TYPES OF CONCRETE SHRINKAGE , WHAT IS SHRINKAGE OF CONCRETE

Types of Concrete Shrinkage | What Is Shrinkage of Concrete

Concrete is a widely used construction material known for its durability and strength. However, it is not immune to a common issue known as concrete shrinkage. Shrinkage occurs due to various factors and can lead to cracks and other structural problems if not managed properly. In this article, we will explore the different types of concrete shrinkage and how they affect construction projects.

What Is Shrinkage of Concrete?

Concrete shrinkage is the reduction in the volume of concrete as it dries and hardens. This volume change is mainly caused by the loss of water during the curing process and the settling of solid particles. Shrinkage can occur in both fresh (plastic) and hardened (set) concrete. Managing shrinkage is essential to maintain the integrity and longevity of concrete structures.

Types of Concrete Shrinkage

There are several types of concrete shrinkage, each with its own causes and consequences. Understanding these types is crucial for preventing potential issues in construction projects.

1. Plastic Shrinkage

Cause: Plastic shrinkage occurs during the initial setting and curing of concrete. It is primarily caused by the rapid evaporation of water from the surface of fresh concrete before it can fully set.

Consequences: Plastic shrinkage can lead to surface cracks and reduced durability if not addressed promptly. To mitigate this, construction workers often use curing compounds or cover the concrete with wet burlap or plastic sheets to slow down the evaporation rate.

2. Drying Shrinkage

Cause: Drying shrinkage occurs as concrete hardens and dries over time. It is primarily due to the continued loss of moisture from the concrete matrix.

Consequences: Drying shrinkage is a common type of concrete shrinkage and can lead to cracks and structural problems if not properly controlled. It is often managed by adding internal or external curing methods such as curing compounds or moisture-retaining covers.

3. Autogenous Shrinkage

Cause: Autogenous shrinkage is an inherent property of concrete caused by chemical reactions within the material, particularly during hydration. It occurs even without external moisture loss.

Consequences: While autogenous shrinkage is less noticeable than other types, it can still contribute to cracks and reduced durability in concrete structures. Proper mix design and curing methods can help minimize its impact.

4. Carbonation Shrinkage

Cause: Carbonation shrinkage is a result of carbon dioxide (CO2) penetrating the concrete surface and reacting with calcium hydroxide to form calcium carbonate, reducing the volume of the concrete.

Consequences: Over time, carbonation shrinkage can weaken the concrete and potentially compromise its structural integrity. Adequate protection measures, such as surface coatings or proper curing, can slow down the carbonation process.

5. Chemical Shrinkage

Cause: Chemical shrinkage occurs due to chemical reactions within the concrete mix, such as the formation of ettringite or thaumasite. These reactions lead to volume changes.

Consequences: Chemical shrinkage can be problematic in certain circumstances and may require adjustments to the concrete mix design to prevent excessive volume changes and subsequent cracking.

Managing Concrete Shrinkage

To effectively manage concrete shrinkage and reduce its negative impact on construction projects, several strategies can be employed:

1. Proper Mix Design: Engineers can adjust the concrete mix proportions to minimize shrinkage potential.
2. Curing Methods: Employing curing compounds, wet curing, or covering the concrete with wet burlap or plastic sheets can help maintain moisture levels, reducing shrinkage.
3. Use of Shrinkage-Reducing Admixtures: These admixtures can be added to the concrete mix to reduce shrinkage cracking.
4. Control Joints: Incorporating control joints in concrete slabs and structures can allow for controlled cracking, preventing random and uncontrolled cracks.
5. Monitoring and Maintenance: Regular inspection and maintenance of concrete structures can identify early signs of shrinkage-related issues and prevent further damage.

In conclusion, understanding the various types of concrete shrinkage and implementing appropriate measures to mitigate their effects are essential for the long-term durability and performance of concrete structures. By proactively managing shrinkage, construction professionals can ensure that their projects remain strong and resilient over time.