Influence of Poor Construction Activity on Strength of Concrete

[BigH]

Hey all,

While this might be up Ron's alley - perhaps others have had some experience. I am looking to see if there is any "hard" or even "luke-warm" information on the actual construction activity affecting the strength of concrete - like, poor vibration - potential loss of 15%; moving concrete with vibrator - 10%, "shooting" pumped concrete through reinforcing steel mats. (my numbers were made up)

Would appreciate any data/references on this . . . am putting together a presentation to our and the contractor inspection staff on inspection of concrete - pre-placement; placement; and post-placement.

Cheers to all - have a great Easter/Passover - or just a great couple of days!

BigH

 

[Ron]

BigH...good to see you on here.

I don't know of any hard and fast rules, just those generalizations we've all come to know. I don't know that any of these effects have been quantified as they are more often prevented than allowed, when in an inspection position to do so.

Interesting question though. I'll check my references. I used to teach an ACI Level II concrete inspection course, so I'll look through my reference material for that to see if there's anything that might help. Out of town till Monday, so will check then. I'm pretty sure my presentations are all "hard slides", so if I find them, I'll scan and send to you.

 

[BigH]

I found the followings estimated "up to" reductions that can occur with concrete cylinders due to improper casting, handling, curing, capping, etc. - See attached. Looking forward to any information you might have Ron.

 

[PEinc]

Interesting table, BigH. Is there any more information available? I'm sure the num,bers can vary greatly, but the table does give some relative information and possibly some priority to problem importance.

http://www.PeirceEngineering.com

 

[BigHarvey]

One big issue in piling is the effect of vibrations on young concrete. I have something on the subject bust must dig it out. From memory it's momething like PPV less than 25 mm/sec until concrete has reached something like 10% of 28 days nominal strength. Concerns chiseling, driving temporary casings, etc.

 

[Ron]

BigHarvey...study done at Florida Atlantic University late 90's showed no effect if separation was 3x pile diameter. Will find and post paper on it.

 

[Ron]

BigH....from what I found going through my references, the most pronounced effect on concrete strength comes in the form of processes or procedures that change the density of the concrete....as you probably already suspected.

There are few direct references but ACI 309, 309.1R, and 309.3R give some info on density and on vibration effects. Check the tables in 309.1R.

Also, the tables on the effect of air entrainment can be used to quantify the void effects in concrete, assuming reasonable distribution of the voids and not isolated honeycomb. As an example, if underconsolidation results in the equivalent of 6% voids by volume, it would have the same effect as a 6% air content...if evenly distributed.

As we know, distribution of inadvertent voids is rarely evenly distributed, so you either have to make a reasonable guess or determine the void quantity through coring.

For estimation of effect, I would look closely at any change in density, quantifiable or not. Even a few pcf density change will affect the strength by 10 to 20 percent with larger voids.

 

[BigH]

Thanks all - haven't been on for a while - busy trying to get our dam construction started . . . even did two graveyard shifts myself when we had no inspectors for it . . . PEInc, the table came from a paper - will try to find it again . . .and send the URL.

 

[PEinc]

Thanks. No rush.

http://www.PeirceEngineering.com

 

[BigHarvey]

An engineer asked us in Dubaï if the vibrations generated by the shock of waves against a marine pile filled with concrete could affect the strength of the concrete. As a first approach I answered no because we never experienced problems on such piles but if somebody has some material on the subject it would help me to justify my natural feeling !

 

[Ron]

BigHarvey and all...see if this helps...

 

[BigH]

Thanks Ron - I'll have a look. Loved the way they spelled the title of Chapter 1! Gave my presentation of Concrete Inspection (Pre-During-Post) to our inspectors and then to the Contractors' - it went fairly well. Hope that the Contractors head the heads-ups!!!!

 

[Ron]

BigH....new word...introduction to education....Introducation.