Variability In Brick Unit Test Results

Abstract

For centuries, brick masonry has been used as a structural and non-structural material, with requirements for strength and other properties often specific to a particular project. To determine these properties, various ASTM and other test methods have been standardized and incorporated into building codes and project documents. The results of standardized testing are typically used as verification that a particular brick meets the property requirements of a particular project. Unfortunately, there is a high degree of variability in some test results. This is due to a combination of variations in actual material properties and variations in the way a particular test method is performed from laboratory to laboratory and operator to operator. This paper reports statistical analyses of previously published and unpublished test results for compressive strength, IRA, absorption, and other properties of various brick tested at a number of laboratories in the United States. Variability in the results is quantified and statistical significance of the variations presented. Recommendations for modifications to standardized tests, including the number of specimens tested as a sample is also presented. Topics including precision, bias, and sampling methods are discussed as they relate to the testing methods and results presented.