Uncertainty of concrete compressive strength determination by a combination of Rebound Number, UPV and uniaxial compressive tests on cubical concrete samples

Abstract

Rebound number (RN) and ultrasonic pulse velocity (UPV) determination provide a non-destructive indirect estimation of concrete compressive strength (CS). They have an extensive uncertainty, both due to limited reproducibility and trueness of these methods. Tests on a uniaxial compressive apparatus generate a destructive result, also with a relatively high uncertainty, which requires repeating this test on multiple samples to produce a mean result with an acceptable uncertainty. In this work, a combination of all three methods was performed on cubical concrete specimens. Three different mixes were designed, each corresponding to a different assigned compressive strength. Six specimens were produced from each mix design, and each specimen was cured for 28 days. During and until that time, each specimen was tested according to all three aforementioned methods. Results were compared in pairs and factors related to equipment tolerance and operator variations were assessed. Regression processes were applied to estimate optimized functions that predict compressive strength based on the non-destructive RN and UPV measurements. Additionally, a function was estimated as the mean of all three different test method results. Finally, a statistically significant multivariate function was established along with a corresponding uncertainty budget. The result is a determination of compressive strength for cubical concrete specimen with known, reduced uncertainty. These lower uncertainty limits enable achieving conformity assessment for concrete compressive strength with minimized decision risk. The calibrated multivariate regression function in combination with its resulting uncertainty intervals are expected to benefit constructors in their aim at interpreting their measurement data to comply with the EN 206 quality control procedure and accredited laboratories to verify the validity of their results by performing internal quality control.