Cost difference between f'c = 4 vs 5 ksi 1

[WWTEng]

We have some 12'x12'x3' footings that we originally spec'd out as 4 ksi. For the sake of appendix-D (tension on ABs) I think we need to go to 5 ksi. Is there a huge cost difference between the two? Obviously its going to be more concrete for the later.

 

[Ron]

Not much. Probably less than $100(US) per footing.

 

[ztengguy]

Ron is more than likely close. Delivery, etc should not increase. Call a few yards and ask them.

 

[dicksewerrat]

And it is more CEMENT not concrete

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[FlashSet]

Work with your ready-mix plant. Maybe their "4 ksi" mix has historically reached 5 ksi, or 4.7 ksi.

My favorite f'c = 4300 psi mix from my local ready mix plants typically reaches 5500+ psi at 28 days (which is fine for my application).

 

[JStephen]

If the job hasn't been priced yet, should be a minimal difference. But you have the potential for some confusion if that's the only place where it's required.

 

[steellion]

I got a quote last year in the northeast U.S. of $5 per cubic yard to increase f'c by 1000 PSI. Therefore, Ron's estimate is pretty close. I'm surprised to see 5 KSI footings though. I have never seen anything other than 3 KSI, and they are sized to work for that concrete strength. Is that becoming more common with Appendix D? We usually try to find a work-around in the anchor design to meet App. D with 3 KSI concrete.

 

[LonnieP]

Higher concrete strengths (4500 psi or more) in footings is becoming the norm in California for several reasons. High alkali soils, soil moisture and LRFD designs are all considerations. Going to 4500 psi seems to be the quick easy way to solve all those issues.

LonnieP

 

[JedClampett]

Embellishing on LonnieP's post, if you have aggressive soils you need 4500 psi concrete. See ACI 318, Table 4.3.1. I'm afraid that those 3000 psi mixes will be going the way of the dodo.