An Investigation of the Durability of FRP in · PDF fileDurability of FRP in Concrete Procedures for Reduced Alkalinity Exposures Sotiris Demis ... BS EN ISO 14125, 1998 BS EN 2746,

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  • 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