Determination of initiating and critical stress levels in compressed plain and high-strength concrete by acoustic methods

New criteria suitable for determining the levels of
initiating stress [ampersand]sigma;i and critical stress [ampersand]sigma;cr in plain and
high-strength concrete under compression by acoustic materials testing methods
have been established. Also the criteria known from the literature on the
subject have been verified. On the basis of the author's own research results
obtained by the ultrasonic method and the acoustic emission (AE) method the
limits of the applicability of the two above methods have been determined. The
new criteria, classified according to their suitability for plain concrete or
high-strength concrete, have been defined using such descriptors as: the
velocity of longitudinal ultrasonic waves, AE counts, the rate of AE counts, the
energy of short AE impulses and the RMS value of AE.