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3 CHAPTER 1 Introduction and Research Approach This section of the report presents the project background, for measuring shape, texture, and angularity characteristics objectives, and descriptions of the tasks performed in the of aggregates used in HMA and hydraulic cement concrete research project. mixtures, and unbound base and subbase layers of highway pavements. The research focused on the characteristics of Project Background coarse aggregates, but also considered the characteristics of fine aggregates. The properties of coarse and fine aggregates used in hot-mix asphalt (HMA) and hydraulic cement concrete mixtures, and unbound base and subbase layers influence the performance Scope of Study of the pavement system in which they are used. Particle shape, This study included collecting and reviewing informa- texture, and angularity are among the aggregate properties that tion relative to the effects of shape, texture, and angularity have significant effect on performance. These properties vary characteristics of aggregate on the performance of HMA and widely with the type and source of aggregates and processing hydraulic cement concrete mixtures, and unbound materials techniques. However the current aggregate specifications do not address in a direct manner the measurements of these used in highway pavements. This information was obtained properties, thus leading to inconsistent interpretation and use from domestic and foreign literature, contacts with public of test results. and private agencies and industry organizations, and other Several methods for measuring aggregate shape, texture, and sources. The collected information was used to (1) identify angularity characteristics were developed in recent years, and aggregate particle characteristics that are likely to influence others are being developed as part of ongoing research efforts. performance and (2) to identify test procedures currently However an evaluation of these methods with respect to their used in the United States and other countries for measuring practicality, labor requirements, ease of use, cost, versatility, these characteristics. The merits and deficiencies of the test field applicability, use in multiple-ratio shape analysis, and methods were evaluated based on the published information other factors has not been performed. Without this informa- with consideration to relevance, practicality, labor require- tion, a rational recommendation for incorporating such test ments, cost, duration of test, repeatability, versatility, field methods in aggregate specifications cannot be made. Research applicability, use in multiple ratio shape analysis, and other was needed to evaluate potential test methods and identify or pertinent factors. develop suitable test methods for measuring relevant properties The evaluation of all available test methods was followed in central and field laboratories, and to develop recommen- with the execution of an experimental plan to evaluate and dations to help improve specifications for aggregates used in validate the most promising test methods, and if necessary, highway pavements. This need was addressed in this NCHRP to develop new methods for measuring shape, texture, and project. angularity characteristics of aggregates. The test methods recommended as a result of the experimental evaluations are presented in Appendix A. Note: Appendixes B through Research Objective E are not published herein. These appendixes are acces- The objective of this research was to identify or develop, sible as Web-Only Document 80 at http://trb.org/news/ for use in central and field laboratories, suitable test methods blurb_detail.asp?id=7276.