Returning the Arizona highway to Portland cement concrete may just prove the benefit of using diamond grinding as an alternative to standard grinding and filling. The outlook shows that over a 30-year period, maintenance costs will be reduced by USD 3.9 billion.
This article is based on a webinar originally held during the International Grooving and Grinding Association (IGGA) Technical Conference in December 2020. Watch the full demo below.
Residents in the Phoenix area want smooth, beautiful, and quiet roads. However, due to explosive population growth in the area and insufficient funds to keep up, the road conditions in the area have been declining in the past decade. The Arizona Department of Transportation (ADOT) is studying creative solutions to maintain its highway network and provide the types of roads the public expects.
Phoenix is the fifth most populous city in the United States, and it is still growing. The city’s 435-mile network of roads and bridges is maintained by the Arizona Department of Transportation (ADOT) central area, most of which consists of four-lane highways with additional high-vehicle-vehicle (HOV) lanes. With a construction budget of US$500 million per year, the region typically carries out 20 to 25 construction projects on a high-traffic road network each year.
Arizona has been using concrete pavements since the 1920s. Concrete can be used for decades and only needs maintenance every 20-25 years. For Arizona, 40 years of successful experience enabled it to be used during the construction of the state’s major highways in the 1960s. At the time, paving the road with concrete meant making a trade-off in terms of road noise. During this period, the concrete surface is finished by tinning (pulling a metal rake on the concrete surface perpendicular to the traffic flow), and tires driving on the tinned concrete will produce a noisy, coherent whine. In 2003, in order to solve the noise problem, a 1-in. Asphalt Rubber Friction Layer (AR-ACFC) was applied on top of Portland Cement Concrete (PCC). This provides a consistent appearance, quiet sound and comfortable travel. However, preserving the surface of the AR-ACFC has proven to be a challenge.
The design life of AR-ACFC is approximately 10 years. Arizona’s highways have now exceeded their design life and are aging. Stratification and related issues pose problems for drivers and the Ministry of Transportation. Although delamination usually only results in a loss of about 1 inch of road depth (because the 1-inch thick rubber asphalt has separated from the concrete below), the delamination point is regarded as a pothole by the traveling public and is regarded as a serious problem.
After testing diamond grinding, next-generation concrete surfaces, and finishing the concrete surface with a slip grinder or micromilling, ADOT determined that the longitudinal texture obtained by diamond grinding provides a pleasing corduroy appearance and good driving performance (As shown by low IRI) numbers) and low noise emissions. Randy Everett and Arizona Department of Transportation
Arizona uses the International Roughness Index (IRI) to measure road conditions, and the number has been declining. (IRI is a kind of roughness statistical data, which is almost universally used by national institutions as a performance indicator of their pavement management system. The lower the value, the smaller the roughness, which is desirable). According to IRI measurements conducted in 2010, 72% of the interstate highways in the region are in good condition. By 2018, this proportion had fallen to 53%. National highway system routes are also showing a downward trend. Measurements in 2010 showed that 68% of roads were in good condition. By 2018, this number had dropped to 35%.
As costs increased—and the budget couldn’t keep up—in April 2019, ADOT began looking for better storage options than in the previous toolbox. For pavements that are still in good condition within the 10 to 15-year design life window-and it is becoming more and more important for the department to keep the existing pavement in good condition-options include crack sealing, spray sealing (applying a thin layer of light, Slowly solidified asphalt emulsion), or repair individual potholes. For pavements that exceed the design life, one option is to grind off the deteriorated asphalt and lay a new rubber asphalt overlay. However, due to the scope of the area that needs to be repaired, this proves to be too costly. Another obstacle to any solution that requires repeated grinding of the asphalt surface is that the grinding equipment will inevitably affect and damage the underlying concrete, and the loss of concrete material at the joints is particularly serious.
What would happen if Arizona returned to the original PCC surface? ADOT knows that the concrete highways in the state are designed to provide long-life structural stability. The department realized that if they could use the underlying PCC to improve its original toothed surface to form a quiet and rideable road, the repaired road might last longer and require maintenance. It is also much less than asphalt.
As part of the project on SR 101 north of Phoenix, the AR-ACFC layer has been removed, so ADOT installed four test sections to explore future solutions that will utilize existing concrete while ensuring smoothness , Quiet riding and good road appearance. The department reviewed diamond grinding and Next Generation Concrete Surface (NGCS), a texture with a controlled soil profile and overall negative or downward texture, which has been developed as a particularly low-noise concrete pavement. ADOT is also considering the use of a sliding grinder (a process in which a machine guides ball bearings to the road surface to improve friction characteristics) or micro-milling to finish the concrete surface. After testing each method, ADOT determined that the longitudinal texture obtained by diamond grinding provides a pleasing corduroy appearance as well as a good riding experience (as indicated by the low IRI value) and low noise. The diamond grinding process has also proven to be gentle enough to protect concrete areas, especially around the joints, which were previously damaged by milling. Diamond grinding is also a cost-effective solution.
