Concrete Cylinder breaks 2

[WDorey]

If you have the compression strength of 4000 psi or greater in your cylinder test breaks.
What are the long-term effects with not having any aggregate fractures (bond failure); cylinders with lateral and Hort. shears and no concrete stink to the rebar (rebar can be washed clean with minimum to no effort)? Need some second opinions.

 

[Ron]

It sounds like there is significant disparity between the concrete in your cylinder breaks and the in-place concrete. I would suggest some cores or other testing to determine the condition of the in-place concrete, including petrography, based on your description.

 

[WDorey]

We have taken cores and are using an expert in this field, He has not commented yet. I think ACI's take is if the compression strength is as spec. then how the cylinder breaks is really not relative, I could be wrong. Do the breaks set the stage of good or bad concrete? Can you have good concrete when the breaks are lateral and Horz shear, no conacial type. no aggregrate shear (None)? Alot of bond failure of aggregrate. Cores are showing same signs and prefect rebar impressions during demo, none is sticking to the rebar.

 

[cvg]

not sure what you mean by good or bad. Compression test is only one method to help indicate what the strength is - doesn't really make a determination of good vs bad.

is the aggregrate crushed or is it rounded/smooth gravel? Was it inspected prior to the construction? Was there any inspection of the steel before the pour? Is there any sign of oil or paint on the steel?

 

[WDorey]

It seems once the cylinders are broke if the compression strength is at the required 4000 psi, everything is then accepted as if you will "good" concrete. When you have acceptable concrete, The question does not come up of how did they break. If you have one break above the required strength and it broke in a Horz. plane is it acceptable?
The aggregrate is round/smooth 3/4 and smaller. Yes, we made a trip to the batch plant and looked at the stock pile of gravel before pours started. All seemed ok. The rebar was inspected and no sign of any oil or paint was present. Are plan once we resume pouring is to have field cured cylinders along with lab cured.

 

[looksatstars]

Concrete stength is in compression so if it meets the 4000 psi spec then the concrete has done its job.
The horizontal shear of the test cylinders show that the compression testing apparatus may by off-kilter or something wrong with capping compound materials or procedure.
As for the rebar, as long as there is not alot of rust or another compound on the rebar, I would not see a problem.

 

[Ron]

WDorey...the type of break is indicative of test parameter control. Keep in mind that you won't make a cylinder break higher than its actual compressive strength, but you can easily make it break lower. This comes about when you see true vertical shear breaks, or lack of shear-cone failure of most any form (true measure of compressive strength comes from a triaxial shear (though the "confining" pressure is 0) mode resulting in shear-cone failure.

Bad "breaks" occur when the testing machine is out of tolerance (usually if the upper or lower bearing blocks are not planar), if the technician puts the sample in off center (eccentric loading), if the cap has not gained full strength, if the cylinder top and bottom are not within plane tolerances,.....and so on.

 

[BigH]

Ron - I had, not too long ago a low break and it too broke horizontally - i.e., we tapped it with a small rubber mallet and it came apart in two sections (horizontal plane). I figured it might be because of the field tech not rodding the second or third layer fully and into the underlying layer.
We should remember Mohr's diagrams? How can the shear plane be horizontally planar? Doesn't make sense.
You can make the cylinder break a bit higher by jacking up the rate of loading (but not if you are following the set rate of loading requirements). Another point - cylinders (and the breaking thereof) has really "nothing to do" with the strength of the concrete in place.

 

[Ron]

BigH...you're right...you can increase the loading rate and run up the "apparent" strength.

Horizontal break planes are usually a result of a cylinder anomaly like you described.

 

[boffintech]

Had some low one day breaks just this morning. The low temp last night was 58 F and of course no initial curing was performed on site. This 5000 HE mix normally comes up to 3500 in 24 hours. The contractor doesn't understand why last week the mix came up at 24 hours but this week it doesn't. I've been explaining "standardized procedures" until I'm blue in the face but with no luck. Now that PT stressing will be held up for 24 hours I'm thinking it will start to sink in.

To paraphrase Ron (I think) from an earlier thread: The purpose of taking cylinder specimens under standardized procedures, curing them under standardized procedures, and testing them under standardized procedures is to see what the MIX DESIGN is capable of doing. The cylinders represent the mix design. If the mix design is capable of producing concrete of a certain strength, then by inference it is OK in place from a design perspective (that's f'c).

 

[Ron]

Hey Boffintech...yup, you quoted right. Ready to move to Florida yet?

 

[boffintech]

Would you get me one of these?

http://www.mastrad.com/slump.htm

 

[Ron]

boffintech...hmm...haven't seen one of those on a jobsite yet! My guess is that you don't do much concrete sampling anymore...too valuable....but then, you wouldn't need one anyway. Considering the condition of most slump cones and plates after about 2 months of use, I would expect the mechanical parts to be unusable in about that time.

Based on your postings, I would also guess that when you were sampling concrete on a regular basis your slump cone and plate would last for years. Am I right?

 

[boffintech]

I don't sample much but if I had to I'd like a little doohickey to pull up the cone for me. Besides I'd love to see the look on the contractors face when I set that thing up. Now THAT would be priceless!

And DO NOT even get me started on the condition of tech's equipment. Why does concrete harden on the inside of a tech's slump come in 2 weeks but not on the inside of mine is 10 years!? Don't know. It's a dang mystery is what it is.

But anyway...

I have a question along these lines but it really needs another thread so I'll start it over in concrete....