NZ627432B2 - A method of forming a gypsum based product - Google Patents
A method of forming a gypsum based product Download PDFInfo
- Publication number
- NZ627432B2 NZ627432B2 NZ627432A NZ62743212A NZ627432B2 NZ 627432 B2 NZ627432 B2 NZ 627432B2 NZ 627432 A NZ627432 A NZ 627432A NZ 62743212 A NZ62743212 A NZ 62743212A NZ 627432 B2 NZ627432 B2 NZ 627432B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- slurry
- alpha
- hemihydrate
- gypsum
- water
- Prior art date
Links
- 229910052602 gypsum Inorganic materials 0.000 title claims abstract description 54
- 239000010440 gypsum Substances 0.000 title claims abstract description 54
- 239000002002 slurry Substances 0.000 claims abstract description 84
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 57
- 238000001354 calcination Methods 0.000 claims abstract description 19
- 239000000203 mixture Substances 0.000 claims abstract description 15
- 238000002156 mixing Methods 0.000 claims abstract description 6
- 238000001816 cooling Methods 0.000 claims description 6
- 238000000227 grinding Methods 0.000 claims description 6
- 238000007792 addition Methods 0.000 claims description 3
- 239000000654 additive Substances 0.000 claims description 3
- 238000001704 evaporation Methods 0.000 claims description 3
- 239000004088 foaming agent Substances 0.000 claims description 3
- 238000010438 heat treatment Methods 0.000 description 7
- 238000006703 hydration reaction Methods 0.000 description 7
- 230000036571 hydration Effects 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 239000002245 particle Substances 0.000 description 5
- 238000001035 drying Methods 0.000 description 4
- ZOMBKNNSYQHRCA-UHFFFAOYSA-J calcium sulfate hemihydrate Chemical compound O.[Ca+2].[Ca+2].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O ZOMBKNNSYQHRCA-UHFFFAOYSA-J 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 1
- OYPRJOBELJOOCE-UHFFFAOYSA-N calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- PASHVRUKOFIRIK-UHFFFAOYSA-L calcium sulfate dihydrate Chemical compound O.O.[Ca+2].[O-]S([O-])(=O)=O PASHVRUKOFIRIK-UHFFFAOYSA-L 0.000 description 1
- 150000004683 dihydrates Chemical class 0.000 description 1
- 238000011049 filling Methods 0.000 description 1
- 238000005755 formation reaction Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- XSQUKJJJFZCRTK-UHFFFAOYSA-N urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 description 1
- 238000001238 wet grinding Methods 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
- C01F11/466—Conversion of one form of calcium sulfate to another
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B11/00—Calcium sulfate cements
- C04B11/02—Methods and apparatus for dehydrating gypsum
- C04B11/028—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained
- C04B11/032—Devices therefor characterised by the type of calcining devices used therefor or by the type of hemihydrate obtained for the wet process, e.g. dehydrating in solution or under saturated vapour conditions, i.e. to obtain alpha-hemihydrate
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2103/00—Function or property of ingredients for mortars, concrete or artificial stone
- C04B2103/10—Accelerators; Activators
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
- C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
- C04B2111/00612—Uses not provided for elsewhere in C04B2111/00 as one or more layers of a layered structure
- C04B2111/0062—Gypsum-paper board like materials
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/14—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements
- C04B28/145—Calcium sulfate hemi-hydrate with a specific crystal form
- C04B28/146—Calcium sulfate hemi-hydrate with a specific crystal form alpha-hemihydrate
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B38/00—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof
- C04B38/10—Porous mortars, concrete, artificial stone or ceramic ware; Preparation thereof by using foaming agents or by using mechanical means, e.g. adding preformed foam
Abstract
method of forming a gypsum based product is disclosed. The method comprises the steps of: calcining a mixture of water and gypsum under conditions of raised temperature and pressure within a vessel to produce an alpha-hemihydrate slurry therein; passing the alpha-hemihydrate slurry from the vessel to a mixer for mixing with additional water to produce a settable slurry, which is arranged to set to form the gypsum based product. to a mixer for mixing with additional water to produce a settable slurry, which is arranged to set to form the gypsum based product.
