Damaging Impact of high strength concrete on structures

[abdulqadeer29]

What could be the damaging impact OF HIGH STRENGTH CONCRETE especially in water retaining structures like dams and spillways.It has been observed that designers mostly propose external 1 meter layer of such structures of high strength concrete as compared to inner one. One of the obvious reason is to ensure economical design and to avoid thermal cracking .High strength concrete provides long term durability ad effective resistant to abrasion. But the worrying point is such kind of difficult arrangement in a reinforced pier cause delay in the progress as well as require special form work.

I am searching for some relevant references that describes the negative impact of using high strength concrete.

[UmarMakhzumi]

AQ,

Can you post a pdf of the attachments. Snapshots are hard to read.

When you say high strength concrete.. what is the strength of that concrete and what is the strength of normal concrete? My first reaction is that why not just pour all the concrete as high strength, then you don't have to do 2 layers or 2 separate pours. Anyway, answer the questions and we will see form there.

Thanks.

[abdulqadeer29]

High strength concrete strength is 50 MPA. Before this, original design was based on 35 MPA that we considered as normal strength concrete.

your second suggestion is already incorporated. The current design have only one layer with 50 MPA strength.

373 WEIR CROSS SECTION (12OF38).pdf

400 WEIR PIER REINFORCEMENT ARRANGEMNET (1OF13).pdf

[abdulqadeer29]

ACI 224R writes:

" For interior concrete , the lowest practical strength should be specified to reduce the cement content.This will reduce the heat of hydration and the consequent thermal gradient , decreasing the likelihood of cracking.More than the necessary amount of cement is detrimental rather than advantageous."

[UmarMakhzumi]

Thanks AQ for sharing the full resolution drawings. Very interesting.

Well, the first thing that comes to my mind is why the compressive strength of concrete is so important for your design team. Let me elaborate on this. What is your project team getting by using a 50 MPa concrete that it is not getting by using a 35 MPa concrete other than compressive strength? Concrete has a number of properties so I would like to understand that if compressive strength solely is driving this? If yes, then there might be another design that would allow use of lower strength concrete. The solution would lie in a design that mitigates water impact or whatever the design basis is to allow use of lower strength concrete mix.  So in summary. I am asking you not to focus on negative impacts of high strength concrete but to change your design to lower the requirement which is triggering high strenght demand.

If compressive strength is not main reason rather its some properties assigned with higher strength concrete, then different mix designs with lower compressive strength might be able to provide same level of non-strength related properties as that of 50 MPa concrete while also keeping lower C3A content. 

Thanks.

[abdulqadeer29]

This demand of increasing the strength is not based on design requirement or compressive strength requirement. it is purely based on getting long term durability against abrasion effect of flowing water with heavy sediment loading.This demand is not from designer 's end , but it is from the lenders technical advisers therefore our own firm is reluctant to increase the strength to 50 MPA. 

[UmarMakhzumi]

Sweet. This is much simple now.

You can have 50 MPa concrete tested for abrasion and submit a mix design for a normal weight 30 MPa concrete having equal abrasion to that of 50 MPa with the help of additives. Lafarge will be able to help you with that. See that attachment for concrete abrasion testing.

Cheers!

Standard Test Methods Abrasion Resistance.pdf

[abdulqadeer29]

Thanks...I hope it will work . I will get back to this forum if i need further help.This idea will make our work easy.