Concerns about climate change and urban heat islands have a lot of experts pointing fingers at black asphalt. It's no secret to anyone that dark colors tend to absorb and retain heat, which can end up increasing the air temperatures around and above paved areas. Cool pavement technology purports to change all of that, but does it actually work? Here are the pros and cons of cool pavement:
The term "cool pavement" is a bit of a catchall. In general, it means any kind of pavement that is engineered to remain cooler than conventional black asphalt. This can include pavements covered with a light-colored coating to reflect sunlight or even grass paving.
Since it's a catchall term, it can be a bit difficult to create a comprehensive list of benefits and downsides for cool pavement in general. Some of the pros of grass paving, for example, won't apply to coated pavement, and vice versa. This makes a cost-benefit analysis of cool pavement a bit more challenging.
White-tinted cool pavement doesn't absorb as much sunlight. This means that it's less of a contributor to heat islands. In some areas, cool pavement technology can keep temperatures from rising by as much as twenty to thirty degrees.
On a sunny day, black asphalt can get as hot as 140 degrees Fahrenheit. This isn't just uncomfortable, it can be dangerous -- especially for small children, pets, and anyone else that might not be wearing foot protection. Cool pavement doesn't increase in temperature as much as black asphalt does, so it can be safer to touch and walk on.
In addition, black asphalt absorbs and retains heat for a while. Cool pavement stops reflecting sunlight as soon as there's no more sunlight to reflect. This means that cool pavement stops contributing to heat long before black asphalt does.
Just because light-tinted cool pavement doesn't absorb as much energy from sunlight doesn't mean that that energy just disappears. Under normal circumstances, black asphalt absorbs solar radiation and radiates it back out as heat. Cool pavement reflects sunlight instead of absorbing it. This can equate to as much as a 10% increase in direct sunlight, which can be very uncomfortable for pedestrians on very sunny days.
This isn't as much of an issue for something like grass paving. Grass paving doesn't reflect sunlight back as coated pavement does, so it avoids increasing the surrounding temperatures for pedestrians.
Dark pavement needs reflective paint to make it visible at night. If this gets old, scuffed, or covered by mud, that visibility is compromised. Cool pavement is generally lighter than the surrounding area at night, so it's still visible. This can make it safer for drivers.
Light-colored pavement may be safer for pedestrians, too. People who aren't wearing reflective gear often don't contrast much with black asphalt. Lighter-colored pavement can provide more contrast, enhancing the visibility of pedestrians and cyclists.
In addition to making people feel hotter by reflecting sunlight, cool pavement can also create glare. Black asphalt absorbs sunlight and radiates it as heat. Since cool pavement reflects sunlight, not all of that radiation is transformed into heat. Some of that reflection is visible light, which can cause visibility issues for drivers.
Asphalt is poured at high temperatures, so it stands to reason that it can handle some heat. Prolonged exposure to very hot weather can still have a detrimental effect on its structural integrity. Very hot weather can soften it, resulting in cracking, tracking, and a host of other issues.
Since cool pavement doesn't absorb as much solar radiation, it stays cooler. This means that it's less likely to get hot enough to experience heat-related damage.
Grass paving is an excellent cool paving technology, but it only works as well as the grass does. This means that it isn't a great strategy for very high-traffic areas, since that level of activity would be detrimental to the plants.
Grass block pavers also only last about half as long as concrete or asphalt. They're good for keeping patios or driveways cool and dry, but definitely not something you'd want to use for a busy thoroughfare.
Some cool paving tech comes with benefits above and beyond reduced temperatures. Permeable cool pavement can help with stormwater management, reduce tire noise, and decrease water spray from tires on rainy days. Cool pavement also doesn't radiate as much heat to stormwater runoff.
In general, cool paving is a good choice to improve the microclimate in areas that are heavily paved. In cities, for example, the sheer amount of asphalt can be a major contributor to the heat island effect. Even so, black asphalt will probably always be with us. It's more durable than grass paving and less expensive than asphalt with a reflective cool coating, so it's likely to remain the best option for highways and other areas where heat islanding is less of an issue.
As the world heats up, cities everywhere are looking for ways to keep cool. Black asphalt is excellent at absorbing and radiating solar heat, so various strategies have been developed to help mitigate that effect. Some of these are great for areas frequented by pedestrians, while others may actually create more discomfort.
POSTED: October 6, 2022
TAGS: Paving Industry