Utilizing recycled asphalt pavements (RAP) in pavement construction is known as a sustainable approach with significant economic and environmental benefits. While studying the effect of high RAP contents on the performance of hot mix asphalt (HMA) mixes has been the focus of several research projects, limited work has been done on studying the effect of RAP fraction and particle size on the overall performance of high RAP mixes produced solely with either coarse or fine RAP particles. To this end, three mixes including a conventional control mix with no RAP, a fine RAP mix (FRM) made with 35% percent fine RAP, and a coarse RAP mix (CRM) prepared with 54% of coarse RAP were designed and investigated in this study. These mixes were evaluated with respect to their rutting resistance, fatigue cracking resistance, and low temperature cracking performance. The results indicate that although the CRM had a higher RAP content, it exhibited better or at least the same performance than the FRM. The thermal stress restrained specimen testing (TSRST) results showed that the control mix performed slightly better than the CRM, while the FRM performance was adversely affected with respect to the transition temperature midpoint and the maximum tensile stress temperature. Both of the RAP incorporated mixes exhibited better rutting resistance than the control mix. With regard to fatigue cracking, the CRM performed better than the FRM. It can be concluded that the RAP particle size has a considerable effect on its contribution to the total binder content, the aggregate skeleton of the mix, and ultimately the performance of the mix. In spite of the higher RAP content in the CRM versus FRM, the satisfactory performance observed for the CRM mix indicates a great potential in producing high RAP content mixes through optimizing the RAP particle size and content. The results also suggest that the black curve gradation assumption is not representative of the actual RAP particles contribution in a high RAP mix.

Recently, significant advancements in the modeling of asphalt concrete have been made in micromechanics to describe the behavior and performance of asphalt pavements using the properties of their component materials. On the other hand, this approach has great potential benefits in the field of asphalt technology for reducing or eliminating costly tests to characterize asphaltic mixtures. In this study, two-dimensional Discrete Element Modeling (DEM) was employed to investigate the deformation characteristics of Stone Matrix Asphalt (SMA). Instead of the randomly generated initial models Image processing techniques were employed to make it possible to compare the actual and virtual test results. For this purpose, a series of Unconfined Dynamic Creep tests were also carried out in the laboratory according to British Standards. It has been concluded that the developed 2D-model can well predict the deformation characteristics of SMA mixes, however the results of simulations under-predict the accumulated permanent strain obtained through laboratory tests.

Modification of the asphalt binder is one approach taken to improve Asphalt pavement performance. Rutting is one of the most important factors that could reduce the life of asphalt pavements.Nowadays, the application of nanotechnologyto achieve materials that are more resistant is expanding in asphalt pavement thatNano-TiO₂ is among the most exciting and promising classes of materials discovered recently. The purpose of this study is laboratory research on the effect of Nano-TiO₂ in improving Bitumen property and rutting resistance in Asphalt pavement under dynamic loading. For this purpose, the wheel-tracking test was carried outon ordinary and Nano-TiO₂ modified hot mix asphalt samples.The results illustrate that using Nano-TiO₂in asphaltbinder samples cause to an improvement in ruttingdepth in comparison with theordinarymixtures.