Recycling asphalt? It’s one trick Tacoma is using to make street repair climate friendly

Tacoma is homing in on improving streets. On Monday, for instance, the city launched the week-long campaign dubbed “Pothole Palooza” to broadcast its efforts toward repairing less-than-pristine roads.

Asphalt and concrete, some of streets’ main ingredients, have been linked to climate change — a phenomenon that the city is working to address. So, how is Tacoma revamping outdated thoroughfares in a climate-conscious way?

What does cutting-edge road maintenance look like?

Jeffrey Jenkins, assistant director of Tacoma’s Public Works Department, told The News Tribune that the city aims to maintain roads in a cost-efficient, environmentally friendly manner. The city regularly conducts maintenance treatments before street surfaces need major replacements or repairs.

“There’s this band of excellence that if you can maintain your roads and kind of stay there before they get to a certain place, then you can save a lot of money,” Jenkins said. “Then we augment that with our commitment to the environment.”

How does the city uphold that commitment? One answer lies in recycling.

What materials are used?

Tacoma uses recycled asphalt products (RAP) to improve streets, Jenkins said. Of the 12,000 tons of asphalt produced in 2023, some 1,200 tons were created with RAP, produced with asphalt grindings from the city’s pavement-repair projects.

Tacoma has its own small asphalt plant, something that makes the municipality unique, he said. Even though deploying RAP has become fairly standard across the industry, not that many cities have their own plants.

How is Tacoma protecting the environment?

Proponents point out that RAP can help slash construction costs and decrease greenhouse-gas emissions. Jenkins said the city is also using recycled concrete as part of its broader climate goals.

Recycled-street materials like RAP help to divert from Tacoma’s waste stream, Jenkins said — nearly 12% of which is composed of demolition and construction debris, according to the city’s website.

Jenkins noted that Tacoma is working to augment its tree canopy to 30%. Reaching that threshold would help mitigate the urban heat island effect, which happens whenever a neighborhood or city is warmer than its adjacent areas — at times by as much as 15 degrees Fahrenheit, The News Tribune previously reported.

Without ample tree canopy, particularly in the downtown area, the sun warms up concrete and asphalt that continue radiating heat into the evening, Jenkins said. Trees act to intercept that heat.

Toasty temperatures can make it easier for streets to crack, according to the U.S. Forest Service Center for Urban Forest Research. One study’s findings suggested that shaded, tree-lined roads enjoy better pavement conditions than ones that are barren, all other factors being the same.

The city also is turning its attention toward acquiring sustainable vehicles, including a recent buy of a hybrid front-end loader that helps make the hot-mix asphalt (HMA) used to repair streets, Jenkins said. That helps cut down the city’s carbon-dioxide emissions.

Tacoma is looking to boost its use of renewable fuels to bring down carbon emissions, too, he said. And green energy isn’t the only method the city is pursuing.

“When we are out doing road work, we’re using what we call ‘best-management practices,’” he said. “So we’re making sure that any water that’s leaving our site is filtered before it enters into the storm system.”’

Prioritizing recycled-street materials is one way to help combat climate change. Another way? Cutting back on traffic.

“I think when cities are planning forward, if they’re thinking about climate change and climate action, more so it’s important to make investments in public transit and divesting from highways and roads,” said Bara Safarova, assistant professor in the School of Urban Studies at the University of Washington Tacoma.

She added that it’s important for local governments to make roads safer and more accommodating for pedestrians, cyclists and scooter riders so that cities can reach their climate goals.

How much does using recycled materials cost?

Jenkins offered a snapshot of some of the cost-saving benefits that using recycled materials has for Tacoma’s roads. He told The News Tribune in an email that the city’s Street Operations Services has deployed 20% recycled asphalt in making its hot-mix asphalt (HMA), depending on factors such as availability. That translates to an approximately $10-per-ton reduction in HMA manufacturing costs.

When it comes to recycled concrete aggregate, he added, there is around a $7-per-ton cost savings for road-subgrade construction: $15.70 for virgin crushed surfacing base course versus $8.50 for recycled.

The price tag of a ton of HMA — sans recycled asphalt — depends on that of the oil and aggregate used during production, Jenkins said. As of Thursday, a ton of non-RAP HMA costs $110.58 for the city to make.

What are the effects on road strength?

Jenkins said that using recycled concrete aggregate or RAP does not affect the structural integrity of roads.

Another expert answered the same question a bit differently.

Nara Almeida, assistant teaching professor in the University of Washington Tacoma’s School of Engineering & Technology/Civil Engineering, explained that using recycled material in concrete can jeopardize its strength.

“However, it doesn’t mean we should not recycle,” she said. “It means that we should find new ways to do it.”

When making concrete, using recycled concrete instead of gravel can present a problem in that it absorbs more water, she said: around 9% absorption versus somewhere in the range of 1% or 2%. Too much water in the mix isn’t good; it can cause “bleeding,” meaning that water rises while segregation occurs in the bottom.

Still, Almeida said, there are ways to bolster the strength of recycled concrete with fine “supplementary cementitious materials” like slag.

“It’s not that we should not recycle,” she added. “There are ways to do that, but we just need to find out how to best do it so we’re able to reuse everything.”

With construction season upon us, The News Tribune will examine the state of Pierce County’s roads and streets over the next several weeks as part of its In the Spotlight initiative.