This article is based on a webinar originally presented during the International Grooving & Grinding Association (IGGA) Technical Sessions, Dec. 2020. Watch the full presentation below, or go to article link at end.
Click to go to YouTube Video of IGGA presentation
www.youtube.com/watch?v=usLRByfWP4c
Returning Arizona highways to Portland Cement Concrete
might just prove beneficial using diamond grinding
as an alternative to the standard mill and fill
The outlook suggests a $3.9 billion reduction in maintenance costs over a 30-year period. Phoenix-area residents expect smooth, beautiful, quiet roads, but due to explosive population growth in the region and funding insufficient to keep pace, pavement conditions across the area have been declining over the last decade. The Arizona Department of Transportation (ADOT) is examining creative solutions for maintaining its highway network and delivering the kind of roads the public expects.
Phoenix is the fifth most populous city in the U.S., and growing. All 435 miles of the city’s road and bridge network, most of which consists of four-lane highways with additional high-occupancy vehicle (HOV) lanes, is maintained by ADOT Central District, which has a $500-million-per-year construction budget, and typically conducts 20 to 25 construction projects per year on the high-volume road network.
Arizona’s Pavement Timeline
1920
Arizona has used concrete pavement because it lasts for decades and requires maintenance only every 20-25 years.
1960s
For Arizona, 40 years of success with the material led to its greater as the state began building the main highways. Paving with concrete the 1960s meant making trade-offs when it came to road noise. During that period, the concrete surface was finished by tining (A metal rake pulled across the concrete surface perpendicular to traffic flow), but drivers’ tires to generate a noisy, tonal whine.
2003
To address the noise, a 1-in. asphaltic rubber friction course (AR-ACFC) was applied on top of the Portland Cement Concrete (PCC). This delivered a consistent look, quiet sound, and comfortable travel. However, with a design life of approximately 10 years, preserving the AR-ACFC surfaces proved to be a challenge! Arizona’s highways have now exceeded that design life and are showing their age. The 1 in. of rubber asphalt has separated from the concrete underneath, called delamination. It has caused the loss of about an inch of pavement depth—creating problems and related issues are for drivers and the DOT—the greatest being perception of potholes by the traveling public—regarded as a serious problem.
Arizona measures pavement condition by the International Roughness Index (IRI), and numbers have been trending down:
IRI is the roughness statistic universally used by state agencies as a performance metric for their pavement management systems:
Lower the numbers = less roughness
• 2010 IRI measurements:
Arizona showed 72% of the area’s interstates were in good condition
National Highway System showed 68% of the highways in good condition
• 2018 IRI measurements:
Arizona fell to 53%
National Highway System fell to 35%
2019
APRIL:
With costs mounting—and budgets falling behind—ADOT started to look for better preservation options than historically done.
For pavement still in good condition within the 10-to-15-year design life window (increasingly important for ADOT to keep existing pavement) options included:
• Crack sealing the pavement
• Fog sealing—applying a light coat of diluted, slow-setting asphalt emulsion
• Repairing individual potholes
For pavement past the 10-to-15-year design life window, nonviable option included:
• Mill off the deteriorated asphalt and put down a new rubberized asphalt overlay
—Proved cost-prohibitive due to the extent of the repair areas
—Milling equipment inevitably impacts and damages the underlying concrete
—Joints experiencing particularly severe loss of concrete material
What if Arizona went back to its original PCC surfaces?
ADOT knew the state’s concrete highways were designed to offer a long life of structural stability:
• If use the underlying PCC, making improvements to its original tined surface would result in
• Quiet roadway
• Rideable roadway
• Rehabilitated roadways [will more than likely] last a lot longer
• Require much less maintenance than asphalt
A Return to Concrete Pavements: Pilot Studies
An AR-ACFC layer had already been removed as part of a project being conducted on SR 101 in the northern part of Phoenix, so ADOT installed 4 test sections to explore future solutions that would take advantage of the existing concrete while ensuring a smooth, quiet ride and good pavement appearance.
