Long Term Monitoring of Mechanical Properties of FRP Repair ...

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Figure 3.19 Areas removed are highlighted in green The smaller of the two voids, approximately 28 cm x 51 cm (11” x 20”) in size, was removed from the extrados of the first bay on the north end of the east arch. This void had a previously identified crack running in the transverse direction on the arch. A right-angle grinder mounted with 11.4 cm (4 ½”) masonry cutting wheel was used to cut through the CFRP layer in a rectangular shape enclosing the area of the void. Once the CFRP was removed, it was reasoned that this area of CFRP was at one time bonded to the substrate, because the crack previously seen in the surface of the CFRP was also present in the substrate. It was likely that the concrete cracked due to service loads or shrinkage. It is possible the crack was present before the CFRP was applied and the crack opened more causing the CFRP to crack. According to CDOT’s construction specifications, cracks in the substrate larger than 1.5 mm (0.06 in) in width were to be pressure injected with epoxy resin prior to the application of the CFRP. When the concrete cracked or the crack widened due to internal tension, the same strain was imposed on the CFRP to cause cracking there as well. A local bond would have been necessary to impose the same strain to the CFRP. Once the CFRP became cracked, water and moisture were able to penetrate the CFRP layer and subsequent freeze/thaw cycles not only opened the crack more, but debonding of the CFRP from the substrate also occurred. The debonded area increased over time due to freeze/thaw cycles and temperature fluctuations. The unidirectional CFRP fabric was more susceptible to cracks in the transverse direction because the carbon fibers were aligned in this same direction and no, or very few, fibers had to rupture. The ultimate tensile strength 90 degrees to the primary fibers of Tyfo® SCH-41, according to Fyfe, is approximately 4.6% of the ultimate tensile strength in the direction of the primary fibers. Upon cutting the lower edge of the CFRP rectangle, water exited the cut at the bottom of the void, revealing standing water at the interface between the CFRP and substrate. Photographs of the void and the removal of the CFRP layer are shown in Figures 3.20, 3.21, and 3.22. 30
Figure 3.20 Void in CFRP with transverse crack identified with red arrows and Cutting the perimeter of the void in the CFRP Figure 3.21 Water exiting the void area directly after the lower cut through the CFRP was completed 31
Page 1 and 2: Long Term Monitoring of Mechanical
Page 3: ABSTRACT Over the years, Fiber Rein
Page 6 and 7: 6.4.3 Freeze-Thaw Cycles ..........
Page 8 and 9: LIST OF FIGURES Figure 2.1 Castlewo
Page 10 and 11: Figure 6.1 Direct shear test repres
Page 12 and 13: this method, and interpretation of
Page 15 and 16: 2. TASK 1: COLLECT INFORMATION AND
Page 17 and 18: Figure 2.3 Castlewood Canyon Bridge
Page 19 and 20: 2.2.2 Repair of Arches and Struts P
Page 21 and 22: The arches and struts were then pai
Page 23 and 24: Tests were performed on both sides
Page 25 and 26: Figure 2.14 Outlined in permanent m
Page 27: particular location because the are
Page 30 and 31: only one arch exceeded 148.6 m 2 (1
Page 32 and 33: crack identified in 2007 had grown
Page 34 and 35: Figure 3.5 Starting a core hole usi
Page 36 and 37: Figure 3.9 Prepared areas for the a
Page 38 and 39: The maximum stress applied and fail
Page 40 and 41: processes and substrates were ident
Page 44 and 45: Figure 3.22 Cracks in the substrate
Page 46 and 47: Figure 3.25 Applying a primer coat
Page 49 and 50: 4. TASK 3: LABORATORY TESTING OF FR
Page 51 and 52: Figure 4.3 Failed tensile test spec
Page 53 and 54: The probability density functions a
Page 55 and 56: Figure 4.9 Probability density func
Page 57 and 58: Available water acts as a plasticiz
Page 59 and 60: Figure 4.14 Ground CFRP specimen Du
Page 61 and 62: Figure 4.18 Ground and diced CFRP D
Page 63 and 64: Figure 4.22 Filler resin DSC result
Page 65 and 66: 5. TASK 4: LITERATURE REVIEW ON ADD
Page 67 and 68: Ongoing work has also been aimed at
Page 69 and 70: inertness does not apply to the fib
Page 71 and 72: procedures. This study has presente
Page 73 and 74: Because no thermographic images wer
Page 75 and 76: 6. TASK 5: ESTABLISH LONG-TERM TEST
Page 77 and 78: 6.2.3 Direct Tension Pull-Off Tests
Page 79 and 80: Figure 6.5 Pull-off test failure mo
Page 81 and 82: 6.4.1 Exposure to Deicing Agents To
Page 83 and 84: Table 6.2 Stage 1 (6-month) Tests P
Page 85 and 86: 6.6.2 Application of CFRP to Concre
Page 87 and 88: using a Devcon high strength epoxy,
Page 89 and 90: mm x 13 mm) steel plate welded at t
Page 91 and 92: Figure 6.19 Pull-off tests 1, 2, an
Page 93 and 94:
Figure 6.22 Beam following crack fa
Page 95 and 96:
Table 6.8 Cylinder Tests for Stage
Page 97 and 98:
The most common failure was identif
Page 99 and 100:
exact same conditioning is due to t
Page 101 and 102:
etween one of the control specimens
Page 103 and 104:
Table 6.13 Stage 2 Pull-off Test Re
Page 105 and 106:
Figure 6.31 Mode G Failure in Dolly
Page 107 and 108:
Table 6.14 Stage 2 Beam Results Bea
Page 109:
Figure 6.36 Average beam results fo
Page 112 and 113:
A recent study conducted by Eveslag
Page 114 and 115:
Figure 7.1 Pull-off Strength Result
Page 116 and 117:
104
Page 118 and 119:
106
Page 120 and 121:
Crawford, K. (2008). Evaluating lon
Page 122 and 123:
110
Page 124 and 125:
Table A1. Summary of Voids on the E
Page 126 and 127:
Bay 1NW: 3 Voids, 1 Rust Spot Figur
Page 128 and 129:
Figure A5. Photograph and thermal i
Page 130 and 131:
Bay 3NE: 5 Voids, 2 Were Identified
Page 132 and 133:
Bay 4NE: 1 Void Figure A13. Bay 4NE
Page 134 and 135:
Figure A17. Void from 2007 has grow
Page 136 and 137:
Figure A21. Photograph and thermal
Page 138 and 139:
126
Page 140 and 141:
Table B1. Continued Global Test Num
Page 142 and 143:
Table B2. Continued Global Test Num
Page 144 and 145:
Figure B8. Test No.9, weak bond str
Page 146 and 147:
Figures B14 and B15. Tests No.17 an
Page 148 and 149:
Figure B24. Test No.27 136
Page 150:
Table C1. Continued Specimen ID Ten
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