Note: Descriptions are shown in the official language in which they were submitted.
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CEMENTITIOUS GYPSUM AND FIBER-CONTAINING
COMPOSITIONS AND MATERIALS MADE THEREFROM
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to cementitious
compositions and in particular to cementitious
construction materials such as fiber boards, roofing
tiles, shingles, and floor underlayment made from a
composition comprising gypsum, Portland cement,
silica fume, and fiber.
Description of Related TechnoloQy
Construction materials, such as backer
boards for showers and exterior applications, such
as sheeting and shingles, typically do not contain
gypsum because gypsum-containing materials are
usually not water resistant. However, gypsum is a
desirable component in construction materials due to
its rapid cure and early strength characteristics.
Attempts to improve the water-resistance of gypsum
boards by mixing Portland cement and gypsum (calcium
sulfate hemihydrate) have met with limited success
because such a mixture can result in the formation
of ettringite, which may cause expansion of the
gypsumjPortland cement product and thus lead to its
deterioration. Ettringites are formed when
tricalcium aluminate (3CaO Al,O,) in the Portland
cement =eacts with sulfate.
A cemenLitious composition useful as a
pave~.=nc patc~:iTcr compound whic~ contains Portl and
f P3
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cement and alpha gypsum is disclosed in Harris, U.S.
Patent No. 4,494,990. The composition also includes
a pozzolan source, such as, for example, silica
fume, fly ash or blast furnace slag. The Harris
patent discloses that the pozzolan blocks the
interaction between the tricalcium aluminate and the
sulfate from gypsum. The Harris patent discloses
mixing a three-component blend of Type I Portland
cement, alpha gypsum and silica fume with a fine
aggregate to prepare a mortar used to cast mortar
cubes for evaluating the strength of the resulting
composition.
Ortega et al., U.S. Patent No. 4,661,159
discloses a floor underlayment composition that
includes alpha gypsum, beta gypsum, fly ash and
Portland cement. The patent also discloses that the
floor underlayment material can be used with water
and sand or other aggregate to produce a fluid
mixture which may be applied to a substrate.
Neither the Harris patent nor the Ortega et al.
patent discloses fiber-containing compositions.
Sattler et al., U.S. Patent No. 5,030,289
discloses a first group of molded construction parts
made from waste paper or cellulose fibers and a
binder made from (1) Portland cements, alumina
cements, belite cements, or mixtures thereof; and
(2) a pozzolan such as amorphous silicic acid,
powdered trass, fly ash, or mixtures thereof.
Sattler et al. also discloses a second group of
molded construction parts made from fiber and a
binder of (1) a latently hydraulic component such as
blast sand or blast slag; (2) hemihydrate gypsum;
and (3) Portland cement. However, the Sattler et
al. patent does not disclose combining gypsum with
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the cement/pozzolan-containing mixtures used to make
the first group of molded construction parts.
SUMMARY OF THE INVENTION
It is an object of the invention to
overcome one or more of the problems described
above.
According to the invention, a cementitious
composition includes about 10 wt.% to about 35 wt.o
fiber and about 65 wt.o to about 90 wt.o of a
cementitious binder. The binder composition further
includes about 30 wt.% to about 75 wt.o calcium
sulfate beta-hemihydrate, about 10 wt.o to about 50
wt.% Portland cement, and about 4 wt.o to about 20
wt.o silica fume.
The invention further includes
construction compositions and materials made from
the inventive cementitious composition and methods
for making the same.
Other objects and advantages of the
invention will be apparent to those skilled in the
art from the following detailed description taken in
conjunction with the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
According to the invention, a composition
for use in construction materials is provided which
is particularly useful in areas where water
resistance is an important consideration for both
interior and exterior applications, such as floor
underlayment, fiber board, sheeting, roofing tile
and shingles.
