Shrinkage of Hardened Concrete

Shrinkage of Hardened Concrete

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Key Points and Concepts

1. Definition of Shrinkage

   • Shrinkage refers to the reduction in volume of hardened concrete after it sets and hardens.

2. Types of Shrinkage

   • Plastic Shrinkage: Occurs while concrete is still in its plastic state.
   • Drying Shrinkage: Takes place after the concrete has hardened and is exposed to the air.
   • Autogenous Shrinkage: Results from the internal consumption of water during the hydration process, primarily in high-strength concrete with low water-cement ratios.
   • Carbonation Shrinkage: Due to the reaction of carbon dioxide from the atmosphere with hydrated cement products.

3. Factors Influencing Shrinkage

   • Water-Cement Ratio: Higher ratios often lead to more shrinkage.
   • Aggregate Properties: Size, grading, and type of aggregates can impact shrinkage.
   • Curing Conditions: Proper curing reduces shrinkage; improper curing increases the potential for shrinkage.
   • Environmental Conditions: Temperature, humidity, and wind speed can affect the rate and extent of shrinkage.

4. Effects of Shrinkage

   • Cracking: Leads to structural weakness and aesthetic imperfections.
   • Reduced Durability: May accelerate deterioration processes such as freeze-thaw cycles or chemical attacks.
   • Warping and Curling: Result from differential shrinkage within the concrete slab.

5. Measurement and Testing

   • Length Change Measurement: Linear measurement techniques to monitor the dimensional changes.
   • Shrinkage Strain Measurement: Using strain gauges and other instruments to quantify shrinkage.

6. Mitigation Strategies

   • Appropriate Mix Design: Adjusting the proportions of materials to minimize shrinkage.
   • Proper Curing Techniques: Ensuring adequate moisture retention and temperature control.
   • Use of Shrinkage-Reducing Admixtures: Chemical admixtures specifically designed to reduce shrinkage.
   • Installation of Joints: Control and expansion joints to manage shrinkage-induced cracks.

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These study notes encapsulate the essential aspects of the shrinkage of hardened concrete, providing a foundational understanding of its causes, effects, and mitigation strategies.