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Strategies for Design and Construction of High-Reflectance Asphalt Pavements. Nam Tran, Buzz Powell, Howard Marks, Randy West and Andrea Kvasnak. Outline. Urban heat island (UHI) effects Cool pavements and LEED credits SRI and how to measure. Background.
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Strategies for Design and Construction of High-Reflectance Asphalt Pavements Nam Tran, Buzz Powell, Howard Marks, Randy West and Andrea Kvasnak
Outline • Urban heat island (UHI) effects • Cool pavements and LEED credits • SRI and how to measure
Background Source: EPA – Cooling Summertime Temperatures
What Causes Heat Islands? Trap hot air and reduce wind flow Replace trees with buildings & infrastructures Source: www.DigitalWorldTokyo.com
U of Washington ACROS Fukuoka, JP Ennis Paint How to Reduce UHI? • More trees • Reflective and green roofs • Cool pavements • Efficient cooling systems
How to be “Cool” and Get Awards • According to LEED, cool pavement strategies include: • Shading hard surfaces • Using high-reflectance materials • Using open grid or porous pavements • LEED awards: • 1 credit for “New” and “School” projects for 50% coverage using cool pavements • 1 credit for 25%, 2 credits for 50%, and 3 credits for 75% coverage for “Retail” projects
Solar Reflectance Index (SRI) • A function of reflectance and emittance – • SRI = 100 for standard white surface • SRI = 0 for standard black surface • Reflectance has profound effect on SRI • More information in ASTM E 1980 • Higher SRI, lower surface temperature
How to Measure Reflectance • Field • ASTM E 1918 • Equip.: ~ $2,000 • Mat: 10 ft x 10 ft • Laboratory • ASTM C 1549 • Equip.: ~ $30,000 • Core: 6 in. dia
Asphalt vs. Concrete Have similar SRI as they get older