Asphalt pavements age due to climatic impact and oxidation. Aging affects the physical and chemical properties of the adhesive and results in an increase of stiffness and reduced sensitivity to deformation. As a result, asphalt pavement usually become harder, stiffer and brittle thus more sensitive to cracking over time.
The Swedish Transport Administration specification document contains calculation formulas (aging models) which take the changes in mechanical properties over time into account. These formulas were derived based on asphalt mixtures with conventional binders. To investigate whether these formulas are valid for asphalt mixtures with modified bitumen, a study was conducted using laboratory manufactured samples of mix type ABb 16 with three different binders from Nynas, namely, 70/100, Nypol 67 and Nypol 73.
The samples were drilled from compacted asphalt slabs and cyclic compression creep and indirect tensile stiffness modules tests were carried out at a predefined time schedule. The drilled samples werestored at room temperature whereas the slabs were stored in a cold storehouse. Before testing, the densities of the constituent material were determined and theoretical air void content in each sample were calculated.
The main purpose of the study was to validate the existing aging models for cyclic compression creep test and stiffness modulus tests using the collected test data. The collected data from the tests were analyzed using non-linear regression. The results indicated that time coefficient (exponent) for both test methods have lower absolute value in this study than stated in the specifications. The coefficients are different for penetration and polymer modified bitumen.
There may be several reasons why the models in this study differ from the results of the previous investigations. The earlier relationships were derived based on analysis of samples aged in the field while the models in this study are based on analysis of samples aging in a more controlled laboratory environment. Another possible reason for the higher time coefficients (exponents) from the previousinvestigations could be that manufacturing temperatures for asphalt mixtures were generally significantly higher at that time.
To establish a broader basis to assesses the impact of aging on asphalt mixture mechanical properties, it is recommended to investigate several types of polymer bitumen. A more frequent field follow-up ofnewly paved pavement sections should be carried out.