Last year, the installation of a concrete driveway became a major spectacle in Victoria, Canada.
“It was a real big thing,” said Ron Manuel, the owner of the driveway in the coastal capital city of the province of British Columbia. About 20 local contractors turned up to watch. “They had the whole street blocked off. They all wanted to see how it was going in and how it was done.”
What makes Ron Manuel’s driveway so special? It’s made out of permeable concrete. When it rains, the water drains right through it and into the soil below.
Nearly two years later, and Manuel’s driveway is still turning heads. “The number of people who have come around to see it — people actually knock on my door asking about my driveway. They think it’s a gravel driveway until they look at it, until they walk on it and realize it’s a solid surface.”
Permeable concrete may look like fantastic, futuristic technology, but it’s really an old idea. Its roots go all the way back to the 1800s in Europe. The United States has dabbled in the tech since at least the 1970s.
It’s made in a similar way to traditional concrete, except that there is no sand and fine particulate in the mix. It’s basically gravel, glued together with cement. Although the material is solid, there are gaps within it that allow water to pass through.
Regular Concrete Is Really Bad for the Natural Water Cycle
But why, you ask? All of the impermeable surfaces in cities — the roads, the roofs, the parking lots, the driveways — really mess with the natural water cycle. Rain that falls has to go somewhere, and so cities have built elaborate and expensive underground pipe systems to capture and divert storm water. But even that doesn’t really solve the issue, because that runoff picks up all sorts of nasty pollution from the urban environment, which, if left untreated, gets dumped into the local water system.
“Every eight months in the United States we have the same amount of oil being discharged off our roads as was spilled in the Exxon Valdez oil spill,” says Geoffrey Scott, a researcher with the Medical University of South Carolina, in a recent lecture.
Scott’s research has shown that the more we cover our coastal cities with impermeable surfaces, the worse it is for human and environmental health. “Anytime we get about 10 percent impervious cover in a watershed, you begin to see alterations in water quality. Anything over 30 percent, you begin to see loss of ecosystem services,” he said. That could include things like beach closures because of high E. coli levels, or fisheries closures because of contamination in the food web.
Letting rain water seep naturally through the ground and back into the water table filters out contaminants and makes for a much cleaner and healthier environment.
When Ron Manuel picked permeable concrete for his driveway, though, it wasn’t strictly out of altruism for the natural world (city officials forced his hand because a typical concrete driveway would require a runoff basin). His contractor, Russ Barry of Interactive Construction, came up with the idea of going permeable.
“I’ve always, always been interested basically trying to do things better — differently,” Barry tells Inverse. “A lot of people try to do the same thing over and over again because it works, and I’ve always thought, hey, we should be trying out new stuff, new technology that has come along.”
As far as Barry can tell, it’s the first time permeable concrete had ever been used in a private driveway in Victoria. That’s what got all the local contractors excited to come and check out the process.
“It’s radically different than pouring regular concrete,” says Barry. “Just because it’s coming out of a truck doesn’t mean it’s the same type of thing at all.” The biggest thing you have to pay attention to is the substrate underneath the concrete — you have to ensure that it will drain properly so water doesn’t back up in the system.
One common perception of permeable pavement is that it doesn’t work in cold climates, because the water will tear apart the material as it freezes and thaws. But so long as there is proper drainage, that’s not the case.
In fact, Manuel saw an unexpected benefit of his permeable concrete in the colder months. One of the banes of Canadian winters is when snow melts slightly then refreezes on driveways and sidewalks, leaving a sheer layer of slippery ice. On his driveway, any melt falls away, leaving a slip-free surface all through the winter.
Victoria is following the lead of a growing list of North American cities charging storm water utility fees and offering similar rebate programs. Perhaps the most obvious customers are municipalities themselves, since they directly bear the costs of storm water infrastructure, roads, and sidewalks.
And they are, in some cases, catching on. Chicago is one of several American cities that has has a green alley program that encourages the use of permeable pavement.
Change Is Slowing Coming
But change can be slow. “One thing that’s absolutely true in civil engineering is that it’s a very risk-adverse environment,” John Harvey, director of the University of California Pavement Research Center, tells Inverse.
“If you’re a government engineer, if you keep doing things the way they’ve always been done, nobody can blame you for anything. Even if it’s not necessarily the best thing. Whereas, if you do something and it goes wrong, you can lose your career.”
His research group found that using permeable pavement shoulders on California highways beats out other water management techniques in terms of long-run costs. “We were somewhat surprised by the results,” says Harvey. The state’s transportation department is moving ahead with some test sections.
Philip Kresge with the National Ready Mixed Concrete Association tells Inverse he’s seen a big uptick in awareness and interest in pervious concrete in recent years. “I think it is actually catching on very well at this point. Three, four years ago, it hadn’t been.”
It hasn’t really come into the mainstream, though, mostly because people still have misconceptions of it as an inferior product, he says. “They look at the material and because it has this open void they think it’s going to be weak, it’s going to be brittle, it’s not going to stand up to traffic. And they’re reluctant to use it in certain areas, in main areas, because of that.”
But the technology has really improved over the years. “It is certainly a very strong, durable, rigid pavement,” Kresge says.
He’d like to see permeable paving become the standard for storm water management. “They used to automatically put in a retention pond. Now they’re automatically putting in rain gardens, bioswales, and so on. I’d like to think that we’re going to be able to replace that.”
Using green spaces and vegetation as natural water managers is lovely, but if space is at a premium, permeable concrete can do double duty.
“How many cars can you park on your retention pond?” asks Kresge.