Revisiting Effects of Cylinder Cap Type and Eccentricity— Part I: Variability of Strength


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Title: Revisiting Effects of Cylinder Cap Type and Eccentricity— Part I: Variability of Strength

Author(s): Michael J. Bolduc, Dan Mullins, and Ken Hover

Publication: Materials Journal

Volume: 115

Issue: 1

Appears on pages(s): 5-12

Keywords: acceptance criteria; bonded caps; compression strength; cylinder testing; neoprene caps; quality control; sulfur caps; test methods; unbonded caps; variability

Date: 1/1/2018

The acceptability of unbonded neoprene caps has been established for over 20 years, and both bonded (ASTM C617) and unbonded (ASTM C1231) caps are currently used in commercial testing and in research. In this study, compressive strength results from one hundred 6 x 12 in. (152 x 304 mm) cylinders cast from a single batch of ready mixed concrete, tested with both types of caps, indicated that while either cap type produced approximately equivalent strength, there was a significant difference in the standard deviations of the two populations. Further, strength obtained with unbonded caps was less sensitive to variations in cylinder eccentricity during testing. Response to eccentricity was most pronounced at 1/4 in. (6 mm), with neoprene-capped specimens showing increased strength and sulfur-capped specimens showing decreased strength. Predominant failure modes differed with both cap type and eccentricity. Observed differences in variability would impact the probability of meeting building code requirements for acceptance based on compressive strength.