18 April 2011 Effect of fiber surface conditioning on the acoustic emission behavior of steel fiber reinforced concrete
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The role of coating in preserving the bonding between steel fibers and concrete is investigated in this paper. Straight types of fibers with and without chemical coating are used in steel fiber reinforced concrete mixes. The specimens are tested in bending with concurrent monitoring of their acoustic emission activity throughout the failure process using two broadband sensors. The different stages of fracture (before, during and after main crack formation) exhibit different acoustic fingerprints, depending on the mechanisms that are active during failure (concrete matrix micro-cracking, macro-cracking and fiber pull out). Additionally, it was seen that the acoustic emission behaviour exhibits distinct characteristics between coated and uncoated fiber specimens. Specifically, the frequency of the emitted waves is much lower for uncoated fiber specimens, especially after the main fracture incident, during the fiber pull out stage of failure. Additionally, the duration and the rise time of the acquired waveforms are much higher for uncoated specimens. These indices are used to distinguish between tensile and shear fracture in concrete and suggest that friction is much stronger for the uncoated fibers. On the other hand, specimens with coated fibers exhibit more tensile characteristics, more likely due to the fact that the bond between fibers and concrete matrix is stronger. The fibers therefore, are not simply pulled out but also detach a small volume of the brittle concrete matrix surrounding them. It seems that the effect of chemical coating can be assessed by acoustic emission parameters additionally to the macroscopic measurements of ultimate toughness.
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D. G. Aggelis, D. G. Aggelis, D. V. Soulioti, D. V. Soulioti, E. Gatselou, E. Gatselou, N. M. Barkoula, N. M. Barkoula, A. Paipetis, A. Paipetis, T. E. Matikas, T. E. Matikas, } "Effect of fiber surface conditioning on the acoustic emission behavior of steel fiber reinforced concrete", Proc. SPIE 7983, Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2011, 79830V (18 April 2011); doi: 10.1117/12.880354; https://doi.org/10.1117/12.880354

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