Influence of Aging Condition on Performance of Fine Aggregate Asphaltic Matrix

Abstract

The major distresses in the flexible pavement are fatigue cracking, rutting, and moisture induced damage. There is lack of consideration of ideal test methods to evaluate the distresses present in the asphaltic pavement. By knowing the majority of the distresses appear within the mortar or Fine Aggregate Matrix (FAM) of the asphalt mixture, researchers have started to use this FAM phase in place of full asphalt mixtures to characterise the performance properties. Additionally, one can also attain higher precision in test results from Dynamic Shear Rheometer (DSR) by maintaining the uniformity in the prepared FAM specimens. The thesis report presents the research study performed on FAM mixtures focusing on its test methodology, rheological investigation results, and conclusions of the study. The main objectives of the present research is (i) to investigate the effect of different long-term oven aging (LTOA) levels on performance properties of FAM mixtures to mitigate the fatigue cracking in asphalt pavement, (ii) to assess and analyse the effect of binder types, different loads, and temperatures on creep and recovery performance of the FAM mixtures, (iii) to assess and analyse the impact of moisture on creep recovery response of FAM mixtures. To achieve this objective, a detailed test plan was prepared based on exhaustive review of research findings related to FAM mixtures and the latest practices for FAM characterisation were adopted by various agencies across the world. Major differences were observed in these practices, particularly with respect to the different aging methods, gradations used/considerations, specimen preparation method, and considerations of air voids, binder content, binder grade, and binder types. In light of the above, the rheological investigation was carried out on FAM mixtures in three stages, i) Cracking susceptibility of FAM mixtures prepared with three different asphalt binders VG-30, VG-40, and PMB(S) is evaluated through the experimental testing and numerical modeling on FAM mixtures produced at design (laboratory) stage. Various criteria and approaches for the prediction of cracking in FAM mixtures are assessed and their correlation is discussed. Different levels of aging in laboratory are simulated, and the effects of long term oven aging (LTOA) on linear viscoelastic parameters, and fatigue characteristics of FAM mixtures are explored. ii) Creep recovery behavior of FAM mixtures were evaluated by vii determining the percent recovery (%R) and non-recoverable creep compliance (Jnr) parameters from the Multiple Stress Creep Recovery (MSCR) test at different stress levels and temperatures. Additionally, strain response from the Burgers four element model was also modelled and compared with the observed experimental results, iii) Resistance to moisture-induced damage of FAM mixtures was evaluated by determining the ratios of %R and Jnr in dry and wet conditions from the Static Creep Recovery (SCR) test at 40°C for different stress levels. Results of the study indicated that irrespective of the aging level applied to the FAM specimens, there is a small difference in the LVE limit was found for all FAM mixtures. Viscoelastic properties (|G*| and δ) for FAM specimen aged for 24 hrs at 135°C, and 12 days at 95°C aged FAM specimens showed similar results from the master curve plots. The fatigue life of FAM mixtures decreased as the aging level increases as expected. Despite of the similar viscoelastic properties, the trend observed between FAM mixtures aged 12 days at 95°C and 24 hrs at 135°C were not found to have similar fatigue life. Among FAM mixtures considered, the F2 mixture prepared with asphalt binder (VG-40) showed good resistance against permanent deformation for all the considered temperatures and corresponding stress levels. An important finding of this study also reported that Burgers model can be successfully applied for creep-recovery response of FAM mixtures under different temperatures and stress levels considered in this research. Further, the F3 mixture shows the highest %Rratio and lowest Jnr_ratio values compared to the other two FAM mixtures, indicating a lower sensitivity to moisture damage which could be possibly due to the use of polymer modifier in F3 mixture. Overall, based on the findings observed from the above rheological investigations, the FAM phase of full asphalt mixtures can be successfully used to characterise the effect of long-term aging on viscoelastic and fatigue properties of FAM mixtures. Similarly, FAM phase can also be used successfully to describe the permanent deformation, and moisture induced damage characteristics of FAM mixtures.