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Description  |
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FIELD OF THE INVENTION
The present invention relates to methods of making molded articles from a
lightweight cementitious composition and in particular, to a method of
making an article from a cement and perlite composition, and a hollow,
decorative article made therefrom.
BACKGROUND OF THE INVENTION
Many property owners have sought to conceal unsightly utility
installations, such as water well heads, septic vent stacks, telephone
junction boxes, and buried gas tank hatches. Existing concealment devices,
such as plantings, planters, and well houses have provided only partial or
seasonal concealment of the utility installations. Such existing
concealment devices are also not sufficiently weatherproof and are
susceptible to damage caused by sun, rain, ice, and wind. Other
concealment devices, such as well houses, are large heavy structures that
are difficult to install and remove and could also present a hazard
individuals nearby.
A device is needed that will adequately conceal utility installations in
all seasons while providing an aesthetically pleasing appearance that
blends with the natural surroundings. A concealment device is also needed
that is structurally sound and weather resistant to withstand sun, rain,
snow, ice and wind while being sufficiently light weight to be easily
installed and moved. Furthermore, a concealment device is needed that can
be made with various different shapes and surface ornamentation's.
Additionally, there is also a need for lightweight outdoor decorative
objects such as posts, birdbaths, etc., that are aesthetically pleasing,
yet can be purchased, moved and installed by a typical homeowner, without
need for a heavy duty truck or similar delivery vehicle or heavy
installation equipment.
Cementitious compositions are commonly used to form structures and articles
in the building industry. Although cementitious compositions, such as
concrete or cementitious compositions including other aggregates, are
desirable in terms of price and weather resistance, the use of
cementitious compositions to form a decorative article or a concealment
device for covering utility installations presents a number of other
problems related to the physical characteristics of the material and the
methods of using the material.
Using concrete, for example, to form a generally hollow article for
covering utility installations results in an article that is heavy and
difficult to install or move. To minimize the weight of a hollow article
made from concrete, the thickness of the walls of the article would have
to be dangerously thin, thereby sacrificing the structural integrity of
the article. Molding structures or articles from concrete is also labor
intensive. Concrete is thus difficult to form into a lightweight article
having various decorative shapes and does not provide a decorative surface
texture or appearance.
Lightweight cementitious compositions including perlite, a siliceous
volcanic rock which has been expanded by heating, have been used in the
building construction field as a lightweight insulating concrete for roof
decks, floor systems, sound/firewalls, and other insulating applications.
However, the prior art does not disclose the use of a lightweight
cementitious composition to cast a hollow, decorative article with various
shapes and surface textures. Typical perlite concrete compositions also do
not provide sufficient strength and weatherability.
Accordingly, a need exists for a hollow, decorative article that is made
from a cementitious composition and is lightweight, easily installable,
weather-resistant, easily molded to a desired shape, for example a shape
that conceals a utility installation, and has a decorative shape and
surface texture. A need also exists for a method of making such an article
from a lightweight cementitious composition by casting the article with
various shapes, surface textures and other decorative features.
SUMMARY OF THE INVENTION
The present invention features a novel method for making an article from a
cementitious composition and also features a hollow, decorative article
made according to the method. The method comprises the steps of: mixing a
castable cementitious mixture including an aqueous slurry of at least
cement and perlite; transferring a quantity of the castable cementitious
mixture into a mold having an internal mold form and an external mold
form; maintaining the castable cementitious mixture between the internal
mold form and the external mold form until the castable cementitious
mixture at least partially cures to form the article; and removing the
external mold form and the internal mold form from the article. The
preferred method includes inserting an internal mold form into the
external mold form and the quantity of the castable cementitious mixture,
for displacing the quantity of the castable cementitious mixture between
the internal mold form and the external form. One method of making a
decorative article from a cementitious composition further includes one or
more steps of finishing the surface of the molded article, such as by
carving.
The preferred cementitious mixture includes portland cement and a
perlite/cement ratio of about 4:1 by volume. The castable cementitious
mixture also preferably includes an air-entraining agent, for entraining
air bubbles, improving mixability and reducing a density of the castable
cementitious mixture to facilitate displacement of the castable
cementitious mixture by the internal mold form. The castable cementitious
mixture further preferably includes a fibrous material, such as
polypropylene fibers, for reinforcing the castable cementitious mixture.
The preferred step of mixing includes: adding water to a heated mixing
apparatus; mixing the air entraining agent into the mixing apparatus until
dispersed in the water; mixing the cement in the mixing apparatus until a
cementitious slurry is formed; mixing the perlite into the cementitious
slurry in the mixing apparatus until a cementitious perlite slurry is
formed with entrained air; and mixing the fibrous material into the
cementitious perlite slurry in the mixing apparatus, for forming the
castable cementitious mixture. The perlite is preferably mixed into the
cementitious slurry by feeding the perlite with a material feeding device.
