U.S. patent number RE29,945 [Application Number 05/681,153] was granted by the patent office on 1979-03-27 for multiple use concrete form liner.
Invention is credited to Sam C. Scott.
United States Patent |
RE29,945 |
Scott |
March 27, 1979 |
Multiple use concrete form liner
Abstract
A multiple use, flexible, elastomeric liner for forms for
concrete faced walls prepared by having a series of rigid panels in
side by side relation, includes panels of liners for rigid panels
having a concrete contacting face of a flexible, elastomeric
synthetic polymer used throughout as a negative mold of a desired
design in the finished concrete and having an opposed planar
surface for face engagement with the form panels. The liner panels
will not support the concrete for the wall without the backing
panels. The elastomeric liner is a soft, flexible, resilient,
elastomeric synthetic polymeric material which permits sharp relief
designs having undercuts, and in edge engagement with similar
panels squeeze together for a seamless surface in the completed
concrete while leaving the impression of itself in exact detail in
the hardened concrete.
Inventors: |
Scott; Sam C. (Denver, CO) |
Family
ID: |
22802725 |
Appl.
No.: |
05/681,153 |
Filed: |
April 28, 1976 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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17423 |
Mar 9, 1970 |
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Reissue of: |
215370 |
Jan 4, 1972 |
03759481 |
Sep 18, 1973 |
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Current U.S.
Class: |
249/80; 249/112;
249/16; 249/189; 249/78 |
Current CPC
Class: |
E04G
9/10 (20130101) |
Current International
Class: |
E04G
9/10 (20060101); E04G 009/10 (); B28B 007/36 () |
Field of
Search: |
;249/113,114,134,189 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lazarus; Richard B.
Assistant Examiner: Brown; John S.
Parent Case Text
This application is a .Iadd.reissue of Pat. No. 3,759,481 and a
.Iaddend.continuation-in-part of copending application Ser. No.
17,423, filed Mar. 9, 1970, and now abandoned, for Flexible Liner
for Concrete Forms.
Claims
I claim:
1. In combination with large smooth surfaced panels for concrete
forms for structural members, a multiple use liner comprising a
sheet of soft, flexible, resilient, elastomeric synthetic polymer
material which is inert to concrete and having a generally smooth
rear surface in face contact with said large smooth surfaced
panels, said sheet being formed independently of said panels and
supported thereby; the opposite face of said liner having a
concrete contacting face formed as a negative mold including
undercuts of a desired pattern on the set concrete; said sheeting
being at least about 3/8 inch thick at its thinnest section; said
sheet having a hardness of from .Badd..[.10-80.]..Baddend.
.Iadd.35-70 .Iaddend.Shore A, which permits said material to be
deformed without damage for releasing from the designs in the set
concrete and having an elongation of from 100-1,000 percent at a
tensile modulus of from 150-2,000 psi at 100 percent elongation, a
.[.tensile.]. .Iadd.tear .Iaddend.strength in excess of 20 pounds
per .Iadd.square .Iaddend.inch, whereby said liner may be removed
from a design in set concrete without damage to the concrete
including undercuts in the design and said liner squeezes against
an adjacent liner under the weight of contained concrete to seal
the joint line therebetween and seal around ties or the like
passing through the liner.
2. The combination of claim 1 wherein said polymeric material is a
polyurethane having a Shore A hardness of about 53-56, tensile
modulus of 212-234 .Iadd.psi.Iaddend. , elongation of 270-300
percent, tear strength of 67-73 .Iadd.psi .Iaddend.and a tensile
strength of 504-563 .Iadd.psi.Iaddend. . .[.3. The combination of
claim 1 wherein said polymeric material is a polyvinyl chloride
having a Shore A hardness of about 47-32, tensile modulus of about
175-368, elongation of 320- 460 percent, a tear strength of 62-102
and a tensile strength of about
810-1,200..]. 4. The combination of claim 1 wherein said sheet
essentially covers the area of said panels forming a moisture
and
temperature barrier for concrete thereagainst. 5. The combination
of claim 4 wherein said sheet has its full negative mold face in a
desired pattern imparting a total simulated look of the desired
configuration to a
concrete face set thereagainst. 6. The combination of claim 1
wherein said sheet is formed with a light colored pigment as a
reflector for heat into
and out of concrete in engagement therewith. 7. The combination of
claim 1 wherein said sheet is sufficiently soft and sufficiently
thick to produce
a gasketing effect around a tie passed through a slit therein. 8.
