Evaluation of the Effect of Recycled Asphalt Shingles on Ontario Hot Mix Pavement
Ddamba, Shirley Jacqueline
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Due to the 15-20 year life span of roofing shingles, 1.5 million tonnes of asphalt roofing shingles are being demolished and replaced annually in Canada from both residential and commercial facilities. These roofing shingles are manufactured from very high quality materials which are considered a valuable by-product. Recycled Asphalt Shingles (RAS), a product containing approximately 30% asphalt cement by mass, is a valuable additive to Hot Mix Asphalt (HMA) pavements and a potential savings for the construction industry. Recycling of demolished asphalt shingles is a significant new step forward in abating the need to put the waste into landfills. This re-use creates a great opportunity in reducing materials being dumped at landfills while providing an additive to HMA mixtures for paving. Therefore, this leads to economic, environmental, and social benefits for all the stakeholders and road users such as reduced need for landfill space, conservation of virgin materials and environment, and financial saving. The research involved evaluating the use of demolished shingles in six typical Ontario Hot Mix Asphalt (HMA) mixtures; HL 3 (1.5% RAS, 13.5% RAP), binder layer mixes SP19 (6% RAS, and 3% RAS, 25% RAP), surface layer mixes SP12.5 FC 1(3% RAS, 17% RAP) and SP12.5 FC2 (6% RAS and 3% RAS, 12% RAP). The six HMA mixes were also designed to contain Recycled Asphalt Pavement (RAP). This further complicated the research as both RAP and RAS were added. All mixes were designed and tested at CPATT laboratory; in addition a test section was paved at the CPATT Test Track. This research involved both laboratory and field evaluations of mixes containing RAS to develop pavement performance modeling for all six mixes using the updated Mechanistic-Empirical Pavement Design Guide (MEPDG). A life-cycle assessment of the six HMA mixes was performed to quantify the environmental impacts using the Pavement Life-Cycle Assessment Tool for Environmental and Economic Effects (PaLATE) and rigorous economic costs/benefits were assessed using Life Cycle Cost Analysis (LCCA). Calibrations of models for Ontario conditions were completed. Test slabs were also constructed to simulate climatic changes by running freeze-thaw cycles based on weather data over the past ten years. Three field test sections located in the Town of Markham and one at the CPATT Test Track were monitored and assessed under as part of the research. Regular pavement condition assessments were carried out on all the test sections by performing non-destructive tests using a Portable Falling Weight Deflectometer (PFWD) and distress survey in accordance with the Ministry of Transportation (MTO) guidelines. The CPATT Test Track was evaluated with both the PFWD and surface distresses, whereas only distress surveys were performed on the three residential streets in the Town of Markham. The evaluations demonstrated that the pavements were in good conditions throughout the monitoring period of the research (four years for the three residential streets in the Town of Markham and two years for the CPATT Test Track). The structural analysis using the MEPDG indicated that Mix 3: SP19 3% RAS and 25% RAP had the best performance followed by Mix 2: SP19 6% RAS when considering all factors in the Life-Cycle Assessment. Mix 3 exhibited maximum savings on environmental emissions, energy and water usage, best adoptability to climatic change and skid resistance properties with minimal life cycle costs. The pavement performance and life-cycle assessment modeling demonstrated encouraging results for the use of RAS in HMA pavements from which guidelines were developed for its use. It is important to note that careful mix design should be carried out when RAS is added to HMA especially when RAP is also used. This includes measuring of all key properties especially at low and high temperatures. In short, RAS can be a valuable additive in both surface and binder layers of HMA pavements. It provides an environmentally friendly and cost-effective innovation for the Ontario paving industry and can be considered for usage elsewhere with appropriate engineering.