The preferred method further includes a step of preparing the external mold
form with a retarding/parting agent, for slowing curing of the castable
cementitious mixture at an outer surface region of the article and for
facilitating separation of the external mold form from the article. The
external mold form liner is preferably made of a light weight flexible
material such that the external mold form can be unfolded and prepared
with the retarding/parting agent. The preferred method further includes
preparing the internal mold form with a parting agent, such as a plastic
film, that also prevents crazing of the castable cementitious mixture upon
curing.
The present invention also features a method for making an article with a
decorative surface texture from a cementitious composition. The method
comprises the steps of: mixing a castable cementitious mixture including
an aqueous slurry of at least cement and perlite; preparing a surface of
the mold with a retarding agent; pouring a quantity of the castable
cementitious mixture into a mold; casting the castable cementitious
mixture in the mold until the castable cementitious mixture substantially
cures to form the article; and removing the article from the mold. The
retarding agent slows down curing of the article at an external surface
region of the article such that the perlite and concrete form a decorative
surface texture. This method preferably includes a further step of
finishing the outer surface of the region of the article upon removal of
the article from the mold.
One embodiment of the retarding agent includes a mixture of at least water,
sugar and glue. The preferred embodiment of the retarding agent further
includes a solvent alcohol in the mixture.
One example of the retarding agent further includes a pigment for
indicating a density of application of the agent and a degree of
penetration of the retarding agent. The glue includes either white or
yellow glue and preferably both.
A decorative molded article made according to this method includes a body
portion formed when the castable cementitious mixture cures between the
external and internal mold forms. The body portion includes a plurality of
walls defining a hollow internal region, for covering a structure, such as
a utility installation. At least one of the plurality of walls includes an
outer surface region having a decorative texture. According to various
embodiments of the hollow, decorative article, the body portion further
includes one or more apertures extending through one or more of the
plurality of walls, for venting the hollow region of the body portion. The
article can also include a recessed top region, for receiving water and/or
earth material, or a flat, peaked or domed top region.
DESCRIPTION OF THE DRAWINGS
These and other features and advantages of the present invention will be
better understood by reading the following detailed description, taken
together with the drawings wherein:
FIG. 1 is a schematic view of a system for molding an article from a
cementitious composition, according to the present invention;
FIGS. 2A-2D are schematic views of the method for molding an article from a
cementitious composition using an external mold form and an internal mold
form, according to the present invention;
FIG. 3 is a side perspective view of the external mold form, according to
one embodiment of the present invention;
FIG. 4 is a side perspective view of the internal mold form, according to
one embodiment of the present invention; and
FIGS. 5A-5G are perspective views of various embodiments of molded,
decorative articles made according to the method of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The system and method 10, shown schematically in FIG. 1, according to the
present invention, mixes a castable cementitious mixture 20 including
cement and perlite and forms a molded article by molding or casting the
castable cementitious mixture into a desired shape. The system 10 includes
at least a mixer or mixing apparatus 12, for mixing the castable
cementitious mixture 20, and a mold 14. In the preferred embodiment, the
mold 14 includes an external mold form 16 and an internal mold form 18,
for casting the cementitious mixture 20 into the molded article. According
to the exemplary embodiment, the molded article is a hollow, decorative
article, such as a decorative lawn ornament, or a cover or cap for utility
installations including, but not limited to, water wellheads, septic vent
stacks, telephone junction boxes, and buried gas tank hatches. The present
invention, however, contemplates using the system and method 10 of the
present invention to make other types of molded articles from various
types of cementitious compositions.
The mixing apparatus 12 preferably includes a conventional drum type mixer
heated with a drum heater 13, such as a kerosene convection heater, before
and/or after mixing begins. Drum type mixers are relatively easy to clean
and help to control the diffusion of airborne silica dust, a component of
the perlite. The present invention also contemplates using paddle type
mixers or other mixers known to those of ordinary skill in the art for
mixing cementitious mixtures.
The system 10 can also include a material feeding device 22, such as a
hopper with an auger drive, that gradually feeds the perlite into the
cementitious mixture 20 in a steady, controlled manner. The material
feeding device 22 thereby eliminates spillage of the perlite, reduces the
airborne diffusion of silica dust, and minimizes excessive loading of
perlite onto the mixer walls. The material feeding device can also include
a coarse meshed screen or grill to filter larger clumps of perlite.
The castable cementitious mixture 20 preferably includes an aqueous slurry
of at least cement, such as portland cement, and perlite, such as a cement
grade perlite of the type manufactured by Whittemore Perlite Company, Inc.
