|
International Hydrolytics Ltd. |
|
United States Patent |
5,194,091 |
|
Laney |
March 16, 1993 |
Geopolymer-modified, gypsum-based construction materials
Abstract
Geopolymer-modified gypsum
construction materials. Compositions derived from combining geopolymer
adhesives with conventional gypsum wallboard slurry formulations produce an
interpenetrating network (IPN) which cures by loss of process water to a
refractory solid having improved fire and water resistance. Geopolymer adhesive
starting compositions includes soluble and insoluble silicates, buffers and
salts, and a chemical setting agent in aqueous suspension.
|
Inventors: |
Laney; Bill E. (Albuquerque, NM) |
|
Assignee: |
The Hera Corporation (Albuquerque, NM) |
|
Appl. No.: |
635735 |
|
Filed: |
December 26, 1990 |
|
Current U.S. Class: |
106/611; 106/614; 106/615; 106/616; 106/618; 106/628;
106/772; 106/778; 106/779; 106/780; 106/782; 156/39 |
|
Intern'l Class: |
C04B 011/28; C04B 012/04 |
|
Field of Search: |
106/609,611,614,615,616,618,628,772,778,780,782,779
156/39 |
References Cited [Referenced By]
U.S. Patent Documents
|
2531496 |
Nov., 1950 |
Bean et al. |
106/611. |
|
3853571 |
Dec., 1974 |
Gelbman |
106/611. |
|
4151000 |
Apr., 1979 |
Bachelard et al. |
106/611. |
|
4482379 |
Nov., 1984 |
Dibrell et al. |
106/611. |
Primary Examiner: Dixon, Jr.; William
R.
Assistant Examiner: Green; Anthony J.
Attorney, Agent or Firm: Freund;
Samuel M.
Claims
What I claim is:
1. Gypsum wallboard materials having improved fire and water resistance produced
from combining a self-hardening mixture comprising a geopolymer adhesive with a
gypsum wallboard slurry, wherein said geopolymer adhesive comprises 43%-65% of
soluble alkali metal silicate solution, 0.0%-0.4% of a pH-lowering and
buffering agent, 1.3%-15.7% of a chemical setting agent for said soluble alkali
metal silicate, 5.2%-23.6% of a strengthening agent, 11%-16% water, and
0.0%-16% of a thickening agent.
2. The gypsum wallboard materials as described in claim 1, wherein said
strengthening agent includes calcium metasilicate.
3. The gypsum wallboard materials as described in claim 2, wherein the
wollastonite form of said calcium metasilicate is used.
4. The gypsum wallboard materials as described in claim 1, wherein said soluble
alkali metal silicate is selected from the group consisting of sodium silicate,
potassium silicate and lithium silicate.
5. The gypsum wallboard materials as described in claim 1, wherein said
thickening agent includes hydrous aluminum silicate clay.
6. The gypsum wallboard materials as described in claim 1, wherein said
chemical setting agent includes sodium fluorosilicate.
7. The gypsum wallboard materials as described in claim 1, wherein said
chemical setting agent includes zinc oxide.
8. The gypsum wallboard materials as described in claim 1, wherein a sufficient
amount of said geopolymer adhesive is present to form an interpenetrating
network which bonds. supports, and provides improved fire and water resistance
to said gypsum board formulation.
9. The gypsum board materials as described in claim 1, wherein said pH-lowering
and buffering agent includes at least one Lewis acid.
10. The gypsum wallboard materials as described in claim 1, wherein said
pH-lowering and buffering agent is selected from the group consisting of
calcium chloride, magnesium chloride, and mixtures thereof.
11. The gypsum wallboard materials as described in claim 1, wherein said
thickening agent includes flyash.
12. Gypsum wallboard materials having improved fire and water resistance
produced from combining a self-hardening mixture comprising
commercially-utilized gypsum wallboard slurry and a geopolymer adhesive, said
geopolymer adhesive comprising 43.0%-65.0% of soluble alkali metal silicate
solution, 0.0%-16% of a thickening agent, 5.2%-23.6% of a strengthening agent,
11%-16% water, and 1.3%-15.7% of a chemical setting agent for said soluble
alkali metal silicate solution.
