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REPAIR OF CONCRETE STRUCTURES
INTRODUCTION TO STRUCTURALREPAIR
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Overview of a Repair Process
Problem statement
Evaluation
Visual
InspectionNDT
Need for Repair
Type of Repair ?
Time and Budgetary
limitations ?
YES
NO
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After a decision to Repair
Detailed Evaluation
Repair Analysis
Repair Strategy
Repair
Type
Life Cycle
Assessment
Life Cycle
CostAssessment
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Repair Process
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Repair Process
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Repair Process
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Repair Process
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Repair Process
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Details of Repair
Repair Strategy
Repair MaterialPreliminaryactivities
RepairImplementation
Locating the
repair areas
Surface
preparation
Defining repair
boundaries
Selection
Property
testing
Special needs
A whole lot of
activities
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Repair Analysis, Strategy and
Design
Emmons, Concrete Repair and Maintenance Illustrated
Repair Analysis
User Needs Structural Needs
Useful Life
Urgency
Cost
Performance
Aesthetics
Effects on structure
Constructability
Environment
Safety
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Look out for
Repair Materials Repair Process
Surface
preparation
Application
MethodBond
Properties
Compatibility withsubstrate
Loading conditions
Environment
Final
performanceOf the Repair
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Performance Requirements of
Repair
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Load and Repair materials
The challenge: Repair under load or repair
after removing load?
How to take care of the steel here?
How to ensure that the repair material also carries load ?
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Cause-Effect influence in Repair
A typical example Freeze thaw damage
When the moisture source is internal,damage will continue behind the surfacerepair
After repair, the damage process may getaccelerated since water pressure mighthave changed now
Surface repairs should stop the flow ofwater completely
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Cause-Effect
Cause Effect
Primary Secondary Primary Secondary
Chlorides
from road
salts
Moisture
F-T cracking
Improper cover
High w/c ratio
concrete
Corrosion
of
reinforcingsteel
Cracking
Delamination
Spalling
SOLUTIONPARTIALDEPTH
REPAIRSOLUTION
NEXT SLIDE
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Taking care of the CAUSE
PREVENTIVE MAINTENANCE
Reduce Cl- ionflow
Reducemoisture flow Protect therebar
Coatings Crack
SealantsOverlays Membrane
Chloride
removal
Epoxycoatings
Cathodicprotecton
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What are the causes and effects?
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Causes and Effects
Causes
Effects
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Culvert damage
Cause
Permeability
Moisture Flowfrom Deck
Freezing
ThawingEffect
Disintegration ofMatrix
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Repair Analysis
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Repair Strategy
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Repair + Protect ?
Solutions Vary Widely.
Many Strategies Include
Not Just Repair But AlsoAdded Measures toProtect the StructureFrom Repeat Attacks
Cost Is an Issue
More Complex RepairsMay Have More
Performance IssuesLater!
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Repair Strategy
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Concrete Repair Process
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PARTIAL DEPTH REPAIR (SURFACEREPAIR)
Fundamentals Pavement Example
http://www.fhwa.dot.gov/pavement/repair04.htmMost of the pictures from:
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Partial Depth Repair
Emmons, Concrete Repair and Maintenance Illustrated
Repair Strategy
Partial depth Repair Full depth Strategy
Appearance Structural
Dead
loads
Impact
loads
Live loads
Barrier to
environment
Aesthetics Wear
resistant
P i l D h i f
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Partial Depth repair of a
pavementTypically, not less than 1/3rd of the pavement
thickness
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Repair challenges for surface repair
Substrate condition
Incompatible materials Shrinkage of repair material
Service conditions and loads
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Design Considerations
Temporary or Permanent partial-depthrepairs ?
Temporary repair life until a permanent repaircan be made.
Tolerances for repair Whether you have an overlay or not ?
Repairing for safety and permanent use vs.
