Title:
Increasing the Usefulness of ACI
214: Use of Standard Deviation and a Tech-nique
for small sample sizes
Author(s):
Robert E. Philleo
Publication:
Concrete International
Volume:
3
Issue:
9
Appears on pages(s):
71-74
Keywords:
coefficient of variation; concrete construc-tion;
concretes; mix proportioning; standard devia-tion;
statistical analysis; strength analysis.
DOI:
Date:
9/1/1981
Abstract:
Until recently the ACI 214 standard contained two features which caused a potential hardship to producers: (1) recommended overdesigns were based on coefficients of variation; and (2) estimates of statistical parameters could be computed only after 30 test results were available. The first mandated un-necessarily high overdesigns for high strength concrete and the second has prevented adjustment of mixture proportions until a large amount of concrete was placed. The most recent version of the standard has corrected the first by basing calculations on standard deviation rather than coefficient of variation. The justification for that change is given here together with a recommendation for dealing with the second.