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7252019 Strengthening of Concrete Structures Using FRP Composites
httpslidepdfcomreaderfullstrengthening-of-concrete-structures-using-frp-composites 13 June 201518
updates and informationon structural materials
BUILDING BLOCKS
Tarek Alkhrdaji PhD PE isVice President of Engineeringwith Structural Technologies Dr
Alkhrdaji is an active member of ACI Committee 437 (StrengtheningEvaluation) and ACI 562 (RepairCode) and he is the past Chair ACI440F (FRP Strengthening) He isalso a member of American Society
of Civil Engineers (ASCE) andthe International Concrete RepairInstitute (ICRI) He can be reachedat talkhrdajistructuralteccom
By Tarek Alkhrdaji PhD PE
Strengthening of ConcreteStructures Using FRPComposites
Fiber-reinforced polymer (FRP) com-posites have been used for structuralstrengthening in the United States foralmost 25 years During this period
acceptance of FRP composites as a mainstreamconstruction material has grown and so has thenumber of completed FRP strengthening projects
As a result the use of FRP for strengthening andretrofit is gaining more popularity among design
professionals over conventional strengtheningtechniques such as installation of supplementalstructural steel frames and elementsFRP strengthening of existing structures can
involve complex evaluation design and detail-ing processes requiring a good understandingof the existing structural conditions along withthe materials used to repair the structure priorto FRP installation Te suitability of FRP fora strengthening project can be determined byunderstanding what FRP is and the advantagesit offers but more importantly its limitations
What is FRPReinforcement
FRP composite materi-als are comprised of highstrength continuous fiberssuch as glass carbon orsteel wires embedded in
a polymer matrix Te fibers provide the mainreinforcing elements while the polymer matrix(epoxy resins) acts as a binder protects the fibersand transfers loads to and between the fibersFRP composites can be manufactured on site
using the wet lay-up process in which a dry fabricmade of carbon or glass is impregnated withepoxy and bonded to prepared concrete substrateOnce cured the FRP becomes an integral partof the structural element acting as an externallybonded reinforcing system FRP composites canalso be prefabricated in a manufacturing facilityin which the material is pultruded to create dif-ferent shapes that can be used for strengtheningapplications such as rods bars and platesTe most common FRP systems for concrete
strengthening applications are carbon fiber based(CFRP) Carbon has superior mechanical prop-
erties and higher tensile strength stiffness anddurability compared with glass fiber based sys-tems Te use of prefabricated CFRP bars andplates is typically limited to straight or slightlycurved surfaces for example the top side orunderside of slabs and beams Prefabricated FRPelements are typically stiff and cannot be bent onsite to wrap around columns or beamsFRP fabric on the other hand is available in
continuous unidirectional sheets supplied on rollsthat can be easily tailored to fit any geometry andcan be wrapped around almost any profile FRPfabrics may be adhered to the tension side of
structural members (eg slabs or beams) to pro-vide additional tension reinforcement to increaseflexural strength wrapped around the webs of
joists and beams to increase their shear strengthand wrapped around columns to increase theirshear and axial strength and improve ductility
and energy dissipation behaviorTe adhesive systems used to bond FRP to theconcrete substrate may include a primer thatis used penetrate the concrete substrate andimprove bond of the system epoxy putty to fillsmall surface voids in the substrate and providea smooth surface to which the FRP system isbonded saturating resin used to impregnate thefabric and bond it to the prepared substrate andprotective coating to safeguard the bonded FRPsystem from potentially damaging environmentaland mechanical effects Most epoxies for FRPstrengthening systems are adversely affected by
exposure to ultraviolet light but can be protectedusing acrylic coatings cementitious coatings andother types of coatingsTe resins and fiber for a FRP system are usually
developed as one system based on materials andstructural testing Mixing or replacing a compo-nent of one FRP system with a component fromanother system is not acceptable and can adverselyaffect the properties of the cured systemTe bond between FRP system and the exist-
ing concrete is critical and surface preparation
FRP fabric is easily tailored to fit any geometryincluding lsquoUrsquo wrapping around beams
Wrapping FRP fabrics around columns increases theshear and axial strength to improve ductility andenergy dissipation behavior
7252019 Strengthening of Concrete Structures Using FRP Composites
httpslidepdfcomreaderfullstrengthening-of-concrete-structures-using-frp-composites 23STRUCTURE magazine June 201519
is essential to most applications Any exist-ing deterioration or corrosion of internalreinforcement must be resolved prior toinstallation of the FRP system Failure to doso can result in damage to the FRP systemdue to delamination of the concrete substrate
Differences between
FRP and Steel