Description
A Method Of g A Gypsum Based Product
The present invention relates to a method of forming a gypsum based product.
Gypsum occurs naturally as a raw material in the form of calcium sulphate dihydrate.
Gypsum containing products, such as rboard, are prepared by forming a mixture of
calcined or dehydrated gypsum, namely calcium sulphate hemihydrate, with water, to
form a settable slurry which is then cast into a pre-determined shape. The hemihydrate
reacts with the water and becomes re-hydrated to the dihydrate crystal, which is then
cured or dried to the solid state.
The hemihydrate form of gypsum is known to depend on the calcination process, and is
rised into two basic forms, the alpha-hemihydrate and the beta-hemihydrate. The
beta-hemihydrate is typically formed by g gypsum under atmospheric conditions,
to drive off any moisture and chemically combined water to form dried crystals, which
may then be ground to a fine powder. The beta-hemihydrate has long been the favoured
hemihydrate in the production of gypsum wall boards or plasterboards, owing to the
rapid re-hydration of the ground crystal in forming the slurry. However, the gypsum
product derived from the emihydrate is lly soft and the beta-hydrate requires
large volumes of water to produce the required slurry fluidity.
The alpha-hemihydrate is formed by heating gypsum under pressure to rly remove
the water associated therewith. The gypsum product d from the alpha-hemihydrate
r, is found to be harder and comprises a higher strength and density compared
with beta-hemihydrate d gypsum.
It is necessary to use substantial amounts of water in gypsum slurries in order to ensure
proper flowability of the slurry. Unfortunately, most of this water must eventually be
driven off by heating, which is expensive due to the high cost of the fuels used in the
heating process. The heating step is also time-consuming. It is known that alphahemihydrate
has a substantially lower water demand than beta-hemihydrate, meaning
that if alpha-hemihydrate could be used in making wallboard, it would substantially
reduce the water demand and hence the expense and time required to produce the
wallboard. This is a further advantage associated with alpha-hemihydrate.
However, alpha-hemihydrate is not generally used commercially in the production of
gypsum wallboard primarily due to its slower hydration rate compared to betahemihydrate
, which would therefore require a slower passage of boards along the
production line.
WO2007/084346 discloses a method for the production of alpha-type gypsum. A
gypsum slurry is delivered into an autoclave, where it is heated typically to a temperature
of about 280 F (about 137 C) under a pressure of 3-4 Bar and converted to alpha
drate. The slurry exits the ave via a pressure let down valve and is
delivered to a flash tank, where it is cooled and excess steam is collected.
US2008/0069762 discloses a process for making a blend of alpha- and beta-stucco.
The process includes a slurry calcination step in which gypsum slurry is held in a reactor
at a temperature of e.g. 149 C and a pressure of e.g. 3.4 to 4.8 Bar. The partially
calcined gypsum product discharges from the reactor as a slurry comprising calcium
te ate and alpha calcium sulphate hemihydrate and feeds an accumulator
tank, which acts as a holding tank and permits release of the steam as the slurry’s
pressure drops to atmospheric pressure. The slurry then discharges from the
accumulator tank and feeds a ering unit which removes water to produce a
dewatered -containing t and a removed water stream. The dewatered
product has a 2-6wt% free water moisture content. The dewatered product is fed to a
board stucco kettle calciner at conditions to convert the majority or all of the gypsum in
the dewatered product to beta calcium sulphate hemihydrate.
