Creep of concrete defined as the deformation of a structure under constant load. Basically, this deformation is due to prolonged pressure or stress on the concrete usually occurs in the direction the force being applied, like a concrete column getting more compressed, or a beam bending.
The stress-strain of concrete is not a straight line but a curve and the strain will go on increasing after a certain value without an appreciable increase in stress.
The creep of concrete can be defined as the time-dependent portion of the stress that occurs as a result of stress.
Here we will learn about Creep of concrete, factors affecting & effects of creep in concrete.
Introduction to creep of concrete:
Creep is the time-dependent deformation of concrete below permanent load (self-weight), PT forces, and permanent displacement.
In RCC columns creep property of concrete is useful the gradual transfer of stress from concrete to steel.
In a mass concrete structure such as a dam, internal and surface temperature conditions, creeps cause cracks in the interior of the dams.
How to prevent creep of concrete:
- Use higher metals.
- Use materials with greater grain size.
- By using alloy.
- Use intelligent design to reduce the possible factors of creep.
Factors affecting creep of concrete:
Quality of aggregate:
Good quality aggregate retards the creep.
Grading, size and maximum size do not greatly affect the creeps of aggregate, but indirectly they affect creeps from aggregate content in concrete.
Concrete Mix Ratio:
The quantity and quality of paste material is the single most important parameter affecting creep.
A poor paste structure will increase excessive creeps and with a rise in water-cement ratio, thus, creeps are inversely proportional to the strength of the concrete.
All other factors that are affecting the water / cement ratio are also affects the creep of concrete.
The type of cement effect also affects the strength of the concrete at the time of application of the load.
The fineness of cement impacts strength development at an early age, thus impacts creep.
The finer the cement the greater the need for gypsum, as the regrinding of cement in the laboratory without the inclusion of gypsum produces an improperly retarded cement, which exhibits high creep.
The rate of creep increases with temperature for a 1:7 mix and o.6 w/c ratio.
It is approximately 3.5 times higher than at 20o°C.
Between 700C and 960C it drops off to 1.7 times tan at 210 °C.
As far as low temperatures are concerned, freezing produces a high initial rate of creep, but it quickly falls to zero.
At temperatures between 3.00°C and 3oo°C, creep of concrete is about half of the creep at 2.00°C.
There is a direct ratio between creep and applied stress.
There is no lower limit of proportionality because the solid stresses creep even under very low stresses.
The higher the stress the higher the creep of concrete.
Age at loading:
The age at which a solid member is loaded will have a major impact on the creep magnitude.
While underweight a young prison is not such a strong imposter.
The moisture of concrete differs at different ages which also affects the amount of creeps.
It is influenced by humidity and drying conditions of the atmosphere.
Also read: Durability of Concrete, Curing of Concrete & Segregation of Concrete
effects due to creep of concrete:
- In reinforced concrete beams, creep will increase deflection over time and it may be an essential consideration in the design.
- In the eccentrically filled columns, creep increases the deflection and may buckle.
- In the case of statistically indeterminate structures, column and beam junction creep can relieve stress concentration induced by stress, temperature changes, or movement of supports.
- The creeps property of concrete can be useful in all concrete constructions to reduce internal stresses on account of non-uniform load or restrained shrinkage.
- In massive concrete structures,i.e. dams, creeps are dangerous and should cause cracks within the interior of the dams, as a result of differential concrete conditions on the interior surface.
- Subsequently, careful steps should be taken so that the rise in temperature does not occur within the interior of the massive solid structure.
- Loss of prestressing is due to the creep of concrete in the prestressed concrete structure.
- In reinforced concrete, it helps to move the steak for reinforcement thereby reduces the possibility of failure due to stress concentration.
Also read: Compaction of Concrete, Workability of Concrete & Durability of Concrete
Creep of concrete is harmful in case of prestressed, there is loss of prestressing, it is a roughly linear function of stress at 30 to 40% of its strength.