Death Valley California Chip Seal Test
It's a safe bet the drivers of the stone-filled semis were not thinking about the engineering significance of the job as they focused on not letting their trailers jackknife and become airborne over the edge of the steep mountain pass.
“I told the drivers they needed good Jake Brakes, and that whatever gear they went up the hill with, to drop a gear on the way down,” said Jeff Wilmot, chief operations officer of Hardrives Construction Inc. Wilmot was overseeing the chip sealing of some 21 miles of Badwater Road in Death Valley National Park under a contract with Federal Lands Highway (FLH) Division, the road-buildingarm of the Federal Highway Administration (FWHA).
Hardrives' contract is one of four pavement preservation surface treatment projects in California and Utah that FLH is gathering data from as part of a federal “White Paper” study on the use of polymer-modified asphalt emulsions (PME).
Filling A Knowledge Gap
Results of the study, which is being conducted by the National Center for Pavement Preservation (NCPP) under a contract with FHWA and the FLH division, are expected to help transportation officials choose appropriate pavement surface treatments. Although PME are increasingly being used to boost the effectiveness of such treatments as chip sealing and micro surfacing, until now little information has been collected in one place on the proper use, application techniques and benefits of PME in thin surface treatments. The study aims to rectify this, with one objective being the preparation of an FHWA-FLH Division manual that will include current best practices, model test methods and specifications, and recommendations for PME use application.
According to Michael Voth, pavement and materials technical leader for FLH, the jobs – located in California's Death Valley National Park, Dinosaur National Park in Colorado/Utah, and four additional national parks in Utah – were selected because they provided a broad range of conditions: varying climate, different aggregate suppliers, diverse emulsion suppliers, different contractors, and even varying levels of traffic.
Stepping Up To The Plate
An important role in the study has been assumed by industry, said Voth. “Private industry has been a very good partner with us in this effort,” Voth said, referring to both pro bono and at-cost laboratory work provided by the private sector.
He explained that samples of aggregate and emulsions from the projects have been sent to three laboratories – BASF Corporation, PRI Asphalt Technologies Inc., and Paragon Technical Services Inc. – for testing and analyses. BASF Corporation is funding the material testing, in conjunction with NCPP. Chris Lubbers, senior technical service engineer for BASF, is conducting tests at the company's laboratory inCharlotte, NC.
“The labs are running conventional tests plus some proposed new tests for the study,” said Lubbers. “We're trying to get away from strictly relying on the old tests and methods. For example, we'll be trying to validate low temperature recovery of asphalt emulsion residue.” Currently, standard methods used to recover asphalt residue require heating samples to much higher temperatures than those experienced in the field. Lubbers said it would be preferable to be able to test polymer-modified emulsion residue that had been recovered at temperatures typically experienced by surface treatment systems.
Target: Performance Specs
FLH's Voth pointed out that one of the objectives is to see if testing of the same materials by independent labs will produce similar, reproducible and predictable results. Furthermore, the agency will monitor project pavements for a couple of years following completion, checking such characteristics as roughness, cracking and rutting, among others.
Voth said results of lab tests on materials would be compared with observations of actual field performance of pavement preservation treatments over a period of time. Hopefully this will help engineers to predict field performance based on the use of specific types and quantities of materials for given application methods. This could lead to the establishment of performance specifications for pavement preservation surface treatments involving PME.
While data collected from selected projects for the study is expected to have major ramifications for those planning and designing pavement preservation treatments, the immediate concern of Hardrives' truckers and equipment operators on the Death Valley project was safely negotiating Badwater Road as they performed their work.
Sometimes broad and level, sometimes steep, narrow and winding, Badwater Road stretches from the southeast corner of Death Valley National Park about 50 miles northward to the intersection with Route 190 near the Furnace Creek Visitor Center. The section being chip sealed began at Mormon Point, one of the lowest points in the U.S. at 260 feet below sea level, not far from the lowest, Badwater Basin, which boasts an elevation of -282 feet. From this low-lying beginning, the project climbed arduously southward to a few miles past Jubilee Pass, stopping at elevation 1,735 feet.
But this wasn't actually the end of the challenge for the project's truckers.
“The stone chips were hauled from Nevada, and the only place large enough for a stockpile was near Salsberry Pass,” Wilmot said. According to the Park's official map, Salsberry Pass is located approximately five miles beyond the project limit at a point on Badwater Road about 3,300 feet above sea level, or 3,600 feet above the job's starting point. And this significant difference in elevation led to white-knuckle trips for truck drivers heading down the precipitous 20-foot-wide mountain pass towing 30 tons of stone chips.
Many of the roads in Death Valley and other national parks were built in the 1930s and essentially followed the existing terrain. Wilmot said Hardrives has worked in at least 50 national parks and national monuments for Federal Lands, and they have found that the agency likes to keep the roads as natural as possible, which means many of them are very steep. “That's why we use an all-wheel-drive Etnyre QUAD chip spreader for the jobs,” he added.
Not A Summertime Job
Chip sealing got under way onNovember 11 during Death Valley's winter, a period running from November through March with daytime temperatures mostly between 65 and 80 degrees Fahrenheit. Trying to perform road work during summer can be perilous in Death Valley, which has the hottest and driest climate in North America. In summer, daytime highs average 120 degrees, and the highest temperature ever recorded in the Western Hemisphere occurred there in July 1913 when it soared to 134 degrees. What's more, the highest ground temperature was recorded there in July 1972 when it soared to 201 degrees Fahrenheit – hot enough to cook an egg on the pavement.
Large Chips, Generous PME
Wilmot fielded a crew of 24 to do the job, which totaled about 253,000 square yards. The crew labored under a tight schedule, limited by contract to working days between 9 a.m. and 4 p.m. In addition to chip sealing the road, they had to sweep it and haul away the stone sweepings, and then follow up with an asphalt fog seal. Workers applied about 425 tons of CRS-2 latex-modified asphalt emulsion, supplied by Western Emulsions' Irwindale, CA, plant, at the rate of 0.4 gallons per square yard. The latex was a styrene-butadiene-rubber (SBR) product. An even higher rate, about 0.42 gallons per square yard, was used where existing pavement was more oxidized or had recently undergone patching or overlay.
Application rates were generous according to Wilmot. “Federal Lands likes large chips – in this case up to 30 percent retained on a 3/8 sieve, so it takes more emulsion,” he said. The contractor spread stone chips, supplied by Wulfenstein Construction of Pahrump, NV, at an average rate of 22 pounds per square yard. For compaction they used two Roscoe 15-ton pneumatic rollers and a Dynapac pneumatic roller.
Preserved RoadAnd Useful Data
Despite the challenges of steep grades, narrow roadway and restricted working hours, Hardrives completed the project in just five days.
Not only does this project ensure that the pavement, which was showing signs of distress, will be preserved for an estimated eight years before requiring another treatment, it is providing valuable information that will lead to long-term improvements in the planning and design of pavement preservation treatments utilizing PME.