Of Andover, Mass. An exemplary ratio of perlite to cement of about 4 to 1
by volume typically provides the desired strength/weight characteristics
for a hollow, decorative article. The present invention contemplates other
proportions having an amount of cement sufficient for the desired strength
and hardness properties and an amount of perlite sufficient to make the
product castable and lightweight.
The preferred castable cementitious mixture 20 further includes a fibrous
material, such as chopped polypropylene fiber sold under the trademark
Fiberstrand 100 by Euclid Chemical Co., that reinforces the cementitious
composition. The fibrous material should be present in a quantity
sufficient to reinforce the cement and perlite particles during curing of
the cementitious mixture and during handling of the molded articles (e.g.
about 1/2 lb. Or 0.3% by weight, thereby preventing disintegration and
abrasion of the molded articles. The fibrous material is preferably not
mixed in a quantity that will cause entrapment of large air bubbles in the
cementitious mixture 20, thereby causing structural weaknesses and surface
cavities in the hollow, decorative articles.
According to the exemplary embodiment, the castable cementitious mixture 20
further includes an air entraining agent, such as the type sold under the
trademark DARAVAIR-M manufactured by W. R. Grace, that causes air
entrainment or small bubbles to form in the cementitious mixture. The air
entraining agent causes the cementitious mixture 20 to form a foam or
lather consistency with a reduced density, and thereby facilitates
hollow-core casting of the castable cementitious mixture between the
external mold form 16 and the internal mold form 18, as will be described
WA in greater detail below. Note that air entrainment (or small bubbles)
in the cementitious mixture is desirable to facilitate the casting while
air entrapment (or large air bubbles) in the cementitious mixture is
undesirable because larger bubbles adversely affect the strength and
surface texture of the molded articles.
The present method generally includes mixing the above materials in the
mixing apparatus 12 containing a quantity of warm water. The air
entraining agent (if used) is preferably mixed first into the warm water
until well dispersed throughout, typically about 5 to 10 seconds. The
cement is then preferably mixed into the water until the cement is
saturated with the water and forms a cementitious slurry, typically 4
minutes. The perlite is then mixed gradually into the cementitious slurry,
e.g. with the feeding device 22, to form a cementitious perlite slurry
with air entrainment. The fibrous material is then mixed into the
cementitious perlite slurry until dispersed throughout.
EXAMPLE 1
According to one example of the castable cementitious mixture, the
following materials in the approximate amounts set forth below were used.
Material Volume Weight (lbs.) % by weight
Perlite .about.4 cu. ft. .about.30 .about.16.1
Cement .about.1 cu. ft. .about.94 .about.50.4
Water (.about.120.degree. F.) .about.7.3 gal. .about.61.4 .about.33.0
Fiber -- .about..5 .about..3
Entraining .about.5 fl. oz. .about..31 .about..2
Agent
According to this example, the drum mixer was pre-heated to approximately
100-110 degrees and rotating at about 30 rpm, and the warm water was added
to the mixing apparatus 12. The air entraining agent was added to the
water and mixed until well dispersed. The portland cement was mixed into
the water one-half bag at a time to minimize loading of the cement onto
the mixer walls. The cement was mixed with the water for about 4 min.
until the cement was saturated with water and formed a cementitious slurry
having a "creamy" consistency. Any cement paste on the walls of the mixer
was blasted with about 1 cup of additional water.
The perlite was then gradually mixed into the cementitious slurry at a rate
of about 1 cu. ft. per minute forming a cementitious perlite slurry. The
walls of the mixer were again rinsed with water (e.g. not more than 3
cups) . The cementitious perlite slurry was mixed for about 8 minutes
until forming a foam-like or lather consistency caused by the air
entraining agent. The chopped, dry polypropylene fiber (3/4 inch in
length) was then added, breaking up the larger clumps of fiber. The slurry
was then further mixed for about 3 additional minutes for a total of about
15 minutes from the time that the cement is added to the water, until the
slurry had a light consistency and the mixer speed was dropped to the
lowest setting.
The particular materials, quantities, and mixing times described above are
merely one example and are not intended to be a limitation on the present
invention. The castable cementitious mixture described above has a density
and consistency that is easily cast into a hollow, decorative article with
a desired shape and surface texture, as described in greater detail below.
