Big Dig Boston ceiling collapse 21

[alehman]

From the photos published in the media, there does not appear to be any insulation on the bottom of the steel T sections. It seems that if one of these failed in major fire event, the entire system would be compromised. The hanger rods and anchors would be exposed, possibly leading to a cascade failure.

 

[epoxybot]

Not an engineer but have worked in the epoxy adhesives industry since 1986.
This link, listed earlier seems to put a lot of the credulity for this scheem on the shoulders of Power Fasteners.

http://www.telegram.com/apps/pbcs.dll/article?AID=/20060727/NEWS/607270465/1052/NEWSREWIND

Never in all my years of advising structural engineers on the use of epoxy adhesives have I ever so much as suggested that you could use them for overhead loading conditions.

As to cored, smooth holes vs. impact hammer drilled holes, back in the mid 1990's an evaluation was done. Cleaning of the core drilled holes was the principal drawback, not smoothness of the concrete. The cored holes properly cleaned (no roughening of the hole) yielded the most consistant results. Roughening of the smooth-sided holes proved to be impractical. For a smooth surface example, consider that lap shear (tensile)strengths for acetone wiped, smooth-aluminum coupons. They can easily exceed 1400psi. The smooth hole problem can be manifested when coring through rebar, since the progress slows and slurry is pumped into the pores of the concrete and the surface becomes highly polished/burnished by and/or with fines.
The pull-out strengths for impact hammer drilled holes were somewhat lower, presumabley due to microfracturing but the results had their own level of consistency based on the easier hole cleaning schedule.

Cleaning cored holes should really be in the first instance, the responsibility of the coring contractor and subsequently by the grouting contractor. A dirty hole is not suitable for any grouting material, polymer or cementitious.

My reasoning for why coring contractors should be assigned the first burden of cleaning is based on the premise that water does not wet-out fines that pass the 400 sieve. So if the coring slurry is allowed to dry and left for the grouting contractor to deal with, the hole will not be substancially cleanable without repeated pressure water blasting and brushing after which you can wait for the holes to dry and come back and dry-brush them again before flushing with oil-free compressed air.

I personally don't see Power Fasteners as a adhesive supplier but rather as a fastener supplier that has a few products to compete in adhesive grouted dowel applications. It maybe that their fastener sense got the better of what limited adhesive sense they have on staff. Cold, Wet, and Overhead. Hydrolisis?, Soponification? Apart from gravity, some thing bad happened.

Frankly, I have always felt that the use of cartridge packaged adhesives lowered the competency level of the labor. The cartridges were important to building code organizations, sense they don't approve materials but building systems.
The cartridges introduced a Idiot-proof perception that many manufacturers and contractors have been more than willing to take advantage of. Truth is your best mixing and assurance of proper proportioning(ratio) is with bulk mixing and single component pumping.

 

[hokie66]

Epoxybot--it is obvious that you know a lot more about the use of adhesives than most if not all of us engineers who have been commenting, and I think you have hit the nail, or bolt in this case, on the head. You have the same opinion as most of us about the use of adhesive anchors in critical overhead applications. I doubt that the coring contractor made much of an effort to clean the holes. So that left the installer with a very difficult cleaning task, which he probably did not fully understand.

 

[kenvlach]

I always used lots of water whenever core-drilling concrete. An article with comments about holes dripping water, not sure whether from initial coring or washing as mentioned by epoxybot.
"...J. Keaveney, the on-site safety officer for the Interstate 90 connector, sent a memo in 1999 that directly warned his superiors the tunnel ceiling could collapse because the bolts could not support the heavy concrete panels, and feared for his conscience if someone died as a result...
He also observated water dripping from the holes that construction workers drilled before the epoxy and bolts were inserted. Given the water pressure on the tunnel ceiling [rather, water from coring or washing], he questioned whether the epoxy would hold..."

http://news.thomasnet.com/IMT/archi...bostons_big_dig_highway_project.html?t=recent

 

[boffintech]

Makes one wonder if those "strength tests" were done in dry lab or under a shade tree.

Also, I worked on one job where 10 columns on 2 column lines from levels 1 to 4 had to be increased in size by 4" on all four sides. This required the drilling of a massive number of holes for epoxied in #3 "J" hooks to hold the additional vertical bars in place. It only took 4 hours on the first day of work to discover the primary impediment to proper placement of the "J" ties: operator fatigue.

