Analysis of Interlaboratory Test Programm Results


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Title: Analysis of Interlaboratory Test Programm Results

Author(s): Rachel J. Detwiler and John A. Bickley

Publication: Special Publication

Volume: 141


Appears on pages(s): 103-116

Keywords: batching; compressive strength; cylinders; laboratories; statistical analysis; strength; tests; General

Date: 12/1/1993

For some years, the Ministry of Transportation of Ontario (MTO) and the Ready-Mixed Concrete Association of Ontario (RMCAO) have separately run programs to measure the reproducibility of test results between commercial laboratories. The comparative test results were made on standard cured 150 mm diameter by 300-mm test cylinders. The reproducibility of test results obtained between testing laboratories on nominally identical test specimens is an important factor in the statistical evaluation of test data. Unless the reproducibility is good, concrete mixes need to be overdesigned, with resulting higher costs. In addition, poor reproducibility between laboratories increases the probability that some test cylinders will fail to meet specified strength requirements. Even if the concrete in the structure represented by these results probes to be adequately strong, disruption and economic loss result from the publication of erroneous results. This paper analyzes the data obtained by the RMCAO, derives repeatability and reproducibility indexes, and discusses their economic consequences. Some data from the MTO program are also reported. Recommendations for improvements are made.