In accordance with the present invention as seen from a first aspect, there is provided a
method of forming a gypsum based product, the method sing the steps of:
calcining a mixture of water and gypsum under conditions of raised temperature
and pressure within a vessel to produce an alpha-hemihydrate slurry therein;
reducing the water content of the alpha-hemihydrate slurry to provide a te
water stream from the alpha-hemihydrate slurry; and subsequently
passing the alpha-hemihydrate slurry from the vessel to a mixer for mixing with
additional water to e a settable slurry, which is arranged to set to form the
gypsum based product,
wherein the step of passing the alpha-hemihydrate slurry from the vessel to the
mixer comprises the step of maintaining the temperature of the alpha-hemihydrate slurry
at over 70 C.
The term ‘comprising’ as used in this specification and claims means ‘consisting at least
in part of’. When interpreting statements in this specification and claims which include
the term ‘comprising’, other features besides the features prefaced by this term in each
statement can also be present. Related terms such as ‘comprise’ and ‘comprised’ are to
be interpreted in a similar manner.
Advantageously, the method eliminates the requirement for drying of the drate,
which is associated with the conventional formation of the settable slurry, and therefore
reduces the energy demands of the .1 Moreover, the reduced water amounts
associated with achieving the desired fluidity of alpha-hemihydrate le slurry
ed with beta-hemihydrate, es a further energy saving since less water must
be removed during the drying of the gypsum product.
Preferably, the calcination step comprises substantially filling the vessel with water and
gypsum so that the vessel is substantially devoid of free space, such that the water
ed during the calcination of gypsum is prevented from evaporating.
Preferably, the raised temperature comprises a temperature within the range between
110 C and 170 C, preferably n 120 C and 150 C, more ably between
130 C and 140 C.
lly, the pressure is adjusted in accordance with the operating temperature, such
that the operating pressure corresponds to the vapour pressure of steam at the
operating temperature. Preferably, the raised pressure comprises a pressure within the
range 2-8 Bars, more preferably 3-5 Bars.
1 This advantage and other stated advantages are advantages of at least preferred embodiments
of the invention. It is not necessary for every embodiment of the invention to meet each stated
advantage.
The method preferably further comprises the step of cooling the alpha-hemihydrate
slurry after the calcination step. Typically, the step of cooling the alpha-hemihydrate
slurry takes place while the alpha-hemihydrate slurry is still held at the raised pressure of
about 2 to 8 Bars. Typically, the step of cooling the alpha-hemihydrate slurry is carried
out using a heat exchanger. ably, the alpha-hemihydrate is cooled to a
temperature less than 100 C, such as 90 C.
Preferably, after the step of cooling the alpha-hemihydrate slurry, the slurry is depressured
to a pressure of 1 Bar (i.e. atmospheric pressure).
Typically, the method further comprises the step of ntially separating the water
from the alpha-hemihydrate slurry after the step of reducing the pressure acting on the
alpha-hemihydrate slurry. This may be done e.g. using a belt filter or a centrifugal
separator, i.e. hydroclone. Preferably, in this case, the separated water is ated for
mixture with a fresh quantity of gypsum, for introducing into the vessel to start a further
calcination process. In this case, the heat energy ned within the separated water
reduces the requirement for heating of the vessel to achieve the raised temperature of
e.g. 110 C to 180 C.
In the case that water is ted from the alpha-hemihydrate slurry, the free water
content of the remaining slurry is typically 1-30wt%, preferably 5-30wt%, more preferably
Preferably, the method further comprises the step of grinding the alpha-hemihydrate
slurry to reduce the size of particulates therein. It is thought that grinding of the alphahemihydrate
slurry results in a greater reactivity of the alpha-hemihydrate les, so
as to increase the hydration rate of the alpha-hemihydrate particles during the step of
g a settable slurry. The step of grinding the alpha-hemihydrate slurry may be
carried out using wet grinding techniques. In this case, the ng may be carried out
at a temperature of 50 C or more, preferably 70 C or more, more preferably 80 C or
more.
Methods for controlling the size of the alpha-hemihydrate particles during the calcination
stage are known in the art and may be used as an alternative or in addition to the
grinding step.
During the step of passing the alpha-hemihydrate slurry from the ation vessel to
the mixer, the temperature of the alpha-hemihydrate slurry is maintained at over 70 C.
