Concrete Compression Test Results 1

[mshemy]

Dears, i need your support in judging on the concrete compression test results.

the test have been done after 7days & 28days, on cylindrical shape (300x150mm) and the design strength is C30 and the cement (kg/cu.m) = 360, the results as below:

7 Days age:
Sample (1-A) = 24.3 MPa
Sample (1-B) = 24.6 MPa
Sample (1-C) = 25.5 MPa

Sample (2-A) = 26.5 MPa
Sample (2-B) = 27.7 MPa
Sample (2-C) = 24.3 MPa

Sample (3-A) = 27.0 MPa
Sample (3-B) = 24.7 MPa
Sample (3-C) = 25.5 MPa

28 Days age:
Sample (1-D) = 24.88 MPa
Sample (1-E) = 24.87 MPa
Sample (1-F) = 27.56 MPa

Sample (2-D) = 24.84 MPa
Sample (2-E) = 23.55 MPa
Sample (2-F) = 27.52 MPa

Sample (3-D) = 24.0 MPa
Sample (3-E) = 23.16 MPa
Sample (3-F) = 28.78 MPa

According to the above results, it means that this concrete is failed?

Thanks in advance

 

[hokie66]

I would say that something very peculiar happened to the samples tested at 28 days. It is inconceivable to have test results at 7 and 28 days which show almost exactly the same strength. Some detective work is required before you make any determination. If the 7 day results are correct, the concrete should have reached 30 MPa at 28 days.

 

[Ron]

Agree with hokie66...something screwy.

Were the samples fabricated, transported and cured under standard conditions?
Is there any chance the samples were mixed up with another batch/project?
Was the curing temperature low?
Were the samples wet cured?

Lots of variables in a situation like this....you'll need to do the detective work hokie66 suggested.

 

[bimr]

Problem with lab's sample handling and data recording?

 

[Cruzi]

The results after 28 days are illogical. Something must have went wrong during those 28 days at the laboratory.

 

[BigH]

Further to Cruzi - perhaps the 7 day tests were illogical - the illogical 28 days come from a "logical" 7-day.

I've had screwy results too - sometimes when the lab is so full of samples that things do get mixed up. Here all the test results are basically the same regardless of sample number or day of testing . . . agree with Ron that you need to collect all the data you can . . . get the batch records from the batch plant, determine how the cylinders were sampled and initially cured, how were the samples transported . . . any possibility that the samples were dropped? did the same person break the samples? Was the compression machine calibrated? Has this particular mix had similar results in the past? at the present? was there a possibility that during casting there was excess water or "liquidy" concrete that was used in the last cylinders where "dryer" concrete made up the initial cylinders? Did you mark the cylinders A, B, C, D, E, and F in the field and then test accordingly? (I would have picked cylinders at random - perhaps doing the 7 day on A, D and E and the 28 on B, C and F). Did you do cores a few days after 28 days to see what the strengths were? That might help.

According to ACI, your concrete would have failed - the average of three consecutive must be greater than the specified and no single test result less than 500 psi (3.5 MPa) lower than the required strength. BS EN has different criteria.

I know that the above doesn't explain, necessarily what happened, but by collecting the information, you might find something that caused the cylinder test results too be screwy.

 

[mshemy]

Really many thanks for all for participating in this problem, appreciated

Eng. M. El-Shemy