Minimum Strength of Concrete 3

[xkybb]

Hello everyone!

I noticed that a minimum concrete strength is usually specified in designed code for concrete subjected to extreme environmental condition (eg. marine concrete).

Could anyone explain the purpose of setting such a limit?

For example,
In BS6349, minimum cube strength of marine concrete was required to be at least 40MPa.
However, I always wonder that why we are not allowed to use concrete of lower strength, say 30MPa, even if I put heavier reinforcement to make the RC design satisfy the ULS.

 

[dik]

Generally higher strength concrete has much better durability in most environments.

Dik

 

[xkybb]

But why does higher strength concrete has better durability?
What are the correlation between strength and durability?

 

[oldestguy]

I suggest doing that question at the concrete associations, perhaps using Google. Ask the concrete experts.

 

[hokie66]

Durability can only be definitively assessed after a lot of time. Strength can be measured very early. Therefore, minimum strength is often specified as an indirect control of durability.

A distinction needs to be made between concrete itself and reinforced concrete. The durability of reinforced concrete is usually controlled by the protection the concrete provides against corrosion of the reinforcement. And there is no question that better quality concrete provides better protection.

 

[dik]

Good answer, Hokie...

Dik

 

[Ron]

Yep! LPS for hokie66!

 

[dik]

Yup... Dik

 

[dik]

But why does higher strength concrete has better durability?

Didn't actually answer your question, but, testing and performance in the field has shown that. It has better abrasion resistance, flexural tensile strength, freeze-thaw resistance, etc. The down side is that it has more cement which causes it to shrink more.

Dik

 

[DamsInc]

As mentioned, a higher compressive strength correlates well with increased durability. The main reason why is due to reduced permeability of the concrete. A higher compressive strength has smaller and more discontinuous capillary pores. This slows down the rate at which water and other harmful substances can penetrate, resulting in less damage from nearly all deterioration mechanisms.