13. The gypsum wallboard materials as described in claim 12, wherein said
thickening agent comprises wollastonite, kaolin, and flyash.
14. The gypsum wallboard materials as described in claim 12, wherein said
chemical setting agent comprises sodium fluorosilicate.
15. The gypsum wallboard materials as described in claim 12, wherein said
chemical setting agent comprises zinc oxide.
16. The gypsum wallboard materials as described in claim 12, wherein said
geopolymer adhesive comprises between 5% and 20% by wet weight of said gypsum
wallboard slurry.
17. The gypsum wallboard materials as described in claim 13, wherein said
flyash comprises between 5% and 18% of the mixture of said gypsum wallboard
slurry and said geopolymer adhesive.
18. A method for producing gypsum wallboard materials having improved fire and
water resistance, said method comprising the steps of:
a. combining a self-hardening mixture comprising commercially-utilized gypsum
wallboard slurry with a geopolymer adhesive, said geopolymer adhesive
comprising 43%-65% of soluble alkali metal silicate solution, 0.0%-16% of a
thickening agent, 5.2%-23.6% of a strengthening agent, 11%-16% water, and
1.3%-15.7% of a chemical setting agent for said alkali metal silicate solution;
and
b. permitting the mixture resulting therefrom to harden.
19. The method as described in claim 18, wherein the thickening agent comprises
wollastonite, kaolin, and flyash.
20. The method as described in claim 18, wherein the chemical setting agent
comprises sodium fluorosilicate.
21. The method as described in claim 18, wherein the chemical setting agent
comprises zinc oxide.
22. The method as described in claim 18, wherein the geopolymer adhesive
comprises between 5% and 20% by wet weight of the gypsum wallboard slurry.
23. The method as described in claim 19, wherein the flyash comprises between
5% and 18% of the mixture of the gypsum wallboard slurry and the geopolymer
adhesive.
24. The method as described in claim 18, further comprising the step of heating
the hardened mixture to remove excess water.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to gypsum wallboard construction
material, and more particularly to the modification of such materials by the
addition of silica-based geopolymer adhesives to produce composites which
exhibit improved fire performance, water resistance, and structural properties.
Gypsum wallboard is a widely used construction material because of its low cost
and fire resistance. Fire resistance capability is generally proportional to
the thickness of the gypsum employed in a fire resisting structure. For
example, a simple structure approved for a fire endurance period of one hour
uses a 5/8 in. thick slab of Type X gypsum wallboard on either side of a 35/8
in. metal stud with an air filled cavity for a non-load-bearing wall assembly.
Other designs provide fire resistance for periods of up to two hours.
Gypsum is a naturally occurring form of the di-hydrate of calcium sulfate. This
material can be readily transformed to its stucco form, the hemi-hydrate of
calcium sulfate, by one of several calcination processes. Gypsum provides fire
protection through two primary mechanisms: the non-combustible nature of
inorganic compounds; and the endothermic, energy-absorbing capacity of the
dihydrate which produces steam when exposed to intense heat. In equation form,
gypsum.fwdarw.Plaster of Paris+Steam-Energy, or CaSO.sub.4 (2H.sub.2
O).fwdarw.CaSO.sub.4 (0.5H.sub.2 O)+1.5H.sub.2 O-4100 cal/mole.
