The approach to predicting moisture sensitivity of asphalt concrete pavements is based on the acceleration of fatigue cracking and wheelpath rutting field distresses. Prediction methods incorporate mechanical properties of the specimen, derived physical property ratios with field time, and environmental effects. In a 1988 trb paper, methods were discussed that resulted in predicted wet performance lives and laboratory cutoff ratios. Specifically discussed was a university of idaho method called "asphalt concrete moisture damage analysis system" (acmodas); acmodas2 in reference to fatigue cracking was emphasized. In this paper, acmodas3 referenced to wheelpath rutting is emphasized. The parts and procedures are examined along with application of results. The effects of moisture on wheelpath rutting aredefined here as being the changes of permanent deformation in the asphalt concrete due to plastic flow. A physical property ratio called wheelpath ratio (wpr) is developed using wet and dry modulus and stripping values from laboratory specimens after performing a moisture conditioning test. Seasonal increase of wpr is related to summer pan evaporation at the pavement location. In the acmodas3 method, 1/10-yr permanent deformation "damage" fractions are summed to yield a relative wet performance life in years. A resilient modulus cutoff ratio is also calculated for laboratory control of the specific asphalt concrete mixture. Application of the acmodas3 and acmodas2 methods shows that a specific pavement mixture can have significant moisture sensitivity only to wheelpath rutting, whereas another mixture can have significant sensitivity only to fatigue cracking. This paper appears in transportation research record no. 1228, Asphalt mixturesand asphalt chemistry.
Abstract