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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
Flexural strengthening of reinforced concrete beams with carbon fibers reinforced polymer (CFRP) sheet
bonded to a transition layer of high performance cement-based composite
material resistance so that the equivalent flexional strength (f
eq,2
)
exceeded the resistance value given by the contribution of the ma-
trix (f
fct,L
) only.
2.3.2 P-CMOD Curves
In order to represent every composite behavior, it was selected
among three curves obtained per group, the average curve, with
intermediary behavior that could be representative of the other two
curves of the group.
In the composites CPA1.5A2.5C, CPA1.5A3.5C and CPM1A1C,
due to distinct performances of the three curves of each group,
it was selected instead of the average curve, the curve of higher
potential to represent these composites. The potential curve is
represents the behavior of exemplar which demonstrated higher
ductility and resistance.
In the Figure [4] are presented the P-CMOD average curves for
composite cement-based of mortar and microconcrete, respective-
ly. The uneven behavior between the curves increased even more
remarkably after the matrix rupture, i.e., when the contribution of
fibers became more effective. The increase in the volume of fibers
A provided a gradual improvement in the ductility of these compos-
ites. Considerably, the incorporation of microfibers C into fibers A
contributed even more.
2.3.3 Fracture resistance curves
The curves of resistance obtained for the mortar composites
CPA1.5A1.5C and CPA1.5A2.5C are compared with the curve of
micro concrete CPM1A2C in the Figure [5], where K
R
is the fracture
resistance and α is the crack depth (a) relatively normalized at the
height (W) of the prismatic specimen, i.e., α = a/W. In the figure are
also represented the curves of resistance for the mortar and micro
concrete with fibers together with the history of loading throughout
the process of rupture.
As shown in Figure [5], from the point where begins the growth
process of cracks in the matrix for the composites CPA1.5A1.5C,
CPA1.5A2.5C and CPM1A2C, it is observed an eminent increase
of resistance to fracture of these materials. For example, analyzing
the top of crack at 70% from the section height, it is inferred that
the fracture resistance reaches values up to four times higher than
verified at 1/3 from the section height.
The extraordinary gain in resistance of these three composites
was approximately similar, with a slight superiority for the mortar
composite CPA1.5A2.5C, followed by microconcrete CPM1A2C
and CPA1.5A1.5C. The development of resistance gain to fracture
occurred for each composite according two well defined stages:
the cracking initial stage (before the yellow dashed line), where
it was verified a slight increase of toughness to fracture, and the
cracking final stage (after the yellow dashed line), where the frac-
ture resistance increased more pronouncedly.
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2
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24
0,0 0,3 0,6 0,9 1,2 1,5 1,8 2,1
CMOD (mm)
P (kN)
CPA
CPA1A
CPA1.5A
CPA2A
CPA1.5A0.5C
CPA1.5A1.5C
CPA1.5A2.5C
CPA1.5A3.5C
0
2
4
6
8
10
12
14
16
18
20
22
24
0,0 0,3 0,6 0,9 1,2 1,5 1,8 2,1
CMOD (mm)
P (kN)
CPM
CPM1A
CPM1A1C
CPM1A2C
CPM1A2.5C
Figure������om�o�i�e���erformance
600
500
400
300
200
100
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
-1,5
(daN.cm ); P x 4 (daN)
R
K
CPA1.5A1.5C
CPA1.5A1.5C
Curve P-
growth crack
point A
CPM
CPA
Curve P-
CPA1.5A2.5C
Curve P-
CPM1A2C
CPA1.5A2.5C
CPM1A2C