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A short class with Sarah and her students. The other ways are under More.
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Today we're going to discuss creep in concrete. Can anyone tell me what creep means in this context?
I think it means the concrete bends over time under constant stress?
That's partly correct! Creep is the gradual deformation of concrete under constant stress over a long duration. It doesn't recover like elastic deformation. Creep occurs because concrete has a viscoelastic nature.
So, does that mean it keeps deforming as long as the stress is applied?
Exactly! This time-dependent aspect of creep is crucial for understanding how concrete will behave in real structures.
Now, let’s examine the mechanisms of creep. What do you think causes this deformation over time?
Is it related to how water moves in the concrete?
Correct! Creep involves moisture movement in gel pores, viscous flow in the cement paste, and microcracking. All these factors affect how concrete behaves under stress.
What about the structure of the concrete? Does that play a role?
Yes, internal structural rearrangements in the C-S-H gel also contribute significantly to creep. This complexity makes predicting creep challenging.
Let’s differentiate the types of creep. Who can explain what basic creep is?
Isn't basic creep the one that happens in sealed conditions?
Exactly! Basic creep occurs without moisture exchange. Now what about drying creep?
That happens when the concrete loses moisture while under load, right?
Yes! And let's not forget autogenous creep, which occurs even without moisture loss. It’s especially significant in high-strength concrete.
Now that we know the types of creep, let’s talk about the factors affecting it. What can you think influences creep?
I think the water-cement ratio must matter. More water means more porosity, right?
Great point! Higher water-cement ratios lead to more creep. The age at loading also plays a significant role; younger concrete is more susceptible to creep.
And temperature can affect it, too, right?
Exactly! Higher temperatures accelerate the creep rate. You’re all grasping these concepts well!
Let’s wrap up by discussing how we measure creep. What do you think we need for a creep test?
Do we use special equipment? Like for measuring strain?
Exactly! We use dial gauges or LVDTs to record the strain during the test, along with a creep frame. The Creep Coefficient is also a vital parameter to understand!
What does it represent?
The Creep Coefficient indicates the ratio of creep strain to elastic strain, providing insight into deformation behavior under sustained load.
When concrete bends and starts to seep, it's called creep, by stress we keep.
Imagine a heavy rock sitting on a soft sponge. Over time, the sponge slowly flattens under the weight; that's like creep in concrete!
CREEP: Constant Relaxation and Elasticity Even Pressing.
Creep: C - Constant stress, R - Rate increases, E - Elasticity changes, E - Effects seen over time, P - Predictability.
Term
Creep in Concrete
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Term
Basic Creep
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Term
Drying Creep
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Term
Creep Coefficient
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Gradual increase in strain in concrete under constant stress over time.
Creep that occurs when concrete is loaded in a sealed environment without moisture exchange.
Creep that occurs when concrete loses moisture under load.
Creep that happens even in the absence of external moisture movement, especially in high-strength concrete.
A parameter representing the ratio of creep strain to elastic strain.
Creep refers to the gradual deformation of concrete under constant stress over time.
Creep is caused by the viscoelastic nature of cement paste in concrete, resulting in time-dependent strain. This section discusses the mechanism, types, factors affecting creep, measurement methods, and control measures for mitigating this phenomenon.
Creep is a critical phenomenon that describes how concrete deforms gradually when subjected to constant stress over a sustained period. Unlike elastic deformation, which occurs instantly and recovers when the load is removed, creep continues as long as the stress is applied.
Creep primarily occurs due to the viscoelastic nature of the cement paste, and several mechanisms contribute:
There are three principal types of creep:
Key factors influencing creep include:
Creep is assessed through specific tests using specialized equipment and parameters like the Creep Coefficient, with typical values varying depending on concrete type. This understanding is important for designing structures, especially in critical infrastructure, to ensure stability and longevity.