By Catherine A. Cardno, Ph.D.
A company based in the United Kingdom has created a treatment for pavements that absorbs ultraviolet rays during the day and glows gently—sometimes in color—at night.
A new surface treatment that can be used for pavements, sidewalks, and driveways absorbs ultraviolet light during the day and glows unobtrusively at night. Pro-Teq Surfacing UK Ltd
November 5, 2013—Energy-saving measures in infrastructure construction are varied. However, a company in the United Kingdom, the Surrey-based Pro-Teq Surfacing Ltd, has come up with a new option that approaches the issue from an entirely different angle: a hardscape treatment it refers to as "Starpath." Once a surface has been treated with the application, luminescent granules absorb ultraviolet rays during the daytime and offer a soft glow at night, so that bicyclists and pedestrians can follow the track of a path or roadway even when other lighting is not available.
The system has particular use in the United Kingdom, where local city councils are turning off street lamps for a portion of each night to save on energy bills, according to Hamish Scott, the owner and managing director of Pro-Teq; Scott developed the system along with his staff.
The application is a layered system that is quick to apply, fast drying, and long wearing, Scott says. First a path or roadway is patched and evened out, if necessary. Then an elastomeric, polyurethane coating layer is sprayed along the surface of the path or roadway. The luminescent granules are mixed with aggregate that measures between 0.5 mm and 3 mm in diameter for paths—larger aggregate would be used for roads or driveways—and then sprayed atop the base coat. Excess aggregate is brushed away to provide as smooth a surface as possible, and then a polyaspartic topcoat is rolled atop the aggregate layer. The entire treatment is approximately 8 mm thick and has no adverse effects on nearby vegetation, according to Scott. (See a video of the system here.)
"These photoluminescent particles basically … store energy during the day, and release it as light during the night," Scott says. "If it's quite a light evening, your pathway won't glow as much. But if it's a very dark evening, it will brighten itself up. It's really working in conjunction with the outside light." An added benefit is that the soft glow emitted by the path is not read by the human eye as direct light—it just offers people a way to navigate paths after dark. "When people are walking down these pathways, their brain doesn't actually compute that they are actually walking on a pathway that is actually sort of glowing," Scott notes. "It's very inoffensive.
"You couldn't read your book on the pathway, or things like that, but you definitely see people coming toward you," Scott says. The system differs from street lighting because of its uniform soft glow; street lamps light only the immediate area. "Unless you've got lots of them on all the time, you get black spots," Scott says. And as people walk in and out of the light, their eyes take time to refocus, he points out; not so for this treatment.
Additionally, because the light emitted is a glow rather than a direct beam, "there is no light pollution," Scott points out. This makes the treatment suitable for areas sensitive to being overly lit at night, such as areas with protected species, nature preserves, or even driveways and other areas where neighbors live in close proximity. "You don't get it shining in your face," he says. "If you had this outside your house, and you were looking out on to the pavement outside, you wouldn't necessarily see it until you walk and get onto it," Scott says.
Although the product is designed to treat existing hard surfaces—asphalt, concrete, or even timber—in highly developed locations, Scott sees its usefulness extending to developing countries or other areas where an electrical grid is unreliable and nighttime lighting unavailable.
In addition to offering the possibility of nighttime navigation, the treatment also repairs and extends the lifespan of existing hard surfacing, Scott notes.
"The really nice thing about the product is that because the polyurethane is flexible, you don't get the situation with tarmac and asphalt that in the winter, they'll crack," Scott says. "With this sort of system, that can't really happen." Because the protective coating does not allow water through, cracks cannot form and become potholes during winter's freeze-thaw cycles. The application thus extends the life of a road or pathway.
While much of the conversation about constructing sustainable hardscapes in urban environments seems to focus on permeable surfaces that can relieve pressure on sewer systems , this treatment takes a different approach. By creating an impermeable surface it extends the lifespan of an existing path or roadway by 10 or 20 years, Scott says. Material that would otherwise be headed to a landfill can thus continue its useful life. But additionally, "What we want to be able to do is get people on nice pathways—walking [and] cycling, which reduces fuel," he says. "And so in some little way, saving energy, saving power rather than producing power."
While the system is currently being tested on a bike path in Christ's Pieces, a Victorian park in Cambridge, the company has been conducting informal testing of the product over the last three and a half years in areas with heavy truck and tractor use. According to Scott, the treatment has been performing "absolutely fine" under heavy use.
The team can treat approximately 100 sq m in an hour and at a cost of approximately £70 per square meter (U.S. $1.60 per 3.2 sq ft) for smaller jobs, according to Scott. A variety of aesthetic options are also available, depending on what color of aggregate is selected and what color of luminescent glow is desired; blue, green, purple, red, and orange are available.
Other advantages of the treatment are that it is nonslip, yet has a very low viscosity, which means that such sticky substances as chewing gum won't stick. "It's very easily cleaned," Scott says.