First the difficulties, as well as fallacies, of the estimation of concrete strength from pulse velocity measurement are discussed. Then an attempt is made to transfer some of the new findings of the research on materials testing by ultrasonic methods to concrete. The role of compositeness, dispersion, and a feature-based computer system are discussed among others. Supporting test results are presented showing that 1. the pulse velocity in the longitudinal direction of a concrete cylinder differs from the velocity in the lateral direction; 2. more specifically, at low velocities the longitudinal velocities are greater, whereas at high velocities the lateral ones; 3. this difference is more pronounced with lower frequencies; 4. the pulse velocity in concrete increases with higher frequencies, that is, concrete is a dispersive material; 5. the dispersive nature of concrete decreases with age; 6. the pulse velocity is independent of the stresses in concrete to a large extent; 7. feature-based computer system is applicable to concrete. The practical consequences of these findings are pointed out. © 1990.
