Durability of FRP Composites for Construction ISIS Educational Module 8: Produced by ISIS Canada.
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Transcript of Durability of FRP Composites for Construction ISIS Educational Module 8: Produced by ISIS Canada.
Durability of FRP Composites for Construction
ISIS Educational Module 8:
Produced by ISIS Canada
Module Objectives
• To provide students with a general awareness of important durability consideration for FRPs
• To facilitate and encourage the use of durable FRPs and systems in the construction industry
• To provide guidance for students seeking additional information on the durability of FRP materials
ISIS EC Module 8
FRPComposites
For Construction
Outline
Introduction & Overview
Moisture & Marine Exposures
Cold Temperatures & Freeze-Thaw
UV Radiation
CreepFatigue
ISIS EC Module 8
FRPComposites
For Construction
Alkalinity & Corrosion
High Temperatures & Fire
Reduction Factors
Case Study
Specifications
Section: 1 Introduction & Overview
ISIS EC Module 8
FRPComposites
For Construction
• The problem: In recent years, our infrastructure systems have been
deteriorating at an increasing and alarming rate
New materials that can be used to prolong and extend the service lives of existing structures ??
Fibre Reinforced Polymers (FRPs)
Section: 1
ISIS EC Module 8
FRPComposites
For Construction Introduction & Overview
• Key uses of FRPs in construction:
1. Internal reinforcement of concrete
2. External strengthening of concrete
Corrosion of steel reinforcement in concrete structures contributes to infrastructure deterioration
Use non-corrosive FRP reinforcement
Provide external tension or confining reinforcement (FRP plates, sheets, bars, etc.)
Section: 1
ISIS EC Module 8
FRPComposites
For Construction Introduction & Overview
• What is FRP? FRP is a composite:
Composite = combination of two or more materials to form a new and useful material with enhanced properties in comparison to the individual constituents (concrete, wood, etc.)
FRPs consist of:1. Fibres2. Matrix
High-strength fibres
Polymer matrix
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
Polymer matrix
Introduction & Overview
• Polymer matrix:
As the binder for the FRP, the matrix roles include:1. Binding the fibres together2. Protecting the fibres from environmental degradation3. Transferring force between the individual fibres4. Providing shape to the FRP component
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
Polymer matrix
Introduction & Overview
• Commonly used matrices:
Vinylester: fabrication for FRP reinforcing bars(superior durability characteristics when embedded in concrete)
Epoxy: strengthening using FRP sheets/plates(superior adhesion characteristics)
Internal reinforcing applications
External strengthening applications
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
Fibres
Introduction & Overview
• Fibres:
Provide strength and stiffness of FRPProtected against environmental degradation by the
polymer matrixOriented in specified directions to provide strength
along specific axes (FRP is weaker in the directions perpendicular to the fiber)
Selected to have:
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
Fibres
Introduction & Overview
• Three most common fibres in Civil Engineering applications:GlassCarbonAramid (not common in North America)
Required strength and stiffness Durability considerations Cost constraints Availability of materials
• Selected based on:
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
Fibres
Introduction & Overview
• Glass fibres:• Inexpensive
• Most commonly used in structural applications
• Several grades are available:• E-Glass• AR-Glass (alkali resistant)
• High strength, moderate modulus, medium density• Used in non weight/modulus critical applications
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
Fibres
Introduction & Overview
• Carbon fibres:
• Significantly higher cost than glass
• High strength, high modulus, low density• E = 250-300 GPa: standard• E = 300-350 GPa: intermediate• E = 350-550 GPa: high• E = 550-1000 GPa: ultra-high
• Superior durability and fatigue characteristics
• Used in weight/modulus critical applications
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
Fibres
Introduction & Overview
• Aramid fibres:
• Moderate to high cost• Two grades available: 60 GPa and 120 GPa elastic moduli
• High tensile strength, moderate modulus, low density
• Low compressive and shear strength
• Some durability concerns• Potential UV degradation• Potential moisture absorption and swelling
Mechanical PropertiesFRPComposites
For Construction
FRP mechanical properties are a function of:
Type of fibre and matrix
Fibre volume content
Orientation of fibres
Here we are concerned mainly with unidirectional FRPs!