FRP composites are different from steel in thatthey possess properties that can vary in differ-ent directions (anisotropic) whereas steel hassimilar properties in all directions (isotropic)Te most common type of fiber sheets for con-crete strengthening application are constructed with continuous unidirectional carbon or glassfiber that runs the length of the fabric Whenloaded in direct tension unidirectional FRPmaterials exhibit a linear-elastic stress-strainrelationship until failure with no yieldingor plastic behavior Due to the linear-elastic
characteristics of FRP and the fact they areapplied externally to structural elements thestandard methods used to design or determinethe amount of steel reinforcement do not applyto FRP Relatively more complex proceduresare used to design FRP which can involveiterative design methodologyBecause the fiber in an FRP material is the
main load-carrying component the type offiber orientation of fiber and thickness of thefabric (quantity of fibers) dictate the tensilestrength and stiffnessFRP composites vary in strength depending
on the type of fiber used While glass providesa tensile strength nearly equal to mild steelyield strength carbon composites provide atensile strength that vary from twice to fivetimes the yield strength of mild steel Whileboth FRP composites have tensile stiffnesslower than that of steel carbon compositestiffness is twice to five times the stiffnessof glass composites FRP composites haveapproximately one fifth the weight of steelTe tensile properties of FRP strengthen-
ing systems can be obtained from the FRPsystem manufacturer Te tensile propertiescan also be determined using the test methoddescribed in ASM D7565
o account for material durability mostavailable design guides identify environmen-tal reduction factors for the tensile strengthof the FRP that can be used in design Tesefactors depend on the type of FRP and theexposure conditions for the element to bestrengthened For CFRP the typical environ-
mental reduction factor for interior exposureconditions is 095 while the reduction factorfor exterior and aggressive exposure condi-tions is typically 085
FRP Application
FRP systems provide a very practical tool forstrengthening and retrofit of concrete struc-tures and are appropriate for
bull Flexural strengtheningbull Shear strengthening andbull Column confinement and ductility
improvementFRP systems have also been successfully usedfor seismic upgrading of concrete structuresTese applications include mitigating brittlefailure mechanisms such as shear failure ofunconfined beam-column joints shear fail-ure of beams andor columns and lap splicefailure FRP systems have also been to confinecolumns to resist buckling of longitudinalsteel bars Tese FRP schemes increase theglobal displacement and energy dissipationcapacities of the concrete structure andimprove its overall behaviorBecause of the resistance to corrosion FRP
composites can be utilized on interior and
exterior structural members in all almost alltypes of environments
Codes and Standards
Tere are several guides and codes published worldwide that address the design of exter-
nally bonded FRP reinforcement systems forconcrete structures In the United States ACICommittee 440 has published ACI 4402RGuide for the Design and Construction ofExternally Bonded FRP Systems for StrengtheningConcrete Structures However this documentis not considered a code and is not refer-enced in any code documents including theInternational Building Code (IBC) and theInternational Existing Building Code (IEBC)Understanding the need for a repair code the
American Concrete Institute (ACI) publishedin 2013 Code Requirements for Evaluation
Repair and Rehabilitation of Concrete Buildings(ACI 562) which is the first performance-based standard developed for the repair ofexisting concrete buildings Tis standard
works with the IEBC where adopted or as astand-alone document for jurisdictions thathave not adopted an existing building codeTe provisions in ACI 562 are not new
to design professionals and include manyof the same requirements as for the tradi-tional design of concrete structures ACI 562directs design professionals to consider thebehavior of the structure at all times duringthe repair process and after the repair is com-pleted ACI 562 permits the use of FRPmaterials for concrete repair and strength-ening and refers to ACI 440 standards fordesign and detailing requirements
FRP Strengthening Limits
Minimum Existing Strength Limit
Per ACI 4402R in order for structural ele-ment to qualify for FRP strengthening theexisting structural member must maintain a
Additional tension reinforcement increases the flexural strength of slabs when FRP is adhered to the tension side
7252019 Strengthening of Concrete Structures Using FRP Composites
httpslidepdfcomreaderfullstrengthening-of-concrete-structures-using-frp-composites 33STRUCTURE magazine June 201520
certain minimum strength Tis requirementis intended to guarantee that the ultimatecapacity of the structural member without theFRP reinforcement is greater than a designforce corresponding to the expected serviceloads under typical situationsTe minimum strength requirement in ACI
4402R isEquation 1 983142Rn = 11DL + 075LL983142Rn = design strength of the existing
member without FRPDL = new design dead loadLL = new design live load
