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Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete.
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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Statistical Methods for Evaluating Core Strength Results
Author(s): Ronald L. Dilly and Woodward L. Vogt
Publication: Special Publication
Appears on pages(s): 65-102
Keywords: coefficient of variation; compressive strength; cores; quality control; samples; standard deviation; statistical analysis; strength; tests; tolerances (mechanics); General
Abstract:Strength interpretation problems are created when standard practices and procedures for sampling and testing concrete mixtures were not followed during construction. Cylinder and core compressive strength records are reported for a project that required extensive coring due to low-standard 28-day cylinder strengths. Records are reported for 4000- and 6000-psi concrete mixtures. Over 80 core strengths correspond to the 6000-psi mixture that was used to cast columns, grade beams, pedestals, and shear walls. The described statistical methods were useful for analyzing the quality of core strength data and interpreting the significance of the results. Core strength results were analyzed by mixture, placements, and type of structural member. For the analysis, "Stem and Leaf" and "Box and Whisker" plots were used to identify outliers. "Analysis of Variance" was used to test for equality of mean strengths. "Fisher's" and "Tukey's" procedures were used in identifying significantly different mean strengths. The Chi-square test was applied to evaluate normality of distributions. The characteristic in-place strength was determined by using the tolerance factor. The analysis shows the importance of obtaining representative core strength samples when determining code compliance.
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