The combination of claim 1 wherein said sheet has a heating element
imbedded
therein for heating contained concrete. 9. The combination of claim
1 wherein said sheet has a heat exchanger tubing imbedded therein
for heating or cooling said sheet.
Description
Concrete forms, particularly for walls, partitions and the like,
conventionally use rectangular panels of plywood, steel sheets,
planks, and the like, supported by various types of reinforcing and
support members. When two or more of these panels are attached
together in planar alignment the form "in-total" is called a gang
form and is usually stripped from hardened concrete as one piece
rather than two or more smaller pieces. The panels are generally
held in side by side relation, mounted on supporting structure, and
generally two series of such panels are mounted in generally
parallel, spaced apart, face-to-face relation so that concrete may
be poured between the two to eventually form the rectangular wall
or partition. Plywood panels for such forms are generally 2 .times.
8 ft., or more commonly 4 .times. 8 ft. sheets. With the steel
sheets, they are usually formed in 2-ft. widths mounted on the
supporting structure for holding such panels in position for
pouring a wall or partition. To keep the walls of the forms
substantially parallel under the weight of the concrete poured
between them, ties of wires, rods, or other material are fastened,
through the space into which the concrete is poured, from wall to
wall, leaving the intervening wire or rod imbedded in the finished
concrete. This, of course, requires apertures or holes in the forms
for the ties.
When the forms are made of plywood, the panels are generally coated
with oil as a parting agent and in an attempt to prevent the
penetration of the cement-loaded water into the wood of the panel.
Long experience has shown that such plywood panels rarely last more
than four pours, particularly since the corners and edges are
easily damaged in the erection, shipping and storing of the panels.
In the reinforcing steel installation in the forms, numerous gouges
and scratches are inflicted on the plywood from the sharp edges of
the reinforcing bars and wire. The steel forms have a somewhat
better life; however, they are quite heavy and are easily bent and
dented in the erection, storage and/or transportation, so that
after a few uses the panels can not make good joints with adjacent
panels and the resulting concrete shows extruded joining lines and
offset joints. With the plywood panels, cement water draining from
the concrete enters the cracks of the joints and any damaged
surface areas of the panels and enters the plywood itself, causing
deterioration of the plywood and warping of the plywood. After both
the plywood panels and steel panels have had several uses, the
joints between the panels become poorer and poorer and alignment
becomes a definite problem. The produced concrete includes
protruding and non-aligned joints, which is particularly noticeable
where there is warping of the plywood panels and bending of the
steel panels. The surface of the finished concrete assumes the
surface of the form, which is equivalent to a negative mold, and
the surface of the finished concrete is generally from rough to
smooth and includes all the blemishes of the panel formed in the
concrete.
According to the present invention, there is provided a flexible,
resilient form liner made of an elastomeric, synthetic polymeric
material, which is castable or moldable and is easily fastened to
the panels of the concrete form. The liner has a concrete
contacting surface of a desired design. The resilient material of
the lining is sufficiently soft to squeeze on adjacent liners under
the weight of the wet concrete in the form, closing the joint lines
between the liners so that the finished concrete does not show
joint lines. The liners are readily attached to existing forms, or
the existing forms are easily modified to accept the liner.
Depending on the nature of the attaching method chosen the
elastomeric liners can be released from the concrete still attached
to the form panel itself or they can be peeled after the form panel
has been pulled and then reapplied to the panel ready for the next
pour of concrete. The form lining is readily placed on the form
panels with simple and varied means of holding the liners on the
form panels. After the concrete has cured, the liners are easily
peeled or released from the concrete even with deep, base relief
features including undercuts. The material is soft enough to
readily free itself, without damage to the concrete, from the
features of the design including the undercuts, and it is
sufficiently strong so as to not tear in the removal process and
therefore may be used over and over. The elastomeric liner has a
hardness sufficient to retain its design shape even under the
weight of the concrete when the concrete is placed either
vertically or horizontally. A definite advantage of the flexible,
resilient liners is that the face of the liners provides a negative
elastomeric mold of the desired wall design which may be of native
rock, stone, striated wood, geometric or random patterns or any
form desired. While the liner is quite soft, flexible and
resilient, it is tough enough to maintain its integrity under the
weight of the concrete in the concrete form. It is sufficiently
soft and flexible to squeeze against an adjoining flexible liner to
close the joints between the liner sections. This prevents water
from seeping through the liners, and retains the concrete within
the form itself. The liners are useful over a long life, and it is
not unusual to have the form panels last as long as the liners,
which may range from 100 to 150 or more re-uses. Also, in using the
liners, it is preferable that the joint lines of the liners do not
match the joint lines of the form panels, so that the joints of the
liners are backed on a smooth surface of the form panel. It is
sometimes desirable to use a form release coating to help the
liners in the removing process.
