Adhesive anchor bolts installed underwater....

[SamEnella]

New to the forum here and wanted to pass along some problems I had with the performance of adhesive anchors installed underwater.

I recently was involved in a project where we mounted a steel structure to the vertical face of a dam underwater in approx. 40F temp water. The structure was designed to rest vertically on corbel brackets that were anchored in to the dam face with stainless steel adhesive anchors (Epcon A7, Redhead).

Due to my own concerns for using adhesive anchors (particularly in a cold, underwater environment) we required the critical anchor bolts to be pull tested to approx. 10% over the maximum design load prior to installation of the brackets. The pull test value was approximately 1/4 of the published ultimate bond strength. In addition, we required the anchor bolts to cure for 12 hours prior to testing (75 minute cure time per manufacturers guidelines).

Out of the first 8 bolts we pull tested - all 8 bolts failed. Several failed at virtually no load. After letting the remaining bolts cure for another 24 to 36 hours, the results improved, but we still had a nearly 20% failure rate. I was on-site to witness the installation of these anchors, and the contractor followed the manufacturer's guidelines to a tee - hole diameters were withing tolerances, thoroughly cleaned holes and removed slurry, injected the holes full of adhesive from the back of the hole forward, slowly twisted the anchors in, etc.. I'm thoroughly convinced that the adhesive (not installation errors) were the issue.

We tried another methacrylate adhesive (Simpson AT) that was recommended for diamond cored holes and let the adhesive anchors cure for 4 days (4 hrs was the published cure time). It performed no better than the Epcon A7 (33% failure rate).

We finally ended up using a hybrid acrylic/epoxy anchor (Unitex PROPOXY 400) and it performed wonderfully on the remaining anchors (100% success at 6 hours cure time). Our final theory (after talking to numerous adhesive/epoxy folks) was that the 100% acrylic adhesives DO NOT work well in the relatively cold environment (40 degF) because of shrinkage issues. After this experience, I would not recommend using adhesive anchors for critical tension fasteners, particularly in cold and/or underwater applications. In the future, I will go with mechanical anchors (undercut or expansion). If my client is hell bent on using adhesive anchors again, I would definitely use Unitex PROPOXY 400 (or something equivalent if it exists) and tension testing the bolts.

 

[JStephen]

I'm just curious if the adhesives were actually rated for that temperature? I know, for example, that epoxy paints have a minimum application temperature, and the cure time can be "never" if you get too far below it.

 

[Zambo]

Samenella,

interesting post.

I have also previously had problems with underwater fixing of anchors, unfortunatly this was in 1994 and I cannot remember the details of the epoxy that we used. In this case we used a pneumatic rock drill rather than a core drill hoping to provide a rougher drill hole (also the equipment is less expensive). We suffered from a large proportion of failures and at the time I assumed that oil imprgnated air from the drill was the problem.

 

[KCRatnayake]

Sam,
I think Vinyl Urathane system is excellently working in these circumstances, even for underwater applications, only if your hole is drilled using a rotary hammer drill. You could have tried Hilti Fastening Methods for this. They have an exclusive method for underwater applications. Visit

http://www.hilti.com

and serch for HIT system for underwater applications.
You can't use all sorts of chemical anchors when the hole is drilled using a diamond tipped core. In this case, the hole wall is so smooth that normal injection type anchors can not have their specified load. Then you'll have to use some epoxy / adhesive sytem.

Let me know if you want more details on this.

Clef

 

[SamEnella]

Clefcon,

We roughened some of the holes with a percussion drill. Didn't improve results.

After observing the pulled out bolts with adhesive still on them, the problem was clearly an issue of shrinkage - not lack of bonding. For most of these failed bolts - there was NO bonding, because the adhesive had shrunk away from the conrete before it cured. I have no doubts that a rougher hole would perform better than a smooth diamond cored hole, but that was not the issue here. Plain and simple, the 100% adhesives we used (Epcon A7 and Simpson AT) shrunk up in the colder temp and formed minimal bond area with the concrete. The hybrid epoxy/acrylic (Unitex Propoxy 400) worked as advertised. I will never use a 100% adhesive anchor underwater and/or in a cold environment again.

I frankly, think this is an issue that needs to be addressed by independent research. In my opinion, there are some adhesive products out there that are claiming to perform in environments (cold, damp, underwater, etc.) that they are not properly suited to handle. I have my doubts if some of these products have been properly tested for these more extreme environments that they are claiming to perform under. Might be a good thesis or dissertation subject for a willing graduate student out there.

 

[TwinCities]

You are correct that many "hybrid" adhesives such as Epcon A7, Simpson AT, Hilti HY 150, etc. do not perform well in underwater conditions. This is due to a couple of issues, these type of adhesives generally do not bond well to smooth core drilled holes and also are specifically not recomended for underwater or water filled holes. Also, these types of adhesives will shink slightly during curing which is why these types of adhesives cannot generally be used in oversized (>1/4 bigger than rod)holes. Another issues is cleaning of the holes underwater, the dust tends to settle and is hard to remove since it is floating in the water. The holes would need to be vacumed or blown out with a reverse flow nozzle. The best solution for these underwater fastings is a "epoxy" type system such as Hilti RE 500. These epoxy systems generally can be used in oversized holes, core drilled holes, water filled holes, and sometimes, if tested by the mfg., underwater holes. I would suggest checking with the mfg or looking at the ICC report(

http://www.icc-es.org)to

see if that product can be used in these situations.

Robert

 

[SamEnella]

Robert - Thanks for the information. Wish I would have spoken with you a couple of months ago.

I do have a problem with the statement "these type of adhesives are....specifically not recomended for underwater or water filled holes". Unfortunately, the manufacturers (Epcon A7 and Simpson AT) did in fact recommend these adhesives underwater. The cut sheet for A7 specifically states that it "works in damp holes and underwater applications" and we were assured by the technical reps from both companies that this adhesive behaves marvelously underwater and in cold temps.

Based on my experience, these acrylic adhesives do not perform well underwater primarily because of shrinkage issues, and these mfg's are recommending products that do not necessarily perform well in these environments. Frankly, it's dangerous, and that's why I am trying to alert fellow engineers of these issues. Bottomline, be careful with acrylic adhesives underwater for critical tension fasteners, and be careful with what the mfg's tell you.

 

[pba]

SamEnella,

Have you spoken to Epcon and Simpson about your findings? Most companies, I'd guess, are unlikely to be keen on recommending their products for jobs they can't do.

I have no knowledge of these companies but surmise that these are reputable suppliers - Maybe they need to update their recommendations...