Cores at Early Ages for In-Place Concrete Acceptance

Practitioners often question the correlation between the performance of a structure and the results of standard 28-day cylinder testing. Testing cores extracted from the structure is one approach to evaluate in-place concrete but is frequently performed at ages greater than 28 days. Due to increasing demands for faster construction timelines, the feasibility of extracting and testing cores at an earlier age to satisfy acceptance criteria was considered. In this study, cores from laboratory-constructed structures were tested on days 3, 7, and 28 using acceptance criteria for compressive strength, rapid chloride permeability (RCP), and electrical resistivity. This research has shown that extracting and testing cores--as early as day 3 from high-strength concretes and day 7 for other concretes--is feasible. Results of 28-day testing were not affected by coring day and duration of conditioning. Electrical resistivity was found to be a feasible alternative for the RCP test. Keywords: core test; coring; durability; early ages; electrical resistivity; rapid chloride permeability test.