Tacoma Builds Award-Winning

Tacoma Builds Award-Winning Greenroad Tacoma Builds Award-Winning Greenroad

BY ASPHALTPRO STAFF

To minimize cold joints and maximize smoothness, Miles Resources pulled two passes side by side and used a third paver to tie in side streets.

NNorth America has a new, high-scoring en- Let’s take a look at the project’s design, McBride explained that the project first revironmentally sound project thanks to po- execution and success. It began in 2017, quired the team demolish the existing hardrous asphalt paving design in the City of Ta- when the City of Tacoma’s environmental scapes and landscaping, replacing them with coma, Washington. The Greenroads Founda- services division let the job to prime con- environmentally driven materials that would tion, headquartered in Washington, manages tractor Northwest Cascade Inc. and paving allow stormwater to infiltrate the new roada third-party certification process that assess- subcontractor Miles Resources LLC, Puy- way, new landscaping and new sidewalks es the sustainability of transportation projects allup, Washington, to rebuild and pave a with the intention of furthering the advanceusing the Greenroads Rating System. For 2020, porous asphalt on East 40th Street. ment of clean stormwater systems in lieu of the foundation has awarded the City of Taco- Pat McBride is the estimator/project further adding to the city’s existing stormwama’s East 40th Street Green Infrastructure manager for Miles Resources, and provided ter systems. Project the Greenroads Silver Certification. details of the mixes and design that made Replacement meant paving with environ-

The project earned 54 points and met all the new pavement structure possible. mentally sound asphalt and best practices to project requirements to become the high- “In Western Washington, the projects ensure a long-lasting pavement structure that est-scoring Greenroads project in the world. requiring porous hot-mix asphalt (PHMA) won’t require frequent maintenance. The Sandy Forks Road project in Raleigh, are becoming more and more common,” “Miles Resources executed the 2,224 tons

North Carolina, which you can read about on McBride explained. “With this trend, the of PHMA and ATPB paving in two lifts over

TheAsphaltPro website, had held this distinc- City of Tacoma, several asphalt paving con- the course of two days,” McBride said. “The tion since November 2017. tractors, asphalt designers and the Wash- goal was to pave the roadway with virtually no The East 40th Street Green Infrastructure ington Asphalt Paving Association (WAPA) joints, as failures tend to occur in these types

Project reduces neighborhood flooding, en- have been constantly working to create of projects at cold joints.” hances safety and increases accessibility, re- higher quality porous asphalt designs. He explained the paving team accomplaces underground utilities including water This project was one of the initial proj- plished this using three pavers; two of which mains and sanitary sewers, and improves wa- ects in Western Washington using designs worked side-by-side to place asphalt down ter quality by 99.8 percent for 39.1 acres in the from this group’s efforts and yielded out- the two-lane road while a third pulled the side

First Creek, Lower Puyallup watershed. Lo- standing results that have helped improve streets in. “This was not only aesthetically calized flooding previously happened along PHMA and asphalt-treated permeable base pleasing, but created a uniform looking roadthis corridor because it is a low point in the (ATPB) design and placement throughout way with a smooth, bump-free surface,” Mc-

East Tacoma neighborhood. Western Washington.” Bride said.

The project features a 16-foot shared space separated from the roadway by bioswales that filter rainwater while increasing the route’s safety and aesthetics. Image by Aaron Copado, courtesy of the City of Tacoma

The porous pavement structure is as follows: • A 6-inch section of filter sand • A filter fabric on top of the filter sand • A 4-inch lift of permeable ballast rock • A 3-inch lift of asphalt treated base • A 2-inch top lift of aramid fiber-reinforced

CI ½-inch PG70-22ER PHMA

“Both the ATPB and PHMA are designed for an equivalent single axle load rating of 0.3 to 3.0 (millions) and used 0.5 percent of Evotherm M1 anti-stripping in the PG70-22ER binder,” McBride said. “The designed air voids for the ATPB were 27 percent and for the PHMA were 19.7 percent.”

