Cutting across the northern third of the state, Interstate 40 in Arizona is 360 miles long. All across the state, I-40 is under a heavy load, serving between 20,750 and 27,600 vehicles each day, according to Arizona Department of Transportation figures. A high percentage of that is interstate truck and tractor-trailer traffic.
Under this strain, the aging interstate has reached the point of needing major repair. "We had a serious problem because of bad weather in the winter of 2004," says Ed Wilson, senior resident engineer with ADOT's Holbrook District. "The Department of Public Safety had to close sections of the road because there were so many potholes."
These sections of road are located between McCarroll and Querino, and Querino and Hawthorne. In the fall of 2005, the Querino to Hawthorne project was in design but was accelerated because of the urgent need to fix the road. Spot milling and filling was done on the McCarroll to Querino section of the road that had potholes to allow time to obtain funding and design the corrective project. The Querino-to-Hawthorne project covered 11 miles of eastbound and westbound traffic.
A second previous mill-and-fill project was a 12-mile stretch between Pinta and McCarroll. Meadow Valley Contractors Inc. was now contracted by ADOT to mill and fill an 11.7-mile section between McCarroll and Querino, linking the previous projects.
Wilson says sections of roadway renovations are scheduled based on need, not years in service. These three sections happened to be in need of repair and connected to each other. "State materials personnel come to the Holbrook District, where these projects are located, every year and go out with the district engineer and drive all of our routes," says Wilson. "They prioritize what roads need to be repaired. There's only so much money allocated every year to pavement preservation, so roads are monitored to see where they can get the best use of that money."
Harry Camptell, project manager for Meadow Valley Contractors, is familiar with the section of Interstate 40 now under reconstruction. "About 20 years ago, I was on the crew that rebuilt this section of road," says Camptell.
Asphalt technology has changed dramatically since then. Camptell says the approach to creating an asphalt mix was much different. "In those days, there was a lot of experimenting with using sand and rounded particulates. We looked for sand and gravel sources. Today, we look for rock sources. The quest now is to find particulates that are angular, and to use less rounded sand particulates," says Camptell. "We know that the round aggregates in the mix didn't make asphalt pavements as stable as they should be. The mixes today are highly stable because of the angular rock."
When the road was last rebuilt, Superpave had not yet been developed. On the current project, when the old asphalt is milled out, it is replaced with a Superpave mix. The current rehabilitation of the road contains two phases. The first phase includes the mill and replacement of the deteriorated asphalt, replacement of 14,000 feet of guardrail and some concrete work on three bridges in each direction. The second phase involves the placement of an asphalt rubber friction course on the new asphalt. The second phase was to be completed during the summer of 2007.
As the project progressed, the crew from Meadow Valley would begin each work day at 2:00 a.m., with milling operations continuing until 11:00 a.m. At 8:00 a.m., the paving crew would start its nine- or 10-hour shift. Asphalt was produced at an asphalt plant on-site.
Five inches in the passing lane and 6 inches in the travel lane are milled and replaced. "We are milling out into the right shoulder because one of the problems we have is the old rolled-in rumble strip on the right shoulder is coming apart," says Wilson. "The project is set it up so 2-1/2 inches of that section is replaced, about 4-1/2 feet wide. We mill out the travel lane and shoulder and put a 3-1/2-inch lift into the travel lane. Then, we pave the second 2-1/2-inch lift in the travel lane along with the 4-1/2-foot-wide shoulder in one pass."
Meadow Valley is using a new Ingersoll Rand PF-5510 paver to lay the asphalt. "We started with three compactors, but we dropped to two because we are getting proper compaction from just two," says Camptell. An Ingersoll Rand DD-138HFA is used as the breakdown compactor and an Ingersoll Rand DD-118 is the finish compactor.
One of the challenges encountered on the project is working around the port of entry, located on the westbound side of the road. The port of entry includes a concrete slab that weighs trucks as they pass by on the roadway. Paving was done around these slabs, and the electronic sensors in the asphalt around the slab were replaced. "We had to replace a series of loop detectors and piezo sensors that are also used in the weighing and truck-handling process," says Wilson. "To accommodate this rehabilitation, port of entry activities were temporarily reduced and relocated to Holbrook."
The rubber friction course was laid this construction season because work on the project was suspended over the winter months due to temperature constraints. This course consists of asphalt rubber and is placed on freeways throughout Arizona. "It provides a lot of friction, which is needed in this part of the state because we get a lot of snow and ice here," says Wilson. "The rubber friction course is smoother and it helps protect the base asphalt courses by sealing out water."
This rubber friction course is applied the entire width of the roadway, including the shoulders, because of the snow and ice that accumulate on the road in the winter. "If this course was paved only inside the lanes, the snowplow would catch the friction course and damage the edges when clearing the 10-foot and 4-foot shoulders. That's why we pave the friction course at full width, to keep everything level across the 38 feet and prevent the snowplow from damaging it," says Wilson.
The fact that the rubber friction course can stand up to the rigors of the snowplows and tractor-trailer traffic, laid in thicknesses of just 1/2-inch or 3/4-inch, is a testament to its strength and durability. The rubber friction course is also versatile. It is used in lower elevations in Arizona, in metropolitan areas, for sound reduction purposes as well as for friction.
According to Camptell, paving the rubber friction course is different than other asphalts. "Because the rubber friction course is more abrasive we have a spare screed plate on hand when paving this material," says Camptell. The friction of the material against the screed wears on the equipment. Camptell expects that he will go through two screed plates while paving the rubber friction course.
Compaction is also different for rubber friction mixes. The ADOT spec does not allow the rubber friction course to be paved any wider than the width of the breakdown compactors provided, which usually requires a minimum of two breakdown compactors. Compactors work in static mode, since the material is in a thin lift. "The compactors don't work in tandem. They only go forward and never back up because there isn't a density requirement to this material. A second, finish compactor works to get all the marks out," says Camptell.
There is a smoothness bonus associated with the project. To Camptell, there is one thing that his crew does to ensure they achieve the bonus. "The number one thing in paving is consistency. The paving equipment runs consistently with the production of the asphalt. The paver is never stopped and runs at the same speed all day. The hot plant keeps a consistent speed of production," says Camptell.
The new roadway is expected to last 10 to 15 years. After that time, Wilson predicts a more extensive rebuild of the road will need to be undertaken. Now, 30 miles of Interstate 40 in northeast Arizona has been renewed due to the three recent ADOT projects. While 30 miles is a small percentage of the thousands of miles Interstate 40 covers, the rebuilding of this section of roadway will ensure more efficient transportation of people and goods across this important route.