Compositions according to the invention
include a binder made from about 30 wt.% to about 75
wt.o calcium sulfate beta-hemihydrate (i.e., beta-
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gypsum), about 10 wt.o to about 50 wt.o Portland
cement, and about 4 wt.o to about 20 wt.o silica
fume. Alternatively, the binder may include about 1
wt.% to about 40 wt.o pozzolanic aggregate. About
65 wt.o to about 90 wt.o of the binder is then mixed
with about 10 wt.o to about 35 wt.o of a fiber
component to result in a gypsum- and fiber-
containing composition according to the invention.
The beta-gypsum component of the binder of
a composition according to the invention is calcium
sulfate beta hemihydrate, commonly referred to as
stucco. Beta-gypsum is traditionally less expensive
than alpha-gypsum. Alpha-hemihydrate powder has a
higher apparent density and smaller related surface
area than beta-hemihydrate, resulting in a lower
water requirement for the same workability and a
higher compressive strength of the set material.
However, boards made from the inventive composition
exhibit more than adequate strength for interior
applications such fiberboards and boards used as
backer boards, and exterior applications, such as
exterior. sheeting, roof tiles and shingles.
The Portland cement component of the
composition according to the invention may be any of
Types I, II, III, IV, or IV (or mixtures thereof) as
set forth according to ASTM standards. However,
Type III Portland cement~s~is preferred. Type III
Portland cement cures faster than Type I and Type II
Portland cement and exhibits an early high strength.
Blended cements also may be used in
compositions according to the invention. Blended
cements are blends of Portland cement with one or
more pozzolanic materials such as fly ash and blast-
furnace slag.
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The silica fume component of the binder of
a composition according to the invention is an
extremely active pozzolan and prevents the formation
of ettringite. Silica fume is very fine (particle
average diameter of between about 0.1 microns and
about 0.3 microns), has a high surface area (between
about 20 meterz/gram and about 30 meter~/gram), and
is highly amorphous (between about 98 wt.o and about
100 wt.o amorphous Si02 (glassy material)).
The alternative pozzolanic aggregate or
filler component of the binder of a composition
according to the invention may be a natural or man-
made aggregate that contains a high percentage of
amorphous silica. Natural pozzolanic aggregates are
of volcanic origin and include trass, pumice, and
perlite. Man-made pozzolanic aggregates include fly
ash and FILLITETM(hollow silicate spheres produced by
Fillite Division of Boliden Intertrade, Inc.
Atlanta, Georgia).
The fiber component of a composition
according to the invention is selected from wood and
paper fibers, including recycled waste paper fibers,
other ligneous materials such as flax and cotton,
and mixtures of such fibers. Wood Tiber is a
preferred fiber component for a composition
according to the invention.
Most preferably, the fiber is obtained
from debarked wood which is refined to long thin
flakes having a thickness of about 0.008 inches
(about 0.2 mm) to about 0.013 inches (about 0.33 mm)
and a length of up to about 1.18 inches (about 30
mm). The flaked wood is then milled and screened
and possibly further refined using known processes
in order to provide fibers or fiber -'takes of
substantially constant geometry.
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If the wood fiber material used in a
composition according to the invention is waste
paper, such paper must first be processed to remove
foreign material such as plastic, dirt and metals.
The paper is then further processed by shredding,
preferably with a heavy hammermill. The shredded
paper is then preferably dry-refined to result in
fibers of substantially constant geometry.
The binder for compositions according to
the invention preferably includes about 30 wt.o to
about 75 wt.o calcium sulfate beta-hemihydrate
(about 36 wt.o to about 47 wt.o is preferred for
fiberboard), about 10 wt.% to about 50 wt.o Portland
cement (about 40 wt.o to about 50 wt.% is
1.5 preferred), and about 4 wt.% to about 20 wt.%
silica fume (about 10 wt.o to about 15 wt.o is
preferred for fiberboard).
About 65 wt.o to about 90 wt.% (preferably
about 70 wt.o to about 85 wt.o) of the binder is
then mixed with about 10 wt.o to about 35 wt.% wood
fiber (preferably about 15 wto to about 30 wt.o wood
fiber) to form a fiberboard.
