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Low-cost Rural Surface Alternatives: Tech Transfer Summary (Civil Project)

ABSTRACT:

This project presents a literature survey of the state of practice for granular surface road construction with respect to freeze/thaw damage and provides recommendations for a phase 2 study.

Problem Statement: Freezing-thawing action induces physical changes to granular surface roads that can negatively impact public users, reduce emergency responder access/time, and result in maintenance costs for secondary road departments.

Stabilization can help reduce frost-susceptible conditions for unbound granular roads, but requires careful engineering design and controlled construction techniques. The comprehensive literature review conducted for this project categorized technical and some economic aspects of freeze-thaw mitigation for granular surfaced roadways.

PROJECT OVERVIEW

A detailed literature survey was conducted on the topic of unbound granular road performance and construction with respect to freeze-thaw damage and resistance. Figure 1 shows typical Iowa gravel roadway conditions during the spring thaw period.

Improvements to reduce rutting due to thaw weakening and preventing frost heave are desired. In this document and the accompanying report, engineering recommendations are provided for (1) collecting local information to better characterize the extent of the problem and (2) constructing test sections to evaluate freeze-thaw mitigation technologies at full-scale.

A worldwide literature review was conducted using many sources, and the results were assessed in a systematic approach using a rating system developed as part of this project. The results of the literature review are organized by engineering categories. Approximately 300 technical articles were reviewed and then down-selected to about 150 sources for full assessment and inclusion in the bibliography.

LITERATURE ASSESSMENT

The literature database was organized in an electronic database (EndNote®), which can be shared with other researchers and practitioners. The database will be used as a future resource to search for information regarding the various repair and mitigation solutions, measurement technologies, and experiences that have been documented by selected domestic and international researchers and practitioners.

DAMAGE MITIGATION AND EVALUATION  TECHNIQUES

Based on the review of the literature, stabilization methods and drainage were identified as feasible mitigation solutions to the problems of frost heave and thaw weakening.

Stabilization works by increasing the shear strength of the surface and/or subgrade layers to resist the actions of freeze-thaw and drainage works by eliminating or reducing water from the freeze-thaw process. Following is a list of different stabilization technologies identified in the literature:

  • Chemical stabilization using active chemical agents such as lime, fly ash, and portland cement, or passive chemical agents such as bitumen, foamed asphalt, bio-fuel byproducts, and polymer emulsions.
  • Mechanical stabilization by blending coarse-grained and fine-grained materials, using non-biodegradable reinforcements (such as fibers, geotextiles, geogrids, geocells, and geocomposites), using recycled materials (recycled concrete or asphalt and industrial by-products), and use of macadam base with large particle size to facilitate drainage and stability.
  • Bio-stabilization involving biological processes. This process is relatively new with very little field data.

SUMMARY OF KEY FINDINGS

Freeze-thaw cycles combined with frost-susceptible soils and inadequate drainage lead to damage in unbound roads, and in severe cases, make them impassable. Intersections and bridge approaches are common trouble locations, but damage due to frost heave and boils can occur throughout a given roadway depending on variations in drainage, construction quality, and traffic loading.

Some approaches currently used by County Engineers to deal with frost boils include temporarily spreading rock on the affected areas, lowering or improving drainage ditches, tiling, bridging the area with stone and geosynthetic covered by a top course of aggregate or gravel, coring bore holes and filling them with calcium chloride to melt lenses and provide drainage, and regrading the crown to a slope of 4 to 6% to maximize spring drainage. However, most of these maintenance solutions are aimed at dealing with conditions after they occur.

Source: Iowa State University
Authors: David J. White | Pavana Vennapusa

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