experimental study of nano clay and crumb rubber influences on mechanical properties of hma

during the recent years, increased traffic load, axis load and tire pressure have influenced asphalt mixtures functions and has decreased transportation and shortened their lifetime.  although asphalt mixture function depends up on its material properties, precise design and manufacturing quality, us¬ing nano materials and crumb rubber in asphalt mixture is improving for asphalt function enhance¬ments. the study purpose is to investigate the impact of using nano clay and crumb rubber together on mechanical properties of binder layer asphalt mixtures by marshall and conventional bitumen tests by modifying the bitumen properties by the crumb rubber and substitution of usual fillers by nano clay. in this study the crumb rubber (5, 10, 15, 20 and 25 weight percent of bitumen) was mixed with the pure bitumen 60/70 in wet method and the nano clay was used with 5 different weight percent (from 1 to 5 weight percent of the aggregates). the study results showed that marshall strength in¬creased by increasing nano clay and crumb rubber composition in the mix, and the highest strength obtained with 10% crumb rubber and 5% nano clay portions. in addition, by increasing nano clay-crumb rubber portion in the asphalt mixture, compared to the control sample, the aggregate pore vol¬ume increased, the total pore volume of the whole mixture was relatively increased and the mixture special gravity was slightly decreased. also, by doing the bi¬tumen tests it was observed that the modi¬fied bitumen thermal sensitivity decreased and its viscosity and penetration degree increased by in¬creasing the crumb rubber portion.