Most preferably, a binder according to the
invention for use in a fiberboard includes about 40
wt.o calcium sulfate beta-hemihydrate, about 46 wt.%
Portland cement, and about 14 wt.o silica fume.
A construction material, such as a
fiberboard according to the invention may be
manufactured by the following process:
Raw gypsum may be calcined at about 160°C
(320°F) to about 175°C (347°F) to form calcium
sulfate hemihydrate. The calcined gypsum can be
post-ground to a finer particle size if, for
example, certain strengths, water requirements, and
working properties are desired.
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All components of the composition,
including gypsum, cement, silica fume, water, wood
fiber, and any other additives preferably are
weighted batch-wise. Moisture in the wood fiber
also is measured.
The gypsum powder is fed to a mixer, such
as a large batch or continuous mixer, and blended
with Portland cement and silica fume.
In a second mixer, the fiber is mixed with
water to allow the fiber/water mixture to loosen.
The gypsum/cement/silica fume binder is then added
to the fiber/water mixture and intensively mixed
with the humid fiber. Although water may be added
to the binder/fiber mixture (or to the binder prior
to mixing with the fiber), preferably, the water is
added to the fiber and then the binder is added to
the water/fiber mixture.
Most preferably, the water addition to the
fiber and the subsequent binder addition to the
wetted fiber are performed with the aid of computer
control so that it is possible to add to the fiber
the total quantity of water required for the process
(i.e. a slight stoichiometric excess amount of water
required for hydration), and then vigorously mix the
wetted fiber with the binder.
Other ingredients, such as set control
additives (e. g. accelerators), water reducing
agents, water repellent additives, retarders, and
latex or polymer modifiers may be added to the
fiber/binder mixture. Some additives may be added
to the dry binder mixture prior to mixture with the
wet fiber. Preferably, the composition includes
about .Ol wt.o to about 1.5 wt.o retarder, based
upon the total weight of the composition.
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_8_
The mixed composition is then conveyed
directly to a forming machine which spreads an
endless mat onto an elongated belt of a continuous
press. The mat enters the press on the conveyor
belt, is pressed and may be cut into sections, and
exits on a conveyor belt in the form of an endless
board-ribbon or panel sections. A pressing machine
which can be used for this purpose is the Bison-
Hydro-Dyn-PressTM(Bison GmbH, Springe, Germany). In
such a press, the hydration of the board occurs
quickly and may be hastened by warming the board in
the press up to an optimal hydration temperature.
Preferred processing conditions include pressing at
room temperature (about 25°C) at pressures up to
about thirty (30) kg/cm2 for a press or clamping time
of about three (3) to about eight (8) hours.
The board-ribbon (or panel sections)
leaving the press has sufficient green strength so
that it can be transferred onto a conveyor which
will carry the board forward to a cutting station.
Hydration may continue as the board-ribbon cr panel
sect_ons are conveyed to the board cutter. The
board-ribbon is then cut or sawed to a desired panel
length. If necessary, the panels are then dried to
a final moisture content.
Finally the board panels are trimmed and,
if desired, split lengthwise to a final dimension.
Boards are typically cut into 3 ft. (0.9 meter) x 5
ft. (1.5 meter) sheets, and have a thickness between
about 1/2 inch (about 1.3 cm) and about 5/8 inch
(about 1.6 cm).
Compositions according to the invention
produce building materials which set up quickl;r,
exhibit high strength and durability, and are water
._ ~es,~stant. Because ~ompositions according tp t~~-:e
t;
21N2~24
g _
invention set up quickly, building materials made
from such compositions can be handled (e. g. sheets
can be cut into smaller sheets or boards) much
faster than products made from Portland cement and
fiber alone. For example, a benefit of a
composition and process according to the invention
is that a fiberboard made from the inventive process
undergoes a total pressing/curing time of under
seven hours (and as little as three hours) as
compared to the seven to twelve-hour pressing/curing
time required for some other Portland cement/fiber
board processes. Furthermore, unlike traditional
gypsum board, boards or other products made from a
composition according to the invention do not
require kiln drying, and in fact, kiln drying should
be avoided.
