Han Ay Lie Procedia Engineering 00 2017 000–000 3
3. Experimental research
3.1. Shear-bond behavior
Shear-bond test methods for FRP are limited; research work on FRP in shear is mostly applied to FRP plates having a much higher rigidity as compared to sheets or wraps [4, 5, 6, 7, 8, 9]. Since the FRP sheets have
significantly less stiffness as compared to FRP plates, the typical one-face-tensile, and the one-face and double-face- push tests as introduced by the majority of researchers, was not applicable. The effect of misalignment would
heavily influence the outcome [10]. Considering all aspect, a modification of the test method based the fib-CEB technical specifications [2, 11] was chosen Fig 2.
Fig. 2. Shear test set up and specimen preparation.
Instead of using steel clamps as was advised by the fib-CEB, a smaller bond area measuring only 50 by 50 mm was designed to localize bond failure. The opposite contact areas were made larger, measuring 50 by 150 mm. An
un-bonded zone 50 mm in width was designated to prevent premature spalling due to high stress concentrations in the concrete corner. This un-bonded area was bridged by a two-ply FRP composite attached by an epoxy layer at the
interface. The epoxy resin was also applied the exposed face of the FRP. The D22 steel bar dimension; its development length and the concrete reinforcements were carefully designed to ensure failure in the bond. Six
specimens were prepared for each surface treatment, and standardized cylinders sized 150 by 300 mm were produced to monitor the 28
th
day’s concrete compression strength. The strength was recorded as 55.60 MPa. At the age of 28 days, the groves were applied to the concrete surface using a circular diamond saw, and
sandblasted to clean the groves of small particles. The FRP sheet was applied using the epoxy-resin and cured for seven days. Upon testing, the specimen was placed in a wooden frame to prevent secondary strains in the bonded
and un-bonded FRP area. The specimen was further placed within the gripping jaws of the Universal Testing Machine, and the D22 steel bars clamed. A direct tensile force with a loading rate of 1.5 kNsec was applied to these
steel bars. The load increment, the failure load, and the strain response in the strain gauge, were recorded. Additionally, the strain in the un-bonded FRP was measured using strain gauges attached to the FRP surface prior to
the application of the epoxy resin Fig. 2. The specimens were designated S
T
, S
D
, S
C
, S
L
and S
N
based on the surface preparation type. All specimens S
T
, S
D
, S
C
and S
L
failed due to concrete-shear failure; the S
N
specimen failed in de- bonding between the epoxy-resin and the concrete Figures 3a and 3b
3.2. A
bond the c
and t
T The
This 55.6
bond prod
A gaug
un-b had
doub from
4 t and a
two a
Shear bond str All specimens S
d mode betwee concrete at the
the concrete, a
The S
N
specime shear-bond str
s concrete-shea 0 MPa concre
d using the ex duced between
A closer observ ges showed tha
bonded FRP se a material stiff
ble play genera m single-ply FR
to the initial sti a 0.50 mm thic
bond faces. a
Fig. 3. Shear-b
rength S
T
, S
D
. S
C
and en the FRP and
un-bounded ar and the stress-fl
en failing in sh rength was calc
ar strength clos te strength is 7
act same mate the FRP and c
vation to the s at the bonded F
ction had a ma fness of 90 kN
ally resulted in RP-resin specim
iffness of the m ckness of the e
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ond and concrete-
S
L
failed due to d the concrete.
