Slab-on-ground joint filler 1

[sbw]

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.

 

[cap4000]

I have used this one at Newark Airport and on NJDOT slabs.
Check out the link. Good Luck.

http://www2.dowcorning.com/DataFiles/090007c880001fb9.pdf

 

[DaveAtkins]

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

 

[Ron]

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.

 

[hokie66]

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.

 

[miecz]

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?

 

[BAretired]

Hokie66 nailed it.

BA

 

[JAE]

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.

 

[sbw]

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 (

http://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.

 

[miecz]

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.

 

[miecz]

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%.

 

[miecz]

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

 

[hokie66]

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.

 

[JAE]

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.

 

[hokie66]

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.

 

[Ron]

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.

 

[JAE]

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.

 

[dik]

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

 

[miecz]

JAE-

I can't open your attached pdf.

 

[JAE]

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