Expansion Joint, Waterstop, and Dowel for Concrete Flume

[ojuego]

Hi,
I am designing a flume to carry stormwater, a cross section depiction of which is attached. We want to have an expansion joint every 20 feet to aid in removing the construction if there is ever a problem with one of the utility lines that is to be buried underneath the flume. I do not want water leaking through the expansion joints, so I want to have a waterstop in between sections. Usually in construction like this (but when it does not include the need to carry water) I include at the expansion joints some dowels to keep the alignment of the construction. The walls (and floor) of the flume are to be only 5 inches thick, and that thickness must include both the vertical and horizontal reinforcement that I am planning on having. The entire outside height of the flume, from the top of the flume walls to the bottom of the flume floor, is to be only 1 foot 1 inch (1.083 feet). So there is some uncertainty about whether or not the steel reinforcement is really even needed or not. But I am still planning on having it "just in case". Because of the thin walls of the flume, and the need for 3" clearance to each unformed surface, the location of the tensile steel can not really be on the tension side of each concrete wall (the side furthest away from the backfill to go next to the wall), but will instead be on the compression side of each wall. Partly because of that, I am planning on using fiber reinforced concrete, to give slightly added strength for the whole wall, but most importantly for the tension side of each wall (which happens to be the part next to the inside walls of the flume). The question I have is whether or not there is a way to include BOTH a waterstop AND dowels at each expansion joint. The problem is that there will be very little room between the dowels and the other reinforcing (the vertical and horizontal bars). My first tendency is to think that such little room does not really negatively impact the structure because the horizontal rebar is not really providing needed strength, but instead really only providing crack control, and because the limited length of the dowels (extending to 12" into each of the adjoining concrete sections) means that only the first vertical rebar will be encroached on by the dowel, because the vertical rebar is to be #4s spaced at 12" on center. If that is the case, then it seems that the dowels can be placed without having negative effects. What do you think? And do you have any other ideas for achieving what is sought?
Thanks!

 

[JedClampett]

Your expansion joints are going to give you a lot of misery. And spaced at 20 ft., that's lot of problems. You'd like to get any waterstop, especially expansion joint waterstop, between two curtains of reinforcing. So that's problem one. There's only going to be a 2 1/2 inch wide unreinforced section on each side of it. And it's going to be hard to form up an 8 inch wide trench. So that's another problem. You probably want to have the grating bear on a steel angle anchored into the concrete. Traditionally, it's a 2 x 2 angle with anchors. But with only a 5 inch wide section, that's going to be tough.
I wouldn't worry so much about those utilities under the trench. It's only a 18 inch wide trench. Can't they work underneath it? It would probably span most utility trenches. But on the other hand I think your trench walls are too thin. I would use 8 inch thick walls, and that if there's not expansion joints. I would make the base 12 inches thick with two mats of reinforcing. As far as the grate and trench, look into Zurn

http://www.zurn.com/Pages/ProductDetails.aspx?NodeKey=390436.

They make the whole trench, grate and frame as a unit, or just the grate and frame.
And as far as the fiber reinforcing, you could do that or you could flush money down a toilet. I'm not a believer. Just use 4000 psi concrete.

 

[ojuego]

Thank you very much for your thoughts. I am reevaluating some of the inclusions. The whole wall is only 1.5 feet tall, which includes the floor, so two mats of steel in the wall seems to just be way more than is needed. But I acknowledge your thoughts about having some steel support on either side of the waterstop. That is part of the reason for considering using fiber reinforcing. Also, because the length of the waterstop is only 4" or 6" long (depending on what model is selected), that means each half of it will extend only 2" or 3" into a particular 20 ft long concrete section. If the vertical and horizontal reinforcing is spaced 12" or 10" or 8" on center, then the first bars can start at 3 inches or 4 inches in from the end of the section. In that manner, the vertical and horizontal bar placement can completely avoid the presence of the waterstop....essentially what I am saying is that the waterstop would end before the horizontal and vertical reinforcing would stop. Yes, of course a good thought then becomes "how is the waterstop held in place sufficiently if there is no rebar immediately in the vicinity?". As an answer to that question, though, I am counting on the fiber reinforcement to provide some tensile strength. That added tensile strength does not have to be much, because the pulling on the waterstop by shrinking and expansion of the concrete is not expected to be much. The other thought, though, is to, instead of providing an internal waterstop, to provide an external waterstop, via silicone joint sealant and a backer rod. What are your thoughts on that?

 

[ojuego]

Oh yeh, the grating is to be fiberglass, and the particular manufacturer located also supplies 1" vertical x 1" horizontal fiberglass angle supports ("embedment angles"), on which the grating is to rest.

http://fibergrate.com/products/molded-gratings/micro-mesh®-grating/

shows the grating (an ADA compliant "micromesh" one is being considered). The "embedment angle" type of support is shown at

http://www.fibergrate.com/media/3662/ezangle.pdf

.

Regarding the difficulty in forming only 8 inches wide, thank you for pointing that out, and, yes, I am aware of that. I believe the contractor will try either one of the following. 1. Use shotcrete. 2. Use "foam" type inserts around which the concrete can be poured. 3. Pour the floor first, then place the "foam" type inserts on top of it and pour the concrete beside them.
Any thoughts on the above?
Thanks!

 

[dik]

I've often used bentonite rod in pour joints ... works really well.

