Questions about high early concrete in compressor foundations 3

[dwedel]

Hi,

I am rebuilding a foundation under a natural gas pipeline compressor. We will use rebar, anchor bolt canisters, and steel oil pan. The foundation will be approximately 15-18 yds, and formed with the compressor in place supported by jacks. The compressor plant will have 7 other compressors running and vibration and cracking is an issue. We would like the repaired foundation to last another 50 years. Downtime is also an issue. We will use an epoxy grout on top of the concrete to hold sole plates for the compressor in place.

What are the problems with with high early that I should be aware of?

What are the problems assosiated with calcium cloride in concrete?

Is thermal cracking from curing a problem?

 

[dicksewerrat]

Mass concrete will generate some heat. Use enough rebar to control cracking and spead the stresses thoughout the foundation. You may want to hire a foundation or concrete specialist. Why aren't the attaching plates attached to the mass concrete with anchors? CaCl2 may attack the rebar.

 

[jheidt2543]

A few thoughts to consider:

1. What are the dimensions of the compressor foundation?

2. The heat generated by concrete hydration is usually not a problem in 15 - 18 cy of concrete. The sizes of most compressor foundations are such that the heat can disapate pretty quickly on five of the six sides.

3. I don't think you need to use high early unless there is a big hurry to use the compressor. Usually the concrete has gained enough strength by the time all the unit is grouted, the piping is done and the controls hooked up that it is not a problem. After 7-10 days the concrete should be pretty close to 3,000 psi. Take four sets of cylinders for breaks a 3, 7, 14 and 28 days.

4. I would not use any "sunshine" (CaCl2) in the mix. One additional bag of cement/cy is just as effective and less expensive than high early too. It is also less trouble than the CaCl2, even though there may be a little more shrinkage.

5. Dicksewerrat is right about the rebar, particularly if there is any amount of vibration from the compressor. Be sure the unit is balanced correctly during the start up.

6. The foundation should be isolated from the floor slab and the rest of the building.

 

[dwedel]

Yes, it would be nice to get this compressor back online quickly. Also, one of the reasons to use the high early is a recomendation from the epoxy grout manufacturer. They recomend to have the concrete reach a high state of cure before the epoxy grout is put onto it. Normally, they call for 28 days of cure before installing the epoxy grout. Water coming out of the concrete seems to be an issue for them, although I have not received a conclusive answer. The epoxy grout is Carter Waters 604, which is now an ITW Philidelphia Resins product. The epoxy grout will be a 5" layer on top of the foundation block.

Block dims are 16' x 9' x 4', we will probably leave some of the old concrete in, as long as we get the anchor bolts installed.

Lots of rebar is the norm in our construction. We will also use an "oil pan", usually a 12ga trough, to go under the compressor to keep oil and junk from accumulating on the concrete.

The sole plates will be embedded in the grout cap and will be points of the foundation where the compressor will sit on. The anchor bolts will come throuth the sole plates and then into the flange of the compressor. The anchor bolts are the tendons that tie the compressor to the foundation block. They are 1-1/2" dia by 3' long and will be torqued to ~900 ft-lbs.

Sorry dicksewerrat, but I am supposed to become a foundation expert. All kidding aside, this is my third foundation in 2.5 years. Unfortuneately as a Mech, I don't have much information in my library on concrete, and know less about adders. I'm not used to building targets. ;-)

As we are rebuilding the foundation, I don't have much choice about how the compressor is connected to the rest of the building. In this case, I'm not sure I would want to try to change it, the place is a swamp. As I'm not too sure where the piers are located, I'm afraid that cutting the foundation block loose from the other compressors would make it sink like the Titanic. I have observed that we normally build new stations with the foundation block seperated from the building and other units.

Does the rate of water coming from the concrete decrease inversly proportional to the stregth?

Are the other non-CaCl2 acceleration adders any good?

 

[BigH]

Why are you needing to sit the sole plates on a grout cap? I would think you'd want them on the concrete proper. I worry about a "thin" new layer atop an existing layer (even if only a couple of weeks old) - about the bond. If the sole plates were integrated with the concrete, then you don't have the possibility of the spalling/debonding, etc. from the capping layer. If concrete strength is a problem, you could always, at the time of the pour, use a stronger mix in the surface ft or so - poured from a "second" truck on top. Anyway, I'm interested to know why the grout cap.

 

[dwedel]

BigH - good question. Its what we have always done. ;-)

Going back in history in this company, a cement grout has always been used in the last layer of the foundation to bed in the compressors. Now the epoxy grout is used to bed in the sole plates which the compressor sits on. In new installations, the epoxy grout will be used to bed in the steel skid the engine/compressor package sits on.

