Factors Influencing In Situ Strength of Existing Concrete Structure Estimated by Core Test and NDTs

The in situ concrete compressive strengths estimated by core tests and nondestructive tests (NDTs) are influenced by various factors, such as level of quality control for concreting operation, carbonation of the concrete surface, and stress history. Most studies of the effect of various factors reported were confined to young concrete (maximum 91 days) cast in the laboratory. The number of studies of the effect of these factors on the in situ compressive strength of aged concrete structures estimated by core tests and nondisruptive tests is limited. It is possible that the effect of some of these factors on the in situ estimated strength identified in studies of young concrete may not be significant for aged concrete structures. The significance of the effect of various factors on the estimated in situ compressive strength of existing aged concrete structures obtained by core tests and nondisruptive tests using 84 sets of the test results of 35 structures aged 4–73 years constructed of concrete with 28-day cube strength of $20–41.5\mathrm{N}/{\mathrm{mm}}^2$ was investigated. The level of quality control of concreting operation of structures constructed during different periods was investigated to identify periods when more structures were constructed with good quality control of concreting operations.