ce 555 - l25-27- structural concrete repair

8/10/2019 CE 555 - L25-27- Structural Concrete Repair

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Neithalath, Spring 2006, CE 455/555 Structural Damage: Assessment, Repair, and Strengthening

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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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



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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

ce 555 - l25-27- structural concrete repair

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