The project evaluated aggregate tests and, based on the results of laboratory tests, identified a set of 11 tests that related to the performance of unbound materials used in base and subbase pavement layers and thus as predictors of pavement performance.

The properties of aggregates used in unbound base and subbase layers are very important to the performance of the pavement system in which they are used. For example, rutting of asphalt concrete pavements and faulting of portland cement concrete pavements can, in many cases, be traced to improper aggregate selection and use in unbound layers. 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. Because widespread use, familiarity, and availability of a database have perpetuated the popularity of some tests, there is a need to evaluate existing aggregate tests, identify new tests that relate to performance, and develop better procedures for testing and selecting aggregate for use in unbound base and subbase layers.

Research included a review of relevant domestic and foreign literature, communications with highway agencies, and the conduct of laboratory tests to identify and evaluate aggregate properties that influence pavement performance. The research also recommended tests that can be used as predictors of performance. Also, the research identified a plan for evaluating the validity of the recommended tests by accelerated pavement testing of specifically constructed pavements and long-term performance monitoring of in-service test pavements. NCHRP Report 453, "Performance-Related Tests of Aggregates for Use in Unbound Pavement Layers," documents the work performed under this project.