Asphalt Pavement Magazine - January/February 2015 - (Page 44)

Examining the Use of Reflective Pavements to Mitigate the Reflective pavements create unintended consequences that can contribute to urban heat island U rban Heat Island (UHI), the phenomenon of increased temperature in urban areas as compared to rural surroundings, endemic to the built environment, has resulted in scientific, legislative, health, and municipal stakeholders implementing various strategies in an effort to mitigate this effect. As efforts focus on one means to mitigate the problem, it is crucial that researchers examine both the results of the mitigating actions and the possible unintended consequences of the solution's widespread use. One method to reduce UHI is focused on retrofitting urban geometry with high-albedo or reflective construction materials. Albedo, the capacity of reflecting solar radiation of a surface, is defined as the ratio of the reflected radiation from the surface to the incident radiation upon it. The greater the albedo, i.e., the higher the reflectivity, the less the radiative energy absorbed by the surface. Over the past few decades, the use of reflective pavement materials has been promoted as a potential mitigation strategy for the UHI effect. A recent Arizona State University research synthesis showed potential unintended consequences of adopting reflective pavements as a UHI mitigation strategy ( unintended-consequences-1013.pdf ). Highlights are included in this article. Reflected Solar Radiation Reflective pavements lead to greater reflected solar radiation, which can be absorbed by surrounding surfaces and subsequently increases their temperatures. Studies have shown that light-colored walls reflect more short-wave radiation and generate a slightly higher heat gain for pedestrians. Studies have also implied that the temperature of building walls would be heated up by the reflected energy from the pavement surface, which could be at maximum ≈2° to 5°C higher around noon. Subsequently, the By Kamil E. Kaloush, Ph.D., P.E., Zhihua Wang, Ph.D., and Jiachuan Yang increased temperature makes air conditioning units work harder, accelerates the heat aging of the membrane, damages surrounding building components, and causes heat discomfort for pedestrians. This effect causes potential problems for the high-density urban areas where building components are in close proximity to each other. For example, increasing the albedo from 0.15 to 0.5 would substantially impact the comfort of people standing on the more reflective pavement, increasing the temperature they feel by 3° to 6°C. Winter Roadways Because reflective pavements have lower surface temperatures, additional deicing salts are required to ensure clear winter roadways and the safety of the traveling public. In fact, at pavement temperatures below 15°F, the use of deicing salts on snow-covered roadways are not as effective and additional chemicals are required. Use of deicing chemicals is costly and continued on page 46 44 * View past issues online at

Table of Contents for the Digital Edition of Asphalt Pavement Magazine - January/February 2015

Chairman’s Commentary
Industry News
PaveXpress: A Simplified Pavement Design Tool
Sustainability Section NAPA’s Asphalt Sustainability Conference
The Federal Highway Administration Sustainable Pavements Program
Environmental Product Declarations in the Sustainable Marketplace
Examining the Use of Reflective Pavements to Mitigate the Urban Heat Island Effect
Pavement Vehicle Interaction and Smooth Asphalt Pavement
The NAPA Diamond Achievement Sustainable
Beyond Compliance: Achieving EH&S Excellence
A World of Asphalt Preview Section the World of Asphalt Education Program: Laying the Base for Innovation
Tools for the Trade
Industry Events
Index of Advertisers/

Asphalt Pavement Magazine - January/February 2015