I've never been involved with hydrodemolition, but I would bet my entire years salary that if it blasts away concrete the way it does, that the epoxy doesn't stand a chance.
yes I have never been involved in any before either, A Contractor has proposed. Not sure I would be willing to bet my entire years salary but aggreed with you it would seem to be a pretty safe bet!
Hydrodemo energy is pretty impressive.
Only seen it done on thick concrete with black steel rebar, but I imagine the epoxy coating will be damaged if not completely removed.
If you are a believer in the effectiveness of epoxy against corrosion, then re-coat the bars before repair. Sika and others have repair products that coat reinforcing prior to cementitious repair; it is not the same as epoxy, but I would suggest it may be more effective. An argument can be made that epoxy effectiveness has been oversold by CRSI and others to the exclusion of other corrosion protection systems.
I've been involved with hydrodemolition on bridge decks with uncoated bars. It does a nice job of cleaning the bars. Epoxy is pretty resillient but some of the coating might be removed during the demolition. Why not have the contractor do a test section? If it does significant damage to the coating the contractor will probably want to rethink hydrodemolition.
Why? The epoxy is pretty worthless from all I hear.
And if you're really convinced it's valuable, have the bars coated (touched up?)with a epoxy system close to the original coating.
What's the reason for the hydrodemolition? Did they goof something up and have to rebuild it?
If contemplating hydrodemolition of a concrete slab with epoxy coated rebar there must be significant areas of concrete deterioration. If there are significant areas of concrete delamination then it stands to reason that the rebar is corroding and thus the original epoxy coating already has significant damage. Alternately, jackhammering out the deteriorated concrete will cause significant damage to the epoxy coating. Either way, your repair procedures will have to take into account that the original epoxy coating is deteriorated.
I have not seen fusion bonded epoxy coated bars after hyrdrodemolition but would guess the epoxy coating would have significant damage.
I have completed a few projects where we took the top half of a parking deck off. There were quite a few areas of localized repairs, from a previous repair program 10+ years ago, where the repair procedures included field coating of the exposed rebar with brush applied epoxy. Most of the epoxy was gone, however, there still were areas that the hydrodemo did not remove. If a hydrodemo machine leaves existing epoxy on the bars, it likely is very very well bonded and I wouldn't worry about it too much.
Jed,
A self consolidating concrete that didn't self consolidate. A cable stay tower is the structure.
Bridgebuster,
Think I'll do exactly that, a test section should they wish...always the accomodating type.
hookie,
Yes somewhat an oxymoron, SCC are truely in the realm of 'mix' design, alchemy/chemistry/cooking etc., and not terribly robust w/o a VMA, however much can go wrong wt them and in this case has but otherwise a very useful and successful concrete type now widely used.
dik,
Agreed galvanic cells and their formation and amplification? when epoxy coated rebar has been discretly damaged has always been the knock on it.
I'll let the Contractor proceed with a test, hydrodemolition, to amuse him. But it will be off the demolition possibilities list shortly thereafter.
First off I am not an Engineer of any type, but had to "check the box" to be able to post on this forum. I am however an employee of a Hydrodemolition contractor.
Epoxy coating would be damaged by hydrodemolition. It is possible that the coating may not all be removed from steel reinforcing, the amount of time the water jet spends over the area will have an impact on how much of the coating would be removed. Other than the amount of time the jet dwells over the epoxy coated bar, other factors affecting the amount of damage to the coating would include: the age of the coating, the “brand, type or quality of the manufacture/installation of the epoxy” (blistering), how it was handled during installation (coating nicks or bending), how much flexing or in service abrasion happened before the hydrodemolition removal operation, any defect in the coating would most certainly be exploited by the hydrodemolition operation.
I am not sure about this particular operation, but hydrodemolition is a great tool for selectively removing any deteriorated concrete that may be in there.
Thanks for that, Blaster. Always good to hear from someone who knows the work first hand. You have confirmed what most of us thought. Hydrodemolition is indeed a good tool to have, but in this case, with the plastic coated bars, it may make the situation worse. With plain or galvanized bars, no problem.
There is a chance the coating would be damaged with most any type of removal method.
If an impact tool comes into contact with any reinforcing, the vibrations would be sent through the steel, possibly causing addtional damage, debonding, micro fractures.
For whatever reason the removal is needed, bad pour or deteriorated concrete; if one can afford hydrodemolition, it offers many advantages over traditional or impact methods. Superior bonding surface, blast cleaned steel, no micro fractures, as the process is wet...there is no dust.
Thank-you very much for joining in the discussion!
It does confirm much of my thoughts and experience and those that have entered this thread. Epoxy coated re-bar can handle very little abuse whether during the shipping, installation, and concrete placing phase never mind demolition or repair! The Contractor feels the possibility exists as the structure is only three months old, the concrete is very poor, re density, extreme amounts of entrapped air with very large areas of segregation, and very poor bond of the concrete to the bars, so therefore the energy requirement to remove the concrete will be lower than otherwise. The diffuculty will be determining, if it does leave the epoxy coating 'intact' just how intact, 'intact' actually is.
Likely this can't be determined with any degree of confidence, so that back to 'bare steel' is the best and recoating a known. The other possibility is complete demolition of the structure, the Lawyers are already lining up, so we are crossing our i's and dotting our t's.
When you say '...if one can afford hydrodemolition ...' could you elaborate a bit on this, unit rates/volume say, i know that's difficult, ballparks might be interesting. In the past we have always found that the water and it's disposal and recycling and use was a difficulty/problematic.
I think that in general the larger scale the project, the easier it is to swallow the hydrodemolition "costs".
On a very small project, say a couple of cubic feet of removal like an isolated pocket, where the GC already has on hand an air compressor and a jackhammer, the cost of hiring a specialty (hydrodemolition) contractor, supplying water, dealing with the wastewater all seems like a lot of extra work on top of what the "bad pour" (for example) is already costing, but from a fix the best way possible stand point, hydrodemolition is sort of like the Rolls Royce of removal.
On a larger scale, hydro can cut down on the amount time and personel required on a job site, the robot can continue to work at "a pace" where a laborer with a jackhammer, doing say vertical or overhead work, will quickly lose the pace, those personel could be preparing for put back, while the hydro robot works ahead of them, possibly putting a project well ahead of schedule. A GC can spread their personel out further and get work done faster.
A hydro robot doing flat work, for example a bridge deck, reinforcing bar exposure in a 10 hour shift, exposes 2,000 SF at 2.5" removal, 1 technician for ten hours at a prevailing wage in a large U.S. city, 250 gallons diesel fuel, parts and supplies a couple hundred dollars, water supply 15,000 gallons, water disposal at $.20/gal, debris cleanup.
The debris cleanup needs done regardless of whether it is done by hydro or hammer. Hydrdeolition cleanup should stay on pace with removal, you do not want slurry drying on the demolished surface whether one chooses to go old school, labor intensive, shovels, air flute, loader and dump truck or by new school (vacuum and water blasting) with one technician.
Most hydrodemolition contractors are offering pretty turn key operations, the technology is available that allows them to do it all, the removal, debris cleanup and handling of the wastewater.
