Post on 10-Apr-2018
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Plastic Shrinkage
Cracking
Evaluation and Repair
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ACI 224.1R-93
Causes, Evaluation and Repair of Cracks in Concrete Structures
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ACI 224.1R-93
Chapter 1 ± Causes & Control
Chapter 2 ± Evaluation
Chapter 3 ± Methods of Crack Repair
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ACI 224.1R-93
Typical Plastic Shrinkage Cracking. (Price 1982)
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ACI 224.1R-93Chapter 1, Section 1.2
³Cracking of Plastic Concrete´
Discusses Causes and Prevention ONLY!
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ACI CP-10
-Certification for Concrete Technicians
and Flatwork Finishers-
Discusses Causes and Prevention
ONLY!
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NRMC A
Concrete in Practice
³If plastic shrinkage cracks shouldappear during final finishing, the
finisher may be able to close them by
refinishing.´
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NRMC A
Concrete in Practice
Disclaimer
³However, when this occurs, precautions,
as described above, should be taken to
avoid further cracking´
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PCA EB001Design & Control of concrete Mixtures
³If plastic shrinkage cracks should
appear during finishing, striking each
side of the crack with a float andrefinishing can close the crack´
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PCA EB001
Design & Control of concrete Mixtures
Disclaimer
³However, the cracking may reoccur
unless the causes are corrected´
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ACI 305R
Hot Weather Concreting
Section 4.3.4
In relatively massive placements,
revibration before floating can sometimesclose this type of cracking.
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PCA EB001
Fig. 11-11.
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ACI 224.1R-93
Typical Plastic Shrinkage Cracking. (Price 1982)
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Much more serious cracking!
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Fig. 11-13.
PCA EB001
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ACI 224.1R-93
Chapter 2
E valuation of Cracks in
Hardened Concrete
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ACI 224.1R-93
Chapter 2
1. I dentify Location and Ex tent of Cracking
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Typical Plastic Shrinkage Cracking
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Much more serious cracking!
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ACI 224
Chapter 2
2 . Determine functionality - Movement
- Structural
- Maintenance issue
- Cosmetic
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ACI 224
Chapter 2
2 .2 Map the cracks!
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ACI 224.1R-93
F ig. 2.1-Comparator for measuring crack
widths Courtesy of
Edmound Scientific
Co.
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Crack Comparitor Card
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ACI 224
Chapter 3
M ethods of Crack Repair
in Hardened Concrete
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ACI 224
Chapter 3
3.2 Epoxy injection
- Bonds cracks as narrow as 0.002 in.
- Provides fixity
- Original cause must be addressed
- Typically deferred to specialist
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ACI 503.7-07
Specification for Crack Repair by Epoxy Injection
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ACI 224
Chapter 3
3.3 Routing and sealing
- Clean cracks
- Enlarge crack along exposed face
- Fill and seal with suitable joint sealant
- Not suitable for structural repairs
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Groove cut wlth saw
or chipping tools7
ACI 224.1R-93
F ig . 3.1- Repair of crack by muting and sealing
(Johnson 1965)
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ACI 224.1R-93
If large enough, treat as an induced crack
Sawcut and fill
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Crack Closed No Bond Breaker With Bond Breaker
F ig . 3.2 -E ffect of bond breaker
ACI 224.1R-93
Chapter 3
See ACI 504R Re. Aspect Ratio
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ACI 224
Chapter 3
3.11 Polymer Impregnation
Methyl Methacr ylate ±Flood surfaces
±Heat to polymerize, or
±Use a catalyst to polymerize
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ACI 224
Chapter 3
3.12.1 Surface Treatments
- Low viscosity penetrating resins
- Urethanes
- Epoxies
- Polyesters- Acr ylics
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ACI 224
Chapter 3
3.12.2 Overlays
- Polymer modified PCC
- Styrene Butadiene
- Bridge decks
- Acr ylic latex- Interior toppings
- Pool decks