want to know about testing of concrete samples 5

[prrog]

II have done testing in concrete ,but my samples were not the normal standard ones, I used samples of 4 inches diameter by 8 inches height.
I have got results scattering from 10 MPa to 18 MPa.
What is the most acceptable value, based in 14 results ?
maybe more.
Thank you.

Paul Rogerio

 

[jdonville]

prrog,

I would be surprised if ASTM C39 does not give guidance on this matter. If, however, there is no guidance, then perhaps ACI or PCA has some definitive answer.

Jeff


Jeffrey T. Donville, PE
TTL Associates, Inc.

http://www.ttlassoc.com

 

[BigH]

Standard cylinders are, as you know, 150mm by 300mm (6 inches by 12 inches). However, there is a trend to go to the 100mm by 150mm cylinder sizes especially with smaller coarse aggregate. I believe that AASHTO has a note in the bridge code about this or else, as jdonville says, there is a note in ASTM. But, in any event, it is a permitted size. There is no "adjustement" that is to be applied. As for your scatter of 10MPa to 18MPa, I would really like to see the average and the standard deviation of the group so a judgment can be made if one or two of the numbers are outliers. You realize that a "test result" is the average of 2 cylinder breaks at 28-days. I see no "meaning" to your having reported 14 break values. Even if all from the same pour on the same day, then you would have 7 test results not an average of 14 break values.

 

[prrog]

My 14 samples of concrete cylinders were taken in different days.
I have got 14 results scattering from10.22 MPa to 18.60 MPa .
Media = 14.04MPa, standard deviation is 3.2MPa.
variance= 22.6%.
Wnat to know if is still acceptable this concrete.
Thanks

 

[henri2]

prrog,

What are the governing codes/standards...are they US..if not what are they? I ask because the strength values you indicate are expressed in metric units.

Smaller specimens will usually result in higher compressive strengths.

 

[dicksewerrat]

Are they all 7 and 28 day breaks? All break results should be reported, not just an average. The spec for the mix should tell you what the strength should be.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[henri2]

Check Table 2 in the paper "Specimen and Aggregate Size Effect on Concrete
Compressive Strength" by Sleiman A. Issa et al

http://journalsip.astm.org/PDF/CCA/CCA2220103/CCA2220103.pdf

While we are on the subject of concrete samples I have a question regarding the application of ACI 318 Section 5.6.1.2. Let's consider the following scenario:

On a given project only 40 cubic yards of a 4000 psi 3/4 inch pump mix are required for CIP NW concrete walls. The mix will only be used for the walls and nothing else. If all 40 cubic yards are deliverd in 4 seperate ready mix trucks and placed in a single day, the code requires a sample to be taken from each truck. If the code is followed this will result in fabrication of 8 cylinders (2 cylinders/sample). However, in my neck of the woods, ACI techs and special inspectors typically only take 1 sample rather than 4. Is there something in ACI 318 that allows this reduction in frequency other than the BO permitting it?

 

[PTslab]

Prrog,

4x8 cylinders are starting to be accepted in different areas of the US. It is becoming generally accepted to use this size for concrete that does not have aggregate sizes above 1" sieve (double check that value). I believe there is currently some work being performed and written with intent for ACI/ASTM to recognize its use. I'm sure you can find some write-ups through ASTM and ACI. If you need actual company contact information - send me another thread.

I believe the original reasoning stems from safety issues with testing personal having to handle the large 6 x12 cylinders. Insurance/Liability issues and such...