The National Academies

NCHRP 04-30A [Completed]

Test Methods for Characterizing Aggregate Shape, Texture, and Angularity

  Project Data
Funds: $450,000
Research Agency: Texas A&M Research Foundation
Principal Investigator: Eyad Masad
Effective Date: 8/28/2003
Completion Date: 5/31/2005

The project identified a rational methodology for classifying aggregates based on the distribution of shape, texture, and angularity characteristics and recommended a test method for measuring these characteristics. The test method measures shape, texture, and angularity characteristics of aggregates used in hot-mix asphalt, hydraulic cement concrete, and unbound base and subbase layers of highway pavements, and it is appropriate for use in central and field laboratories.

The properties of coarse and fine aggregates used in hot-mix asphalt (HMA) and hydraulic cement concrete and unbound base and subbase layers are very important to the performance of the pavement system in which they are used. Particle shape, texture, and angularity are among the aggregate properties that have significant effects on performance. These properties vary widely with the type and source of aggregates and processing variables. However, current aggregate specifications do not address, in a direct manner, the measurement of these properties, thus leading to inconsistent interpretation and use of test results. Also, a thorough evaluation of available methods for measuring aggregate shape, texture, and angularity characteristics has not been performed to identify appropriate methods. Without this information, a rational recommendation for incorporating such test methods in aggregate specifications can not be made. Thus, research was needed to evaluate potential test methods and identify or develop suitable test methods for measuring relevant properties in central and field laboratories, and to develop recommendations to help improve specifications for aggregates used in highway pavements.

Research included a review of information relevant literature and identification of available test methods for measuring aggregate characteristics; the conduct of tests using different coarse and fine aggregates to evaluate test methods considering accuracy, repeatability, reproducibility, ease of use, and ease of interpretation of results, and other factors, such as cost, readiness for implementation, portability, and applicability for the different aggregate sizes and types; and the evaluation and ranking of 13 potential test methods using an Analytical Hierarchy Process. The highest ranked method—the Aggregate Imaging System (AIMS)—was recommended for implementation. Also, the research developed a methodology to classify aggregates based on the distribution of characteristics—not average values–for use in materials selection and specifications, and prepared a draft protocol for a proposed "Standard Method of Test for Shape, Angularity, and Texture of Aggregate Particles Using the Aggregate Imaging System (AIMS)" for consideration by AASHTO. The final report was published as NCHRP Report 555.

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