Concrete Core Strength—The Effect of Length to Diameter Ratio

Abstract The ASTM Method for Obtaining and Testing Drilled Cores and Sawed Beams of Concrete (C 42–68) currently contains length to diameter ratio correction factors for soaked cores but not dried cores. However, it is widely recognized that for structures which will be substantially dry in service dried cores are more appropriate. It is sometimes difficult—because of constraints of aggregate size, reinforcing bar placement, and member dimensions—to obtain drilled cores of the preferred dimensions, with a length twice the diameter. Research performed in two laboratories involving the drilling and testing of a large number of 4-in. (102-mm) diameter soaked and dried cores with length to diameter ratios of 1.0, 1.25, 1.5, 1.75, and 2.0, taken from six structural-size members, indicates that the same correction factors can be used for both moisture conditions and that the factors now in ASTM Method C 42–68 should be lowered slightly. In addition, data were gathered on the effect of end preparation procedure on core strength. For the methods used (three capping procedures and grinding of the ends) no important differences in measured strength were noted.