rexresearch.com



David STONE, et al.
Ferrock




https://www.geek.com/news/ferrock-a-carbon-dioxide-sponge-thats-harder-than-concrete-1609410/

Ferrock: a carbon dioxide sponge that’s harder than concrete
By Graham Templeton



https://www.youtube.com/watch?v=Di4b-7_Vp8c
Tech Launch Arizona-Ferrock



https://www.youtube.com/watch?v=wOE4UegzJ_M
https://www.theb1m.com/video/how-to-cure-our-concrete-dependency

How to Cure our Concrete Dependency

...REPLACING CEMENT

While cement has long been the go-to binding agent for concrete, a failed experiment at the University of Arizona unintentionally created a material five times stronger than concrete, with a recycled content of 95%.

Ferrock – or iron-rich ferrous rock – is made primarily from steel dust, a waste product from various industrial processes, and silica made from ground-up recycled glass.

Above: Ferrock is made up of 95% recycled material, primarily steel dust and crushed glass and is up to five times stronger than concrete ( image courtesy of Guy Shovlin).

When mixed together, the iron in the steel dust reacts with CO2 and rusts to form iron-carbonate fusing the components together. Like concrete, Ferrock cannot return to its liquid state once hardened.

However, unlike the manufacturing of cement which creates large amounts of carbon dioxide, the hardening process of Ferrock actually absorbs and traps CO2, creating a carbon-negative product.

While advantageous as a concept, the large-scale implementation of Ferrock does have limitations.

While the materials used to create Ferrock are currently cheaper than cement, the price of large-scale adoption could become uneconomical if demand for steel dust and recycled glass creates a lucrative new resource market for waste products...



http://www.hrltech.com/2014/12/02/an-in-depth-look-at-ferrock-and-how-it-compares-to-concrete/

An In-Depth Look At Ferrock And How It Compares To Concrete



Concrete is one of the most common construction materials in the U.S., with over 68 million metric tons of the material produced in 2004. It's considered the standard building material for a wide range of construction projects, from ordinary residential homes to towering skyscrapers and massive hydroelectric dams.

Recently, a University of Arizona student created an eco-friendly alternative that offers its own set of useful benefits. The following takes a look at how this new material, known as Ferrock, stacks up to traditional concrete.

What Makes Ferrock so Special?

Ferrock's origins lie with University of Arizona Ph.D. student David Stone, who set out to develop a carbon-neutral material that could be used in the same manner as cement. Stone's findings came about after years of studying Portland cement's unique properties.

As the name implies, the basic building blocks of Ferrock come from iron discards in the form of waste steel dust. A common byproduct of numerous industrial processes, the iron in waste steel dust reacts with carbon dioxide (CO2) to form iron carbonate. The iron carbonate becomes part of the material's mineral matrix, adding to its overall strength.

Ferrock's greatest strength lies with its eco-friendly properties. Although Ferrock releases CO2 during production, it also absorbs large amounts of CO2 as it hardens. This makes Ferrock an effective carbon sink that permanently locks in those potentially harmful greenhouse gases. This unique trait may prove appealing to those who wish to lower their carbon footprint through the use of ecologically sustainable materials.

In addition to being eco-friendly, it also possesses incredible durability thanks to a unique property. When it hardens, it does so in a way that mimics solid rock. This allows Ferrock to resist certain forces differently from concrete, giving it excellent overall durability and stability. Because of iron carbonate's hardening properties, Ferrock can also be used in underwater applications in saltwater environments

Downsides to Ferrock

As a relatively new material that hasn't seen much use in the industrial arena, Ferrock's overall capabilities remain largely unproven. It's also unknown how Ferrock behaves under a wide range of building conditions or whether traditional concrete techniques can be used on the new material. On the other hand, concrete is a tried-and-tested quantity for the vast majority of builders and developers.

Cost is also another factor that puts concrete ahead in most construction projects. Given Ferrock's unique production process, it's likely that its overall cost will be significantly more than that of Portland cement. There's also concern that steel producers may catch on to waste steel dust's newfound uses and charge for it accordingly. The economics of Ferrock must not only account for this potential development, but also for other changes in production and marketing methods.

Will It Replace Concrete Anytime Soon?

The chances of Ferrock completely replacing concrete are pretty slim. After all, concrete has a lot going for itself – not only is it relatively cheap to purchase, but it's also easy to produce and it can be used to build a wide variety of structures. Its sheer versatility is what makes it attractive in so many ways.

Concrete can also prove effective when it comes to neutralizing CO2 emissions. For instance, magnesium silicate-based cement can also absorb large amounts of CO2 as it hardens. The abundance of magnesium silicates also makes it a lower-cost alternative to Ferrock.

