Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DRY GROUT AND METHOD OF DISTRIBUTING ALUMINUM THEREIN
The present invention relates to grouting utilizing cementitious
material, or materials, finely divided aluminum powder and water, without or
with fine aggregate or admixtures, to produce a pumpable wet grout, and, more
particularly, to a packaged blended dry grout comprising cementitious
material, such as cement, blended together with protected aluminum flakes,
with or without other materials such as sand, and to the type of aluminum
flake product used therein.
Various practices have been previously used to introduce finely divided
10 aluminum into a wet grout. The aluminum particles react with the alkaline
water of the wet group to function as an expanding agent for the grout.
One such previous practice has been to mix at the jobsite about 3 to 5
grams of commercially available polished aluminum powder, such as leafing
flakes used as pigments for paints, with about fifty lbs. of cement at the
jobsite (to achieve dispersion); then this was added to more cement, and
usually other materials, plus water to obtain a pumpable or pourable grout.
This procedure is frowned upon in practice in that it is difficult to obtain
the correct proportions and dispersion of the aluminum flakes. One known
abortive effort to factory package blended aluminum flakes as commercially
20 available and cement for mixing with water at the jobsite was given up withina matter of weeks because of the reaction of aluminum flakes in the package
caused by the presence of the cement and the moisture in the blended dry mix.
Grout fluidifiers to be mixed at the jobsite with cement, water, and
perhaps other materials, have involved the factory blending of the aluminum
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flakes with a non-alkaline powder, such as fly ash or limestone dust and/or
other grout property-enhancing materials, with the blended materials being
packaged in accurate amounts by weight for use with a stated quantity of
cementitious materials at the jobsite.
Also, a prior and continuing commercial practice, is based on U.S. Patent
No. 3,197,323 and U.S. Patent No. 3,579,366 to Solomon J. Rehar, involving
preparing a dry grout including a cementitious material(frequently a portland
cement), a fluidifier comprising commercially available polished 100 mesh
aluminum flakes of the leafing type, and other materials, often a fine
10 aggregate(sand in common practice), and packaging the blend for storage and
shipment to a construction site where it is mixed with water to form a
pumpable wet grout for use in filling a construction form or other space to
form a hardened grout structure. Before the aluminum flakes are blended with
the cement of the dry grout, they are encapsulated in a methyl cellulose
matrix to protect them against reacting because of the alkali nature of the
dry blend caused by the presence of the cement and the relatively small
moisture content of the dry grout. Methyl cellulose is a non-alkaline
sensitive material and does not form a film coating which adheres to the
flakes. In this known practice, agglomerates or granules of encapsulated
20 aluminum flakes are formed. Flakes on the outside periphery of the
agglomerate are not adhered or protected by a coating and are lost.
When methyl cellulose is used to encapsulate the aluminum leafing type
powder, the methyl cellulose is baked after the agglomerate is formed to drive
out the solvent for the methyl cellulose. When the solvent is driven off, the
methyl cellulose frequently forms a hard matrix about the encapsulated
aluminum and it is difficult for the water of a wet grout to penetrate the
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methyl cellulose coating so that it can react properly with the aluminum
flakes. To address this problem, the matrix has been made porous. See U.S.
Patents No. 3,579,366 and 3,709,707.
Agglomerates of aluminum flakes and methyl cellulose, are of a relatively
large size~from about 300 microns to 1700 microns), each usually involving a
relatively large number of flakes. This has caused concentration of the
aluminum in the grout at the discrete locations of the agglomerates and the
failure to secure a sufficient distribution of the aluminum in the grout.
Accordingly, the agglomerates should be mechanically broken up when the dry
10 grout is mixed with water to form a wet grout for pouring or pumping so that
the necessary number of individual particles for the proper distribution of
the aluminum flakes throughout the grout are present, as well as to facilitate
penetration by the water of the wet grout into the particle to the aluminum.
The necessity to breakup the agglomerates is a problem but also
disadvantageously increases the mixing time for the wet grout.
