A major result of the research conducted under the Strategic Highway Research Program from 1987 to 1993 was the development of the Superpave (Superior Performing Asphalt Pavement) system for the comprehensive design of asphalt pavements. These 14 contributions describe the experience to date in the

This reports document research that was performed to (1) determine causes of variability and tolerances for volumetric and mechanical properties of dense-graded asphalt mixtures measured within and among the three specimen types; and (2) propose a practice for state departments of transportation to incorporate these results in specifications and criteria for quality assurance, mix design verification or validation, and structural design and forensic studies. The research was conducted in two phases. In Phase I, datasets of laboratory and field test data were collected and pooled in a meta-analysis in an attempt to determine levels of variability in asphalt mixtures and the factors causing variability among and between the three specimen types. Despite the inclusion of 25 extensive datasets representing roughly 8,000 individual mixtures in the meta-analysis, the results of the analysis were inconclusive. Phase II was then undertaken--a program testing specimens from paving projects across the United States to quantify the effects of process-based factors on the variability of volumetric and mechanical properties of the specimen types. The key outcome of the research is a proposed practice for evaluating the cause and magnitude of variability within and among the three specimen types. In addition, tolerances of volumetric and conversion factors between the three specimen types of mechanical properties evaluated are proposed based on the average difference between specimen comparisons for the mixtures evaluated in Phase II. Agencies may use these proposed values to evaluate and adjust their current tolerances.