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Volumetric Change of Repair Materials

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

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Volumetric Change of Repair Materials

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  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 >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

  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 > 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. Thank you Questions ?

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