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What You Need to Know to Perform

Precast Concrete Repairs in the Field

Claude Goguen, PE, LEED AP

National Precast Concrete Association


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WE WILL DISCUSS…

• Evaluation of Repair

• Repair Preparation

• Repair Material Selection

• Repair Best Practices

• Newer Technologies in Concrete Repair

• Resources


FIRST THING TO DO

• Document and

take photos

• Establish severity

of damage


EVALUATE THE EXTENT OF DAMAGE

• How much of the structure has been compromised? Follow the crack

• Is it a local issue, or is it present throughout the structure?


EVALUATE THE NEED TO REPAIR

Will defect impair functionality and durability of structure?

Sometimes the best repair method is no repair

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DETERMINE THE CAUSE OF DAMAGE

Selection of repair materials and processes depend on cause of damage.

Damage resulting from freeze-thaw, sulfate exposure, and alkali-aggregate reaction can appear to be similar. Important to distinguish which mechanism is present.


PERFORM RCA TO DETERMINE CAUSE


IS IT A MINOR OR MAJOR REPAIR?


EVALUATION

Minor Defect

Defects that will not impair the functional use orexpected life of a product.


EVALUATION

4.7.1 Repairing Minor DefectsDefects not impairing the functional use or expected life of a precast concrete product shall be considered minor defects. Minor defects may be repaired by any method that does not impair the product.

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EVALUATION

Major Defect

Defects that could impair the functional use or expected life of a concrete product.


EVALUATION

4.7.2 Repairing Major DefectsDefects in precast concrete products that impair the functional use or the expected life of products shall be considered major defects. Unless major defects are repaired the product shall be rejected. Major defects shall be evaluated by qualified personnel to determine if repairs are feasible and if so, to establish the repair procedure.


SURFACE DEFECTS

• Voids

• Honey Comb


SURFACE DEFECTS

• Bug Holes

• Spalling


LARGER CRACKS


DETERMINE THE CAUSE OF DAMAGE

Selection of repair materials and processes depend on cause of damage.

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SURFACE DEFECTS

• Surface Cracks• Plastic Shrinkage

• Scaling


TWO MAIN TYPES OF CRACKS

Active

Dormant


ACTIVE VS DORMANT


ACTIVE VS DORMANT


ACTIVE VS DORMANT


ACTIVE VS DORMANT

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ACTIVE VS DORMANT


EVALUATION

What are tolerances for cracks?

• Owner specifications

• Plant Manual

• ACI

Sometimes, a repair is worst than no repair

• Project specifications

• Your established tolerances


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THE IMPORTANCE OF CRACK WIDTH HAIRLINE VS. VISIBLE CRACKS

Crack Width (in)

0 0.002” 0.005” 0.013~0.016” 0.333”

No Leakage Leakage Corrosion

Controllable Leakage

Visible Leakage

Crack Healing

Beginning of Visible Cracking

Visible Corrosion with Deicers

Crack Width (in)

0 0.002” 0.005” 0.013~0.016” 0.333”

No Leakage Leakage Corrosion

Controllable Leakage

Visible Leakage

Crack Healing

Beginning of Visible Cracking

LimitationACI Limitation

Visible Corrosion with Deicers


EVALUATION


SPALLS


SUCCESSFUL REPAIR DEPENDS ON..

• Surface Preparation• Compatibility of Repair Materials• Application Conditions• Proper Application• Curing

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START WITH CHOOSING REPAIR MATERIAL

• This will dictate:

• Surface preparation

• Necessary application conditions

• Curing time and conditions


REPAIR MATERIAL

Things to consider when selecting a repair material:

• What materials do specifications permit?

•Application Conditions

•Compatibility of materials

•Surface Requirements

•Mechanical Properties

•Time of Set

•Color Matching


MECHANICAL PROPERTIES

• Coefficient of thermal expansion

• Drying shrinkage

• Permeability

• Modulus of Elasticity


Expansive properties


Modulus of Elasticity is important:

• The concrete and the repair material must react similarly to loads

• When an external load (compressive or tensile) is applied parallel to the bond line, low modulus materials deform more than the high modulus materials

• Loads will be transferred from low modulus materials to high modulus materials

• Stress concentration may cause failure of the high modulus materials

Modulus of Elasticity


REPAIR MATERIAL

Cementitious materials

• Portland cement concrete

• Portland cement mortar

• Modified concretes and mortars

Grouts

Epoxy

Acrylic resins

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Advantages

• Compatible with concrete

• Economical

• Mix with water, easy cleanup

• Resist high temperatures

Limitations

• Critical water/cement ratio

• Shrinkage, curing

• Slow reactions

• Low tensile, flexural, bond strengths

• Surface preparation

Cement Based

REPAIR MATERIAL


REPAIR MATERIAL


• Portland Cement Concrete

• Advantages: Similar properties, low shrinkage

• Limitations: Aggressive environments, shrinkage

• Applications: Thick sections (over 2 inches) and large volumes

• Add: Water reducer and air entrainer


REPAIR MATERIAL


• Portland Cement Mortars

• Advantages: Thinner sections (1.5-4”)

