The article aims to answer the question “What is creep in concrete?”. It will also discuss the reasons and factors affecting the creep in concrete.
Read on to know more:
What is creep in concrete?
the “ time-dependent” element of the strain caused by stress is known as creep. Long-term stress can also be regarded as an increase in stress. Elastic and inelastic deformations occur in the structure when concrete is loaded.
According to Hooke’s Law, the concrete deforms as soon as it is subjected to a particular load. As the concrete is subjected to a continuous load, inelastic deformations grow in frequency and severity.
Creep, a type of inelastic deformation, increases at a decreasing rate as the loading period progresses Concrete’s creep and shrinkage are two physical characteristics.
C-S-H calcium silicate hydrates (C-S-H) in Portland cement paste (the binder of mineral aggregates) cause concrete to creep, unlike metals and polymers, which do not. It happens at all stress levels and is linearly dependent on the stress within the service stress range if the pore water content is constant.
When compared to polymers and metals that age over months or years due to polymer or metal creep, the C-S-H shows multi-year aging due to long-term relaxation of self-equilibrated micro-stresses in its nanoporous microstructure. Concrete does not creep when completely dried, however, this is very impossible to achieve without causing severe cracks.
What causes creep in concrete?
Continue reading to understand what causes creep in concrete.
The term “creep” is used to describe the distortion of a structure under long-term stress. Pressure or tension on concrete can cause it to change its shape over time. It is common for defamation to occur in the direction of the force application.
Like the compression of a concrete column or the bending of a beam. The failure or disintegration of concrete is not always caused by creep. When designing concrete structures, creep is taken into consideration.
Aggregates move relatively little when they are under the influence of a person. The creep is actually caused by the paste. The aggregate, on the other hand, has a restraint impact on the amplitude of creep that contributes to concrete creep.
Creasing paste is prevented from moving underweight by aggregate that does not creep. The restraining impact is amplified and the quantity of creep is reduced in proportion to the strength of the aggregate.
When it comes to creeping, one of the most critical determinants is the aggregate’s modulus of elasticity. One of the most crucial aspects of creep is the amount and quality of paste in the mix. Cryogenic creep is greater for a lower-quality paste structure.
It can thus be claimed that the creep rate increases as the water/cement ratio increases. To put it another way, the strength of concrete is inversely related to creep. Creep is affected by all other variables that affect the water/cement ratio.
As the concrete member is loaded, the age at which it is will have a significant impact on the amount of creep seen. The fact that gel gets better with age lends credence to this theory. This type of gel is less likely to creep, while a younger gel that isn’t as strong tends to creep more.
Since concrete’s moisture content fluctuates throughout its lifespan, what has been stated above isn’t entirely true.
What factors affect the creep in concrete?
The factors affecting the creep in concrete are:
- Concrete strength
- Incomplete or improper curing
- Type of cement
- Entrained air
The rate at which concrete creeps is a function of time. “Sustained tension” causes concrete to deform in an “inelastic” way. If you crush concrete from both sides, the length of the cylinder will alter in two ways: one elastic and one inelastic.
When the load is removed, the member’s length will return to its pre-load length, resulting in an elastic change (shortening). There is a long period of time that creep shortening will occur, say 5 years, but the member will be permanently deformed and cannot return to its original length (but only a part of total shortening happened due to elastic shortening).
Creep is no longer only dependent on stress. Additionally, the amount of stress, time since the first loading (in the case of hardened concrete), total loading time, relative humidity during the early days of concrete, and other factors all play a role.
Other factors include quality of concrete, cement & aggregate types used, curing conditions, and so on.
What is the difference between creep and shrinkage in concrete?
The article has explained below the difference between creep and shrinkage.
Compressive loading causes instantaneous deformation of concrete. Instantaneous strain is the technical term for this kind of rapid deformation. For example, if the load is held for a long period of time, the concrete deforms even though there is no extra load.
Creep is the name given to this time-dependent strain. Drying shrinkage (commonly referred to as “shrinking”) is the diminution in volume caused by the evaporation of moisture from hardened concrete. Creep and shrinkage have many parallels and differences.
To begin, the hydrated cement paste is the same source of adsorbed moisture that causes both effects. The loss in shrinkage is caused by a change in the relative humidity between the concrete and the surrounding environment, whereas the loss in creep is caused by a persistent application of force.
It’s also worth noting that the strain-time curves of both phenomena are remarkably similar. Creep and shrinkage are both influenced by the same reasons. Greater cement concentration, higher water content, lower aggregate content, lower relative humidity, high temperature, small thickness of the member, etc. both increase
In contrast, shrinkage is not influenced by the loading circumstances, unlike creep In the preceding graphs, you can observe how much of the shrinkage strains can be recovered. When concrete shrinkage is restricted by structural components, tensile tensions arise, resulting in cracking.
It’s possible to reduce the impacts of shrinkage and creep by reducing the water content in the concrete mix, which is the principal culprit. Creep and shrinkage are two distinct phenomena.
Conclusion
Creep in concrete can be described as the long-term deformation of concrete under a continuous load that is elastic and long-lasting. Most concrete structures distort when subjected to long-term pressure.
This deformation tends to occur in the same direction as the applied load. The strain immediately decreases as the continuous load is withdrawn. The elastic strain at the given age is equal to the reduced strain. That fast recovery is followed by a steady decrease in the total strain suffered by the concrete known as creep recovery.
Frequently asked questions (FAQS): What is creep in concrete?
What is creep in concrete?
“The time-dependent” element of the strain caused by stress is known as creep. Long-term stress can also be regarded as an increase in stress. Elastic and inelastic deformations occur in the structure when concrete is loaded.
According to Hooke’s Law, the concrete deforms as soon as it is subjected to a particular load. As the concrete is subjected to a continuous load, inelastic deformations grow in frequency and severity.
What is the difference between creep and shrinkage in concrete?
Compressive loading causes instantaneous deformation of concrete. Instantaneous strain is the technical term for this kind of rapid deformation. For example, if the load is held for a long period of time, the concrete deforms even though there is no extra load.
Creep is the name given to this time-dependent strain. Drying shrinkage (commonly referred to as “shrinking”) is the diminution in volume caused by the evaporation of moisture from hardened concrete. Creep and shrinkage have many parallels and differences.
What causes creep in concrete?
The term “creep” is used to describe the distortion of a structure under long-term stress. Pressure or tension on concrete can cause it to change its shape over time. It is common for defamation to occur in the direction of the force application.
Like the compression of a concrete column or the bending of a beam. The failure or disintegration of concrete is not always caused by creep. When designing concrete structures, creep is taken into consideration.
Bibliography
What is the difference between Creep and Shrinkage?. Read Civil. Retrieved from: https://readcivil.com/what-is-the-difference-between-creep-and-shrinkage/#:~:text=In%20shrinkage%2C%20the%20loss%20is,effect%20creep%20also%20effects%20shrinkage.
