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Streets, Highways & Bridges
Phoenix test drives cooler pavement product
By BETH ANNE BRINK-COX | The Municipal
Roads appear to shimmer during the hottest days of summer: Some see it as the road looking wet. It’s not. Science Focus Magazine says, “As the sunshine beats down on the road, the road surface becomes hot, making the layer of air above it expand and become less dense. This, in turn, changes the way light passes through it from points further down the road. However, the effect is not uniform. The rising air is turbulent, so its density and thus optical properties are constantly fluctuating. This is what creates the shimmering effect we see as we look down the road.” In cities where the heat is consistently high, the charm of shimmers quickly wears away. Heather Murphy, of the Communications and Public Engagement Department in Phoenix, Ariz., is a fan of something called Cool Pavement, a pilot program that differs from other road seal products. Murphy said CP has the same basic components as other road sealants, but they’re formulated differently. 56 THE MUNICIPAL | JULY 2022
ABOVE PHOTOS: Pictured is the finished parking lot. (Photo provided by the city of Phoenix, Ariz.)
“The ingredients are mineral fillers; an emulsifying agent, which is actually soap, and they’re bound together; as well as finely crumbled asphalt, water, polymers and recycled fillers. It has the grit and strength you want, and what’s most important to us is that it’s recyclable. It can be ground into asphalt millings.” Asphalt milling is more durable than conventional gravel. It perfectly seals together when compacted by machines, unlike gravel, and makes a more solid surface. “When we can do that, it cuts down on the aggregates — inert granular materials such as sand, gravel or crushed stone — that we need to buy,” she explained.
