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RE: Expansive Grout

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Nels,

The first non-shrink grouts were made with iron shavings, later they were
made with aluminum powder.  All was well 'till they looked at the grouts
with some age (the NRC did this).  The cementitous metallic non-shrink
grouts performed inconsistently or poorly when it came to controlling both
plastic and drying shrinkage, and there was a problem with reactivity.  

In the mid 60's non-metallic, non-shrink grouts came along.  With that the
air bubble making ingredients became secret.  Non-metallic, non-shrink
grouts developed tiny air bubbles in the plastic state, retained the
alkalinity of the cement, and remained stable after set.  The cement based
non-expansive, non-shrink grouts expand slightly and work fine for building
columns, but the epoxy grouts should be used for sensitive machinery, bases
subject to impact or vibration, or bases subjected to corrosive chemicals.

As far as grout for masonry, I believe that manufacturers are very tight
lipped about what makes the bubbles.  I would contact the manufacturer
directly.  I believe their grouts are non-expansive and non-metallic, but I
don't know that for sure.  As you stated it is the potential for unrecalled
aluminum compounds that may put the grout at risk for long term durability.
An indicator of potential for corrosion is the pH of the grout after it is
hardened and has reacted with the magic bubble making compounds.  You should
stay on the alkaline side.  I would compare the pH with and without the
admixture.

The fluidifiers generally used for auger-cast piles generally use an
aluminum compound, but it is not a problem if there is a degree of expansion
in an auger cast pile.  And corrosion and expansion in the hardened state is
not a problem as long as the aluminum compounds become totally chemically
bound in the plastic state.

A practitioner very experienced in cement based grout injections of historic
masonry structures is Mike Schuller of Atkinson - Noland
http://www.ana-usa.com/masonry.htm.  I would give him a buzz on this one.
There are some very old grout injected masonry buildings in Italy.

Regards,
Harold Sprague

> -----Original Message-----
> From:	NRoselund(--nospam--at)aol.com [SMTP:NRoselund(--nospam--at)aol.com]
> Sent:	Tuesday, February 08, 2000 9:48 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Expansive Grout
> 
> Years ago, on my first existing building project, the bottom of an
> existing 
> concrete footing needed to be exposed so that a deeper footing could be 
> placed under it.  The contractor placed the new footing to within a 
> convenient few inches of the old footing and then made a batch of concrete
> to 
> fill the space between the new and old footing -- it was a conventional 
> site-made mix with a handful of aluminum powder added.  The fill was
> formed 
> and packed into place, but not with the care we expect today for a drypack
> 
> fill.  The fill material was expansive in the plastic state and resulted
> in a 
> tight fill.  My understanding was that the aluminum reacted with
> "something" 
> in the portland cement with hydrogen gas being one of the byproducts; tiny
> 
> bubbles of hydrogen gas kept the concrete expansive as long as it was in
> the 
> plastic state.
> 
> Sika Grout Aid and PMP Grout Additive seem to have similar action in the 
> grout used in concrete block construction today.  Apparently they consist
> of 
> aluminum powder and a fine aggregate.  My understanding is that these 
> admixtures act on portland cement and on flyash (which is principally 
> amorphous silicon dioxide). 
> 
> I have a project for conservation of the walls of an old stone building in
> 
> which I would like to use an injected grout that includes Sika Grout Aid
> or 
> PMP Grout Additive to control shrinkage.  I've developed a mix that has
> the 
> mechanical properties of appropriate strength, pumpability and shrinkage 
> control that I want.  A question from the materials conservator has
> arisen, 
> "How do I know that the aluminum admixture is not detrimental to the 
> surrounding materials in the long term?"  
> 
> I don't know, but I think that an understanding of the specific chemical 
> reaction would help us evaluate the long term effects.  Does anyone know
> the 
> specific chemical reactions?  My assumption has been that the reaction 
> includes a break down of water to produce hydrogen, leaving oxygen to
> combine 
> with the aluminum to produce alumina (Al2O3), which is a usual component
> of 
> portland cement.  The alumina (by my understanding) gets incorporated into
> 
> the binder as a calcium aluminate or a calcium aluminaferrite so that
> there 
> is nothing particularly unusual about the resulting concrete except
> perhaps 
> there is some un-reacted metallic aluminum remaining in the hardened 
> concrete. 
> 
> Can anyone help me with the specifics of the chemical reaction?
> 
> Nels Roselund
> Structural Engineer
>