The main objectives of this research project are to: - evaluate the thermal effect on the bond behaviour in function of the temperature and diameter of the bar; the temperature is used as environmental accelerating agent. - compare the behaviour of the curve of bond stress versus loaded end slip using different temperatures.
This research program included three phases. In phase I, 72 glass fibre specimens were tested, using three different embedment length 5 db, 10 db and 15 db, at three different temperature including: room temperature, 40°C and 60°C. Only two specimens for each parameter were tested. A total bar length of 1500 mm embedded vertically in 150mm x 300mm concrete cylinder was used for each specimen. The specimens were tested after 4 months.
The results of phase I indicated that some specimens exhibit (rupture of the bar and concrete splitting). It was also found that for longer embedded length (10 db and 15 db), the effect of the bond strength decreased. Thus, phase II of the research project focuses on specimens with only one embedded length (5 db) and the number of specimens is increased to four specimens for each parameter to have enough result for comparison purposes. One additional specimen is instrumented with strain gauges in both direction and one thermocouple to analyze thermal effects. In this phase, two types of bars were used: Carbon and Glass. Four nominal diameters (9.5, 12.7, 15.9, 19.1 mm) for glass bars and only one nominal diameter for carbon (9.5 mm). Four different temperatures: -20°C, 40°C, 60°C and 80 °C are compared to room temperature (23°C). Freeze/thaw cycles are also included in this investigation using two periods: 100 and 200 cycles. The test specimens consist of 1200 mm long bar embedded vertically in 150mm x 300mm concrete cylinder for bar diameter of 9.5,12.7 and 15.9 mm. For bar diameter of 19.1 mm, the concrete cylinder was 200mm x 300mm. These specimens follow the CSA Code and the change in specimens dimension are intended to avoid concrete splitting. The specimens were tested after 28 days of curing.
In phase III, a second set of specimens identical to those used in phase II will be subjected to 100 and 200 freeze/thaw cycles.
Completed
The test results of phase I, (for 5 db) indicated that after 4 months, the bond strength for all diameters of bars at 40°C has not been significantly affected. However, for specimens with the same exposure time at 60°C, a reduction of 15% for 15.9 and 19.1 mm bar diameters was found. For small bar diameters, no significant effect was observed.
Based on test results of both phase I and II, for all bar diameters, a reduction of bond strength was observed as the temperature increase, with exception of 12.7 mm bar diameter as shown on Table 2.5.1. At 80°C the bond loss was around 30%, which is a significant effect. At -20°C the bond strength increased, because the specimens were tested after 60 days and the concrete strength of the specimens was higher.
Test results for room temperature (23°C), -20°C, 40°C, 60°C, and 80°C.
|
Bar
Size (mm) |
Type of Bar |
Average Bond
Strength t
=Pu/pdla (MPa) |
||||
|
References |
-20°C |
40°C |
60°C |
80°C |
||
|
9.5 |
Glass |
15.1 |
15.5 |
12.9 |
12.4 |
10.6 |
|
9.5 |
Carbon |
16.5 |
16.6 |
16.2 |
14.6 |
11.3 |
|
12.7 |
Glass |
14.1 |
16.5 |
13.1 |
14.6 |
11.7 |
|
15.9 |
Glass |
15.2 |
16.0 |
14.4 |
12.6 |
10.7 |
|
19.1 |
Glass |
12.6 |
13.8 |
12.4 |
11.3 |
9.4 |
Alvarez, A. (2004). "Temperature effect on bond properties of FRP bars embedded in concrete". M.SC.A. Thesis, Department of Civil Engineering, Université de Sherbrooke, Sherbrooke, Québec, August, 119 p.