bond-breaker vs tilt-wall rebar ??
bond-breaker vs tilt-wall rebar ??
(OP)
Am an inspector (not EOR) on some work on a tilt-wall project. I have not asked the EOR about this yet but will if needed. No tilt panels have been poured yet. Thirty to 40 are under construction. The contractor is using Maxi-Tilt as the bond-breaker between SOG and tilt-panels. It says right in the Dayton instructions "Do not spray on reinforcing steel." But regardless I'm apparently the only one on the project that thinks it a bad idea to spray the reinforcing steel with the bond-breaker. Do I have it all wrong?






RE: bond-breaker vs tilt-wall rebar ??
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: bond-breaker vs tilt-wall rebar ??
Bond breaker, by definition, interferes with bond, and should be avoided.
Some overspray of things like form oil is inevitable. Very thin mists of oils have not been shown to be deleterious to bond, but the line between acceptable and problematic is not well defined.
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
1. slab sprayed
2. slab sprayed
3. rebar placed
4. rain
5. rain again
They all think I'm crazy and that some how tilt-wall panels are exempt from this ACI rule.
RE: bond-breaker vs tilt-wall rebar ??
Any bond breaker will have the exact same warning. How do you propose that they form the panels?
You have to trust that the subcontractor knows what he's doing. If you are going to micromanage every aspect of a project based on potential problems, it will not come close to being done on time or under budget. That's not to say you shouldn't be vigilant or speak up when it comes to pointing out errors or shortcuts, but the sub who does the tilt wall panels will be experienced with potential issues.
RE: bond-breaker vs tilt-wall rebar ??
http://www.concreteconstruction.net/concrete-const...
AND can show that the bond breaker will not increase corrosion in the bars.
Depending on the type of material applied, one or both could be an issue. Bar development is primarily a function of deformations wedging against the surrounding (well-consolidated) concrete, so a very thin film of material may be OK. A film-forming, membrane-type bond breaker may well significantly interfere with bond, while a waterborne material may form a reactive salt or soap layer which could lead to increased corrosion. Some bond breakers would do neither, and may be perfectly acceptable.
Remember that the EOR can waive provisions of ACI 301 when they have compelling reasons to do so. (Or no reason at all, if they really want to, and have the insurance to back it up.)
There are instances where our business is excessively conservative, but I don't think particular prohibition this is one of those.
RE: bond-breaker vs tilt-wall rebar ??
From the article:
" "When concrete is placed, all reinforcement shall be free of materials deleterious to bond." Inspectors often cite this sentence when requiring contractors to remove form-release or bond-breaker overspray and cement splatter from contaminated rebar. But is this work really necessary?"
Well over-spray is one thing and re-spraying an entire panel area with the rebar already in place in my estimation is something else altogether. I mean if rebar has been placed is a panel and the panel area next to that panel is being sprayed with bond-breaker and some "over-spray" drifts over in a breeze well OK, but if the rebar is already in the panel and the panel area is re-sprayed holding the wand 1' above two-mats of rebar so that all the rebar get thoroughly coated well that's just bad practice.
When any engineer says: "a little over-spray is OK" you have to try imagining that run through contractor DNA which is hardwired at birth to actually hear/interpret that as "100% coated with bond-breaker OK".
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
Read the OP's original post. He simply asked whether the bond breaker could be used. I took his scenario about raining as a hypothetical situation against which he was guarding by prohibiting the use of this bond breaker. It never occurred to me that anyone on this thread could seriously consider that a subcontractor would respray without removing the steel. Again, if the subcontractor knows what he is doing he absolutely knows that this is simply not OK.
But as to you being dumbfounded at my suggestion that at some point you have to trust that your subs know what they are doing.. why is this such an outlandish suggestion? Do you seriously micromanage every decision made by subs? That is precisely why you specify what inspections are required and you require an independent inspector. The subs are free to use means and methods they see fit and which, in theory at least, have worked successfully in the past. Provided they pass the inspections and your requirements, why would you micromanage. I'm assuming, of course, that part of your requirement is that all rebar be free of materials deleterious to bond.. or other such verbiage. If you have this in your inspection requirements, as most engineers do, then how do you think they will be able to justify spraying with the cage in place?
We work with a lot of tilt wall. I've never once had a contractor request spraying after the cage is in place. That's not to suggest it can't happen, but in the many tilt wall jobs I've worked on, it hasn't happened once.
I'd appreciate it if you were be a bit more judicious when throwing around words like "shortcuts". I explicitly stated that an inspector should be vigilant about compliance and spotting shortcuts. How do you take what I wrote and then literally suggest I'm advocating the contrary?
RE: bond-breaker vs tilt-wall rebar ??
Shouldn't that read:
1. slab sprayed
2. rebar placed
3. rain
4. slab sprayed through rebar
5. rain again
6. slab sprayed through rebar again???
BA
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
This has nothing to do with micro-managing and everything to do with the poor state of construction education, training, certification and licensing in the US (I am only referring to US construction as I know that boffintech is in the US). boffintech is exactly right to call them on this and exactly right to do his research and show them the error of their ways. He is being diligent and protective of the necessary process. The SEOR will hopefully laud his attention to detail and diligence. He should.
Removing the steel takes time and effort. The spraying is probably being done by a subcontractor that has nothing to do with the steel placement, perhaps even the GC is doing that. Again...the guy probably knows how to spray bond breaker, but doesn't know the repercussion on other systems. If such a condition has not occurred on any of your jobs, you are dealing with a much better than average group of contractors. Congratulations. I know quite a few, but they are not the norm.