Tis limit stipulates that externally bondedFRP reinforcement should be consideredas secondary reinforcement and used tosupplement the existing interior steel rein-forcement Should the FRP reinforcement becompromised the structure must maintainsufficient capacity to carry existing service
loads without collapseSince FRP composites are designed to lastfor the service life of the structure the impactof possible future renovations and modifica-tions should be considered where the FRP isaccidentally damaged Such damage may notbe observed immediately and the structure orstructural component may remain in serviceuntil the damage is identified and the affectedareas are repaired Equation 1 is intended toaddress these situationsTe limit of Equation 1 is intended to mini-
mize the possibility of collapse due to FRPfailure or damage In cases where the designlive load has a high likelihood of being presentfor a sustained period of time (such as storageareas) a live load factor of 10 should be usedinstead of 075Tis limit is independent from fire rating
requirements It must be satisfied even iffire protection is applied to the FRP systemTe limit is applicable to all types of strengthincrease such as shear flexure and axial strength-ening but it does not apply to extreme loadingevents (seismic events blast loading or otherloads classified by ASCE 7 as extreme events)
Depending on dead load to live load ratiothe strength increase using FRP that satisfiesEquation 1 typically results in up to 40increase in strength If the strength increaseis higher than 40 other conventionalstrengthening options should be considered
Concrete Strength Limit
Te existing concrete substrate strength is animportant parameter for bond-critical appli-cations such as flexure or shear strengtheningFor FRP to develop and transfer the designstresses at the bond line the concrete substrateshould possess sufficient strength to transferthese stresses And in order for the concreteto provide the minimum bond strength of200 psi (14 MPa) specified by ACI 4402Rthe compressive strength of concrete f c mustbe more than 2500 psi (17 MPa) Tis limitdoes not apply for contact-critical applications
like FRP column confinement which reliessolely on contact between the FRP systemand the concrete
Fire Rating and Protection
While carbon fibers are capable of resist-ing high temperatures adhesive systemshave a much lower threshold temperatureFireproofing of the FRP is an option but thehigh costs for specialized fireproofing materialarenrsquot always justifiableTe fire rating of strengthened structures
should be evaluated without FRP A deter-mination needs to be made as to whether
or not the reduced strength is sufficient ifthe FRP fails If it is there is no need infireproofing the FRP If it is not fireproof-ing materials should be evaluated for costefficiency and the ability to meet satisfac-tory fire ratings
Installation
Procedures for installing FRP systems havebeen developed by the system manufactur-ers and may differ slightly emperature andsurface moisture of concrete at the time ofinstallation are the main parameters that affectthe installation procedure and performanceof FRP systemsSurface preparation to create a bond
between the FRP system and the existingconcrete is critical Any existing deteriora-tion and corrosion of internal reinforcingmust also be resolved prior to installationof the FRP system Strengthening can only
be applied after all corrosion problems havebeen determined and resolved following theappropriate procedures Failure to do so canresult in locking in contaminants whichmay cause further deterioration and result infailure of the FRP system due to delamina-tion of the concrete substrateTe International Concrete Repair Institute
provides several guidelines for selection sur-face preparation and installation of repairmaterials Once installed the curing of theFRP system depends on the time after installa-tion and temperature during curing Similarly
temperature extremes or fluctuations canretard or accelerate FRP curing time Tehigher the temperature the faster the system
will cure ndash anywhere from one to three daysSeveral grades of resin are generally availablethrough the system manufacturer to accom-modate special situations
Conclusion
FRP systems have been successfully used tostrengthen buildings bridges silos tanks tun-nels and underground pipes Te higher costof FRP materials is offset by reduced costs oflabor use of equipment and downtime duringinstallation making them more cost-effectivethan traditional strengthening techniques While strengthening with FRP caninvolve complex processes this systemoffers a number of advantages comparedto conventional strengthening methodsUnderstanding the properties and limita-tions of FRP is important step in developingthe right design solution and utilizing it forthe right application
CFRP reinforcement on parking garage beams
Installation of CFRP on an industrial silo
7252019 Strengthening of Concrete Structures Using FRP Composites
httpslidepdfcomreaderfullstrengthening-of-concrete-structures-using-frp-composites 23STRUCTURE magazine June 201519
is essential to most applications Any exist-ing deterioration or corrosion of internalreinforcement must be resolved prior toinstallation of the FRP system Failure to doso can result in damage to the FRP systemdue to delamination of the concrete substrate