The department reviewed:
• Diamond grinding
• Next Generation Concrete Surface (NGCS)—texture with a controlled land profile and an overall negative or downward texture developed to be a particularly low-noise concrete pavement surface
• Finishing concrete surfaces with a skid abrader—a machine directs ball bearings at the pavement to improve friction characteristics
• Finishing concrete surfaces with micro-milling
After testing each method, ADOT determined that the longitudinal texture achieved with diamond grinding offered a pleasing corduroy appearance as well as a nice ride (as indicated by low IRI numbers) and low sound emissions. The diamond-grinding process also proved to be gentle enough to protect areas of the concrete, especially around joints, that had previously been damaged by milling. Diamond grinding was also a cost-effective solution.
MAY:
ADOT decided to diamond grind a short section of SR 202 in southern Phoenix.
• 15-year-old AR-ACFC badly raveling and delaminating, to the point that loose rock was being thrown at windshields with daily complaints from drivers that windshields had been damaged by the flying rock
• Higher percentage of damage claims than the rest of the nation
• Very loud
• Very rough to drive on
ADOT selected a diamond-ground finish for the two right lanes along a half-mile stretch of SR 202
• Removed existing AR-ACFC layers without damaging underlying concrete by using a loader bucket—method the department had successfully experimented with in April when they were brainstorming ways to return to PCC road surfaces
• Noticed drivers moved from the AR-ACFC lanes to the diamond-ground concrete lanes to experience the improved ride and sound characteristics!
At about this time, a Maricopa Association of Governments (MAG) released a report on assessing the noise and [smoothness] of local freeways. The report acknowledged the difficulty of maintaining the road network and also focused on the noise characteristics of the road. A key takeaway was that, since the noise benefits of AR-ACFC vanish so quickly, “consideration should be given to replacement of the rubberized asphalt overlay with a diamond ground treatment.” Another concurrent development was a maintenance procurement contract that allowed diamond grinding contractors to be brought in for maintenance as well as for construction.
2020
FEBRUARY:
SR 202—ADOT decided it was time to take the next step for a bigger diamond grinding project
• 4-mile section
• 4 lanes wide
• Ramp sections included
• Area was too big to remove asphalt using a loader, so a milling machine was used
• Cut strips in the rubberized asphalt to be used by the milling contractor as a guide during the milling process
• Allowed operator to see the PCC surface below the overlay more easily
• Milling equipment could be adjusted
• Damage to underlying concrete was minimized
The final diamond-ground surface of SR 202 met all ADOT’s criteria
• Quiet
• Smooth
• Attractive
• IRI numbers in the 20s and 30s … comparing very favorably to asphalt surfaces—Comparable noise characteristics were achieved because, while new AR-ACFC pavement is about 5 dB quieter than diamond-ground surfaces, by the time AR-ACFC pavement is 5 to 9 years old, it is measuring at comparable or higher dB levels
• Pavements generated less noise in nearby neighborhoods
The success of their early projects prompted ADOT to begin 3 other diamond grinding pilot projects. Diamond grinding on the Loop 101 Price Freeway has been completed
2021
Diamond grinding Loop 101 Pima Freeway took place early
Next 5 Years
Loop 101 I-17 to 75th Avenue construction project is expected to occur. ADOT will be tracking the performance of all projects to see how joints are holding up, whether the concrete spalls and how well sound and ride quality are maintained.
…not all pilot projects have been completed, but data collected so far
justifies consideration of diamond grinding as an alternative to the standard mill & fill.
Initial findings on costs … savings associated with using concrete road surfaces,
diamond-ground to optimize appearance, smoothness, and sound,
could be as much as a $3.9 billion reduction in maintenance costs
over a 30-year period!
By using existing concrete pavement in Phoenix, not only will maintenance budgets stretch farther and allow more roads to be kept in good condition, but concrete’s durability ensures that interruptions associated with road repair will be minimized. Most importantly, the public will be able to enjoy driving surfaces that are smooth and quiet.
For the article titled “Diamond Grinding Pilot Projects Show Promise as Cost-Effective Fix for Phoenix Highways” by author Randy Everett, Senior Division Administrator-Arizona Department of Transportation, Central District, please go to: www.forconstructionpros.com/concrete/article/21389918/igga-international-grooving-grinding-association-the-phoenix-highway-concrete-pavement-preservation-diamond-grinding-pilot-program
For the presentation video link, please click on image at top, or go to link provided.