By maintaining the temperature of the hemihydrate slurry at this level, it is thought
that hydration of the alpha-hemihydrate particles to form a settable gypsum product may
be avoided until entry of the alpha-hemihydrate slurry into the mixer. Preferably, the
ature of the alpha-hemihydrate slurry is maintained at over 80 C, more preferably
over 85 C.
In addition, it is desirable that the step of passing the alpha-hemihydrate slurry from the
calcination vessel to the mixer should not take too long, so as to further avoid hydration
of the alpha-hemihydrate les until entry of the particles into the mixer. lly the
time taken for the hemihydrate slurry to pass from the calcination vessel to the
mixer is less than 120 minutes, preferably less than 60 minutes, more preferably less
than 30 minutes.
It is thought that the addition of cold water (e.g. about 20 C-30 C) in the mixer, for
mixing with the alpha-hemihydrate slurry will rapidly decrease the temperature of the
alpha-hemihydrate slurry, so as to e the hydration of the alpha-hemihydrate
particles to form a settable gypsum product.
The method further comprises the on of one or more further additives to the
drate slurry within the mixer, such as accelerators and foaming agents.
Preferably, the gypsum based product comprises a gypsum board.
In accordance with the present disclosure as seen from a second aspect, there is
provided a method of forming a gypsum based product, the method comprising the steps
calcining a mixture of water and gypsum under conditions of raised temperature
and pressure within a vessel to produce an alpha-hemihydrate slurry therein;
passing the alpha-hemihydrate slurry from the vessel to a mixer for mixing with
additional water to produce a le slurry, which is arranged to set to form the
gypsum based product, wherein the hemihydrate slurry is passed from the vessel
to the mixer without undergoing a drying stage.
Preferred features of the method of the second aspect may comprise one or more of the
preferred features of the method of the first aspect.
An embodiment of the present invention will now be described by way of example only
and with reference to the accompanying drawing which provides a schematic ration
of the steps ated with the method according to an embodiment of the present
invention.
Referring to the drawing, the method according to an embodiment of the present
invention comprises the initial step of g a mixture 20 of water and gypsum 10 in a
ratio of approximately 1 part gypsum to 1.5 parts water, pressurising the mixture in a
pressuriser 30 and pre-heating it by means of a heat exchanger 40 (e.g. a water/water
heat ger). The mixture is then introduced into a calcination vessel 50, e.g. by
means of a pump or in a long water column. The mixture is subsequently heated to a
temperature in the range 1300C-1400C and the vessel 50 is pressurised to a pressure in
the range 3-5 Bars. The vessel 50 is substantially filled with the mixture to remove any
free space therein, such that the water within the vessel 50 and principally the water
derived from the calcining of the gypsum, is prevented from evaporating and thus
escaping from the vessel 50.
ing the calcination stage the resulting mixture of water and alpha-hemihydrate
slurry 60 is cooled to a temperature of approximately 900C using the heat exchanger 40,
de-pressurised in a de-pressuriser 70 and passed to a separation unit 80, wherein the
hemihydrate slurry is substantially separated from the water. The water is ated from
the separation unit 80 back to the vessel 50 to preheat subsequent water and gypsum
before entering the vessel 50 and thus reduce the energy demands associated with the
heating of the mixture. The alpha-hemihydrate slurry sing approximately 6% water
is passed from the separation unit 80 to a mixer 90, for subsequent post processing of
the slurry which includes the addition of water 100 and optional additives, such as
accelerators 110 (for reducing the setting time) and foaming agents 120 to produce a
settable slurry. It is also envisaged however, that the post processing may r
comprise the grinding of the hemihydrate slurry (e.g. in a screw grinder 140) to reduce
the size of particulates disposed therein before the alpha-hemihydrate slurry is
introduced into the mixer 90. In this respect, the hemihydrate slurry is passed to the
mixer 90 to achieve the required fluidity and setting characteristics, without undergoing
any drying stage, thereby reducing the energy demand in producing the gypsum
product. Moreover, the resulting settable slurry comprising 30-40% water which is then
passed to a production line 130 for subsequent preparation of a gypsum t such as
a plasterboard, will require less curing owing to reduced amounts of water which are
required to attain the desired ty of the alpha-hemihydrate settable slurry, compared
with the amount of water required to attain the desired fluidity of a beta-hemihydrate
settable slurry. Since hemihydrate typically has a slower hydration rate than
beta-hemihydrate, the setting times for hemihydrate slurry are typically longer than
for beta-hemihydrate slurry. Thus, in the cture of gypsum boards, it is lly
desirable when using alpha-hemihydrate slurry, to have a longer forming belt to provide
sufficient time for setting of the slurry.