• Limitations: More susceptible to drying shrinkage

• Applications: Thinner sections

• Can be applied without bonding agent

• Add water reducer and air entrainer


REPAIR MATERIAL


• Pre-Packaged Mortars / Rapid Setting Cements

• Advantages: Convenient. Different applications. Quick Set

• Limitations: Different mechanical properties. Limit exposure to sulfates

• Applications: Thin sections (up to 1/8”)


PRE-PACKAGED REPAIR MATERIALS

What to look for:

Set Time: Faster is not necessarily better

Compressive Strength: equal or greater to surrounding concrete.

Volume Stability: less sand, more shrinkage.


REPAIR MATERIAL


• Cement Grouts

• Advantages: Easy to install. Compatible

• Limitations: Width has to be large enough to allow largest particles

• Applications: Filling of cracks

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PATCH MIX DESIGN EXAMPLE

Very large patches – use the same concrete as the product was produced from

or

a stiff mixture of:

1 part cement, 3 parts sand + water

Smaller, more refined patches – very stiff paste

1 part cement, 2-1/2 to 3 parts sand + water

Water = clean water


Advantages

• Improved adhesion

• High strengths

• Low permeability

• Abrasion, impact resistance

• Improved durability

Limitations

• Workability problems

• Finishing (sticky)

• Curing is critical

• Mixing is critical

• Higher cost

Cement Based with Mineral Additives

REPAIR MATERIAL


Advantages

• Excellent adhesion

• Adhesion on damp concrete

• Very low permeability

• Corrosion protection

• Chemical resistance

Limitations

• Three components (typically)

• Ratios are critical

• Must not freeze

• Finishing difficulties

• Higher cost

Epoxy Modified Cement Based

REPAIR MATERIAL


Advantages

• Impervious to moisture and de-icing salts

• High abrasion, skid resistance

• Minimal added dead weight

• Rapid turnaround - open to traffic in 4 - 6 hours

Limitations

• Mixing is critical

• Vapor barrier

• Thermally incompatible

• Creep

• Higher cost

• Solvents needed for cleanup

Epoxy Mortar

REPAIR MATERIAL


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PATCHING MATERIALS EPOXY MORTARS

• Epoxy resin and aggregate (usually sand)

• Sand must be “oven dry”

• Maximizing sand content minimizes heat and shrinkage cracking.

• Dimensional compatibility issues can arise due to differing E with the base concrete


REPAIR MATERIAL

Epoxy

• Chemical Grouts (Epoxy Injection)

• Advantages: Can be applied in moist environments. Cracks as thin as 0.002 inches

• Limitations: Different mechanical properties. Skilled labor.

• Applications: Repair of fine cracks

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REPAIR MATERIAL

Modifed Blends

• Fiber Reinforced Concrete

• Advantages: Resistant to shrinkage and cracking

• Limitations: Workability

• Applications: Thinner sections that may not allow conventional reinforcing.


REPAIR MATERIAL

Bonding materials

• Epoxy

• Latex

• Cements


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PATCHING MATERIALS BONDING AGENTS

• Increase the bond between a hardened concrete and fresh mortar

• Unsanded cement paste, a commercially available latex-based material or epoxy

• Follow manufacturer’s recommendations for forbonding agents

• Bonding agents are not required but advisable if the patch surface is large and thin.


Recommended for:• Low slump mixes• No slump mixes

Acceptable bonding agents

• Polymer liquids• Not all polymers equal, generic term• Basic performance

• Proper scrubcoat• SSD substrate, no dilution

• Epoxies• Wet on wet

• Epoxy cements• Extended open times

BONDING AGENTS


REPAIR APPLICATION CONDITIONS

Cold Weather

• Requires protection procedures

• Consider using an accelerator

• Do repair work in a controlled environment

Hot Weather

• Keep product in cool place prior to use

• Cover mixing bucket with a wet towel and keep out of the sun


REPAIR PREPARATION

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1. Original concrete substrate; prepared to receive repair material.

2. Interface between existing concrete and new repair material.

3. New repair material.

3 ELEMENTS OF A REPAIR AREA


BOND IS EVERYTHING


BOND IS EVERYTHING

• What we are creating essentially is a cold joint.

• Use the open pore structure. It will provide capillary suction of the repair material, or bonding agents, into the substrate concrete

• Saturated, surface dry condition is generally best for achieving bond

• Substrate at proper temperature (usually 50 to 90F)

• Ensure intimate contact between new material and bond line.

