ملخص
Abstract
The stiffness modulus of asphalt in hot arid climatics was found to increase rapidly with pavement age and loading rate this reflects the rapid hardening and a complex change in the composition of the asphalt binder occurs due to high thermic susceptibility of the asphalt binder material in hot arid zones of sever climate.Besids this there is an increase in traffic heavier loads and higer tire pressures, the chemical composition of asphalt binders material and their rheological and visco-elastic properties also having a great role on the performance of these the asphalt binder material, a higer performance pavement requires asphalt that is less susceptible to high temprature ruttings or low temprature cracking and having sufficient bonding to stones aggregates. The durability of asphalt concrete is greatly influenced by the enviromental changes during the year between hot and cold tempratures and btween day and night high temprature can soften the asphalt making the mix more suscebtiple to rutting on the other hand low winter tempratures can increase the stiffness of asphalt reduce the flexibility of the asphalt concrete inducing fatique failure and serious cracks which adversly affects the pavement performanance the problem accetuated in hot arid site The loss of flexibility of the binder material will make the asphaltic mix susceptible to shrinkage cracking in the large temperature ranges that occur in these climates. For many years, researchers and development chemists have experimented with modified bitumen’s, of diffrent types . In the last thirty years many researchers have looked at a wide spectrum of modifying material Research continues in the quest to find materials that could enhance the properties of asphalt mixes thus enhancing pavement performance and reducing road maintenance costs. Addition of polymers has become common practice in several countries, with the main objective is improving flexibility and reducing thermal susceptibility of modified asphalt binders. There is growing interesting in asphalts modification with crumb rubber recycled from used tires, since this constitutes an important unique properties for asphalt improvement. The rubber used to produce tires comprises a mixture of different components, of valuable engineering characterstics, when crumb rubber is incorporated. The behavior of modified asphalt-rubbers depends on several factors, such as, the origin, fabrication process and grain size, the type of base conventional binder used in the mixture, temperature and time of the mixing process or digestion., a conventional base binder material having a penetration grade of 60/70 was mixed with rubber tires of (1-10 % by asphalt weight contents, was mixed for variable digestion times. The binder-rubber mixtures, produced using the wet process, were subjected to conventional tests, such as, penetration, softening point, Brookfield viscosity. The objective of the present work was to investigate the main characteristics of crumb rubber that affect the physical and the flow and the mehanical properties of modified binders. The results and findings from the study shows that the rubber additive can be added up to 5 % by asphalt weight did improvements in asphalt intrinsic characerstics