This project was designed to (1) develop a rational method for determining the minimum levels of agency and contractor testing and inspection activities necessary to satisfactorily construct hot-mix asphaltic concrete (HMA) overlays using the AASHTO Quality Assurance Guide Specification and the AASHTO Implementation Manual for Quality Assurance and (2) apply the findings of this research to other construction activities. The minimum level of testing and inspection is defined in this report as the minimum amount of testing and inspection resources to allocate for a given project. Satisfactorily constructing an HMA overlay is defined as meeting specifications, which are determined by test properties and compliance measures.

Specific recommendations were required for quality control, quality acceptance, and verification testing levels. Inspection-level recommendations, implementation guidelines, and case applications of the research were needed for important tasks and for projects where a limited number of agency inspectors were available. A rational method based on the results of this research project was also necessary for determining testing and inspection levels in other areas of highway construction.

The University of Wisconsin at Madison was awarded a contract to conduct this project. The Asphalt Institute assisted the research team as a subcontracted agency. Arizona, Florida, Kentucky, Minnesota, Ohio, and Wisconsin DOTs and their contractors provided the project-specific testing and inspection data for the 16 HMA overlay projects that measured statistical properties of the construction test data and documented current inspection practices. Actual performance data and life-cycle cost data were not included in the scope of the research. FHWA regulations (23 CFR 637) do not permit the use of split sampling techniques for state DOT verification of contractor testing for the quality of the material; independent sampling must be done. Split sampling is permissible when used for verifying testing techniques, equipment, and laboratories. The final report recognizes both independent and split sampling but encourages split sampling for all verification scenarios, principally split sampling based on AASHTO guidance and existing state practice. Consequently, recommendations in the report may be at odds with the current CFR; however, a debate continues on the issue.

Status and Product Availability: The agency's revised final report was published as NCHRP Report 447, "Testing and Inspection Levels for Hot-Mix Asphalt Concrete Overlays."