Gravel roads often experience significant deterioration that requires costly maintenance. To mitigate this deterioration, transportation agencies can apply chemical stabilizers to improve aggregate cohesion. This project examined the mechanical, environmental and economic performance of five gravel stabilizers and three application methods to determine the best options for reducing deterioration.
What Was the Need?
More than half of the total road network in Minnesota consists of unpaved gravel roads, which are susceptible to rapid deterioration from frost heaving, freeze-thaw cycles, rutting and potholes. To slow the decline of gravel road surfaces and reduce maintenance costs, transportation agencies often use chemical stabilizers to improve the cohesion of gravel aggregates.
However, numerous stabilizers are available, and additional research was needed to evaluate their performance, cost and environmental impacts. This project evaluated and compared the mechanical, environmental and economic performance of five stabilizers and three application methods at 28 sites across Minnesota.
“The stabilizer comparisons will provide valuable information to transportation agencies at all levels as they manage and maintain gravel roads in Minnesota,” said Terrence Beaudry, Grading, Aggregate and Base Engineer at MnDOT’s Office of Materials and Road Research.
What Did We Do?
The evaluation of gravel road stabilizers began with an analysis of historical maintenance records from five Minnesota counties: Cass, Itasca, McLeod, Polk and St. Louis. Investigators collected construction, maintenance, traffic and climate histories for stabilized gravel roads in these counties to assess their performance.
Next, investigators stabilized gravel roads at 28 sites across Minnesota using calcium chloride, magnesium chloride or one of three proprietary stabilizers. Three application methods were used to apply the stabilizers: direct injection (three sites), blade mixing (10 sites) and spray-on surface treatment (15 sites). Over a two-year period, field performance was monitored using a Dynamic Cone Penetration, a Lightweight Deflectometer, Nuclear Gauge density, and International Roughness Index measurements.
Environmental impact evaluations included testing pH, electrical conductivity, metal concentrations and acute toxicity to determine potential risks associated with stabilizer use. The life-cycle assessment and life-cycle cost analysis evaluated, respectively, the environmental impacts and costs for a 1-mile, two-lane gravel road over a 30-year service life with an average daily traffic volume of 200 vehicles.
Finally, investigators used a normalized performance index (NPI) that combined mechanical, environmental and cost indicators to provide an overall ranking of stabilizer options.
What Did We Learn?
Historical maintenance records from five Minnesota counties showed that stabilizers reduced maintenance needs compared with untreated gravel roads. Field testing found that while all stabilizers reduced gravel loss, maintenance frequency and costs compared with untreated roads, performance varied among products and application methods. Three stabilizer treatments stood out as the top performers:
- One proprietary stabilizer (NPI ≈ 0.91) applied with the blade-mix method achieved the highest mechanical performance, increasing California Bearing Ratio by 11% after two years and saving $6,578 per mile annually.
- Calcium chloride (NPI ≈ 0.90) applied with the direct-injection method experienced 80% to 82% less gravel loss than untreated roads, reduced maintenance costs by approximately 23% and saved $8,582 per mile annually.
- A second proprietary stabilizer (NPI ≈ 0.88) applied using the blade-mix method also experienced 80% to 82% less gravel loss than the untreated roads, reduced maintenance costs by approximately 17% and saved $7,746 per mile annually.
In contrast, spray-on chloride treatments, in which the stabilizer was applied directly to the road surface without mixing, had the lowest mechanical, environmental and economic performance. These treatments increased maintenance costs by approximately 89% due to the need for repeated applications.
Environmental testing results found that metal concentrations at all sites remained below U.S. Environmental Protection Agency limits, and acute toxicity testing detected no acute toxicity at stabilized sites.
Overall, results demonstrated that stabilization reduced gravel loss, maintenance frequency and long-term costs. Results also showed that both the stabilizer type and the construction method affect gravel road performance and long-term maintenance needs. The blade-mix and direct-injection methods generally outperformed spray-on surface treatments.
What’s Next?
These findings provide valuable information to state and local transportation agencies as they make budget and maintenance decisions for gravel roads. Future research could include monitoring sites beyond two years to better evaluate long-term performance and durability of chemical stabilizers. Additional research could also focus on developing performance measures based on California Bearing Ratio, elastic modulus and International Roughness Index, as well as evaluating stabilizer leaching behavior to better understand their long-term presence and movement under traffic loads.
Crossroads 