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Effect of core geometry and size on concrete compressive strength.
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2016-07-01
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[PDF-4.46 MB]
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Abstract:To evaluate the in-place concrete strength for acceptance for a structural member with
potentially substandard strength, the compressive strength of cores may be required for
assessment. Depending on the geometry and size of the core specimen, the compressive test
results may need adjustment to characterize the in-place concrete strength. The
comprehensive experimental study performed examines core test results for factors including:
three targeted strengths (6,000, 8,000, and 10,000 psi), two coarse aggregate sizes (No. 67
and 57), five core length-to-diameters (1.0, 1.25, 1.5, 1.75, and 2.0), two core diameter sizes (3
and 4 in.), and two coring directions (parallel and perpendicular). The data represent 390 core
specimens obtained from 12 separate concrete castings.
The data indicate that the core diameter significantly affects the strength correction factors
for various length-to-diameters (l/d). For 4 in. diameter cores, only a slight difference from the
currently recommended core l/d strength correction factors in AASHTO T 24 (2007) is
observed. However, 3 in. diameter cores do not behave the same as 4 in. diameter cores when
evaluated for core l/d effects on compressive strength. The analyzed data indicate that as the
volume of the core specimen decreases, the compressive strength results become less
reliable. Additionally, AASHTO T 24 (2007) recommends a core diameter of at least 3.75
inches. Based on the analysis, cores having a l/d less than 2.0, should not have a core
diameter less than 3.75 inches.
For cores having l/d of 2.0, the data indicate that the average strength of 3 in. diameter
cores is 94 percent of the average strength of a 4 in. diameter core. Results also indicate the
average strength of cores drilled perpendicular to the placement direction is 96 percent of the
average strength of cores drilled parallel to the placement direction.
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