But one shouldn't discount the usefulness of Ferrock as an eco-conscious alternative. When used in conjunction with other eco-friendly materials and building strategies, it becomes possible for entire countries to lower their overall greenhouse gas output and create more sustainable environmental conditions for future generations to enjoy.


 
https://buildabroad.org/2016/09/27/ferrock/

Ferrock: A Stronger, More Flexible and Greener Alternative to Concrete?



BINDER COMPOSITIONS AND METHOD OF SYNTHESIS
US2016264466
[ PDF ]

Some embodiments of the invention include cementitious iron carbonate binder precursor compositions that includes powdered iron or steel, a first powdered additive including silica, a second powdered additive including calcium carbonate, at least one powdered clay, and a fibrous and/or woven additive. In some embodiments of the invention, the precursor composition includes an alumina additive. In some further embodiments, the powdered clay includes kaolinite clay and/or metakaolin clay. In some further embodiments, the precursor composition includes an organic reducing agent such as oxalic acid. Some embodiments include up to about 60% by weight of powdered iron or steel, up to about 20% by weight of the first powdered additive, up to about 8% by weight of the second powdered additive, up to about 10% by weight of at least one powdered clay, and up to about 2% by weight of an organic acid.

BACKGROUND

[0003] Ordinary Portland Cement (OPC)-based materials (in particular, conventional cement concretes) are among the most common and cheapest ceramic matrices that are widely used for buildings and infrastructural applications. It is well recognized that OPC production is a significant emitter of CO2, a major greenhouse gas, which is responsible for the global warming. The global concrete industry has embraced the idea of sustainability in construction through the use of waste/recycled materials as supplementary cementitious materials. For example, the use of materials such as fly ash, blast furnace slag, and limestone powder in concrete have reduced the scale of OPC production. Several non-conventional means of developing novel and sustainable matrix materials for infrastructural composites are also on-going.

[0004] Some binder systems can provide multiple environmental benefits through trapping of CO2 emitted from industrial operations. For example, the utilization of a waste material (iron powder) that is otherwise land-filled, can also be used to reduce OPC production/use. The anoxic carbonation of (waste) metallic iron powder at ambient temperature and pressure has been shown to yield beneficial mechanical properties when use as a structural binder (see for example Das S, Souliman B, Stone D, Neithalath N. Synthesis and Properties of a Novel Structural Binder Utilizing the Chemistry of Iron Carbonation. ACS Appl. Mater. Interfaces 2014; 6(11):8295-304, and co-pending U.S. Patent Application No. 62/051,122 filed Sep. 16, 2014).

[0005] One of the major drawbacks of ceramic matrices in general and cementitious matrices in particular relate to their low toughness. In addition, these low-toughness ceramics lose a significant portion of their strength because of service-related damage such as crack growth under static load or cyclic fatigue. Thus, enhancing the toughness of these materials contributes to minimization and control of strength loss. In the synthesis of the iron-based binder, metallic iron powder is carbonated only to a small fraction (necessitated by limitations in reaction kinetics), which results in the presence of large amounts of residual metallic powder in the microstructure. The presence of this phase, a significant fraction of which is elongated, will likely render notable increase in the toughness of this binder because of the energy dissipation by plastic deformation imparted by the metallic particulate phase. In addition, the matrix contains other processing additives including harder fly ash particles, softer limestone particles, and ductile clayey phases which influence the overall fracture performance of the novel binder significantly.

[0006] Further opportunities exist to address the toughness performance of this novel binder system using additive reinforcement for applications such as building envelope components (e.g., exterior wall panels), precast elements, architectural claddings, as well as in electrically conductive ceramic composite applications.

SUMMARY OF THE INVENTION

[0007] Some embodiments of the invention include a cementitious iron carbonate binder precursor composition comprising powdered iron or steel, a first powdered additive comprising silica, a second powdered additive comprising calcium carbonate, at least one powdered clay, and a fibrous and/or woven additive.

[0008] In some embodiments of the invention, the precursor composition comprises an alumina additive. In some further embodiments, the at least one powdered clay includes kaolinite clay and/or metakaolin clay. In some further embodiments, the precursor composition comprises at least one organic reducing agent. Some embodiments include an organic reducing agent that comprises oxalic acid.

[0009] In some embodiments of the invention, the fibrous or woven additive includes at least one of carbon fiber, cellulosic fiber, and metal fiber. In some further embodiments, the at least one fibrous of woven additive comprises glass fiber. In some embodiments, the glass fiber comprises alkali-resistant (“AR-glass”). In other embodiments, at least a portion of the glass fiber is in the form of glass mat, cloth, fabric, mesh, woven roving, an interwoven material, or combinations thereof.

