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Slab-on-ground joint filler

Slab-on-ground joint filler

Slab-on-ground joint filler

(OP)
I am hoping someone may be able to clarify why ACI 360R-06, section 5.4 suggests that semi rigid epoxy provides sufficient shoulder support for joints subjected to wheeled traffic and discourages the use of elastomeric joint filler? Any knowledge gained from practical experience would also be greatly appreciated.

To expand on this question, I understand that even with delayed installation of the joint filler, say 90 days after concrete placement, the floor slab will continue to shrink. With semi-rigid epoxy filler this can and often does leed to filler separation. I have seen written that the consensus of the industry is that separation void of the filler of 1/32" or less is considered acceptable. Wouldn't the slab shrinkage after joint filler installation (and prior to joint filler separation) actually induce tension in the shoulder effectively making it more susceptible to spalling? Furthermore, once the joint filler has separated and even being within the 1/32" tolerance, it's not clear to me why this would be considered a supported joint shoulder.

The general concept of using a filler that has a more compatible stiffness to the concrete makes sense; however, actual practice and performance does not seem to support this rationalization. Based on this, the elastomeric joint filler would seem to be a better choice because, if nothing else, it reduced maintenance (no joint separation to deal with). Your feedback will be much appreciated.
 

RE: Slab-on-ground joint filler

sbw,

I think you raise excellent points.  On a recent project, we specified semi-rigid joint filler (due to anticipated lift truck traffic)and the filler is doing exactly what you said--it is separating.  I look forward to hearing from others on this subject.

DaveAtkins

RE: Slab-on-ground joint filler

If a semi-rigid epoxy is used as a joint filler/sealer, it cannot be placed soon after construction for conventional concrete.  For low w/c ratio concrete and large aggregate concrete, the time for installation is reduced, but as long as the initial primary shrinkage is still going (can be up to year in many cases), you will get separation.

Provided you have adequate aggregate interlock, a sufficiently rigid subgrade, or doweled joints, there is no reason that elastomeric joint sealants can't be used.

Semi-rigid epoxies do very little to stop edge spalling.

RE: Slab-on-ground joint filler

A lot of different opinions on this.  I wouldn't use an epoxy in pavement joints.  But neither would I use a low modulus sealant like the one cap4000 suggested.  Did Dow Corning recommend that sealant for the application?  We have good experience with high modulus polyurethane sealants, provided the joint preparation, configuration, priming, and application are controlled.

RE: Slab-on-ground joint filler

I'd be interested to know where it is written that a 1/32" separation is acceptable.  That just doesn't make sense.  I believe the way it's supposed to work goes like this:

1. There is no separation.
2. The semi rigid epoxy will initially be in tension.
3. The epoxy will relax over time, and the tension dissipates.
4. The filler can support the joint after the filler has relaxed.

As you say, the initail tension would actually contribute to spalling, but over the long run, ther will be less spalling than having a soft filler.
I suppose the ideal solution would be to use a soft sealant and then come back after a year or two and install a semi rigid epoxy, but I'd never spec that.
If your sealant has separated, I think it needs to be cleaned out and reinstalled.  How thick was your slab and how far apart were the joints?

RE: Slab-on-ground joint filler

Hokie66 nailed it.

BA

RE: Slab-on-ground joint filler

Many semi-rigid epoxies have about a 20 to 24 percent elongation capability.  For sawn joints, which might be about 3/16" wide, that means a 24% elongation takes it out to almost 1/4".  Anything more than that an you risk the tearing.

Ron's comment that you need to wait a long time is correct.  I think "good" owners would allow the basic elastomeric filler for the first year and then tear it out along high-traffic areas and re-fill with the semi-rigid epoxy.  

However, most owners don't want to mess with that and contractors don't want to come back to do that either.  

I'm uncertain of Ron's comment that semi-rigid products don't help the joint edges against hard wheel loads.  Might be true - I just don't know.  I thought that the whole existance of semi-rigid epoxies developed just because of this issue.

RE: Slab-on-ground joint filler

(OP)
Thank you all for your responses. ACI 360R table 13.1 provides a great overview of various items that adversely effect shrinkage. Addressing as many of these items as possible with the mix and set up is certainly an important first step.