Differences between
FRP and Steel
FRP composites are different from steel in thatthey possess properties that can vary in differ-ent directions (anisotropic) whereas steel hassimilar properties in all directions (isotropic)Te most common type of fiber sheets for con-crete strengthening application are constructed with continuous unidirectional carbon or glassfiber that runs the length of the fabric Whenloaded in direct tension unidirectional FRPmaterials exhibit a linear-elastic stress-strainrelationship until failure with no yieldingor plastic behavior Due to the linear-elastic
characteristics of FRP and the fact they areapplied externally to structural elements thestandard methods used to design or determinethe amount of steel reinforcement do not applyto FRP Relatively more complex proceduresare used to design FRP which can involveiterative design methodologyBecause the fiber in an FRP material is the
main load-carrying component the type offiber orientation of fiber and thickness of thefabric (quantity of fibers) dictate the tensilestrength and stiffnessFRP composites vary in strength depending
on the type of fiber used While glass providesa tensile strength nearly equal to mild steelyield strength carbon composites provide atensile strength that vary from twice to fivetimes the yield strength of mild steel Whileboth FRP composites have tensile stiffnesslower than that of steel carbon compositestiffness is twice to five times the stiffnessof glass composites FRP composites haveapproximately one fifth the weight of steelTe tensile properties of FRP strengthen-
ing systems can be obtained from the FRPsystem manufacturer Te tensile propertiescan also be determined using the test methoddescribed in ASM D7565
o account for material durability mostavailable design guides identify environmen-tal reduction factors for the tensile strengthof the FRP that can be used in design Tesefactors depend on the type of FRP and theexposure conditions for the element to bestrengthened For CFRP the typical environ-
mental reduction factor for interior exposureconditions is 095 while the reduction factorfor exterior and aggressive exposure condi-tions is typically 085
FRP Application
FRP systems provide a very practical tool forstrengthening and retrofit of concrete struc-tures and are appropriate for
bull Flexural strengtheningbull Shear strengthening andbull Column confinement and ductility
improvementFRP systems have also been successfully usedfor seismic upgrading of concrete structuresTese applications include mitigating brittlefailure mechanisms such as shear failure ofunconfined beam-column joints shear fail-ure of beams andor columns and lap splicefailure FRP systems have also been to confinecolumns to resist buckling of longitudinalsteel bars Tese FRP schemes increase theglobal displacement and energy dissipationcapacities of the concrete structure andimprove its overall behaviorBecause of the resistance to corrosion FRP
composites can be utilized on interior and
exterior structural members in all almost alltypes of environments
Codes and Standards
Tere are several guides and codes published worldwide that address the design of exter-
nally bonded FRP reinforcement systems forconcrete structures In the United States ACICommittee 440 has published ACI 4402RGuide for the Design and Construction ofExternally Bonded FRP Systems for StrengtheningConcrete Structures However this documentis not considered a code and is not refer-enced in any code documents including theInternational Building Code (IBC) and theInternational Existing Building Code (IEBC)Understanding the need for a repair code the
American Concrete Institute (ACI) publishedin 2013 Code Requirements for Evaluation
Repair and Rehabilitation of Concrete Buildings(ACI 562) which is the first performance-based standard developed for the repair ofexisting concrete buildings Tis standard
works with the IEBC where adopted or as astand-alone document for jurisdictions thathave not adopted an existing building codeTe provisions in ACI 562 are not new
to design professionals and include manyof the same requirements as for the tradi-tional design of concrete structures ACI 562directs design professionals to consider thebehavior of the structure at all times duringthe repair process and after the repair is com-pleted ACI 562 permits the use of FRPmaterials for concrete repair and strength-ening and refers to ACI 440 standards fordesign and detailing requirements
FRP Strengthening Limits
Minimum Existing Strength Limit
Per ACI 4402R in order for structural ele-ment to qualify for FRP strengthening theexisting structural member must maintain a
Additional tension reinforcement increases the flexural strength of slabs when FRP is adhered to the tension side
7252019 Strengthening of Concrete Structures Using FRP Composites
httpslidepdfcomreaderfullstrengthening-of-concrete-structures-using-frp-composites 33STRUCTURE magazine June 201520
certain minimum strength Tis requirementis intended to guarantee that the ultimatecapacity of the structural member without theFRP reinforcement is greater than a designforce corresponding to the expected serviceloads under typical situationsTe minimum strength requirement in ACI