Herein lies one of the problems. Design professionals usually refrain from dictating means and methods for liability purposes and under the sometimes false assumption that the contractor knows better ways to accomplish the end game. The difference is that the "end game" has to be performance of the system over its expected useful life. The "end game" to a subcontractor is often the lesser of either "when I get paid" or "when my warranty is up". That leads to the commonly used statement "I have over 20 years of experience doing this and I've never seen a problem"....well the problem is that they probably have 1 year of experience, 20 times over, having never seen the failed result of their work because either no one pursued it or no one could find them when a problem occurred. They usually don't know if their techniques have worked well in the past, they just know that no one has called them on it. Big difference. It is similar to the false assumption that is made about structural performance of buildings....they haven't failed in the past so they are not likely to fail in the future! Not true either. They probably have never been close to the design conditions.
Keep it up boffintech.
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
And he did: OK as-placed - spraying rebar with bond breaker not as issue.
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
BA
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
BA
RE: bond-breaker vs tilt-wall rebar ??
BA
RE: bond-breaker vs tilt-wall rebar ??
BA
RE: bond-breaker vs tilt-wall rebar ??
On a project that I am currently involved in calls for a 3" concrete face 3" of insulation and a structural back up. I don't think there is any reinforcing in the face but I may be wrong (I'm not designing these panels). The panels are cast face down against the SOG with the lifting lugs on the back side of the panel. Once the bond breaker is placed and the face case they should need to use bond breaker again. So, on my projects I would think it would be difficult to spray the structural reinforcing with bond breaker.
RE: bond-breaker vs tilt-wall rebar ??
BA
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
BA
RE: bond-breaker vs tilt-wall rebar ??
I didn't get a chance to read all your articles... doesn't it matter if the bondbreaker is petroleum-based vs. water-based?
RE: bond-breaker vs tilt-wall rebar ??
I don't think we can conclude that this is standard practice, and it is definitely not allowed by most engineers where I am. Actually, I doubt that anything about tilt wall construction can be said to be "standard practice", as there are lots of different ideas about best practice in tilt wall construction.
RE: bond-breaker vs tilt-wall rebar ??
Petroleum based and water based bondbreakers were included in the tests.
hokie,
I'm not sure that "standard practice" was the right choice of words. Perhaps "acceptable practice" would have been better.
Prior to seeing this thread, I would never have even considered allowing form oil to come in contact with reinforcement and I believe that most engineers in my area feel the same way. However, the cost of removing the reinforcement to spray the forms, then replacing it is being questioned in the above named literature and I am simply wondering if we have been overly cautious in the past.
BA
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
BA
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
The reinforcing industry obviously needs to clarify what is required and why. When it comes to how much effect there is from "materials deleterious to bond", it seems that we are talking in terms of fractions rather than orders of magnitude. There is a good bit of research going on right now into straight and hooked bar development length, and we expect results on these projects within the next year.
As far as development of deformed bars goes, only about 15-30% or bond strength is generally considered to rely on surface bond between steel and concrete. One of the previously-linked articles noted that "initial slip" was affected. This could very well be the critical part of the equation, since once slip starts, the only resistance remaining is provided by resistance to splitting (that is, concrete tension strength and confining reinforcement and geometry.) Splitting failures of unconfined splices can be brittle and sudden. In the case of a thin wall reinforced in one plane only, reduction of adhesion between bars and concrete could decrease the force required in the bar to induce splitting along the plane of reinforcement.
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
Three items that would be of concern are the initial slippage, and a greater tendency to cracking due to lack of bond and the consequences of this. OHIOMatt has, somewhat, addressed this item. The second item would be the possible interaction of the chemical with the reinforcing steel and the promotion of corrosion. The third item that Ron alludes to, is that in accepting this 'silliness', it's only moved the 'goalposts'... and permits 'greater silliness' down the road...
Dik
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
Always remove the reinforcement and apply bond breaker to the form slab. This is for a couple of reasons:
1) Bond breaker applied through placed reinforcement will have irregularities in thickness and surface that will cause shadowing of reinforcement patterns onto exposed surfaces. And
2) Thick applications of bond breaker can result in adhesion of tilt slabs to form slabs, resulting in pop-outs and other defects in the tilt panels.
This is what TCA tells their member contractors and designers.
They tell us that they have seen drips and such cause both of these problems, as well as recognizing that ACI prohibits materials deleterious to bond on the reinforcement (and a bond breaker is by definition going to interfere with bond.)
I will be reviewing ACI 551 (best practices for tilt-up concrete) and will get back to the forum soon.
John Turner CSP PE
CRSI Greater Southwestern Regional Manager
RE: bond-breaker vs tilt-wall rebar ??
Also, it's interesting that there is no reference to bond... one of my bigger concerns.
Overall, I don't think spraying with the rebar in place is a good practice... I've not encountered this problem, but, wouldn't permit the contractor to do it...
Dik
RE: bond-breaker vs tilt-wall rebar ??
In a thin slab, layers of unbonded bar will create shear planes that negatively affect performance.
RE: bond-breaker vs tilt-wall rebar ??
RE: bond-breaker vs tilt-wall rebar ??
Always remove the reinforcement and apply bond breaker to the form slab.
BA