Those guys could only operate that gun for so long before just giving up. By the end of the first day 2 electric guns were ordered.

We also performed pullout tests on this job. We hooked up a jack (similar to a PT stressing jack) but with hand pump and tested different installation methods on #4 bars. For drilled holes nothing held better than a hole that was blown/brushed/blown (oil free air).

 

[hokie66]

Boffintech--drilling holes overhead would be even more fatigueing than horizontally as in your columns. Wonder how they supported the core drill.

 

[dik]

kenvlach... that memo is dynamite! and should be a real concern for the recipient...

Dik

 

[epoxybot]

Not an Engineer
I going to step out on a limb here and make some assumptions. So I may wind up making a fool out of myself. On the other hand, you guys might find some information and understanding in what I think worth future polymer anchoring material selection consideration.

One anchoring material supplier’s name has come up in the media, so I ventured to their website and searched for the material that I would select, if I were so cavalier, as to use a polymer anchoring material for overhead grouting in a tensile-shear loading application.
Based on the magnitude of the project, need for longevity, consideration for heat/strength reduction, damp or wet conditions, anticipated underground low-ambient and low-substrate temperature and the benefit of speed of construction/cure schedule; my knee-jerk choice would be the material with the 176 deg. F. HDT (Heat Deflection Temperature).

The product certainly has lots of comfort notations i.e., IIC Research Report #, City of LA-RR#, references to DOT’s blah, blah, blah. It also claims it “meets” with ASTM C881 Type IV (Structural) Grade 3 (Paste) Class A, B, & C.

Reviewing the IIC-RR and the LA-RR, there ARE in fact provisions for the use of this material in overhead grouting, which to some extent, caution the structural engineer, (from here you’re on your own). I was surprised somewhat, to see this.

Fastener companies have been manufacturer-members of ICBO/ICC far, far longer than adhesive manufacturers. Prior to circa 1990 (Loma Prieta, Earthquake) few epoxy adhesive manufacturers were willing to forfeit the money to join regional organizations such as ICBO and submit their products for UBC evaluation. The test criteria were mostly developed for and influenced by the fastener producers and relevant to Polyester and Vinyl Ester capsule anchoring systems. Subsequently, in the wake of Loma Prieta, if you were fortunate enough that your product had, at the very least, a LA-RR and independent test results demonstrating compliance with ASTM C881-87; your product became an engineer’s preferred, specified brand.

The provincial aspects of City of Los Angeles-Research Reports and the esoteric properties of ASTM C881 were not always enough for Code compliance officials, who were now looking hard at a long overlooked area of concern, the pull-out strength of polymer grouted dowels, rebar and threaded rod. And while construction adhesive producers had flirted with cartridge type packaging for years, the cost of this packaging (including labor) was and still is very high, especially when considering the volume of material supplied per package. Necessity proved to be the courage that forced adhesive producers supplying the California construction market, to swallow the bitter pill of applying to ICBO now ICC for a UBC harmonized research report regulated product.

The problem I find is that the research reports focus so much on the pull-out data that little information is revealed or caveats made about the handling of the materials reported.

According to one Big Dig media blurb, wet - in other words, more than damp (ASTM C882 Bond Strength-saturated surface dry) test conditions were a frequent jobsite condition. WET Conditions existed.

According to the manufacturer -

NOT A PROBLEM – The material is used in “wet environments”. It is “All-Weather” and fast cure, even in low temperatures. Better still it is an optimal material for use in “diamond core drilled holes” It is also non-flammable, something worth noting when working underground.

This is the best product – Yes?
It has charts coming out the yin-yang and thousands of numbers.

So what’s wrong?

There is no % tensile elongation value and no compressive, tensile or flexural modulus values. Any of these might give an engineer cause to think twice. The valves shown are not qualified by test temperature. You have to therefore “assume” standard conditions (23 deg C).

