measuring Concrete Compressive Strength 2

[JohnRwals]

Hello!

Let's say I have very stiff concrete, which need strong vibration to consolidate.
In this case, tamping rod several times according to ASTM C31 to make test cylinders
is very different from actual concrete placement with strong machine vibration.
Though consolidation conditions are totally different,
should I compare concrete strengths between cylinders and actual structure?
For example, zero slump concrete is used to make hollow-cores under strong pressure.
And then, will cylinder compression strength of C31 and high-pressurized actual hollow core concrete be identical?
Should I use different ASTM than C31 to make test cylinders?

Thanks!

John R.

 

[dik]

There is a standard cylinder making process... you have to follow it for the tests to mean anything.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Ron]

The purpose of sampling and testing for compressive strength is to test the mix design, not the in place concrete. Sampling and testing in accordance with ASTM standards is appropriate. If you want to test the in-situ concrete, use cores cut from the in-place concrete.

 

[IDS]

There is a standard cylinder making process... you have to follow it for the tests to mean anything.

The question is asking if there is an alternative standard for low slump concrete, and that seems a perfectly reasonable question to me.

The purpose of sampling and testing for compressive strength is to test the mix design, not the in place concrete.

Cores are also used to test the quality and maturity of concrete placed during construction, at least they have been on every job I have ever worked on.

This link discusses an alternative method for testing maturity of zero slump concrete:

https://www.pci.org/PCI_Docs/Public...y Method for Zero-Slump Concrete Products.pdf

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Ron]

@JohnR....You could do some correlation testing where you use the standard ASTM procedures and do a couple of companion cylinders by vibrating the concrete in the mold. Compare the results.

 

[Eric C.]

ASTM C31 allows for the use of a vibrator to consolidate concrete in the cylinder mold if the concrete slump is less than 1". The requirements are in Section 9 I believe.

 

[JohnRwals]

While reading some papers related with hollow core shear strength,
I found they referred to ACI concrete shear strength formula including f'c.
But, hollow core is generally different from typical beams
which compacted manually or mechanically with relatively simple vibrator.
(Also, section profiles are different; bulky vs. slender.)
As special equipment is applied with different compaction/pressure during manufacturing hollow cores,
I wonder C31 method with typical manual tamping can represent actual concrete strength.
Also, I guess concrete strength should be different throughout whole hollow core section
as compaction pressure is different.
But, none of these papers did not mention how they made test concrete cylinders specifically.

(in my opinion, that's why it is realistically impossible to derive unified shear strength formulas including diverse hollow cores.)

Thanks for responses!

John R.