Top-Down Cracking in Washington State Asphalt Concrete Wearing Courses

Abstract

For years, pavement engineers within the Washington State Department of Transportation (WSDOT) have observed that longitudinal and fatigue (multiple-interconnected) cracks in their thicker asphalt concrete (AC) pavements appeared to crack from the top of the wearing course downward. Often, the cracks stop at the interface between the wearing course and the underlying bituminous layers (a depth of about 50 mm). Studies done elsewhere in the United States and internationally have reported similar results. The results of extensive coring that WSDOT routinely collects in its pavement rehabilitation process were compared in a study. WSDOT normally cores AC pavements to determine thickness for use in mechanistic-empirical design. In addition to coring for AC thickness, specific information noting surface-initiated (top-down) cracking with the crack depth or full-depth cracking was noted. WSDOT observed top-down cracking occurring in the thicker sections, with thinner sections cracking full depth. Top-down cracking generally started within 3 to 8 years of paving for pavement sections that were structurally adequate and were designed for adequate equivalent single-axle loads.

Evaluation of Surface (Top Down) Longitudinal Wheel Path Cracking

“…Surface defects can cause surface cracking based by Uhlmeyer et al (2000). A study by Schorsch et al (2001) found that surface cracks initiated from the segregate pavement areas.…”

“…In a study by Uhlmeyer et al (2000) three to eight year old pavements which were more than 160 mm (6.3 in) thick exhibited top-down cracking in and around the wheel paths. They concluded that the pavement thickness has an effect on the surface cracking initiation which contradicts the previous findings.…”

Reliability-Based Design Procedure for Fatigue Cracking in Asphalt Pavements

“…Load induced top-down fatigue cracking (i.e., cracking that initiates at the surface of asphalt concrete (AC) layer and propagates downward) has been observed in many parts of the world (e.g., [1][2][3][4]. It is widely accepted that top-down cracking results from a critical combination of load, thermal and aging effects.…”

Causes, mechanisms, and remedies of top-down cracking of asphalt pavements : state-of-the-art

“…In some cases, this type of crack, TDC, has been the predominant type of deterioration mode of pavement. It could appear as longitudinal crack just outside the wheelpaths, over time, it forms an extensive network of longitudinal cracks connected by short transverse cracks, which ultimately reduce the service life of the road pavements (Uhlmeyer et al, 2000). TDC has also been experienced as transverse cracks just after the compaction process which was attributed to the conventional compaction process using the steel drum roller followed by the pneumatic roller .…”

“…Since the surface course is the exposed layer to traffic load and carries the direct loads per area as compared to other layers, researchers assumed that surface failure was caused by excessive load-induced tensile stresses. These tensile stresses are considered to affect on the surface course when TDC is first observed (Uhlmeyer et al, 2000). The uniformity of the cracking patterns has always suggested that uniform loading conditions, such as those induced by low temperature, are the main contributor to the observed surface cracking.…”