Note: Descriptions are shown in the official language in which they were submitted.
1
CARBON DIOXIDE-ADSORBING ARTIFICIAL STONE COMPOSITIONS
TECHNICAL FIELD
The technical field generally relates to artificial stone products. More
specifically,
the present disclosure relates to carbon dioxide-adsorbing artificial stone
compositions.
BACKGROUND
One of the major contributing factors to global warming and ocean
acidification is
atmospheric carbon dioxide (CO2) emissions. One targeted strategy for reducing
the impacts of global warming and ocean acidification is carbon sequestration
to
reduce the CO2 levels in the atmosphere.
One carbon sequestration technique is in situ carbonation in building
materials,
such as cement bricks. This includes a carbonation step in a wet mixture or
through already carbonated aggregates. For example, one conventional concrete
composition included a mixture of cement, steel slag, and aggregates that
undergoes a carbonation curing step to expose the mixture to a CO2 environment
to accelerate the carbonation reaction. However, this convention technique
only
results in an uptake of about 10% CO2 based on the weight of the slag.
SUMMARY
According to one aspect, there is provided an artificial stone formed from an
uncured mixture comprising: between 25 wt% and 40 wt% binder; between 20%
and 35% filler; between 1.5 wt% and 2 wt% polycarboxylate-based admixture;
and a diluent; wherein at least a portion of the filler comprises a component
capable of mineral carbonization.
In some embodiments, the binder comprises cement.
In some embodiments, the component capable of mineral carbonization
comprises a metal oxide.
In some embodiments, the component capable of mineral carbonation comprises
at least one of a calcium oxide, a silicon oxide, a magnesium oxide, an iron
oxide, a magnesium iron silicate, a nickel oxide, and a manganese oxide.
In some embodiments, at least a portion of the filler is olivine.
Date Regue/Date Received 2022-09-29
2
In some embodiments, the component capable of mineral carbonation comprises
at least one of forsterite, fayalite, monticellite, kirschsteinite, and
tephroite.
In some embodiments, the filler is a powder or an aggregate.
In some embodiments, the filler is less than 2 cm in diameter.
In some embodiments, the artificial stone adsorbs at least 10 kg/m3 of carbon.
In some embodiments, the cured mixture further comprises a pigment.
In some embodiments, the pigment is derived from stones.
In some embodiments, the cured mixture further comprising an air entrainer
admixture.
In some embodiments, the air entrainer admixture is about 0.5 wt% to about 2
wt% of the cured mixture.
According to another embodiment, there is provided an artificial stone
comprising
cement and olivine, wherein the artificial stone is configured to adsorb a
weight of
carbon that is at least equivalent to a weight of the olivine.
In some embodiments, the uncured mixture comprises between 20 wt% and 35
wt% olivine.
According to another embodiment, there is provided an artificial stone formed
from an uncured mixture comprising between 25 wt% and 40 wt% cement and
between 20 wt% and 35 wt% olivine.
According to another embodiment, there is provided an artificial stone
comprising
an inner layer and an outer layer, wherein the inner layer and the outer layer
are
formed from an uncured mixture comprising between 25 wt% and 40 wt% binder,
between 20 wt% and 25 wt% filler, between 1.5 wt% and 2 wt% polycarboxylate-
based admixture, wherein the filler in the outer layer comprises a component
capable of carbon mineralization.
Date Regue/Date Received 2022-09-29
3
In some embodiments, the binder comprises cement.
In some embodiments, the component capable of mineral carbonation comprises
a metal oxide.
In some embodiments, the component capable of mineral carbonation comprises
at least one of a calcium oxide, a silicon oxide, a magnesium oxide, an iron
oxide, a magnesium iron silicate, a nickel oxide, and a manganese oxide.
In some embodiments, the component capable of mineral carbonation comprises
an olivine mineral.
In some embodiments, the component capable of mineral carbonation comprises
.. at least one of forsterite, fayalite, monticellite, kirschsteinite, and
tephroite.
In some embodiments, the filler is a powder or an aggregate.
In some embodiments, the filler is less than 2 cm in diameter.
