Conservative characteristic strength of concrete from non-destructive and partially destructive testing

Abstract

In this article, the strategy for evaluation of conservative characteristic strength of concrete from the non-destructive and partially destructive testing on the existing structures is elucidated. Such evaluations becomes essential for health assessment and re-evaluation of the existing structures to fulfill the requirements of periodic assessment, revised loading, changed functionality, regulatory guidelines or post-accident scenario. The non-destructive tests considered were ultrasonic pulse velocity (USPV) and rebound hammer (RH) records. This started with examination of the dataset for outliers, and elimination of the same, if any. Subsequently, the forms of correlation expression best suited for evaluation of compressive strength from USPV and RH were ascertained from the limited number of combined records of USPV, RH and core strength obtained from the structure. Stratified sampling was adopted to divide the data into modeling and testing data for this exercise, the latter being employed for performance evaluation. From the results, it was concluded that for the dataset involved, linear equation would be best suited for evaluation of compressive strength from both USPV as well as RH. The total records of the USPV, RH and core results were thereafter employed to determine the correlation expressions, which were subsequently applied on the USPV and RH records from the entire structure to arrive at the estimates of equivalent cube strength. The conservative characteristic strength of concrete in the structure was suggested from considerations of Indian standard code and may be extended for other codes as well. The conservative characteristic strength of concrete can hereafter be utilized for health assessment and re-evaluation studies for the structure. This case study would be useful as a reference for engineers engaged in condition assessment and re-evaluation exercises of existing concrete structures.