Full-depth reclamation (FDR)—an effective and efficient pavement reconstruction method—can be made even more sustainable by strengthening the road base. Laboratory and field testing of proprietary stabilizers used to amend FDR material illustrated improvements in pavement stiffness and economic benefits over time. New pavement design standards for base stabilizers can guide road engineers in choosing the optimal products for sustainable roads.
When roads are built or reconstructed in areas with weak or vulnerable soils, amending the base layer with stabilizing additives can enhance foundational integrity. FDR is a sustainable road reconstruction practice with many economic and environmental benefits. Various stabilizers are available to mix with FDR material to ensure a strong, durable road base.
While nonproprietary stabilizers such as cement, fly ash and asphalt emulsion have been studied extensively, limited research exists on the effectiveness of proprietary stabilizer blends. Though manufacturers suggest application rates and provide expected performance metrics, additive performance may depend on the aggregate or other materials in the mix. Comprehensive testing was needed to evaluate proprietary stabilizer performance.
This project sought to evaluate the efficacy of proprietary additives through laboratory and field evaluation, determine optimal application rates and prepare pavement designs and construction specifications. Additionally, MnDOT and local transportation agency engineers wanted to test the mixes on full-scale construction projects to understand the cost-effectiveness of the proprietary additives in pavement construction.
What Did We Do?
This study began with a review of existing studies and construction manuals that detail current practices of base stabilization and strengthening using additives. Then researchers collected FDR aggregate, limestone aggregate and subgrade soils from a Minnesota highway site. Laboratory evaluations of the material properties included particle size distribution, moisture characteristics and compaction behaviors.
Next, researchers determined optimum dosages of several proprietary additives for FDR materials, including:
- Base One: Emulsion of heat-liquified sand and soda ash containing surfactants and emulsifying agents.
- Claycrete: Liquid ionic soil stabilizer that reduces clay shrink and swell, allowing it to interlock into a tightly bonded layer that increases soil density.
- EMC SQUARED: Product system that creates improved base flexural stiffness while retaining elasticity.
- Roadbond EN 1: Patented stabilizer that uses electrical attraction to alter the ability of clay to hold adsorbed water.
Various dosages of the additives were combined with the FDR materials. Then soil classification and compaction tests identified engineering properties of the mixes. Freeze-thaw tests explored the durability of the stabilized mixtures.
Five 1,000-foot pavement test sections included four road bases with stabilizer additives and one control section. Immediately following the asphalt paving, investigators evaluated the stiffness of the stabilized base layers. Performance tests over two years continued to measure strength and surface roughness.
A life cycle cost analysis of each test section identified initial costs, such as materials, transportation, equipment, labor and water costs of construction, and assumed maintenance scenarios, such as crack filling and seal coating.
What Did We Learn?
In the laboratory, the EMC SQUARED stabilizer provided the best performance in the freeze-thaw tests, though water intrusion during the freezing period corresponded to a significant strength decrease in all specimens.
“The proprietary base additives, applied in pavement foundations as recommended after the laboratory analyses, showed promising results after two years. We hope the value we’ve seen in the short term will continue over a longer period of observation,” said Chad Hausmann, county highway engineer, Wright County.
The control test pavement section exhibited the best immediate performance, which was likely due to its strong subgrade and compaction from traffic. (The section was open to traffic two weeks before the other sections.) Over time, however, the stiffness of all stabilized sections increased, exceeding the stiffness of the untreated section after two years. The Roadbond EN 1 stabilizer exhibited the greatest stiffness, and all stabilizers enhanced the structural properties of the FDR base layer, resulting in improved pavement performance over time.
The economic analysis illustrated that stabilizing FDR base layers could result in lower life cycle costs than the control test pavement section. Laboratory and field evaluations, additional calculations for stiffness values and granular equivalency values allowed researchers to develop design guidance for stabilized FDR base layers.
What’s Next?
Study results give county engineers confidence in knowing the use of stabilizers for FDR base will result in stronger pavement after two years. MnDOT may consider amending pavement design guidance to reflect the recommendations. The Local Road Research Board has approved continued study of the field sections created for this project and will update the life cycle costs of each stabilizing additive based on future findings.
Crossroads 