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WW--5252Concrete Surface Defects: Concrete Surface Defects:
Causes, Prevention, and Cure. Causes, Prevention, and Cure.
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Michelle L. Wilson, FACIDirector, Education
Portland Cement Associationwww.cement.org
Wednesday, March 5, 2014
Disclaimer and Waiver of Liability
This document is for informational purposes only and is not to be construed asexplicit engineering advice, or professional engineering services. This serviceis provided on the terms and understanding that the author(s) or companiesrepresented by the CONEXPO-CON/AGG 2014 or author(s) makes no warranty,guarantee, or promise, express or implied, concerning the content or accuracyof the material herein and accessible via this service.
No person or business entity should rely on the sole contents of this documentto make any decisions The CONEXPO-CON/AGG 2014 or author(s) or the
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to make any decisions. The CONEXPO-CON/AGG 2014 or author(s) or thecompanies that they represent are not responsible for the results of any actionstaken on the basis of information in this service, nor for the actions of personsusing this document, nor for any error in or omission contained in thisdocument.
The CONEXPO-CON/AGG 2014 or author(s) or any represented companyexpressly disclaims all and any liability and responsibility to any person inrespect of anything, and of the consequences of anything, done or omitted tobe done by any such person in reliance, whether wholly or partially, upon thewhole or any part of the contents of this document.
Learning Objectives
1. Learn how to survey concrete in the field.
2. See how poor construction practices lead to concrete defects.
3. Understand how construction materials affect
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concrete performance and discover practical solutions to correct existing problems.
Portland Cement Association
• Founded in 1916
• Headquarters: Washington D.C.
• Labs: Skokie, Illinois
• Mission:
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To improve and extend the uses of portland cement and concrete.
• When troubleshooting concrete problems it is important to relate the symptom to causes of distress and deterioration.
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of distress and deterioration.
Identify Processes or Materials Causing Distress or Failure
• Design- Constructability
• Materials Selection
• Mix Design
Design
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• Placement Procedures
• EnvironmentWorkmanship Environment
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Identify Concrete Surface DefectsACI 201.1 R• Cracking
• Dusting• Blisters• Delaminations• Crazing • Popouts
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Popouts• Mortar Flaking & Scaling• Spalling• Bugholes• Cold Joint• Discoloration• Efflorescence• Honeycombing (Internal?)
References
• ACI 201- Condition Survey
• PCA- IS177- Concrete Surface Defects
• Corps of Engineers- Evaluation and Repair Guide
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Observations on Cracking
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Observations on Cracking
• Surface Appearance
• Depth & Width of Cracking
• Current State of Activity
• Physical State of Concrete When Crack Occurred
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Crack Occurred
• Structural Nature of the Crack
Surface Appearance
Pattern Cracks– map cracks, crazing,
checking, D-cracking
Individual Cracks (Isolated)
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– diagonal, longitudinal, transverse, vertical, horizontal
Depth of Cracking
Depth-– Surface, Shallow, Deep, Through
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Width of Cracking
Width-– Fine
generally less than 1 mm (0.04 in.)
– Mediumbetween 1 2 mm
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between 1-2 mm (0.04-.08 in.)
– Wide over 2 mm
(0.08 in.)
Current State of Activity
• Active
• Dormant
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Physical State of Concrete When Cracking Occurred
Before Hardening– Plastic
Shrinkage
Settlement
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– Construction MovementFormwork Movement
Subgrade Movement
Physical State of Concrete When Cracking Occurred
After Hardening– Physical
Drying Shrinkage
Crazing
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– Chemical
Corrosion of Reinforcement
Alkali-Aggregate Reactions– Thermal
Thermal Contraction
Freeze-Thaw Cycles
Physical State of Concrete When Cracking Occurred
After Hardening– Structural
Accidental Overload
Creep
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Design Loads
Surface Appearance
• Pattern Cracks– map cracks, crazing, checking, D-cracking
• Individual Cracks (Isolated)– diagonal, longitudonal, transverse, vertical, horizontal
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Plastic Shrinkage
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Plastic Shrinkage
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Subsidence
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Drying Shrinkage
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Thermal Shrinkage
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Repair Approach - Cracking
• Consider:– Future movement
– Active vs. dormant
– Strengthening required
Moisture
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– Moisture
– Degree of restraint for repair material
Repair Approach - Cracking
• Consider:– Is mechanism likely to remain active?
– Feasibility of repair
– Should crack be treated as spall (corrosion)?
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Dormant Cracks
Isolated Cracks
WaterCondition
Strengthening Required ?
NoNo
YesYes
NoneNone MajorMajor
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• Injection (epoxy)• Routing & sealing• Flexible sealing• Drilling & plugging• Dry packing• Grouting (cement-based)• Autogenous healing• Judicious neglect
• Injection (epoxy or polyurethane)• Routing & sealing• Flexible sealing• Drilling & plugging• Grouting (cement-based)• Autogenous healing• Judicious neglect
• Injection (polyurethane)• Flexible sealing
jj
MinorMinor
Dormant Cracks
Isolated Cracks
WaterCondition
Strengthening Required ?
