Concrete Strength of Bored Cast In-situ Pile

[Civilfreak]

Hi friends,

The recommended grade of concrete for our pile is M30 grade. We are using 400Kg/cum of cement but we are not achieving 30 N/mm2 on 28 days due to PPC cement. After 42 days some cubes have crossed 30N/mm2 whereas other cubes didn't. The piles load carrying capacity are calculated based on soil profile and we don't consider concrete strength in load carrying capacity.

1. I would like to know what will happen to pile if the concrete doesn't achieve the required strength ?

2. I like to know what factors are involved in the concrete strength of the pile ? Is it only the durability of the pile ?

Please kindly share your experience as well as any reference document. Thank you

 

[dik]

Concrete strength is not normally a criteria for load carrying for friction piles. Cement content, as you have noted is, for durability. As long as you have the cement content, it shouldn't be a really big problem. You can replace some of the cement with flyash, or some other cementitious material.

Dik

 

[Civilfreak]

Thank you Dik for your reply.
1. what do you mean by "load carrying capacity is not normally a criteria for friction piles"

2. Already we are using Portland Pozzolana Cement so i guess no need of any fly ash to be added. But in American and British code for pile foundation, they have provided formula to find the compressive resistance for a pile. What is the purpose of that ?

 

[Retrograde]

I would like to know what will happen to pile if the concrete doesn't achieve the required strength ?

That depends on how much load is on the pile. Re-do your structural calculation for the pile capacity with the reduced concrete strength and see if it is still OK.

we don't consider concrete strength in load carrying capacity.

You should. While it is normally not the governing criteria, it can be - especially if there are significant eccentricities or lateral loads.

 

[dik]

OP... that was an error... what I meant to say was that concrete strength is not normally a criteria for load carrying. Concrete strength (and hence cement content) generally has importance with durability.

I've edited my posting to reflect this. Sorry for the 'screw-up'.

Regarding"they have provided formula to find the compressive resistance for a pile. What is the purpose of that"; I'm not sure what the formulae are, they may be a chart that gives a reasonable strength gain over time depending on the mix of PCC and pozzolan. I don't know. Other than a delay in gaining strength pozzolans can improve the quality of concrete significantly. We often have issues with Sulphate and Chloride resistance and the manner of producing a resistant concrete is to use normal portland cement and maybe 25% fly ash. Type 5, 50, or in these environs HS, does not work and a blended PCC should be used.

Dik