Variability in the results obtained from laboratory tests of the strength of cylindrical concrete specimens is considered possible due to random fluctuations in the actual concrete, the testing procedure itself, and a possible bias due to the particular testing machine (e.g., incorrect calibration or from the operator incorrect placement of the specimens) in the testing laboratory. The authors describe an experiment which was carried out to compare the variability in the results of tests performed at six testing laboratories in the Wellington area. Each laboratory was provided with six cylinders from concrete made at each of three different strengths - nominally 25, 45 and 65 mpa. The 8 in. x 4 in. diameter specimens were cast from two batches of concrete mixed at each nominal strength. They were cured at 100 per cent rh and 21 degrees C + or - 1 degree C, for in excess of 28 days, wrapped in plastic and delivered for testing, each laboratory being assigned three cylinders from each batch of concrete. The test results obtained are presented in tabulated form. Statistical tests on these failure loads showed no evidence of significant inconsistancies in the differences between laboratories for the different concrete batches. However, highly significant consistent differences were detected. Further examination of this effect entailed ranking the mean laboratory strength in order and assessing which difference was most significant. The laboratory mean strength as a percentage of the overall mean strength was found to vary from 97.94 for the laboratory giving the lowest results to 101.55 for the highest. This difference (about 3 1/2 per cent) although found to be statistically significant was considered so small as to be of little practical significance. /TRRL/

  • Availability:
  • Corporate Authors:

    New Zealand Portland Cement Association

    Securities House, 126 The Terrace, P.O. Box 3644
    Wellington,   New Zealand 
  • Authors:
    • Boult, B F
    • Ball, M E
  • Publication Date: 1976-10


  • English

Media Info

  • Features: References; Tables;
  • Pagination: p. 13-15
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00152567
  • Record Type: Publication
  • Source Agency: Transport and Road Research Laboratory (TRRL)
  • Files: ITRD, TRIS
  • Created Date: Jun 17 1977 12:00AM