Message from the Director

It’s a well-understood principle of civil engineering that long-lasting structures begin with a firm foundation. This applies not only to buildings, dams, and bridges, but also to pavements. Unfortunately, on many occasions, I’ve seen first-hand where a well-designed and produced asphalt mixture and well-constructed overlay were built on top of an existing pavement structure with a serious problem. The outcome of this scenario is predictable, and the cost is not just in dollars and cents, but also a damaged reputation for the agency and the contractor, and another data point indicating that asphalt pavements aren’t durable. 

With that in mind, it concerns me to hear about “standard” pavement rehabilitation strategies, such as a 2.5-inch mill and fill, where there is essentially no engineering in the decision about what’s needed to correct the underlying distress. I know it’s not just me; I’ve heard similar complaints from pavement stakeholders across the country.  

I was once involved in a case where an expensive interstate rehabilitation project failed because the underlying patches and leveling that had been covered in the previous rehabilitation were stripping and crumbling. I’ve also seen numerous overlays fail prematurely because they were paved over a milled surface that was riddled with scabs left behind from the milling operation. Recently, I examined a set of over 60 cores for a project on a US highway scheduled for rehabilitation because it had extensive longitudinal and fatigue cracking ranging from 18 to 33% of the lane area. 75% of the cores had debonded between the last overlay and the underlying asphalt pavement.  

This lack of pre-design investigation is especially frustrating because we have many tools available to evaluate the structural health of a pavement. Although pavement condition surveys can provide information about the type, magnitude, and extent of distresses, they don’t tell us the cause. Falling weight deflectometer (FWD) tests and ground penetrating radar (GPR) can provide additional information about the structural health of a pavement, but the interpretation of data from those tools is imperfect. In my mind, nothing can substitute for good, old-fashioned coring to evaluate the condition of the underlying pavement. Coring can tell us so much about an existing asphalt pavement. It can tell us the actual thickness of asphalt layers, the condition of those layers, the types of mixes used, the depths of any cracking, and also if there is any stripping or delamination between layers.  

I’ve heard the argument that agencies don’t have enough funding to do a proper rehabilitation to fix underlying problems. I understand budget constraints, but an agency that repeatedly fails to consider the long-term costs of covering up underlying issues is wasting taxpayer money. Taking the time and effort to understand what exists below the surface is the first step to achieving better performing rehabilitated pavements. 

Randy C. West, Ph.D., P.E. | Director and Research Professor