Continuous Strain in Concrete - Creep

Creep is the continuous strain that occurs in concrete when it is subjected to external loads over a long period of time. It is a time-dependent phenomenon and can cause significant deformation and cracking in the concrete structure if not accounted for during the design and construction process.

Explanation:

1. Definition of Creep:
Creep is the phenomenon of time-dependent deformation in concrete under constant stress. It refers to the gradual increase in strain that occurs in concrete over a period of time when it is subjected to external loads. Creep is a result of the viscoelastic properties of concrete, which causes it to deform over time even under a constant load.

2. Causes of Creep:
Creep in concrete is primarily caused by the following factors:

- Chemical reactions: The chemical reactions that occur during the hydration process of concrete can lead to the development of creep. These reactions cause the concrete to undergo internal changes, leading to creep deformation.

- Moisture content: The moisture content of the concrete can also affect its creep behavior. Higher moisture content tends to increase the creep strain in the concrete.

- Temperature: Temperature variations can significantly influence the creep behavior of concrete. Higher temperatures generally result in increased creep deformation.

3. Effects of Creep:
Creep in concrete can have several detrimental effects on the structure, including:

- Excessive deformation: Creep can cause significant long-term deformation in concrete structures, leading to cracks and other structural issues.

- Loss of prestress: In prestressed concrete structures, creep can cause a loss of the initial prestressing force, reducing the structural capacity and performance.

- Redistribution of stresses: The continuous deformation caused by creep can lead to the redistribution of stresses, affecting the overall structural stability.

4. Prevention and Mitigation:
To prevent or mitigate the effects of creep in concrete structures, several measures can be taken, including:

- Proper mix design: Choosing the right mix design with suitable materials can help minimize the creep deformation in concrete.

- Control of moisture content: Proper curing and moisture control techniques can help reduce the creep strain in concrete.

- Temperature control: By controlling the temperature during the curing process and in service conditions, the effects of creep can be minimized.

- Reinforcement and prestressing: The use of reinforcement and prestressing techniques can help counteract the effects of creep and provide additional strength to the structure.

In conclusion, creep is the continuous strain that occurs in concrete when it is subjected to external loads over time. It is a time-dependent phenomenon that can cause deformation and cracking in concrete structures. Understanding and accounting for creep is crucial in the design and construction process to ensure the long-term performance and durability of concrete structures.