Road improvement methods vary
WALKER -- Cass County Board members toured county roads from Pillager to Bena on Monday to see how different types of road surfaces survive wear from traffic and weather.
They also looked at road improvements County Engineer David Enblom proposes for the next five years. Their last road tour was in 1997.
Highway improvements have focused the last 50 years on placing asphalt pavement over gravel road surfaces.
Today, new gravel supplies are dwindling, making that increasingly expensive. Oil prices have escalated.
The two main components of a traditionally paved road cost more. County, state and federal highway tax resources to pay for road improvements have not risen as much as costs.
Road traffic does keep rising, causing increased wear on county road surfaces.
Five years ago, Enblom began a program to put calcium chloride on gravel county roads carrying 100 vehicles per day or more.
Public reaction to less dust and fewer washboards has been positive. During dry spells, however, the calcium chloride treatment is less effective.
This year, Cass County is one of two pilot sites in Minnesota to test Ottaseal, a cold oil road treatment applied directly to the gravel road surface. It is used extensively from Iceland to Australia.
Calcium chloride treatment costs about $2,400 per road mile. It has to be treated annually.
Ottaseal costs $15,000 to $17,000 per mile, but is advertised to last 15 years. The surface can be ground in place and re-oiled when it wears out.
Paving a mile of hot mixed bituminous road today costs at least $50,000 to $60,000 per mile, said Enblom.
County State Aid Highway 25 west of Pine River is Cass' pilot road segment for Ottaseal.
Cold oil is spread over the gravel road base, then covered with an inch and a half layer of sand. Traffic and sun beating on the road draw the oil to the surface, Enblom said, giving it the appearance of a hot mix paved road.
Plant mixed asphalt can be shoveled into any potholes that might develop, Enblom added.
Unlike hot mixed asphalt pavement, Ottaseal does not require crack sealing. Enblom said spring frost cracks will lay flat again under spring traffic and re-bond with the sun's heat.
Enblom said if the system works as well here as it has in other countries, he will recommend Ottaseal be used rather than hot mixed asphalt on any roads not already blacktopped.
The cold oil and gravel system can be laid by county employees at a rate of two to three miles per day, Enblom said. Contractors then would have to be hired only to replace existing bituminous pavement surfaces, he said.
As bituminous road surfaces are re-paved, Enblom recommends increasing the number of layers to make the county's paved road system strong enough to carry nine and 10-ton loads, depending upon traffic volume.
He showed the board examples of different ways existing road pavement is being recycled into re-paving projects.
Where pavement has not been replaced soon enough or road base material was poor to begin with, a few roads have had to be completely rebuilt before being re-paved, he said.
That new base should set over at least one winter to harden before new pavement is laid over it, he said.
In some cases like a portion of County State Aid Highway 5, re-paved in the mid-1990s, this was not done. New cracks and ripples formed more quickly than normal as the road base settled, Enblom said.
More often today, existing pavement is ground up and recycled.
It can be mixed in place with existing road base gravel to make a stronger base material, Enblom said. It can be mixed in this manner, then have cold oil spread over it before hot mixed bituminous is spread over it as was done on CSAH 45 east of Hackensack.
It can be carried to the bituminous hot plant mix site and mixed with new asphalt material as that is made, then trucked back to the road and re-spread as a new pavement layer.
Recycled glass is being mixed with gravel for base material, Enblom said. It was used as surface gravel only for a short term experiment. While pulverized glass did not cause flat tires when mixed with surface gravel, it did create a glare for drivers, Enblom said.
Which pavement recycling method is used usually depends upon the extent of deterioration in the existing bituminous road surface, Enblom explained.
In some cases where roads crossed boggy areas, the county has laid rubber mats over the road base, then filled several feet of new gravel base before installing new road pavement, Enblom said.
A specially skilled design engineering firm's services will be engaged when the county re-paves a section of CSAH 7 east of Longville. That area is very boggy.
Severe ripples and frost heaves have been an historic problem there, he noted, as the tour bus lurched, bumped and rolled over the pavement even in August.