evaluate the extent of damage evaluate the need to repair · determine the cause of damage...
TRANSCRIPT
The Precast Show
NPCA 1
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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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SOMETIMES…$#*&! HAPPENS!
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WE WILL DISCUSS…
• Evaluation of Repair
• Repair Preparation
• Repair Material Selection
• Repair Best Practices
• Newer Technologies in Concrete Repair
• Resources
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FIRST THING TO DO
• Document and
take photos
• Establish severity
of damage
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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?
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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.
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PERFORM RCA TO DETERMINE CAUSE
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IS IT A MINOR OR MAJOR REPAIR?
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EVALUATION
Minor Defect
Defects that will not impair the functional use orexpected life of a product.
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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.
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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.
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SURFACE DEFECTS
• Voids
• Honey Comb
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SURFACE DEFECTS
• Bug Holes
• Spalling
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LARGER CRACKS
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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
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TWO MAIN TYPES OF CRACKS
Active
Dormant
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ACTIVE VS DORMANT
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ACTIVE VS DORMANT
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ACTIVE VS DORMANT
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ACTIVE VS DORMANT
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ACTIVE VS DORMANT
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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
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EVALUATION
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SPALLS
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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
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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
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MECHANICAL PROPERTIES
• Coefficient of thermal expansion
• Drying shrinkage
• Permeability
• Modulus of Elasticity
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Expansive properties
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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
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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
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REPAIR MATERIAL
Cementitious materials
• 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
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REPAIR MATERIAL
Cementitious materials
• 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
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REPAIR MATERIAL
Cementitious materials
• 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”)
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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.
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REPAIR MATERIAL
Cementitious materials
• 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
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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
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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
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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
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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.
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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.
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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
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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
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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
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BOND IS EVERYTHING
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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
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BOND/SURFACE ROUGHNESS
• Clean Sound Substrate
• Roughen Profile to Get
Interlock
• Open “Pore Structure”
• Bonding Agent
• Initial Strength
• Bond Durability• Shrinkage, Freeze-Thaw, Loading
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REPAIR PROCESSES
• Repair Area
Recommended AreaDamaged Area
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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
X
…and HAVE THEM READY!
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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
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REPAIR PROCESSES
• Bugholes
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BUGHOLE REPAIR
• Apply grout of 1 part Portland cement, 1 ½ parts sand + water
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REPAIR PROCESSES
Larger Spalls
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REPAIR PROCESSES
Application of Repair Material
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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
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SMALL SURFACE CRACKS
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CRACK REPAIR METHODS
• Epoxy Injection,
• Routing and Sealing
• Stitching and Doweling
• Gravity Filling
• Polyurethane Injection
• Dry Packing
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EPOXY INJECTION
• As narrow as 0.002 inches
• Restores soundness and integrity
• Full depth repair
• Not for active cracks
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RESIN PROPERTIES DESCRIBED BY ASTM* STANDARD C-881
• Type – Intended Uses (Strengths)
• Grade – Viscosity (Flowability)
• Class – Usage Temperature Range
*American Society for Testing & Materials
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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.
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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.
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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
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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.
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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.
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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)
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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)
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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
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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
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ROUTING AND SEALING
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ROUTING AND SEALING
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ROUTING AND SEALING
minimum ¼” to ½” wideminimum ½” to 1” deep
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ROUTING AND SEALING
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ROUTING AND SEALING
sand supports sealant
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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
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• Small volume cartridges
GRAVITY FILLING
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• Small volume cartridges
GRAVITY FILLING
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• 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
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SUMMARY OF OPTIONS
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MIC DETERIORATION REPAIR
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ARCHITECTURAL REPAIRS
• Mock-ups
• Patching materials
• Color Matching
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REMEMBER THAT A SUCCESSFUL REPAIR DEPENDS ON..
• Surface Preparation• Compatibility of Repair Materials• Application Conditions• Proper Application• Curing
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CURE REPAIR PROPERLY
Often most neglected
step of repair
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NEWER TECHNOLOGIES
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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
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REPAIR MATERIAL
Modified Blends
Microsilica Modified Portland Cement Concrete• Advantages: Higher strengths, low permeability
• Limitations: Range of application temperature
• Applications: Patching, thicknesses over 1”
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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
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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
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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
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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
precast.org/education
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