With the intense temperature rise associated with climate change, it is no surprise that our roads are under intense stress almost all year round. Currently, our options for pavement materials, basically asphalt and concrete, have a few drawbacks. Asphalt, the predominantly used material, is easier to fix and repair, cheaper (often half the price of concrete roads per square foot but at mercy of petroleum prices), but suffer the consequences of a lower measure of reflectance and shorter life spans than concrete[7]. The measure of reflectance, as known as albedo, is important as a surface of high albedo reflects more sunlight and heats up less. Due to concrete having a higher albedo than asphalt, it’s been recommended that we may switch to concrete. Despite this, we see it best fit to stick with our asphalt roads because of the higher convenience of asphalt. However, the rising number of high temperature days as projected by the CCVA pose the problem of heat stress on the pavements.[9] This can often lead to heaves or buckles in the road, resulting in both potentially unsafe driving conditions and, furthermore, higher traffic (due to construction).[3] In order to address this problem, we propose implementing ways to cool the asphalt through cooling technology such as cool coatings and nanotechnology. Not only would cooling the pavement help facilitate transportation on roads but help mitigate the heat island effect: where urban activities and constructs trap heat.[4]
Cool coatings are essentially lightly colored sealants that can be placed over asphalt or other dark pavements to address the problem of albedo. These coatings leave asphalt a light grayish color while substantially decreasing the temperature of the pavement. Research done by scientists at Berkeley Lab has noted that the pavements covered in these cool sealants have reflect from 30% to 50% of the sun’s energy back into the atmosphere (instead of absorbing such energy). This is an extreme increase compared to the traditional 5% that asphalt usually has.[8] The higher reflectiveness of these surfaces accounts for the lower temperatures they obtain under hot summer days. A sample of this can be seen in the trial case in Canoga Park, California, where a coated intersection went from 93 degrees to 70 degrees after the coating.[1] Not only would the lower temperatures reduce the chances of buckling and heaving to occur, but the coatings have numerous more positive effects as listed by the EPA including “reduced stormwater runoff and improved water quality, lower tire noise, enhanced safety, better nighttime visibility, and improved local comfort” and mitigating the heat island effect.[4] As of now, according to the case in California, the coating process costs about $40,000 per mile and lasts for about 7 years.[1]
Although cool pavements are a good strategy to combat heat stress on roads in the near future, scientists are still making advancements in nanomaterials that could see possible application in pavements not too far down the road. Nanomaterials are tiny sized particles within the length of 100 nanometers. Because of their small size, they interact differently than particles in conventional materials. Advancements in nanosilica, nanoclay and carbon nanotubes have seen applications in asphalt mixtures resulting in higher resistance to water, snow, and deicers (which is highly relevant to MIT’s climate), as well as longer lasting pavements with less deformability, all the while saving energy and maintenance costs.[2] Also, MIT is building a new nano building. Amongst the projects of the nano department, as climate change presses, we encourage the possibility of nanomaterial research for possible implementation in our roads. Furthermore, although cool pavements are sure to decrease road temperatures and increase safety of public and private transport under the influence of climate change, a Californian study noted that cool pavements don’t necessarily decrease total energy consumption (nearby buildings have lower energy costs for cooling due to decreased ambient temperatures) when taken into account their manufacturing and resource obtention.[6] As new coatings come to market, we should be diligent in using the least energy intensive technology in order to mitigate future climate damage.
As of now, in response to high surface temperatures of roads and the heat island effect, the employment of cool pavements is a necessary countermeasure to climate change. However, as the future imminent, we should reexamine the possible solutions available to us. Nanotechnology and more efficient cooling sealants seem to be the most promising options as we dive headfirst into climate change adaptation.
By Yousef Mardini
References
- Bartholomew, D. (2017, August 28). ‘Cool pavement’ to cut urban street heat gets first California tryout in Canoga Park. Retrieved November 23, 2017, from http://www.dailynews.com/2017/05/20/cool-pavement-to-cut-urban-street-heat-gets-first-california-tryout-in-canoga-park/
- Yang, J., & Tighe, S. (2013, November 20). A Review of Advances of Nanotechnology in Asphalt Mixtures. Retrieved November 27, 2017, from http://www.sciencedirect.com/science/article/pii/S1877042813022702
- Cool Pavements. (n.d.). Retrieved November 27, 2017, from https://heatisland.lbl.gov/coolscience/cool-pavements
- Using Cool Pavements to Reduce Heat Islands. (2016, August 12). Retrieved November 28, 2017, from https://www.epa.gov/heat-islands/using-cool-pavements-reduce-heat-islands
- Sess, D. (2016, July 13). Why do roads buckle in the summer heat? Retrieved November 20, 2017, from http://wkbn.com/2016/07/13/why-do-roads-buckle-in-the-summer-heat/
- Not all cool pavements are created equal. (2017, May 18). Retrieved November 28, 2017, from https://phys.org/news/2017-05-cool-pavements-equal.html
- Asphalt vs. Concrete: Not a Black and White Choice. (2016, May 25). Retrieved November 23, 2017, from http://www.ayresassociates.com/asphalt-vs-concrete-not-black-white-choice/
- Chao, J. (2012, September 14). ‘Cool pavement’ technologies studied to address hot urban surfaces. Retrieved November 28, 2017, from https://phys.org/news/2012-09-cool-pavement-technologies-hot-urban.html
- Hayhoe, K., Stoner, A., & Gelca, R. (2013). CCVA Appendix B. Climate Change Projections for the City of Cambridge, 6-6. Retrieved November 20, 2017, from https://www.cambridgema.gov/cdd/projects/climate/~/media/A9D382B8C49F4944BF64776F88B68D7A.ashx.