Combatting heat islands by paving roads with a new type of asphalt
Research project headed by Michel Vaillancourt of ÉTSThursday, July 9, 2020
Heat islands, which have become a significant public health issue, are caused by the capacity of materials to accumulate heat and release it into the air, driving temperatures up and diminishing the quality of air in urban areas. Preliminary studies conducted by Michel Vaillancourt, a Professor-Researcher in the Construction Engineering Department at École de technologie supérieure (ÉTS), appear to indicate that the impact of this phenomenon can be reduced by incorporating glass and other materials with high heat-resistant properties into the asphalt mixture that is used to pave roads.
In effect, glass is a good insulator and a poor conductor, and has a lower thermal capacity than the aggregates that are normally contained in asphalt mixture. In other words, this material can slow down the transfer of heat while reducing the capacity of the road to store heat, not to mention the fact that glass also reflects light. Considering that glass is too often found in landfill sites, incorporating it into asphalt mixture will not only reduce heat islands, but also serve as a way to reuse glass. In short, it is a double win for the environment!
To date, very little research has been conducted into the thermal properties of asphalt mixture that incorporates glass. However, the results of a preliminary study headed by Professor Vaillancourt appear to be promising. He explains: “Our data indicate that, at a depth of 90 mm, the heat transferred by asphalt can be reduced by up to 6 ºC compared to conventional asphalt”.
In conducting the study, the research team used an infrared lamp and asphalt of varying compositions and thicknesses in order to compare the performance of each sample, some of which contained glass, while others contained calcareous stone. The team also measured the level of light reflection of the asphalt containing glass, with a view to corroborating the results obtained in the laboratory.
The results show that the decrease in temperature is greater when using a lower grade of asphalt than what is required for paving roads and asphalt that incorporates glass. In light of this, Michel Vaillancourt’s team will continue their work to find a formulation that improves the thermal capacity of the asphalt without compromising its mechanical performance, or resistance.
By the same token, it is important to consider that asphalt is also used to cover surfaces other than roads. Michel Vaillancourt points out: “Asphalt with attractive thermal properties but with a mechanical performance level that is not optimal for use on roads can still be used to pave school yards or parking lots”. School yards and parking lots are not subjected to the same load levels from thousands of vehicles and heavy trucks on a daily basis.
In addition, other materials with thermal properties comparable to glass, such as porcelain or brick, can be incorporated into asphalt mixture. Finally, the team also plans to measure the decrease in performance related to the use of asphalt that incorporates glass.
These are a few of the research hypotheses that Michel Vaillancourt and his team will be studying in the coming months – tangible proof that applied research in the area of construction engineering can have a real-world effect on the environment, and more specifically, on the health of city dwellers.
About Michel Vaillancourt
An expert in geotechnical engineering for roads, Michel Vaillancourt has been a Professor in the Construction Engineering Department at ÉTS since July 2012. His research focuses primarily on the design, assessment and rehabilitation of roads and on the base soil and materials used for roads. Since 2014, he has been focused on incorporating post-consumer glass into road structures. He sits on a number of technical committees, including with CERIU, the AQTR and RILEM. Before joining ÉTS, Michel Vaillancourt worked in the industrial sector. Designing the extension of Autoroute 30 is one of his greatest professional achievements.
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