CONCRETE PAVEMENT PROGRESS 14 WWW.ACPA.ORG smoother riding surface. A diamond ground pavement is the only carbon negative surface treatment with a higher return on investment than asphalt-overlayed sections. Lower Temperatures Heat is the number one weather-related killer in the United States,6 and city planners and other decision-makers are beginning to consider ways to enhance urban heat island (UHI) resilience. The UHI effect is caused when features of the built environment absorb and re-emit the sun’s heat more than a natural landscape. Concrete pavements are lighter in color than asphalt pavements and twice as reflective when new, leading to a reduced UHI. The result is lower temperatures in the area’s surrounding concrete pavements that have been remediated using diamond grinding as opposed to ones overlayed with asphalt. A surface’s degree of reflectance is known as its albedo, which is expressed as a numerical value between zero and one. A light-colored object has a high albedo—near one, or 100% reflectance. A dark-colored object has a low albedo—closer to zero. The albedo of a new asphalt pavement is about 0.05. Aged asphalt, which has faded to a lighter color, generally has an albedo between 0.10 and 0.18. New, cured gray cement concrete pavement, however, has an albedo in the range of 0.35 to 0.40. As concrete ages, it tends to darken because of dirt and tire wear, so older concrete may have an albedo in the range of 0.20 to 0.30. The use of light-colored aggregates, white cements and slag cements can improve albedo; white cement concrete pavements have albedos in the range of 0.70 to 0.80 when new and 0.40 to 0.60 after aging. Concrete surfaces become darker over time due to oxidation and petroleum-based fluids leaking from vehicles. Diamond grinding removes this darkened layer, re-establishing the like-new light color of the pavement and enhancing the reflective nature. Case Study: High Albedo Lowers Temperatures Phoenix is one of the nation’s fastest-warming big cities. In August 2021, IGGA partnered with ACPA to conduct infrared testing of diamond ground concrete and asphalt-rubber-surfaced pavements in the Phoenix area. continued from page 13 Data was collected for three pavement structures on eastbound SR 202 between 40th Street and Dobson Road. 1. A concrete pavement with a diamond ground surface. 2. A concrete pavement overlaid with a oneinch-thick asphalt rubber surface. 3. An asphalt concrete pavement overlaid with a half-inch-thick asphalt rubber surface. Test results showed higher temperatures on the asphalt rubber compared to diamond ground concrete over a 24-hour period. Diamond ground concrete surfaces consistently remained cooler. Just before sunrise, diamond ground concrete measured one degree to 10 degrees Fahrenheit cooler than asphalt rubber surfaces. At peak temperature, diamond ground concrete was 27 degrees Fahrenheit cooler than asphalt pavement overlaid with asphalt rubber. IGGA DIAMOND GRINDING Fig. 2—Pavement shoulder temperatures for three pavement structures from a drone infrared test. The roadway’s shoulder best represents the heat disparity among surface types because it is a non-trafficked area with minimal convection cooling from traffic. Fig. 3—Temperature recording of diamond ground concrete versus asphalt pavement overlaid with asphalt rubber.
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