When mixing the dry grout with water to form a wet grout, the
agglomerates, if not broken up into smaller particles to provide the proper
distribution of aluminum throughout the grout, will cause the aluminum in the
wet grout to be too concentrated at the locations of the agglomerates and the
20 aluminum will not properly function as an expanding agent. Accordingly, highspeed propeller type mixers are recommended, and normally used, for mixing the
dry grout with water to form the wet grout. The action of such mixers and the
abrasion caused by the mixing will break up the agglomerates sufficiently to
provide the proper aluminum dispersion and dissolution of the methyl cellulose
prior to the pumping of the grout. It is appreciated by those in the art that
when the agglomerates are mixed into the water of the wet grout and are broken
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up by the mixing, the aluminum flakes will start to react(i.e., gas) with the
rate of reaction depending on the alkalinity of the wet grout, temperature,
and the size of the aluminum flakes. Conventionally the reaction takes place
over a period of 2 to 3 and sometimes 4 or 5 hours during the pumping and
setting of the grout.
The relatively large size of the known agglomerates also presents
problems when bags of the dry grout are sampled for testing to see if the
constituents of the dry grout are within limits. In practice, the bags of dry
grout are sampled at the construction location before mixing the dry grout to
10 form a wet grout for pumping. The size of the presently used agglomerates
limit the number locations in the dry grout for the aluminum content. The
concentration of aluminum flakes in agglomerates results in a relatively
limited number of agglomerates and makes it possible to obtain test samples
from a bag that will not test within the required limits for the aluminum
content even though the bag, as a whole, is within limits and would function
properly when mixed properly to form a slurry.
In the known commercial practice of encapsulating aluminum flakes, methyl
cellulose has been used as a coating and binder for the aluminum flakes
because of its relative insensitivity to the alkali nature and moisture
20 content of dry mix. Aluminum flakes which are commercially available will, as
supplied, react in a dry grout blend including cement. While the flakes have
a stearate coating for preventing oxidation of aluminum, the stearate coating
applied to the aluminum flakes in commercial practice is not effective to
protect the aluminum flakes against deterioration during the normal storing
and shipping periods of a dry grout. It is believed that the primary reason
for this is that the stearate coating is not durable enough to survive the dry
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grout blending operation which is abrasive because of the presence
of cement, and perhaps other solids. However, it is questlonable
that the thin stearate coating of leafing flakes would survive the
alkalinity and moisture of a packaged dry grout including cement
even if the coating were not abraded by the blending operation.
According to one aspect of the present invention there
is provided a product for use as an expanding agent in a wet grout
comprising aluminum flakes and a coating for the flakes which has
a durability to survive a dry grout blending operation and of a
nature to have limited sensitivity to the alkaline nature and the
moisture of a dry grout blend comprising cement but of a high
sensitivity to the water of a wet grout containing cement so as to
deteriorate and allow the aluminum flakes to function as an
expanding agent for the grout, the particle size of said aluminum
product being such that the number of particles for a given
quantlty of aluminum is substantially that necessary to provide
the requlred distribution of the aluminum in the dry and wet
grouts.
Acc~rding to a further aspect of the present invention
there is provided a method of preparing aluminum leafing powders
for use in cementitious grouts comprising the following steps:
providing a quantity of aluminum flakes which are substantially
free of an oxide film and micro-particles which are inert to
aluminum and sufficient in number to provide a proper distribution
of the aluminum flakes in the cementitious grout in which the
admixture i8 to be used, coating the micro-particles and the
aluminum flakes with a material which has a high sensitivity to
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the alkaline water of the wet grout but a limited sensitlvlty to
the moisture and alkaline nature of dry cementitious grout to form
a film coating on the aluminum flakes and to adhere the aluminum
flakes to the micro-particles, the sald materlal being a blnder
which is resistant to the abrasion of the blending process for dry
blending the aluminum coated microspheres with cementitious
material, and drying the micro-particles with the aluminum flakes
adhered thereto.
