The strength of this polymer (crumb rubber) is the resistance to rutting is improved because of the high viscosity. High softening point and better rebound, the resistance to the surface is improved, the fatigue / reflection crack is reduced, the temperature sensitivity is reduced, the durability is increased, the maintenance cost of the pavement is reduced and the energy and nature are saved by using waste resources (Liu et al, 2009).The weakness of the crumb rubber includes it must be applied at a specific temperature. Under normal circumstances, it is expected to be 65°c or more to properly apply it. In warm climates, this is usually not a problem. This method can be applied throughout the year. However, under certain climatic conditions, this may limit the month of laying roads in a year, which may cause great delays in the project. Rubber asphalt is sticky when used, so the road surface needs to be sprinkled with water. The amount of water required to cool crumb rubber may be very expensive, making the crumb rubber less economical.
The mixing type of asphalt and the polymer (crumb rubber) includes 11% Acetone extract, 50.5% Rubber hydrocarbon, 32.5% Carbon black content, 34.0% Natural rubber content and 6.0% of Ash content. The optimum content of the crumb rubber is 1.5-2%. Under the optimum CR content, the rutting resistance of dry asphalt mixture is the same as that of SBS and CR modified asphalt mixture. Therefore, the CR modified asphalt mixture with dry process can be used in flexible pavement to reduce rutting disease. On the other hand, it promotes the recycling of waste tires and is beneficial to environmental protection.
The mixing temperature and mixing speed is described as below. Rubberised bitumen binder was prepared in laboratory at 180°c mixing temperature (Navarro et al. 2004) and 60 minutes mixing time (Jeon et al. 2010). By heating the bitumen to 180°c first, five different concentrations of crumb rubber are prepared. When reaching 180°c, a weighted amount of rubber (4, 8, 12, 16 and 20% by weight of bitumen binder) were slowly added to the original bitumen and the propeller blade mixer is mixed at 180°c at the same time. Mixing speed is 200 rpm and mixing time is 1 hour.