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!

NRMCAConcrete in Practice

“If plastic shrinkage cracks should appear during final finishing, the finisher may be able to close them by refinishing.”

NRMCAConcrete 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!

Fig. 11-13.

PCA EB001

ACI 224.1R-93Chapter 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 Repairin 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

Groove cut wlth sawor chipping tools7

ACI 224.1R-93

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

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

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