In the practice of the invention, a film type coating
which adheres to the aluminum flakes is used with the film having
sufficient resistance to abrasion to survive normal dry grout
blending with cement. The coating while having a limited
sensltivity to the alkaline nature and moisture of the dry grout,
has a hlgh sensltivity to the alkaline water of the wet grout (the
alkalinity being caused by the presence of cement) so as to cause
the film coatlng on the aluminum flakes to break down (or
dissolve) and expose the aluminum to the ~ater of the wet grout to
obtaln the necessary reaction for the aluminum to function as an
expanding agent. One such alkaline water sensitive coating and
binder is water glass (sodium silicate). Other coatings and
blnders of slmilar characteristlcs may be utilized. For example,
the coating and/or binder may be neutral to an alkaline
envlronment but highly soluble in water, if lt has limited
sensitlvity to the moisture and alkalinity of the dry grout.
Accordlngly, ln the inventlon, the alumlnum used in the
grout ls coated with a film forming material, e.g. sodium
slllcate, which forms a film that coats and adheres to the
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aluminum with the coating being sensitive to the water and/or the
alkaline nature of a wet grout but which also has a sufficiently
limited sensitivity to the alkaline nature and moisture of dry
grout including cement and the abrasive nature of the dry grout
blending operation so that it is able to protect the aluminum
flakes for commercially
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acceptable time periods for storage and/or shipping.
In the preferred embodiment of the present invention, the aluminum
flakes, before being blended into dry grout materials, are film coated and
adhered to small micro-particles, e.g., commercially available glassy silica
microspheres, by use of a film forming coating and binder. The invention,
however, contemplates that the particles of finely divided aluminum may be
individually provided with a proper film coating, e.g., during the manufacture
of the aluminum and mixed into the dry grout without adhering them to another
particle.
In accordance with the preferred embodiment utilizing micro-particles,
aluminum flakes and small glassy micro-particles are coated with a film binder
which also adheres the flakes to the small glassy particles. The size of the
glassy particles is such that the coated glassy particles are sufficient in
number for the required quantity of finely divided aluminum to provide a
sufficient distribution of aluminum in the grout so that a significant
releasing or breaking off, and disbursement of, the aluminum from the micro-
particles by mechanical action or otherwise is not required for the proper
functioning of the aluminum as an expanding agent for the grout. Preferably,
the micro-particles have a maximum size of about 350 to 400 microns with the
20 average size as determined by weight preferably being about 100 microns.
Tests have shown that the sodium silicate film coating for protecting
the flakes will not be detrimentally affected by the dry grout blending or the
alkalinity and moisture content of the dry grout for time periods commercially
acceptable for the storage and shipping of the dry grout. While sodium
silicate has been used as a coating, it will be appreciated that other
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coatings or binders which are sensitive to the water of the wet grout but have
limited sensitivity to that of the moisture content and the alkalinity of the
dry grout and are abrasion resistant to the blending with cementitious
materials may be used.
In practice, the smaller the average size of the micro-particles
utilized, the greater the number of discrete aluminum coated particles
involved for a given quantity of aluminum, and the more the number of
distribution points for the aluminum up to a one to one correspondence in the
number of coated particles and the number of aluminum flakes.
In tests, I have used a commercially available grade of glassy silica
microspheres having particle sizes from about 10 to about 350 microns with
about 20% of the particles having particle sizes of between about 125 and 350
microns and about 65% between about 50 and 125 microns. Other grades of micro
particle may also be used to provide a sufficient number of individual coated
particles for a given quantity of aluminum. The particle size used is not
critical as long as a sufficient number of coated particles are present to
provide the desired number of distribution points for the aluminum. However at
the present I prefer a maximum size of 400 microns.
