Thermomechanical modeling and analysis of pavements with embedded heating ribbons

Adam Quentin Félix

Research output: Book/ReportPh.D. thesis

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Abstract

Cold regions are characterized by snow and ice accumulation on infrastructures. On pavements, such conditions create dangerous conditions for users due to reduced skid resistance and masking of road markings. Traditional winter activities to combat these weather events include snow plowing and applying deicing agents. For concrete pavements and interlocking block pavements, an alternative solution to plowing and deicing is embedding near-surface pipes within the pavement circulating hot fluid. For asphalt pavements – the most common pavement type worldwide – an emerging solution for mitigating snow and ice is electrical systems based on ribbon-like heating elements.

Furthermore, cold regions are characterized by low-temperature levels combined with fast cooling rates. For asphalt pavements, such weather conditions promote two distress types: low-temperature cracking, caused by an accumulation of thermally-induced stress exceeding the asphalt layer’s tensile strength; and frost action, caused by below-freezing temperature levels entering the subgrade and forming ice lenses (which melt as spring starts). Such seasonal cycles cause heaves and settlements and limit the pavement’s usability during certain year periods. The first distress type is partially addressed by modifying the bitumen within the asphalt mix to improve overall resistance to low-temperature cracking. Solutions to the second distress type consist of utilizing low thermally-conductive layers or non-frost-susceptible materials (or a combination of the two). These solutions are only useful for new pavements or when existing pavements are reconstructed.

This study was concerned with electrically-heated asphalt pavements. The specific objectives of the work were: (i) propose and demonstrate in full-scale a method for introducing heating ribbons into the construction process of asphalt pavements; (ii) develop and apply a model for simulating the progression of snow melting on surfaces of electrically-heated asphalt pavements; (iii) numerically explore the possibility of actively mitigating low-temperature cracking; and (iv) numerically explore the possibility of actively suppressing frost action.

In order to achieve the first objective, it was suggested to deploy ribbons after an asphalt concrete lift has been paved and compacted, and before paving and compacting the next lift(s). It was also suggested to make shallow channels in the asphalt concrete for cradling each ribbon. These ideas were demonstrated via the full-scale construction of a heated road. The protective ribbon channels were grooved with a customized milling machine. The installation concept appeared practical and up-scalable. Out of all deployed ribbons, 97 % of them survived the construction process.

In order to attain the second objective, a model was developed; it combines two formulations: a thermal formulation concerned with solving the heat equation and providing the temperature history within a layered domain representing an asphalt pavement covered with snow; and a snow melting formulation concerned with simulating the progression of snow melting. The application of the model provided the melting pattern over time, the amount of snow melted, and the melting rate on an electrically-heated asphalt pavement. The progress of snow melting was found to be similar to field observations.

To complete the third objective, a thermomechanical model was developed; it considers a one-dimensional stratified medium to represent the asphalt pavement system, a thin embedded heat-generating layer to represent the heating system, and measured weather conditions from Nuuk (Greenland) to emulate a cold region that can potentially produce thermal cracking. Also considered is a three-dimensional mechanical formulation based on linear viscoelasticity that assumes thermo-rheological simplicity. This mechanical formulation was utilized to calculate thermally-induced stresses within the medium’s top layer – representing asphalt concrete. The application of the thermomechanical model allowed the identification of a cold-weather event leading to a thermal crack. The model was reapplied with the heat-generating layer activated; it was demonstrated that mitigating low-temperature cracking with an embedded electric heating system is attainable and workable.

The final objective was attained by outlining a thermal model based on the one-dimensional heat equation, including latent heat effects. This model was applied to a multilayer medium containing a buried heat source representing the heating system. Utilizing measured cold-climate weather data from Sodankylä Tähtelä (Finland), calculations were performed to track the evolution of the frost front depth in an idealized pavement structure with no heating. Then after, model calculations were repeated with the heating activated. It was numerically demonstrated that embedded electric heating can suppress frost action. Conclusively, embedded electric heating systems can potentially suppress real-life frost action in asphalt pavements with practical operational settings, i.e., embedment depth and intensity of the heating system.

The study contributes to promoting the use of electrically-heated asphalt pavements based on ribbon technology. The up-scalability to larger road surface area of such technology was demonstrated. Additionally, several numerical models were developed to fulfill the mentioned objectives. These models were implemented in Fortran 90 codes, which were made freely accessible.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages159
Publication statusPublished - 2022

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