4402R isEquation 1 983142Rn = 11DL + 075LL983142Rn = design strength of the existing
member without FRPDL = new design dead loadLL = new design live load
Tis limit stipulates that externally bondedFRP reinforcement should be consideredas secondary reinforcement and used tosupplement the existing interior steel rein-forcement Should the FRP reinforcement becompromised the structure must maintainsufficient capacity to carry existing service
loads without collapseSince FRP composites are designed to lastfor the service life of the structure the impactof possible future renovations and modifica-tions should be considered where the FRP isaccidentally damaged Such damage may notbe observed immediately and the structure orstructural component may remain in serviceuntil the damage is identified and the affectedareas are repaired Equation 1 is intended toaddress these situationsTe limit of Equation 1 is intended to mini-
mize the possibility of collapse due to FRPfailure or damage In cases where the designlive load has a high likelihood of being presentfor a sustained period of time (such as storageareas) a live load factor of 10 should be usedinstead of 075Tis limit is independent from fire rating
requirements It must be satisfied even iffire protection is applied to the FRP systemTe limit is applicable to all types of strengthincrease such as shear flexure and axial strength-ening but it does not apply to extreme loadingevents (seismic events blast loading or otherloads classified by ASCE 7 as extreme events)
Depending on dead load to live load ratiothe strength increase using FRP that satisfiesEquation 1 typically results in up to 40increase in strength If the strength increaseis higher than 40 other conventionalstrengthening options should be considered
Concrete Strength Limit
Te existing concrete substrate strength is animportant parameter for bond-critical appli-cations such as flexure or shear strengtheningFor FRP to develop and transfer the designstresses at the bond line the concrete substrateshould possess sufficient strength to transferthese stresses And in order for the concreteto provide the minimum bond strength of200 psi (14 MPa) specified by ACI 4402Rthe compressive strength of concrete f c mustbe more than 2500 psi (17 MPa) Tis limitdoes not apply for contact-critical applications
like FRP column confinement which reliessolely on contact between the FRP systemand the concrete
Fire Rating and Protection
While carbon fibers are capable of resist-ing high temperatures adhesive systemshave a much lower threshold temperatureFireproofing of the FRP is an option but thehigh costs for specialized fireproofing materialarenrsquot always justifiableTe fire rating of strengthened structures
should be evaluated without FRP A deter-mination needs to be made as to whether
or not the reduced strength is sufficient ifthe FRP fails If it is there is no need infireproofing the FRP If it is not fireproof-ing materials should be evaluated for costefficiency and the ability to meet satisfac-tory fire ratings
Installation
Procedures for installing FRP systems havebeen developed by the system manufactur-ers and may differ slightly emperature andsurface moisture of concrete at the time ofinstallation are the main parameters that affectthe installation procedure and performanceof FRP systemsSurface preparation to create a bond
between the FRP system and the existingconcrete is critical Any existing deteriora-tion and corrosion of internal reinforcingmust also be resolved prior to installationof the FRP system Strengthening can only
be applied after all corrosion problems havebeen determined and resolved following theappropriate procedures Failure to do so canresult in locking in contaminants whichmay cause further deterioration and result infailure of the FRP system due to delamina-tion of the concrete substrateTe International Concrete Repair Institute
provides several guidelines for selection sur-face preparation and installation of repairmaterials Once installed the curing of theFRP system depends on the time after installa-tion and temperature during curing Similarly
temperature extremes or fluctuations canretard or accelerate FRP curing time Tehigher the temperature the faster the system
will cure ndash anywhere from one to three daysSeveral grades of resin are generally availablethrough the system manufacturer to accom-modate special situations
Conclusion
FRP systems have been successfully used tostrengthen buildings bridges silos tanks tun-nels and underground pipes Te higher costof FRP materials is offset by reduced costs oflabor use of equipment and downtime duringinstallation making them more cost-effectivethan traditional strengthening techniques While strengthening with FRP caninvolve complex processes this systemoffers a number of advantages comparedto conventional strengthening methodsUnderstanding the properties and limita-tions of FRP is important step in developingthe right design solution and utilizing it forthe right application
CFRP reinforcement on parking garage beams
Installation of CFRP on an industrial silo
7252019 Strengthening of Concrete Structures Using FRP Composites
httpslidepdfcomreaderfullstrengthening-of-concrete-structures-using-frp-composites 33STRUCTURE magazine June 201520