Section: 1
ISIS EC Module 8
Strain [%]
1 2 3
500
1000
1500
2000
2500
Stre
ss [M
Pa]
FRP vs. SteelMechanical Properties
• FRP properties (in general versus steel):• Linear elastic behaviour
to failure• No yielding• Higher ultimate strength• Lower strain at failure• Comparable modulus
(carbon FRP)
Steel
CFRP
FRPComposites
For Construction
GFRP
Section: 1
ISIS EC Module 8
Quantitative ComparisonFRPComposites
For Construction
Typical Mechanical Properties*
Ultimate Strength
517-1207 MPa
1200-2410 MPa
1200-2068 MPa
483-690 MPa
Elastic Modulus
30-55 GPa
147-165 GPa
50-74 GPa
200 GPa
Material
Glass FRP
Carbon FRP
Aramid FRP
Steel
Failure Strain
2-4.5 %
1-1.5 %
2-2.6 %
>10 %
* Based on 2001 data for specific FRP rebar products
Section: 1
ISIS EC Module 8
Section: 1
• Physical, mechanical, durability properties of FRPs
ISIS EC Module 8
FRPComposites
For Construction
Overall properties and durability depend on:
• The properties of the specific polymer matrix• The fibre volume fraction
(i.e., volume of fibres per unit volume of matrix)• The fibre cross-sectional area• The orientation of the fibres within the matrix• The method of manufacturing• Curing and environmental exposure
FRP
Introduction & Overview
ISIS EC Module 8
Examples of FRP
Glass fibre roving
Carbon fibre roving
Unidirectional glass FRP bar
Carbon FRP prestressing
tendon
Glass FRP grid
FRPComposites
For Construction Section: 1Introduction & Overview
• In the design and use of FRP materialsThe orientation of the fibres within the matrix is a key
consideration
• Most important parameters for infrastructure FRPs: Uniaxial tensile properties
→ strength and elastic modulus
FRP-concrete bond characteristics→ transfer and carry the tensile loads
Durability
ISIS EC Module 8
FRPs
FRPComposites
For Construction Section: 1Introduction & Overview
Section: 1
• What is durability?
ISIS EC Module 8
FRPComposites
For Construction
The ability of an FRP material to:
“resist cracking, oxidation, chemical degradation, delamination, wear, and/or the effects of foreign object damage for a specified period of time, under the appropriate load conditions, under specified environmental conditions”
Introduction & Overview
Section: 1 CAUTION!
ISIS EC Module 8
FRPComposites
For Construction
Data on the durability of FRP materials is limitedAppears contradictory in some casesDue to many different forms of FRPs and fabrication processes
FRPs used in civil engineering applications are substantially different from those used in the aerospace industry Their durability cannot be assumed to be the same
Anecdotal evidence suggests that FRP materials can achieve outstanding longevity in infrastructure applications
Section: 1
• Environments
ISIS EC Module 8
FRPComposites
For Construction
Durability
All engineering materials are subject to mechanical and physical deterioration with time, load, and exposure to various harmful environments
FRP materials are very durable, and are less susceptible to degradation than many conventional construction materials
Introduction & Overview
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
• Factors affecting FRPs’ durability performance:
The matrix and fibre typesThe relative portions of the constituentsThe manufacturing processesThe installation proceduresThe short- and long-term loading and exposure
condition (physical and chemical)
Durability
Introduction & Overview
Section: 1
ISIS EC Module 8
FRPComposites
For Construction
• Potentially harmful effects for FRP:Durability
Introduction & Overview
Environmental Effects
Physical EffectsMoisture & Marine Environments
Alkalinity& Corrosion
Heat & Fire
Cold & Freeze-Thaw Cycling
Sustained Load:
Creep
Cyclic loading:
Fatigue
Ultraviolet Radiation
POTENTIAL SYNERGIES
DURABILITY
OF FRPs
Section: 2 Moisture & Marine Exposures
ISIS EC Module 8
FRPComposites
For Construction
• FRPs are particularly attractive for concrete structures in moist or marine environmentsFRPs are not susceptible to electrochemical corrosionCorrosion of steel in conventional structures results in severe
degradation
HOWEVER• FRPs are not immune to the potentially harmful
effects of moist or marine environments
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• Some FRP materials have been observed to deteriorate under prolonged exposure to moist environmentsEvidence linking the rate of degradation to the rate of sorption of fluid