The aluminum flakes may be adhered to a micro-particle by the use of
20 various conventional methods for coating microspheres or other small particles
with metal particles or flakes. In the process which I have used,
microspheres and the aluminum powder are dry blended to provide a uniform mix
of the powder and microspheres, with the mix then being spread on a flat
surface to form a thin layer. Droplets of a sodium silicate solution are then
applied by dropping the droplets onto the whole of the entire layer to evenly
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spread the solution over the entire layer. The microspheres in the mixture
are then rolled laterally in a mixing fashion to pick up and coat the flakes
and adhere them to the microspheres. In the process of rolling, the water
glass forms a film on the aluminum flakes and microspheres and the aluminum
flakes become adhered to the microspheres. In coating the aluminum and
adhering the aluminum to the microspheres, the microspheres do not tend to
agglomerate but essentially retain their individual identity and the size and
number of the microspheres as well as the film coating combine to limit the
number of flakes which can adhere to an individual microsphere.
A preferred recipe for forming individual aluminum coated micro-spheres
is as follows:
Material % by Wght.
Aluminum leafing powder
Alcoa No. 322, 100 mesh
polished 3
Hollow glass spheres
size: 10 - 350 microns;
particle size: 25% above
125 microns by weight,
65% between 49 and 126 microns
by weight; bulk density: 25 lbs
per cubic foot; average si7e
by weight: 100 microns. 83
40 Baume sodium silicate
solution (50% water) 14
The coated particles are prepared by the described method, baked briefly,
e.g., for five minutes, at a temperature of about 130 F, and then air dried
to complete the drying of the sodium silicate.
I contemplate that the distribution of aluminum may also be accomplished
30 by coating the aluminum flakes with a first alkaline water sensitive coating,and then adhering the coated aluminum flakes to micro - particles with another
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coating and/or binder which will readily disintegrate in the wet grout to
release the aluminum flakes from the particles for further dispersion during
the wet grout mixing and pumping operation or for a faster reaction in the wet
grout. The binder adhering the coated flakes to the micro-particles may also
be soluble or otherwise disintegrate in the presence of the moisture and/or
the alkalinity of the cementitious dry grout so as to release the bond between
the coated aluminum flakes and the micro-particles after being blended
therewith. It will be appreciated that the binder for adhering the coated
flakes to the micro-particles may deteriorate while in the dry mix without
10 adverse results if the coating for the flakes is sufficient to protect the
flakes from the moisture and alkalinity of dry grout with cement.
It will be further appreciated that the quantity of coated microspheres
used for a given quantity of aluminum will depend on the number of aluminum
flakes which are adhered to the individual microsphere. The number of flakes
on a particle is, in turn, dependent on the size of the micro-particle. If
the number of coated micro-particles is determined to be too few to provide
the desired number of distribution points, a finer grade of particles may be
used in the coating process.
Conventionally in the art of grouting, a fluidifier(which is an admixture
20 of grout enhancing materials) is utilized in the grout recipe and contains the
coated aluminum flakes as a component thereof. The admixture will normally
constitute, for example, about one percent by weight of the cementitious
material in the dry grout. A typical wet grout may contain, by weight (lbs.),
Cement 282
Fly Ash 70
Sand 360
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Water 167
Fluidifier 3.52
The quantity of coated micro-particles needed to provide the necessary
aluminum content may be determined by first reacting a given unit quantity of
coated micro-particles in an alkaline grout slurry and measuring the gas
produced. Knowing this, one of ordinary skill in the art may determine the
quantity of coated microsphere units necessary to produce the total gas volume
required for the grout.
A simple method of determining the total gas volume required is to mix
10 a unit of the quantity of aluminum flakes required into a solution of sodium
hydroxide and measure the gas volume released to determine the gas generated
for the unit quantity. Knowing this, the total gas volume for the whole
quantity of aluminum to be used can be readily computed as well as the
necessary quantity of coated microspheres to produce the total gas quantity
since the gas volume for a unit quantity of the coated microspheres has been
determined, or is determinable, as described above.
Whether there is a sufficient number of particles for the aluminum to
effect the proper distribution of the aluminum can be determined, as is
appreciated by those in the art, by examination of a sample of hard grout made
20 from a test batch of the dry grout. If a wider distribution is necessary, this
can be accomplished by using a finer grade of coated micro-particles which
will have, on the average, a lesser number of aluminum flakes on the micro-
particles, on the average. If more or less aluminum is required, the number
of coated particles can be increased or decreased to adjust the aluminum
content.
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