In some embodiments, the artificial stone has a carbon adsorption rate of at
least
10 kg/m3.
.. In some embodiments, the outer layer is about 1/3 of a volume of the
artificial
stone.
In accordance with another aspect, there is provided a method of producing an
artificial stone as defined herein, the method comprising: mixing the binder,
the
filler, the diluent, and the polycarboxylate-based admixture to produce a
homogenous or near-homogenous uncured mixture; and allowing the uncured
mixture to cure in a mold.
In some embodiments, the method further comprises mixing a pigment with the
uncured mixture.
In some embodiments, the method further comprises mixing an air entrainer
admixture with the uncured mixture.
Date Regue/Date Received 2022-09-29
4
In some embodiments, the air entrainer admixture comprises between about 0.5
wt% and about 2 wt% of the cement.
In accordance with another aspect, there is provided a method of producing an
artificial stone as defined herein, the method comprising mixing the binder,
the
.. filler including the component capable of mineral carbonation, the diluent,
and the
polycarboxylate-based admixture to produce a homogenous or near-
homogenous uncured outer layer mixture; providing the uncured outer layer
mixture in a mold; mixing the binder, the filler, the diluent, and the
polycarboxylate-based admixture to produce a homogenous or near-
homogenous uncured inner layer mixture; providing the uncured inner layer
mixture in the mold; and allowing the inner layer and the outer layer to cure
in the
mold.
In some embodiments, the method further comprises mixing a pigment with at
least one of: the uncured outer layer mixture and the uncured inner layer
mixture.
.. In some embodiments, the method further comprises mixing an air entrainer
admixture with at least one of: the uncured outer layer mixture and the
uncured
inner layer mixture.
In some embodiments, the air entrainer admixture comprises between about 0.5
wt% and about 2 wt% of the binder.
In some embodiments, the outer layer is provided to the mold prior to the
inner
layer being provided to the mold.
In some embodiments, the inner layer is provided to the mold prior to the
outer
layer being provided to the mold.
In accordance with some aspects, there is provided an artificial stone
comprising
.. a cement material, wherein an outer layer of the artificial stone that is
configured
to be exposed to the atmosphere comprises between about 20 wt% and about 35
wt% olivine.
Date Regue/Date Received 2022-09-29
5
DETAILED DESCRIPTION
The present disclosure relates to artificial stone products that have an
enhanced
carbon dioxide (CO2) adsorbing capability. Also disclosed is an artificial
stone
product comprising a binder, a filler comprising a component capable of
mineral
carbonation, a diluent, and a polycarboxylate-based admixture. In some
embodiments, the artificial stone product comprises entrained air and/or a
pigment.
Mineral carbonation is the result of a reaction between CO2 with a metal oxide
containing material to form insoluble carbonates. In some embodiments, the
metal element can be magnesium (Mg), iron (Fe), calcium (Ca), manganese (Mn)
and/or nickel (Ni). When this reaction occurs naturally in the environment,
the
phenomenon is referred to as silicate weathering, which consumes atmospheric
CO2. This natural occurring reaction can be utilized to create artificial
stones that
capture atmospheric CO2 in the stone throughout its the lifetime.
Artificial stones can be used for a variety of purposes, such as cladding for
a
building, floor tile, countertops, paving stones, landscaping tile, steps,
edges or
corner pieces, wall caps, window frames, cornices, columns, terrazzo stone,
etc.
By including a filler that includes a component capable of mineral
carbonation,
the artificial stones can be used to sequester atmospheric carbon, thus
creating
an artificial stone product that can help reduce the overall CO2 levels in the
atmospheric and help combat climate change.
One promising filler that includes a component capable of mineral carbonation
is
olivine. Olivine is a group of silicate minerals that have a composition of
A2SiO4.