The liners may be attached by any suitable means to the form
panels. The choice of fastening means is determined by the
composition of the form panel itself, the thickness of the liner,
and the design in the negative mold side of the liner. The process
of making the form liners is, precast, site cast, poured in place,
etc. Among the various forms of attachment are lugs extending from
the planar surface of the liner to extend through the concrete form
panels, and these lugs are held in any convenient way. The lugs
provide a means for sighting along a series of such panels for
correct alignment and to produce a very uniform wall. The liners
may, also, be nailed, stapled, cemented, or otherwise attached to
the form panels.
The elastomeric synthetic polymer liners are inert to the chemicals
of the concrete, whether the concrete is a conventional concrete or
some of the new exotic concretes having various ingredients for
various hardening and fast setting purposes. This is obviously an
improvement over rubber, or similar materials. The liner may be
used in the concrete form with high cycle vibrators to muddle the
concrete in the forms without damage to the liner or to the form.
This allows very fine surface detail in the hardened concrete
surface while eliminating much of the air entrapment generally
associated with poured concrete. The elastomeric polymer liner is
not damaged if the high cycle vibrator accidentally touches it in
the vibrating process. The liner is soft enough so that a slit in a
liner permits the passage of the tie wire or rod, and the
elastomeric polymeric plastic liner seals back around the tie in a
gasketing action to form an excellent surface at the intersection
of the tie with the finished concrete. Furthermore, the slits do
not need to be filled or otherwise closed in subsequent re-use
where there is no tie passing through the slit. The soft material
squeezes together sealing the opening and thereby permits re-use of
the form in different positions on concrete forms and with
different positioning of the ties which pass through the liner.
It is, therefore, among the objects and advantages of the invention
to provide an elastomeric lining system for concrete forms which
produce a fine detail of predetermined design in the surface of
finished poured concrete and also increases the life of the
supporting concrete forms.
Another object of the invention is to provide a flexible, resilient
concrete form liner made of a synthetic plastic, elastomeric
polymer which does not readily adhere to the concrete and is
sufficiently soft to be readily stripped from the form including
the undercuts of the design of the mold without damage to the
resulting concrete surface or itself.
A still further object of the invention is to provide a concrete
form liner which provides a negative elastomeric
concrete-contacting face mold with a predetermined pattern to
produce a fine detail design in the resultant surface of the
concrete structure.
These and other objects and advantages of the invention may be
readily ascertained by referring to the following description and
appended illustrations in which:
FIG. 1 is a front elevational view of a portion of the concrete
form liner according to the invention positioned against a concrete
form panel with a corner folded back;
FIG. 2 is a cross sectional detailed view of a form liner according
to the invention temporarily sealed on a portion of a concrete form
panel;
FIG. 3 is a detailed view of the portion of a wall form showing the
positioning of the liner according to the invention in a concrete
form for a wall;
FIG. 4 is a plan view of a concrete form liner section according to
the invention illustrating the positioning of liners on concrete
form panels;
FIG. 5 is a cross sectional view of a form liner according to the
invention illustrating a longitudinal stabilizing member imbedded
in the liner itself to reduce expansion and contraction without
disturbing the elastomeric engaging face; and
FIG. 6 is a side elevational view of a section of a modified form
liner according to the invention.
An elastomeric concrete form liner, according to the invention, may
be made of a soft, flexible, resilient, elastomeric synthetic
polymeric material and may include such materials as .[.polyvinyl
resins,.]. silicone resins, polyethylene resins, polypropylene
resins, .[.various vinyl copolymers, polytetrofloro.].
