crushers in remote areas where pit material is sparse.
Don’t bury the problem. Crush it.
Linear road crushers can rehab roads with on-site material at a fraction of the cost compared to traditional methods.
A common gravel road repair and road building approach is to remove oversized rocks and bury subgrade problems, such as potholes or protruding rock, under additional gravel. Yet, this approach does not deal with underlying problems, and it is costly. It can require hauling in 200 to 300 percent more material than necessary to resurface a gravel road, only to have problems come up again.
About 50 percent of the cost of any gravel road project comes from hauling in material. It costs about $10,000 to get a mobile crusher into a local pit, and that cost can rise if pit permitting and development is required.
While using a pit crusher makes sense on massive freeway projects and where stringent aggregate specifications for structures like bridges are justified, there are other options for gravel roads, particularly remote ones.
Pit mining versus linear crushing
Sweet Grass County, Mont., depends on good gravel roads for much of its timber, oil, mining and agricultural transportation. But maintaining these gravel roads became too costly and difficult with traditional pit mining.
“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 drivable surface,” says Cory Conner, Sweet Grass County public works director.
Instead of burying near-surface subgrade problems under excess gravel from a pit, a growing number of counties and road contractors, as well as timber, oil or mining companies, are discovering that linear crushers can repair a gravel road for significantly less money, while also correcting the underlying subgrade problems.
Unlike mobile rock crushers that remain stationary when operating, linear crushers move along the road being repaired, crushing oversize rock on it in a crushing chamber. The oversized rock, existing gravel and natural fines are all windrowed and processed through the crusher in one pass, leaving 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 that, when wet, can prolong the life of the road surface beyond that of cleaner gravel from a pit that typically lacks soil mixed in as a binding agent.
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 shopping and watching demonstrations of two on-road crushing systems, he chose a front 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 says.
Vanway International, a linear crusher manufacturer, makes machines capable of crushing any rock, including construction grade rock such as basalt, gabbro, 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 says. “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.”
Conner says properly blending fines and crushed rock with the linear crusher is critical for Sweet Grass County to achieve the gravel road surface sought.
“Without blended crushed rock and fines, you’ll get rock pockets, rocks kicking out, washboard or potholes,” Conner says. “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.”
After purchasing the linear crusher, Conner says he can take existing roads that are wearing out and rehab them without having to open a pit or complete a Department of Environmental Quality pit process or reclaim process.
“We’ll save a lot of money using existing material on the road shoulder and surface,” Conner says. “Compared to our typical gravel road cost of about $20,000 per lane mile hauling from a pit, we expect to rehab the same road for about $5,000 to $7,500 per lane mile with our Vanway linear crusher. We should be able to do about two to three times the road repair we’d done previously with the same crew, while extending the lifespan of our roads and vibratory rollers.”
Another perspective
processed through the crusher in one pass, leaving the reduced material
in place as a stable crushed layer.
Travis Clark, Roadtech operations manager, also relies on a linear crusher for cost-effective gravel road repair and construction. Roadtech, based in St. Maries, Idaho, is a contract road construction firm.
“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 percent savings with our Vanway linear crusher,” Clark says. “All that material that’s been pushed off the edge of the road for years – from ditches, berms, subgrade, oversize – becomes our lift material. Our linear crusher usually runs at a cost comparable to a pit crusher, but doesn’t need a pit, have setup costs or need to be permitted.”
When building remote gravel roads for timber, oil or mining projects, the cost of hauling in gravel can escalate, Clark says. The farther away the road is from the pit, the higher the cost. The more remote the road, the fewer the pits.
“That’s when your price per mile of gravel road goes through the roof,” Clark says. “Fortunately with a linear crusher, your price stays constant. Without the material-hauling cost, it costs the same per mile. This allows our Vanway linear crusher to do remote projects for the same price you would pay for a local project.”
Better roads for less
Vanway’s linear crusher has performed well for Clark’s customers, ranging from logging, oil and mining companies to county public works departments that require building or maintaining good gravel roads at a low cost.
Clark says a timber company in St. Maries had been struggling for years to keep a steep, two-mile stretch of single-lane gravel road in shape with traditional blading and dust abatement.
“For heavy logging truck use, the consistent 15-plus grade was challenging,” Clark says. “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. There weren’t enough fines in the road to bind the aggregate together, so dust abatement didn’t work very well.”
The traditional approach to address the challenge would be to haul dirty gravel onto it, but Clark says that would have been about $35,000 per mile of lane, including dust abatement. Instead, Roadtech did the rock hammering, proper grader work, used the linear crusher to break down oversized material and blended 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 says. “They’ve been running on that road for three years now, and it’s holding up beautiful for them.”
Compared with the cost of hauling in dirty gravel from a pit at about $35,000 per lane mile, including dust abatement, with the linear crusher, Roadtech was able to restore the gravel road for about $18,000 per lane mile, including dust abatement. Using the Vanway linear crusher, Roadtech saved the timber company about $12,000 per lane mile in gravel road restoration costs, and thousands of dollars each year in road maintenance.
“Logging trucks are now able to keep a higher average speed on the road, which has increased work turnaround times on their trucks,” Clark adds.
Del Williams is a technical writer based in Torrance, Calif.