2015 - NZ - Chip Seal Cracking

The fatigue cracking behaviour of laboratory prepared chipseal beams and beams cut from field samples was studied using a four-point bending test method. Preliminary results indicate that chipseal fatigue lives at 5ºC are up to eight times greater than those of estimated values for asphalt mix under the same loading conditions. The results suggest binder oxidation was not the dominant factor in seal cracking and that cracking in the field may be primarily due to very high, localised deformations. Such deformations may arise through weak basecourse patches formed during construction or more likely, from water damage (to both the basecourse and seal structure itself) arising from leaking seals.

Data from long-term pavement performance sites show that overall, the average number of cracks initiated per site increased approximately linearly from the time of crack initiation. The average annual increase in crack length is approximately half the crack length, so as the crack grows the rate of crack growth in mm/year increases. A brief analysis was carried out for two sites that showed an approximately three-year lag between crack initiation and pothole formation.

The report proposes practice guidelines and the outline of a performance-based specification for the crack repair of chipseals.