Volumetric Change of Repair Materials

1
Volumetric Change of Repair Materials

• Low Shrinkage Materials

2
Shrinkage of Concrete

• Drying Shrinkage
• Due to the Evaporation of pore water which is
  about 50 of concrete volume.
• It takes place in the first 30 days.
• Plastic Shrinkage
• Due to high evaporation rate if it exceeds the
  rate of bleeding.
• Takes Place after the free settlement period.

3
Effects of Drying Shrinkage on Repair Materials
Cracking Spalling Delamination
Loss
Corrosion of Embedded Reinforcing Steel
Drying Shrinkage
4
Effects of Drying Shrinkage on Repair Materials
Cracking Spalling Delamination
Loss
Corrosion of Embedded Reinforcing Steel
Drying Shrinkage
5
Shrinkage Mechanism

• Thermal Coefficient of Expansion (a)
• an ? ao Shear bond is stressed
  
• Modulus of Elasticity (E)
• En ? Eo - Shear bond is stressed
• - Brittle material may
• become over stressed

6

• Drying Shrinkage (S)
• Sn gt0 - Shear bond is stressed
• - Loads carried by repair are reduced
• - Tension in repair material
• Creep (C)
• Cn gt0 - Shear bond is stressed
• - Loads carried by repair are reduced

7
Shrinkage Process

• Contract in volume in 1st 30 days
• Bond with substrate do not allow repair material
  to shrink
• Accumulate internal tensile stress
• Tensile strength increases
• Net tensile stress
• Tensile creep effect Shrinkage tensile
  stress
• Net tensile gt Tensile strength Crack

8
Volume stability Evaluation

• ASTM C 157/C 157M, C 596, and C 806
• involve monitoring the length of test specimens
  over time under different curing conditions
• ASTM C 157/C 157M, as modified by ICRI
  (2003)ICRI (2003)
• makes recommendations for reporting properties
  appropriate for cement-based repair materials

9

• ASTM C 827
• involves monitoring the height of cylindrical
  test specimens until the specimens harden
• ASTM C 1581
• Involves measuring the strains and observing
  cracking in donut-shaped specimens with inner
  steel rings

10
Drying Shrinkage Reduction
11
Low Shrinkage Materials

• Optimum Drying Shrinkage between
• 0.00 To 0.05
• Proper Concrete Mixes
• Shrinkage-Compensating Concrete

12
Proper Concrete Mixes

• Max. aggregate content
• Clean sound aggregate
• Large Aggregate
• Low water content
• Min. Cement content
• Proper wet curing
• Proper placement

13
Low Shrinkage
Aggregate/Cement
Water/Cement
14
Shrinkage-Compensating Concrete

• Expansive cement concrete is used to minimize
  cracking caused by drying shrinkage
• Type K, Type M, or Type S expansive Portland
  cements are used to produce Shrinkage
  compensating concrete
• Increase in volume after setting and during
  hardening is observed

15
Influence of Shrinkage Reducing Admixtures on
Shrinkage

• SRA (typically 2 - 5 by weight of water)
• Results in a substantial reduction in overall
  shrinkage
• Reduction in drying shrinkage independent of the
  w/c (assuming constant aggregate volume and type)

16
Limitations

• Proper amount of internal reinforcement must be
  provided
• Early curing and proper curing are very important
• Some shrinkage-compensating concrete mixtures
  will show early stiffening and a loss of
  workability
• Mixture water should not exceed maximum w/c

17
Conclusion

• Two methods of shrinkage reduction were
  discussed
• Proper Concrete Mixes
• Shrinkage-Compensating Concrete

18
Questions ?

• Thank you