McBride shared that it can initially be difficult for inspectors and some agencies to grasp that the paving team isn’t shooting for normal compaction ranges seen with standard asphalt paving. The densities of 93 percent and higher would destroy this system.

“You have to picture aggregates in porous asphalt as a bunch of marbles stacking up next to each other,” McBride explained. This “stacking” creates the desired voids in mineral aggregates (VMA), which makes the structure porous. “The necessary voids will cause a much lower compaction result from a nuclear gauge than a standard asphalt mix but in fact will be fully compacted.

“For example,” he continued, “on this project our top lift of half-inch porous HMA was designed for 19.7 percent air voids (VA), so this would be designed for 80.3 percent compaction. The base lift of Asphalt Treated Porous Base was designed for 27 percent VA, so we would be shooting for 73 percent compaction. Because there are primarily only a few sizes of coarse aggregate in porous asphalt, the mix compacts quite readily and achieving the design levels of compaction isn’t an issue.”

After each lift was placed, the Construction Testing Laboratories, located in Puyallup, Washington, took samples for infiltration testing. “The project specifications called for infiltration rates of a minimum rate of 100 inches per hour,” McBride said. “We achieved an average of 3,000 inches per hour on the ATPB and 600 inches per hour on the PHMA.”

He explained that the infiltration testing was performed, in place, per ASTM C1701 Standard Test Method for Infiltration Rate of In Place Pervious Concrete. While that might sound a little strange, because the test method was originally designed to test pervious concrete pavements, it’s now often specified to test porous asphalt as well. “A 12-inch-diameter pipe is sealed to the pavement surface with plumbers putty and 40 pounds of water is timed being poured into the pipe and down into the pavement,” he explained. (See sidebar “How to Check In-place Air Voids.”)

The new road features narrower lanes than before to improve safety and reduce speeding, and was built with permeable pavement to allow stormwater to filter through the soil. This reduces stormwater flow and helps filter pollution from the water before it reenters the First Creek ecosystem, alleviating 38 percent of the site runoff for downstream impacts.

“The project is a green gem for transportation in the State of Washington,” said Dr. Jeralee Anderson, CEO of Greenroads International. “We are thrilled for Tacoma's team and so proud of their leadership and commitment to environmental sustainability.”

This is the fifth certified Greenroads project in Tacoma, reinforcing the city’s commitment to environmental policy leadership. Tacoma is a Greenroads member and was the first to adopt a resolution establishing the city as a “Green Roads Community” by creating its roads and infrastructure as “models of environmental, economic and social stewardship,” according to Resolution 38945.

The $4.5 million project was funded with a grant from the Washington State Department of Ecology, the City of Tacoma’s Public Works’ voter approved Streets Initiative Fund, the Environmental Services Department’s Surface Water Fund, and the Tacoma Water Bond Fund.

Numerous unique partnerships across organizations and the community helped to create a valuable asset for the Eastside Tacoma Neighborhood. The construction and design of the project was created by a partnership between the City of Tacoma’s Environmental Services, Public Works, and Public Utilities Departments, along with the Washington Department of Ecology, KPG, GeoDesign, Northwest Cascade Inc., Totem Electric,

Extra Parts of the Puzzle

A 16-foot-wide shared-use path was built along the new roadway from East McKinley Avenue to Portland Avenue East, creating a safe connection for pedestrians and cyclists traveling to nearby schools or accessing the new Pipeline Trail. Thirteen biofiltration swales, or sloped channels designed to capture and filter stormwater runoff, were installed between the roadway and the path. Over 150 trees were planted within these bioswales to create a safety buffer.

The project team also partnered with local eastside elementary and high schools to beautify the new shared-use path. Students from Lister, Lincoln, Stewart and First Creek schools used a superhydrophobic coating to paint poetry into the pavement.

