Cocrete Testing 1

[gosai]

One of Testing lab test concrete cylinders 1 at 7, 1 at 28, and 1 at 56, The cylinder tested at 28 days achieved strength less than specified. Lab hold third cylinder for 56 days, 56 days test result passed as per ASTM and CSA international minimum 2 cylinders required to be tested at 28 days. Is there any way I can justify above test results as per ASTM, CSA or ACI?

Thanks to all in advance for helping me

 

[Ron]

The testing was not done in accordance with ACI standards, so you are left with doing verification from the in-place concrete. I would core the concrete and test the cores in accordance with ASTM and ACI requirements.

The original testing should have been 1 test at 7 days and 2 at 28 days (assuming 6"x12" cyls). ACI requires an average of 2 specimens at 28 days for the record strength. If you want to do testing at 56 days (which you don't know on the front end), there should have been two extra cylinders on hold. In lieu of testing cylinders at 56 days, coring is acceptable. Follow the procedures in Chap. 20 of ACI.

What were the actual strength results and percentages of design strength at 7 and 28 days? It's possible you didn't actually have a problem...just a poor interpretation of results. Did the mix design have slag cement or fly ash in it?

 

[bb29510]

make four cylinder, use the hold cylinder for the 56.But concrete is suppose to met spec at 28 days, if you have a lot of sample not meeting at 28. the amount of cylinder is not your problem. I would be making 6 to 8 cylinder per set. The problem is elsewhere

 

[JAE]

gosai, how far below spec was the 28 day test?

 

[gosai]

Instead of two cylinders i have only one cylinder tested at 28 days the strength achieved by concrete at 28 days is less than specified and the difference between achieved strength and specified strength is more than 3.5 MPa. my question is can i use only one test result and consider concrete as failed to achieve specified strength.

Thanks

 

[JAE]

gosai,
Check out this thread -
thread507-252689

I have a post there that summarizes ACI Chapter 5 acceptance of concrete - that may or may not be the same as CSA but check it out. Basically, if you have one flawed test, you don't need to immediately go to core tests. You can evaluate the lower strength and see whether the lower f'c is acceptable in the concrete portion of the structure the flawed test represents.

If the lower f'c still works in calculations - you as the EOR can approve it but the contractor is compelled to adjust the mix to avoid lower strengths in the future.

 

[bb29510]

my question is can i use only one test result and consider concrete as failed to achieve specified strength.

not really, it very common to shear a corner of a cylinder in a bad test, since alot is riding on this results, you have to be 100% correct that your findings are accurate. You need to be breaking two 28, no if, or, buts.

 

[gosai]

Thanks to all for answering my question and helping me

 

[BigH]

brownbagg - agree that 2 at 28 is a "must" - but if when broken, one is low because of casting problems, you would then be permitted to base the "test result" on the single cylinder break. On our job, with fly ash being used in excess of 20%, we are using 90 day strengths instead of 28 day as the criteria.