Core testing is the most direct method to determine the in-place compressive strength of concrete in a structure.Generally, cores are obtained to:•Assess, if required, whether concrete in a new structurecomplies with strength-based acceptance criteria; or•Determine in-place concrete strengths in an existingstructure for evaluation of structural capacity.In new construction, cylinder strength tests failing to meetstrength-based acceptance criteria can be investigated usingprovisions given in ACI 318.
These criteria specify thecircumstances when core tests are permitted, the number ofcores to be tested, the conditioning of the cores before testing,the limits on the time interval between coring and testing, andthe basis for determining whether the concrete in the arearepresented by the core strengths is structurally adequate. Thisguide presents procedures for obtaining and testing cores andinterpreting results in accordance with ACI 318.If strength records are unavailable, the in-place strength ofconcrete in an existing structure can be evaluated usingcores.
This in-place strength determination is simplifiedwhen in-place strength data are converted into an equivalentspecified compressive strength fc′ value that can be directlysubstituted into conventional strength equations withcustomary strength reduction factors. This guide presentsprocedures for performing this conversion in a mannerconsistent with the assumptions used to derive strengthreduction factors for structural design.