Durability of FRP in Concrete
Procedures for Reduced Alkalinity Exposures
Sotiris DemisProfessor Kyrpos Pilakoutas
Dr Ewan Byars
Department of Civil & Structural EngineeringThe University of Sheffield, UK
Definition of the Problem
What is the main aggressive agent for FRP ?
Is deterioration affected by the pH level ?
Can cement replacements address the issue?
Can carbonation address the issue?
What is the rate of deterioration ?
Pilot Studies
Programme
FRP type: GFRPConcrete mix : OPC 40
Exposure Environnent
Air, 20 C (lab temp.)
Testing Technique
GFRP Tensile Testing GFRP Flexural (3-point bending)Direct Cube pull-out
Programme
FRP type: GFRP
Concrete mixes:OPC 40OPC/PFA 40/30OPC/GGBS 40/70
Exposure Environment
CO2: 15%, RH: 55 %
Test ages: 0, 1, 6, 12, 24 months
Standards
BS EN ISO 14125, 1998BS EN 2746, 1998
BS 2782-10 (1005), 1977BS EN ISO 178, 2003
BS EN 2562, 1997ACI 549 R, 1997
ACI 440.3 R, 2004
Standards
fib T.G. 9.3, 2006 BS EN 13295, 2004
Programme
FRP type: GFRP
Exposure Environnent
Air (control) 20 C Alkali: pH 9, 20 C
pH 12, 20 C
CO2 : 15 %, 23.94 C
Test ages: 0, 1, 6, 12 months
Standards
BS EN ISO 527-4, 1997 BS EN 2561, 1995BS EN 2747, 1998ACI 549 R:, 1997
ACI 440.3 R:, 2004
GFRP Tensile Testing
Concrete strength Carbonation development
Programme
Concrete mixes:OPC 40OPC/PFA 40/30OPC/GGBS 40/70
Exposure Environment
WaterCO2: 15%, RH: 55 %
Test ages:0, 1, 6, 12, 24 months
Standards
BS 12, 1989BS 1881 (125), 1986BS 1881 (112), 1983
BS 146, 1996BS 6588, 1996BS 5328, 1997
ACI 232.2 R, 2003ACI 233 R, 2003
Pull-out Testing
Experimental Programme
Results Samples in Solution
Reductions in the tensile capacity of the FRP bars up to 41.6 %.
Caused by alkali ingress to fibre/matrix interface
fibresmatrix
Accelerated with a non-perfect quality of FRP bars tested.
Results Samples in Concrete
0
2
4
6
8
10
12
1 6 11 16 21 26
Time of Exposure (months)
Mea
n B
ond
Stre
ngth
(MPa
)
OPC (control)OPCOPC/GGBSOPC/PFA
Initial bond strength value of control samples
Embedment length: 150 mmBar size: 8 mm squareConcrete Strength: 40 MPa
Results Samples in Concrete
0
2
4
6
8
10
12
1 6 11 16 21 26
Time of exposure (months)
Nor
mal
ised
Bon
d St
reng
th (M
Pa)
OPC (control) OPC OPC/GGBS OPC/PFA
Initial bond strength value of control samples
-20
-15
-10
-5
0
5
1 6 11 16 21 26
Time of exposure (months)
Loss
of b
ond
(%)
OPC OPC/GGBS OPC/PFA
Carbonated OPC bond reduced by 12.9 %
PFA bigger increase in bond after 1 year
Considerable changes in bond after 6 months
Results Samples in Concrete
Position of the FRP bar at the centre of the 150 mm cube
70.4 mm
Edge of the 100 x 100 x 500 mm concrete prism
Carbonation Test on 100 x 100 x 500 mm prisms
Carbonation Test on 150 mm pull/out cubes
Car
bona
tion
Dep
th (m
m)
0
20
40
60
80
100
120
Time of Exposure (months)0 5 10 15 20 25 30
Car
bona
tion
Dep
th (m
m)
0
20
40
60
80
100
OPCOPC/GGBSOPC/PFA
Carbon Dioxide
Phenolphthalein
WaxedSurfaces
Uncarbonated Area
CarbonatedArea
Carbon Dioxide
100100
500
exposed concrete
freshly brokenand then re-waxed
waxed surfaces
0.90
0.95
1.00
1.05
1.10
1.15
1.20
0 20 40 60 80 100 120
Carbonation Depth (mm)
Rat
io o
f Con
cret
e C
ompr
essi
ve
stre
ngth
to th
e co
ntro
ls O
PC
com
pres
sive
stre
ngth
OPC OPC/GGBS OPC/PFA