YesYes
NoneNone MajorMajor
NoNo
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• Injection (epoxy)• Stitching• Post-tensionning• Reinforcement• Autogenous healing
• Post-tensionning &epoxy injection
• Reinforcement• Autogenous healing
• Post-tensionning & epoxy injection
jj
MinorMinor
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Dormant Cracks
Pattern Cracks
WaterCondition
Strengthening Required ?
NoNo
NoneNone MajorMajor
YesYesImprobableOccurrence
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• Injection (epoxy)• Routing & sealing• Bonded overlay• Autogenous healing• Judicious neglect
• Injection (epoxy orpolyurethane)
• Routing & sealing• Bonded overlay• Autogenous healing• Judicious neglect
• Injection(polyurethane)
• Bonded overlay
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MinorMinor
Active Cracks
Isolated cracks
StrengtheningRequired ?
Yes No
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• Stitching• Post-tensionning• Reinforcement
• Flexible sealing• Drilling & plugging• Injection (polyurethane
or flexible epoxy)
Active Cracks
Pattern cracks
StrengtheningRequired
Yes No
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• Improbable• Occurrence• Post-tensionning• Overlay
•Unbonded•Overlay
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Surface Defects-Dusting
• Development of a fine, powdery material at the surface of hardened concrete.
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Use Ventilated Heaters
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Surface Defects-Blistering
• The irregular raising of a thin layer at the surface of placed mortar or concrete during or soon after completion of the finishing operation.
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Blisters
Causes:
Too many fines
Too much or too little vibration
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Too much or too little vibration
Early finishing
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Blisters
Prevention:
Avoid high slumps and excess fines
Use appropriate cement content
W b d i ld th
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Warm subgrade in cold weather
Do not place slab directly on vapor retarder
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Blisters
Prevention:
Do not overwork the concrete
Do not seal (finish) the surface too soon
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Use proper finishing techniques and timing
Reduce evaporation
Avoid air contents of more than 3% for interior slabs
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Surface Defects-Delamination
• A separation along a plane parallel to a surface. In the case of a concrete slab, a horizontal splitting, cracking, or separation of a slab in a plane roughly
ll l t d ll th
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parallel to, and generally near, the upper surface.
Sealing The Surface
• Improper Tooling
• Traps Bleed Water and Air Beneath Layer of Mortar
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Surface Defects-Crazing
• Fine, random cracks or fissures in the surface of plaster, cement paste, mortar, or concrete.
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Crazing
Causes:
Rapid surface drying after setting
Applying dry cement to surface during
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Applying dry cement to surface during finishing
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Surface Defects-Popouts
• Conical fragment that breaks from the concrete surface. A fractured aggregate particle is often at the bottom of the hole.
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bottom of the hole.
Popouts
Causes:
• Porous rock with high absorption, low specific gravity:– Pyrite
– Hard-burned dolomite
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Hard burned dolomite
– Coal
– Shale
– Soft, fine-grained limestone
– Chert
• Alkali-aggregate reactivity
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Popouts
Prevention:
Use low slump, low water content mix
Use durable crushed stone or beneficiated aggregate
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Slope the slab surface to drain water properly
Use supplementary cementing materials to control ASR-induced popouts
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Surface Defects-Mortar Flaking
• A form of scaling over coarse aggregate (“popoffs”)
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Surface Defects-Scaling
• Local flaking or peeling away of the near-surface portion of concrete or mortar.
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Surface Defects-Spalling
• A fragment, usually in the shape of a flake, detached from a larger mass by a blow, by the action of weather by pressure or by
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weather, by pressure, or by expansion within the larger mass.
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Surface Defects-Bugholes
• Small regular or irregular cavities, usually not exceeding 15 mm in diameter, resulting from entrapment of air bubbles in the surface of formed concrete during
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surface of formed concrete during placement and compaction.
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Surface Defects-Cold Joint
• Visible lines on the surfaces of formed concrete indicating the presence of joints where one layer of concrete had hardened before
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concrete had hardened before subsequent concrete was placed.
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Surface Defects-Discoloration
• A departure of color from that which is normal or desired.
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Surface Defects-Staining
• Spotted or mottled light or dark blotches.
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Surface Defects-Efflorescence
• Deposit, usually white, formed on a surface, the substance having emerged in solution from within concrete or masonry and
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concrete or masonry and subsequently having been precipitated by evaporation.
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Surface (Internal?) Defects-Honeycombing
• Voids left in concrete due to failure of the mortar to effectively fill the spaces among course aggregate
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p g gg gparticles.
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• When troubleshooting concrete problems it is important to relate the symptom to causes of distress and deterioration
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distress and deterioration.
Questions and Further Information
Michelle L. Wilson, FACIMichelle L. Wilson, FACI
Director, Education
Portland Cement Association
t ?93 93www.conexpoconagg.com
www.cement.org
847.972.9034 phone
www.cement.org
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