• Greater than 12” or 1.5” deep, consider reinforcing (Application will dictate this)

Concrete Repair and Maintenance by Emmons


BOND/SURFACE ROUGHNESS

• Clean Sound Substrate

• Roughen Profile to Get

Interlock

• Open “Pore Structure”

• Bonding Agent

• Initial Strength

• Bond Durability• Shrinkage, Freeze-Thaw, Loading


REPAIR PROCESSES

• Repair Area

Recommended AreaDamaged Area


REPAIR PREPARATION

Avoid Feathered Edges

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REPAIR PREPARATION

• Remove defective concrete down to sound concrete.

• Clean substrate and remove all loose

material, dust, etc.

• After initial removals, surface should be sounded for delaminations and voids

• Any areas found unsound should be re-chipped


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BEFORE WE START…

Have all materials readily available including proper PPE.


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USE PROPER TOOLS

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…and HAVE THEM READY!


REPAIR PROCEDURES

• Documented repair process

• Use Mock-ups

• Training is key to getting consistency

• Make it fun


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PATCHING PROCEDURES

• Ideally, the concrete substrate should be saturated surface dry (unless using an epoxy bonding agent or patching mortar, in which case the presence of moisture may not be allowed).

• The bonding agent, if used, should be applied thoroughly over the entire area to be patched, following manufacturer’s instructions. Following is information on the various commonly used patching materials:


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HORIZONTAL OVERLAYS

• One of the Most Common Repair Problems

• Trowel in At Edges

• As thin as 1/8” (Special Materials) to very Thick

• Typically No Additional Reinforcement

From Concrete Repair and Maintenance Illustrated Emmons © 1994

Trowel in At Edges

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REPAIR PROCESSES

• Honeycombing


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HONEYCOMBED CONCRETE

• Defective areas, such as honeycomb, must be chipped out of the solid concrete.

• The edges must be cut as straight as possible at right angles to the surface (Some recommend slightly undercut to provide a key at the edge of the patch)

• If a shallow layer of mortar is placed on top of the honeycomb concrete, moisture will form in the voids and subsequent weathering will cause the mortar to spall off.


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REPAIRING A HONEYCOMBED AREA

• May be cosmetic or structural

• Loose material should be removed

• If proprietary materials are usedthey should be done in accordance

with the manufacturers instructions

• If a conventional material is used the substructure should be damp but not wet

• A cement-sand grout can be used as a bonding agent followed immediately by the application of a repair material


REPAIR PROCESSES

• Bugholes


BUGHOLE REPAIR

• Apply grout of 1 part Portland cement, 1 ½ parts sand + water


REPAIR PROCESSES

Larger Spalls

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REPAIR PROCESSES

Application of Repair Material


REPAIR MATERIAL

Added Reinforcing

• Rebar or dowels

• Mesh or Wire

• Fibers

• Anchors


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REPAIRING CRACKS

• Cracks do not always require repair

• If needed, low viscosity epoxy is usually best

• Surface preparation is important.

• The crack should be clean and clear of loose material, and oil, grease, and dust.

• If moisture is present, use a moisture resistant epoxy

• It is important to follow the manufacturer’s directions in mixing and applying epoxies


SMALL SURFACE CRACKS


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CRACK REPAIR METHODS

• Epoxy Injection,

• Routing and Sealing

• Stitching and Doweling

• Gravity Filling

• Polyurethane Injection

• Dry Packing


EPOXY INJECTION

• As narrow as 0.002 inches

• Restores soundness and integrity

• Full depth repair

• Not for active cracks


RESIN PROPERTIES DESCRIBED BY ASTM* STANDARD C-881

• Type – Intended Uses (Strengths)

• Grade – Viscosity (Flowability)

• Class – Usage Temperature Range

*American Society for Testing & Materials


ASTM C-881TYPE = INTENDED USE (STRENGTHS)

• Type I Non load-bearing applications, bonding hardened concrete to hardened concrete or as a binder for epoxy mortars.

• Type II Non load-bearing applications, bonding freshly mixed concrete to hardened concrete.

• Type III For use in bonding skid resistant materials to hardened concrete.


ASTM C-881TYPE = INTENDED USE (STRENGTHS)

• Type IV Load-bearing applications, bonding hardened concrete to

hardened concrete or as a binder for epoxy mortars.

• Type V Load-bearing applications, bonding freshly mixed concrete to

hardened concrete.