In May 2019, ADOT decided to diamond-grind a small section of SR 202 located in the southern area of Phoenix. The 15-year-old AR-ACFC road was so loose and layered that loose rocks were thrown on the windshield, and drivers complained about the windshield being damaged by flying rocks every day. The proportion of loss claims in this region is higher than in other regions of the country. The sidewalk is also very noisy and difficult to drive. ADOT chose diamond-finished finishes for the two right-hand lanes along SR 202 half a mile long. They used a loader bucket to remove the existing AR-ACFC layer without damaging the concrete below. The department successfully tested this method in April when they were brainstorming ways to return to the PCC road. After the project was completed, the ADOT representative noticed that the driver would move from the AR-ACFC lane to the diamond ground concrete lane to experience the improved ride and sound characteristics.
Although not all pilot projects have been completed, preliminary findings on costs indicate that the savings associated with the use of concrete pavement and diamond grinding to optimize appearance, smoothness, and sound could reduce maintenance by as much as $3.9 billion in a year cost. Over a 30-year period. Randy Everett and the Arizona Department of Transportation
Around this time, the Maricopa Government Association (MAG) released a report assessing local highway noise and drivability. The report acknowledges the difficulty of maintaining the road network and focuses on the noise characteristics of the road. A key conclusion is that because the noise advantage of AR-ACFC disappears so quickly, “diamond ground treatment should be considered instead of rubber asphalt overlay.” Another simultaneous development is a maintenance procurement contract that allows diamond grinding The contractor was brought in for maintenance and construction.
ADOT believes that it is time to take the next step and plans to start a larger diamond grinding project on SR 202 in February 2020. The project covers a four-mile-long, four-lane-wide section, including sloped sections. The area was too large to use a loader to remove the asphalt, so a milling machine was used. The department cuts strips in rubber asphalt for the milling contractor to use as a guide during the milling process. By making it easier for the operator to see the PCC surface under the cover, the milling equipment can be adjusted and damage to the underlying concrete can be minimized. The final diamond-ground surface of SR 202 meets all ADOT standards-it is quiet, smooth and attractive-compared to asphalt surfaces, the IRI value was very favorable in the 1920s and 1930s. These comparable noise characteristics can be obtained because although the new AR-ACFC pavement is about 5 dB quieter than the diamond ground, when the AR-ACFC pavement is used for 5 to 9 years, its measurement results are comparable or higher The dB level. Not only is the noise level of the new SR 202 diamond ground very low for drivers, but the sidewalk also generates less noise in nearby communities.
The success of their early projects prompted ADOT to start three other diamond grinding pilot projects. The diamond grinding of Loop 101 Price Freeway has been completed. The diamond grinding of Loop 101 Pima Freeway will be carried out in early 2021, and the construction of Loop 101 I-17 to 75th Avenue is expected to be carried out in the next five years. ADOT will track the performance of all items to check the support of the joints, whether the concrete has peeled off, and the maintenance of sound and ride quality.
Although not all pilot projects have been completed, the data collected so far justifies the consideration of diamond grinding as an alternative to standard grinding and filling. The preliminary results of the cost investigation show that the savings associated with using concrete pavement and diamond grinding to optimize appearance, smoothness and sound can reduce maintenance costs by up to $3.9 billion over a 30-year period.
By using the existing concrete pavement in Phoenix, not only the maintenance budget can be extended and more roads are kept in good condition, but the durability of the concrete ensures that disruptions related to road maintenance are minimized. Most importantly, the public will be able to enjoy a smooth and quiet driving surface.
Randy Everett is a senior department administrator for the Department of Transportation in Central Arizona.
IGGA is a non-profit trade association established in 1972 by a group of dedicated industry professionals, dedicated to the development of diamond grinding and grooving processes for Portland cement concrete and asphalt surfaces. In 1995, IGGA joined an affiliate of the American Concrete Pavement Association (ACPA), forming today’s IGGA/ACPA Concrete Pavement Protection Partnership (IGGA/ACPA CP3). Today, this partnership is a technical resource and industry leader in the global marketing of optimized pavement surfaces, concrete pavement repair and pavement protection. IGGA’s mission is to become the leading technology and promotion resource for the acceptance and correct use of diamond grinding and grooving, as well as PCC preservation and restoration.
Post time: Sep-08-2021