Extending the Lifespan of Extending the Lifespan of Structural ConcreteStructural Concrete

Jeff West, Ph.D., P.E.Jeff West, Ph.D., P.E.Dept. of Civil and Environmental EngineeringDept. of Civil and Environmental Engineering

Extending the LifespanExtending the Lifespanof Structural Concreteof Structural Concrete

•• Two focus areas:Two focus areas:

Prof. K.A. Prof. K.A. SoudkiSoudki–– H.T. H.T. ChoiChoi–– A. El A. El RefaiRefai–– T. QuayleT. Quayle–– Md. Md. SafiuddinSafiuddin

Prof. C.M. Prof. C.M. HanssonHansson–– K. TranK. Tran

Strengthening of Strengthening of existing structures existing structures

using using fibrefibre--reinforced reinforced polymer materialspolymer materials

Improved concrete Improved concrete materials formaterials for

new structuresnew structures

Research Colleagues:Research Colleagues:

Strengthening of existing structures Strengthening of existing structures using FRP materialsusing FRP materials

•• Strengthening of existing structures:Strengthening of existing structures:–– Compensate for damage or deteriorationCompensate for damage or deterioration–– Compensate for design or construction errorsCompensate for design or construction errors–– Address changes in use (increased loads)Address changes in use (increased loads)

•• Research Goals:Research Goals:–– Study the effectiveness of FRP materials:Study the effectiveness of FRP materials:

–– Strength increaseStrength increase–– Deflection controlDeflection control–– Improved fatigue lifeImproved fatigue life–– Failure modesFailure modes

–– Develop and calibrate models to predict behaviourDevelop and calibrate models to predict behaviour

Develop practical design toolsDevelop practical design tools

FRP Materials for StrengtheningFRP Materials for Strengthening

RodsRods Plates or StripsPlates or Strips FabricsFabrics

Strengthening Methods InvestigatedStrengthening Methods Investigated

••ExternalExternalpostpost--tensioning tensioning with CFRP with CFRP tendonstendons

••Externally bonded Externally bonded CFRP platesCFRP plates

FRP plateEpoxy

Cross SectionFRP plate

Epoxy

Cross SectionFRP plate

Epoxy

Cross Section

••Near surface mountedNear surface mountedCFRP barsCFRP bars

Cross Section

Epoxy FRP barCross Section

Epoxy FRP barCross Section

Epoxy FRP bar

Cross Section

ExternalFRP rod

Elevation

ExternalFRP rod

Anchor

Deviators

Investigation Investigation of of ““partially partially

bondedbonded””systemssystems

Research Tools / TechniquesResearch Tools / Techniques

Small and Large Scale

Structural Testing

Modeling using Finite

Element Analysis

C.L.

External PostExternal Post--tensioningtensioningwith CFRP Tendonswith CFRP Tendons

•• Two external CFRP tendons Two external CFRP tendons installed on reinforced installed on reinforced concrete beamconcrete beam–– Prestress = 40% Prestress = 40% fffrpufrpu

–– Deviators at 1/3 spanDeviators at 1/3 span

•• Beams tested under:Beams tested under:–– Static loadingStatic loading–– Cyclic loading Cyclic loading load load

ranges varied to establish ranges varied to establish fatigue behaviourfatigue behaviour

C.L.

C.L.

P

P

(a)

(b)

CFRP tendon

anchor

deviator deviator

P

P

PostPost--tensioning Configurationstensioning Configurations

StraightStraight

HarpedHarped

CFRP Tendon &CFRP Tendon &Anchor AssemblyAnchor Assembly

External PT with CFRP Tendons External PT with CFRP Tendons Research FindingsResearch Findings

•• Fatigue tests of CFRP Tendon Fatigue tests of CFRP Tendon and anchorage system:and anchorage system:–– Meets Meets PostPost--Tensioning Tensioning

InstituteInstitute proofproof--tests tests –– Establish fatigueEstablish fatigue--limitlimit

•• PostPost--tensioned beam tests:tensioned beam tests:–– Failure occurs due to Failure occurs due to

fatigue of steel barfatigue of steel bar–– PT increases strengthPT increases strength–– PT reduces deflectionsPT reduces deflections–– PT improves fatigue PT improves fatigue

behaviour:behaviour:–– Longer life Longer life (load constant)(load constant)–– Increased live loads Increased live loads

(constant fatigue life)(constant fatigue life) LoadLoad--Deflection ResultsDeflection Results

Partially BondedPartially BondedFRP Strengthening SystemsFRP Strengthening Systems

•• NearNear--surface mounted surface mounted (NSM)(NSM) and externallyand externally--bonded bonded (EB)(EB) strengthening systems have been investigatedstrengthening systems have been investigated–– Provide increased load carrying capacity, butProvide increased load carrying capacity, but–– Ductility is dramatically decreasedDuctility is dramatically decreased

