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Frontiers of Structural and Civil Engineering

Front. Struct. Civ. Eng.    2019, Vol. 13 Issue (1) : 190-200     https://doi.org/10.1007/s11709-018-0487-1
RESEARCH ARTICLE |
Experimental investigations of internal energy dissipation during fracture of fiber-reinforced ultra-high-performance concrete
Eric N. LANDIS(), Roman KRAVCHUK, Dmitry LOSHKOV
Department of Civil & Environmental Engineering, University of Maine, Orono, ME 04469, USA
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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     
Corresponding Authors: Eric N. LANDIS   
Just Accepted Date: 15 May 2018   Online First Date: 27 June 2018    Issue Date: 04 January 2019
 Cite this article:   
Eric N. LANDIS,Roman KRAVCHUK,Dmitry LOSHKOV. Experimental investigations of internal energy dissipation during fracture of fiber-reinforced ultra-high-performance concrete[J]. Front. Struct. Civ. Eng., 2019, 13(1): 190-200.
 URL:  
http://journal.hep.com.cn/fsce/EN/10.1007/s11709-018-0487-1
http://journal.hep.com.cn/fsce/EN/Y2019/V13/I1/190
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Eric N. LANDIS
Roman KRAVCHUK
Dmitry LOSHKOV
constituent mass (g)
cement 621
sand 600
silica flour 172
silica fume 241
superplasticizer 11
water 129
Tab.1  UHPC constituents
designation fiber type fabrication
U (no fibers) cast
Z Dramix ZP305 cast
B Bekaert OL13/.20 cast
Zc Dramix ZP305 cored
Tab.2  Summary of different specimen types
Fig.1  3D renderings of undamaged cylinders. (a) “B” specimen with both fibers and matrix; (b) “Zc” (cored) specimen with the UHPC matrix removed to reveal the fiber distribution and alignment
Fig.2  Images showing region of interest for orientation analysis. (a) Specimen; (b) fibers only. Tensile reinforcement is most critical in this central region
Fig.3  (a) Optimum and (b) pessimum orientation of fibers for a small segment of the specimen. The load axis is oriented top to bottom in images. Only a small region is shown for better clarity
Fig.4  Split cylinder testing configuration. LVDTs measure platen-to-platen displacement, while six sensors are mounted on the specimen to capture AE activity
Fig.5  Load-deformation plots showing three specimen optimum/pessimum pairs. (a) “B” series; (b) “Z” series; (c) “Zc” series
designation peak load (kN) net work of load (J)
optimum pessimum optimum pessimum
B 110 84 183 148
Z 100 96 147 124
Zc 78 60 99 76
Tab.3  Peak load and net work of load for different specimens
designation event count (×1000) total AE energy (arbitrary units)
B-optimum 64.2 4.12
B-pessimum 48.1 0.42
Z-optimum 59.2 0.56
Z-pessimum 12.0 0.49
Zc-optimum 28.3 0.25
Zc-pessimum 32.0 0.28
Tab.4  Summary of AE results
Fig.6  Load-deformation response and corresponding AE energy release for “B” series (a) and “Z” series (b) specimens. (c) Relationship between net work of load and AE energy release for all tests.
Fig.7  3D renderings of (a) a B specimen (smaller fibers) and (b) a Z specimen (larger fibers). Images reveal the internal crack networks and the fibers that bridge those cracks. Note the flattened “plug” segment that appears on the upper left side of the B specimen (a). This flat side is typical of all the fiber-reinforced specimens
Fig.8  Unreinforced UHPC specimens subjected to split-cylinder loading: (a) Load-deformation plots; (b) top half specimen cross-sectional CT slice; (c) bottom half specimen cross-sectional CT slice
Fig.9  Fiber pullout length measurement: (a) Original slice; (b) segmented to solid/void; (c) segmented to fibers only; (d) “masked” image in which fibers appear in cracks; (e) 3D rendering of fibers exposed inside a crack
Fig.10  Typical force-pullout response for single fiber pullout tests. Also shown is the idealized model, P(v), used for analysis of fiber pullout in split-cylinder specimens
specimen energy (J) %Wf: %Wp Wint/Wext
Wf Wp Wint Wext
B-optimum 22 88 110 183 20: 80 60%
B-pessimum 19 72 91 148 20: 80 61%
Z-optimum 29 80 109 147 27: 73 74%
Z-pessimum 21 27 49 124 44: 56 39%
Zc-optimum 13 41 54 99 24: 76 55%
Zc-pessimum 12 32 44 76 27: 73 57%
Tab.5  Breakdown of measured energy dissipation in different specimens
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