Rebuilding better gravel roads more efficiently
First publishedin World Highways
The unit fits on the front of a conventional wheeled loader
Using a linear road crusher can rebuild gravel roads using material onsite at a fraction of the cost of conventional methods
Gravel roads are common in many rural areas in the US to provide access to temporary work sites and are also used widely in developing countries. Maintaining and repairing these roads can pose challenges and new methods may offer improvements in efficiency.
A commonly used gravel road repair and road building approach is to remove oversize rocks and bury subgrade problems, such as potholes or protruding rock, under additional gravel. But this approach does not deal with underlying problems and is costly. It can require hauling in 200-300% more material than actually necessary to resurface a gravel road, only to have the problems resurface at a later point.
Around 50% of the cost of any gravel road project comes from hauling in material. In the US it can cost roughly US$10,000 to rent a mobile crusher at a nearby pit and this cost can quickly rise if pit permitting and development is required. While the cost of obtaining permits in developing countries may be lower, distances between construction sites and quarries can be large and transportation costs can be high.
While using a pit crusher makes sense on massive highway projects and where stringent aggregate specifications for structures like bridges are well justified, there are better, more economic options for gravel roads, particularly remote ones.
In the US, Sweet Grass County, Montana depends on good gravel roads for much of its timber, oil, mining, and agricultural transportation. But maintaining these gravel roads was becoming too costly and difficult using conventional methods. “Previously, we used pits or when the haul got too far, we’d push shale rock on the road and run it over with vibratory rollers, trying to break it down to make a driveable surface,” said Cory Conner, Sweet Grass County, Montana Public Works director.
Instead of burying near-surface subgrade problems under excess gravel from a pit, some counties, road contractors and timber, oil, or mining companies are discovering that linear crushers can repair a gravel road at lower cost, while correcting underlying subgrade problems.
Unlike mobile rock crushers that are stationary when operating, linear crushers move along the road being repaired, crushing oversize rock along it in a crushing chamber. The oversized rock, existing gravel/crushed rock, and natural fines (soils) are windrowed together and processed through the crusher in one pass. This leaves the reduced material in place as a stable crushed layer. When used in on-road repair, it can help achieve aggregate lock, a natural binding of soil and gravel when wet. This can prolong the life of the road surface beyond that of cleaner gravel from a pit, which typically lacks soil mixed in as a binding agent.
Vanway claims its crusher units help improve gravel road quality while reducing maintenance costs
Unsatisfied with the traditional approach to maintaining gravel roads and concerned about shortening the lifespan of the county’s vibratory rollers, Conner favored the linear crusher approach. After watching demonstrations of two on-road crushing systems, he chose a wheeled loader-based design over a tow-behind design. “The tow-behind design would’ve required us to buy a dedicated tractor for about $400,000, while the Vanway linear crusher works with the front loaders we already have,” Conner said.
Vanway International makes linear crushers capable of crushing any rock including construction grade rock (110-210MPa compression strength) such as trap rock like basalt and gabbro, as well as quartzite, granite, and dense limestone. “The tow-behind also did not blend fines or crushed rock so we would’ve had to do that manually,” Conner said. “The Vanway, however, can uniformly crush rock to the size we need, and blend it with fines so we can just blade it, roll it out, and call it a finished product.”
According to Conner, properly blending fines and crushed rock with the linear crusher is critical for Sweet Grass County to achieve the good gravel road surface sought. “Without blended crushed rock and fines, you’ll get rock pockets, rocks kicking out, washboard, or potholes,” he said. “Half your road will be a muddy mess, half will be nothing but rock because the fines will turn to mud or slime when really wet. When you lay crushed rock and fines in the right blend, you get a good, lasting driving surface that won’t easily dust up, kick off rocks, or allow water penetration and damage to the road surface.”