.Iadd.polytetrafluoro .Iaddend.alkalines, polyesters, polyethers,
and such similar synthetic resins; the hydrocarbon resins being
generally considered saturated. A preferred type of resin is a
polyurethane resin which is provided with a particular chain
linkage in its chemistry to maintain the dense polyurethane soft,
resilient, elastomeric and tough. The synthetic resin liner is
manufactured by casting or molding in shallow, planar molds,
usually having a minimum thickness of at least about 3/8 inch of
liner to a thickness in excess of 4 or 6 or more inches. Since the
liner is a negative mold for a desired configuration of surface,
the thickness of the liner may vary throughout the extent of the
panel from a minimum thickness to the maximum which represents the
height between the lowest depression and the highest elevation of
the base relief of the finished concrete. To provide for a fine
detail base relief of the finished surface, the liner must be
flexible enough to permit undercuts in the finished concrete
whereby the liner may be pulled from the base relief without
breaking the concrete and without tearing the liner itself.
Concrete has a tendency to shrink as it sets and the stretchable
liner still strips easily. It has been determined that a material
having a Shore A [ASTM hardness method D2240] of from .Badd..[.10
to 80, with a preferred range of.]..Baddend. 35 to 70, will have
the desired softness and flexibility for the liner. Below Shore A
.Badd..[.10.]..Baddend. .Iadd.35 .Iaddend.the material is too soft
to maintain its integrity under the weight of the concrete. This
soft material flattens out and will not give a reasonable or
commercial reproduction of the desired design. Above Shore A
.Badd..[.80.]..Baddend. .Iadd.70 .Iaddend.the material is too hard,
losing its elasticity and flex, and attempted removal from the
concrete surface will break the desired surface of the concrete at
undercuts, destroying the effect of the desired base relief, and
also may damage the liner. The material should have a tensile
modulus of between 150 and 2,000 psi at 100 percent elongation
[ASTM method at 23.degree. C. D412]. The elongation at the same
ASTM method D412 should run from 100 to 175 percent at 23.degree.
C., providing for the flexibility necessary to perform as a
negative mold for multiple use. The material having a tear strength
in excess of 20 pounds per square inch [ASTM method D624 Die C at
23.degree. C.] prevents the rupture of material being removed from
the concrete product. The flexible, synthetic polymeric plastic
should have a tensile strength in excess of 100 pounds per square
inch [ASTM method D412 at 23.degree. C.] to provide a material
which will maintain its integrity during the concrete pour and
removal from the concrete surface. Concrete contains considerable
amount of sand and gravel and sharp aggregate, and the plastic
should have a high abrasion resistance so that it does not scratch
or tear under the concrete pour into the mold, and does not readily
tear during erection or placement of reinforcing steel. The Taber
Abrasion test using 1,000 grams, 1,000 cycles H-22 wheels, shows
allowable loss from of frm 0.10 grams to 1.5 grams.
The above properties define a soft, flexible, resilient,
elastomeric material completely differentiated from the .[.rigid.].
lining materials used to date. The liners show a commercial
improvement in concreting not before used to attain the dramatic
results obtainable with the invention.
The liners of the invention are useful for concrete forms which may
be formed for walls, partitions and the like in which a concrete
form is made of a plurality of side by side panels of such
materials as plywood, steel and the like. Such concrete forms are
useful for pre-cast concrete products, or for concrete products
cast in situ, and they may include such pre-cast products as
columns, beams, panels, various wall structures and the like, and
may be formed as castings for ceilings, floors and the like. The
configuration, therefore, of the concrete mold in which the lining
is to be used is determined by the use for which the particular
structure is to be used. In the casting of concrete structures, it
frequently occurs that the forms for the particular article are
quite large (gang form) and the lining of the invention is highly
useful and economical because it can be made in large sizes to form
the particular gang form without any jointing and to minimize labor
and handling at job site. The liners may be made in relatively
small standard panels to line the forms for the finished articles.
Thus, while the illustrations are directed to a liner for planar
concrete forms, particularly upright walls, the concept of the use
of the liner is not limited to any concrete form but it is
contemplated that the liner may be used in any type of form for
concrete or other cementous material which sets or hardens with
standing at ambient temperatures.
