Asphalt additives to control rutting and cracking

This thesis presents the results of an investigation of the performance of a variety of materials added to asphalt binders and mixtures to change their properties, particularly with respect to rutting and cracking. Two approaches were taken. The first was a field trial of seven polymer and particulate modifiers, supplemented by laboratory characterization of the materials used in the field. The modifiers evaluated included PAC, Novophalt, Multigrade asphalt cement, polyester fibers, Neoprene, SBR and asphalt rubber. The second approach was a laboratory study of the effects of reclaimed asphalt pavement (RAP) on asphalt binders and mixtures. The field trial showed that different modifiers do yield different performance. Modifiers are not essential to ensure that the pavement will not rut. None of the mixtures evaluated here exhibited appreciable rutting. Dramatic differences were noted in the cracking behavior, however. Newly developed laboratory tests were able to identify binders that would be more prone to cracking. The RAP study demonstrated that RAP is indeed an asphalt modifier, not merely a black rock. The effects of the RAP on binder and mixture properties were also investigated. The stiffening effect of the hardened RAP binder must be accounted for in binder selection and mixture design. When using RAP contents higher than approximately 15% by weight of mix, it is necessary to use a softer virgin binder grade to compensate for the hardened RAP binder. This is also standard practice with certain conventional modifiers, such as asphalt rubber. All of the materials evaluated did change the properties of the binders or mixtures in some way. Some of the modifiers, however, were more effective at modifying the properties to provide improved field performance in a cost effective manner.