Aggregate Degradation Characteristics of Stone Mastic Asphalt Mixtures

Abstract

Stone Mastic Asphalt (SMA) mixtures are designed to have a high coarse aggregate content and stone-on-stone contact, which results in more stress on the coarse aggregates during compaction and traffic loading. As a result, aggregates tend to break down more in SMA mixtures than in conventional dense graded mixtures. Aggregate degradation during compaction and traffic loading may cause changes in the original gradation and thus may also affect the volumetric parameters of SMA mixtures. Therefore, this  study was conducted to determine the degree of aggregate degradation in SMA mixtures due to the compaction process. Aggregates of two Nominal Maximum Aggregates Sizes (NMAS), designated as SMA14 and SMA20, were compacted using 50 blows of the Marshall Hammer and 100 gyrations of the Superpave Gyratory Compactor (SGC). The verified samples were then prepared and extracted using the Centrifuge Method. The relationship between aggregate degradation and influencing factors, such as compaction effort and volumetric properties were investigated. Aggregate degradation by the Marshall Hammer was found to be significantly higher than degradation by the SGC. Voids in the mineral aggregate (VMA) of either compaction method decrease or are almost the same when aggregate degradation is not significant. SGC method can be selected to represent the field roller that results in a similar trend of aggregate degradation.