Pennsylvania Partners to Recycle More
BY Sandy Lender
According to the March 2018 Reclaimed Asphalt Pavement Optimization Study prepared by Gibson-Thomas Engineering, Camp Hill, Pennsylvania, on behalf of the Pennsylvania Department of Transportation (PennDOT) Bureau of Maintenance and Operations, the urban districts in the commonwealth have “an ever-increasing amount of reclaimed asphalt pavement (RAP) being generated (mainly from pavement milling construction projects).” The authors of the report stated: “Based on the responses to Question 1 of the initial questionnaire, the tonnage of clean RAP that is currently stockpiled in each district varies throughout PennDOT’s 11 districts, from a high of 688,121 tons in District 1 to a low of 27,700 tons in District 9. The current statewide total tonnage of clean RAP is 1,043,092.”
This presents the challenge to include RAP in more projects at higher percentages while keeping quality top of mind. Special Advisor to Transportation Secretary Leslie Richards for Strategic Initiatives, Scott Young, explained the department looked at successes with RAP seen in District 1 and is now applying those best practices in additional districts. One of those practices is to use recycled asphalt pavement (RAP), via a cold mixing unit from Pugmill Systems Inc., Columbia, Tennessee, to create flexible base pavement for low-volume roads. The vision, Young shared, is to produce about 100,000 tons per year in each district.
“We use 100 percent recycled asphalt in our low-volume roads, which meet the criteria of 3,000 average daily traffic (ADT) with 10 percent truck traffic,” he said. And he explained how the high-RAP mixes can be produced and placed with DOT personnel and contractors working side by side.
Partner to Place High-RAP Cold Mix
What Young described as a success in District 1 is the use of a pugmill to create flexible pavement mixes with stockpiled millings, and then use the high-RAP mixes for a variety of maintenance and other projects. “We don’t just use the RAP for paving,” Young said. “We also use it for widening, shoulders, base repair, shoulder back-up as well as screening the #8 stone for our seal coat programs.”
The machine in use in District 1 is the portable pugmill plant from Pugmill Systems. Jaren Allen, vice president of Pugmill Systems, has employees who assisted in training PennDOT field staff in its use. Allen spoke highly of their willingness to learn and take on the specific stage of a project that the pugmill introduces. PennDOT developed a 75-hour training program for this purpose, according to Young.
“The training focuses on stockpile set-up to include proper storage and handling of the RAP material to best utilize efficient and effective operations to include safety features identifying truck spray down areas as well as ingress and egress to maximize safety and efficient movement in confined areas,” Young explained.
A long-range RAP strategic plan has also been deployed over a 10-year period focusing on projects that generate RAP for all uses. This is key as it identifies a RAP network and creates a cycle to prompt department force prep work to be completed prior to the next scheduled overlay, Young explained. In addition to the RAP-generation exercise, the quantities identified will indicate the availability of surplus RAP, which is given back to the industry for use in high RAP warm-mix asphalt mix designs, further passing along the savings to customers.
Allen’s company offers several models of the portable plants ranging from 5 to 1,500 tons per hour capacity. Young said the districts sharing the machines target daily production ranging from 1,000 to 2,500 tons a day, and will continue to move up to the higher range as the expertise, planning and logistics are further refined.
For 2018, Allen said PennDOT has purchased an additional pugmill that the districts share. Young explained that six counties in the northwest part of the commonwealth have been placing RAP mixes with pugmills both rented and department-owned for a better part of the last 35 years.
“The current paving program places 100,000 tons per year,” Young explained. “In its peak, District 1-0 was placing over 200,000 tons per year as part of a program to eliminate gravel roads. The plan for the three new pugmills is to share them throughout the Commonwealth as part of a Regional Equipment Sharing
Innovation. The idea of sharing resources in this way, as well as other operations, lends itself to rightsizing the fleet in an effort to save capital and refurbishment costs to be utilized in other areas of our business.”
Because the pugmills are portable in nature, the districts schedule when they need a machine. Young said mobilization, which includes set-up and calibration, takes the crew about two days. Using a Gantt chart, the PennDOT scheduler knows where the districts have RAP capacity, how much work is available and what kind of work is to be done.
RAP is always the key ingredient. Seeing about $5 million in savings per year in Northwest Pennsylvania (District 1) using RAP for paving, base repair and widening, the return on investment for one machine is about one year, according to Young.
“The savings in this one engineering district is what prompted the Governor and Secretary Richards to expand this to the other 10 engineering districts and create the Commonwealth’s Road Maintenance and Preservation initiative (known as Road MaP).”
While PennDOT field staff man the pugmills, contractors in the state aren’t left out of the picture. “There’s more than enough material for everyone,” Young stated. “There’s more demand than time. We have capacity to do the work.”
That work includes maintaining and preserving the rural, low-volume roadways as well as the urban roadways. “We’re very mindful of extending pavement life with the right treatment at the right time,” Young said.
To work alongside PennDOT, contractors are crushing RAP onsite and loading directly into the pugmill. Trained PennDOT workers use a crusher and screen the incoming material as it is fed into the pugmill. An E8 oil is typically added at 9.2 to 9.7 gallons per ton with 1 to 1.5 gallons per ton of water. The E-8 working temperature range for placement is between 90 and 150oF. The 100 percent RAP mix is typically produced between 200 to 300 tons per hour.
“It’s not the same as hot-mix asphalt,” Young said. “You can still lute it and adjust it, but unlike hot mix asphalt, the rollers will need to stay off the mat for about 45 minutes. When you start your rolling pattern too soon, you may see it brings the oil to the top of the mat and causes a bleeding problem. Working with this mix will be quite a learning curve.”
“We have a hybrid project scheduled in Southwest Pennsylvania this year where a contractor is milling an interstate project adjacent to a RAP candidate road,” Young said. “The contractor is going to mill and deliver the RAP to our stockpile, crush and size it into our pugmill. The contractor will haul the mixed RAP from our pugmill onsite and place it via their paver and crew.”