In the mix

Jan. 28, 2009

Two challenging recycling projects have received recognition for achieving their goals of maximizing results while minimizing costs. The city of Santa Ana, Calif., received the Roads & Bridges/Asphalt Recycling & Reclaiming Association Recycling Award for its cold in-place project, Delhi and Willard Residential Neighborhood Improvements, and the City of Mequon, Wis., received the award for its hot in-place project, 2008 Hot In-Place Recycling/Boiler Slag Seal.

Two challenging recycling projects have received recognition for achieving their goals of maximizing results while minimizing costs. The city of Santa Ana, Calif., received the Roads & Bridges/Asphalt Recycling & Reclaiming Association Recycling Award for its cold in-place project, Delhi and Willard Residential Neighborhood Improvements, and the City of Mequon, Wis., received the award for its hot in-place project, 2008 Hot In-Place Recycling/Boiler Slag Seal.

The City of Santa Ana in Orange County was determined to find a better solution to roadway rehabilitation than conventional remove-and-replace strategies. Street rehabilitation, representing a large share of city expenditures, was an obvious candidate for recycling.

The project involved 50-year-old streets that had seen better days. At first, conventional reconstruction methods were considered for this project, and a soils report recommended extensive full-depth base repairs in addition to a relatively thick overlay. In response to a city council desire to implement green technologies into construction and reduce the cost, recycling the roadways was determined to be the best option.

The section selected was to header cut at the gutters, cold in-place recycle (CIR) 3 in. of the existing asphalt, and then cap with an inch of Hot Mix Asphalt (HMA). The project had a rocky start, with the CIR equipment getting bogged down in a soft and wet subgrade.

“By coincidence, the CIR was started on the worst two streets with respect to this soft subgrade issue,” Don Matthews, division manager for Pavement Recycling Systems Inc., told Roads & Bridges. “The first street we could not CIR at all as the train kept breaking through into the subgrade.” The worst areas were removed and replaced with a deep lift of cold central plant recycled (CCPR) asphalt produced from the header cut millings. However even the repair areas showed signs of distress in some areas upon traffic loading.

“By coincidence, the CIR was started on the worst two streets with respect to this soft subgrade issue,” Don Matthews, division manager for Pavement Recycling Systems Inc., told Roads & Bridges. “The first street, we could not CIR at all as the train kept breaking through into the subgrade. The second street was able to be recycled, but the train still broke through in many areas.”

This led to some questioning as to whether CIR was the right process for this project. The entire construction project and construction methods were reviewed. Santa Ana concluded that CIR had promise, but was not applicable in all circumstances. The city decided to continue, but cautiously. Prior to proceeding on the remaining streets, dynamic cone penetrometer was utilized for additional coring to investigate the relative strength of the subgrade. Over 90% of the streets were determined to be suitable for the CIR train and related construction traffic. The CIR process resumed with an occasional subgrade failure in isolated areas. These isolated failed areas were removed and replaced with a 6-in. CCPR material to bridge the soft subgrade. The city determined that even if some areas of the sections being recycled were marginal, the ultimate cost savings were substantial.

On the two streets that did not have enough structural integrity for the CIR process, the city was still determined to do some type of recycling as opposed to removal and deep lift HMA. Full-depth reclamation was selected to repair these streets with an 8-in. section of cement treated followed by an asphalt overlay.

What impressed the City was how well the recycled mat performed in areas with stable subgrade. And the job was deemed a success, as evidenced by the approximately 40% cost savings over conventional reconstruction methods and that 100% of the old asphalt originally planned to be removed was actually reused onsite.

The 2008 Hot In-Place Recycling/Boiler Slag Seal project also was a success and claimed the Roads & Bridges/ARRA Recycling Award in the hot in-place recycling category.

The city of Mequon has a pavement management system where all streets are given a surface condition rating based on what type of treatment each pavement needs. The city felt it was doing a good job at preventive maintenance like crack sealing and seal coating for streets already in good condition, but they were falling behind with the streets that needed more extensive rehabilitation.

“Our streets were deteriorating faster than we could rehabilitate them,” said Timothy J. Weyker, engineering technician with the city of Mequon. “We needed to try to address streets that are beyond routine maintenance, but can still have their pavement life extended before they need total rehabilitation.”

Hot in-place was chosen basically to save money, both in the short and the long term, said Weyker. The city has over 200 miles of asphalt streets to take care of, and with the near 40% increase in the cost of asphalt starting in 2006, they needed to find other alternatives.

“Hot in-place seemed to fill the gap,” Weyker said. “By rejuvenating the existing asphalt, we were able to get much more done for far less money. Long term, we hope to be able to extend these pavement lives so that we can catch up on the streets that need total rehabilitation.”

The streets were first evaluated to determine if any drainage improvements were needed. City crews replaced cross-road culverts as needed and then the trenches were patched in with asphalt. Then the contractor, Gallagher Asphalt, performed the hot in-place recycling, which involved giant infrared heaters. One heater pre-heated the pavement, and the next heater had multiple rows of spring-loaded “scarifiers” to penetrate the softened asphalt to the desired depth, which was approximately 2 in. During the process, a rejuvenating asphalt modifier was added to the existing material. That material was then redistributed with augers and leveled with a conventional paver screed, then rolled.

When Gallagher Asphalt was finished with their part, Scott Construction moved in and seal-coated the streets. After sweeping up the excess aggregate from seal coating, the streets were finished. Because the city was not adding any new asphalt layers, no shouldering work or driveway matching was required. One-hundred-percent RAP was used, and the cost savings was $575,000.

The biggest challenges were determining what streets were best suited to the project and keeping the public informed on what was happening, Weyker said.

“We try to use hot in-place recycling on streets that have adequate base material and a pretty good existing cross section. We core through the pavement and base to determine thicknesses. If we don’t have adequate base, other rehabilitation, like full pulverizing and paving, would be required.”

As for keeping the public up to date on the situation, Weyker said letters were sent out to the residents of the streets where the work is performed so that they stay informed on the process.

Another challenge was to make sure the streets got swept thoroughly when finished. “People like the finish of the rejuvenated pavement prior to seal coating, but hot in-place recycled pavement needs to be sealed by a seal coat or an overlay,” Weyker said. Signs were placed to advise people to drive slowly until the excess aggregate was swept up.

Both the hot in-place recycling and the seal-coating processes were user-friendly when it comes to the traveling public, Weyker said. “The recycling process moves along like a train of equipment and rejuvenates one lane at a time. After the train goes by, the new pavement can be driven on. The only traffic control required was flaggers. The seal coating was done full-width. Again, after the equipment passes, the street can be driven on.”

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