The project reviewed and evaluated aggregate tests and, based on the results of this evaluation, identified those tests that related to the performance of portland cement concrete pavements and provided guidance on their use for evaluating aggregates for use in specific pavement applications.

The properties of coarse and fine aggregates used in portland cement concrete mixtures are very important to the performance of the highway pavements in which they are used. Clearly, proper aggregate selection is necessary for attaining desired performance. However, little consideration is often given to the testing of aggregates. Many of the current aggregate tests were developed empirically to characterize an aggregate and may not have any demonstrated relationship to the performance of the final product. Also, some of the most commonly used test methods are not easy to perform and do not yield reproducible results. To allow comparing different aggregates and determining the potential impact of an aggregate on performance, there is a need to identify user-friendly, reproducible, precise tests that relate key aggregate properties to pavement performance.

The research included a comprehensive review of literature and current practices to identify relevant aggregate properties and test methods. Then, building on the results of this review and the findings of three earlier related NCHRP projects (4-20, 4-20A, and 4-20B), the research identified two sets of test methods, desinaged Levels I and II, that closely related to performance. Level I tests were considered essential for evaluating specific aggregate properties; results of Level I tests will determine if Level II tests are needed. The research also provided guidance on how these tests can be used for determining the suitability of a specific aggregate for use in a specific application. A somewhat shortened version of the final report has been published as NCHRP Research Results Digest 281.