"A" is often magnesium (Mg) or iron (Fe) but can also be calcium (Ca),
manganese (Mn) and/or nickel (Ni). Common compositions of olivine include
forsterite (Mg2SiO4), fayalite (Fe2SiO4), monticellite (CaMgSiO4),
kirschsteinite
(CaFeSiO4), and tephroite (Mn2SiO4). When exposed to the atmosphere, olivine
reacts quickly with CO2 and water to create an innocuous carbonate solution,
such as bicarbonate, embedded within the artificial stone, thus removing the
CO2
from the atmosphere. For example, when used in a moderately humid climate,
forsterite reacts with CO2 and water to form magnesium, bicarbonate, and
silicic
acid according to the following formula:
Mg2SiO4 +4 CO2 + H20 4 2 MG2+ +4 HCO3- + H4SiO4
In drier climates, forsterite can react with CO2 and water to form magnesium
carbonate and chrysotile according to the following formula:
2 Mg2SiO4 + CO2 +2 H20 4 MgCO3 + Mg3Si205(OH)4
Date Regue/Date Received 2022-09-29
6
Accordingly, the climate-dependent weather reaction results in the sustainable
capture of CO2, regardless of the humidity level.
Olivine has a hardness of between 6.5 and 7 oh the Mohs hardness scale, which
is almost as hard as quartz. However, olivine is significantly heavier than
quartz,
making it more resistant to erosion.
In some cases, the olivine can be self-cementing, such as when olivine is used
with marine constructions in shallow seawater. Shallow seawaters is often
slightly
supersaturated with calcium carbonate (CaCO3). When the seawater fills pores
created in the artificial stone (for example, via air entraining or through
use of
pumice aggregate as a filler), the pH of the olivine grains will increase due
to the
reaction with the sea water. This pH rise, through its effect on the carbonate
equilibria will strongly increase the calcite supersaturation and calcite will
begin to
precipitate between the olivine grains, thus cementing them into a solid
structure.
Thus, artificial stones using olivine as a filler can be used in marine
constructions,
such as seawalls, piers, etc.
In some embodiments, pumice aggregate can be used as a filler to increase the
porosity in the artificial stone and increase the overall surface area within
the
artificial stone for the component capable of mineral carbonation to react
with the
atmospheric CO2.
Other types of fillers can also be used, such as metal oxides that are capable
of
mineral carbonation or carbon adsorption. By using the unique properties of
fillers
that include components capable of mineral carbonation, such as olivine or
other
metal oxide containing minerals, the artificial stone can be capable of
adsorbing
carbon at a significantly higher rate than that of compositions that include
only
cement and aggregate. In some embodiments, the artificial stone can adsorb at
least about 10 kg/m3, at least about 20 kg/m3 or at least about 30 kg/m3.
Artificial Stone Compositions
The artificial stone with an enhanced CO2 adsorbing capability can be formed
from an uncured mixture comprising a binder, a filler, a diluent, and a
polycarboxylate-based admixture. At least a portion of the filler includes a
component capable of mineral carbonation. In some embodiments, the artificial
stone product comprises entrained air and/or a pigment.
The binder can be cement, such as white cement, grey cement, or Portland
cement. The total percentage of binder can depend on the amount of tricalcium
silicate (Ca3Si05) or alite in the binder. In some embodiments, the uncured
Date Regue/Date Received 2022-09-29
7
composition forming the artificial stone comprises between about 25 wt% and
about 40 wt% binder.
The diluent can be any suitable solvent that acts to decrease the density of
the
binder and the filler. In some embodiments, the diluent is distilled water,
water,
process water, etc.; however, other diluents suitable for use with cement are
also
contemplated. In some embodiments, the diluent is mixed with the
polycarboxylate-based admixture prior to being mixed with the binder.
The polycarboxylate-based admixture can be polycarboxylate ethers (PCE), or
other suitable superplasticizers. In some embodiments, the uncured mixture
comprises between about 1.5 wt% and 2 wt% polycarboxylate-based admixture.
