i.i.u.c.
they can mix any strength concrete for dozens of applications,

but how does mr. home owner know , after the pour,
what went in the forms?

did the basement footing mix go on the side walk or patio?
did the garage floor mix go in the garage or
in the basement walls?

how do the know for certain what went where?

can you drill out a sample to have it tested?

quote:

Originally posted by bendable:
i.i.u.c.
they can mix any strength concrete for dozens of applications,

but how does mr. home owner know , after the pour,
what went in the forms?

did the basement footing mix go on the side walk or patio?
did the garage floor mix go in the garage or
in the basement walls?

how do the know for certain what went where?

can you drill out a sample to have it tested?

yes, you could drill a core and have it tested.

in the commercial world, all concrete is specified to be a certain strength by the engineer and then they drill out some cores for testing along the duration of the project.

residential construction simply has a lot fewer qualified contractors and oversight than commercial construction.

Bendable, you worry too much.

Commercially they generally pour test cylinders as they're pouring the project. Once cured the test cylinders are tested, and if they fail, that portion of the project may have to be torn out and replaced.

In reality your house foundation or sidewalk isn't going to be subject to the forces that the commercial guys are generally concerned about.

You don't, unless you are an expert on scene when they pour and you inspect the concrete (and even then, you can be wrong), get test cylinders, or you drill and test a core.

Case in point, when I lived in an HOA community, there were poured concrete sidewalks, which were supposed to be 3,000 psi. My 1,200 psi pressure washer would engrave them quite nicely. Was shit concrete used by the developer. Could have been a load that was too wet, could have been a load that was about to go off, so they added water to it, but what ever, the sidewalks in front of my house were soft. Glad they used good stuff in my pad. I never had any problems with the house or garage pad.

In most cases, the soil under the concrete (poor compaction and drainage, organic material that rots away, etc.) will cause the problems, than the concrete itself.
Also as already mentioned, poor handling by the contractor can cause the concrete you purchased to be less than the specs.
Best protection is to get a quality contractor unless you want to be there watching and know what to watch for.

quote:

Originally posted by smschulz:
Bendable, you worry too much.

no worry involved here, just curious.


so getting a sample during the pour or
obtaining a core ten days after the pour.

can be sent to some sort of testing company for verification, sound like that would work

It's usually test cylinders made from the concrete coming out of the truck, they will take some and immediately test the slump. Slump is a test where they fill a cone shaped metal container, then lift it allowing the concrete to fall / slump. This gives an indication of how much water is in the mix. A slump of 3-4" would be a normal slightly stiff mix. This is the initial test that allows the inspector to give the go ahead to pour it. After that test cylinders are made and allowed to cure. They are broken 3,7, 14 and 28 days. Concrete reaches 90% strength in usually 3 days. If it hasn't reached 100% by 7 days you need to keep an eye on the 28 day break.

Strength of concrete comes from the water to cement ratio. Higher cement less water more strength. It's rare that concrete doesn't come up to strength. Trucks now a days have live in real time monitoring. Drivers cant add water like they use to without the on board computer knowing. They added water to keep the mix workable. Truck only has 90 mins. Then the concrete can not be used. With the on board computers they will send the mix out short on water and the computer will add water as needed.

I would start with the building inspector's office. Ask them your questions and ask how do they know it was done correctly. Footers have to be inspected by the local building inspector.

Concrete will obtain 75% of its compressive strength at 30 days and 95% at 90 days if I remember correctly.
The ticket from the plant will tell you what mix was used and any additives that were used.

It is very rare for a plant to mistake the pour as it would be their liability if something were to fail.

As was mentioned above a core sample can be taken at the 90 day timeframe and will give you a good idea of the concrete’s strength.

Just for your information in VA the minimum strength used in construction by code is 2500 psi. Most contractors use 3000 to 3500 psi depending on the application. I have used 4000 psi when doing certain flat work that we wanted a very slick finish and needed it to be very strong such as pouring a commercial floor in a warehouse etc.

awesome thanks

would 35,000 psi crete be twice as expensive as 15,000 psi ?

quote:

Originally posted by bendable:
would 35,000 psi crete be twice as expensive as 15,000 psi ?

A little more. About 2.34 times as expensive.

That would be 1500psi and 3500psi. I have never seen a 1500 mix even for a footing. I batched a lot of concrete, at least 500,000 yards. You would want a test cylinder over a core. No need to core a hole in your slab unless you suspect the strength is not there. Hold on to your delivery slip that stated the mix you received, the time it was batched, delivered, water added, and the time the pour was completed.

This message has been edited. Last edited by: rtquig,

quote:

Originally posted by ArtieS:
Case in point, when I lived in an HOA community, there were poured concrete sidewalks, which were supposed to be 3,000 psi. My 1,200 psi pressure washer would engrave them quite nicely. Was shit concrete used by the developer.

It may or may not have been bad concrete, but that isn't what the strength rating means. The strength rating of concrete is the amount of force per area in compression loading required to fracture the concrete. Your ability to damage it with a pressure washer is almost completely unrelated to that measure of strength.

That’s SigForum. You ask a concrete question, you get concrete answers.

How does a pump mix vary from a regular mix? Also, is it as strong?

quote:

Originally posted by sjtill:
That’s SigForum. You ask a concrete question, you get concrete answers.

if you search the website, there are 237 pages of
posts with the word concrete in them

quote:

Originally posted by c1steve:
How does a pump mix vary from a regular mix? Also, is it as strong?

In our area the difference is the size of the gravel. Normal concrete uses #57 gravel and pump concrete uses #8 gravel which is smaller.

As for strength if you order 3000psi concrete that’s what you get.