A wall which is to endure fire for a period of at least one hour must be able
to withstand temperatures well in excess of 1500.degree. F. This temperature is
considerably in excess of the ignition temperature of most organic materials
(about 450.degree.-800.degree. F.). Thus, a fire-resistant wall must maintain
the temperature of the unexposed face of the wall at a moderately low
temperature in order to prevent the spread of the fire. A further consideration
for an acceptable fire-resistant wall is the integrity of the wall assembly
against penetration by a water stream from a fire hose at the termination of
the fire exposure period. Masonry walls achieve these conditions as a result of
the high structural/thermal mass and large heat capacity inherent in the dense
materials utilized. Lightweight wall assemblies, by contrast, require good
thermal insulation in lieu of large thermal mass. The utilization of the heat
of dehydration of gypsum can provide an effective cooling mechanism for a
fire-resistant wall. However, as this water of hydration, which binds the
gypsum material, is converted to steam, the gypsum is recalcined into a fine
hemi-hydrate powder, or stucco, leaving a wall component that is devoid of
structural integrity, lacking dimensional stability, and without strength after
fire exposure. Moreover, the recalcined gypsum material is easily washed away
with water from a fire hose. At a minimum, the wall is easily crumbled by the
action of water from fire hoses because of shrinking and bending of the studs
as well as from the shrinking of the gypsum itself which produces cracks
therein.
Structural rigidity of gypsum wallboard, which is proportional to the moment of
inertia of the paper facing sheets about the bending axis, derives from the
bond of the paper to the core. This bond is affected by the degree of
saturation of the paper which also promotes rehydration and crystalline growth
of the gypsum into the paper. In addition, the compressive strength of the
gypsum core is proportional to the density, the type of crystallization, and
the degree of rehydration. Of the naturally occurring forms of gypsum, three
are common. Acicular or needle-like satinspar and plate-like selenite do not
have adequate structural integrity to be of interest in the construction
trades, and physical conditions which promote the growth of these forms prevent
the formation of structural gypsum. Massive gypsum, or alabaster, has random
three-dimensional crystalline orientation, and while not highly soluble in
water, it is hygroscopic and will soften when wet. During this condition, it
loses most of its strength and in a wallboard structure, the gypsum/paper
crystalline bond is easily destroyed or damaged. If properly dried, the core
strength will return.
Care must be exercised in the selection of additives for gypsum wallboard,
since a poor choice of additives may cause improper recrystallization
(development of an interpenetrating network through random crystalline growth),
with a resulting loss of strength both in the core and in the paper facing
sheet bond. In addition, the presence of soluble salts and other impurities affects
the gypsum/paper bond and the core strength detrimentally. Finally, the setting
time, which is directly related to the rate of rehydration and release of heat,
must be maintained within strict limits to meet operational criteria of a
wallboard manufacturing process specification; that is, the mix must retain a
working viscosity while in the mixer and during the wetting of the paper facing
sheets, must be plastic but hold its form while passing through the forming
rolls and smoothing bars, and must cure to moderate handling strength
sufficient for cutting and transport to the dryer within the length of a
production line which is typically 4-5 min. for a 1000 ft. line and a board
movement rate of 200-250 ft./min.
Retarders are used to prevent initial setting during the first phase and
accelerators are used to produce final set within the proper time period.
Different compounds affect the initial set and rehydration cycle and the
chemistry becomes complex and highly proprietary. The primary accelerator is the
addition of freshly ground massive gypsum as a seed crystal. Without
retardation, typically by using water-soluble organic acids or bases, the
nucleation will proceed to rapid initial set, thereby preventing proper wetting
and forming. Additional accelerators such as potash, for example, are employed
to enhance the rehydration phase to produce "Vicat Set." That is, the
point where the strength measured by a Vicat hardness tester is adequate for
cutting and drying, at which time the rehydration exotherm has reached
completion and the temperature of the material remains approximately constant.
Natural massive gypsum has a density of about 2.35 g/cm.sup.3 (147
lb/ft..sup.3) which is approximately three times the density of typical
fire-resistant gypsum wallboard (47 lb/ft..sup.3). Reconstitution of massive
gypsum di-hydrate at atmospheric pressure will not produce the high density of
the natural gypsum because of the requirement of excess water to generate a
workable slurry mixture. The cured density of Plaster of Paris ranges from a
high of about 75 lb/ft..sup.3 with a water:stucco wet weight ratio of 0.8 to a
low of 36 lb/ft..sup.3 with a corresponding ratio of 1.7. Compressive strength
falls from 2000 psi to 170 psi, respectively. The exact formula specification
of 1.5 moles of water added to one mole of calcium sulfate hemi-hydrate to
produce the massive gypsum corresponds to a water:stucco ratio of 0.186.
