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Marginal hard asphalt possesses high stiffness and modulus; however, due to poor ductility at low temperature, it was seldom applied into road structures. Increasing asphalt content seemed to be an effective way to minimize the thermal cracking problem of hard hot-mix asphalt (HMA). Therefore, three types of methods (Groups 2–4) aiming to improve hard asphalt content were designed and compared with the traditional method (Group 1). Specifically, Groups 2 and 3 were designed with coarser gradation and lower gyration levels (Ndes), respectively, and Group 4 was designed following the enrobé à module élevé 2 (EME2) method. The high- and low- temperature, fatigue, modulus, and cracking performance were then conducted for each group. It can be seen that with the increase of asphalt content, the low-temperature strain increased in all three groups, of which Groups 2 and 3 improved more significantly. In addition, with the coarser gradation or lower Ndes , the high-temperature and cracking resistance of hard HMAs was lost to some degree; however, they can still compete with traditional neat HMAs. The hard HMAs designed with EME2 method performed excellent dynamic modulus and rutting resistance. Moreover, the hard HMAs designed with EME2 method and lower Ndes showed a surprising improvement in the fatigue life. These results may contribute to the better use of hard HMAs. [ABSTRACT FROM AUTHOR]

Using recycled materials in construction of asphalt pavements yields both economic and technical advantages. Recycled asphalt shingles (RAS) and reclaimed asphalt pavement (RAP) are two major sources to serve this purpose for which proper design and characterization are key elements. In this study, engineering properties of asphalt concrete containing RAP and RAS under dynamic loading were investigated. Three asphalt mixes were designed and included in this research: a conventional mix with no RAP/RAS as a control, a mix with 35% RAP, and finally a mix with 35% RAP and 5% RAS. A conventional resonant column (RC) apparatus was retrofitted and used for testing the specimens in torsional mode. Testing was conducted at five temperatures ranging from 10 to 45°C. Damping ratios and moduli of the mixes were analyzed and compared to assess the effect of the recycled materials on dynamic properties of asphalt concrete. Results clearly show the impact of RAP and RAS in increasing the mix stiffness. The study also included uniaxial dynamic modulus (DM) testing of the control mix to compare the moduli measured at high frequencies through RC testing to those estimated by the DM master curve through extrapolation. Results show that the modulus obtained from RC testing correlates well with that extrapolated from DM tests. Results also indicate that the accuracy of such correlation is significantly increased once dependency of Poisson's ratio on modulus is incorporated. [ABSTRACT FROM AUTHOR]

Polymers are commonly used to modify asphalt binder in order to satisfy the performance-grade binder's rheological properties, such as shear, storage, loss, and bending stiffness. However, it is not known what types and percentages of polymers affect these properties under conditions of aging. To this end, base asphalt binders were modified with styrene-butadiene and styrene-butadiene-styrene polymers at 3, 4, and 5% and then aged in the laboratory using a rolling thin film oven for short-term aging, a pressure aging vessel for long-term aging, and a draft oven for intermediate aging. The stiffness properties of the modified binders were determined using dynamic shear rheometer (DSR), multiple-stress creep recovery (MSCR), Brookfield rotational viscometer (RV), and bending beam rheometer (BBR) tests. Comparison of aging indexes for storage and loss modulus indicated that aging increases the elastic or storage component more than the viscous or loss component of the complex shear modulus. It was shown that increasing the percentage of polymer results in a decrease in aging for both SB- and SBS-modified binders. Those modified with SB are more resistant to aging than are those modified with SBS. [ABSTRACT FROM AUTHOR]