plastic shrinkage cracking evaluation and repair
TRANSCRIPT
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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-93 Chapter 1, Section 1.2
“Cracking 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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NRMCAConcrete in Practice
“If plastic shrinkage cracks should appear during final finishing, the finisher may be able to close them by refinishing.”
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NRMCAConcrete in Practice
Disclaimer
“However, when this occurs, precautions, as described above, should be taken to avoid further cracking”
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PCA EB001 Design & Control of concrete Mixtures
“If plastic shrinkage cracks should appear during finishing, striking each side of the crack with a float and refinishing can close the crack”
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PCA EB001 Design & Control of concrete Mixtures
Disclaimer
“However, 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 sometimes close 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-93Chapter 2
Evaluation of Cracks in Hardened Concrete
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ACI 224.1R-93 Chapter 2
1. Identify Location and Extent 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
• Fig. 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
Methods of Crack Repairin 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 sawor chipping tools7
ACI 224.1R-93
Fig. 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
Fig. 3.2-Effect 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 Methacrylate–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 - Acrylics
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ACI 224 Chapter 3
3.12.2 Overlays - Polymer modified PCC - Styrene Butadiene
- Bridge decks - Acrylic latex
- Interior toppings- Pool decks