into the polymer matrix
• All polymers will absorb moistureDepending on the chemistry of the specific polymer involved, can
cause reversible or irreversible physical, thermal, mechanical and/or chemical changes
• It is important to recognize that…Results from laboratory testing are not necessarily indicative of
performance in the field
Moisture & Marine ExposuresMoisture
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• Selected factors affecting moisture absorption in FRPs: Type and concentration of liquid Type of polymer and fibre Fibre-resin interface characteristics Manufacturing / application method Ambient temperature Applied stress level Extent of pre-existing damage Presence of protective coatings
Moisture & Marine ExposuresMoisture
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• Overall effects of moisture absorption:
Moisture & Marine Exposures
Moisture absorptionPlasticization of the matrix caused by interruption of Van der Walls bonding between polymer chains
• Reduced matrix strength, modulus, strain at failure & toughness• Subsequently reduced matrix-dominated properties: Bond,
shear, flexural strength & stiffness• May also affect longitudinal tensile strength & stiffness• Swelling of the matrix causes irreversible damage through
matrix cracking & fibre-matrix debonding
Moisture
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• Typical moisture absorption trend for a matrix polymer:
Moisture & Marine ExposuresMoisture
Time (years)
1 20
< 1%
% M
ass
Gai
n
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• Strength loss trend of typical FRPs due to moisture absorption:
Moisture & Marine ExposuresMoisture
5 100
100 %
% S
tre
ng
th R
ete
nti
on
Time (years)
Note: no strength reductions in some lab studies
Further research needed
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• Potentially Important degradation synergies:
Moisture & Marine Exposures
Moisture absorption Sustained stress Elevated temperatures
Stress-induced micro-cracking of the polymer matrix
Moisture-induced micro-cracking of polymer matrix in a GFRP
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• The effect of moisture on fibres’ performance:
Moisture & Marine Exposures
Glass fibres:Moisture penetration to the fibres may extract ions from the fibre and result in etching and pitting. can cause deterioration of tensile strength and elastic modulus
Aramid fibres:Can result in fibrillation, swelling of the fibres, and reductions in compressive, shear, and bond properties. Certain chemicals such as sodium hydroxide and hydrochloric acid can cause severe hydrolysis
Carbon fibres:Do not appear to be affected by exposure to moist environments
Fibres
Section: 2
ISIS EC Module 8
FRPComposites
For Construction
• FRPs can be protected against moisture absorption by appropriate selection of matrix materials and protective coatings:
Moisture & Marine Exposures
• Vinylester:currently considered the best for use in preventing moisture effects in infrastructure composites
• Epoxy:also considered adequate
• Polyester:Available research also suggests poor performance and should typically not be used
Resins
Section: 3
ISIS EC Module 8
FRPComposites
For Construction
• Effects of alkalinity on FRPs’ performance:
Alkalinity & Corrosion
The pH level inside concrete is > 11 (i.e., highly alkaline) Becomes important for internal FRP reinforcement
applications within concrete (particularly for GFRP)
pH > 11
GFRP bar
• Protection by matrix• Level of applied stress• Temperature
Damage to glass fibres depends on
Alkalinity
Section: 3
ISIS EC Module 8
FRPComposites
For Construction
• Degradation mechanisms for GFRP reinforcement:
Alkalinity & Corrosion
GFRP bar
Alkaline solutions
Alkaline solutions cause embrittlement of the fibres
• Reduction in tensile properties
• Damage at the fibre-resin interface
Alkalinity
Section: 3
ISIS EC Module 8
FRPComposites
For Construction
• The effect of alkaline environments on fibres:
AR-glass fibres• Significant improvement in alkaline environments, but $$$
Aramid fibres• Strength reduction of 10 – 50 % of initial values
Carbon fibres• Strength reduction of 0 – 20 % of initial values
Alkalinity
Alkalinity & Corrosion
E-glass fibres• Strength reduction of 0 – 75 % of initial values
Need further research
Section: 3
ISIS EC Module 8
FRPComposites
