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The interaction of fatigue and permanent deformation is very complex phenomenon and little attempt is made on this topic. This paper presents an investigation on the interaction of the two damages using the energy approach. Laboratory tests were conducted for both fatigue and permanent deformation on two different asphalt concrete in a sequential test procedure. A new failure criterion is proposed based on the dissipated energy ratio (DER). The proposed criterion for permanent deformation gives more damage indicator (inflection points) than the conventional flow number/strain rate criterion. The sequential test procedure is also found economical that can be standardized. From the study, strain hardening (pre-deformed) accelerates fatigue cracking susceptible. Similarly, high fatigued samples are more prone to permanent deformation than new samples. The energy approach is convenient for potential coupling of fatigue and permanent deformation interactions.

This master’s thesis focuses on different methods for designing pavement structures, mainly the empirical and the mechanistic-empirical methods. The first one is used in Norway, and the design is done by following a handbook with empirical data. The other one is up for consideration in Norway and uses, together with empirical data, mechanistic data regarding the properties of the different layers measured by a falling weight deflectometer (FWD). The thesis aims to analyze if the mechanistic-empirical method will reduce the total thickness of the pavement structure compared to the empirical method. Therefore, the research question is as follows: How does the thickness of the pavement structure change when using the mechanistic-empirical method compared to the empirical method? Different methods were used to solve this question. Handbook N200 was used for the empirical design, while PMS Objekt was used for the mechanistic-empirical design. To compare the results between N200 and PMS Objekt, with backcalculated E-moduli. FWD-data was also imported into the program. The FWD-data are backcalculated in Elmod. E6 Soknedal and E39 Lønset-Hjelset were used as case-projects for the design of the pavement structures. When the mechanistic-empirical method is used at E6 Soknedal, the thickness is reduced by 30 cm compared to the empirical method. For E39 Lønset-Hjelset, where the frost depth is almost one meter less than in Soknedal, the thickness is raised by 10 cm. This is because the FWD-data used for this calculation is done on an old pavement structure. That causes low E-modules from the backcalculation for the different layers, resulting in increased layer thicknesses for compensating the reduced moduli. Therefore, as long as it is ensured that a valid E-moduli is used, the mechanisticempirical method will reduce the thickness of the pavement in most cases. In addition to that, the mechanistic-empirical method also assures that the pavement structure is designed so it would last its designated lifetime.