0 Deflection

Load

Unstrengthened beam

FRP strengthened beam

Prestressed FRP strengthened beam

Load Load CarryingCarryingCapacityCapacity

DuctilityDuctility

FlexuralFlexuralImprovementImprovement

Objective:Objective: Develop FRP strengthening systemDevelop FRP strengthening systemto balance strength and ductilityto balance strength and ductility

PartiallyPartiallyBondedBondedSystemSystem

Fully Bonded Fully Bonded vs.vs. Partially BondedPartially Bonded

•• FRP Strain increases at a slower rate within unbonded lengthFRP Strain increases at a slower rate within unbonded length•• Concrete and steel strains increase faster to satisfy equilibriuConcrete and steel strains increase faster to satisfy equilibriumm•• Section curvature is increased Section curvature is increased increased ductilityincreased ductility

εf

εsεf

Load Steel Reinforcement

FRPBonded Unbonded Bonded

Epoxy

FRP stress before steel

yielding

Fully bondedPartially bonded

FRP stress after steel yielding

εc

εs

εc

Strain profile at mid-span

φ φ

Fully bonded

Partially bonded

εf

εsεf

εc εcφ φ

Control beam

Partially BondedFully

Bonded

Experimental ResultsExperimental Results

LoadLoad--Deflection BehaviourDeflection Behaviour

Concretecrushing

Partially bondedNSM System

rupture

debonding

Partially bondedEB Plate System

Deflection (mm)Deflection (mm)

Load

(Lo

ad ( k

NkN))

Analytical ModelingAnalytical Modeling

Analysis based on:Analysis based on:•• Force equilibrium Force equilibrium

at critical sectionsat critical sections–– CrackingCracking–– YieldingYielding–– TransitionTransition–– Load pointLoad point

•• Overall strain Overall strain compatibility within compatibility within unbonded lengthunbonded length

Partially Bonded FRP SystemsPartially Bonded FRP SystemsResearch FindingsResearch Findings

•• Partial bondingPartial bonding–– Enhances flexural ductilityEnhances flexural ductility–– Delays debonding failure in Delays debonding failure in

EB plate systemsEB plate systems

•• Failure modeFailure mode (FRP rupture or (FRP rupture or concrete crushing) depends concrete crushing) depends on the unbonded lengthon the unbonded length

•• Designer can achieve desired Designer can achieve desired balance between balance between increased increased strengthstrength and and required ductilityrequired ductilityby varying unbonded length.by varying unbonded length.

FRP rupture

φφcr

MuConcrete crushing

My

Mcr

M

0 φy φu

Unstrengthened beam

Balanced pointLub=Lubb

Fully bonded beam Partially

bonded beamFully unbonded

beam

FRP rupture

φφcr

MuConcrete crushing

My

Mcr

M

0 φy φu

Unstrengthened beam

Balanced pointLub=Lubb

Fully bonded beam Partially

bonded beamFully unbonded

beam

NonNon--Prestressed BeamPrestressed BeamMomentMoment--Curvature RelationshipCurvature Relationship

FRP rupture

φφcr

Mu Concrete crushingMy

Mcr

M

0 φy φu

Unstrengthened beam

Balanced pointLub=LubbFully bonded

beam

Partially bonded beam Fully unbonded

beam

FRP rupture

φφcr

Mu Concrete crushingMy

Mcr

M

0 φy φu

Unstrengthened beam

Balanced pointLub=LubbFully bonded

beam

Partially bonded beam Fully unbonded

beam

Prestressed BeamPrestressed BeamMomentMoment--Curvature RelationshipCurvature Relationship

= u

yDuctility φ

φ

Concrete Materials Research:Concrete Materials Research:Extending Lifespan Using Improved MaterialsExtending Lifespan Using Improved Materials

•• High performanceHigh performanceselfself--consolidatingconsolidating concreteconcrete

•• Use of Use of ““waste materialswaste materials””–– Rice husk ashRice husk ash–– Concrete plant wash waterConcrete plant wash water

ConventionalConcrete

Self-consolidatingConcrete

High strengthHigh strengthHigh workabilityHigh workabilityHigh durabilityHigh durability

Structural EfficiencyStructural EfficiencyFaster ConstructionFaster ConstructionLonger Service LifeLonger Service Life

SelfSelf--consolidatingconsolidatingHighHigh--performance Concreteperformance Concrete

•• Highly flowable concrete Highly flowable concrete that:that:–– Achieves consolidation under selfAchieves consolidation under self--weightweight–– Spreads through congested reinforcementSpreads through congested reinforcement–– Fills every corner of the formworkFills every corner of the formwork–– Maintains stability during and after placementMaintains stability during and after placement