With the project at hand, an additive was utilized that is supposed to reduce shrinkage in the 20-25% range. Contraction joints are being troweled in with a square edge trowel with a finished joint width of about 1/8" to the 1/4-slab depth. Construction joints utilize diamond plate dowels sized and spaced in accordance with current recommendations. Joints are spaced 15' maximum and the pour is done out of the elements (enclosed space). Typical slab thickness is 6" with reinforcing 2" clear from top.

In terms of the delayed timing on the joint filler installation and the suggestion that the joints are filled then later removing the filler and re-filled, I have a couple comments. First, if project timing allows the joints to be filled 90 days or later that's great, but in a fair number of my projects the owner wants to occupy the space within 60 days. Even so, at 90 days after pouring my understanding is that the concrete still has 50-70% of total shrinkage to go. This can be significant. Second, to remove the filler and re-fill would likely require saw cutting the joint to properly prepare them. This would be unacceptable to most (and likely all) of my clients once the space is occupied.

miecz, I was not aware that these products creep/relax. Can you please provide a reference for this? The 1/32" allowance that you questioned can be found in a technical bulletin by Metzger/McGuire (www.metzgermcguire.com, bulletin T11). I have not confirmed this statement with other resources.

JAE, I would be interested to know which epoxy product has the 20+% elongation capability. I understood this to be more in the range of 5-10%. That makes a big difference and might be enough tolerance for many/most projects. I understood, like you, that the epoxies were developed and are used specifically to support the joint shoulders. My impression, though, is that these joints are not maintained/re-filled and the owners live with joint separation. At this point it seems to me better to have an elastomeric joint that keeps dirt and liquids out than a separated epoxy joint.

To continue on the topic of separation, ACI 360R notes that this does occur with the epoxy fillers, that it's not considered a failure of the filler, and that the separation should be subsequently filled (unlike the 1/32" tolerance that is the supposed industry tolerance). My issue with this is that I am not convinced that in practice for a narrow separation that the re-filling of these joints would penetrate down into the separation deep enough to be effective at supporting the joint shoulder.

Just like many of the engineering challenges we are faced with on a daily basis, there are many variables and so surely not one answer for every case. Incidentally, I sent this question to ACI's tech department before submitting it to this site. If I hear back I will post their answer.

Thank you all and I look forward to further discussion.

RE: Slab-on-ground joint filler

sbw-
I'm still looking for a reference that states outright that semi-rigid is plastic under sustained stress.  I thought that was the difference between semi-rigid and rigid.

RE: Slab-on-ground joint filler

sbw-
My old Euclid catalog listed a Modulus of Elasticity for rigid epoxies, but not for semi-rigid.  For semi-rigid, Euclid listed Elongation at 7 days of 55%.

RE: Slab-on-ground joint filler

That 55% must have been a typo.  They must have meant 5%.

RE: Slab-on-ground joint filler

I don't see any merit in the idea of installing a low modulus sealant first, then removing it and installing something harder.  Compatibility of the materials would be deal breaker, especially if the soft stuff is silicone.  Nothing sticks to silicone except silicone, and completely removing the original silicone from a concrete edge would be impossible without cutting out some concrete.  

RE: Slab-on-ground joint filler

hokie66, I would agree.  But many of the semi-rigid epoxy mfrs. recommend re-saw-cutting the joints prior to application anyway so any left-over sealant would be gone.

The 20%-24% was for one product we recently looked at.  I think there is actually a Euclid product that claims higher elongation.  Keep in mind that these elongations are probably the stretch that occurs right at initial tearing in the tests.  So with a safety factor of sorts on the material, perhaps 24/3 = 8% is the "safe" stretch.

 

RE: Slab-on-ground joint filler

I am not really familiar with the term "semi-rigid", as I don't believe it is used in Australia.  Sounds like an oxymoron to me when it applies to an epoxy.  This must be a combination sealant, maybe a urethane with some epoxy to make it harder?

What dimensions are used for these joints?  When I have seen sealants come away from one side of a joint, it has been because the depth to width ratio is too large, the bottom of the joint is not debonded, or the surface has not been prepared/primed.

RE: Slab-on-ground joint filler

JAE...my comment on the joint edges applies to normal width joints (1/4" or less).  These joints don't exhibit as much edge spalling as wider joints anyway, so the type of sealant is somewhat irrelevant.  That depends to some degree on the "hardness and diameter" of the wheels, but generally anything over about 16 inches in diameter and reasonable hardness will not usually cause issues with otherwise durable concrete.

RE: Slab-on-ground joint filler

hokie66,
Yes, semi-rigid sounds weird but it is simply like hard rubber when cured.  I've attached one product data sheet for reference (I'm not a salesman - just had this one handy).