Here is what else I see: The compressive strength is low for so high and HDT “Epoxy”. The C882 bond strengths are low and no explanation is given for the 2 values shown. Wet? Dry? What is this information? The values are low, very low if 23 deg C. is the test temperature. Well… 2 days is not that long, WHAT IS THE FULL CURE CYCLE, DOESN’T SAY ANYWHERE. The Slant shear number looks good, but then slant shear and ASTM C882 are supposed to be the same thing, so just what does ASTM C732 represent?

http://www.ides.com/property_descriptions/ASTMD732.asp

Oh, Punch Shear, but how thick was the test specimen? Thickness vs. result in this case, is kind of important; they make the same mistake on there other literature, wrong test description.
+ The Shore D hardness is very good. You can barely dent this material with a sharp spring loaded needle.
+ The shrinkage is very low and the absorption is right on target for a high strength epoxy.

I scratch my head when it comes to the flexural strength. For epoxies, the flexural strength ought to be half way between the tensile strength and the compressive strength, or more towards the compressive strength. Modulus numbers would help to explain the low flexural strength. Without the modulus numbers I can’t really tell if there is something weird about the product. One possibility is that the modulus numbers are higher that usual, which follows with the HDT and a very respectable Shore D. This causes me some worry, because the shrinkage is very low, not too low but this material is described as an epoxy-acrylate. Acrylates shrink. And fast reacting materials generate a lot of reaction heat. Could this material have a high internal stress? The product is listed and approved for live loading, so even though it may be high-stressed in its cured state - for highly confined applications such as grouting dowels into holes with minimal bond line thickness and “proportionally”, a low volume of adhesive and a very large surface area for bond; internal stress and the strain it would impart to the bond line does not appear to be problematic.

This material really does have some outstanding properties. The high HDT, the ability to cure in wet conditions AND over a wide range of temperatures (even below freezing). This material is not your everyday epoxy something else is going on.

To begin with, the 176 deg F. HDT is virtually impossible to achieve using the kinds of epoxy materials that engineers are accustom to seeing. At best under standard laboratory (room temp) cure conditions (23 deg. C), the maximum HDT for the best civil engineering epoxy adhesives tops out at about 145 deg. F., with a full cure of 14 days. Elevated temperature post curing for some formulations will yield HDT’s of around 165 deg. F. This elevated (120 deg. F +) temperature cure would not occur in a cold dank tunnel.

These typical epoxy formulas are frequently used for composites but the gel-time, cure to handling time, and subsequent “oven-cure” time are all scheduled. Under these conditions, the same formula can yield HDT’s as high as 250 deg. F.

Epoxy materials also have different stages of cure or “cure envelopes”. The cure stages are A, B, and C.
Stage A – is working life to gel time, Stage – B is a hard material, that is brittle (you can handle it, but you shouldn’t apply dynamic or sustained static loads) it is not impact or creep resistant and Stage – C, Full cure. Sometimes materials get stuck in the B stage; this is usually because temperatures have dipped below the activation energy temperature of the curing agent. If or when temperatures return to the activation energy temperature, the epoxy will continue to cure. The material will not usually gain the full strength that it would have if the cure cycle had been uninterrupted but in many cases a C stage cure is obtained. Think of it this way, for the molecules trying to hook-up (crosslink) it is like getting frozen in water as it plunges over the falls and after thawing out into hip deep muck. It is much much harder to get around. Inertia…

So how does the 176 deg. F, material obtain the high HDT? Looking at the MSDS reveals that this product is not cured using the Amine type curing agents typical of most civil engineering epoxy adhesives. The reactant is Dibenzoyl Peroxide. The “epoxy-acrylate” resin is also a vinyl ester, so some polyester is part of the monomer.

This material reacts via Free Radical/Homo-polymerization. This is why it cures at low temperatures, cures quickly and develops enough energy to gain such a high HDT. And, both the resin and the initiator are immiscible in water, which is why it can cure largely unaffected by immersion in water. It is fast like MMA polymer concrete or Bondo autobody filler. It is low temperature cure like MMA polymer concrete and some HMWM bridge deck sealers.

And like MMA and HMWM it can suffer oxygen inhibition. When Free Radical polymerization gets stuck it stops completely and does not start back up. It dead and you’ve got crap. Wet aggregate can inhibit MMA polymer concrete. HMWM bridge deck sealers can suffer surface inhibition under cold damp “heavy dew” conditions (this happened to Sika and CalTrans years ago on the San Mateo-Hayward bridge). Likewise, moisture/oxygen inhibition can inhibit adhesion/cure properties at the bond line.

