Browsing by Subject "Skid Resistance"
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Item Analysis of aggregate imaging system (AIMS) measurements and their relationship to asphalt pavement skid resistance(2009-05-15) Luce, Anthony DavidThis thesis consists of two parts. The first part includes analyses of the correlation between the results of two Aggregate Imaging System (AIMS) units. These analyses have led to refinements of the AIMS analysis methods of angularity and texture, which resulted in reduced variability in the results and better correlation between the two AIMS units. The refined analysis methods were used to establish a database of the shape characteristics of about 100 aggregate samples from the state of Texas and to propose a new method for the classification of aggregates based on their shape characteristics. This new method of classification is for use in the Texas Department of Transportation (TxDOT) wet weather accident reduction program (WWARP). The use of AIMS texture index and variability in texture within an aggregate source is proposed instead of the British Polish Value (BPV) for classifying aggregates used in pavement surfaces. The second part of the thesis investigates the relationship between shape characteristics and asphalt pavement skid resistance. Many states have implemented wet weather accident reduction programs aimed at maintaining acceptable levels of pavement skid resistance. Proper aggregate selection before construction aids in maintaining acceptable levels of skid resistance throughout the life of the pavement. Several predictive models of pavement skid resistance have been developed over the years. Some of these models account for the influence of aggregate characteristics on pavement skid resistance, primarily through incorporating the results of the BPV test in the model. However, the BPV test is known to have high variability and dependence on experimental factors that are not related to the actual aggregate resistance to polishing. AIMS offers a method to measure aggregate shape characteristics directly in a relatively short period of time. The new method for relating aggregate shape characteristics to pavement skid resistance was verified by relating skid resistance measurements from field test sections to measured aggregate properties from the laboratory. This methodology is expected to be the basis for further study to form a more comprehensive and verified model for the prediction of pavement skid resistance that incorporates measured aggregate properties from the AIMS system.Item Development of experimental methods for the evaluation of aggregate resistance to polishing, abrasion, and breakage(Texas A&M University, 2007-04-25) Mahmoud, Enad MuhibAggregate 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.