Precision of Air-Permeability, Turbidimeter, and No. 325 Sieve Fineness Data

Data on air-permeability and turbidimeter fineness from an interlaboratory test program involving eight different portland cements and from about 80 to 150 laboratories over a period of a year and a half are presented and analyzed from the standpoint of between-laboratory and within-laboratory precision. Scatter diagrams for the four pairs of samples are presented and used as an aid in the analysis. For six of the cements, results of determinations of fineness by the No. 325 sieve are also analyzed and scatter diagrams shown. The effect on the calculated standard deviation of the elimination of some outlying results is assessed. A method of determining within-laboratory or single-laboratory precision without the use of duplicate determinations is presented. Laboratory bias was found to be significantly larger than the random error for all three tests. There was no indication of any significant difference in precision or in laboratory bias between the Type I and Type IA cements for any of the tests.