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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 3
Post-strengthening of reinforced concrete beams with prestressed CFRP strips.
Part 1: Analysis under static loading.
The aggregates used to produce the concrete were the ones avail-
able in the Switzerland region and the cement was the Portland
CEM I 42,5 (95% of clinquer, and 5% of other components), equiv-
alent to the Brazilian CPI. The average compressive stress (cube
strength) of the concrete, after 28 days, was 44MPa.
The 8mm steel bars had average yield stress, yield strain, ultimate
stress and modulus of elasticity of 554MPa, 2,51º/
oo
, 662MPa e
220Gpa, as indicated by tensile tests. The 12mm steel bars had
average values of: 436MPa, 1,98º/
oo
, 688MPa e 215GPa.
3.3 Post-strengthening system
Sika® Carbodur (Carbodur S 512 and Sikadur®-30) was the CFRP
system used to post-strengthen the beams. However, Sikadur®-
30LP adhesive was used to bond the prestressed strips to the con-
crete, due to its extended pot life. Table [2] shows the characteris-
tics of the strips and adhesive, provided by manufacturer.
3.4 Post-strengthening procedure
The application of Sika® Carbodur system demands a surface
preparation for the concrete and the strip. The concrete surface
must be clean and free from grasses and oil, dry and have no loose
particles. Considering the application of prestressed strips, after
concrete and strip surface preparation, the strip is clamped, pre-
stressed and covered with Sikadur®-30LP adhesive. Then, ther-
mocouples are settled at the strip aiming to control the temperature
applied to accelerate the cure of the adhesive. Figure [7] shows
the application of epoxy adhesive on the strip and the procedure to
clamp the strip on the prestressing device.
Table 2 – Post-strengthening system characteristics
Carbodur S 512
Strip
Thickness (mm)
1,2
Width (mm)
50
Tensile Strength (MPa)
2.800
Ultimate Strain (‰)
17
Young’s Modulus (MPa)
165.000
Ò
Sikadur -30
Resin
Sikadur -30LP
Ò
Resin
Components
3Part A:1Part B
2Part A:1Part B
Pot life at 25°C (min)
-
60
Pot life at 35°C (min)
40
-
Pot life at 55°C (min)
-
30
Tg (°C)
62
107
Young’s Modulus (MPa)
12.800
10.000
Figure 7 – (a) Application of epoxy adhesive; (b) e (c) Procedure to clamp the
strip on the prestressing device
A
B
C