FOR RESIN SELECTION, YOU ALSO NEED TO CONSIDER THE RESIN’S ASTM C-881 GRADE(VISCOSITY OR FLOWABILITY)

• Grade 1 Low Viscosity (less than 2,000 cps)

• Grade 2 Medium Viscosity (2,000-100,000 cps)

• Grade 3 Non-Sag (Above 100,000 cps)

Because a resin has one viscosity, it can only be classified as a single grade.

cps = Centipoise

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SAMPLE VISCOSITIES

• Acetone 0.3 cps

• Water 1 cps

• 30 Weight Motor Oil 200 cps

• 60 Weight Motor Oil 1,000 cps

• Honey 3,000 cps

• Corn Syrup 110,000 cps

• Peanut Butter 250,000 cps

Note: 100 CPS = 1 Poise


WHY IS THE RESIN’S ASTM C-881”GRADE” IMPORTANT?

• Grade indicates how easily the resin will flow into or through a crack.

• For narrow cracks, you will need a grade 1, for very wide cracks, you may need a grade 3.


ASTM C881 CLASS

Finally, you may need to know the temperature at which an epoxy resin can be used. This is shown by a resin’s class. Some epoxy resins can be used in more than one temperature range and may therefore be in two classes.


ASTM C-881CLASS = TEMPERATURE OF CONCRETE

• Class A (Below 40o F)

• Class B (Between 40o and 60o F)

• Class C (Above 60o F. to maximum temperature determined by manufacturer)


MOST INJECTION SPECS WILL READ:

• ASTM C-881

Type I or IV (For Bonding Hardened Concrete to Hardened Concrete)

Grade 1 (Low Viscosity)

Class B and C (40O and Above)


EPOXY INJECTION

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CRACK REPAIR PROCESSES

• Epoxy Injection

• Min 0.002 inches(0.05mm)• Skilled applicator• Clean crack• Seal surface and allow to cure• Insert entry and venting ports• Mix epoxy• Inject epoxy and allow to cure• Remove surface seal


ROUTING AND SEALING

• For fine and large cracks

• Crack sealing (not integrity repair)

• Both active and dormant cracks

• Ideal for horizontal surfaces but can be used for vertical surfaces

• Sealers include epoxies, urethanes, polyureas, polymers.

• Adequate reservoir needed for active cracks


ROUTING AND SEALING


ROUTING AND SEALING


ROUTING AND SEALING

minimum ¼” to ½” wideminimum ½” to 1” deep

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ROUTING AND SEALING


ROUTING AND SEALING

sand supports sealant


GRAVITY FILLING

• Crack sealing

• For narrow cracks (widths of 0.001 inches)

• Lower viscosity materials for finer cracks

• Dormant cracks

• Ideal for multiple surface cracks such as plastic shrinkage cracking

• Horizontal surfaces


• Small volume cartridges

GRAVITY FILLING


• Small volume cartridges

GRAVITY FILLING


• Squeeze bottles

GRAVITY FILLING

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POLYURETHANE INJECTION

• For wet and leaking cracks

• As narrow as 0.002 inches

• Reactive resin

• Hydrophilic or hydrophobic

• For active of dormant cracks

• Crack sealing


SUMMARY OF OPTIONS


MIC DETERIORATION REPAIR


ARCHITECTURAL REPAIRS

• Mock-ups

• Patching materials

• Color Matching


REMEMBER THAT A SUCCESSFUL REPAIR DEPENDS ON..

• Surface Preparation• Compatibility of Repair Materials• Application Conditions• Proper Application• Curing


CURE REPAIR PROPERLY

Often most neglected

step of repair

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NEWER TECHNOLOGIES


REPAIR MATERIAL

Modified Blends

Polymer-cement concrete and polymer concrete• Advantages: Ease of installation. Long term performance. Very thin

sections (1/4” to 1.5”)

• Limitations: Range of application temperature

• Applications: Patching


REPAIR MATERIAL

Modified Blends

Microsilica Modified Portland Cement Concrete• Advantages: Higher strengths, low permeability

• Limitations: Range of application temperature

• Applications: Patching, thicknesses over 1”


REPAIR MATERIAL

Acrylic Resin

• MMA (Methylmethacrylate Concrete)• Advantages: Thin sections (.25 to .5”) Cures quickly. Wide range of app

temps. High strength

• Limitations: Drying shrinkage

• Applications: Repair of cracks


RESOURCES

• ACI 224 – Causes, Evaluation, and Repair of Cracks in Concrete Structures

• ICRI No. 320.1R–1996 Guide for Selecting Application Methods for the Repair of Concrete Surfaces

• ICRI No. 320.2R–2009 Guide for Selecting and Specifying Materials for Repair of Concrete Surfaces


RESOURCES

• Concrete Repair and Maintenance Illustrated –Peter Emmons

• NPCA Architectural Repair Guide

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QUESTIONS

Claude Goguen – [email protected]

Tel: 317-223-9918


What You Need to Know to Perform

Precast Concrete Repairs in the Field

Precast Show 2020

March 7th, 2020

Claude Goguen, PE, LEED AP

National Precast Concrete Association


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evaluate the extent of damage evaluate the need to repair · determine the cause of damage...

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