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47 CHAPTER 4 Conclusions and Suggested Research General Conclusions are not suitable to distinguish between these two characteristics. Also, some of the analysis methods do not distinguish between The literature review conducted in this study revealed that changes in texture and angularity. The following analysis the shape properties of coarse and fine aggregates used in hot- methods are recommended: mix asphalt, hydraulic cement concrete, and unbound base and subbase layers influence the performance of the pavement Texture: Wavelet analysis of gray images of particle surface system in which they are used. Aggregate characteristics can be (Implemented in AIMS software). decomposed to three independent scales: shape, angularity, Angularity: The gradient method (implemented in AIMS and texture. Methods currently used for measuring these char- software) and the changes in the slope of a particle outline acteristics have several limitations: they are laborious, subjec- (implemented in the UIAIA software). tive, lack direct relation with performance parameters, and have Shape: Sphericity or the proportions of the three particle limited ability to separate the influence of angularity from dimensions (implemented in MRA, AIMS, and UIAIA). that of texture. A number of research studies have shown that aggregates, especially coarse aggregates that exhibit high texture, Accuracy of test methods was assessed through statistical do not necessarily have high angularity. Consequently, it is analysis of the correlations between the results from test important to develop methods that are capable of quantifying methods and measurements of shape using a digital caliper each of the aggregate characteristics rather than a manifestation and visual rankings of surface irregularity and texture by of their interactions. experienced individuals. Test methods used for measuring aggregate shape proper- The Analytical Hierarchy Process (AHP) was implemented ties were evaluated in this study. The evaluation considered in a program to rank the test methods. This process provided accuracy, repeatability, reproducibility, cost, ease of use, ease flexibility to examine the influence of changes in the importance of interpretation of the results, readiness of the test for imple- of the characteristics on the ranking of test methods, and also mentation, portability, and applicability for the analysis of provided extensive information on the relationship between different sizes and types of aggregates. Thirteen different coarse test methods and desirable characteristics. aggregate types and five different fine aggregate types were The Aggregate Imaging System (AIMS) is recommended used in this evaluation. for measuring the characteristics of both coarse and fine Analyses of repeatability and reproducibility results were aggregates. It employs methods based on sound scientific conducted under the guidelines of ASTM standards E 177, concepts for the analysis of shape, angularity, and texture C 802, and C 670. Accuracy of the analysis methods used in and provides the distribution of each of the characteristics the imaging systems was assessed by analyzing some particle in an aggregate sample. It has very good control of lighting projections that have been used by geologists for visual eval- and provides repeatable and reproducible results. The Uni- uation of particles' shape. Also, all analysis methods were used versity of Illinois Aggregate Image Analyzer (UIAIA) can also to analyze images of aggregate particles in order to identify the be used for measuring the shape, angularity, and texture of ability of these methods to accurately rank aggregates and cap- coarse aggregates. For measuring the coarse aggregate shape ture unique characteristics of aggregates. The analysis results only, the Multiple Ratio Shape Analysis method (MRA) is revealed that some of the available analysis methods are influ- most desirable, and is much cheaper than all the other test enced by both angularity and shape changes and, therefore, methods. The MRA provides the distribution of shape in an