Experimental Study of the Effect of Crumb Rubber on Properties of Asphalt Mix by Wet Process

Abstract

The increase in the number of vehicles during the past twenty years has dramatically increased the traffic density and axial loading. In addition to the construction failures and lack of periodic maintenance, rapid deterioration of the road condition happens. So, it was necessary to find solutions to these problems that have been growing for years. One of these solutions is to improve the asphalt mixture to resist excessive loads and weather fluctuations. This research aims to investigate the addition of crumb rubber derived from recycled tires; to the asphalt mixture for improving performance characteristics and to compare the improved and unimproved samples. It is worth mentioning that crumb rubber addition to the asphalt mixture is considered one of the smart solutions for sustainability that the world is heading towards today, considering that the crumb rubber comes from waste tires, which is difficult to eliminate and pollute the environment. Four different proportions of crumb rubber have been added in this research (6, 9, 12, and 15%); by weight of bitumen to (60-70) asphalt binder, with a particle size passing from sieve no.50 (0.3 mm). The aggregate gradation is designed according to the Marshall method with a (12.5 mm NMAS) wearing course to obtain the optimum asphalt content and to prepare laboratory samples to perform various laboratory tests. Marshall Stability and flow, indirect tensile strength (ITS), moisture susceptibility, and permanent deformation of asphaltic mixes with different contents of crumb rubber were investigated. The results of the tested samples were compared with the original samples. It is shown that the asphaltic mixes performance has been improved when adding a certain amount of crumb rubber. Marshall Stability is increased by 29.2% when adding 9% CR by the weight of bitumen. However, the addition of crumb rubber can increase the stiffness of the asphalt mixture resulting in a more rigid pavement structure that is less prone to moisture damage and rutting under traffic load.