By: Mike Douglas and Gary Williams
The Nevada Department of Transportation (NDOT) has long been a proponent of the use of cold in-place recycling (CIR) as a strategy to optimize its pavement preservation program. CIR has proven to be a very cost-effective strategy in Nevada for asphalt pavement experiencing medium- to high-severity non-load related cracking. NDOT has completed almost 1,000 lane-miles of CIR in the past decade and has a lot of experience with this type of rehabilitation treatment. This strategy has known advantages such as minimizing user delay and is more environmentally sustainable. In addition, the national trend away from new construction to the preservation of the existing highway system is requiring NDOT as well as other highway agencies to seek alternative approaches to pavement preservation that will conserve resources. Recently, NDOT pushed its CIR experience to the limit by requiring a CIR with overlay rehabilitation strategy on Rte. 207, Kingsbury Grade, near Carson City, Nev.
Kingsbury Grade is a mountainous road with steep grades and tight curves that connects the Carson Valley to Stateline on the south shore of Lake Tahoe. This road is situated in an area that is exposed to extreme temperature changes, significant snow levels and an elevation rise of 2,500 ft over 7 miles. Reflective and thermal cracking are major causes of pavement deterioration on this roadway, and the most effective options for eliminating the wide transverse cracking or preventing reflective cracking are to either completely remove the plant mix or recycle the existing plant mix. Since complete removal is not a cost-effective option, a 3-in. CIR with a 3-in. plant mix bituminous surface overlay was decided as the best course of action to rehabilitate this section of roadway.
The project was awarded to Q&D Construction Inc., a company that is a newcomer in the recycling business. Despite having nominal experience with CIR work, the company took a very active approach to ensuring a successful project through discussion with industry experts, hiring an experienced recycling subcontractor, utilizing their most experienced personnel and using state-of-the-art paving equipment.
Before you start . . .
Effective communication and preconstruction planning are very important for achieving successful CIR projects. Both Q&D and the CIR subcontractor personnel from Valentine Surfacing Co., along with the assigned NDOT construction crew, attended a two-hour training and informational workshop provided by NDOT staff. This workshop was designed to address all relevant aspects of the CIR process as well as any special provisions.
The workshop included the review of a checklist that lists all preconstruction and construction requirements required for a successful CIR project. Topics included weather conditions, plans, equipment and train calibration. Core reports, samples and testing, and lay down and compaction were reviewed in detail. The discussion about lay down and compaction was divided into 14 subtopics that covered everything from control strips for compaction to the use of the nuclear gauge for quality assurance testing.
All topics were freely talked about in a round-table discussion. There was an atmosphere of cooperation that was to linger throughout the duration of the project. Expectations about how the work should be accomplished were made known and any anticipated problems were brainstormed until reasonable solutions were agreed upon. This preconstruction communication was crucial to getting the project off to a good start.
Preventing runaways
Q&D’s primary concern about this project was safety . . . given the use of the massive 25-ton pneumatic rollers required on the steep and winding road. The potential for runaway rollers or other equipment was a continual cause for concern, and workers maintained vigilance throughout the process.
Several precautions that were used to ensure safety and production were to have extra equipment on standby, experienced equipment operators and an experienced mechanic on staff during the entire operation. There also was the challenge of placing the precise amount of sand blotter that would prevent sticking and pulling and yet not so much sand to leave a slick surface on the steep graded roadway.
Numerous road cuts with high walls having the potential for rock falls are present on this stretch of roadway. However, no significant rock fall was encountered even though the energy of the milling and compacting operations could be felt in the ground over several yards from the work.
The use of the recycle train on a roadway with such challenging geometrics had never been tried before at NDOT. It was decided that recycling the roadway would be possible if the recycling train were to travel downhill. Knowing that the cold recycle train could only travel downhill presented an additional consideration for engineers tasked with the responsibility for reducing traffic restrictions. This concern was overcome by use of 24-hour traffic control operations.
From the planning stage forward, public safety and the potential for public travel restrictions were of major importance on this project. During the recycling operations, Q&D maintained a 24-hour pilot car operation with flaggers at either end of the restriction. This kept traffic speeds down and resulted in a safer environment for both the contractor personnel and the traveling public. Use of 24-hour traffic control allowed for the recycle train to remain intact and on grade throughout the recycling process. Therefore, no time was wasted tearing down and setting up every day. Another benefit of 24-hour traffic control was the completion of the recycling in 10 days.
The new cold recycled road surface was very stable and able to withstand traffic for several weeks without experiencing deformation or any other distresses. The result was a very well-prepared work surface for final paving, with minimal safety issues throughout the construction operation.
The traveling public is very impressed with the outcome of the rehabilitative effort on Kingsbury Grade and has expressed numerous positive comments to NDOT. This project was successfully completed because of the hard work and dedication that took place between Q&D’s Mike Paquin and Barry Baker, Valentine Surfacing Co.’s Randy Thompson and NDOT’s Resident Engineer Gary Williams. Effective communication along with the shared values of placing safety first and producing a quality product were sufficient enough basis to result in a noteworthy accomplishment when stretching recycling limits.
About The Author: Douglas is a project manager at Q&D Construction Inc. Williams is a resident engineer with the Nevada DOT.