To obtain a simulated pattern in the set concrete, so as to make
the concrete appear in the shape of the simulated material and not
requiring any further finishing other than perhaps painting, the
concrete contacting face must be a soft, flexible, resilient,
elastomeric synthetic polymeric plastic liner. A polymeric material
which has Shore A hardness of .Badd..[.10-80.]..Baddend.
.Iadd.35-70.Iaddend., an elongation of 100-1,000 .Iadd.%
.Iaddend.and tear strength in excess of 20 pounds per .Iadd.square
.Iaddend.inch is satisfactory for the liner.
The liner panel for the form of FIG. 1 illustrates a liner for
forming a simulated barnwood [weathered wood] concrete wall. This
concrete wall will have the appearance, particularly when painted,
of that of a wall formed of weathered boards, without the
maintenance that would be required of real barnwood, etc. A liner
10 formed of soft, resilient, flexible elastomeric synthetic
polymeric plastic 10 is arranged with a face 12 formed as a
negative elastomeric mold of the desired configuration and a planar
surface face 14 which is arranged to lie in face engagement with a
concrete form panel 16. In the liner illustrated in FIG. 1, the
panel of the liner includes raised portions 18 and 20 which form
depressions or lines simulating an open joint between boards in the
finished concrete. Also, included are simulated knot holes 22 and
various raised grain in the boards actually simulating the surface
effect of barnwood. The surface may include circular depressions
24, 26, for example, which produce slight knobs on the finished
concrete surface indicating nail heads such as might be found in
old barnwood. The undercutting is obviously a tremendous asset to
the total "look" of the finished concrete.
The liner is formed by casting or molding or curing liquid
polyurethane precursors, or other suitable precursors for synthetic
polymers, in a shallow planar mold which has the positive of the
desired design in the bottom of the mold. The mold for the liner
may be elastomeric itself so as to further enhance the detail
obtainable. It may, also, be of a rigid material such as set
concrete or aluminum, etc., and may use external or interior
heating sources to accelerate the chemical action that cures the
elastomeric liner material into a tough elastomeric sheet. The
polyurethanes are generally poly-functional long chain alcohols
with a plurality of hydroxyl groups reacted with a polyisocyanate.
The polyurethanes themselves are esters of dicarbamic acids and
glycols, or inter-molecular esters of gamma-hydroxic carbamic
acids. The polyurethane elastomers are made from diisocyanates,
aliphatic polyesters, etc. Several types of polyurethanes are
commercially available as 2 part pourable liquids, which have a
good shelf life and are easily mixed with the necessary
polymerizing or curing agent. One form is a polyester made from
ethylene and propylene glycols with adipic acid. A curing agent
such as toluene, naphthylene or diphenylmethane diisocyanates may
be used. The resultant polymer should have the hardness, tensile
modulus, elongation, tear strength, tensile strength and abrasion
resistance in the ranges set forth above for forming the liner of
invention. One of the specific liners manufactured by the assignee
at present invention .[.is called "Red Flex", which is a colored
polyvinyl plastisol which has a Shore A hardness of 47-32, tensile
modulus of 175-368, elongation of 820-460 percent, a tear strength
of 62-102 and a tensile strength of 810-1,200. Another specific
liner.]. is a polyurethane called "Flexliner" having a Shore A
hardness of 53- 56, a tensile modulus of 212-234
.Iadd.psi.Iaddend., an elongation of 270-300 .Iadd.% .Iaddend.tear
strength of 67-73 .Iadd.psi .Iaddend.and a tensile strength of
504-563 .Iadd.psi.Iaddend. .
In many base relief designs which may be desired, an uncercut in
the finished product is necessary to give the fine detail desired.
As shown in FIG. 2, a liner 10a includes a series of undercuts 30a,
30b, as well as elevated lands, 32a, 32b and 32c. The liner 10a is
attached by any convenient means to a concrete form panel 16. The
thickness x which is the minimum thickness of any portion of the
liner should be at least about 3/8 inches which will provide the
liner with sufficient integrity to maintain its strength in its
thinnest sections. It is noted that the higher lands produce a
substantial thickness of the liner. Various types of base relief
may include portions of the liner which exceed a thickness of 4, 6
or more inches, again depending on the type of base relief which is
desired in the finished concrete. It is obvious that the
elastomeric liner may be smooth with no detail on the concrete
contacting face. This allows the user to take advantage of many of
its benefits such as non-absorbing of cement water, gasketing at
tie holes, lining curved or odd-shaped forms, insulating, etc.
