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This study evaluates the crack performance of stone mastic asphalt (SMA) mixtures according to the performance of a modified asphalt binder, evaluated based on the asphalt performance grade (PG) and the elastic recovery of multiple stress creep and recovery (MSCR) according to AASHTO M 320 and T 350. The cracking performance of the mixture was evaluated using the asphalt mixture performance tester (AMPT) according to AASHTO T 378 and T 400 through dynamic modulus and direct tension cyclic fatigue tests. Furthermore, the recently developed viscoelastic continuum damage (VECD) theory was utilized to evaluate the cyclic fatigue index parameter (apparent damage capacity, Sapp) and the permissible heavy vehicle class. For performance evaluation, six modified asphalt mixtures were prepared and tested using SMA aggregate gradation with a nominal maximum aggregate size (NMAS) of 10 mm. The MSCR test results revealed that, of the six asphalt mixtures, the rubber-based PG76-28 exhibited the least initial strain and the highest elastic recovery. The dynamic modulus test results demonstrated that using a rubber-based modifier increased the elastic modulus at high temperatures and decreased it at low temperatures, thereby enhancing resistance to plastic deformation in the summer and reducing low-temperature cracking in the winter. Finally, the correlation between the Sapp performance index and the elastic recovery of modified asphalt and the number of direct tension cyclic loads until failure of the mixture was evaluated as 0.87 and 0.76, respectively. [ABSTRACT FROM AUTHOR]

This study evaluates the crack performance of stone mastic asphalt (SMA) mixtures according to the performance of a modified asphalt binder, evaluated based on the asphalt performance grade (PG) and the elastic recovery of multiple stress creep and recovery (MSCR) according to AASHTO M 320 and T 350. The cracking performance of the mixture was evaluated using the asphalt mixture performance tester (AMPT) according to AASHTO T 378 and T 400 through dynamic modulus and direct tension cyclic fatigue tests. Furthermore, the recently developed viscoelastic continuum damage (VECD) theory was utilized to evaluate the cyclic fatigue index parameter (apparent damage capacity, Sapp) and the permissible heavy vehicle class. For performance evaluation, six modified asphalt mixtures were prepared and tested using SMA aggregate gradation with a nominal maximum aggregate size (NMAS) of 10 mm. The MSCR test results revealed that, of the six asphalt mixtures, the rubber-based PG76-28 exhibited the least initial strain and the highest elastic recovery. The dynamic modulus test results demonstrated that using a rubber-based modifier increased the elastic modulus at high temperatures and decreased it at low temperatures, thereby enhancing resistance to plastic deformation in the summer and reducing low-temperature cracking in the winter. Finally, the correlation between the Sapp performance index and the elastic recovery of modified asphalt and the number of direct tension cyclic loads until failure of the mixture was evaluated as 0.87 and 0.76, respectively.

Modification of asphalt binders has been one of the common techniques to overcome the climatic and traffic-related distresses that develop in bituminous materials. Over the past decade, many new methods of incorporating recycled tire rubber as a modifier have been developed and evaluated by states and county road departments. This study focuses on the use of the so-called devulcanized recycled tire rubber modifier and its effects on the performance grade, fatigue cracking resistance, and rutting resistance of asphalt binder. Devulcanized rubber was incorporated into hot liquid asphalt at various percentages using high and low shear blending, consecutively. First, the effect of modifications on continuous performance grades (PG) at low, intermediate, and high temperatures was investigated. Second, equistiffness temperatures of the binder-rubber mixes were established, and the fatigue cracking resistances of the rubber-binder blends were measured by using the linear amplitude sweep (LAS) test at different strain levels. Last, the multiple stress creep and recovery test (MSCR) was conducted on the modified asphalt samples to characterize the high-temperature performance. Although there was a significant improvement on high PG as the modifier amount increased, the improvement for intermediate and low PGs was minimal. The same trend observed for high PG of the modified asphalt binders was also obtained for fatigue cracking resistance and rutting resistance. The results showed that the use of devulcanized rubber modification could successfully extend the life of bituminous materials. [ABSTRACT FROM AUTHOR]