The filler can comprise any suitable cement filler, such as quartz, sand,
clay,
silica fume, olivine, crushed stone, sawdust, small gravel, limestone, pumice
aggregate, etc. The filler can be a powder or an aggregate. At least a portion
of
the filler comprises a compound capable of mineral carbonation. The compound
capable of mineral carbonation can be compounds that comprise a metal oxide,
such as calcium oxides, silicon oxides, magnesium oxides, iron oxides,
magnesium iron silicate, nickel oxides, manganese oxides, etc. (for example,
clay, sand, silica fume, olivine). In some embodiments, the filler is olivine,
which
includes compounds capable of mineral carbonation (Le., compounds that adsorb
carbon), particularly in humid environments. In some embodiments, the filler
is a
combination of natural sand with a purity above 70%, silica fume, and
magnesium, and thus at least a portion of the compound capable of mineral
carbonation is silicon dioxide.
The filler can be any size under about 2 cm in diameter. The filler can be a
light
filler having a particle size of between about 50 pm and about 200 pm and/or a
heavy filler having a particle size of between about 200 pm and about 2 cm. In
some embodiments, the filler is pulverized to a size less than 50 pm.
The particle size of the filler capable of mineral carbonation can impact the
artificial stone's rate of carbon adsorption. Smaller particle size have a
higher
surface to volume ratio, which can provide more area for the filler to react
with
atmospheric CO2, thus potentially increasing the artificial stone's rate of
carbon
adsorption. Furthermore, the total amount of binder required to form the
artificial
stone can depend on the particle size of the filler. For example, when the
individual particles of the filler have a higher volume, the amount of binder
required to form the artificial stone can be reduced.
In some embodiments, the artificial stone can comprise multiple layers having
different compositions. For example, as the carbon adsorption reaction with
the
Date Regue/Date Received 2022-09-29
8
filler capable of mineral carbonation is dependent on exposure to CO2 and
water,
the artificial stone can comprise an outer layer (or façade layer) that
comprises a
filler capable of mineral carbonation and an inner layer that comprises any
suitable filler, regardless of the filler's capacity to adsorb carbon.
According,
during use, the outer layer would be outwardly facing to the environment. For
example, an artificial stone configured for use as building cladding would
have an
inner layer intended to face the outer wall of the building it is installed
on, and the
outer layer would be exposed to the outer environment, thus exposing the outer
layer to atmospheric CO2 and water from humidity and/or precipitation.
In some embodiments, the outer layer is formed from an uncured mixture
comprising a binder, a filler that includes a component capable of mineral
carbonation, a diluent, and a polycarboxylate-based admixture and the inner
layer is formed from an uncured mixture comprising a binder, a filler, a
diluent,
and a polycarboxylate-based admixture. Olivine has a hardness of between 6.5
and 7 on the Mohs hardness scale, which is almost as hard as quartz, making it
a
suitable material to be used as the filler that includes a component capable
of
mineral carbonation in the outer layer of the artificial stone. However, use
of other
components capable of mineral carbonation in the outer layer is also
contemplated.
In some embodiments, the outer layer is formed from an uncured mixture
comprising between about 25 wt% and about 40 wt% binder, between about 20
wt% to about 25 wt% filler, between about 1.5 wt% to about 2 wt%
polycarboxylate-based admixture, and a remainder of diluent. The filler can
comprise between about 1% and about 100% olivine.
The addition of the filler capable of carbon mineralization significantly
increases
the carbon adsorption rate of the artificial stone, in some cases, by a rate
of at
least tenfold that of composition that include only cement and aggregate. The
optimal temperature for the carbon adsorption reaction occurring within the
artificial stone has been found to be around 40 C under 1 atmospheric pressure
(Le., normal atmospheric pressure). The carbon adsorption rate can vary
depending on the type of water the artificial stone is exposed to (ex.,
alkaline
water, distilled water, rain water, etc.) and the amount of air contact. In
some
embodiments, when the filler capable of mineral carbonation is olivine, the
artificial stone can sequester carbon at a rate of 1 1/2 times the weight of
olivine
over the lifetime of the artificial stone. In some embodiments, the natural
reaction
time of olivine to undergo complete mineral carbonation (Le., all or
substantially
all of the olivine has undergone the carbon adsorption reaction) is
approximately
15 to 20 years. For example, 1 kg of olivine has the potential the sequester
1.5
kg of carbon over 15 to 20 years. Accordingly, an artificial stone comprising
25
Date Regue/Date Received 2022-09-29
9
wt% olivine could be capable of adsorbing up to 37.5% of the stone's weight in
carbon, if the entire content of olivine undergoes the carbonation reaction.
