Cool Pavement Product Information

What Kinds of Cool Paving Products Are Currently Available?

A number of cool pavement alternatives are currently available. These products are light in color to reflect solar energy. They may also be porous, which keeps the pavement cool by retaining water and allowing it to pass directly through the pavement structure.

Cost ranges given below are estimates. They vary because construction expenditures differ with region, contractor, time of year, materials chosen, site, underlying soils, size of the project, expected traffic, and life of the pavement. In addition, some cool paving options are new to the industry or used only in specialty projects. This adds additional uncertainty to cost information.

Most cool paving options use components with high solar reflectance. Lighter colored aggregate, sand, and cement products all contribute to the overall reflectance of a pavement. In some cases, lighter colored components may already be in use and have no extra cost. In other cases, light-colored materials may be difficult to locate and therefore more expensive.

The cool paving options listed below leave color choice up to the consumer. Research shows that light gray and tan colors can reduce pavement surface temperatures by 20 to 40°F (11°C to 22°C), and that this may increase pavement life. To date, few paving materials have measured solar reflectance, and there is no organization collecting and validating measurements.

• Portland Cement Concrete (PCC)
• Asphalt Chip Seals
• Asphalt Emulsion Sealcoats
• Plastic Grid Pavement Systems
• Porous Asphalt Pavements
• Porous Block Pavement Systems
• Porous Portland Cement Concrete
• White-Topping
• Resin-Based Pavements

Portland Cement Concrete (PCC)

Commonly referred to as "concrete," this paving material is a mixture of aggregate (gravel and sand), water, air, and portland cement binder. Typically, new PCC has an albedo – or solar reflectance – of about 0.35 to 0.40.

Concrete pavements can have service lives in excess of 40 years, with maintenance typically limited to joint and crack resealing. The average cost of concrete ranges from $2.00 to $6.00 per square foot, excluding surface preparation. While PCC is durable and often used in highway construction, it can also be cost-effective in city street and parking lot applications. This is especially true when the existing pavement is severely damaged and must be fully reconstructed.

A thin overlay of PCC may also be used to rehabilitate damaged streets and intersections. Rapid paving techniques allow city streets to reopen in as few as 12 hours, minimizing the inconvenience of closing busy urban routes.

Asphalt Chip Seals

This resurfacing technique involves spreading a thin layer of asphalt emulsion binder over an existing pavement, immediately covering it with a layer of aggregate (or chip seal), and pressing the aggregate into the binder with a heavy roller. Chip seals are most frequently used in low-to-medium traffic applications to protect the underlying pavement and provide enhanced skid resistance. Developers can choose a light-colored aggregate so that reflectance increases with wear.

The application of high-albedo chip seals to an asphalt roadway also makes the surface temperature cooler. This minimizes daily surface temperature fluctuations – and the resulting expansion and contraction process – that can prematurely wear down heat-absorbing pavements. The service life of asphalt chip seals usually is five to seven years. The average cost ranges from $0.09 to $0.14 per square foot installed, excluding surface preparation.

Asphalt Emulsion Sealcoats

Emulsion sealcoats are pre-mixed products that consist of a fine aggregate – or small rocks – suspended in water with an asphalt binder. These products are brushed over existing pavements to seal small cracks and protect the surface, and must be applied over a clean, dry surface. They are available in gray, tan, and other lighter colors to increase reflectance.

When applied properly, asphalt emulsion sealcoats last 3 to 10 years depending on the weight of the sealcoat. The average cost ranges from $0.06 to $0.10 per square foot installed, excluding surface preparation. Adding pigments to lighten the sealcoats may add to overall costs depending on the type and amount of pigment used.

Plastic Grid Pavement Systems

Plastic grid systems are designed to allow water to drain through while supporting pedestrian or light traffic loads. These prefabricated pavements consist of a plastic lattice structure filled with rock aggregate, soil and grass, or ground cover. The result is a high-strength surface ideal for pedestrian walkways, driveways, parking lots, and other relatively low-traffic areas.

