Using the Results of Contractor-Performed Tests in Quality Assurance. Research Results Digest 323

摘要

The construction quality assurance process is comprised of process (quality) control, acceptance, and independent assurance procedures. Traditionally, contractors are responsible for their quality control, and state departments of transportation (DOTs) are responsible for acceptance and independent assurance. However, with the enactment of a federal regulation in 1995, commonly referred to as 23 CFR 637B, the roles of state DOTs and contractors have become less clear cut. Under certain conditions, 23 CFR 637B permits the use of contractor test results for acceptance. There is general agreement on the value of contractor quality (process) control. Issues may arise, however, when the results of contractor performed tests are used in the acceptance process. This research employed statistical procedures to evaluate whether state DOTs can effectively use contractor-performed test results in the quality-assurance process. The results of state DOT- and contractor performed tests for hot mixed asphalt concrete (HMAC), portland cement concrete (PCC), and granular base course were collected and statistically compared. Field projects were selected to allow evaluation of as many as possible of the quality-assurance variables that might affect the comparisons. The null hypothesis of this research was that the contractor-performed tests for use in the acceptance decision provide the same results as state DOT-performed tests. To test this hypothesis, contractor and state DOT results from six states were statistically compared to determine if differences between them in (1) variability and (2) proximity to target or limiting values were significant at alpha = 0.01.