Authored By: Bryan Gee
When a pavement fails to reach its expected design life, how often is this the result of problems with the hot mix asphalt used? In my experience, the answer to this question is, “not very often.” Modern asphalt mix design and quality control have boosted the reliability of these materials to a high level. Yet, we still see many roads in poor condition, and consistently hear that roads aren’t lasting as long as expected. Why is this? If it’s not the asphalt’s fault, what happened?
There are many possible reasons why pavements fail earlier than expected, here are six common ones that are sometimes misunderstood:
- Traffic loading above design values: The road is asked to carry more than it was designed to carry.
- Design practice: In many cases, designers don’t properly characterize and account for the traffic loading.
- Variability in materials and site conditions: While asphalt quality has gotten more consistent over time, other inputs, such as subgrade strength and aggregate quality, can be much more variable than accounted for in design.
- Subgrade and aggregate base failure: Asphalt requires a firm foundation to do its job carrying traffic. If the lower layers of a pavement aren’t properly designed, the road will fail.
- Reflective cracking: The life of asphalt overlays can be compromised by water intrusion and reduced ride quality due to cracking.
This isn’t a comprehensive list, but each of these factors can be addressed effectively with a better understanding and innovative design approaches. We don’t have to just throw more materials and money at our pavements to get them to perform better.
Tensar has just added a new course, titled "Understanding Pavement Failures" to the Tensar Professional Education portal. This online webinar looks at these causes of pavement failure and shows how they can be addressed with new thinking and innovative materials. We hope you’ll find something interesting that will help you make your pavements last longer.