Underpinning with Shrinkage Compensating Concrete
Underpinning with Shrinkage Compensating Concrete
(OP)
Is is a common practice in my country to use expansive cement(Type K) in the mix to control the shrinkage of the concrete when underpinning structures, avoiding the use of dry packing. I believe that this methodology works great because all the voids are filled in the process giving a 100% transfer of bearing loads. Does anyone has any experience here in the States? Does anyone has any ideas what may go wrong with this process?






RE: Underpinning with Shrinkage Compensating Concrete
RE: Underpinning with Shrinkage Compensating Concrete
RE: Underpinning with Shrinkage Compensating Concrete
RE: Underpinning with Shrinkage Compensating Concrete
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RE: Underpinning with Shrinkage Compensating Concrete
In certain areas of Florida, USA and under specific circumstances, subsurface pressure grouting is used to fill voids and compact soils, as well as seal off cavities in the limestone. This procedure is normally terminated 10 feet down from grade to prevent damage to the existing structure. A more recent technique to densify loose, near-surface sandy soils directly below structures is the use of chemical grout, or expansive polyurethane foam. It looks a lot like "Great Stuff", the expansive yellow foam in a can used in building construction to seal gaps and voids.
Subsurface compaction grouting is not referred to as underpinning here, which is why I asked for clarification. Underpinning here means generally steel pipes pushed down into the ground to competent material and mechanically attached to the foundation...
The grout is a non-expansive type, a similar mix to grout used in masonry grouting but it can be a lower strength.
Do you have more info on the type you are referring to? Any links to websites?
RE: Underpinning with Shrinkage Compensating Concrete
I wouldn't use it. We often underpin with normal concrete and have no problems. For a couple of feet the shrinkage isn't enough to worry about.
RE: Underpinning with Shrinkage Compensating Concrete
RE: Underpinning with Shrinkage Compensating Concrete
dcarr82775, your statement is partially correct, the shrinkage comp. concrete has an initial volume, then it expands, and then it can go back to the desired or designed mix design volume.
PEInc, when the concrete expands, don't you think that the contact surface is the same or maybe more than the one you can achive with the drypack. How the drypack help preloading the the underpinning pier?
Thanks everybody. This is my first time asking a question, and I am thrilled with your responses.
RE: Underpinning with Shrinkage Compensating Concrete
Welcome to the list and the US. Your country is beautiful, everyone should visit the Andes and Machu Pichu once at a minimum in their life...
RE: Underpinning with Shrinkage Compensating Concrete
I agree, but my point is the concrete is not allowed to expand. It is restrained by the structure above so the actual expansion doesn't occur. Therefore it shrinks from its 'as cast' volume, not the theoretical expanded volume. I suppose the expansion could actually lift the structure above, but I doubt this happens.
RE: Underpinning with Shrinkage Compensating Concrete
When you drypack an underpinning pier, you pack the damp sand/cement mixture into a 2.5 to 3 inch space between the bottom of footing and the top of the underpinning pier. The mixture is rammed into place using a sledge hammer and a short length of 2x4 lumber. When you hammer on the end of the 2x4, the other end packs the damp (not wet) mixture tightly into place. The cumulative packing effort pushes significantly against the bottom of the footing.
The attached PDF is one the few, but better, underpinning references. Enjoy.
www.PeirceEngineering.com
RE: Underpinning with Shrinkage Compensating Concrete
dcarr82775, below there are 2 links that shows graphically the shirnkage of a compensating concrete vs the regular portland cement concrete. I placed those two links even they are the same just to validate the statement of those graphs. As you can see, on day 7, the portland cement concrete starts it's contraction. After 21 + days, it has reached it's maximum contraction. If you place the drypack next day, or within the following 7 days after pouring an underpin block, that section of dry pack will just go down together with the shrinkage of the regular mix you have below. Now, if you use a shrinkage-compensating concrete, the first expansion (day 1)mostly will allow the concrete to fill all the voids, the rest of the expansion, according to the poisson effect, should be relieved to the side that has no resistance (the face side), placing the block in a distress. It means that the contraction also will be lower.
With all these my brain is shrinking now...LOL
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RE: Underpinning with Shrinkage Compensating Concrete
Here is another reference in two different volumes:
http://isddc.dot.gov/OLPFiles/FHWA/009755.pdf
http://isddc.dot.gov/OLPFiles/FHWA/009757.pdf
RE: Underpinning with Shrinkage Compensating Concrete
www.PeirceEngineering.com
RE: Underpinning with Shrinkage Compensating Concrete
I fail to see your point. According to the graphs there is really no significant difference to the amount of shrinkage the main difference is just that compensated concrete expands prior to undergoing that shrinkage.
RE: Underpinning with Shrinkage Compensating Concrete
Also, even the best underpinning procedures and materials may not prevent building settlement. References indicate that you should still expect some settlement of possibly up to 3/8 inch. I have designed and underpinned a few hundred buildings without any non-shrink or expansive cements , concretes, or drypack. Some buildings settle. Some do not. The theoretical amount of settlement associated with shrinkage of concrete and drypack is minor compared to the amount of settlement that may often result from things such as overburden removal prior to underpinning, soil settlement below the piers, or poor workmanship.
www.PeirceEngineering.com
RE: Underpinning with Shrinkage Compensating Concrete
Thanks everybody!
PEinc, is there anyway to contact you?
RE: Underpinning with Shrinkage Compensating Concrete
RE: Underpinning with Shrinkage Compensating Concrete
www.PeirceEngineering.com