Dik

 

[ojuego]

Thanks, Dik. Can you give some kind of reference where I can find out more information (and what exactly to spec) for bentonite? I did a look online, and all I found so far were references to powdered bentonite being contained in some kind of paper wrapping, or similar. Are there actually rods that could instead be used? Can you recommend where online to find a reference to such? Also, I am concerned about the swelling of such a potential bentonite rod? Is there a risk that when such bentonite swells it can crack the concrete? Do you know how much swelling there is? For instance, if I have a 3/4" diameter bentonite rod in a joint, and then it gets wet, how much will such swell? And, when it swells, does the bentonite just partially extrude out of the joint (and then retract when the bentonite dries)? Also, does the use of a bentonite rod need to have some kind of backer rod in back of it?

Thanks!

 

[dik]

From my General Notes file:


GEOSYNTHETIC CLAY LINER (GCL)

THE INSTALLING CONTRACTOR SHALL HAVE PRIOR EXPERIENCE IN GCL INSTALLATION AND HAVE COMPETENT WORKERS AND SHALL HAVE A QUALITY CONTROL PROGRAM IN PLACE

GCL SHALL BE BENTOFIX SUPPLIED BY BENTOFIX TECHNOLOGIES INC OR APPD EQ

ALL MATERIAL SHALL BE PLACED IN ACCORDANCE WITH MANUFACTURER'S PRINTED INSTRUCTIONS

GCL ROLLS SHALL BE HANDLED, STORED AND INSTALLED WITH CARE TO PREVENT BENDING OR OTHER PHYSICAL DAMAGE

INSTALLATION SHALL UTILISE EQUIPMENT SUITABLE FOR THIS WORK

GCL MATERIAL SHALL CONSIST OF A BENTONITE MATERIAL ENCASED BY NON-WOVEN GEOTEXTILE MATERIAL AND SHALL BE NEEDLE PUNCHED AND THERMALLY LOCKED

GCL SHALL BE PLACED TO PROVIDE 6" MIN SIDE LAPS

GCL SHALL BE PLACED TO PROVIDE 12" MIN END LAPS

SUPPLEMENTAL BENTONITE SEAMING MATERIAL SHALL BE WET APPLIED AT ALL LAPPED SEAMS AND IN THE QUANTITIES RECOMMENDED BY THE MANUFACTURER. CARE SHALL BE EXERCISED TO PREVENT THE INCLUSION OF DELETERIOUS MATERIAL INTO THE SEAM ZONE

GCL SHALL BE PLACED ON A SLOPE SO THAT THE SIDE LAP SEAMS ARE PARALLEL TO THE SLOPE

GCL SHALL BE PROPERLY SECURED AT THE ANCHORAGE TRENCH USING PROPER ACCESSORIES AND CONSTRUCTION TECHNIQUES

DAMAGED GCL SHALL BE REPAIRED AS DIRECTED BY THE ENGINEER

COVER MATERIALS SHALL BE PLACED WITH CARE TO PREVENT DAMAGE TO GCL MEMBRANE

and, from the Waterstop Notes:


WATERSTOPS SHALL BE VOLCLAY WATERSTOP-RX 101 U/N, BENTONITE BASED WATERSTOP CONFORMING TO ANSI/NSF 61 OR APPD EQ

WATERSTOPS SHALL BE SECURED TO THE STRUCTURE BY VOLCLAY WB ADHESIVE OR APPD EQ

WATERSTOPS TO BE SECURED TO STRUCTURE BY A WATERBASED ADHESIVE FORMULATED FOR THIS PURPOSE

SURFACE PREPARATION AND INSTALLATION SHALL BE STRICTLY IN ACCORDANCE WITH THE MANUFACTURER'S PRINTED INSTRUCTIONS

I've used the Volclay product on over 20 projects and I assume it works... no leaks, anyway. This is a flexible 'rod' about 1/2"-3/4" dia. It is cast into a cold joint often tied to dowels in a keyway or adhered to the concrete surface. I don't have a spec for the material here, but will see if I can dig one up as well as a detail tomorrow, time permitting. I included the clay liner because it is often used for 'water' projects. The bentonite swells to form a tight 'filler' in the 'self formed void' and is very effective as an easy to install and ecologically 'friendly' waterstop. Have to be careful with some salts as the bentonite swelling is an electro chemical action caused by charges on the clay surface and water being a polar molecule. Some salts can interfere with this.

Dik

 

[ojuego]

Thank you very much for those specs. I may indeed go that direction, but I have also been considering using, in the cross section taken through the expansion joint location, a 3/4" silicone joint sealant along the inside of the flume, with 3/4" backer rod in back of the silicone, and then expansion joint material for the remaining thickness. Through that expansion joint material would be dowels that help to align the 2 concrete sections on either side of the expansion joint. I have stayed away from using a waterstop (even though I originally wanted to use such) because the very limited width of the walls (only 5 inch thick) could cause enough conflict between the presence of the dowels and the presence of the waterstop that such could induce randomly angled cracks in that area near the expansion joint. I have used this general approach on another project and it seemed to work well. The only difference between that project and this project is that that project was for a retaining wall that was not meant to really contain water, while the present project construction is intended to contain depth of water for some time during a storm event. I will decide which direction to go after I read through the material you sent in more detail. Thanks again!

 

[dik]

A properly installed silicone joint will likely do the trick... but, may not have the longevity.

Dik

 

[ojuego]

Yes, thanks, Dik, I realize the longevity may not be there, but, given my hesitancy about the potential for the presence of a waterstop taking up more room to potentially cause cracking in the thin walls, such "shortevity" may just be something that the owner has to deal with periodically by having the silicone replaced/reapplied. Thanks again!