Plastic grid systems provide a number of environmental benefits. Their lattice structure can control soil erosion on hillsides, and reduce storm water runoff by channeling it directly into the ground. If light-colored aggregate is used, the pavement surface will stay cool by reflecting solar radiation. Grass systems mitigate the heat island effect through the natural cooling process of evapotranspiration, or evaporation of water from plant material.

Plastic grid systems cost between $1.50 to $3.00 per square foot for materials and installation. However, accounting for environmental attributes can lower expenditures. For example, city officials in Chicago eliminated a local flooding problem by installing a plastic grid system filled with rock aggregate in a neighborhood alleyway.

Porous Asphalt Pavements

Porous, or "open-graded," asphalt pavement contains no small aggregate particles thereby creating void spaces in the pavement. This allows water to collect within – and drain through – the pavement, keeping it cool. This material can be made more reflective by using lighter colored aggregates.

Porous asphalt is appropriate for both road and parking lot traffic, which acts to remove debris clogged in the void spaces. Costs range from $1.00 to $2.00 per square foot for materials and installation, and can increase if lighter-colored aggregates are used.

Porous asphalt is used on a stretch of California Highway 49 running through Sutter's Mill State Park to reduce water runoff and keep traffic noise levels down.

Porous Block Pavement Systems

These pavement systems are constructed from interlocking brick, stone, or concrete blocks, which channel water through them to the underlying substrate. Block materials come in a wide variety of designs, patterns, and colors, and are usually installed over a conventional aggregate base and sand bedding. Because the interlocking design helps transfer stress among the blocks, porous systems are suitable for high load conditions as well as low-traffic applications like sidewalks and driveways.

Block pavement systems can be tinted with light-colored pigments to enhance solar reflectance. Their average cost ranges from $1.50 to $3.00 per square foot, excluding surface preparation. These systems may cost slightly more up front, but storm water infrastructure requirements may be lower than for a comparable impervious surface.

Porous Portland Cement Concrete

This pervious concrete lot in Fair Oaks, California's Bannister Park saved money by avoiding the need for a drainage system. (Courtesy of the California Cement Promotion Council)

Porous portland cement concrete differs only from non-porous concrete in that fine particles such as sand and small aggregates are left out of the pavement mix. This leaves void spaces between the large aggregate materials and allows water to drain through. Porous concrete is appropriate for most applications, including parking lot and street traffic loads.

Like standard concrete pavements, porous concrete is available in light colors. Although a slightly rougher surface texture can lower solar reflectance by 5 percent, porous materials remain cooler than comparable impermeable surfaces when moisture is stored in the void spaces.

Initial costs range from $2.00 to $6.00 per square foot for materials and installation. With some porous concrete pavement applications, the expense of installing and maintaining a drainage system can be avoided.

White-Topping

This resurfacing technique covers existing pavements with a layer of concrete. Though additional research on the performance of white-topping is necessary, there is evidence that under certain conditions, this technique can extend the life of the underlying pavement. Because new concrete has a high reflectance, white-topping contributes to heat island mitigation.

The white-topped layer is typically four to eight inches thick. However, reinforced concrete mixtures called ultra-thin white-topping only require a thickness of two to four inches to withstand residential and other low-volume traffic loads.

The construction process involves coring the underlying pavement (to determine its depth, type, and condition), preparing the road surface by abrasion and cleaning, placing the white-topping, and finishing and texturing the resulting surface. Special mixtures with higher cement content can also be used for surfaces that must be cured and ready for traffic within 24 hours.

The average cost ranges from $1.50 to $3.00 per square foot installed, excluding surface preparation.

Resin-Based Pavements

A resin-based pavement used at Crissy Field along the San Francisco Bay.

Instead of a petroleum-based binder, resin modified emulsion pavements use a binder made primarily from tree resins. It is mixed with aggregate materials to produce a compact pavement of high strength and resistance to fuel spills.

The resin binder is clear so the pavement retains the color of whatever aggregate is used. Use of lighter aggregates allows for a more reflective, cooler pavement.

Resin-based pavements are particularly useful for environmentally sensitive sites. They cost about $3.00 per square foot for materials and installation.