Comparison of Non-Destructive Testing Findings to Laboratory Testing Findings from a Concrete Wall with Strength Deficiencies

摘要

An engineering assessment was performed for a load bearing reinforced concrete basement wall upon discovery that multiple truckloads contained concrete with substantially low strength concrete. In-situ testing of the wall consisted of Windsor Probes for initial in-place estimation of strength as well as zoning of substandard sections. Subsequently stress wave based non-destructive evaluation (NDE) Impact Echo testing in accordance with ASTM C1383 was utilized, since the wall was accessible on one side only. Subsequently core locations were selected based on the areas identified by in-situ testing findings and cores were removed from areas with varying indicated properties. Laboratory testing of cores consisted of resonant frequency based dynamic Young's modulus testing of cores (ASTM C215) and direct determination of stress-wave velocity (ASTM C597) on unconfined specimens removed from the wall. Both the in-situ impact echo and laboratory pulse velocity testing were effective in identifying the differences in the quality of the concrete across the wall. A comparison between the determined concrete compressive strengths and non-destructive Windsor Probe strength testing indicated in-situ and core test results were in agreement, but variability should be expected. Comparison of the dynamic Young's modulus with the American Concrete Institute (ACI) static elastic modulus approximation based on the compressive concrete strength indicated consistent results with approximately 15% higher value of dynamic modulus compared to static elastic modulus, as stated in the literature.