Concrete Cylinder break

[civeng231]

7 day break at 2100 psi for 28 day 3000 psi mix. Would you considered this falling in the acceptable range for any early break. The break itself is non-conical and split from the center of the cap to one side. What type of break would this be classified as?

 

[Ron]

Yes that is an acceptable result for your mix. Sounds like you had a bad cap, but you won't make the concrete break higher than actual with such anomalies...only lower. Considering the internal stress state of the cylinder was not the classic cone-shear, your result is likely conservative.

 

[concretemasonry]

Non-conical breaks are usually a sign of either a bad cap, poor cylinder preparation or damage in transporting and handling.

Hopefully, the later tests will be more representative, except the cylinders could have been made by the same technician.

If you had fly ash in the mix the strength gains will show up at the magic 28 days.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[civeng231]

thanks for the information.

Just got a copy of the design mix 88lbs of fly ash or 0.63 cf of total the mix. what impact, if minor would this amount of fly ash have on the overall strength?

 

[concretemasonry]

In a properly designed mix, it would have minor effects on the ultimate strength and the early strengths may be slightly less than a "pure" cement mix design, but there are other off-setting benefits depending on the ash properties and intended use.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Ron]

Little or no effect. As CM noted, some early strength gain retardation, but you're past that anyway.

 

[Hoaokapohaku]

It kind of depends on why you are asking the question. If you only want to know if these test cylinders are on track to meet the 3000 psi minimum requirement at 28 days, I agree with the others. However, if you have 2100 at 7 days and you normally have say 2800 at 7 days, the 2100 psi break may indicate a production problem that needs to be fixed. If the production problem gets worse, or the inherent random variation in materials or processes further compounds the problem, you could easily have failing concrete in other loads or on other days.

 

[BigH]

Further to Hoaokapohaku's post, what were the results for batches from the ready mix supplier on either side of the suspect batch? Remember that the acceptance criteria is based on the average of three consecutive samples achieving the required strength with no single sample falling more than 500 psi (3.5 MPa) lower.