EXAMPLE 1
A cementitious composition according to
the invention was prepared with the binder
components set forth in the amounts stated in Table
I below:
TABLE I
Material Weiaht Percent
Beta-gypsum (Stucco) 40
Type III Portland Cement 46
Silica Fume 14
About 75% by weight of the binder
materials identified in Table I were mixed with
about 25 wt.o (dry weight) of fiber that had been
mixed with water (slight stoichiometric excess).
The wetted fiber and binder were vigorously mixed,
formed into mats and pressed into sample boards
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using a Bison laboratory press (Bison GmbH, Springe,
Germany). The pressing conditions included 30 kg/cm'
pressure; press temperature of about 25°C; and a
press time of three hours.
The samples exhibited excellent dry and
wet durability even when subjected to a continuous
water spray. The final products had an extremely
smooth surface.
Certain physical properties of boards made
according to Example 1 were tested, including
percent linear variation (ASTM D 1037), percent
water absorption (ASTM D 1037), Mor's 3-Point
Loading (ASTM C 947; and nail pull (ASTM C 473).
For each of these tests, gypsum/cement/silica fume
(GCSF) boards made according to Example 1 were
compared to cement fiber boards made of about 82
wt.o Portland cement and about 18 wt.o wood fiber.
The press time required for the cement fiber boards
ranged between seven to ten hours. The
results of the tests are set forth in the following
tables:
TABLE II
LINEAR VARIATION (o) (ASTM D 1037)
70F/ 50 70F/ 50
o RFI3 o RH3
to to
90F/ 90% 109F (Bone
RH3 Dry)
Long Short Long Short
Direction Direction Direction Direction
GCSFl +0.125 +0.125 -0.155 -0.155
Cementz +0.177 +0.175 -0.195 -0.192
lGypsum/cement/silica fume fiber board.
zCement fiber board.
3Relative humidity.
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TABLE III
WATER ABSORPTION (o) (ASTM D 1037)
Percent Percent Caliper
by Weight Swell
2 Hours 24 Hours 2 Hours 24 Hours
GCSF1 4.5 8.4 0.47 1.1
Cement2 12.4 21.6 0.64 1.1
lGypsum/cement/silica
fume
fiber
board.
ZCement
fiber
board.
TABLE IV
MOR'S 3 POINT LOADING (DRY) (ASTM C 947)
MOR3 PEL4
Long Short Long Short
Direction Direction Direction Direction
GCSFl 2146.5 2297.9 1269.5 1986.2
Cement2 2123 1928.9 1458.8 1146.2
lGypsum/cement/silica fume fiber board.
zCement fiber board.
3Modules of Rupture ( lb/ inZ ) .
4Proportional Elastic Limit (lb/in2).
TABLE V
MOR'S 3 POINT LOADING (WET) (ASTM C 947)
MOR3 PEL4
Long Short Long Short
Direction Direction Direction Direction
GCSF1 1141.4 1332 509.2 474.3
Cement2 1402.7 1385.8 760.7 462.3
lGypsum/cement/silica fume fiber board.
ZCement fiber board.
3Modules of Rupture (lb/inz) .
4Proportional Elastic Limit (lb/in2).
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TABLE VI
NAIL PULL (ASTM C 473)
Pounds Force (dry)3 Pounds Force (wet)3
GCSF1 688 356
Cement2 615 439
lGypsum/cement/silica fume fiber board.
2Cement fiber board.
3Testing parameters included:
0.400 inch nail head diameter;
0.121 inch shank diameter; and
a loading rate of one foot/minute.
As shown in the tables above, boards made
according to the invention exhibited comparable or
improved physical properties as compared to cement
fiber boards which did not include gypsum or silica
fume. Furthermore, the boards according to the
invention advantageously took much less time to
process (three hour press time) as compared to the
cement fiber boards (seven to ten hour press time).
The foregoing detailed description is
given for clearness of understanding only, and no
unnecessary limitations should be understood
therefrom, as modifications within the scope of the
invention will be apparent to those skilled in the
art.
