One of the common defects of flexible road pavement is the loss of bonding between two layers of asphalt concrete: the base course and the binder course. The occurrence of this phenomenon has a major impact on the observed state of deflection and deformation of the pavement. This effect affects the results of non-destructive tests which are used to calculate material parameters and then are used in the diagnostics of the pavement condition or design of structural strengthening. This paper discusses the influence of the various level of bonding on the result of backcalculation and the obtained elastic moduli. For the obtained values of moduli, calculations of key deformations and pavement durability were performed. Improper assumptions about the interaction between the layers affects the observed results. Additionally paper discusses the effect of pavement displacement discontinuity on the observed deflection basin and compares the results with those for a model with continuity. Numerical calculations were carried out using Simulia Abaqus software, the computational model was verified using analytical solution.

The introduction of new road pavement materials causes the need to verify whether the existing pavement design methods enable correct incorporation of their properties. In the case of asphalt pavements, the origins of contemporary methods may be traced back to the mid-20th century, when solely unmodified binders were used. The introduction of highly SBS-modified binders in 2009 significantly changed the behaviour of the asphalt mixtures and the entire pavement structure. Asphalt courses are now characterised by very high flexibility, elasticity and fatigue resistance, with simultaneous high resistance to rutting. The aim of the article is to present the effect of the use of asphalt mixtures with HiMA (Highly Modified Asphalt) binders in different variants of flexible pavement structures – including one, two or three courses containing HiMA. Fatigue life calculations were performed using the “Similarity Method”, which enables estimation of the fatigue life of the structure based on its relationship with the results of laboratory fatigue tests. The layer system with HiMA in the asphalt base course proved the most advantageous, combining excellent fatigue properties of the mixture containing HiMA with greater stiffness of the wearing and binder courses containing classic binders. The other aspect taken into account in the calculations was the effect of changing the mixture in the asphalt base course from AC 22 to AC 16. This change proved advantageous in all the analysed structures. The deflections and critical strains decreased, while pavement life, determined by fatigue and permanent deformation criteria, increased.