Generally, the amount of available water directly determines the final cured
gypsum density.
Accordingly, an object of the present invention is to provide a gypsum-based
construction material having improved dimensional and structural stability when
exposed to fire.
Another object of this invention is to provide a gypsum-based construction
material having improved resistance to water after being exposed to fire.
Yet another object of the present invention is to provide a gypsum-based
construction material derived from less expensive materials than those
currently employed.
Additional objects, advantages and novel features of the invention will be set
forth in part in the description which follows, and in part will become
apparent to those skilled in the art upon examination of the following or may
be learned by practice of the invention. The objects and advantages of the
invention may be realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects and in accordance with the purpose
of the present invention, as embodied and broadly described herein, the
composition hereof includes gypsum board materials having improved fire and
water resistance produced by combining a self-hardening geopolymer adhesive
with a gypsum board formulation slurry, wherein the geopolymer adhesive
includes a soluble alkali metal silicate solution, a pH-lowering and buffering
agent, a thickening agent, and a slow-dissolving chemical setting agent, and
the gypsum board slurry formulation includes stucco, water, lignin, retarder,
potash, glass, fiber, starch, paper pulp, boric acid, dextrose, and soap.
Soluble alkali metal silicate solution, a thickening agent, and an activator.
Benefits and advantages of the subject invention include gypsum-based materials
having improved dimensional stability, structural integrity, and water
resistance after exposure to fire. Additionally, in the case where the present
compositions include wallboard, only slight modification to existing wallboard
plants are required, and, because of the possibility of substitution of less
expensive components, materials can also be produced at lower cost.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a part of the
specification, illustrate two embodiments of the present invention and,
together with the description, serve to explain the principles of the
invention. In the drawings:
FIG. 1, curve 1 illustrates a typical
setting-temperature versus time rehydration for conventional gypsum wallboard
formulations.
Curve 2 illustrates a similar rehydration profile to that shown in curve 1
hereof for a composition including the gypsum wallboard formulation thereof
with added geopolymer adhesive according to the teachings of the present
invention (the formulation does not contain accelerator, retarder, or flyash
materials).
Curve 3 illustrates a similar rehydration profile to that shown in curve 2
hereof, except that flyash has been added to the formulation.
FIG. 2 illustrates the compressive yield of
materials produced according to the teachings of the present invention as a
function of the density thereof.
FIG. 3 illustrates a comparison fire test between
conventional gypsum wallboard and wallboard produced according to the teachings
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Briefly, the present invention includes compositions that result from combining
geopolymer adhesives with gypsum slurry formulations to produce
interpenetrating networks (IPNs) which cure to form refractory solids by loss
of process water. Geopolymer adhesive components include: soluble and insoluble
silicates; buffers; salts in aqueous suspension; and chemical setting agents.
The curing cycle of the geopolymer material begins with the formation of a
complicated liquid or gel of cations (Ca.sup.2+, Zn.sup.2+, etc.) and anion
complexes. The anionic constituents then polymerize, forming chains that are
cross-linked by the cations. The final composition of the geopolymer IPN (in
the absence of the gypsum-based materials) is a polymerized silica matrix which
may incorporate dispersed-phase particles, fibers, fillers, and extenders. In
addition, since there is no chemical or structural dependence on water in the
resulting silica matrix, when incorporated into gypsum-based construction
materials according to the teachings of the present invention, the refractory
IPN provides the remaining structure to gypsum-based wallboard after such
compositions are exposed to fire.
