Development of experimental methods for the evaluation of aggregate resistance to polishing, abrasion, and breakage



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Texas A&M University


Aggregate properties influence different aspects of asphalt pavement performance. Aggregate polishing characteristics are directly related to pavement surface frictional properties and thus to skid resistance. Aggregate resistance to degradation (abrasion and breakage) is another important property that influences pavement performance. Aggregate degradation could take place during production due to plant operations and during compaction, leading to change in aggregate characteristics and mix properties. In addition, aggregate resistance to degradation is important in mixes such as Stone Matrix Asphalt (SMA) and Open Graded Friction Course (OGFC) that rely on stone-to-stone contacts among coarse aggregates. Some aggregates in these mixes fracture due to the high stresses at contact points. Many test methods exist for measuring aggregate polishing and degradation, but a critical review of these methods reveals that they suffer from being time consuming, are unable to differentiate between aggregates with distinct resistance to polishing, or unable to differentiate between aggregate resistance to abrasion and breakage. New methodologies are needed to give better assessment of aggregate resistance to polishing, abrasion, and breakage. The thesis presents the development of new methods for measuring aggregate resistance to polishing, abrasion, and breakage. These methods rely on measurements using the Aggregate Imaging System (AIMS) and Micro-Deval. The new method for measuring aggregate resistance to polishing monitors change in aggregate texture as a function of polishing time. As such, it provides the initial texture, rate of polishing, and final texture. The new method for measuring aggregate degradation is capable of distinguishing between breakage and abrasion. In this method, abrasion is defined as the reduction in aggregate angularity, while breakage is defined by fracture of particles. The new methods are shown to be rapid and accurate, and they require reasonable training. Since both AIMS and Micro-Deval are used in the new methods, it was necessary to evaluate the repeatability of these two methods. Measurements using two AIMS units and two Micro-Deval machines were used to assess the variability. There was no statistical difference between the measurements of the two AIMS units or between the measurements of the two Micro-Deval units.