Manufacturing
The method of manufacturing an artificial stone includes mixing between 25 wt%
and 40 wt% binder, between 20% to 35% filler, between 1.5 wt% to 2 wt%
polycarboxylate-based admixture and a remainder of diluent to form a
homologous uncured mixture. The filler can comprise any suitable type of
filler,
with between 1% and 100% being a filler that includes a component capable of
mineral carbonation. The uncured mixture is poured into a mold, such as a
silicon
mold, that has been sprayed or otherwise treated to receive the uncured
mixture.
The uncured mixture is then allowed to dry (cure) before being removed from
the
mold. The mold can be any desired shape, including in brick form, corner
pieces,
cornices, statues, etc. In some embodiments, the forms are about 1 cm to about
4 cm thick.
In some embodiments, the artificial stone can be formed in multiple layers
having
different compositions. For example, the artificial stone can include an outer
layer
and an inner layer each formed from an uncured mixture comprising between 20
wt% and 40 wt% binder, between 20% to 35% filler, between 1.5 wt% to 2 wt%
polycarboxylate-based admixture and a remainder of diluent. However, the
filler
used in the outer layer (Le., the layer that is configured to be exposed to
the
atmosphere/environment) can include a higher percentage of a component
capable of mineral carbonation than the inner layer.
In some embodiments, the outer layer is about 1 cm thick, which provides a
layer
with a high surface area to volume ratio to allow a faster reaction time of
the filler
capable of mineral carbonation with atmospheric CO2. In such embodiments, the
artificial stone is produced by providing the uncured mixture of the outer
layer,
which comprises a higher concentration of filler capable of mineral
carbonation,
in a mold. The uncured mixture of the inner layer, which may or may not
include
a filler capable of mineral carbonation, is also provided in the mold. The
inner and
outer layers are then allowed to dry (cure) before being removed from the
mold.
In some embodiments, the outer layer is provided in the mold before the inner
layer. Alternatively, in some embodiments, the inner layer is provided in the
mold
before the outer layer. A small amount of mixing can occur between the inner
and
outer layer, or in some embodiments, between all the layers, such that the
artificial stone appears as a homologous product despite the difference
between
the type of filler used in the different layers.
Date Regue/Date Received 2022-09-29
10
To facilitate a specific aesthetic, a pigment can be added to the mixture
prior to
being poured into the mold. The pigment can be any suitable pigment, such as
concrete pigments. In some embodiments, the pigment is derived from natural
stones to provide a natural color. In some embodiments, the surface of the
artificial stone can undergo a finishing step to provide a suitable façade for
the
stone's purpose. For example, the finishing step can include polishing, adding
texture, etc. In some embodiments, the method can include a step of
restoration
after the cured artificial stone is removed from the mold and/or before a
surface
finishing step.
In some embodiments, an air entraining admixture can be added to the diluent,
filler, polycarboxylate-based admixture, or the uncured mixture prior to being
poured into the mold. Air entraining admixtures produce interconnected air
void
structures with varying internal size, although they are often less than 1 mm
in
diameter. Including an entrained air admixture in the uncured mixture can
increase the carbon adsorption rate of the artificial stone by increasing the
surface of contact between the adsorbent (Le., the filler capable of mineral
carbonation, and to a certain extent, the binder) and the absorbate
(atmospheric
CO2). The adsorption rate of atmospheric CO2 can also be referred to as the
carbon sequestration rate.
