Effect of Concentration and Size of Crumb Rubber on Rheological and Cold Bending Properties of Bitumen

Hypothesis:

 Annually, large amounts of waste tire are disposed into environment. Since decomposition process of these tire materials takes a long time, the governments have imposed regulations to find environmentally-friendly solutions to recycle the waste tires. There are different approaches to take on the modification of physical and mechanical properties of bitumen or asphalt with crumb tires. The results of those studies have illustrated positive effect of crumb rubber on bitumen properties. Therefore, it is reasonable that concentration and size of crumb rubber could affect the bitumen properties.

The effect of concentration (3%, 7% and 10 wt%) and size (1, 0.6, 0.3 and 0.1 mm) of crumb rubber was considered on the viscosity, physical and rheological properties of bitumen/rubber blends. Furthermore, to better decide on the use of crumb rubber for bitumen, the viscosity of modified bitumen was studied.

The results of this study identified that high concentration and smaller dimension of crumb rubber improved cold flexibility and rheological properties of bitumen. Increasing in crumb rubber concentration to 10 wt% resulted in lowering flexibility temperature of bitumen from 20°C to 10°C and even, in smaller sizes (0.1 mm) the flexibility diminished to 8°C. Furthermore, this research showed that at higher concentration and smaller size of crumb rubber the resistance to rutting of bitumen enhanced from 35°C to 60°C. However, the viscosity results showed that a high level of crumb rubber (above 7 wt%) increased the viscosity dramatically and restricted its application. So, adding 7 wt% of crumb rubber with a size of less than 0.1 mm can optimize the physical and mechanical properties of bitumen.