Experimental investigations of internal energy dissipation during fracture of fiber-reinforced ultra-high-performance concrete

Abstract

Split-cylinder fracture of fiber-reinforced ultra-high-performance concrete (UHPC) was examined using two complementary techniques: X-ray computed tomography (CT) and acoustic emission (AE). Fifty-mm-diameter specimens of two different fiber types were scanned both before and after load testing. From the CT images, fiber orientation was evaluated to establish optimum and pessimum specimen orientations, at which fibers would have maximum and minimum effect, respectively. As expected, fiber orientation affected both the peak load and the toughness of the specimen, with the optimum toughness being between 20% and 30% higher than the pessimum. Cumulative AE energy was also affected commensurately. Posttest CT scans of the specimens were used to measure internal damage. Damage was quantified in terms of internal energy dissipation due to both matrix cracking and fiber pullout by using calibration measurements for each. The results showed that fiber pullout was the dominant energy dissipation mechanism; however, the sum of the internal energy dissipation measured amounted to only 60% of the total energy dissipated by the specimens as measured by the net work of load. It is postulated that localized compaction of the UHPC matrix as well as internal friction between fractured fragments makes up the balance of internal energy dissipation.

Keywords

ultra-high-performance concrete / concrete fracture / X-ray computed tomography / acoustic emission

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Acknowledgements

This work was supported by the Engineer Research and Development Center (ERDC) of the U.S. Army Corps of Engineers through a subcontract with ES3 Inc. The work Todd Rushing and the ERDC Materials Branch for their assistance fabricating the UHPC specimens is gratefully acknowledged, as is the assistance of Jeramy Magruder and George Lopp at the University of Florida Advanced Materials Characterization Laboratory. Permission to publish this information was granted by the Director, Geotechnical and Structures Laboratory, ERDC.

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