Feasibility of Gravel Road and Shoulder Recycling

Project Investigators

Charles Jahren, Jeramy Ashlock

Project Schedule

Jan 2015 to Feb 2018


Iowa Department of Transportation, Iowa Highway Research Board


aggregate stabilization

Project Description

Unpaved aggregate road surfaces and shoulders frequently experience extensive damage due to degradation of materials under heavy traffic loading and winter/spring freeze-thaw cycles. Additionally, substantial amounts of material are typically lost to whip-off and dusting. The damage results in several problems including surface deterioration, loss of crown, surface water erosion, rutting, and potholes. Unfortunately, the most unfavorable scenarios usually occur during spring thaws and rainy seasons, when aggregate roads are heavily used by planting and harvesting traffic.

Current maintenance practice typically involves covering the entire damaged road surface using virgin aggregate without compaction. However, due to the continually increasing price and scarcity of virgin aggregates, this is not the most sustainable and economical solution.

Most previous research on aggregate road stabilization has primarily focused on using costly chemical stabilizers or geosynthetics to improve performance and durability. However, the gradation, angularity, and plasticity of surface course, subgrade, and shoulder materials are also important influence factors that evolve with time due to weathering, erosion, and abrasion by traffic loads. More cost-effective solutions may be realized by focusing on recycling and processing the existing materials to return them to the optimum gradation, angularity, and plasticity index, while minimizing the amount of virgin aggregates required. Recycling of existing materials could also be used in conjunction with chemical and mechanical stabilizers for improved performance where necessary.

With this project, several series of laboratory tests will be conducted to determine the optimum target gradation and fines properties of the aggregate course that provide the best performance and durability. Field screening and recycling methods will be examined to restore existing aggregate materials contaminated by excessive fines to the optimum gradation to improve their performance and durability. Demonstration sections will be constructed using the most promising technologies to compare their relative performance, durability, and costs through at least one freeze-thaw cycle. Construction and maintenance of the demonstration sections will be documented, and the performance of the selected technologies will be assessed by in situ testing. Lifecycle costs will be analyzed to identify the most effective and economical solutions.

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