Plastic Shrinkage Cracking Evaluation and Repair ACI 224

Plastic Shrinkage Cracking • Evaluation and Repair

ACI 224. 1 R-93 Causes, Evaluation and Repair of Cracks in Concrete Structures

ACI 224. 1 R-93 Chapter 1 – Causes & Control Chapter 2 – Evaluation Chapter 3 – Methods of Crack Repair

ACI 224. 1 R-93 Typical Plastic Shrinkage Cracking. (Price 1982)

ACI 224. 1 R-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 EB 001 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 EB 001 Design & Control of concrete Mixtures Disclaimer “However, the cracking may reoccur unless the causes are corrected”

ACI 305 R Hot Weather Concreting Section 4. 3. 4 In relatively massive placements, revibration before floating can sometimes close this type of cracking.

PCA EB 001 Fig. 11 -11.

ACI 224. 1 R-93 Typical Plastic Shrinkage Cracking. (Price 1982)

Much more serious cracking!

PCA EB 001 Fig. 11 -13.

ACI 224. 1 R-93 Chapter 2 Evaluation of Cracks in Hardened Concrete

ACI 224. 1 R-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. 1 R-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. 1 R-93 Groove cut wlth saw or chipping tools 7 Fig. 3. 1 -Repair of crack by muting and sealing (Johnson 1965)

ACI 224. 1 R-93 • If large enough, treat as an induced crack • Sawcut and fill

ACI 224. 1 R-93 Chapter 3 Crack Closed No Bond Breaker With Bond Breaker Fig. 3. 2 -Effect of bond breaker See ACI 504 R 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