Iveta Plšková

The Effect of Concrete Quality on the Acoustic Emission Parameters during Three-Point Bending Fracture Test

Acoustic emission is an experimental tool well suited for monitoring fracture processes. The paper presents experiment focused on analysing acoustic emission signals captured during three-point bending fracture test of specimens of concrete. Quantitative acoustic emission techniques were used to measure micro fracture properties. For three different concrete mixtures typical acoustic emission patterns were identified in the acoustic emission records to further describe the under-the-stress behaviour and failure development. If we have a better understanding of the relationships between micro structural events and macroscopic behaviour we can better formulate predictive models for large-scale structural performance and reliability. An understanding of microstructureperformance relationships is the key to true understanding of material behaviours. Three-point bending fracture tests were conducted on these specimens and load versus crack mouth opening displacement (Load-CMOD) diagrams were recorded during the testing.

Nonlinear Acoustic Spectroscopy Method for Nondestructive Testing of Thermally Damaged Concrete

Most concrete structures are subjected to a range of temperature corresponding to normal environmental temperatures. However, there are important cases where concrete structures may be exposed to much higher temperatures (e.g., jet aircraft engine blasts, building fires, chemical and metallurgical industrial applications in which the concrete is in close proximity to furnaces, and some nuclear power-related postulated accident conditions). Exposure of concrete to high temperatures affects its mechanical properties. In this paper we examine the dependence of the fundamental frequency on temperature to which the concrete beams were heated. Fundamental frequencies were obtained by an innovative method used Pseudorandom Binary Sequence of Maximum Length as a perturbation signal. For the verification of the results the Ultrasonic Pulse Velocity in concrete were also measured and flexural bending strengths were determined. The results show method with Pseudorandom Binary Sequence of Maximum Length as a perturbation signal as a very promising for non-destructive testing of thermally damaged concrete.

Comparison of Ultrasonic Methods for Thermally Damaged Concrete Nondestructive Testing

Behaviour of concrete under elevated temperatures is very complex. There is a change of mechanical and physical parameters with temperature. In this paper we study the relations of thermal damage processes in concrete and parameters obtained by different ultrasonic methods. The concrete specimens were heated in programmable laboratory furnace. Selected temperature (200°C, 400°C, 600°C, 800°C, 1000°C and 1200°C) were maintained for 60 minutes. The first ultrasonic measurement technique in this paper was Ultrasonic Pulse Velocity method. The pulse velocity in a concrete depends on its density and its elastic properties. Therefore, it is possible to deduce the quality and the compressive strength of the concrete from the ultrasonic pulse velocity. The second ultrasonic measurement technique in this paper uses broadband pulse-compression signal, with variable amplitude to measure the change of fundamental frequency. This method is based on Nonlinear Elastic Wave Spectroscopy. Nonlinear Elastic Wave Spectroscopy methods takes advantage of the fact, that nonlinearities in material manifest themselves as a resonant frequency shifts and harmonics or dumping coefficients changes. The progress of nondestructive testing parameters was confirmed by results from the destructive tests.