physical optimisation of pavement materials, coupled with mechanical testing, showed that it was possible to achieve a wide range of thermally-modified pavements that can also meet the rigorous functional requirements of an airfield pavement. The experimental comparison between the thermally modified and unmodified concrete pavements revealed that there was potential to enhance both the heat collection and storage capability of concrete pavement structures. In addition, the model’s predicted temperatures in concrete pavements were in good agreement with the experimental ones with a mean error of less than 1°C. A similar comparison on asphalt pavements showed that although the surface temperature was lowered by asphalt modification, there were significant discrepancies between the measured and predicted surface temperatures for both modified and unmodified pavements. Further study was conducted on the pipe/pavement interface using X-Ray Computed Tomography (XRCT). The X-ray images revealed improper bonding between the pavement’s matrix and the pipe that was evidenced by the presence of air voids accumulation around the pipe perimeter, and could explain the significant discrepancy in the modelled temperatures.
Furthermore, the validated model was used, for genuine temperature patterns, to simulate the relative influence of both the thermo-physical properties of pavement materials and the pavement layer sequences on the performance of the PES and to determine the implications for pavement design. It was concluded that the enhancements could allow pipes tobe installed deeper within the pavement without having any negative effect on their thermal performances. Pipe installation deeper in the pavement is expected to reduce ‘reflective cracking' under traffic loading as well as enabling future resurfacing of the pavement without damaging the pipe network.
Thesis (University of Nottingham only)
||T Technology > TE Highway engineering. Roads and pavements
||UK Campuses > Faculty of Engineering > Department of Civil Engineering
||09 Nov 2012 13:41
||13 Sep 2016 14:00
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