2500 psi concrete
2500 psi concrete
(OP)
I have a contractor who wants to use 2500 psi concrete, but usually use a minimum of 3000 psi on all of my projects. The thing is, this has just become standard operating procedure for me over the years and I have no real reason to back it up other than "It's what I've always done." So, does anybody out there use/not use 2500 psi and have a solid reasoning behind their decision? I'm curious what people do and welcome any and all reasons so let 'em fly. Thanks!






RE: 2500 psi concrete
RE: 2500 psi concrete
RE: 2500 psi concrete
RE: 2500 psi concrete
I see a lot of concrete that is 25, 30, 40+ years old - some of it is in excellent condition; the rest - not so much. Specifying 2,500 psi (assuming strength is not controlling) I think long-term durability would be your reasoning for rejecting its use.
So the contractor's main reason for requesting 2,500 psi is so that no SI is required? Maybe a red flag!
RE: 2500 psi concrete
I think everything on the commercial side and highway concrete is a minimum of 3000psi.
RE: 2500 psi concrete
Post-Tensioned residential slabs too?
RE: 2500 psi concrete
RE: 2500 psi concrete
In Australia, 3000 is the minimum recognised. Anything less is not really considered to be structural concrete! It might be used for mass concrete. And 3000 is only used for footpaths and residential driveways (by those who do not want overly good performance).
Floors without vehicular traffic would use minimum of 3500. Anything with vehicular traffic is a minimum of 4500 up to 6000 for non-pneumatic tyres.
Commercial would be a minimum of 4500 with most using about 6000 these days for durability.
RE: 2500 psi concrete
RE: 2500 psi concrete
All the production builders do a double-cable post tensioned system with predominately 2,500 psi concrete. There was one cable set on top of the pads and a second cable draped in the beams.
I'm sure there are exceptions, but when I was building homes 5 years ago they were all 2500psi. Prior to being an engineer, I worked for a large homebuilder and we did over a
thousand slabs a year all at 2500psi.
If I were building my own house, I would use at least 3000, but that's just me.
RE: 2500 psi concrete
Then, from what we hear about US PT house slabs in practice, cracking does not appear to be a worry.
RE: 2500 psi concrete
However, I have seen may architects in Texas prepare drawings with such small foundations for residential homes with 2500 psi concrete. Based on IRC and IBC codes, minimum requirement is 2500 psi. But I am never confident with that, especially in mid and South Texas with medium to to highly active clayey soil. When I receive those drawings for review and PE signature, I definitely revise them to minimum 3000 psi or 3500 psi depending on the application. I also do not hesitate to go for a completely different foundation design.
RE: 2500 psi concrete
You are hiring a contractor and you cannot tell him what strength of concrete to use?
Around here, it is rare to get anything other than 4000 psi. It it even sounds like a curb, sidewalk or driveway you get 4000 psi air entrained or sign a complete waiver/release before unloading. For a concrete supplier, they recognize that contractors that use the bottom end materials result in getting into durability disputes with the claim of poor materials when it
The cost of some cement is about the same or less than a truck going a mile or two further since the trucks, labor and time are the major cost of delivered concrete in comparison to a little cement.
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: 2500 psi concrete
Minimum used (good engineering practice) for structural concrete : class C25/30
RE: 2500 psi concrete
RE: 2500 psi concrete
Dik
RE: 2500 psi concrete
3-day avg 3,340
7-day avg 3,760
14-day avg 5,060
28-day avg 5,360
w/c was 0.4, 3 1//2 inch slump and 5.9% air
this mix contained fly ash, so long term strength gain may be even higher.
this is not that unusual, so depending on local practices, the 2,500 psi concrete (minimum) may be perfectly fine since the final product delivered on site is likely stronger than specified minimum
RE: 2500 psi concrete
I think a CA reviewer once made me use 2000 psi. It was existing concrete that we were anchoring into and they didn't want to determine the strength. I don't know that I would a start a new design based on 2,500 psi. Even an average Joe mixing it in a wheelbarrow can get 3000 psi.
Juston Fluckey, SE, PE, AWS CWI
Engineering Consultant
RE: 2500 psi concrete
Problem is some clever person might successfully create and deliver a 2500psi mix that is really 2500psi, and it is not really concrete!
RE: 2500 psi concrete
well, I guess that's three reasons
RE: 2500 psi concrete
Well Judge, I really wanted 3500psi concrete strength because it is much better so I ordered 2500psi knowing that they always supply much higher at these low strengths and as I asked for 2500 they charge me less. Unfortunately they actually supplied 2500psi and that is not fair. So it is their fault!
RE: 2500 psi concrete
You can specify/buy any strength of concrete you want. It's just that the design must be based on f'c=2500 psi to avoid the Special Inspection requirement. For example, you can tell them to provide 3000 psi and just indicate on your notes that your design is based on 2500 psi and avoid the SI. The more common practice here is to require 4000 or 4500 psi (for soil sulfate durability concerns) and do the strength design calcs based on 2500 psi.
RE: 2500 psi concrete
RE: 2500 psi concrete