Ron,
I don't have any grand expertise with whether this stuff helps for wheel loads.  I would tend to see your point that anything with any level of flexibility probably can't provide enough lateral support to avoid joint edges from failing.  Larger rubber tire wheels probably don't do this sort of damage anyway.  The wheels I've seen in Postal Service work rooms are small, hard wheels with very heavy weight and they (the USPS) have all sorts of joint problems because of them.

 

RE: Slab-on-ground joint filler

This is what I use... and no problems, yet <G>.

SLAB SAWCUT AND CONTROL JOINT SEALANTS TO BE:
  SIKA LOADFLEX 2 IN HEAVY TRAFFIC AREAS
  STERNSON DUOFLEX 333 IN MODERATE TRAFFIC AREAS
  STERNSON DUOFLEX SL IN LIGHT TRAFFIC AREAS

and I have a standard detail sheet for the joint.

Dik

RE: Slab-on-ground joint filler

JAE-

I can't open your attached pdf.

RE: Slab-on-ground joint filler

I can't open my attachment either now - I'll repost it Monday...sorry.
 

RE: Slab-on-ground joint filler

That's the one....thank you hokie66.

 

RE: Slab-on-ground joint filler

hokie66,

Did you read both articles and side with one guy or the other?  

I thought the response by Weiss was insufficient to counter the issue of hard wheel loads on joint edges that Tarr put forward.

I can't see how a polyurea material with that much flexibility would do anything to help the joint spalling under hard wheels.

 

RE: Slab-on-ground joint filler

JAE,

I have mixed feelings about the two viewpoints.  Weiss has made his points well, but has a proprietary interest.  On the other hand, Tarr just seems to me to be parroting the ACI position, and I believe that ACI now gets into a lot of things they know little about.  I would not specify a system which has a track record of separating.  As Tarr says, there is no ideal material which serves as both a joint support and as a filler.

I think there is still an argument for armouring joints, not with angles as was the historical practice in industrial floors, but with flat bars or proprietary preformed epoxy bars.  The attached is a system widely used in Australia for floors where the owner is serious about joints.


http://www.lesasystems.com.au/products/joint_protection/lesastrip.aspx


  

RE: Slab-on-ground joint filler

(OP)
I recieved a response from ACI this morning and I must say I am rather dissapointed. I feel the response is fairly "canned", without specific thought given to the subject. The question I posed it pretty much verbatim what I posted on this forum. Here's the response:

-----

ACI publishes codes, specifications, and reports for the concrete user.  This message is in response to your technical question/inquiry.

Below find the response (with minor modification) as received from the committee addressing your question:

Elastomeric sealants are inherently inappropriate for floors supporting hard wheeled vehicles because the relatively soft sealant (typically Shore A45-65) will deflect under load, thus leaving the joint edges vulnerable to impact. To support hard wheel traffic, especially small 4" diameter hard wheels such as those on pallet jacks, a filler must have a minimum Shore hardness of A80 or it too will deflect under load. A80 has been an industry standard for 35+ years and is thus proven successful.
  
The inquirer's comment about a semi-rigid filler inducing tension in the joint shoulder would be correct IF the filler had adhesive strength that see it tearing the shoulder off as the joint opens during slab shrinkage.  But a properly formulated filler should have a lower adhesive and tensile strength, thus ensuring it will separate at its bond to the concrete OR within itself before it tears concrete. There are broad range of both epoxy and polyurea fillers in the industry all have low range strengths.
  
If one looks at a filler after typical joint opening he will usually find the filler bonded to the concrete only on one side. If the filler has been installed to the proper depth in a saw cut, a cross-section view would show that in effect the filler is a bar of solid rubber sitting on a concrete shelf for support. This bottom-basing
concept is the key to the success of semi-rigid fillers.
  
If the inquirer will go to any of the manufacturers' websites; i.e., (www.metzgermcguire.com), (www.euclidchemical.com), (www.daytonsuperior.com) or equal, will find relevant information their.  For example, Metzger McGuire's website has a sketch shown on sheet T1 that makes the concept of semi-rigid fillers clear.
 

RE: Slab-on-ground joint filler

sbw,

There is too much divergence of opinion on this issue to get a good answer from ACI or anyone else.  Armoring the joints as hokie suggested may be the only sure way to guard against damage from hard wheels.

BA

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