TECHNICALLY SPEAKING

A more resilient and sustainable future for the asphalt paving industry

Doubra C. Ambaiowei - Director, Technical Services

The threat from climate change to our planet is critical. To address this, the Glasgow Climate Pact, the main political outcome of the 26th meeting of the conference of the parties in October 2021 (COP26), saw countries jointly agreeing to cut down on the emissions of carbon dioxide (CO 2 ) to reduce the current average global temperature to well below 1.5°C. This referendum requests that governments revisit and strengthen their nationally determined contributions (NDCs) before the end of 2022 to bring them in line with the desired temperature goal.

To limit warming to 1.5°C, global emissions must be reduced by 45 per cent by 2030. This window of opportunity for avoiding the most disastrous impacts of climate change is closing quickly. To keep 1.5°C within reach, it will be absolutely essential that the asphalt paving industry, as is expected from other sectors, returns to the table with significantly enhanced strategies for empowering a more resilient, and sustainable future. We MUST not relent!

Consequently, conversations in the quest toward net zero are becoming more and more prominent. I’m one of many advocates who believes that the asphalt paving industry has not only been responsible, but also quite proactive in terms of recommending resilient, sustainable pavement strategies that can combat environmental challenges while also satisfying the performance needs for our roadways. This is not a new outlook. I have always favoured recommending pavement strategies to enhance performance and improve durability. If it performs well for many years, it is most likely good for the environment!

Hence, some fundamental questions: What more can or should the asphalt paving industry do to empower a more resilient and sustainable future? What could be the impeding and or constraining factors to this drive? How can these be resolved technically, politically, or otherwise? These questions and more are what we at OAPC will aim to explore from the basics to in-depth analysis using webinars, technical presentations and written articles as the year rolls on.

As a lead-in, let us briefly refresh our minds with some asphalt strategies with great potential for the desired environmental improvements. First is the Reclaimed Asphalt Pavement (RAP) subject. Given the growing rates of RAP stockpiles in and around the province, RAP provides a sure path to meeting both performance and environmental goals, be it through the various cold and/or hot recycling processes. Hence, advocating for responsible and optimal use of RAP would mitigate the risks from sending this valuable material to the landfill, preserving our aggregate resources and reducing our carbon footprint. The key is to pay attention to the processes and practices associated with design, crushing, screening, processing and handling to ensure quality and performance.

Second is warm mix asphalt (WMA) which provides a guarantee for reductions in energy and green-house gas (GHG) emissions during production, and the promise of increased pavement performance in the longer term. In addition to these proven benefits of using warm mix, it again offers the potential to better integrate RAP which could further drive down the cost of production, all helping towards realizing the value of RAP. The Ontario Ministry of Transportation’s (MTO) renewed interest in exploring the benefits from WMA through trial implementation using its recently published Non-Standard Special Provision (NSSP) BITU0029 is a welcome development, and great for the industry. This is an opportunity to re-validate what we already know, and an important way to encourage more municipalities to employ similar innovations in asphalt technologies.

Third is crumb rubber modifier (CRM) in asphalt paving mixtures. This strategy is of particular interest to me owing to its proven successes for good compatibility and interaction between rubber particles and asphalt binder, resulting in various improved properties and performance of asphalt mixtures. Rubberized asphalt mixtures have also shown good compatibility with RAP and WMA. In addition to the hot mix asphalt applications, crumb rubber is valuable in chip seal coat applications, for undersealing (a waterproofing function), and as a porous friction course for open graded applications.

My most vivid recollections of CRM applications in Ontario were the demonstration study projects completed on Highways 7, 35 and 115, a collaboration between the MTO, Ontario Tire Stewardship (OTS), and the Centre for Pavement and Transportation Technology (CPATT) at the University of Waterloo. A recommendation from my involvement with the aforementioned CRM studies is that CRM used in typical Ontario rubberized mixtures should be subjected to both cryogenic and ambient methods of grinding prior to blending with the asphalt cement. This could be a more effective way of ensuring better or comparable performance outcomes.

The implication would be higher initial construction costs, but the many benefits associated with rubberized pavements including its extended service life would provide a trade-off over the pavement’s lifecycle, especially in terms of maintenance or the need to carry out major rehabilitation. Incentive programs could be encouraged to drive the demand and use of CRM in HMA mixtures. Exploring the integrated opportunities with CRM could further mitigate the risks from sending this valuable material to the landfill, and thus enhance the industry’s resilient and sustainable drive.

The subject of recycled plastics in asphalt pavements is fast becoming an area of opportunity while also bringing its own challenges. Driven by the desire to reduce waste and negative impacts on the environment, the key questions on the minds of industry experts are the long-term performance and true environmental impact of plastic in asphalt pavements, material costs, worker health and safety, operations, and re-recyclability of plastic-asphalt mixtures. The answers to these important questions are currently being pursued through numerous experiments and research projects being carried on globally. However, the reassuring message is that the asphalt industry is capable of responsible advancements by taking the ambitious steps towards being more sustainable. Another consideration may include revisiting the potential of incorporating recycled asphalt shingles (RAS) in asphalt mixtures.