What alternative does the contractor have when concrete test cylinders show strengths are below specification? Is core testing required whenever this happens or are nondestructive tests like the rebound hammer sufficient? Who is responsible when the specified concrete strength is not met?

Nicholas J. Carino, a research engineer at the National Institute of Standards and Technology in Gaithersburg, Md., and Ronald G. Burg, vice president at Construction Technology Laboratories in Skokie, Ill., comment on these questions.

While the standards can, and do, prescribe a systematic means to obtain and test cores, they should not be viewed as taking the place of sound engineering judgment, they should be viewed as one important tool that should be used when it is necessary to evaluate the strength of in-place concrete.