The project evaluated previously recommended aggregate tests related to hot-mix asphalt (HMA) performance and, based on the results of laboratory tests and accelerated tests of full-scale pavement sections, developed recommendations for a set of eight performance-based aggregate tests and provided guidance on using these tests for evaluating and selecting aggregates for use in specific mixture applications.
The properties of coarse and fine aggregates used in HMA mixtures significantly affect the performance of the highway pavements in which they are used. Despite their obvious importance, little consideration is usually given to the testing of aggregates. Many currently used aggregate tests are empirical--they were developed without establishing a direct relation to pavement performance. Furthermore, some of the most commonly used test methods are not easy to perform and do not yield reproducible results; compliance with these tests does not consistently result in acceptable performance. Thus research was needed to recommend precise tests that measure key aggregate properties related to pavement performance. The research previously performed under NCHRP Project 4-19, reported in NCHRP Report 405: Aggregate Tests Related to Asphalt Concrete Performance in Pavements
, identified a set of nine aggregate tests that relate to the performance of HMA mixtures used in pavement construction and thus can be used as predictors of pavement performance. However, these tests were identified based on a study of literature and laboratory tests There was a need to assess the validity of these tests by in-service performance tests or accelerated pavement tests.
Research included a review of information relevant to the testing and evaluation of aggregates used in HMA pavements; characterization of a wide variety of aggregate types and selection of five coarse and six fine aggregates representing a range of properties for use in the research; conduct of accelerated fatigue and rutting tests of full-scale pavement sections constructed with HMA mixtures containing aggregates of different types and properties to correlate performance with the aggregate properties measured in the laboratory using the test methods identified in NCHRP Report 405; and analysis of test results to evaluate the effect of specific aggregate properties on performance, determine sensitivity of these aggregate properties to traffic level, and evaluate the validity of the previously identified tests; and recommendation of a set of tests for evaluating aggregates used in HMA pavements and proposed acceptance criteria for different levels of traffic. The recommended set of eight aggregate tests deals with particle shape, angularity, surface texture, durability, and soundness of the aggregates and with the characteristics of the fines in aggregates. The final report, not including the appendixes, has been published as NCHRP Report 557
. The appendixes to the final report have been published as NCHRP Web-Only Document 82