CIA Z11-2002

This Recommended Practice is intended to facilitate the evaluation of concrete strength from the results of testing cores taken from the hardened concrete in a structure. The document commences by dealing with the reasons for strength evaluation by the use of cores. Directions are then given on how to obtain cores from concrete structures so that they will be suitable for testing and the test results will be "significant" in the true statistical sense. Steps in the determination and evaluation of concrete strength from the results obtained from testing cores are then explained. These steps include providing for corrections to the indicated compressive strength of the core for the following: length to diameter ratio of the core; presence of reinforcing bar in the core; position of the core axis in relation to the standard cylinder axis; age of the concrete; quality of compaction of the concrete; the curing regime experienced. A feature of the correction for quality of compaction of the cores is a series of photographs kindly provided by the Concrete Society (UK) of concrete of known void contents. This visual means of correcting for excessive voids in the cores is presented with an alternative procedure using actual density measurements of the cores.