Acoustic emission behavior of steel fibre reinforced concrete under bending

The present paper describes the acoustic emission (AE) behavior of concrete under four-point bending. Steel fibres of varying content were used as reinforcement in concrete slabs and their influence on the fracture process and the acoustic activity was investigated. The total acoustic emission (AE) activity was found to be directly proportional to the fibre content. Analysis revealed that particular AE parameters change monotonically with the progress of damage and can be used for the characterization of the failure process

Surface wave dispersion in cement-based media: Inclusion size effect

This paper presents the experimental study of surface wave propagation in cementitious material with different shape and size but same volume content of thin inclusions that simulate distributed damage. The Rayleigh wave velocity changes almost up to 20% depending on the inclusion shape, while the longitudinal velocity, the experimental variance, as well as the coherence of the signals is also affected. It is demonstrated that the material is strongly dispersive and caution should be taken for the interpretation of the wave measurements since the velocity is sensitive not only to the damage content but also to the “crack” size

Evaluation of grouting in tunnel lining using impact-echo

The shield tunneling method is commonly used for tunnel excavation. After the excavation, curved reinforced concrete members are used to support the surrounding ground/rock and seal the tunnel. Grouting is performed to provide adhesion between the concrete members and the ground. The assessment of the grouting quality by pull-out tests and core sampling is destructive, time-consuming and expensive. In the present case, impact-echo was applied as a means of non-destructive and time-effective evaluation. Excitation was conducted by an impact hammer on the surface of several concrete plates and the reflection was acquired by a low frequency accelerometer. Combined use of time domain characteristics, spectral content and wavelet transform reveal the effectiveness of grouting and indicate that impact echo is valuable for quick and reliable assessment of grouting in such cases

Characterization of surface crack depth and repair evaluation using Rayleigh waves

The issues of surface crack depth determination and the evaluation of repair effectiveness are not trivial for concrete engineers. In the present paper, surface waves are applied on concrete blocks with artificial slots to correlate wave parameters with crack depth. To simulate crack repair with an injected material, epoxy is applied to the slots in the laboratory and quantification of the filling percentage is attempted. Simultaneously, a frequency domain boundary element method is employed for the numerical simulation of transient pulses interacting with surface breaking cracks. Experimental results compare well with the numerical ones, showing that the repair effectiveness, which so far can be evaluated only by destructive techniques, is possible by simple surface wave measurements