Plastic Shrinkage
Cracking
•Evaluation and Repair
ACI 224.1R-93
Causes, Evaluation and Repair of
Cracks in Concrete Structures
ACI 224.1R-93
Chapter 1 – Causes & Control
Chapter 2 – Evaluation
Chapter 3 – Methods of Crack Repair
ACI 224.1R-93
Typical Plastic Shrinkage Cracking. (Price 1982)
ACI 224.1R-93
Chapter 1, Section 1.2
“Cracking of Plastic Concrete”
Discusses Causes and Prevention ONLY!
ACI CP-10
-Certification for Concrete Technicians
and Flatwork Finishers-
Discusses Causes and Prevention
ONLY!
NRMCA
Concrete in Practice
“If plastic shrinkage cracks should
appear during final finishing, the
finisher may be able to close them by
refinishing.”
NRMCA
Concrete in Practice
Disclaimer
“However, when this occurs, precautions,
as described above, should be taken to
avoid further cracking”
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”
PCA EB001
Design & Control of concrete Mixtures
Disclaimer
“However, the cracking may reoccur
unless the causes are corrected”
ACI 305R
Hot Weather Concreting
Section 4.3.4
In relatively massive placements,
revibration before floating can sometimes
close this type of cracking.
PCA EB001
Fig. 11-11.
ACI 224.1R-93
Typical Plastic Shrinkage Cracking. (Price 1982)
Much more serious cracking!
PCA EB001
Fig. 11-13.
ACI 224.1R-93
Chapter 2
Evaluation of
Cracks in
Hardened
Concrete
ACI 224.1R-93
Chapter 2
1. Identify Location and
Extent of Cracking
Typical Plastic Shrinkage Cracking
Much more serious cracking!
ACI 224
Chapter 2
2. Determine functionality
- Movement
- Structural
- Maintenance issue
- Cosmetic
ACI 224
Chapter 2
2.2 Map the cracks!
ACI 224.1R-93
• Fig. 2.1-Comparator
for measuring crack
widths Courtesy of
Edmound Scientific
Co.
Crack Comparitor Card
ACI 224
Chapter 3
Methods of Crack Repair
in Hardened Concrete
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
ACI 503.7-07
• Specification for Crack Repair by Epoxy
Injection
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
ACI 224.1R-93
Groove cut wlth saw
or chipping tools7
Fig. 3.1-Repair of crack by muting and sealing
(Johnson 1965)
ACI 224.1R-93
• If large enough, treat as an induced crack
• Sawcut and fill
ACI 224.1R-93
Chapter 3
Crack Closed
No Bond Breaker
With Bond Breaker
Fig. 3.2-Effect of bond breaker
See ACI 504R Re. Aspect Ratio
ACI 224
Chapter 3
3.11 Polymer Impregnation
•
Methyl Methacrylate
–Flood surfaces
–Heat to polymerize, or
–Use a catalyst to polymerize
ACI 224
Chapter 3
3.12.1 Surface Treatments
- Low viscosity penetrating resins
- Urethanes
- Epoxies
- Polyesters
- Acrylics
ACI 224
Chapter 3
3.12.2 Overlays
- Polymer modified PCC
- Styrene Butadiene
- Bridge decks
- Acrylic latex
- Interior toppings
- Pool decks