Connor said, “Compared to our typical gravel road cost of about $20,000/lane mile hauling from a pit, we expect to rehab the same road for about $5,000-$7,500/lane mile with our Vanway linear crusher. We should be able to do about 2-3 times the road repair we’d done previously with the same crew, while extending the lifespan of our roads and vibratory rollers.”
Travis Clark, operations manager for Roadtech, a contract road construction firm based in St Maries, Idaho, also relies on a linear crusher for cost-effective gravel road repair and construction. “Compared to burying a road’s subgrade problems with gravel from a pit crusher, we can often repair the wear surface and correct subgrade problems for up to 66% savings with our Vanway linear crusher,” he said.
“All that material that’s been pushed off the edge of the road for years – from ditches, berms, subgrade, oversize – becomes our lift material,” he added. “Our linear crusher usually runs at a cost comparable to a pit crusher, but doesn’t need a pit, have set-up costs, or need to be permitted.”
According to Clark, when building remote gravel roads for timber, oil, mining projects, the cost of hauling in gravel can quickly escalate the cost. “The farther away the road from the pit, the higher cost; and the more remote the road, the fewer the pits,” Clark said. “That’s when your price/mile of gravel road goes through the roof.”
“Fortunately, with a linear crusher your price stays constant,” he added. “Without the material hauling cost, it costs the same/mile. This allows our Vanway linear crusher to do remote projects for the same price you would pay for a local project.”
Clark said that for years a timber company in St Maries, Idaho had been struggling to keep a steep stretch of single-lane, gravel road in shape with traditional blading and dust abatement.
The Vanway machine is said to be productive, powerful and durable in use
“For heavy logging truck use, the consistent 15+ road grade was challenging, the road profile was off, the aggregate was loose, and a big outcrop of rock near the top of the hill required lifting the road profile to go up and over it,” he said. “There weren’t enough fines in the road to bind the aggregate together, so dust abatement didn’t work very well.”
The conventional approach would be to haul dirty gravel onto it, but that would have been costly. Instead, Roadtech did the rock breaking and grader work, then used the linear crusher to break down oversized material and blend in the fines.
“With the linear rock crusher, we were able to get the fines back in so dust abatement would hold in better,” Clark said. “They’ve been running on that road for three years now.”
Compared with the cost of hauling in dirty gravel from a pit, at around $35,000/lane mile including dust abatement, with the linear crusher, Roadtech was able to restore the gravel road for about $18,000/lane mile, including dust abatement.
Roadtech has also found that the linear crusher carries out cost-effective gravel road repair in Ferry County, Washington. Clark said that the county previously used a grader to smooth its gravel roads because it lacked the funding to re-gravel the routes. But grading roads has limitations. “Traditionally with a grader when you pull out large rocks, it makes a mess, you’ll never get it compacted right again, and you’ll get ruts forming in your road,” he explained. “After pulling out the large rocks, you have to cast them over the side of the road, which widens your road and costs more to maintain.”
As an alternative, the county now runs its own grading crew, and Roadtech follows with its Vanway linear crusher. “With our Vanway linear crusher, we can typically re-gravel and rehabilitate from 2-6 miles of gravel road for essentially $36,000/week, plus crew cost,” Clark claimed. “With the traditional way of burying the problem, it would cost over $100,000/week for a similar project.”
According to Clark, this approach has allowed Ferry County to put in a new maintenance protocol for its roads and he said, “The linear crusher allows the county to work on roads they would normally have to wait 5-10 years to re-gravel.”
Clark explains that the county not only gets to reuse the material on the road, but also gets to correct the road. This allows the county to pull the big rocks out, and use the grader to correct the road, improving the profile and water drainage, further lowering road maintenance costs.
Clark continued, “On a typical county road project, you’ll save roughly $15,000/lane mile, plus about $2,500/year/lane mile in gravel road maintenance. With proper subgrade preparation, instead of burying the problem, you can gain an additional 3-5 years of road life. A linear crusher can also decrease how frequently you do general blade maintenance by about 50%.”