temporary use
Cost effectiveness repair materials and
procedures
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Finding unsound Concrete
Chain drag to detect unsound
concrete
Sounding with a mini-hammer
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Sizing a Repair Area
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Removal of damaged concrete - 1
Sawing and Chipping
Depth 1-2 in
Straight and vertical cut
Pneumatic hammers tobreak the concrete
Chip the area until cleanand sound concrete isobserved
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Removal of damaged concrete - 2
Carbide Milling
Milling machines with 12
in to 18 in (300 - 450mm) cutting heads
Avoid excessive removal
Reinforcement obstruction
Damaging dowel bars
Mill across lanes forspalling along an entire
joint
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Use of Chipping hammers
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Clean / Replace the
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Clean / Replace thereinforcement
Residual rust in the steel rebar can causefurther problems
Grit blasted reinforcing
steel
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Placing the joint insert
Needed for repairs abuttingjoints or cracks
Compressible insert keepsthe repair material frombearing on the adjacentconcrete
Without the insert,pavement expansion in hotweather may cause the pop-
out / delamination of therepair material POINT BEARING
Styrofoam insert
Asphalt impregnatedFiber board
Applying Bonding
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Applying BondingAgent
Bonding agent should beapplied in a thin even coat
The contact time for cementgrout < 90 minutes
Epoxy agents may permit aless vigorous application
Cover the entire area withthe bonding agent, includingthe repair walls or edges
Overlapping the pavementsurface also will helppromote good bonding
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Placing the Repair material
The volume of material required for a partial-depthrepair is usually small
For partial-depth repair, repair materials are typicallymix on site in small mobile drums or paddle mixers
Vibrate the fresh concrete to eliminate any voids,especially at the interface of the repair and existing
concrete. Use small penetrations of the vibrator throughout the
repair area
On very small repairs, hand tools should be sufficient towork the repair material and attain adequateconsolidation.
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Finishing the repaired surface
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Full Depth Repairs
Most commonly adopted for distressedpavements
Involves removing a certain part of thepavement all the way through to the bottom
NOT a recommended procedure for beamsor slabs
Problems with load transfer
May need the entire beam / slab to bestrengthened / retrofitted
h ll d h i ?
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Why Full depth repair?
Removing and replacing at least a portion of aslab to the bottom of the concrete
Improves pavement rideability and structuralintegrity and extends pavement service life
ACPA
easons necess tat ng u
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depth repairs
Joint Deterioration
Cracking
Breaking Spalling (deep spalls)
ACPA
easons necess tat ng u
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depth repairs
Corner breaks and shattered slabs
Support problems
Lack of structural strength
ACPA
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F ll Depth Repai s Steps
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Full Depth Repairs - Steps
Define repair boundaries area
Saw old concrete
Remove old concrete
Prepare patch area
Provide load transfer
Place and finish concrete
Cure and insulate concrete Saw and seal joints
FHWA Procedure
Defining boundaries 1
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Defining boundaries - 1
Examine distressed area, mark the boundaries Recommended minimum repair length:
1.8m (6 ft) for repairs provided with mechanicalload-transfer devices 2.4 - 3m (8 -10 ft) for repairs with aggregate
interlock joints
All repairs should be full-lane width Minimum distance from repair joints to the
nearest transverse crack or joint is 1.8m (6 ft)
Patch length more than 4.6m (25 ft), usereinforcement in the repair also
Sawing Old Concrete
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Sawing Old Concrete
Full depth sawing minimal damage to the
surrounding areas Saw through the joint
to avoid spalling
Pressure relief cuts ifthe temperature ishigh
http://www.fhwa.dot.gov/pavement/full5.htm
Sawing the boundaries
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Sawing the boundaries
Partial depth cutbeyond the actual
repair boundaries Partial cuts act as
confined boundaries to
limit the extent ofdamage while liftingthe slab
Be prepared to repairthe entire area inbetween the partial
cuts
Removing Old Concrete
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Removing Old Concrete
Lift the entire areawhenever possible
Lift pins to lift theconcrete
Old concrete may
swing and hit partsof the pavementcausing more
damage
http://www.fhwa.dot.gov/pavement/full5.htm
Old Concrete Removed
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Old Concrete Removed
Removing Old Concrete
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Removing Old Concrete
Sometimes lifting maynot be possible
because of the extentof damage
Break the concrete and
then remove thefragments
Drop hammers
Problem: sometimesdamages the sub basealso
Preparing the Patch Area
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Preparing the Patch Area
Adding andcompacting new sub
base material may beneeded
Vibratory plate
compactors
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Drilling holes
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Drilling holes
Dowel Bar details
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Dowel Bar details
Grout retaining disc Bond breaking board
Place and finish new concrete
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Place and finish new concrete
Avoid need for excessive shoveling
Straight edge and vibrating screed
Patch should match the surrounding profile
Placing Concrete
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Placing Concrete
Finishing the Repaired Section
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s g t e epa ed Sect o
Curing, Saw and Seal Joints
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g,
Liquid membrane forming curing compound
Proper curing very critical for repairmaterials
Need to develop good bond with the parent
material Need to develop strength evenly
Sawing joints and sealing
Opening to Traffic
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p g
Recommended strengths before opening (generalrule)
2000 psi compressive strength 300 psi flexural strength
General times of opening to traffic
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