ACI 214.4R-10 | Guide for Obtaining Cores and Interpreting Compressive Strength Results | Free Download
Core testing is the most direct method to determine the inplace compressive strength of concrete in a structure. Generally, cores are obtained to:
• Assess, if required, whether concrete in a new structure complies with strength-based acceptance criteria; or
• Determine in-place concrete strengths in an existing structure for evaluation of structural capacity.
In new construction, cylinder strength tests failing to meet strength-based acceptance criteria can be investigated using provisions given in ACI 318. These criteria specify the circumstances when core tests are permitted, the number of cores to be tested, the conditioning of the cores before testing, the limits on the time interval between coring and testing, and the basis for determining whether the concrete in the area represented by the core strengths is structurally adequate. This guide presents procedures for obtaining and testing cores and interpreting results in accordance with ACI 318.
If strength records are unavailable, the in-place strength of concrete in an existing structure can be evaluated using cores. This in-place strength determination is simplified when in-place strength data are converted into an equivalent specified compressive strength fc′ value that can be directly substituted into conventional strength equations with customary strength reduction factors. This guide presents procedures for performing this conversion in a manner consistent with the assumptions used to derive strength reduction factors for structural design.
This guide summarizes current practices for obtaining cores and interpreting core compressive strength test results in light of past and current research findings. Many of these findings are based on older references as the research has reached a mature state. Parallel procedures are presented for cases where cores are obtained to assess whether concrete strength in a new structure complies with strength-based acceptance criteria, and to determine a value based on the actual in-place concrete strength equivalent to the specified compressive strength fc′. The latter can be directly substituted into conventional strength equations with customary strength reduction factors for strength evaluation of an existing structure. It is inappropriate to use procedures for determining the equivalent specified concrete strength to assess whether concrete strength in a new structure complies with strength-based acceptance criteria.
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- • What are some of the problems in interpreting concrete strengths obtained by coring?