certain minimum strength Tis requirementis intended to guarantee that the ultimatecapacity of the structural member without theFRP reinforcement is greater than a designforce corresponding to the expected serviceloads under typical situationsTe minimum strength requirement in ACI
4402R isEquation 1 983142Rn = 11DL + 075LL983142Rn = design strength of the existing
member without FRPDL = new design dead loadLL = new design live load
Tis limit stipulates that externally bondedFRP reinforcement should be consideredas secondary reinforcement and used tosupplement the existing interior steel rein-forcement Should the FRP reinforcement becompromised the structure must maintainsufficient capacity to carry existing service
loads without collapseSince FRP composites are designed to lastfor the service life of the structure the impactof possible future renovations and modifica-tions should be considered where the FRP isaccidentally damaged Such damage may notbe observed immediately and the structure orstructural component may remain in serviceuntil the damage is identified and the affectedareas are repaired Equation 1 is intended toaddress these situationsTe limit of Equation 1 is intended to mini-
mize the possibility of collapse due to FRPfailure or damage In cases where the designlive load has a high likelihood of being presentfor a sustained period of time (such as storageareas) a live load factor of 10 should be usedinstead of 075Tis limit is independent from fire rating
requirements It must be satisfied even iffire protection is applied to the FRP systemTe limit is applicable to all types of strengthincrease such as shear flexure and axial strength-ening but it does not apply to extreme loadingevents (seismic events blast loading or otherloads classified by ASCE 7 as extreme events)
Depending on dead load to live load ratiothe strength increase using FRP that satisfiesEquation 1 typically results in up to 40increase in strength If the strength increaseis higher than 40 other conventionalstrengthening options should be considered
Concrete Strength Limit
Te existing concrete substrate strength is animportant parameter for bond-critical appli-cations such as flexure or shear strengtheningFor FRP to develop and transfer the designstresses at the bond line the concrete substrateshould possess sufficient strength to transferthese stresses And in order for the concreteto provide the minimum bond strength of200 psi (14 MPa) specified by ACI 4402Rthe compressive strength of concrete f c mustbe more than 2500 psi (17 MPa) Tis limitdoes not apply for contact-critical applications
like FRP column confinement which reliessolely on contact between the FRP systemand the concrete
Fire Rating and Protection
While carbon fibers are capable of resist-ing high temperatures adhesive systemshave a much lower threshold temperatureFireproofing of the FRP is an option but thehigh costs for specialized fireproofing materialarenrsquot always justifiableTe fire rating of strengthened structures
should be evaluated without FRP A deter-mination needs to be made as to whether
or not the reduced strength is sufficient ifthe FRP fails If it is there is no need infireproofing the FRP If it is not fireproof-ing materials should be evaluated for costefficiency and the ability to meet satisfac-tory fire ratings
Installation
Procedures for installing FRP systems havebeen developed by the system manufactur-ers and may differ slightly emperature andsurface moisture of concrete at the time ofinstallation are the main parameters that affectthe installation procedure and performanceof FRP systemsSurface preparation to create a bond
between the FRP system and the existingconcrete is critical Any existing deteriora-tion and corrosion of internal reinforcingmust also be resolved prior to installationof the FRP system Strengthening can only
be applied after all corrosion problems havebeen determined and resolved following theappropriate procedures Failure to do so canresult in locking in contaminants whichmay cause further deterioration and result infailure of the FRP system due to delamina-tion of the concrete substrateTe International Concrete Repair Institute
provides several guidelines for selection sur-face preparation and installation of repairmaterials Once installed the curing of theFRP system depends on the time after installa-tion and temperature during curing Similarly
temperature extremes or fluctuations canretard or accelerate FRP curing time Tehigher the temperature the faster the system
will cure ndash anywhere from one to three daysSeveral grades of resin are generally availablethrough the system manufacturer to accom-modate special situations
Conclusion
FRP systems have been successfully used tostrengthen buildings bridges silos tanks tun-nels and underground pipes Te higher costof FRP materials is offset by reduced costs oflabor use of equipment and downtime duringinstallation making them more cost-effectivethan traditional strengthening techniques While strengthening with FRP caninvolve complex processes this systemoffers a number of advantages comparedto conventional strengthening methodsUnderstanding the properties and limita-tions of FRP is important step in developingthe right design solution and utilizing it forthe right application
CFRP reinforcement on parking garage beams
Installation of CFRP on an industrial silo
