1 Introduction
2 Experimental Program
2.1 Pull-out Test of GFRP-Concrete Bond Specimens
2.1.1 Specimen Geometry
2.1.2 Fabrication of Pull-out Specimens and Materials Properties
Concrete Batch | Target compressive strength (MPa) | Measured 28 days cylinder compressive strength (MPa) | Maximum aggregate size (mm) |
---|---|---|---|
2 | 32 | 42.0 | 10 |
2.1.3 Exposure Conditions
2.1.3.1 Control Specimens
2.1.3.2 Exposed Specimens
Exposure condition | Number of specimens | Name of specimens | Exposure period |
---|---|---|---|
Control | 5 | GControl-1 to 5 | – |
Temperature cyclea
| 3 | GT2-1 to 3 | 5 weeks |
Wet–dry cycleb
| 5 | GH1-1 to 5 | 1 month |
Outdoor environment | 5 | GE1-1 to 5 | 2 months |
Temperature cyclea
| 3 | GT3-1 to 3 | 3 months |
Wet–dry cycleb
| 5 | GH2-1 to 5 | 6 months |
Outdoor environment | 5 | GE2-1 to 5 | 6 months |
Temperature cyclea
| 3 | GT4-1 to 3 | 12 months |
Wet–dry cycleb
| 5 | GH3-1 to 5 | 12 months |
Outdoor environment | 5 | GE3-1 to 5 | 12 months |
Wet–dry cycleb
| 5 | GH4-1 to 5 | 18 months |
Outdoor environment | 5 | GE4-1 to 5 | 18 months |
Total number of specimens | 54 |
2.1.4 Test Set-Up and Instrumentation
2.1.5 Experimental Procedure
3 Test Results and Discussion
3.1 Pull-out Strengths
3.1.1 Control Series
3.1.2 Exposed Series
Exposure duration (days) | Mean pull-out strength (MPa) | CoV of pull-out strength (%) |
---|---|---|
0 | 1027 | 6.0 |
35 | 1056 | 5.5 |
90 | 1065 | 1.9 |
365 | 1113 | 1.7 |
Exposure duration (days) | Mean pull-out strength (MPa) | CoV of pull-out strength (%) |
---|---|---|
0 | 1027 | 6.0 |
28 | 1022 | 10.8 |
168 | 961 | 12.4 |
364 | 1011 | 6.9 |
546 | 1034 | 5.0 |
Exposure duration (days) | Mean pull-out strength (MPa) | CoV of pull-out strength (%) |
---|---|---|
0 | 1027 | 6.0 |
60 | 941 | 7.0 |
180 | 931 | 6.3 |
365 | 970 | 7.0 |
555 | 1023 | 6.3 |
3.1.2.1 Temperature Cycles
3.1.2.2 Wet–Dry Cycles
3.1.2.3 Outdoor Environment
3.2 Failure Modes
3.2.1 Control Series
3.2.2 Temperature Cycles
3.2.3 Wet–Dry Cycles
3.2.4 Outdoor Environment
3.3 Strain Profiles
3.3.1 Control Series
3.3.2 Temperature Cycles
3.3.3 Wet–Dry Cycles
3.3.4 Outdoor Environment
3.4 Discussion
4 Conclusions
-
Temperature cycles
-
The temperature cycles did not have any negative effect on the pull-out strength of GFRP-concrete bond. In fact, temperature cycles improved the pull-out strength by 8 % for GFRP-concrete bond. This improvement of pull-out strength is attributed to the increased concrete compressive strength as the failure of bond occurred within the concrete substrate with minimal reduction in concrete thickness.
-
Strain profiles did not show any changes with the exception of longer effective bond length observed in some exposed series.
-
Wet–dry cycles
-
Performance of GFRP-concrete bond under wet–dry cycles was marginally poor (strength reduction by 6.4 % only). The degradation can be attributed to the epoxy degradation as the most series failed with almost no concrete attached to the debonded GFRP.
-
The trend of the loads at the change of initial stress transfer length also changed with time and followed almost a similar trend to the pull-out strength. Effective bond lengths for most of exposed specimens were longer than that of unexposed specimens for most exposure durations.
-
Outdoor environment
-
Exposure to outdoor environment caused the most serious deterioration of pull-out strength (9.3 %). Deterioration of bond strength due to outdoor environment can also be attributed to the degraded epoxy properties since unlike the control specimens, very thin or almost no concrete layer was found to be attached to debonded FRP for exposed specimens.
-
The change in strain profiles, in terms of the loads at the shifting of initial stress transfer length, and increase in effective bond lengths were identified.