According to present understanding of the invention, the addition of geopolymer
adhesives to gypsum slurries provides the following:
1. Cross-linking of the gypsum through geopolymer IPN structures; that is, a
reticulated co-structure, parallel to the random crystallization of the gypsum;
2. The geopolymer IPN is not destroyed upon recalcining of the gypsum, and the
structural integrity of the composite after fire exposure resists crumbling to
a degree which is proportional to the amount of geopolymer adhesives employed;
3. The insoluble nature of the geopolymer IPN improves the performance of the
composite matrix when exposed to water, minimizing softening, etc.; and
4. The addition of relatively inert inorganic additives to the slurry minimally
affects the gypsum chemistry while providing seed nucleation sites for both
gypsum and geopolymer material. Examples of such dispersed-phase inert
materials are expanded perlite, vermiculite, flyash, diatomaceuos earth, etc.
A brief description of the chemistry of geopolymer adhesives, gypsum slurries,
and mixtures thereof will be instructive. Geopolymer adhesives, mixed to a
viscosity suitable for workability in the range of 150-200 centipoise, contain
about 55% solids, not including the dispersed-phase additive (DPA) materials. These
mixtures are alkaline with a pH of approximately 11.0-11.5, and further
reduction of the pH without dilution produces a wide variation of gelation
rates. In addition, anhydrous material which quickly absorbs water will also
produce gelation by dehydration of the geopolymer adhesive, as will the
introduction of soluble calcium ions. Since the rehydration reaction of gypsum
proceeds in the pH range of 6-7, modest quantities of gypsum slurry added to
the geopolymer adhesive will cause rapid gelation and setting of the
geopolymer. These reactions proceed so quickly that adequate mixing is
generally precluded, and attempts to buffer the pH of gypsum to the range of
11.0-11.5, thereby preventing gelation by pH depression, are countered by the
presence of adequate calcium attached to the sulfate radical. Therefore, a
composite material comprising geopolymer adhesive with minor amounts of gypsum
as an additive is not a viable material for wallboard production because rapid
setting of the mixture precludes proper blending and mixing.
The alternative approach, which overcomes the above-identified difficulties, is
to use geopolymer adhesives as a minor constituent additives to the gypsum
slurry. This technique has been found to:
1. eliminate premature setting of the gypsum and provide adequate time for
paper wetting and board forming;
2. permit the addition of dispersed-phase additives such as flyash to increase
the density of the resulting compositions to the desired level, thereby
providing improved bulk material strength and improved bonding to paper facing
sheets;
3. reduce the amounts of relatively expensive potash accelerator used in
conventional gypsum-based wallboard slurries to decrease the reaction time for
stucco rehydration;
4. provide adequate bonding to standard gypsum wallboard paper facing sheets
and other exterior laminating media; e.g., polyester fabric, fiberglass mat,
etc.;
5. improve fire performance of the resulting material by incorporating the
desirable characteristics of gypsum, while reducing shrinkage and warpage,
eliminating crack formation, and enhancing structural integrity after
recalcination of the gypsum; and
6. improve resistance to softening in the presence of water as is
characteristic of ordinary gypsum-based wallboard.
Having generally described the present invention, the following specific
examples are given as a further illustration thereof.
