Pictures

[SKIAK]

I designed an underground concrete structure this past winter that is now in construction; I have been going out and doing rebar inspections and watching concrete pours. During the pours I have noticed the contractor doing three things against the recommendations in the specs: dropping concrete approx. 14'-0" through the walls and rebar, placing approx. 7'-0" lifts in the walls, and flowing concrete approx. 6'-0" horizontally through the formwork with vibrators.

The problems regarding these issues have already been worked out with the owner and contractor but it still comes up when I'm out there. The contractor told me for the third time that its not in the spec so I said "you want to bet?" He said yes and here are the terms of the bet: If I can find how he violated the spec with the abovementioned procedures he buys pizza for his entire crew and I give a presentation on proper concrete placement. If I can't, I buy pizza for his entire crew and they get to point and laugh at me. I won.

Now I'm putting together a presentation about proper concrete placement techniques, going into the why's and how's and what happens if you don't, but I am looking for pictures that demonstrate what happens to concrete if not properly placed. I did some google searches but didn't really find what I was looking for. If anybody has pictures from projects they worked on and were willing to upload them and give a description of the situation it would be much appreciated. Also, if you have better Google skills than myself and can find pictures and can provide a link, that would be much appreciated as well.

 

[dik]

so... do you buy pizza for the forum? could be more onorous <G>

Is the ACI standard for formwork design specified? If so, I seem to recall there being a limit of 4' per hour for placing concrete in the forms (I'm not sure and my copy of the standard is at the office.) Maybe someone on the forum has a copy handy...

Dik

 

[dik]

Seem to have second thoughts about the rate... this can effect formwork pressures and it may be that this is not limited only that the formwork be designed for it... also 4' per hour seems slow... will have to check later... sorry for the bum steer...

Dik

 

[SKIAK]

We state in our spec "design, erect, support, brace, and maintain formwork to support vertical, lateral, static, and dynamic loads that might be applied until concrete structure can support such loads" and also "deposit concrete in forms in horizontal layers no deeper than 24 inches."

Not sure on the ACI standard... as for the pizza, anybody who provides a picture I use in the slideshow is more than welcome to stop by during the presentation to have some pizza courtesy of (insert construction company name here).

 

[msucog]

7' lifts!? whoa....from my contractor days that's a recipe for bowed walls, blown out forms, etc. if theyre not vibrating the concrete properly, you could easily pour 7' lifts. maybe the forms are better braced. maybe theyre just lucky. the drops is excessive, they should not move the concrete laterally with vibration, and the lifts are too thick. are you seeing honeycombing or visible layering immediately after the forms are removed? either way, there are some things that may not be visibly evidenced. if special inspections are required, then they are not following special inspection requirements so it doesnt matter if it is working or not. plenty of contractors wet stick rebar and it may seem to do just fine...but it is in violation of code requirements. will try to remember to pull a few references this week.

 

[DRC1]

You may want to check with ACI or Concrete Construction magazine (

http://www.concrete

construction.net ) They may have some really good material put together that they could send you, espcially if you explain how the presentation came to be. By the way, I think that was really a very proactive bet. Congrads.

 

[SKIAK]

The forms are pretty sturdy although I haven't checked them as they are the contractors responsibility, they seemed to hold OK. I have not been able to visually see separation but I don't take that to mean there is none.

I have been meaning to shoot some emails to PCA and ACI but I've been pretty busy lately so have been forgetting. I should do that now.

 

[BigH]

7' lifts ? In China, they were forming walls some 4 to 5 m high in one lift - but the forms were like tanks. Agree that moving concrete by vibrators - not good idea - I'll look around to see if I've some good pix.