•• Key propertiesKey properties–– Filling ability, passing ability & segregation resistanceFilling ability, passing ability & segregation resistance–– High strengthHigh strength–– High durability:High durability:

–– Low permeabilityLow permeability–– High resistivityHigh resistivity–– Resistance to freezing and thawing damageResistance to freezing and thawing damage

does notdoes notrequire require vibrationvibration

Characteristics of Characteristics of SelfSelf--consolidating Highconsolidating High--performance Concreteperformance Concrete

Special MaterialSpecial MaterialComponentsComponents

HighHigh--rangerangeWater reducerWater reducer

SupplementarySupplementaryCementing MaterialsCementing Materials

ViscosityViscosity--modifyingmodifyingAdmixtureAdmixture

Special MixtureSpecial MixtureProportionsProportions

Low WaterLow Water--Binder RatioBinder Ratio

HigherHigherFine Aggregate ContentFine Aggregate Content

LowerLowerCoarse Aggregate ContentCoarse Aggregate Content

More BinderMore BinderLess WaterLess Water

Special mixture designSpecial mixture designprocedures andprocedures and

performance criteriaperformance criteriaare requiredare required

Research Techniques:Research Techniques:Paste and Mortar PropertiesPaste and Mortar Properties

Purpose:Purpose:•• Assess performance of Assess performance of

binding materials and binding materials and admixturesadmixtures–– Determine saturation Determine saturation

dosage and water dosage and water reduction of HRWRreduction of HRWR

–– Determine water demand Determine water demand of supplementary of supplementary cementing materialscementing materials

•• Determine influence of mortar Determine influence of mortar proportions on flowing abilityproportions on flowing ability

•• Predict the filling ability of Predict the filling ability of concretesconcretes

Paste Flow Cone TestPaste Flow Cone Test

Mortar Flow Mortar Flow MoldMold TestTest

Research Techniques:Research Techniques:Fresh Concrete PropertiesFresh Concrete Properties

Purpose:Purpose:

•• Assess:Assess:

–– Flowing Flowing abilityability

–– Passing Passing abilityability

–– DynamicDynamicsegregation segregation resistanceresistance

Orimet Flow Inverted Slump Cone Flow

Slump Slump Flow

Research Techniques:Research Techniques:Fresh Concrete PropertiesFresh Concrete Properties

Purpose:Purpose:•• Assess Assess staticstatic segregation resistancesegregation resistance

Screen Segregation Column Segregation

Research Techniques:Research Techniques:Hardened Concrete PropertiesHardened Concrete Properties

•• Compressive strengthCompressive strength

•• Ultrasonic pulse velocityUltrasonic pulse velocity–– Quality or condition of concreteQuality or condition of concrete–– Coarse aggregate segregationCoarse aggregate segregation

•• Water absorption and permeable porosityWater absorption and permeable porosity–– Influence water and chloride ion permeabilityInfluence water and chloride ion permeability

•• ResistivityResistivity–– Influences corrosion resistanceInfluences corrosion resistance

Research Areas:Research Areas:SelfSelf--consolidating Highconsolidating High--performance Concreteperformance Concrete

•• Tools for development of SCHPC mixturesTools for development of SCHPC mixtures

–– StepStep--byby--step procedures for mixture proportioning step procedures for mixture proportioning

–– Relationships between flowing ability of paste/mortar and Relationships between flowing ability of paste/mortar and flowing characteristics of selfflowing characteristics of self--consolidating concreteconsolidating concrete

–– Development of semiDevelopment of semi--empirical models for prediction of empirical models for prediction of fresh and hardened propertiesfresh and hardened properties

•• Simplified testing procedures for assessing filling Simplified testing procedures for assessing filling ability, passing ability, and segregation resistanceability, passing ability, and segregation resistance

–– Single operator, field suitableSingle operator, field suitable

Reduced numberReduced numberof trial batchesof trial batches

Research Areas:Research Areas:SelfSelf--consolidating Highconsolidating High--performance Concreteperformance Concrete

•• Investigate the use of Investigate the use of rice husk ashrice husk ash as a supplementary as a supplementary cementing material in SCHPCcementing material in SCHPC

–– Effect on fresh propertiesEffect on fresh properties–– Flowing ability, passing ability, segregation resistanceFlowing ability, passing ability, segregation resistance–– AirAir--void stability in fresh concretevoid stability in fresh concrete

–– Effect on hardened propertiesEffect on hardened properties–– StrengthStrength–– PorosityPorosity–– ResistivityResistivity–– Air void systemAir void system

Questions?Questions?