This material may be fast and it may have a high HDT, it may cure at low temperatures and it may cure to a very hard solid underwater; it just can’t be all these things at the same time. And the data provided by the manufacturer, WHOOPS! Actually the manufacturer is a company, according to my internet sleuthing is called SOCOM in Cardet, France that private labels. The data does not come anywhere near to demonstrating just how it can do all these things at the same time.

Here are three scenarios, each of which could/probably did happened.

- Low Temperature, Wet, Slow Cure & Difficult placement (bar was pushed in repeatedly while trying to make it fast) = Inhibition & brittle material, degraded overtime by hydrolysis. OH! And damp threaded rod.

- 60 deg. Air temp & 50 deg. Concrete (wet or damp). OH! And damp threaded rod and fast cure = Hard full strength material with some oxygen inhibition at the concrete and threaded rod bond lines. Consequently hydrolytic degradation.

- 60 deg. Air temp & 50 deg. Concrete (dry). Everything is great except it is really difficult to squirt material out of a long nozzle, get it to stick to the end of the hole and somehow tweek the nozzle, without being able to see what is going on, up in there, to get it to stick to the sides of the hole. Building layer upon layer, it would take a lot of time. Otherwise you stick the nozzle in the hole a keep filling until you feel resistance and start withdrawing the nozzle, creating air pockets as you go. = You took to much time; the material has started to gel beyond its ability to wet-out the threaded rod. THIS stuff goes off like polyurea that’s why the bond strengths are so low. I question whether the 2 day, bond strengths increase and would not be surprised it the Wet bond strength was less at 14 days. It is so fast that it is starting to thicken before it exits the static mixer and quickly reaches a gellation phase where it sticks together internally but doesn’t grab the substrate.

There is nothing about this material that suggests it bonds better to wet or damp concrete than other epoxy formulations; it is the immiscible property of the material that lends itself to a high degree of mechanical bond in the confines of a hole than would give it some (maybe temporary) advantage. I think its elcometer tensile pull-off values would be relative to other moisture tolerant epoxies but possibly degrade much faster over time if oxygen inhibition plays a role. Given conditions where immiscibility and mechanical bond are the pull out resistance building properties, internal stress in the adhesive and subsequent strain to the bond line would become a concern. And field testing threaded rod by sounding with a hammer would not be beneficial.

I’m not a Guru when it come to Free-Radical polymerization so the full depth of how much oxygen inhibition and the role water can play in such a circumstance is based on my knowledge of MMA and HMWM.

I think it would be well worth it to ACI, ASTM and Building Code organizations to qualify manufactures (perhaps on a proprietary basis) as genuine formulator or private label/repackager, and restrict their committee participation accordingly. Absent in-house formulating knowledge gross assumptions are frequently made. To make a point, please note that Dibenzoyl Peroxide is a DOT Haz Class, Packing Group II, Oxidative Peroxide material with its very own Yellow Hazard label and label # 5.2, UN3108, PG II, seemingly the epoxy-acrylate from this source has the special ability to transcend DOT restrictions by Air, Sea and Land. Can’t find another MSDS for a material that includes Dibenzoyl Peroxide were this is kind of exemption exists. Wishful thinking or greed?


I started out with a remark about the assumptions I have made here, so enough said.

 

[dik]

epxoybot... that post was worth a couple of stars!

thanks for the excellent work, Dik

 

[hokie66]

Epoxybot, you are just showing off now. Most of us don't understand what you are talking about, and I wager neither did the engineer who specified and/or approved this system. But thank you for showing us how complicated this stuff is. Materials like concrete, steel, aluminum, timber, etc. are enough to get my mind around without trying to be a chemist. Whatever else may come out of this disaster, I think the use of adhesives in structures will take a big hit.

 

[wiktor]

An Engineer
Epoxybot, thank you for presenting to all of us, that the king is really naked. I really do not think that any epoxy expert was consulted prior to specifying and approving the system. I will even say more - common sense should suffice to determine that the bond in between any epoxy and wet, water saturated concrete could be questionable and some probes or inquires should be done. It was not a string budget project - for $14.6 billion and counting, such services could be expected.

 

[bostonjohn]

Check out the pictures in the article.

http://www.cdc.gov/elcosh/docs/d0100/d000067/d000067.html

 

[adhesiveman]

"Manufacturer" has been determined to be Powers Fasteners from Brewster NY. Powers is a repackager selling "epoxies" from many sources both US and European. They are the only "manufacturer" to be supeoned to date.