For Construction
• Galvanic Corrosion:Corrosion
Alkalinity & Corrosion
Galvanic corrosion = accelerated corrosion of a metal due to electrical contact with a nonmetallic conductor in a corrosive environment
FRPs are not susceptible to electrochemical corrosion• Certain FRPs (e.g., CFRPs) can contribute to increased
corrosion of metal components through galvanic corrosion
Section: 3
ISIS EC Module 8
FRPComposites
For Construction
CFRPs should not be permitted to come in to direct contact with steel or aluminum in structures
Corrosion
Alkalinity & Corrosion
• Guarding against galvanic corrosion:
Internal reinforcement: place plastic spacers between steel and CFRP bars
External strengthening:
apply a thin layer of epoxy or GFRP sheet between CFRP and steel
Steel bar CFRP barSpacer
Steel girder
GFRP sheet CFRP sheet
Section: 4
ISIS EC Module 8
FRPComposites
For Construction
• FRP materials are now widely used for reinforcement and rehabilitation of bridges and other outdoor structuresFRPs have seen comparatively little use in building applications
• FRP materials are susceptible to elevated temperaturesSeveral concerns associated with their behaviour during fire or in
high temperature service environments
• Extremely difficult to make generalizations regarding high temperature behaviour Large number of possible fibre-matrix combinations, manufacturing
methods, and applications
High Temperatures & Fire
Section: 4
ISIS EC Module 8
FRPComposites
For Construction
• FRPs used in infrastructure applications suffer degradation of mechanical and/or bond properties at temperatures exceeding their glass transition temperature
High Temperatures & Fire
Glass transition temperature, Tg
the midpoint of the temperature range over which an amorphous material (such as glass or a high polymer) changes from (or to) brittle, vitreous state to (or from) a rubbery state (ACI 440 2006)
• All organic polymer materials combust at high temperatures• Most matrix polymers release large quantities of dense, black,
toxic smoke
Section: 4
ISIS EC Module 8
FRPComposites
For Construction
• Potential problems of FRPs under fire:
High Temperatures & Fire
Internal FRP reinforcement
Sudden and severe loss of bond at T > Tg
External FRP strengthening
Too thin for self-insulating layer, loss of bond at T > Tg
Section: 4
ISIS EC Module 8
FRPComposites
For Construction
• Mechanical properties of FRPs deteriorate with increasing temperature• “Critical” temperature commonly taken to be Tg for the polymer matrix• Typically in the range of 65-120ºC• Exceeding Tg results in severe degradation of matrix dominated
properties such as transverse and shear strength and stiffness• Longitudinal properties also affected above Tg
• Tensile strength reductions as high as 80% can be expected in the fibre direction at temperatures of only 300ºC
Important that an FRP component not be exposed to temperatures close to or above Tg during the normal range
of operating temperatures
High Temperatures & Fire
Section: 4
ISIS EC Module 8
FRPComposites
For Construction
• Degradation of mechanical properties is mainly governed by the properties of the matrix:
• Carbon fibres
High Temperatures & Fire
No degradation in strength and stiffness up to 1000 ºC
• Glass fibres20-60% reduction in strength at 600 ºC
• Aramid fibres20-60% reduction in strength at 300 ºC
Section: 4
ISIS EC Module 8
FRPComposites
For Construction
• Deterioration of mechanical and bond properties for GFRP bars:
High Temperatures & Fire
0
20
40
60
80
100
0 100 200 300 400 500 600
Temperature (deg. C)
% o
f R
oo
m T
em
pe
ratu
re V
alu
e
Elastic Modulus
Tensile Strength
Ave. Bond Strength
Critical temperature (T > Tg)
Section: 4
ISIS EC Module 8
FRPComposites
For Construction
• The use of FRP internal reinforcement is currently not recommended for structures in which fire resistance is essential to maintain structural integrity
• Exposure to elevated temperatures for a prolonged period of time may be a concern with respect to exacerbation of moisture absorption and alkalinity effects
High Temperatures & Fire
Section: 5
ISIS EC Module 8
FRPComposites
For Construction
• Potential for damage due to low temperatures and thermal cycling must be considered in outdoor applications
• Freezing and freeze-thaw cycling may affect the durability performance of FRP components through:1. Changes that occur in the behaviour of the component materials at
