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32 and unrepaired specimens. Using epoxy injection to restore 3.3 Epoxy Injection Testing tensile capacity of concrete cracked under the effect of pre- stressing bursting forces is unwarranted and misleading. 3.3.1 Introduction Even if the injected cracks are assured to be completely The epoxy injection test was developed and conducted at filled with epoxy and the interface surface between epoxy an early stage of the project to investigate (1) if epoxy injec- and concrete have adequate adhesion, the tensile capacity tion repair of end zone cracking is able to restore the tensile restoration would only be assured at the injected cracks. capacity of the cracked concrete, (2) if epoxy injection is capa- In the meantime, there would be numerous cracks, some of ble of completely filling the crack through the width of the web, which are too narrow to effectively inject or are even invis- and (3) if variations of the end zone reinforcement details have ible. At these locations, the tensile capacity of the concrete a significant effect on the number, width, and pattern of end perpendicular to the crack lines would be lost even if wider zone cracks. cracks are satisfactorily injected with epoxy. Thus, the value To shed light on these issues, the research team had two of epoxy is to act as a sealant preventing penetration of water 12-ft long specimens fabricated by Concrete Industries Inc., and salts into the concrete member. For this purpose, epoxy Lincoln, Nebraska, as part of an NU 1350 (53 in. deep) bridge sealing may not be the most economical or efficient method, girder production. Details of these specimens and discussion unless the cracks are very wide. on the experimental activities conducted on them are given The full-scale testing also validated the statement that prop- in the following sections. erly designed and detailed end zone reinforcement is impor- tant in controlling end zone cracking. The AASHTO LRFD method produced acceptable results. The proposed method 3.3.2 Description of the Test Specimens resulted in further improvements in crack control. The exper- Figure 3.32 shows the cross section of the test specimen. An iments demonstrated that reinforcement should not just be NU 1350 section was used in making the specimens. Specified placed at the very end of the girder. The reinforcement should release strength was 6,500 psi and final strength was 8,000 psi. gradually diminish over a distance equal to h/2 of the girder The bottom flange was reinforced with thirty-two 0.6-in., depth. If reinforcement is placed only at the very end, there may 270 ksi, low relaxation straight strands in two rows, and the be instances where wider cracks appear beyond the concen- web top was reinforced with twelve 0.6-in., 270 ksi, low relax- trated reinforcement. This was confirmed in the Washington ation straight strands. The strand stress just before release was State experiments, where relatively large prestressing was 202.5 ksi. Four additional 0.5-in., 270 ksi strands stressed at applied. 13.2 ksi were provided in the top flange. Vertical shear web (4) 0.5" Dia. Low-Lax 270K Strands Stress to 13.2 ksi WWF6 2" 2" 2" 2" 2" 2" 2" (12) 0.6" Dia. Low-Lax 270K Strands Stress to 202.5 ksi 4'-5 1/8" 3'-1 1/8" (2) #4 bars (32) 0.6" Dia. Low-Lax 270K 2" 2" Strands Stress to 202.5 ksi 1" Figure 3.32. Cross section of test specimen (NU 1350).
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33 12'-0" 1 1/2" 11'-9" (WWF5 @ 3") 1 1/2" 2" 11'-8" ( #4 bar EA. FACE @ 4" ) 2" 2'-0" 8'-0" 2'-0" (2) WWF6 #4 bar EA. FACE @ 4" Figure 3.33. Specimen #1: S1L (no EZR), S1R (no EZR). reinforcement consisted of pairs of #4 at 4 in. for the full 12-ft The test specimens were not provided with sole plates at the length of each specimen. No confinement reinforcement was ends, or with transverse confinement reinforcement in the bot- provided in the bottom flange. tom flange. The research team believes in the importance of No special end zone reinforcement was provided in either these two elements. However, they were intentionally omit- end of the first specimen, as shown in Figure 3.33. Both ted to demonstrate their value. The production girders, made ends of the second specimen were provided with special end in the same production run as the test specimens, had these zone reinforcement, where the left end was designed using elements, thus offering an opportunity for comparison. the LRFD Specifications (18) and the right end was designed Both specimens, as well as the production girders, experi- using the proposed end zone reinforcement detail that is given enced end zone cracking. Figures 3.35 through 3.37 show the in Section 3.7 of this report, as shown in Figure 3.34. The pro- end zone cracks of the test girders. As expected, both ends of posed detail was developed at the University of Nebraska (16). the first specimen, S1L and S2R, which had no special end zone 12'-0" 1 1/2" 11'-9" (WWF5 @ 3") 1 1/2" 2" (6) SPA. 1 1/2" 10'-0" ( #4 bar EA. FACE @ 4" ) 1 1/2" 1 1/2" @ 2" = 1' (3) SPA. 2'-0" 8'-0" 2'-0" @ 2" = 1' (2) WWF6 #5 EA. #6 EA. #4 bar EA. FACE @ 4" FACE FACE Figure 3.34. Specimen #2: S2L (LRFD), S2R (proposed).
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34 Figure 3.35. Specimen #1 with no special end zone reinforcement (cracks traced for clarity). reinforcement, experienced a greater amount of cracking than those of the second specimen, which was provided with spe- cial end zone reinforcement. One end of Specimen #1 has cracks that were longer and wider than the other end. For Specimen #2, the end designed according to the AASHTO LRFD specifications experienced more severe cracking than the end designed using the proposed detail. The lack of bot- tom plate and bottom flange reinforcement contributed to in- creased cracking near the bottom flange. At one end, splitting cracks occurred at a corner strand. The precast producer used epoxy injection to repair one end of Specimen #1 (the girder without bursting end reinforcement) and the end designed according to the LRFD specifications of Specimen #2. The epoxy injection repair was conducted according to the pro- cedure given in the Manual for the Evaluation and Repair Figure 3.36. Specimen #2: S2L (LRFD). of Precast, Prestressed Concrete Bridge Products (11). Then, Figure 3.37. Specimen #2: S2R (proposed).