The amount of air entrainer admixture included in the uncured mixture can be
between about 0.5 wt% and about 2 wt% of the binder, which can entrain
between about 1.5% and 6% air in the artificial stone. In some embodiments,
the
air entrainer admixture can be included in the uncured mixture at a rate of
about
16 mL to 195 m L per 100 kg of binder to entrain between 4% and 6% air. In
some embodiments, the air entrainer is Sika0 AIR. Consideration for the
specific
use for the manufactured artificial stone should be given when determining the
amount of air entrainer admixture to include in the uncured mixture. For
example,
for a non-structural/non-weight bearing purpose, such as cladding, the overall
amount of air entrainer admixture can be increased to increase the amount of
entrained air, thus increasing the overall available surface area for the
carbon
adsorption reaction to take place. For structural/weight bearing purposes,
such
as floor tile, less entrained air may be desirable to retain a higher overall
strength
of the artificial stone.
Experimental Data
The carbon adsorption capacity of an artificial stone product was conducted in
a
carbonation chamber using a sensitive digital balance scale to determine the
weight difference over a period of time. The samples were enclosed in a
carbonation chamber box made of plexiglass that measured 30 cm by 50 cm by
Date Regue/Date Received 2022-09-29
11
50 cm. The carbonation chamber included an emergency outlet, an inlet coupled
to a CO2 tank, and a pressure gauge. The pressure in the carbonation chamber
was between 10 bar and 50 bar to mimic the artificial stone being exposure to
atmospheric CO2 over several years. The carbonation chamber was placed on a
sensitive digital balance and the artificial stones were weighed before being
exposed to CO2, and after being in the carbonation chamber for 1 week, 1
month,
and 3 months. The increase in weight over time can be attributed to the weight
of
the carbon adsorbed or sequestered in the artificial stone product.
Table 1
Percentage of Weight
Size (Lx Starting Increase (%)
Surface Area
No. H x W in Weight
2
(cm )
cm) (kg) After 1 After 1
After 3
week month month
1 20 x 3 x 10 1.28 580 0.01 0.02 0.04
2 30 x 3 x 20 4.5 1,500 0.01 0.025 0.05
3 20 x 3 x 10 1.28 580 0.02 0.035 1
4 30 x 3 x 20 4.5 1,500 0.02 0.04 1.2
5 20 x 3 x 10 0.77 580 0.02 0.03 1
6 30 x 3 x 20 2.7 1,500 0.02 0.03 1.2
Powder
7 1.28 -- 0.03 0.08 1.8
(<50 pm)
Powder
8 4.5 -- 0.03 0.085 2.1
(<50 pm)
Table 2 -Carbon Adsorption
Est. Weight of Carbon Adsorption
No Sequestered Carbon Volume (kg/m3)
.
After 3 Months (g) (cm3)
1 0.512 600 0.85
2 2.25 1,800 1.25
3 12.8 600 20.83
Date Recue/Date Received 2022-09-29
12
4 54 1,800 30
7.7 600 12.83
6 32.4 1,800 18
7 23.04 --
8 94.5 --
Stones 1 and 2 were used as a control and comprised a cured product formed
from an uncured mixture of cement, crushed stone, sand, water, and a
polycarboxylate-based admixture. The cement component included about 0.5
5 .. wt% air entrainer admixture to produce about 1% entrained air. The
entrained air
increases the porosity in the artificial stone by creating internal voids and
increasing the interconnected pores in the artificial stone.
Stones 3 and 4 comprised a 2 cm thick inner layer and a 1 cm thick outer
layer.
The inner layer and the outer layer comprised a cured product formed from an
uncured mixture of cement, 25 wt% filler, water, and polycarboxylate-based
admixture. The cement component of both layers included about 0.5% air
entrainer admixture to produce about 1% entrained air. The 25 wt% filler in
the
outer layer was comprised entirely of olivine sourced from recycled olivine
extracted from nickel mines. Due to the high density of olivine, the outer
layer
weighs about 25% of the total weight of the artificial stone. The 25 wt%
filler in
the inner layer was crushed stone and sand.