low temperatures2. Differential thermal expansion
• between the polymer matrix and fibre components • between concrete and FRP materials
Could result in damage to the FRP or to the interface between FRP components & other materials
Cold Temperatures
Section: 5
ISIS EC Module 8
FRPComposites
For Construction
• Exposure to subzero temperature may result in residual stresses in FRPs due to matrix stiffening and different CTEs between fibres and matrix
Cold Temperatures
Matrix micro-cracking and fibre-matrix bond degradation
May affect FRPs’
• Stiffness• Strength• Dimensional stability• Fatigue resistance• Moisture absorption• Resistance to alkalinity
Section: 5
ISIS EC Module 8
FRPComposites
For Construction
• Increasing # of freeze/thaw cycles
Cold Temperatures
The effects on FRP properties appear to be minor in most infrastructure
applications
HOWEVER
• Increased severity of matrix cracks
• Increased matrix brittleness• Decreased tensile strength
Section: 6
ISIS EC Module 8
FRPComposites
For Construction
• Ultraviolet (UV) radiation damages most polymer matrices
Ultraviolet Radiation
• Thus, potential for UV degradation is important when FRPs are exposed to direct sunlight
• The effects of UV on:• Aramid fibres: significant• Glass fibres: insignificant• Carbon fibres: insignificant
Section: 6
ISIS EC Module 8
FRPComposites
For Construction
• Photodegradation: UV radiation within a certain range of specific wavelengths breaks chemical bonds between polymer chains and resulting in:
Ultraviolet Radiation
• UV-induced surface flaws can cause: Stress concentrations → may lead to premature failure
Increased susceptibility to damage from alkalinity & moisture
Discoloration Surface oxidation Embrittlement Microcracking of the matrix
Section: 6
ISIS EC Module 8
FRPComposites
For Construction
• Combined effects of UV and moisture on FRP bars:
Ultraviolet Radiation
• Protection of FRPs from UV radiation: UV resistant paints
Coatings
Sacrificial surfaces
UV resistant polymer resins
CFRP: tensile strength reduction of 0-20 % GFRP: tensile strength reduction of 0-40 % AFRP: tensile strength reduction of 0-30 %
Section: 7
ISIS EC Module 8
FRPComposites
For Construction
• Creep: A behaviour of materials wherein an increase in strain is observed with time under a constant level of stress (L = final length)
Creep & Creep Rupture
ideal
PP Steel
P = P
L = L1
L1
with creep
PP Steel
P = P
L > L1
L1
Section: 7
ISIS EC Module 8
FRPComposites
For Construction
• Relaxation: a reduction in stress in a material with time at a constant level of strain (P = final load)
Creep & Creep Rupture
ideal
Steel
P = P
L = L1
L1
with relaxation
Steel
P > P1
L = L1
L1
P P P P1 1
Section: 7
ISIS EC Module 8
FRPComposites
For Construction
• Effects of creep on the performance of FRPs:
Fibres → relatively insensitive to creep in absence of other harmful durability factors
Matrices → highly sensitive to creep
Thus, creep is potentially important for FRP
(Because loads must be transferred through the matrix)
Creep & Creep RuptureCreep
Section: 7
ISIS EC Module 8
FRPComposites
For Construction
• For good performance under sustained loads:Use an appropriate matrix materialTake care during the fabrication and curing processes
• Creep behaviour of different FRP materials is complex and depends on: Specific constituents and fabricationType, direction, and level of loading appliedExposure to other durability factors such as alkalinity, moisture,
thermal exposures
• Few standard test methods for creep testing FRP materialsDifficult to make generalizations about FRPs’ creep performance
Creep & Creep RuptureCreep
Section: 7
ISIS EC Module 8
FRPComposites
For Construction
• Under certain conditions… creep can result in rupture of FRPs at sustained load levels that are significantly less than ultimate
• Creep rupture is influenced largely by the types of fibres and susceptibility to alkaline environments (glass FRPs in particular)
Creep & Creep Rupture
Called Stress Rupture, Creep Rupture, or Stress Corrosion
Creep Rupture
Section: 7
ISIS EC Module 8
FRPComposites
For Construction
• Endurance time: the time to creep rupture of FRPs under a given level of sustained load
Creep & Creep Rupture
Sustained stress
Ultimate strengthEndurance time