[0010] In some embodiments of the invention, the first powdered additive comprises or is derived from limestone. In some further embodiments, the second powdered additive comprises or is derived from fly ash. In some embodiments of the invention, the powdered iron or steel originates or is derived from a by-product of one or more industrial processes. In some further embodiments, the limestone has a median particle size of about 0.7 µm conforming to ASTM C 568. In some other embodiments, the limestone has a particle size between 0.7 µm and 20 µm.

[0011] In some embodiments of the invention, the fibrous or woven additive comprises polymer fiber. In some embodiments, the polymer fiber comprises polypropylene, polyaramid, polycarbonate, polyvinyl alcohol, and/or nylon.

[0012] Some embodiments of the invention include a cementitious iron carbonate binder precursor composition comprising up to about 60% by weight of powdered iron or steel, up to about 20% by weight of a first powdered additive comprising silica, up to about 8% by weight of a second powdered additive comprising calcium carbonate, up to about 10% by weight of at least one powdered clay, and a fibrous and/or a woven additive.

[0013] In some embodiments, the first powered additive consists of fly ash, the second powdered additive consists of limestone, the at least one powdered clay consists of 10% metakaolin. Some embodiments also include at least one organic acid present as up to about 2% by weight of the precursor composition. In some further embodiments, the at least one fibrous or woven additive comprises a glass fiber.

DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 illustrates particle size distributions of metallic iron powder, OPC, Fly ash, metakaolin, and limestone powder in accordance with some embodiments of the invention.



[0015] FIGS. 2A-2C illustrate micrographs showing the microstructure of iron-based binders in accordance with some embodiments of the invention.

[0016] FIG. 3 illustrates the flexural strengths of plain and fiber-reinforced iron carbonate binders after 6 days of carbonation and the corresponding OPC pastes after 28-days of hydration for comparison in accordance with some embodiments of the invention.

[0017] FIGS. 4A-4C show representative load-CMOD responses for iron carbonate binder compared with OPC systems in accordance with some embodiments of the invention.

[0018] FIG. 5A shows a plot of peak load for OPC and iron carbonate binders as a function of fiber volume fraction in accordance with some embodiments of the invention.

[0019] FIG. 5B shows a residual load of OPC and iron carbonate binders as a function of fiber volume fraction in accordance with some embodiments of the invention.

[0020] FIG. 6A shows a plot of fracture toughness for iron carbonate and OPC-based binders in accordance with some embodiments of the invention.

[0021] FIG. 6B shows a plot of critical crack tip opening displacements of iron carbonate and OPC-based binders in accordance with some embodiments of the invention.

[0022] FIG. 7A shows a plot of fracture toughness-critical crack tip opening displacement relationship with change in fiber dosage for iron carbonate binder and OPC in accordance with some embodiments of the invention.

[0023] FIG. 7B illustrates a plot of variation in critical crack length with change in fiber dosage for iron carbonate binder and OPC in accordance with some embodiments of the invention.

[0024] FIG. 8 illustrates resistance curves for the unreinforced and fiber reinforced iron-based and OPC binder systems in accordance with some embodiments of the invention.

[0025] FIG. 9A illustrates elastic and inelastic components of crack growth resistance with varying crack extension for iron carbonate binder for different fiber dosage in accordance with some embodiments of the invention.

[0026] FIG. 9B illustrates elastic and inelastic components of crack growth resistance with varying crack extension for OPC paste for different fiber dosage in accordance with some embodiments of the invention.

[0027] FIG. 10A shows a load-CMOD response for iron carbonate binder with 1% fiber volume fraction in accordance with some embodiments of the invention.

[0028] FIG. 10B shows a horizontal (u) displacement field represented as a 3D surface plot for iron carbonate binder with 1% fiber in accordance with some embodiments of the invention.

[0029] FIGS. 11A-11F show horizontal displacement fields and the 3D surface plots for unreinforced and reinforced (1% fiber volume fraction) iron-based binders in accordance with some embodiments of the invention.

DETAILED DESCRIPTION

[0030] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

[0031] The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention.

[0032] Some embodiments of the invention include various compositions and synthesis methods of structural binders utilizing the chemistry of iron carbonation. In some embodiments, a structural binder can be formed by reaction of iron with carbon dioxide. Some embodiments include at least one fibrous and/or woven additive. For example, some embodiments include the addition of glass fiber to the iron-based binder systems. In some embodiments, glass fiber can be added to increase the toughness of the iron-based binder systems significantly over similarly reinforced OPC systems. In some embodiments, the glass fiber can be alkali-resistant glass (“AR-glass”) that is typically used in concrete applications. In some further embodiments, any conventional glass fiber compositions can be used. Further, some embodiments can include mixtures of various types of glass fibers. Further, some embodiments can include glass fibers, whiskers, and/or wires in the form of glass mat, cloth, fabric, mesh, woven roving, and/or any sheet of interwoven glass or other fibers with various size openings.