The castable cementitious mixture described above cures to form a hollow,
decorative article that is sufficiently lightweight to be easily moved and
installed over a utility installation, sufficiently strong and abrasion
resistant to prevent damage when moving or installing, and sufficiently
weatherproof to prevent damage from sun, rain, ice and wind. The present
invention contemplates other types of materials in varying quantities and
proportions as well as various mixing times and sequences depending upon
the desired characteristics of the castable cementitious mixture and the
resulting article molded therefrom. For example, fine masonry sand, baked
or bisqued shale, or other harder aggregate materials could be added to
the mixture to increase abrasion resistance. The present invention also
contemplates the addition of a chemical accelerator to the cementitious
mixture as well as a water reducing admixture.
Once the castable cementitious mixture 20 has been formed, the mixture 20
is transferred to the mold 14. The system 10 preferably includes a
transfer device 24 that receives the mixture 20 from the mixing apparatus
12 and guides the mixture 20 into the external mold form 16 while
minimizing air entrapment. When the desired quantity of castable
cementitious mixture 20 is deposited into the mold 14, the mixture is
allowed to cure between the external mold form 16 and the internal mold
form 18 to form a molded article 30 having a plurality of walls defining a
hollow region, as will be described in greater detail below.
The system 10 preferably includes a vibrating mechanism 26, for vibrating
the mold 14, thereby facilitating the molding of the cementitious mixture
between the external mold form 16 and internal mold form 18 and dispelling
entrapped air. One example of the vibrating mechanism 26 is a vibrating
table that provides between about 3600 to 8000 vib/min, preferably with a
vertical vibration component.
Prior to transferring the cementitious mixture to the mold, a parting agent
is preferably applied to the internal mold form 18 and external mold form
16 to facilitate removal of the article 30 from the external and internal
mold forms 16, 18. One example of the parting agent used on the internal
mold form 18 includes a plastic film applied around the internal mold form
18, as will be described in greater detail below. The plastic film also
acts as a sealing agent that seals the castable cementitious mixture after
form removal and during curing to prevent shrinkage and crazing of the
cementitious mixture.
One example of the parting agent used on the external mold form 16 is a
retarding/parting agent that retards or slows the curing of the outer
surface of the article 30 while alsofacilitating the separation of the
article 30 from the external mold form 16. As a result of the slowed
curing process at the outer surface region of the article, the perlite and
cement in the cementitious mixture can form a decorative texture that
simulates a fine grained granite.
One type of retarding/parting agent includes a mixture of at least water,
sugar and glue. The sugar, such as corn syrup, has a retarding effect on
the setting action of the cementitious mixture. The glue, such as a white
glue and/or a yellow aliphatic resin wood glue, both of the type made by
Elmer's, provides a high bodied consistency that allows the agent to cling
easily to vertical surfaces of the external mold form 16. The preferred
retarding/parting agent further includes solvent alcohol. The mixture of
glue with solvent alcohol results in a composition having a unique webbing
property and further enhances the consistency of the retarding agent. The
resulting retarding agent dries relatively quickly and is time-released to
allow for the cementitious mixture to flow between the external and
internal mold forms.
One example of the retarding agent further includes a pigment, such as
Superconcentrated Mortar Color #891 Black (i.e. carbon black) made by the
Euclid Chemical Co., for indicating a density of application of the agent
and a degree of penetration of the retarding agent. The retarding/parting
agent can be applied to the external mold form 16 by brushing or could
also be reduced with water (e.g. about 10%) and sprayed onto the external
mold form 16.
EXAMPLE 2
According to one example of the retarding/parting agent, the following
materials in the approximate amounts set forth below were used.
Min.
Ingredient Batch Volume
Carbon Black .about.2 tsp.
Water .about.5 tsp.
Corn Syrup .about.3 tblspns.
Yellow Glue .about.5 fl. oz.
White Glue .about.10 fl. oz.
Solvent Alcohol .about.16 fl. oz.
The above example of the retarding parting agent was made by first mixing
in a container the carbon black and a small amount of the water to form a
paste. The remaining water was then added gradually while mixing
thoroughly. The corn syrup (pre-heated) was then added and mixed with a
high speed hand mixer. The yellow glue was then added and mixed with the
mixer, and then the white glue was added and mixed with the mixer. The
mixture was allowed to sit while pouring the solvent alcohol into a
separate container. The glue mixture was then pre-mixed by pouring into
the solvent alcohol through a fine funnel such that glue flows as a thread
into the solvent alcohol. The glue mixture and alcohol were then mixed to
form the retarding/parting agent.
The particular ingredients, quantities, and mixing sequences described
above are merely one example and are not intended to be a limitation on
the present invention. The present invention contemplates using the
retarding/parting agent in other applications with other types of
cementitious compositions and molding methods. The present invention also
contemplates other applications for the unique mixture of glue, such as
white or yellow wood glue, with solvent alcohol to form a composition
having high webbing and high clinging characteristics.
The method of molding a hollow, d | | |