The term EPOXY is used in a very general sense on each post I have read. Everyone is eager to blame poor specification and poor installation, but not so quick to demonstrate knowledge about the type of anchoring used.

Epoxies come in many forms and many of the most often used "epoxies" today are actually not epoxies at all but acrylic based.

Wet, damp applications can be overcome with the proper adhesive.

Almost any load strength can be met with the proper adhesive, proper depth, and proper installation.

Overhead applications can be easily handled with the proper adhesive (gel), proper installation, and proper embedment depth.

Epoxies have a chemical resistance to 41F degrees so cold installation is often a deterrent. This can be overcome by many non-epoxy adhesives manufactured by ITW Red Head, Hilti, and Simpson.

There is plenty of blame to go around. Sounds to me like the engineer did not properly follow-up on his specification, the installation is questionable, and the "epoxy" used might not have been the right choice.

The most important question to me is - Why, on a project of this magnitude, was there not better oversight of specification, installation inspection, and products used for this application???

Lastly, what were the designers thinking when they designed this 3,000lb drop-ceiling?

 

[unclesyd]

Just saw on the news that the big lawsuit, victims family, has been filed. It names the Mass Turnpike Authority, and 9 other companies.
I dont think it will get to trial as too many skeletons would fall out of the tunnels.

 

[kenvlach]

Interesting development: The memo (cited above) by John J. Keaveney, former safety official for Modern Continental Construction Co., may be an after-the-fact, CYA effort. See
Memo writer gets 2d lawyer

http://www.boston.com/news/local/articles/2006/08/09/memo_writer_gets_2d_lawyer/?page=full

"The field notes say Keaveney did not make his ``first weekly safety inspection" of the tunnel until June 3. The engineer's notes say that Keaveney found no safety violations by Modern Continental that day.

The engineer's notes also show that by the date of Keaveney's memo, construction workers had not yet begun drilling holes in the tunnel roof. In his May 17 memo, Keaveney said he could see water dripping from holes in the roof, but the field notes show that drilling did not begin until June 10."

 

[kenvlach]

Some new info divulged here:
Big Dig designers asked to reduce bolts
thread507-165697

Original design was 4 anchor bolts per plate, but in a 1998 memo
'Gannett Fleming officials agreed to reduce the number of bolts, calculating that the ceiling would be safe "assuming proper installation and quality of the product materials,"'

So, 2 to 4 anchor bolts per plate, installed in possibly drippping wet holes using epoxy rated for damp conditions, with the epoxy possibly not filling the drilled holes, installed by workmen posssibly tired from overhead work. And, an inspector in legal trouble for backdating reports in an attempt to cover his you-know-what. Although we shouldn't speculate (too much), it seems like a clearcut example of the assume rule.

 

[HgTX]

Assuming proper installation and quality in an engineering calculation is not unreasonable. What factor of safety should one use when one assumes bad workmanship or poor equipment quality?

On the other hand, taking steps to ASSURE that quality is also not unreasonable.

Hg

Eng-Tips policies: faq731-376

 

[DRC1]

The difference is not quality of workmanship, but rather reasonable constructibility. The first is the responsibility of the constructor the second is the responsibility of the designer.

 

[rorschach]

After reading all of this I'd venture to guess that everyone looking at it assumed someone else had verified things. This is the way of group projects, nobody takes ownership. The PE probably based his approval on a "baffle them with BS" dog and pony show by Power Fasteners' salesman based on the vauge and misleading data form HIS supplier that epoxybot pointed out. I too give him a star for that BTW. I'd be willing to bet there is a BIG LEGAL DISCLAIMER in the cut sheet on this material stating that they are not liable for basically anything and you are basically using it at your own risk. I'm sure that bit was not emphasized very much during the dog and pony show. The guys doing the work I'm sure probably had little to no training in the proper procedures and probably none of the tools required to do a proper job. This sounds like a charlie-foxtrot all around.

HgTX, when I'm designing something for field installation, I do my best to make it as idiot resistant as possible because I KNOW that if there is a possible way to screw it up, the guys doing the work will find it. Even if there is NO WAY to screw it up, they will often INVENT a way to do it, idiots are most clever in that manner. Assuming technical competence on the part of others is a recipe for disaster most of the time.

