For any asphalt recycling endeavor, each project owner must determine the method best suited for the particular pavement.
The hot in-place asphalt recycling (HIR) option, though a less common method for hot asphalt recycling, appeals to some asphalt paving project owners for its more convenient and less disruptive approach.
According to James Campbell, the division manager for Topeka, Kansas-based paving contractor Bettis Asphalt’s HIR group, there are a few typical rationales given by an agency for choosing a hot in-place recycling approach over alternative methods. “One of them is that DOTs get concerned about the amount of waste that’s generated from their standard operations,” Campbell told Roads & Bridges. “So the recycling part of the hot in-place recycle, it’s 100% recycle. The only thing that’s added is some emulsion that gets the old asphalt to come back alive.”
Another reason Campbell often hears for selecting HIR is that a standard mill-and-inlay job requires an excessive amount of load put on the roadways along the project footprint as a result of trucks driving back and forth carrying milled material or hot-mix asphalt. Some states also do not have a hot-mix asphalt plant in close enough proximity to a particular project site or lack access to an aggregate supply. “When you do a hot in-place recycle, you don’t need any of that stuff, and by the time we’re done, that road looks brand new,” Campbell said. “So it’s actually a sense of convenience. And this process is quite a bit cheaper than, say, a standard process of milling and inlaying.”
Moving things along
In the summer of 2019, Bettis Asphalt served as the HIR contractor for the Colorado DOT’s (CDOT) 23-mile asphalt recycling project along SH 141 between Whitewater and Gateway, south of Divide Road. This project consisted of a 2-in. HIR and a 1.5-in. hot-mix asphalt (HMA) overlay. The two-lane highway has lane widths of 11 ft each, and CDOT had to add 2-ft shoulders, with some areas getting wider shoulders to accommodate bicycle traffic.
“This [area] has a striking landscape with rivers, tall canyon walls, red rock features, and then there’s mountains in the distance,” Elise Thatcher, CDOT Region 3 Communications Manager, told Roads & Bridges. “So this is really where recreational tourism is starting to take off in Colorado, like in other parts of the state, but it’s pretty critical for the local economy.”
CDOT initially decided to carry out the hot in-place recycling operation since it was determined to be a less expensive and more environmentally friendly option. According to Bettis Asphalt, the existing pavement was riddled with alligator cracking and severe fatigue, which required the in-place material to be recycled and the road to be repaved. “The road was in pretty bad shape,” CDOT Project Engineer Damian Leyba told Roads & Bridges. “I think it’s been 15-20 years since that road had any attention drawn to it. And our CDOT maintenance folks have patched it here and there with chip seals and a little bit of asphalt to keep it maintained and drivable.”
For CDOT, one of the biggest obstacles for completing this project, which began in April 2019, was managing a one-lane closure along the two-lane SH 141. This proved to be particularly arduous since the roadway serves as a major connection to the Gateway Canyons Resort, which attracts plenty of tourism that generates vehicular as well as bicycle traffic coming from Whitewater on a regular basis. “We had to communicate with the resort, because they had bicyclists coming from Whitewater all the way up to Gateway Resort twice a week,” Leyba said. “So that meant they had to go through our construction zone, so we were constantly coordinating the one-lane closure with the Gateway Resort community and the fire department for emergency services.”
Additionally, CDOT had to coordinate with other stakeholders throughout the project’s duration, which included 90 landowners along the project footprint. The agency also had to coordinate with Colorado Parks & Wildlife as the region sees significant levels of elk and deer migration, for which CDOT made sure to minimize impact.
For the project’s timeline, CDOT estimated the entirety of the work in the field would take 110 working days to complete.
Laying it down
For the asphalt testing process, CDOT had a quality assurance (QA) lab set up in Whitewater, while prime contractor United Companies had a quality control (QC) lab. The two labs would share test data in a timely manner in order to see a quick turnaround time, usually by the following morning, to ensure a quality mixture on the roadway.
