Volumetric Change of Repair
Materials
Low Shrinkage Materials
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.
Effects of Drying Shrinkage on Repair
Materials
Bond With
Substrate
Loss
Local
Carrying
Capacity
Corrosion of
Embedded
Reinforcing
Steel
Structural
Repair
Material
Needs
Durability
to Service
Conditions
Cracking
Spalling
Delamination
Dimensional
Stability
Drying Shrinkage
Effects of Drying Shrinkage on Repair
Materials
Bond With
Substrate
Loss
Local
Carrying
Capacity
Corrosion of
Embedded
Reinforcing
Steel
Structural
Repair
Material
Needs
Durability
to Service
Conditions
Cracking
Spalling
Delamination
Dimensional
Stability
Drying Shrinkage
Shrinkage Mechanism
• Thermal Coefficient of Expansion (a)
an ≠ a o
Shear bond is stressed
• Modulus of Elasticity (E)
En ≠ Eo
- Shear bond is stressed
- Brittle material may
become over stressed
• Drying Shrinkage (S)
Sn >0
- Shear bond is stressed
- Loads carried by repair are reduced
- Tension in repair material
• Creep (C)
Cn >0
- Shear bond is stressed
- Loads carried by repair are reduced
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 > Tensile strength
Crack
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
• 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
Drying Shrinkage
Reduction
Low Shrinkage Materials
Optimum Drying Shrinkage between
0.00% To 0.05%
• Proper Concrete Mixes
• Shrinkage-Compensating Concrete
Proper Concrete Mixes
•
•
•
•
•
•
•
Max. aggregate content
Clean & sound aggregate
Large Aggregate
Low water content
Min. Cement content
Proper wet curing
Proper placement
Aggregate/Cement
Water/Cement
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
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)
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
Conclusion
• Two methods of shrinkage reduction were
discussed:
– Proper Concrete Mixes
– Shrinkage-Compensating Concrete
Thank you
QUESTIONS ?