The U.S Department of Transportation reports that 1.42 million miles, or 35 percent of roads in the United States are unpaved as of 2012. Many of these roads include gravel roads which can be effective depending on the traffic conditions the road will see. Gravel roads are best suited for areas that do not see a lot of traffic and do not have the budget to construct and maintain an asphalt road.
So what is a gravel road? A gravel road is an unpaved road that has a top layer of aggregate (gravel) as a driving surface to provide strength and add friction to the road. They’re often used for rural residents, transporting products out of farms, timber out of forests, access to campgrounds, lakes, and other remote areas.
Benefits of Gravel Roads
A gravel road can be a cost-effective solution for areas that see light traffic in counties where there is a tight budget. They are cheaper to construct compared to typical asphalt roads and may be cheaper to maintain if built properly. Compared to an asphalt road, potholes on an unpaved road can be patched more effectively and gravel can be put over the road and compacted. If a road has been lightly paved, heavy vehicles may damage it requiring resealing or additional construction. Gravel is much easier and cost efficient.
Disadvantages of Gravel Roads
While gravel roads are more affordable and easier to maintain compared to paved roads, they do have their disadvantages. They are difficult to use in wet weather which can lead to rutting, potholes, washboarding, and absorption of water. Drains must be implemented at intervals to prevent the road from flooding. Gravel roads deteriorate quickly and require routine maintenance especially after a wet period or increased traffic. When it’s dry traffic may displace gravel from the surface off the road and significant amounts of dust can be kicked up. An unpaved gravel road requires routine motor grader maintenance to fix all of these problems.
Gravel Road Construction
When it comes to properly maintaining gravel roads there are two principles one should follow, proper use of a motor grader and quality surface gravel.
A grader is needed to shape the road and for proper maintenance the operator needs to focus on three key aspects. First the road must have a crowned driving surface. A crown is defined by the Federal Highway Administration as part of the roadway shape in which the center of the road is higher than the outer edges of the surface to provide drainage of water from the center of the road surface to curbs or ditches. The second important aspect the motor grader operator must focus on is building a shoulder area that slopes directly away from the edge of the driving surface. Lastly, forming an adequate ditch on the side of the road is important as well. Having a proper crown, sloped shoulder area, and ditch will prevent the road from flooding and save on maintenance costs and time.
When choosing surface gravel for an unpaved road quality, volume, depth, and size distribution must all be considered as well as the amount of traffic the road will see. If the road will see frequent or heavier traffic, such as from hauling timber the strength of the subgrade material and the depth of the road and aggregate must be considered. Some common aggregate includes limestone, quartzite, and granite. When choosing surface gravel, it is important that the gravel has the appropriate percentage of stone or coarse aggregate to give the road its strength. It also needs the right percentage of fine aggregate, sand size particles that fill the void between the large stones to give stability to the road. Lastly, the aggregate needs to contain the right percentage of plastic, very fine particles that bind all the aggregate together which allows the gravel road to form a crust and shed water. These particles are so small they cannot be seen by the human eye. These fine particles will be kicked up off the road from traffic in the form of dust so it’s important to continue to bring in fine particles. Using a dust suppressant such as Surfa-Zyme will cut down on your dust making it easier to drive on and save on material costs.
Long Lasting Gravel Roads
As discussed, gravel roads require routine maintenance including bringing in more aggregate and regrading the road with a motor grader. This can be time consuming and costly. A permanent solution to gravel road maintenance is treating the road with a soil stabilizer like Perma-Zyme. Perma-Zyme is an enzyme based soil stabilizer used in paved and unpaved road construction. It bonds clay particles present in soil together via an electrochemical reaction that creates a concrete-like surface that lasts up to 15 years with little to no maintenance. Used on a gravel road the Perma-Zyme and clay particles will bond around the aggregate to create an even stronger surface. Perma-Zyme bonds clay particles so tightly that it becomes impermeable to water, meaning you will not have to regrade the road after rainfall. Since everything is bonded together gravel will not be lost and dust will be significantly reduced. This saves on material and labor costs. An unpaved road constructed with Perma-Zyme can save up to 60% on construction costs. Perma-Zyme is environmentally friendly so it doesn’t require PPE to use and won’t harm the surrounding area.
Applying Perma-Zyme to an unpaved road is simple. First use a motor grader to rip up the soil, excavating 6 inches for light traffic, 12 inches for heavy traffic. You would then use a water truck to get the soil up to optimum moisture. The next step is to mix the Perma-Zyme with water in the water truck and spray the mixture on to the soil. Lastly you would compact, ideally with a sheepsfoot compactor for aggressive compaction and then a smooth wheel roller to smooth out the road. The road can have traffic after 3 days and will continue to cure and get harder over the course of 6 weeks.
An unpaved gravel road can be effective in rural areas that don’t have the budget for an asphalt road. However, they do require frequent maintenance, especially unpaved roads that see heavy traffic and rain. This drives up material and labor costs. To alleviate these problems Perma-Zyme is an effective solution. The soil stabilizer will bond clay particles together around the unpaved roads aggregate and create a concrete-like surface that will last 15 years.