The epoxy grout has the ability to resist the oil better than the cementous grout. The epoxy is more flexible, and doesn't crack as redily. The epoxy is also not as porous as concrete. If oil gets into a crack the vibration cycles fast enough that the when the crack closes, the oil cannot be driven back out of the crack and acts as a wedge making the crack larger. I think there is also a chemical reaction between oil and concrete. When we jackhammer oil soaked concrete out, it is like cheese.

There are a couple of things we do to make sure the layers are not the weak link. The rebar wickets are cast into the lower foundation block. These wickets will stick up into the epoxy grout and help form a mechanical bond. The bond the epoxy has with concrete is very strong as long as care is taken in the preperation of the concrete (according to the epoxy manufacturer). We "rake" the concrete when it is getting stiff with a piece of rebar to provide deep grooves to lock the epoxy and concrete together with. The ends of the anchor bolts are buried into the concrete foundation. With 900 ft-lbs of torque and a 65 ton compressor, we have lots of downforce to keep the layers together.

In the grand scheme of this project, $100/cy vs $150/cy concrete doesn't change the cost of very much. The crew working on the project and the lost throughput eat up most of the costs.

To continue the original question in this thread; it appears that water from the concrete curing may cause problems with the epoxy grout and concrete bond. Does a faster curing concrete give off more water at first, and then at 7 days is giving off the same amount of water as normal concrete at 28 days? Does anyone know where I can get data on this?

I think shrinkage could also be an issue with the epoxy/concrete bond.

 

[jheidt2543]

dwedel,

I would suggest you call the Portland Cement Association (PCA) and the American Concrete Institute (ACI) and talk to people in their Technical Services Departments about your questions and concerns. They would have the most up to date industry practice information on grouts. Also, call the manufacture of the grout product you intend to use and verify what you are being told by the supplier.

I don't have any experiance with epoxy grouts but, I do know from my experiance with epoxy toppings on concrete that they are VERY sensitive to moisture in the concrete. I personally would use a non-metalic, non-shrink grout product from Master Builders. I think it would be more compatible with the concrete base. MB also has a Technical Services Department with extensive experiance in grouting materials and installation proceedures. I'm sure they would help and more than likely send out their area rep.

The base plate grouting I've been involved with for machinery bases (like paper machine sole plates) is usually installed after the equipement is set and leveled. So, the grout is basically used as a "permenant shim". I have seen a few times where the plates are set then the concrete is poured. When done this way, it demands precise installation and heavy blocking to maintain the plates in the correct location. As one of my superintendants use to say, "Using the concrete eraser is very expensive".

Lastly, high early strength and curing are two different things and they don't necessarily relate to excess moisture disipation from the concrete.

 

[dwedel]

jheidt2543 - Thanks for your thoughts. Can you explain more on the high early strength and curing, and the moisture disipation from the concrete?

In between our sole plates and the compressor frame we use "chocks", two pieces of steel plate machined parrallel with shims of various thicknesses between them. After we are done with the foundation we will align the compressor frame by adding and removing shims.

This is our vendor

http://www.miltechmachine.com

Go to the link called Microline Products.

 

[dicksewerrat]

Use a water reducer to cut the actual amount of water used. The idea of substituting Cement for CaCl2 is a very good suggestion. going to a denser stonger concrete may help. Ask a micro silica and or fly ash in the mix. your concrete supplier will have more info than you want. If you are suppoed to learn to be the foundation guru, go to the 'World of Concrete' the trade show. Its ussually in Vegas each year.

 

[jheidt2543]

You could also try the website for L&M Concrete News, it is a newletter published by L&M Construction Chemicals, Inc. They are a structural grout manufacturer and have a line of cement based grouts as well as epoxy grouts. I haven't yet had the opportunity to use their grouts (I've only discoverd them recently), but I do read their newsletter and it is full of useful information.

Their website is at

http://www.lmcc.com

High early strength cement is produced through the chemical make up of the cement. It can have the same ultimate strength as normal Type I cement, but because of its chemcial composition the RATE of strength gain is faster.

Curing really relates to the period of time it takes the concrete to perform the chemical changes during hydration. If the concrete dries out too fast, it could leave a good portion of the cememt past unhydrated, which would affect the strength and durability of the concrete. There are a number of ways to cure concrete: curing within the forms, moist curing, covering with vapor barriers, spray on curing agents, steam curing (used in precasting) and they can all be used in different combinations.

 

[dwedel]

Allow me to recap what I have learned.

Concrete uses water to cure. Water film tests show that water is still in the concrete. This water means that the concrete hasn't cured or that there was too much water in the original mix. With this project, I will need to make sure that there isn't too much water in the reciepe, in fact I will probably use a plastiziser to make the concrete more flowable.

Sunshine "CaCL2" is undesireable with the amount of steel in the foundation.

Extra cement, Micro Silica, or fly ash can help speed up the cure rate.

If I use a fast curing concrete, I will probably need to make sure that I keep the surface wet. I think burlap would work best.

Places to get more information PCA, ACI, World of Concrete.

Thanks for your input,
David