EXAMPLE I
Although exact industrial formulations for gypsum-based wallboard material are
proprietary, the major components thereof include starch, pulp paper, lignin,
potash, glass fiber, stucco, massive gypsum, water, soap, boric acid, dextrose,
and retarder in addition to the paper facing, trim tape, etc. In a laboratory
demonstration of the present invention, the geopolymer adhesive is formulated
as a Wet Mix Additive (WMA) and a Dry Mix Additive (DMA). The WMA includes a
suspension of non-expanding aluminum silicate clay or other suitable silicate
material, as a thickener, in an aqueous solution of an alkali metal silicate,
buffered by a Lewis acid salt. The DMA includes finely divided sodium
silicofluoride or zinc oxide and calcium metasilicate. The sodium
fluorosilicate is a slowly-dissolving, pH-lowering and buffering chemical
setting agent, the zinc oxide is also a slowly-dissolving chemical setting
agent, and the wollastonite form of calcium metasilicate is added to control
shrinkage and promote long-term strength of the geopolymer IPN. Flyash is
preferable as the thickener material because of its lower cost, but kaolinite,
halloysite, illite, and attapulgite or other thickeners such as wollastonite
and kaolin may be used. Kaolin includes the hydrous aluminum silicate clay
mineral group of materials. The sodium silicate solution, generally expressed
by the formula Na.sub.2 O.SiO.sub.2, and also known as water glass (in
concentrated solution) or sodium metasilicate, consists of about 61% by weight
of water, the dissolved solids including alkali, represented by Na.sub.2 O, and
silicate, represented by SiO.sub.2, the silicate to alkali weight ratio ranging
between 1.7 and 4.5, with a preferred ratio of approximately 3.2. Solutions of
sodium silicate useful in the practice of the present invention include between
30 and 40 weight percent of solids (approximately 34.degree. Baume density),
and preferably, 35-39 weight percent (39.degree. Baume). Potassium or lithium
silicate may be substituted for the sodium silicate in some situations. Lewis
acid materials can be MgCl.sub.2 or CaCl.sub.2, or a mixture thereof, in the
range between 0 and 0.4 weight percent; however, MgCl.sub.2 is preferred. A
summary of the useful geopolymer adhesive composition ranges is found in Table
I.
TABLE I
______________________________________
Material Weight % (min.)
Weight % (max.)
______________________________________
wollastonite 5.2 23.6
sodium silicofluoride
0.0 15.7
zinc oxide 1.3 5.2
sodium silicate
43.0 65.0
alkaline earth chloride
0.0 0.4
water 11.0 16.0
Kaolin 0.0 16.0
flyash 0.0 16.0
______________________________________
The first two materials comprise the DMA, while the second five comprise the
WMA. The zinc oxide may be used as a replacement setting agent for the sodium
silicofluoride. Finely divided particles of zinc oxide also function as a
retarder in the gypsum wallboard formulation.
First, the alkaline earth metal chloride salt is dissolved in water. Aluminum
silicate clay or other suitable silicate material is mixed with sodium silicate
solution, and after thorough blending, the metal chloride salt solution is
added. The density of the WMA is typically about 1.4 g/cc, and as stated above,
the DMA is typically a dry blend of finely screened sodium fluorosilicate or
zinc oxide and calcium metasilicate, each of which are relatively insoluble.
Flyash, which is high in alumino-silicates, has a large surface area and serves
as a nucleation site and density modifier, is added to the mixture.
Typical ranges for the geopolymer-modified gypsum wallboard formulation are set
forth in wet weight percent in Table II.
TABLE II
______________________________________
Components Weight %
______________________________________
stucco 34.56-54.14
water 24.43-38.28
ball mill accelerator
0.09-0.14
starch 0.36-0.56
pulp paper 0.27-0.43
lignin 0.11-0.18
soap 0.005-0.01
potash 0.001-0.002
glass fiber 0.11-0.16
WMA 3.70-14.80
DNA 1.30-5.20
flyash 1.00-20.00
______________________________________
The first two components listed constitute the basic gypsum slurry formulation
for gypsum wallboard material, while the next seven materials in various
combinations and with additional small amounts of other materials (the exact
formulations quantities and identities being proprietary with the wallboard
manufacturers) constitute less than one percent of the initial composition. The
WMA and DMA constitute the geopolymer adhesive and are added according to the
teachings of the present invention. The addition of flyash to the composition
as a dispersed-phase additive is desirable since it is quite inexpensive and
improves the quality of the final product.