During the HIR portion of the project, Bettis Asphalt submitted a method statement showing a production rate of 1 mile per day. However, when construction began, Bettis averaged 2.5 to 3 miles per day, far exceeding the initial method statement. Work for Bettis included placing approx. 360,000 sq yd of HIR along SH 141. When the HIR was complete, there were approx. 75 mat densities taken, all of which were in specification of 91-97% or fell under the breakover spec showing the maximum density before breaking over. In some areas along the project footprint, the elevation was at over 7,800 ft, making it difficult for mat densities.
For Bettis Asphalt, one of the biggest challenges was mobilizing the eight hot in-place recycling machines into position. “It was a canyon road, so it had all the challenges that come with canyon driving,” Campbell said. “So you have a changing altitude and sharp curves in it. And these machines are roughly 70 ft long, and there’s eight of them that had to be mobilized into position. So initially that was a challenge for us, but by the time the project was over, we found a mechanism that allowed us to do that very well and safe.” The contractor also found the narrowness of the canyon road and the ability to move the HIR machines along some tighter road-bending to be a challenge.
During the 1.5-in. HMA recycling portion of the project, the HMA contractor United Companies was allowed to use 23% RAP in its mix. The prime contractor stayed below that percentage. “The admixture that we had going into the heater remix was 20% RAP,” David Fife, quality control manager for United Companies, told R&B. “When we did the top lift over the top of the heater remix, we had 15% RAP in that mixture.”
United’s role included adding 18% HMA to the pavement in order to help with the widening of the road and level out any smoothness issues at the bumps. “So we were adding HMA to the treatment to try to compensate for any holes or pits,” Fife added. “So basically we were milling up a certain width, and then we also laid it out 2 ft wider, so we had to add some asphalt to compensate for that.” Fife explained that his team also used an Ergon ARA 2P rejuvenating agent to revitalize the existing asphalt. Once Bettis Asphalt began their work on the project, United Companies supplied them with HMA as Bettis came through the project through a heater-refire process. Once that was complete, United came over the top with a 1.5-in. HMA overlay.
When construction began on this part of the work, the contractor submitted a method statement showing 1,200 tons per day. The actual tons per day in the field came to about 1,900, again exceeding the method statement. United Companies was also subject to mat densities ranging between 92-96%. There were approx. 62 mat density tests taken on the project, and 95% of all mat densities were within specification. The contractor was also subject to a HMA-MRI Category III smoothness specification. The average MRI achieved on the project was 53.15, and United received a $329,240 incentive for smoothness.
Depending on where along SH 141 the team was paving, the transporting time from the project site to the lab could be anywhere from a half hour at the top of the project closer to Whitewater, to over an hour from the end of the project near Gateway. Whenever samples had to be run over to Grand Junction, about another hour was added to the transporting time. Transporting distances from the HMA plant to the project site were approximately 40 miles roundtrip.
Overall, the SH 141 asphalt recycling project between Whitewater and Gateway proved successful, finishing ahead of schedule and under budget with no accidents reported along the project during its lifetime.
This was achieved in part through CDOT and the contractors’ commitment to maintaining a culture of safety. “We really wanted to keep people aware of the dangers of the process, not only the equipment running down the road, but also the traffic going through the project,” Fife said. “We had our morning meetings to discuss the daily hazards. So we spent quite a bit of time discussing how we were going to prevent some kind of incident or accident at certain phases of the project ahead of time. There’s a pretty good curve on the back end of that project where sight is limited, and so I think there was quite a bit of conversation about how we were going to bring that train around the corner and try to do that safely.”
The project finished approximately three weeks ahead of schedule on Oct. 2, 2019. Maintaining a safe work environment and overcoming the number of challenges it did earned the SH 141 project a spot on this year’s Roads & Bridges / ARRA Recycling Awards for the Hot In-Place category.