Disposal of waste tires has been known as a serious environmental problem. Since burying tires in landfills is not an easy solution either, highway engineers around the world have tried to incorporate scrap tire rubber in asphalt pavements as a modifier. This book investigate the use of Crumb Rubber Modifier (CRM) as a waste material in modifying the performance of the asphalt concrete mixtures. HMA mixtures characterization in terms of fatigue cracking and rutting resistance was analyzed and evaluated to determine the effects of the crumb rubber on the mixtures’ performance. In addition, studying the effect of various environmental effects such as temperature, aging and moisture damage on the mechanical properties of the asphalt concrete mixtures. Several tests were used such as indirect tensile strength, indirect tensile fatigue and static creep test.