The dry ingredients of Table II are blended. These ingredients include starch,
stucco, potash, flyash, and one-half of the glass fiber bulk. One-half of the
water, the lignin, and the paper pulp, along with the remaining one-half of the
glass fibers are well mixed and dispersed. The DMA is added to this suspension
and the entire mixture is blended. The temperature of the mixture is adjusted
to about 100.degree. F. by the addition of hot water. The WMA is then added and
the mixture is blended. The resulting warm, wet mixture is transferred to
another mixing container where the dry mixture is added. The remaining water is
also added at this time. All of the components are mixed for a period not to
exceed fifteen seconds and transferred to paper-lined forming molds.
Reference will now be made in detail to the present preferred embodiments of
the invention, examples of which are illustrated in the accompanying drawings.
Turning now to the drawings, FIG. 1, curve 1
illustrates the temperature dependence versus time for a typical setting/cure
of a gypsum wallboard formulation. The rehydration is essentially complete by
about six minutes. This is evidenced by the flattening of the temperature
profile in that the mixture is no longer generating additional heat. At this
time, the board is sufficiently strong to handle and cut.
FIG. 1, curve 2 illustrates a similar rehydration profile in the laboratory
environment for a mixture of gypsum wallboard materials and geopolymer adhesive
according to the teachings of the present invention, except that the flyash has
been omitted. The onset of initial setting is seen to be delayed about ten
minutes as opposed to that of FIG. 1, curve 1 hereof, and final temperature
achieved by the mixture is reduced, as a result of the larger thermal mass of
the formulation.
FIG. 1, curve 3 shows a similar profile to that illustrated in FIG. 1, curve 2
hereof, except that flyash has now been included in the formulation. The set
time has decreased by half. The temperature rise is smaller due to the
increased mass of the added flyash.
As has been stated hereinabove, the strength of gypsum wallboard compositions
is directly related to the density of the final material. This density is in
turn related to the amount of water used during the mixing process. FIG. 2 shows the measured values of compressive
yield strength versus density for a variety of samples prepared according to
the teachings of the present invention with final densities ranging from 35 to
46 pcf (open boxes). Six strength versus density measurements for typical
gypsum formulations are plotted in FIG. 2 as circles for comparision. These are
reproduced from CRC Practical Handbook of Materials Science, Table 5.4-11, page
275 thereof from data of Barron and Laroque. Most of the measurements for the
compositions of the present invention fall in the density range between 35 and
58 pcf plotted as open squares on the figure. The three data points indicated
by triangles having about 41 pcf density were control formulations of standard
gypsum wallboard material at 1700 lbs/msf, while the three black square data
points at about 46 pcf were vermiculite-doped gypsum/geopolymer formulations
where flyash was omitted. This illustrates that adequate density can be
achieved with proper selection of additives in the formulations of the present invention.
FIG. 3 shows a comparison of the exposure of a
1/2-inch gypsum wallboard and a 1/2-inch wallboard fabricated according to the
teachings of the present invention having identical paper facing sheets to a
direct flame. The board material in each case was horizontally oriented about
1.5 inches above a propane-fired Meeker gas burner for one hour. Measurement
thermocouples were placed in contact with the face exposed to the flame, and on
the unexposed face. The conventional gypsum board was fully recalcined,
cracked, warped, and structurally weakened after the firing period, while the
board prepared according to the teachings of the present invention not only
exhibited excellent dimensional stability; that is, minimal shrinkage, warpage,
and cracking, but also maintained good structural integrity.
It has therefore been found that under laboratory conditions, addition of 5-20%
by weight of geopolymer adhesive to conventional gypsum wallboard formulations
and the further addition of 5-18% by weight of flyash as a DPA is successful in
producing wallboard having desired characteristics. In the concentrations
investigated, the geopolymer acts as a dilute impurity and does not upset the
crystal growth of the gypsum and attendant attachment of the core material to
facing sheet materials.
The following examples illustrate the application of the teachings of the
present invention in a conventional gypsum wallboard plant. The ordinary gypsum
slurry flow rate in the plant employed was 2124 lbs/min. After reducing the
gypsum flow rate, the geopolymer adhesive was added as three separate
components: sodium silicate solution, water, and DMBL, a blend of DMA and the
solid components of WMA, in amounts such that the final flow rate was again
2124 lbs/min.. All materials were added to the gypsum slurry through a
high-shear pin mixer which achieved uniform mixing within 2 seconds. The
resulting geopolymer-modified gypsum wallboard material was processed according
to ordinary plant procedures. In some experiments, additional flyash was added
to improve the resulting wallboard product and reduce overall materials costs.