Was there a written procedure or work instruction on how to install these things? were the guys trained in using it? was anyone verifying that it was followed or understood or even possible to follow given the circumstances? or was there merely some vague wording about following manufacturer instructions?

He who does not specify what he wants, deserves what he gets.

 

[epoxybot]

Our product has been tested in compliance, to the conformance that it meets.
Yes, that right, we state what we say because we mean what you want.

I once worked for a very reputable adhesive manufacturer that has since been absorbed by one of the concrete building materials giants; they too are a very reputable company. It was and probably still is, the habit of both of these companies, when required to write manufacturers letters of certification, to use strict guidelines. Sadly, product literature does not always adhere to the same principals.

Manufacturer certified test results are typically written by laboratory testing personnel and product data sheets are written by marketing product managers. A good letter of certification will include a stamp from a notary public and be signed by the senior lab QC testing person or the Manager of R&D. Signing off on Certs. can be, well kind of, sort of iffy, if you in fact are not the actual producer; but you can, as long as you have all your manufacturer’s QC records and are specific as to what you are certifying to.

Sometimes, product managers have a background in construction and some have educations in business marketing and are learning the construction stuff as they go. Some companies require R&D management to give their approval to the information presented in product literature and a lot don’t.

It used to be that compliance testing meant that a manufacturer could present data that demonstrated a particular product had been tested in accordance with a specified test or standard. It used to be that conformance, meant that a particular product conformed to the general intent of the specification with certain, possibly inconsequential exceptions “as noted”. It used to mean, and it should without exception, mean that if a material meets a specification, then that material has point for point, been tested and “meets or exceeds” the minimum requirements set forth in the specification.

Well, my mother was born in the “Show Me” state and I was raised according to the caveat – “Believe only half of what you see and nothing that you hear”. My material manufacturers experience has made me skeptical about the claims that many manufactures make on their data sheets. As I read a competitors data sheet, the features and benefits are less important to me, than whether the ASTM test results are in context and representative of the material, and that the results demonstrate the material actually meets the requirements of a given specification.

“Hypothetically”, let’s take an example:
Specification:
ASTM C881 - Standard Specification for Epoxy-Resin-Base Bonding Systems for Concrete
Material: Power Fasteners - AC100

I take exception to Power Fasteners published literature, with regard to its “meeting ASTM C881, Types I and IV Grade 3”. It is true that types I & IV are the categories relevant to grouting a fastener into a hole in concrete. They are also the categories relevant to general purpose bonding and the repair of cracked concrete. AC100 could be used for general purpose bonding and if I were a boat owner, who fished in the gulf of Mexico or the sea of Cortez; I would keep a couple cartridges of this stuff in my emergency repair kit, except, I would also need an epoxy primer because this material would not bond very well to fiberglass. This is because it is not an epoxy; it is a vinyl ester. And it would be a lousy concrete crack repair material.

In fairness to Power Fasteners, most the ASTM tests embodied in ASTM C881 are tests that characterize the properties of plastics. The tests have been culled from ASTM testing methods and assembled into a specification with minimum performance values attributable to epoxy resin systems used for concrete. The tests presented in specification C881 are relevant to AC100. AC100 just isn’t an epoxy.

I decided to bone-up on vinyl esters; I already had a good idea why this material was being called an epoxy acrylate instead of the well established nomenclature: vinyl ester. So dust off you Bunsen burner, break out your Erlenmeyer flask, pour yourself some brandy, warm gently (see Bunsen burner) and let’s get small.


A vinyl ester is a polymer, in the middle of which is an epoxy molecule but the functionality of the epoxy molecule is used up. Attached to the functional groups, at the ends of the epoxy molecule are either, methyl-acrylic acid or acrylic acid molecules. What left are half used acrylic molecules, the remains of which are characterized by a constellation of atoms that have been ascribed the term vinyl group. They, in turn, are tipped by a functional ester. Hence vinyl-ester or if you don’t feel that people will have good feelings about vinyl esters you can stretch it a bit and call it an epoxy acrylate.

