Concrete 'splatter' on reinforcing steel 3

[Ingenuity]

Does any one know of a (preferably) ACI reference that deals with excessive concrete 'splatter' on reinforcing steel?

We have wall reinforcing steel on a project site that has a 'coating' of concrete "splatter" from the previous slab pour over many many rebars such that the deformations are now hidden around many bar perimeters and lengths above the previous pour.


Does any one know of a reference that deals with what is excessive etc?

TIA

 

[SperlingPE]

Reinforcing should be clean and free from ..... is what is in the specifications that I use. Now to find out where this comes from.

See ACI 318-02 5.7.1.e - it doesn't say anything specific about "splatter", but it does emphasize that the reinforcing should be clean.

 

[LCruiser]

They can cheaply sandblast to expose the deformatons.

 

[JStephen]

I wonder if you couldn't just take a light bar or chipping hammer and knock it off pretty handily.

 

[LCruiser]

You can do that too, to remove heavier deposits. I recall sandblasters with a hammer in the other hand...

 

[boffintech]

5.7 — Preparation of equipment and place of deposit
5.7.1 — Preparation before concrete placement shall include the following:
(e) Reinforcement shall be thoroughly clean of ice or other deleterious coatings;


The commentary reads “Reinforcement should be thoroughly cleaned of ice, dirt, loose rust, mill scale, or other coatings.”

Other coatings meaning other coating that are deleterious to bond between the fresh concrete being placed and the rebar. Splatter is bonded to the rebar and fresh concrete will bond to the splatter; however, my take has always been that it really depends on the volume of splatter. A little splatter on the bars is OK, but how much splatter is too much splatter? It’s difficult to quantify; it’s a “I know it when I see it” sort of thing. If I hit the bar with a hammer and it easily pops off than it’s too much. If concrete was spilled on a bundle of bars in the lay-down yard then that’s too much.

 

[Zambo]

sandblasting isn't cheap and has the disadvantage of blasting sand all over the place.

Wire brushing is more convenient but is labour intensive, a mechanical wire bush on a grinder could also be considered.

But I think that boffintech has a good point that the cleaning of rebar shouldn't be taken too far.

 

[LCruiser]

Sand is cheap and non-toxic. It would depend on the cost of labor on your project. Union Labor at a cost of $30 an hour to the company buys a lot of sand, but if it's $10 an hour labor wire brushes begin to sound better...

 

[concretedoc]

Go to

http://www.concreteconstructiononline.com.

Enter "clean" and "rebar" as search terms. The article, "How Clean Must Rebar Be?" was in the June 1998 issue of Concrete Construction magazine. Bondbreakers, form relase agents, cement splatter, and some other contaminants were placed on rebar before concrete was cast around the bar. None of the contaminants reduced bond strength in pullout tests. Researchers at the University of Missouri-Rolla (Belarbi et al) using beam tests got similar results that were published in ACI SP 209. Cement splatter was one of the contaminants included in the UMR study. Recall that the key phrase is "deleterious coatings." If the splatter doesn't affect bond, it wouldn't appear to be deleterious.

 

[boffintech]

Wow, fascinating article. I'm not an engineer. I'm an inspector who is at project sites every day watching rebar and concrete placements. At any rate I'm willing to take a poke at The Aberdeen Group's series of tests:

1) All of the tests were performed on concrete samples with ideal concrete consolidation

And that happens in the field how often? Almost never.

2) All of the tests were performed with the concrete cast so it would settle in the direction of the applied
load, eliminating any effect bleeding might have on the measured bond.

And that happens in the field how often? What about top bars in beams? Top bars in deep slabs? Top bars have longer laps for a reason.

3) None of the tests were spliced bars but rather all were single bars with 100% concrete cover.

Almost all concrete splatter is on dowels that will have bars spliced to them.

4) The concrete mix was at nearly 6K psi at the time of the pullout tests. Obviously that strong a mix is going to have a positive effect of pullout strength.

5) The concrete mix they used had a 3 1/2" slump! Were they kidding?!

When contractors start placing 6K psi mixes with 3 1/2" slumps I'll stop worrying about deleterious material on the bars. OK that will be never.

 

[pba]

Folks,

Am I reading the article correctly? They applied bond breaking material to the bar and didn't notice any significant reduction in pull out strength. I'd be switching suppliers!

What they seem to be saying is that the surface deformations provide the ultimate bond strength. Note however that the slip value is eight times higher than for plain rebar. That suggests that serviceability cracking may be more of an issue that strength.

There is a good photo of the bars with cement splatter. They do not show any build up - just a surface coating. For REAL splatter the surface deformations are not visible so the pull out tests don't relate to the behaviour of the rebar in that circumstance. It is also not usual for the splatter to remain so clean. What would be the effect of combinations of rust, splatter and release oils? That is what we are normally fighting against.

There is of course nothing stopping us stating "...free from deleterious coatings and excessive cement splatter as may be determined by the engineer on site".

On the subject of sand blasting - Isn't the dust a health risk?

 

[LCruiser]

pba said:
"There is of course nothing stopping us stating "...free from deleterious coatings and excessive cement splatter as may be determined by the engineer on site"."

Except, of course, that whenever you say "may be determined by engineer (or owners PM, or inspector, etc.)" you will be paying higher bids as responsible bidders' contingencies will go up, or possibly getting a contractor more apt to fight than do a good job.

 

[Ingenuity]

Thank you for the reference "concretedoc".

I did find Position Statement #3 by the American Society of Concrete Contractors entitled "Coatings that Affect Bond to Reinforcement" dated September 2003 that references the Concrete Construction article.