The Bailey method was created in the United States in the early 1980s by Robert Bailey of the Illinois Department of Transportation. It enables the selection of an aggregate gradation that guarantees the best interlocking of aggregate particles, a suitable amount of VMA, and proper voids in the final asphalt mix. It was primarily intended for designing continuously graded mixtures with high deformation resistance, but it may also be applied to designing SMA gradation.
The method for gradation selection is based on the principle of the packing characteristics of aggregates and finally allows designing mixtures with expected aggregate interlocking. The complete method is used only for aggregate gradation design, not for full SMA (with binder) recipe design.
Those who are interested in Bailey’s method can refer to the publication by Vavrik et al. (2002), which contains a very detailed description of the consecutive stages of the procedure, calculations, and some examples of design.