EXAMPLE II
A.1. 95% gypsum slurry and 5% geopolymer adhesive
The gypsum flow rate was reduced to 2017.8 lbs/min. in order to add 106.2
lbs/min. of geopolymer adhesive as 57.0 lbs./min. of sodium silicate solution,
14.4 lbs./min. of extra water, and 34.8 lbs/min. of DMBL.
A.2 95% of (95% gypsum slurry and 5% geopolymer adhesive) plus 5% of flyash
Along with the addition of the materials as described in A.1., 5% of flyash was
added as follows:
The gypsum flow rate was reduced to 1960.9 lbs/min., and 54.1 lbs/min. of
sodium silicate solution, 13.7 lbs/min. of extra water, 33.1 lbs/min. of DMBL,
and 106.2 lbs/min. of flyash were added.
A.3 90% of (95% gypsum slurry and 5% geopolymer adhesive) plus 10% of flyash
Along with the addition of the materials as described in A.1., 10% of flyash
was added as follows:
The gypsum flow rate was reduced to 1816.0 lbs/min., and 51.3 lbs/min. of
sodium silicate solution, 13.0 lbs/min. of extra water, 31.3 lbs/min. of DMBL,
and 212.4 lbs/min. of flyash were added.
B.1. 90% gypsum slurry and 10% geopolymer adhesive
The gypsum flow rate was reduced to 1911.6 lbs/min. in order to add 114,.0
lbs/min. of sodium silicate solution, 28.8 lbs./min. of extra water, and 69.7
lbs/min. DMBL.
B.2 95% of (90% gypsum slurry and 10% geopolymer adhesive) plus 5% of flyash
Along with the addition of the materials as described in B.1., 5% of flyash was
added as follows:
The gypsum flow rate was reduced to 1816.0 lbs/min., and 108.3 lbs/min. of
sodium silicate solution, 27.4 lbs/min. of extra water, 66.2 lbs/min. of DMBL,
and 106.2 lbs/min. of flyash were added.
B.3 90% of (90% gypsum slurry and 10% geopolymer adhesive) plus 10% of flyash
Along with the addition of the materials as described in B.1., 10% of flyash
was added as follows:
The gypsum flow rate was reduced to 1720.4 lbs/min., and 102.6 lbs/min. of
sodium silicate solution, 25.9 lbs/min. of extra water, 62.7 lbs/min. of DMBL,
and 212.4 lbs/min. of flyash were added.
Tests on the resulting wallboard demonstrated that the addition of geopolymer
adhesive and flyash to standard gypsum slurry in a wallboard plant environment
produced superior quality wallboard materials having similar characteristics to
that produced in the laboratory demonstration of Example I.
The foregoing description of several preferred embodiments of the invention has
been presented for purposes of illustration and description. It is not intended
to be exhaustive or to limit the invention to the precise form disclosed, and
obviously many modifications and variations are possible in light of the above
teaching. The embodiments were chosen and described in order to best explain
the principles of the invention and its practical application to thereby enable
others skilled in the art to best utilize the invention in various embodiments
and with various modifications as are suited to the particular use
contemplated. It is intended that the scope of the invention be defined by the
claims appended hereto.
* * * * *
[ Home ] [ AHC
Products ] [ AHC Applications ]
[ AHC Markets] [ AHC Technology ] [ SolGel Chemistry ] [ Materials Testing ] [ Materials
Comparison ] [ Company Profile ]
[ Marketing ] [ Franchise opportunities ] [ Exclusive Licensing ] [ Marketing Representatives ] [ University Consortia ] [ Literature and Reference ]
[ Contact Us ]