What is the creep of concrete ?
When a concrete structure is subjected to any load then it deforms instantly. This is known as instantaneous deformation which is temporary in nature. But, what will happen if we provide a load for a long period of time? It will be deformed permanently.
If the load is given to any concrete structure for some period of time without increasing load, then there will permanent deformation in the concrete. So, this strain which depends upon the time is known as creep.
Points which describe creep in concrete
- Concrete creep is defined as the deformation of structure under sustained load
- Basically, long-term pressure or stress on concrete can change the shape of the structure
- This deformation usually occurs in the direction the force is being applied
- Creep does not necessarily cause concrete to fail or break apart
- When a load is applied to concrete, it experiences an instantaneous elastic strain which develops into creep strain if the load is sustained.
- Creep is a factor for which concrete structures are designed
- In a creep failure, the material fails at stress less than the maximum stress
- Creep is a permanent deformation
- Creep mainly depends upon the temperature to which material is subjected and the time up to which it is stressed
A creep curve is a plotting between the total creep or strain and the time for the entire duration of test.
AB – Elastic deformations
BC – Primary creep
CD – Secondary creep
DE – Tertiary creep
BC – Rapid strain rate at beginning but it slow down due to strain hardening.
CD – Deformation continues at a constant rate and work hardening rate balanced.
DE – Strain rate increases rapidly, which results in necking and finally fracture of metal.
Factors affecting Creep
- Mix proportions
- Age of concrete
Types of Creep
- Primary Creep
- Secondary Creep
- Tertiary Creep
1) Primary Creep
- Due to dislocation movement
- Creep rate decreases with time
- Effect of work hardening is more than the recovery process
2) Secondary creep
- Rates of work hardening and recovery are equal
- Steady creep rate
- Plastic in character (depends on temperature)
3) Tertiary creep
- Creep increases until failure/ fracture
- Necking occurs
- Time shortens at an elevated temperature.
How Creep in concrete Occurred?
- The water-cement ratio is high
- Cement content is high
- Aggregate content is low
- Air entrained is high
- Temperature is high (early loss of water)
- Humidity is low
- Loading occurred for a long time
- Application of load at an early age
How Creep can be reduced?
- Using the high-grade concrete
- By adding Reinforcement
- By delaying application of finishing, portion wall, etc.
I hope this article on “What is creep in concrete Structure? How creep occurs?” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Ranjeet Sahani