Claims (15)
1. A method of forming a gypsum based product, the method comprising the steps 5 calcining a mixture of water and gypsum under conditions of raised temperature and pressure within a vessel to produce an alpha-hemihydrate slurry therein; reducing the water content of the alpha-hemihydrate slurry to provide a separate water stream from the alpha-hemihydrate slurry; and subsequently passing the alpha-hemihydrate slurry from the vessel to a mixer for mixing with 10 additional water to produce a settable slurry, which is arranged to set to form the gypsum based product, n the step of passing the alpha-hemihydrate slurry from the vessel to the mixer comprises the step of maintaining the temperature of the alpha-hemihydrate slurry at over 70 C.
2. A method according to claim 1, wherein the calcination step comprises substantially g the vessel with water and gypsum so that the vessel is substantially devoid of free space, such that the water produced during the calcination of gypsum is prevented from evaporating.
3. A method according to any one of the preceding claims, n the raised temperature comprises a temperature within the range 110 C to 170 C.
4. A method according to any one of the preceding claims, wherein the raised 25 pressure comprises a re within the range 2 to 8 Bars.
5. A method according to any one of the ing claims, further comprising the step of cooling the alpha-hemihydrate slurry after the step of calcining the mixture of water and gypsum.
6. A method according to claim 5, n the hemihydrate slurry is cooled to a temperature less than 1000C.
7. A method according to claim 5 or claim 6, comprising the further step, after the step of cooling the alpha-hemihydrate slurry, of de-pressurising the slurry.
8. A method according to claim 7 further sing circulating the separated water 5 stream to preheat further gypsum before entering the vessel.
9. A method according to claim 7 or claim 8, wherein after the step of reducing the water content of the hemihydrate slurry, the water content of the alphahemihydrate slurry lies within a range of 1-10wt%.
10. A method according to any preceding claim, further comprises the step of grinding the alpha-hemihydrate slurry to reduce the size of particulates therein.
11. A method according to any one of the preceding claims, wherein the time taken 15 for the alpha-hemihydrate slurry to pass from the vessel to the mixer is less than 120 minutes.
12. A method according to any one of the preceding claims, further comprising the addition of one or more additives to the hemihydrate slurry within the mixer, such as an 20 accelerator and/or a foaming agent.
13. A method ing to any ing claim, wherein the gypsum based product ses a gypsum board. 25
14. A method according to claim 1, substantially as herein bed with reference to any embodiment disclosed.
15. A method substantially as herein described with reference to any embodiment shown in the accompanying drawings. 4mmmm> 02_._.<m_I m_._.<N_n_>I-__>_m_I >mm3._w r 02_._.<m_Im_N_n
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB1121589.4A GB2497574B (en) | 2011-12-15 | 2011-12-15 | A method of forming a gypsum based product |
| GB1121589.4 | 2011-12-15 | ||
| PCT/EP2012/075353 WO2013087754A1 (en) | 2011-12-15 | 2012-12-13 | A method of forming a gypsum based product |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| NZ627432A NZ627432A (en) | 2016-03-31 |
| NZ627432B2 true NZ627432B2 (en) | 2016-07-01 |
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