Most commonly there are Bis A epoxy resins, Bis F and Novalac epoxy resins and by extension vinyl esters are usually built from one of the 3. It’s just that calling a vinyl ester an epoxy acrylate is like calling a paper clip a wire fastener; it lacks for something. School’s Out, no more chemistry.

If you are not new to dowel grouting, then you are probably familiar with capsule anchors. Capsule anchors look really cool. The capsules are glass and shaped like a test tube. The contents are usually a thick liquid in the form of polyester or a vinyl ester and these materials set up very quickly. There are certain problems with capsule anchors and for some engineers the association between vinyl ester and capsules probably has a lot to do with fastener companies, not just Power Fasteners, renaming this material.

To begin with, capsules have a specific volume of material and you can’t break one in two to make up the difference. You can make up the difference with material dispensed from a cartridge but you would probably want to use the cartridge first, and then insert the capsule except you might not know if you were going to need extra material. Depth and diameter of the hole makes capsules a problem because field experience has proven that contractors will use one capsule per hole and not consider the complete filling requirement.

Capsules also require in-place mixing; the glass capsule must be broken and pulverized. The procedure for doing this, involves an attachment inserted in the chuck of a power drill to which a thread rod is mounted. The rod is inserted in the hole breaking the capsule and the drill then pulverizes the glass while mixing the material. Some contractors, finding they lacked the attachment would try and do this by hand; this is a VERY bad idea.

Vinyl ester and capsules are for some engineers a bad memory. “Allakhazam - Epoxy Acrylate”

The ASTM C882 bond strengths of AC100 are, for me, a concern. ASTM C881 provides for a 14 day room temperature cure. Are the AC100 test results for wet or dry specimens? It is possible that the 14 day wet cure bond strengths are LOWER than the 2 day results. Here is why…

http://www.wes.army.mil/REMR/pdf/cs/mg-1-1.pdf

and

http://www.wes.army.mil/REMR/bulls/vol14/no2/text/grouting.html

I firmly believe that any engineer encountering a bond strength at 14 days that was less than the 2 day value would want a in-depth explanation as to just how this phenomenon occurs.

It should be noted that the REMR testing was done years ago and that Rawl and Power Fasteners are historically the same company. Furthermore, while epoxy resins are water insoluble the typical amine curing agents are not, so they suffer hydrolysis more readily than vinyl esters. It should also be noted that in the testing, vinyl esters did out-perform the epoxies and the polyester but there is definitely a lot to take into consideration and a statement of “Used in wet environments” for a bolt grouting material, is attributing a boiler plate level of performance that is, at best questionable, especially when used overhead. This brings me to the matter of Non-Sag. I don’t believe it.

ASTM C881, Grade 3 materials are non-sag; the requirement is 1/4 inch (approx. 6mm), from time of application to gel. It is a pass or fail test. The adhesive is mixed and troweled into a trough 1/4" deep and about 1 & 1/2" wide. The material must hold its shape supporting its own weight until it is hard.

AC100 does not indicate the non-sag thickness. Likewise, it does not list a viscosity. Viscosity is actually a meaningless number for non-sag materials because a very high viscosity material, lacking internal bonding, will nevertheless sag under its own weight; it is only a matter of time. See the Pitch Drop experiment.

http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml

I just do not believe that a material with a gel time of 7 minutes at 68 degrees F. is NOT a high viscosity flowing liquid. A 1/4" inch a non-sag paste in a cartridge would require some effort to dispense using a manual delivery gun and if AC100 were a paste, even with a compressed air gun, the speed at which free-radical polymerization thickens is so fast, a contractor, without machine-like execution; would be throwing away static mix nozzles left and right.

So I am going to ASSUME, having not ever seen this material. I get the feeling that it is goopy, molasses goopy, vinyl ester capsule goopy. If it is, would any engineer seriously consider specifying a flowing material for overhead application? I don’t think so. Mind you, at 68 degrees F, after 7 minutes you are not to disturb the dowel.

If I am right, then it does not meet ASTM C881, Grade 3 and this might be important to know. There is certainly enough about the AC100 bulletin to give ME reason to doubt.
ASTM C881… Show Me an independent test result, point on point.

I don’t know which Power Fasteners material was used on the Big Dig. If not a vinyl ester and wet conditions exited, judging from the REMR testing, I would be even more concerned.

For the record, I am not currently working in the adhesive industry so every house is built of glue and glass.