Wisconsin Department of Transportation Hot-Mix Asphalt Round Robin Laboratory Qualification Testing Program

The Wisconsin Department of Transportation (DOT), Madison, uses a quality management program (QMP) specification for acceptance and payment of hot-mix asphalt (HMA) pavement. The QMP allows for product acceptance on the basis of contractor quality control (QC) testing when verified by the Wisconsin DOT quality verification (QV) tests. The contractor is required to do daily QC testing of mix properties in a department-certified, qualified laboratory located at the plant site. The Wisconsin DOT maintains a QV program (QVP) and conducts QV tests to determine the quality of the final product. QV and QC test results are compared, and a mix is considered acceptably verified if the two results are within specified limits. When test results do not meet these limits, the Wisconsin DOT performs referee tests to determine mixture conformance, acceptability, and payment. In 2011, the Wisconsin DOT began to see significant increases in the number of requests for referee testing as a result of wide disparities between QC and QV laboratory test results. To investigate this disparity, the department initiated a round robin laboratory test program. Results from the investigation proved to be insightful. The program was expanded and is now a key component of the Wisconsin DOT annual laboratory qualification certification program. This paper describes the program, how it is administered, how tests results are analyzed, and how nonconforming laboratories are identified. Test results obtained from the program are presented and recommendations developed for program improvements. The program details should be useful to other state highway agencies that use contractor QC tests for acceptance.