High-strength concrete – NDT with rebound hammer: influence of aggregate on test results

Abstract

Rebound hammer is the most frequently used non-destructive method for estimation of concrete strength. Measurement results are influenced by various factors (components and composition of concrete, humidity or age), which are well known for normal-weight concrete. High-strength concrete (HSC) differs in quality and the question is to which extent these factors influence the test results. Knowledge about influence of aggregate and results of measurements with Schmidt rebound hammer is stated. Test results and evaluation of compressive strength are considerably influenced by the strength of parent material from which the coarse aggregate is made. Influence of granulometric curve is less important and for aggregate with strength over 90 MPa, it is negligible. To determine compressive strength of HSC with Schmidt rebound hammer, it is necessary to elaborate special calibration relationships for aggregate with various strength of parent rock. Use of calibration relationships elaborated for normal-weight concrete for determination of strength of HSC is problematic (different properties of aggregate and upper limit of calibration relationships is 70 MPa). Shifting the upper limit of calibration relations for normal-weight concrete up to the maximal rebound number measured at testing HSC is not recommendable; values of compressive strength calculated in accordance with adjusted formulas are smaller than real strength of HSC.