Date of Award
Doctor of Philosophy
Civil, Construction, and Environmental Engineering
Jeramy C. Ashlock
David J. White
Unpaved roads in seasonal frost regions frequently experience severe damage during spring thaws, which adversely affects traffic safety and significantly increases maintenance costs. Current maintenance practices such as spreading new aggregate to cover the damaged roadway surface aim at repairing damage after it occurs, rather than minimizing or preventing its occurrence in the first place. Dust emission and aggregate loss are also severe issues for unpaved roads that are attributed primarily to the mechanical degradation of the surface aggregates. Due to the considerable variation in aggregate quality, most transportation agencies use the Los Angles (LA) abrasion test to set specifications for unpaved road surface materials. However, this testing method does not simulate the actual compaction or traffic loading conditions responsible for degradation of the materials in service. Furthermore, the LA abrasion test does not test the full material gradations and therefore cannot quantify the influence of the missing material on the actual field performance.
The goal of this study is to cost-effectively improve the performance and sustainability of unpaved roadway systems. To identify the most cost-effective stabilization methods for improving freeze-thaw performance of unpaved roads, several promising technologies were selected based on a comprehensive literature review, and used to construct a total of 17 test sections over a 3.22 km stretch of unpaved road in Hamilton County, Iowa. Design methods and construction procedures and costs were documented for each test section. Mechanistic-based field tests and visual inspections were conducted over two seasonal freeze-thaw periods (from 2013 to 2015) to compare the relative performance and durability of the various test sections. Based on the field testing and statistical analysis results, it was found that test sections stabilized with macadam stone base layers yielded the best overall performance for both pre-freezing and post-thawing conditions.
In this research, a newly improved surface wave method (SWM) was also evaluated for determining the very shallow near-surface stiffness profiles of unpaved-road systems. By combining the SWM and falling weight deflectometer test, a new method of testing and analysis was developed to determine the in-situ nonlinear modulus reduction curves of each material layer in an unpaved road profile. The new method may provide significant improvements to current mechanistic-based design methods for both paved and unpaved roads.
To address the shortcomings of the commonly used LA abrasion test for evaluating degradation and abrasion of granular materials, a new laboratory testing method termed the Gyratory Abrasion and Image Analysis (GCIA) method was also developed in this study. The new testing method employs a gyratory compaction device and two-dimensional (2D) image analyses to determine changes in gradation, morphology, and mechanical properties of granular materials under simulated compaction or traffic loads. Based on the new GAIA test results, the density-strength-compaction energy relationships of granular materials can be rapidly established, and used to develop performance-based specifications that can improve the material’s field performance, minimize its degradation, and save compaction time and energy
Li, Cheng, "Improving performance and sustainability of unpaved roads: Stabilization and testing" (2016). Graduate Theses and Dissertations. 15960.