• Other factors influencing endurance time include:• Elevated temperature• Alkalinity• Moisture• Freeze-thaw cycling• UV exposure
Endurance time
Section: 7
ISIS EC Module 8
FRPComposites
For Construction
• Creep rupture stress limits for FRP reinforcing bars (50 years creep rupture strength) :
Creep & Creep Rupture
GFRP: 29-55 % of initial tensile strengthAFRP: 47-66 % of initial tensile strengthCFRP: 79-93 % of initial tensile strength
Note: Laboratory testing is not necessarily representative of field performance
Section: 8
ISIS EC Module 8
FRPComposites
For Construction
• Fatigue: all structures are subjected to repeated cycles of loading and unloading due to:
Fatigue
Traffic and other moving loads Thermal effects (differential thermal expansion) Wind-induced or mechanical vibrations
• Fatigue performance of most FRPs is as good as or better than steel
Section: 8
ISIS EC Module 8
FRPComposites
For Construction
• Good fatigue performance of FRPs depends on:
Toughness of the matrixAbility to resist cracking
CFRP: bestGFRP: goodAFRP: excellent
• Performance of FRPs under fatigue load:
Fatigue
• NOTE: Fatigue performance of FRP reinforced concrete appears to be best when GFRP reinforcement is used
Section: 9
ISIS EC Module 8
FRPComposites
For Construction
• Numerous factors exist that can potentially affect the long term durability of FRP materials in civil engineering and construction applications
• Durability factors remain incompletely understood
• Reduction factors in existing design codes and recommendations:Applied to the nominal stress and strain capacities of FRPslimit the useable ranges of stress and strain in engineering
design
Reduction Factors
Section: 9
ISIS EC Module 8
FRPComposites
For Construction
• For non-prestressed FRPs
Reduction Factors (FRP bars)
0.70Exposed to earth and weather
0.80Not exposed to earth and weatherGFRP
0.90Exposed to earth and weather
1.00Not exposed to earth and weatherCFRP
0.80Exposed to earth and weather
0.90Not exposed to earth and weatherAFRP
ACI 440.1R-06
0.75AllAllCSA S806-02
0.50AllGFRP
0.75AllCFRP
0.60AllAFRP
CHBDC, 2006
Reduction Factor
Exposure ConditionMaterialDocument
Section: 9
ISIS EC Module 8
FRPComposites
For Construction
• Sustained (service) stress levels are limited to avoid creep rupture and other forms of distress:
Reduction Factors
20GFRP
55CFRP
30AFRP
ACI 440.1R-06
30GFRPCSA S806-02
25GFRP
65CFRP
35AFRP
CHBDC, 2006
Stress limit (% of ultimate)
FRP BarsDocument
Section: 10
ISIS EC Module 8
FRPComposites
For Construction
• ISIS Canada has recently published a product certification document:Specifications for Product Certification of Fibre
Reinforced Polymers (2006)• Test methods are given for quantitatively defining the
durability of FRP reinforcing bars for concrete• Classifies FRP bars into different durability
“categories” (e.g. D1, D2, etc.)
Specifications: Durability of FRP Bars
Section: 10
ISIS EC Module 8
FRPComposites
For ConstructionSpecifications: Durability Criteria
Property Specified limits
Void content ≤ 1%
Water absorption ≤ 1% for D2 FRP bars and grids; ≤ 0.75% for D1 bars and grids
Cure ratio ≥ 95% for D2 bars and grids; ≥ 98% for D1 bars and grids
Glass transition temperature
DMA = 90°C, DSC = 80°C for D2 bars and grids; DMA = 110°C, DSC = 100°C for D1 bars and grids
Alkali resistance in high pH solution (no load)
Tensile capacity retention ≥70% for D2 bars and grids; tensile capacity retention ≥80% for D1 bars and grids
Alkali resistance in high pH solution (with load)
Tensile capacity retention ≥60% for D2 bars and grids; tensile capacity retention ≥70% for D1 bars and grids
Creep rupture strength Creep rupture strength:≥35% UTS (Glass)≥75% UTS (Carbon)≥45% UTS (Aramid)
Creep Report creep strain values at 1000 hr, 3000 hr and 10000 hr
Fatigue strength Fatigue strength at 2 million cycles:≥35% UTS (Glass)≥75% UTS (Carbon)≥45% UTS (Aramid)
Section: 11
ISIS EC Module 8
FRPComposites
For Construction
• Laboratory experiments have suggested that FRPs may be susceptible to deterioration under many environmental conditions Field data are scant for FRPs used in
infrastructure applications
• Available field data indicate that in-service performance can be much better than assumed on the basis of laboratory testing
Case Study: Field Evaluation of GFRP
ISIS EC Module 8
FRPComposites
For Construction