These qualities all contribute to a smooth, well-cured and
unstreaked concrete wall or floor. Until now only rigid type liners
have been commerically available. The invention attains a high
level of sophistication and versatility in concreting.
In using the form of the invention, as shown in FIG. 3, a pair of
concrete form panels 35 and 36 are arranged in parallel spaced
relation to each other, and a pair of liners 37 and 38 are shown
secured to panel 35 with the negative elastomeric face mold section
facing inwardly of the parallel concrete forms to produce, on the
face adjacent to panel 35, the positive of the desired base relief
configuration. As is well known, in the concrete wall construction
the panels of the concrete form are held in parallel position by a
plurality of ties which may be wire, rod, or the like, which extend
through both of the parallel concrete panels and are imbedded in
the finished concrete. To remove the concrete forms from the
finished concrete the ties must be cut to permit the removal of the
form from the cured concrete. Furthermore, to permit the ties to
pass through the concrete forms, holes must be formed in the form
that are big enough to allow passage of the head of the tie, which
has a greater circumference than does the shank or tie itself.
This, of course, permits concrete-laden water and some of the
concrete itself to ooze out of the holes if they are not packed or
gasketed from the outside of the form itself. Visual inspection of
conventionally formed concrete walls shows just how unsatisfactory
this can be. With applicant's soft, resilient liner, however, the
ties may be merely passed through slits which stretch to accomodate
the tie head, formed in the liner at the necessary locations. The
material of the liner itself will squeeze down on the shank of the
tie preventing any oozing of concrete or water through the opening
through which the tie passes. This forms a very smooth joint for
the concrete form tie. In addition, when the form is used in the
next location on a different wall form, a tie does not necessarily
have to pass through the same slits, since the material will
squeeze on itself sealing the slits, causing no blemish on the
finished concrete surface.
Preferably, the liners are arranged in abutting position on the
concrete forms with their joints in the middle of the form panel
rather than on the joints of the form panel to provide a good
backing for the liner joints. This is desirable, but not essential.
Since the liner itself will not support the heavy concrete which is
poured therein, misalignment of the joints of the concrete forms
will be covered by the liner. As shown in FIG. 3, a series of three
concrete form panels 40, 41 and 42 are arranged in side by side
abutting position, and liner panels 43, 44, 45 and 46 are arranged
thereon. The abutting joints between each of the liner panels are
in the middle of the concrete panels rather than on the joint
lines. Thus the joint 50 between panels 43 and 44 are in the middle
of panel 40 rather than on the joint 51 between concrete panel 40
and 41. In a similar manner joint 52 between the liner panels 44
and 45 are in the middle of panel 41. This provides good backing
for the edge abutting joints of the panels. As pointed out above,
the material is sufficiently soft that it squeezes together
completely closing the joint and forming a seamless surface of the
finished concrete. It is obvious that the elastomeric liners can be
placed with joints abutting over joints in the form but good
concreting practices dictate the system detailed herein.
As shown by the physical properties of the desired concrete form
liner sheets the synthetic polymer plastic material is soft,
flexible, and resilient, to allow for the fine detail obtainable
from poured concrete and yet be easily stripped. It is known that
all elastomeric materials have coefficients of liner expansion and
contraction under conditions of heat and cold. The synthetic
polymeric liner may be stabilized so as to control this effect in
applications where it is required for good results. It is obvious
that a steam-heated precast bed can attain temperature approaching
200.degree. F. Concrete itself can approach 140.degree. F. as it
takes its set. In summertime or hot weather concreting, this heat
generation plus the hydration process plus the ambient temperature
can generate higher temperatures in the concrete against the
plymeric liner itself. By imbedding a perforated sheet, screen,
cloth or film into the liner at the time of manufacture (before the
precursors change from a liquid to an elastomer sheet) a plane of
stabilization can be added to the liner. When a perforated sheet is
used, the perforations act as individual stabilizing points,
usually 1 inch on center throughout the entire planar surface of
the elastomeric liner. Since the elastomeric material either
completely surrounds the stabilizing sheet or at least flows to the
top of each perforation and bonds totally to the entire sheet, the
elastomeric face engagement side of the liner is not affected and
will still stretch and bend and flex from detail and undercuts on
set concrete. The tie holes are still slit in the surface but the
imbedded stabilizing sheet must be drilled the same circumference
as the tie head for it to pass through, but the liner slit still
stretches and closes on the shank to obtain the gasketing action.