rea. This was d flow propagatio
Fig. 4. Concrete
hear-bond had culated to be 5
sely approache 7.46 Nmm
2
. T erial resulted in
oncrete, conse strain response
FRP had a mu aterial stiffness
Nmm in combin n a higher elast
mens [12]. The material. The Y
poxy resin laye
Procedia Enginee
b
shear failure; a D
o concrete shea Except for the
due to the high on in the direct
spalling due to hig
a significantly 5.24 Nmm
2
, co es the concrete-
The report on t n average shea
quently the fai e in the un-bo
uch higher stiff s of 63 kNmm
nation with a Y tic modulus as
e double layere Young’s modul
ers. The tensile
ering 00 2017 00
De-bonding failure
ar-cracking, wh predicted patte
h stresses in th tion outward of
gh shear-stress con
y lower failure ompared to the
-shear capacity the single-lap s
ar-bond streng ilure mode shou
nded and bon fness as compa
m with a Young Young’s modu
compared to t ed FRP and the
lus was determ e load was also
00–000
e; b Concrete-sh
hile the S
N
spe ern as seen in F
e vicinity of th f the maximum
ncentrations.
stress as comp e concrete-shea
y as predicted shear test perf
gth of 16.6 MP uld be due to c
nded FRP secti ared to the un-
g’s modulus of ulus of 67 GPa
the Young’s m e additional ep
mined based on o assumed to b
hear failure.
ecimens failed Fig. 3, spalling
he border betw m shear stresses
pared to S
T
, S
D
ar strength of 8 by the ACI co
formed on the Pa [12]. If a g
concrete-shear. ion recorded b
-bonded FRP f 57 GPa. The
. The composit modulus of 55 G
poxy-resin trea a 0.13 mm FR
be distributed e in the shear-
g occurred in ween the FRP
s Fig. 4.
D
. S
C
and S
L
. 8.12 Nmm
2
. ode that for a
FRP-to-FRP good bond is
. by the strain
Fig. 5. The bonded FRP
te FRP-resin GPa resulted
atment added RP thickness,
equally to the
3.3. D
To betwe
and a Th
T
N
. T Upon
the sl draw
failur
3.4. T
Al failur
streng calcu
test r surfa
Direct tensile b o test the resp
een the FRP an an accuracy lev
he concrete sur The synthetic s
n testing, a cyl lab. The alumin
-bolt. This dra re, and the load
Tensile bond st ll but one of t
re due to tensio gth measured t
ulated from the results. The cra
ce showed a cl
F
behavior onse in direct
nd concrete. T vel of less than
rface was prep heet was attach
inder with a d num test disc w
aw bolt had a d recorded Fig
trength he T
N
specime on. The tensile
to be 3.20 MP e fib-CEB mod
acking pattern lear breaking m
Han Ay Lie
Fig. 5. Stress-strain
tension, an ex he Dyna Proce
2 with a stro ared in the sam
hed to the con diameter of 50
was attached to conical head
g 6.
Fig
ens failed in te e-bond failure r
a. This value w del code 2010
was easily dis mode in the inte
Procedia Engine
n behavior of bond
xperimental m eq haftprufer p
oke of 3.5 mm, me manner as t
crete surface a mm was core-
o the FRP with to ensure a co
. 6. Direct tensile t
ensile-bond mo resulted in a st
was taken as av predicted a ten
tinguishable fr erface between
eering 00 2017 00
ded and un-bonded
model was cons pull-off tester Z
, was used. the shear specim
and the specim -drilled in the
h resin, and con oncentric tensi
testing method.
ode. All other tress of 1.29 N
verage of all th nsile strength o
rom the tensile n the aggregate
00–000
d FRP wraps
structed that ta Z16 having a p
mens, and den mens were teste
concrete surfa nnected to the
ion force. The
surface treatm Nmm
2
, compar he data. The co
of 3.84 MPa, w e-bond failure,
e and the morta argets only the
pull-out capaci noted as T
T
, T
D
ed after seven d ace, creating a
pull-off tester e specimen wa
ments resulted red to the conc
oncrete tensile which is very
since the conc ar Fig 7.
5
e bond area ity of 16 kN
D
. T
C
, T
L
and days curing.
cone inside through the
as tested till
in concrete crete-tensile
e strength as close to the
crete failure
Sri Tudjono Procedia Engineering 00 2017 000–000
a. b.
Fig. 7. a De-bonding in tension; b Mortar tension failure.
4. Analysis and discussion