Superpave protocols for modified asphalt binders

One of the main objectives of the Strategic Highway Research Program (SHRP) was to develop test methods for the characterization of asphalt binders that are equally applicable to unmodified and modified asphalt binders without exceptions. However, the research conducted during the SHRP program focused on the use of unmodified binders. Because of this, there are concerns that the SUPERPAVE specifications may not be applicable to various modified asphalt binders. Recent studies have indicated that the parameters used in these specifications, which are based on linear visco-elasticity, do not apply equally to modified binders and do not relate well to paving mixture behaviors. These concerns about the applicability of the Superpave protocols to modified binders resulted in the launch of a new study in 1996 called the NCHRP 9-10 project, “Superpave Protocols for Modified Asphalt Binders”. This thesis is a part of the NCHRP 9-10 program.; In this study, performances under repeated loading (fatigue and rutting) and storage stability of modified asphalt binders were investigated to test the hypothesis that modified binders can be characterized using the SUPERPAVE binder testing system. The tests results from this thesis indicated that most modified asphalts are affected significantly by repeated loading and that the majority of these asphalts are two-phase systems that require special handling to keep them stable. The study was then expanded to develop testing protocols and specification parameters that allow better evaluation of the role of asphalts in pavement performance. Testing protocols were developed to differentiate the damage-related characteristics (fatigue and rutting resistance) among modified asphalt binders and also to measure the storage stability as a function of storage time. The results collected using the new tests indicated that by selecting the proper test conditions, these protocols could give reliable results that estimate the storage stability and that correlate well with mixture performance.