bituminous asphalt binder materials which are modified by the addition of crumb rubber or ground tire rubber and a cross - linking agent are described . in addition , methods are provided for producing a modified asphalt binder containing crumb rubber or ground tire rubber and a cross - linking agent . the modified asphalt binders comprise neat asphalt , crumb rubber , one or more acids and a cross - linking agent . optionally , the modified asphalt binder may include one or more polymer additives . the crumb rubber may be obtained from recycled truck and / or automobile tires . the addition of crumb rubber in asphalt binders can improve the consistency and properties of the asphalt binders at high and low temperatures . in particular , the modified asphalt binders of the present invention exhibit improved elastic behavior , resulting in improved performance of roads or other surfaces paved using the modified asphalt binder . road resistance to permanent deformation , fatigue cracking and thermal cracking is improved by use of the modified asphalt binder .