Development of rational pay factors based on concrete compressive strength data

This research project addresses the opportunity to contain the escalating costs of concrete materials in construction projects. Both statistical process control and rational acceptance criteria show that quality improvement and cost savings can be achieved. The report presents a comprehensive statistical evaluation of the compressive strength of concrete used in various sectors of the transportation infrastructure in Arizona. The proposed methodology is applicable to the concrete materials specified at other industrial sectors such as privately financed construction projects. Several case studies are conducted based on actual field data to show that performance based specification procedures can be used to improve the quality control process while decreasing the overall construction costs. Three sets of compressive data from various construction projects were selected. These data were evaluated by means of statistical process-control tools while state-of-the art procedures were utilized to evaluate the strength as a measure of quality. Several acceptance criteria based on the percent within limit (PWL) and operational-characteristic curves (OC) are proposed and evaluated. Various pay factor equations are considered and the historical records are evaluated based on hypothetical pay factor equations. The report furthermore addresses the strengths and weaknesses associated with the present acceptance criteria in comparison to a PWL based method. Opportunities in sampling, optimization, operational-characteristics curves, and quality specification are discussed in detail. It is shown that the cost savings associated with both performance based-specification and quality control, sufficiently justify the amount of effort needed in order to implement these methodologies in the development of specifications.