Stones 5 and 6 also comprised a 2 cm thick inner layer and a 1 cm thick outer
layer. The inner layer and the outer layer comprised a cured product formed
from
an uncured mixture of cement, 25 wt% filler, water, and polycarboxylate-based
admixture. The 25 wt% filler in the outer layer was comprised entirely of
olivine
recycled from nickel mines. The 25 wt% filler in the inner layer was crushed
stone
and pumice aggregate, which is a volcanic ash constituent. An air entrainer
admixture was not used for Stones 5 and 6, as the pumice aggregate contains
air
porosity (small voids filled with air) that acts to entrains air in the
artificial stone
.. without the addition use of an air entrainer admixture. While the outer
layer
containing olivine of Stones 5 and 6 did not contain pumice aggregate as a
filler
component, use of pumice aggregate in the outer layer in addition to olivine
or
another compound capable of mineral carbonation can increase the porosity of
the artificial stone, which can increase the overall rate of carbon
adsorption. In
some embodiments, use of pumice aggregate in both the inner and outer layers
can also increase the homogeny between the two layers.
Date Regue/Date Received 2022-09-29
13
Stones 3 and 4 and Stones 5 and 6 each have the same composition but vary in
their size. Stones 3 and 5 are smaller artificial stones, having a size of 20
cm x 3
cm x 10 cm, and Stones 4 and 6 are larger artificial stones, having a size of
30
cm x 3 cm x 20 cm.
Compounds 7 and 8 were powders comprising a pulverized or crushed mixture of
an artificial stone having the same composition as Stones 3 and 4 (Le.,
olivine,
cement, crushed stone, sand, water, and a polycarboxylate-based admixture).
Compounds 7 and 8 were tested to determine the impact of increasing the
surface of contact (Le., the overall surface area).
As shown in Tables 1 and 2, after 3 months control Stones 1 and 2 showed a
0.04% and 0.05% weight increase, respectively, equating to adsorbing 0.85 and
1.25 kg/m3 of carbon, respectively. The carbon adsorption of Stones 1 and 2,
which do not contain olivine, show a baseline of carbon adsorption by the
cement
component, which includes active carbonization elements that can also react
naturally with the atmospheric CO2, albeit at a significantly lower rate.
On the other hand, the artificial stones that included an outer layer with 25
wt%
olivine (Stones 3 to 6) showed a 1% to 1.2% weight increase, which equated to
adsorbing between 12.83 and 30 kg/m3 of carbon. As can be seen, Stones 3 and
4 adsorbed more carbon than their respectively sized counterparts that used
pumice aggregate instead of sand in the inner layer (Stones 5 and 6). Also
shown is that the small artificial stones (Stones 3 and 5) adsorbed less
carbon
than the large artificial stones having the same composition (Stones 4 and 6,
respectively).
After 3 months, Compounds 7 and 8 showed a higher total amount of adsorbed
carbon, which was almost double that of Stones 3 and 4, which comprised the
same compounds in the same weight. Accordingly, this significant increase in
adsorption rate can likely be attributed to the increase in surface area.
Thus, it is
contemplated that the total carbon adsorption capacity of the artificial
stones (in
this case, Stones 3 to 6), for example over 15 to 20 years, will be higher
than the
adsorption observed after 3 months at 10 to 50 bar.
The larger artificial stones (Stones 2, 4, and 6) have a slightly lower
surface area
to volume ratio than the smaller artificial stones (Stones 1, 3, and 5).
Having a
high surface area to volume ratio allow materials, such as atmospheric CO2, to
diffuse into the pores of the material (Le., react with the component capable
of
carbon adsorption in the middle of the artificial stone). Accordingly, it
would be
expected that the smaller artificial stones would have a higher carbon
adsorption
rate; however, the opposite was observed. As noted above, Stones 1, 3, and 5
Date Recue/Date Received 2022-09-29
14
have the same composition as Stones 2, 4, and 6, respectively, and differ only
in
their size. In each case, the carbon adsorption of Stones 2, 4, and 6 were
significantly higher than the carbon adsorption rate of Stones 1, 3, and 5,
respectively. This significant increase in carbon adsorption for artificial
stones
having a lower surface area to volume ratio could be attributed to the
increased
amount of cement and/or different air entrainer ratios causing higher overall
surface area when the surface area of the internal pores created by entrained
air
are accounted for.
Date Recue/Date Received 2022-09-29