“The project created connections to other neighborhoods and provided access to multi-use centers in the city. Not only was mobility improved, but the project’s attributes addressed multiple stormwater and transportation issues facing this particular neighborhood,” said Olivia Mathison, associate engineer with the City of Tacoma’s Environmental Services Department.

Greenroads® Summary

Environment & Water ................ 18 Construction Activities ............... 8 Materials & Design ................... 5 Utilities & Controls ................... 6 Access & Livability ................... 6 Creativity & Effort ................... 10 Score ...............................54

Miles Resources, Silver Streak Inc., AESI, and Watershed Environmental Solutions LLC.

The project received the Pacific Northwest Clean Water Association’s “2018 Innovative Stormwater Project Award”andWashington Asphalt Pavement Association’s “2019 Special Innovative Pavement for Western WA.” It also placed third in the National Association of Flood Stormwater Management Agencies’ “2018 Green Infrastructure Award” for cities with medium and large populations.

McBride is proud of more than the awards. The project offered Miles Resources an opportunity to test best practices and prove the environmental benefits of asphalt. “Installing the porous asphalt treated base allowed for increased infiltration as opposed to putting directly on ballast or choker,” he said. “The use of aramid fibers alleviated drain down concerns and helped keep the binder on the rocks as well as strengthen the overall asphalt. The use of multiple pavers to eliminate joints will help extend the life of the asphalt.”

In the end, the project was recognized not just for its environmental stewardship, but also for its special and innovative use of HMA.

There are currently more than 130 projects registered for the Greenroads Project Rating Program in 11 states and 8 countries valued at more than $32 billion USD. Washington State has the most certified Greenroads in the world, and the City of Tacoma’s project is the 29th to certify in the state since the program began in 2011.

Established in 2010, Greenroads Foundation is an independent 501(c)(3) non-profit corporation which advances sustainability education and initiatives for transportation infrastructure. As the developer of the Greenroads Rating System, the foundation manages the certification process for sustainable transportation development projects in the U.S. and internationally.

How to Check In-place Air Voids

The National Center for Asphalt Technology (NCAT) asphalt permeameter is one device paving crews can use to double-check in-place air voids during construction. Similar instruments are available through testing equipment suppliers and are typically constructed of four-tiered, clear plastic for non-destructive field testing. With the instrument, a technician measures the rate of water-level fall in the permeameter over a defined period of time.

To begin, a technician selects an area of about one square foot of unsealed asphalt mat of known thickness and brushes it clean of any debris.

The technician applies a moldable sealant to the underside of the permeameter base. She places the bottom section on the asphalt mat and uses gentle foot pressure to temporarily attach and seal the permeameter to the asphalt pavement. She then affixes the top section of cylindrical piping to the bottom section with the same sealant. She places weights on the base section to counteract the head pressure developed when the permeameter is filled with water. At least four 5-pound weights are recommended, but notice the jack on the back of the work truck that NCAT uses in the photos herein to apply more adequate down-pressure.

To fill, the technician inserts a funnel in the top section of the assembled permeameter and slowly adds water, attempting to minimize the introduction of air bubbles. Once the permeameter is filled, she checks for leaks; assuming there are none, she proceeds with testing, recording the initial water level (h1) in centimeters, and the start time at the beginning of the test.

Coarse or open-graded asphalt mixes will take less time and will normally require the technician use the larger diameter tiers to determine volume of flow through the pavement, while finegraded mixes will take more time and require the top, smaller diameter tiers. Ultimately, the testing time should be long enough that there is a measurable and steady rate of water-level-drop in the permeameter.

The technician records the final water level (h2) in centimeters and the elapsed time (t) at the conclusion of the test. The elapsed time and total water volume (ln (h1/h2)) are used to calculate and report a coefficient of permeability (K).

NCAT personnel set up the permeameter with a jack on the back of a work truck to apply adequate down-pressure to counteract the head pressure developed when the instrument is filled with water. Both photos courtesy of NCAT