It is preferred to use as a stabilizing element a material that has
a very low coefficient of expansion and contraction as well as a
low moisture content, since at elevated temperatures water vapor
gas may form during liner curing and expand, causing difiguration
and degradation of the element and surrounding elastomeric
material. It is obvious that other stabilizers could be imbedded in
or glued to the liner providing the same degree of lateral
stability when required. Such materials are hardware cloth, glass
fiber strands or webs, perforated metal films, perforated plastic
films or sheets, screening or the like may be used. Expansion
and/or contraction has always been a problem in any concrete form
liner since the negative face can be distorted, thus making the
concrete surface distorted or out of line, etc. The addition of the
lateral stabilizing sheet which is perforated or absorbent (as in
glass matting) corrects this deficiency when required in the
elastomeric concrete form liner of this invention.
It is known that the liners absorb or reflect radiant or convective
heat or cold at different rates. The more heat absorbed the greater
expansion, etc. By the addition of a light reflective color "white"
to the elastomeric material, the concrete liner becomes itself a
reflector of heat. Since reflection will occur the liner itself
does not become overly heated, thus reducing expansion or
contraction. It is obvious that this is desirable in many instances
where the stabilizer sheet is not suitable to the application.
Also, both white color and a stabilizer could be used to attain
even a greater degree of stability. White or lighter type colors
are, also, desirable so the user of the elastomeric liner is more
able to see any dirt or refuse that may be on the liner before
concrete is placed against it, causing a speckled or dirty
appearance on the set concrete surface. It is not common commercial
practice to add white pigment to the preferred urethane elastomer.
However, because of its inherent heat reflective qualities it is
desirable for the addition in the synthetic polymeric liner of
invention. It is obvious that other colors may be added for
identification of product by both sellers and customers of said
liners.
Another important function of the invention is to provide a vapor
barrier far superior to plain plywood. Concrete in the curing
process must retain most of the original water content of the mix,
otherwise the particles of cement will not hydrate and adequately
bond together and the concrete will not attain acceptable strength.
In hot weather concreting, it is especially important to protect
the wet concrete from losing too much moisture. General practice is
to have burlap sacks draped over forms after a concrete pour and a
worker keeping the sacks and the forms wet with a hose. Evaporation
will rob the water from the wet concrete right through the plywood
or wood form if this procedure is not followed, and this could be
disastrous to the pour. When the concrete form is lined with the
elastomeric liner of invention the moisture vapor can not escape
from the concrete through the forms. The insulating value of the
elastomeric liner is far superior to wood or steel and other
currently available thin section rigid concrete form liners.
Insulation is needed even in summertime to keep too much heat out
of the concrete. In some cases curing blankets are actually thrown
over wet concrete to this end. Too much heat obviously causes the
evaporation process to increase. For wintertime concreting, the
same curing blankets are sometimes thrown over the wet concrete to
retain the generated heat therein. The elastomeric liner of
invention, being at least 3/8 inch thick at its median thickness,
acts as an insulator to hold the heat. If it becomes necessary to
actually put heat into the wet concrete to maintain its curing
temperature, electrical heating tapes may be imbedded in the
elastomeric liner much as the stabilizing sheet is to accomplish
this end without affecting the elastomeric concrete contacting face
of the liner of invention. Heated, rigid, forms have been used
extensively for many years but they are expensive and do not allow
for the fine detail and undercutting available in the synthetic
polymeric elastomeric liner of invention.
A heating cable or tape, in the form of interconnecting mesh, may
form of type of stabilizing sheet within the elastomer liner as it
provides the heat source necessary to reverse the heat flow in cold
weather concreting. Also, a coolant could be circulated through
small tubes imbedded in the liner of invention to help in hot,
summertime concreting.
As shown in FIG. 6, a portion of a liner 70 has electric resistance
wires 71 embedded in the plastic material, and power leads 72 and
73 are connected therewith. This provides a heating mat for liner.
A plug 74 indicates attachment to a power source. The resistance
wires may be replaced by small tubes which form a heat exchange
duct through the liner. Through the tubes heating or cooling liquid
may be circulated for a desired temperature treatment.
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