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Four-point bending fatigue tests following the Strategic Highway Research Program (SHRP) M009 test protocol were executed to investigate to what extent gradation has an effect on fatigue performance of asphalt aggregate mixes. Gradations and mixes were selected that would satisfy all volumetric Superpave designs passing below the restricted zone. Other mixes were prepared with gradations passing through and above the restricted zone. The measured fatigue lives of 130 actual laboratory tests were compared with predictions by the Shell, Asphalt Institute, and SHRP-A003A fatigue-predictive equations.The fatigue life of an asphalt concrete mixture is influenced by several factors, such as bitumen type and content and air-void content. Others factors, such as temperature, frequency, and rest periods of applied loads, as well as other material properties, may also affect fatigue life. Although the influence of binder type and content has been studied extensively, the effect of some aggregate properties, such as the aggregate gradation, has not been widely presented.Superpave volumetric mix designs (previously referred to as Level I in the research documents) select a binder content and a gradation that are dictated by the behavior of the mix at compacting temperatures in the gyratory compactor. No performance-based tests are executed on the mix to evaluate its behavior at in-service temperatures.In the process of evaluating the possibility of adopting the Superpave volumetric mix design procedures in Portugal, the road administration (Junta Autónoma de Estradas) investigated to what extent mixes proposed by the Superpave volumetric procedure are superior in performance to other mixes. For that evaluation process, one of the tools used in comparing mixes was the determination of fatigue life using the Strategic Highway Research Program (SHRP) M009 four-point bending fatigue test. Fatigue performance needs to be evaluated to prevent dense-graded mixes from being too "dry," because that could lead to premature fatigue failures. Furthermore, criteria are needed to evaluate the performance of mixes to be placed on structural fatigue-resistant layers.The gradations proposed by the Superpave volumetric design procedures generally pass below the restricted zone. For comparison purposes, other gradations were selected that pass through and above the restricted zone. The other gradations were selected on the basis of standard specifications used by some highway agencies. As such, gradations were selected that would satisfy (or at least come

A new and innovative mechanistically based pavement overlay design method is described that considers the most predominant type of overlay distress observed in the field: reflective cracking above old cracks in the underlying pavement surface. Both dense-graded hot-mix asphalt (HMA) and gap-graded asphalt rubber (wet process) mixes were studied in the laboratory and in the field to derive the necessary mechanistic relationships and statistically based equations. The models proposed are based on a finite element model that closely approximates actual field phenomena. Many field test sections, mainly in Arizona, were studied during the course of the research. Other HMA mixes used for overlays may also be calibrated and used through the proposed method, but the relevant mix properties of any additional materials or environmental zones must first be determined. The two mix types studied are mainly used in the desert southwest region of Arizona and California. The overlay design program is available from the Rubber Pavements Association or Arizona Department of Transportation in the form of an Excel spreadsheet with an easy-to-use Visual Basic computer program (macro).

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