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Literature was analyzed to determine the relationship between strength of 150-mm (6 in.) diameter cylinders and smaller 100-mm (4 in.) and 75-mm (3 in.) diameter cylinders. The precision of measurement of strength when smaller cylinders are used was also examined. Almost 8000 cylinder strengths ranging from less than 20 MPa to greater than 100 MPa were analyzed. Results show: (1) over all strength ranges the coefficients of variation of strength (CV) for 100- and 150-mm cylinders are equivalent, (2) For 75-mm cylinders with strengths in the 20 to 60 MPa range, the mean CV is 5.2%, significantly higher than a mean CV of 3.0% for both 100- and 150-mm cylinders, (3) for 100- or 150-mm cylinders, the CV is significantly higher for strengths less than 60 MPa (3.0%) than for strengths greater than 60 MPa (1.8%), (4) within the range 20 to 100 MPa, the expected strength using 100-mm plastic or steel molds is 5% greater than if 150-mm plastic or steel molds are used.
Professor, University of Calgary, Alberta,
Stock #: CCA10557J