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70
Cube compressive strength (MPa)
Bon
d St
reng
th (M
Pa)
OPC (control) OPC
OPC/GGBS OPC/PFA
Results Samples in Concrete
Results Samples in Concrete
Bon
d S
treng
th (M
Pa)
5
6
7
8
9
10
11 OPC (control)OPCOPC/GGBS
OPC/PFA
Nor
amlis
edBo
nd
Stre
ngth
with
resp
ect t
o co
ncre
te c
ompr
essi
ve
stre
ngth
(MPa
)
6
7
8
9
10
Concrete Compressive Strength (MPa)
30 35 40 45 50 55 60Nor
mal
ised
Bond
Stre
ngth
with
re
spec
t to
revi
sed
conc
rete
co
mpr
essi
ve s
treng
th
(MP
a)
5
6
7
8
9
10
11
Mea
n B
ond
(MPa
)
5
6
7
8
9
10
11
opc control opcopc/ggbsopc/pfa
Cla
ssic
al N
orm
alis
edB
ond
(MPa
)
5
6
7
8
9
10
11
Time of Exposure (months)0 5 10 15 20 25 30
Nor
mal
ised
Bon
d w
ith
resp
ect t
o fc
u' (M
Pa)
5
6
7
8
9
10
11
Results Samples in ConcreteBefore carbonation reached
the barAfter carbonation reached
the barBefore and after
carbonationSignificant statistical
differenceNo significant statistical
differenceNo significant statistical
difference
Model to predict the penetration of the carbonation front
Model to predict the effect of carbonation
on bond strength
Chemical Deterioration takes place once the
carbonation front reaches the FRP bar
2 models required to predict this behaviour
Key finding
Results Samples in Concrete
Rt
ty(years)
28 days
5
10
20
30
50
100
(%)
100
4.6
81.6
78.6
76.9
74.6
71.6
fcm(ty)
(MPa)
35.7
51.1
51.6
51.9
52.1
52.2
52.4
(MPa)
6.81
9.30
9.35
9.39
9.41
9.73
9.45
(MPa)
6.81
7.87
7.63
7.38
7.23
7.04
6.77
1
1.24
1.20
1.11
1.08
1.04
1.00
D
(mm)
0
8.32
11.8
16.6
20.4
26.3
37.2
Rt
Rttt tRt
: Relative bond retention
fcm(ty)
t
Rtt
tRt
: OPC concrete strength as enhanced by time and carbonation
fcm(t) = cc(t) fcm
cc(t) =0.528exp 1s
t
The strength is calculated according to Eurocode 2 as,
and is increased by 15% to account for the effect of
carbonation
: expected bond strength calculated according to Eurocode 2, taking into account the gain in compressive strength.
: expected bond strength due to the effect of carbonation
: total bond strength retention in time
The above table assumes that concrete had zero cover and carbonation took place at 28 days
Results Samples in Concrete
the negative effect of carbonation is counteracted by the gain in strength with time and as such does not reduce the initial bond strength for length of exposure up to 100 years.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 20 40 60 80 100 120
Time of Exposure (years)
Tota
l Bon
d R
eten
tion
no cover10 mm cover
20 mm cover30 mm cover
Conclusions pH 9 and pH 12 solutions had detrimental effect on the GFRP tensile strength
Although pH has impact on FRP in solutions, its impact may be assignificant as the impact of moisture on FRP.
Alkalinity does not have a major impact on FRP bond
As concrete strength increases due to time and carbonation, bond also increases
Carbonation operates as a switch on deterioration of FRP
Expected bond deterioration due to carbonation is more than compensated by the increase in strength of concrete due to time and carbonation
There is no need to take into account the carbonation effect on the stress reduction factors used for durability design
Blended cements reduced alkalinity but did not improve behaviour