• ISIS Canada Research project to study in-service performance of glass FRP reinforcing bars in concrete structures in Canada:• Joffre Bridge (Sherbrooke, Quebec)• Crowchild Bridge (Calgary, Alberta)• Hall’s Harbour Wharf (Hall’s Harbour, Nova Scotia)• Waterloo Creek Bridge (British Columbia)• Chatham Bridge (Ontario)
• Samples studied for evidence of deterioration using various optical and chemical techniques
Case Study: Field Evaluation of GFRPSection: 11
ISIS EC Module 8
FRPComposites
For Construction
• There are many methods to investigate durability performance of GFRP reinforcing bars:
Case Study: Field Evaluation of GFRP
Optical Microscopy (OM) Scanning Electron Microscopy (SEM) Energy Dispersive X-ray Analysis (EDX) Infrared Spectroscopy (IS) Differential Scanning Calorimetry (DSC)
Section: 11
ISIS EC Module 8
FRPComposites
For Construction
• Optical Microscopy (OM):
Field Evaluation of GFRPCase study
To visually examine the interface between the GFRP reinforcing bars and the concrete
Interface
Crowchild Trail Bridge
Interface
Chatham Bridge
After 8 years of exposure to alkalinity, freeze-thaw, wet-dry, and chlorides
No evidence of damage or deterioration
Section: 11
ISIS EC Module 8
FRPComposites
For Construction
• Scanning Electron Microscopy (SEM):
Field Evaluation of GFRPCase study
To conduct highly detailed visual examination of GFRP
Crowchild Trail Bridge Chatham Bridge
After 8 years of exposure to alkalinity, freeze-thaw, wet-dry, and chlorides
No evidence of damage or deterioration
Section: 11
ISIS EC Module 8
FRPComposites
For Construction
• Energy Dispersive X-ray Analysis (EDX):
Field Evaluation of GFRPCase study
To determine if any chemical changes had occurred in glass fibres or in polymer matrix
After 8 years of exposure to alkalinity, freeze-thaw, wet-dry, and chlorides
No Sodium or Potassium are present
Section: 11
ISIS EC Module 8
FRPComposites
For Construction
• Other techniques…
Field Evaluation of GFRPCase study
• Infrared Spectroscopy (IS): to determine the extent of alkali-induced
hydrolysis of the matrix No evidence of damage or deterioration
• Differential Scanning Calorimetry (DSC): to determine the glass transition temperature of a
polymer material No evidence of damage or deterioration
Section: 11
Durability Research Needs
ISIS EC Module 8
FRPDesign with
reinforcement
• The durability performance of FRP materials is generally very good in comparison with other, more conventional, construction materials
• However, it should be equally clear that the long-term durability of FRPs remains incompletely understood
• A large research effort is thus required to fill all of the gaps in knowledge
Durability Research Needs
ISIS EC Module 8
FRPDesign with
reinforcement
• Moisture:Effects of under-cure and/or incomplete cure of the polymer matrixEffects of continuous versus intermittent exposure to moisture when
bonded to concrete
• Alkalinity:Determination of rational and defensible standard alkaline solutions
and alkalinity testing protocols and database of durability informationDevelopment of an understanding of alkali-induced deterioration
mechanismsThe potential synergistic effects of combined alkalinity, stress,
moisture, and temperature are not well understood, particularly as they relate to creep-rupture of FRP components.
Durability Research Needs
ISIS EC Module 8
FRPDesign with
reinforcement
• Fire:Non-destructive evaluation methods for fire-exposed compositesFire repair strategiesDevelopment of relationships between tests on small scale material
samples at high temperature and full-scale structural performance during fire
• Fatigue:More fatigue data on a variety of FRP materialsMechanistic understanding of fatigue in composites in conjunction
with various environmental factorsDevelopment of a rational and defensible short term representative
exposure to evaluate long-term fatigue performance
Durability Research Needs
ISIS EC Module 8
FRPDesign with
reinforcement
• Synergies:Potentially important synergies between most of the
durability factors considered in this module remain incompletely understood
Research needed to elucidate the interrelationships between moisture, alkalinity, temperature, stress, and chemical exposures
Additional Information
ISIS EC Module 8
FRPDesign with
reinforcement
Additional information on all of the topics discussed in this module is available from:
www.isiscanada.com