Larimer County's process for grading non-paved roads helps to insure the best road conditions possible for the traveling public. The process procedures are as follows:
The road is watered thru out the entire grading process, graded to a specific template, compacted, watered and then sprayed with a dust suppressant to achieve the desired finished product. Here is a breakdown of each process:
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Watering Process:
A water truck waters the road before the beginning of the grading process. Watering is done numerous times thru out the process to ensure that the gravel stays at optimum moisture which enables grading and shaping of the road. Watering is continued after the grading is complete to keep moisture in the gravel until the road is treated with a dust suppressant. Proper moisture is a crucial part of our success of grading and compacting the roads.
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Grading Process:
Once the roads are watered enough to grade efficiently, motor graders work to cut the pot holes and/or wash boards out. The road is cut to a depth sufficient to ensure the imperfections are gone and a smooth surface is obtained. It may take numerous passes to accomplish this. Once the pot holes and/or wash boards are cut out, the road is graded to establish a 5% crown in the road and up to a 6% super-elevation (bank in the curve) in the curves. The road is worked until the desired template is obtained.
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Compaction Process:
For this process two different types of compactors are utilized. Typically, a vibratory steel drum roller is used, which leaves a smooth finish on the road way. A rubber tired roller is used at times, to assist in the process of compaction. Depending on the circumstances and desired outcome of the road, we will use a combination of the two rollers. The process of compaction begins after the pot holes and/or washboards have sufficiently been cut out of the road. As the road is graded to the template desired, the roller begins compacting behind the grader. After the grading is finished, the steel drum compactor is run over the road to put the finishing touches to it.
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Dust Suppressant Process:
After the road is graded and compacted to our specifications, watering is continued on the surface to keep moisture in the road. A top coat of dust suppressant is applied by a contractor. This is applied at three-tenths (3/10) gallon per square yard, and is kept approximately 12” from each edge of the road. This helps to ensure the treatment stays on the road surface and not in the roadside ditch. As the treatment cures and penetrates the road, occasionally a light coat of water is applied to prevent traffic from pulling up the treatment before it cures.
This completes our grading process and the results are a smooth, dust-free road.
Cross Slope Changes
Each year the non-paved roads division is faced with many challenges maintaining our roadway system. New ideas are experimented with to aid in developing a better road system for the traveling public. One idea that has been implemented is experimenting with the percentage obtained on the cross slopes of the road. The cross slope is the amount of fall that the road has from the center of the road to the edge of the road. Before the changes were implemented, the cross slope maintained on Larimer County non-paved roads was a 4% cross slope. Now, the cross slope maintained on the non-paved roads is a 5% cross slope on the roads, where it is possible to obtain. This 5% cross slope helps the water that accumulates on the road to run off sooner and this results in fewer potholes and wash boarding in the driving lanes. The results and observations have been very promising to date. Observations show less potholes and therefore an improved road to travel on. This practice will continue to be used to further analyze the results.
During the maintenance of many of non-paved roads in Larimer County, a dust suppressant is applied to complete the grading process. This treatment provides a finished surface that helps repel moisture and control the dust generated by traffic. This helps reduce maintenance costs by resulting in the roads needing to be graded fewer times per year.
Larimer County uses dust suppressants for three main reasons;
1. We are required by the Colorado Department of Public Health and Environment (CDPHE) Regulation 1 to minimize emissions of “Fugitive Particulate Emissions” (dust) from unpaved roads carrying more than 200 vehicles per day.
2. Dust Suppressants limit the loss of fines in the aggregate structure therefore protecting the publics investment in the road surfacing material. The dust created by traffic on a gravel road is the result of fine soil particles being lifted from the road's surface and carried away. These fine soil particles are a vital component of the gravel surfacing material and help to hold the gravel together reducing wash boarding and segregation. If not treated with dust suppressants, the surfacing material degrades over time and we are left with nothing but sand and coarse aggregate, a poor- quality road surface requiring replacement.
3. The dust suppressant attracts moisture out of the atmosphere which helps to hold the fines in the material and reduce dust, but it also hardens/stabilizes the surface of the road helping to reduce the rate of degradation. This stabilization quality extends the life of each grading operation and results in a higher quality road surface for a longer period of time, therefore reducing cost.
The Dust suppressant Larimer County uses on most roads is a product called Durablend. Durablend is a chloride based product that is enhanced with a polymer that allows us to apply less product per square yard and lowers the migration of chloride from the road. We apply Durablend at a rate of 0.3 gallons/sy. The following is a link to the product brochure with more specific information on the Durablend product. (https://envirotechservices.com/?s=Durablend&post_type=post)
As a result of weather, traffic and repeated grading operations, gravel surfacing wears out. As a road ages, a surface is left that has lost the fines required to bind the larger aggregate together making it difficult to maintain the road shape and causing wash boarding and potholing. Historically, when a road reached this point of degradation, we resurfaced the road with new gravel.
In 2017, Larimer County purchased a road reclaimer that allows us to re-mix the existing gravel to a depth of 6" and if necessary add soil fines to restore the overall quality of the surfacing material. Not all roads can be salvaged with the road reclaimer, but when appropriate, this method saves time and money and results in a quality surface for many more years.
The road reclaimer has proven to be a great asset to our operations.
As with all road surfacing materials, gravel surfacing has a limited life and must be replaced occasionally. Traffic, weather and repeated grading operations all act to degrade the gravel surfacing and when this degradation cannot be repaired with the reclaimer, it must be replaced.
Each year several miles of road are resurfaced with 4" to 8" of new aggregate base course. The aggregate base course may be purchased from outside vendors or produced in-house at the County's Strang Gravel Pit.
In some cases more extensive work is required to restore the shape of the road, improve roadside drainage and improve safety. In these cases, Road and Bridge will perform a light reconstruction of the roadway platform and adjacent ditches and slopes prior to resurfacing with new aggregate base course.
