Executive Summary
Road ripples are an emerging and poorly understood form of asphalt pavement distress that has begun to appear with notable frequency on North Carolina roadways. Characterized by repeating surface undulations or shallow cracks that can form in the wheel paths or extend across entire lanes, they differ from conventional distress patterns and are not addressed in existing pavement distress manuals. They have been described as producing a “washboard-like" surface that degrades ride quality and draws the attention of both drivers and maintenance personnel. The phenomenon is particularly challenging because it does not have a single, well-established cause; instead, evidence suggests a complicated interplay of residual moisture in asphalt mixtures, moisture-sensitive subgrades, poor drainage or base support, and possibly traffic or environmental factors such as freeze-thaw cycling. This lack of clarity has meant that road ripples are frequently mischaracterized in pavement evaluations and, more importantly, that no standardized diagnostic or treatment methods exist to guide agency practice.
In light of this need, the proposed research plan will seek to achieve four objectives: 1) evaluate the extent and severity of road ripples and the causative factors in North Carolina, 2) evaluate the potential for residual moisture to exist in asphalt mixtures produced in North Carolina, 3) evaluate the potential long- and short-term implications of road ripples on pavement performance, and 4) develop a targeted research plan for a follow-up study to systematically evaluate and quantify the impacts of different causative factors on causing road ripples.
Schematic view of the vapor pressure mechanism that can cause blistering and road ripple formation
These objectives will be met with six tasks:
- Perform a literature review to understand the state-of-the-art and state-of-the-knowledge with respect to road ripples.
- Conduct an evaluation of pavements in North Carolina that are experiencing road ripples to understand the extent and severity of the distress in the state and also identify potential causative factors.
- Conduct experiments to evaluate residual moisture contents in North Carolina mixtures.
- Conduct an assessment to understand the potential long-term performance implications of road ripples.
- Develop a detailed work plan for conducting a Phase II study to systematically evaluate the causative factors.
- Prepare a final report summarizing the methodology, results, and recommendations.
The primary outcome of this research will be the establishment of a foundational understanding of road ripple distress in North Carolina, including its likely mechanisms, diagnostic indicators, and performance implications. While road ripples have been observed across the state, there is currently no standardized method to investigate, quantify, or manage them. This study will combine field investigations, laboratory studies, and analytical assessments, to provide clarity on the potential causes of this distress. Ultimately, the outcome of this work will be a clear, evidence-based foundation for the NCDOT to use to make informed decisions about repair, prevention, and long-term management of pavements affected by road ripples.