[0033] In some embodiments, the fibers can be any length from about 3 mm to about 24 mm. Some other embodiments can utilize fibers that are less than about 3 mm and/or greater than about 24 mm. In some embodiments, the volume fraction of glass fibers can be from 0.02% to 2% depending on the application. Further, in some embodiments, the specific gravity can be about 2.6, and in some embodiments, the moisture content can be less than about 0.5%. In some embodiments of the invention, the tensile strength can be about 1000 to about 1700 MPa. Some embodiments of the invention include glass fiber with a modulus of elasticity of about 72 GPa. In some embodiments, the glass fiber can comprise glass fibers manufactured by Corning Incorporated.

[0034] In some further embodiments, other types of fibers can be used including inorganic oxide fibers, metal fibers, polymer fibers (e.g., polypropylene), carbon fiber, or mixtures thereof. For example, other fibers that have been traditionally used in conventional concrete can be used including steel, carbon, aramid, polypropylene, polycarbonate, polyvinyl alcohol (“PVA”), nylon, asbestos, and natural plant-based fibers (e.g., plant derived materials comprising cellulose). In some embodiments, the reinforcing fibers including nylon, polypropylene, AR glass, steel, macro, high-dosage synthetic fibers, PVA, and steel/synthetic blends available from Nycon at http://nycon.com/ can be used. Further, in some embodiments, woven steel wire cloth of the type commonly used to make “ferrocement” structures for water tanks, boat hulls, and thin shell structures can be used.

[0035] In some embodiments, the carbon dioxide can be waste carbon dioxide obtained from one or more industrial processes. Some embodiments include methods to form a sustainable binder system for concretes through carbonation of iron dust. For example, in some embodiments, iron can react with aqueous CO2 under controlled conditions to form complex iron carbonates which have binding capabilities. Further, some embodiments can include additives comprising silica and alumina. In some embodiments, silica and/or alumina additives can facilitate iron dissolution, which in some embodiments can provide beneficial rheological characteristics and properties. In some embodiments, the binder system can rely on the effects of corrosion of iron particles to form a binding matrix. In this instance, binder formation can result in the consumption and trapping of CO2 from an industrial operation and subsequent carbonate formation by conversion of at least a portion of the iron particles. Further, the binder formation can provide a means to reduce the overall ordinary Portland cement production (which is itself a significant emitter of CO2) through the use of carbonated metallic iron powder as the binder material for concrete.

[0036] In some embodiments, dissolution agents (such as organic acids) can be added to enhance the corrosion rate of iron. Further, in some embodiments, the rheological behavior (flowability and castability) and early strength development can be improved using one or more additives. For example, additives common to Portland cement concretes such as class F fly ash, powdered limestone, and metakaolin can be used as minor ingredients along with metallic iron powder to form pastes with adequate binding capabilities. The fly ash can be added as a source of silica to potentially facilitate iron silicate complexation. Further, in some embodiments, limestone powder can be added to provide additional nucleation sites. Some embodiments include one or more “powdered” clays having a layered structure which retains water and which can be used to improve the rheological properties. For example, in some embodiments, a clay source such as kaolinite and/or metakaolin can be used to provide consistency cohesiveness as the iron-based mixtures are prepared. This added clay source can also minimize the required water content.

[0037] Some embodiments provide compositions comprising fly ash, limestone, and a clay source such as metakaolin and/or kaolinite in various proportions. In some embodiments, the limestone powder can comprise a median particle size of about 0.7 µm conforming to ASTM C 568. In some embodiments, limestone can be added with a particle size that can range from a median size of about 0.7 µm to about 20 µm. In some embodiments, the fineness determines its nucleation ability. For example, in some embodiments, added limestone powder can provide nucleation sites for one or more cure reactions within the binder composition. In some embodiments, added water can be reduced in chemical reactions within any of the disclosed binder compositions (however it does not form part of the binder). In some embodiments, to minimize water demand, while maintaining binder consistency and cohesiveness, added metakaolin can be added to the binder composition. In some embodiments, the composition can comprise metakaolin conforming to ASTM C 618.

[0038] Some embodiments of the invention include compositions comprising metallic iron powder. In some further embodiments, an organic reducing agent/chelating agent of metal cations can be included in the binder composition. In some embodiments, the organic reducing agent comprises an acid. In some embodiments, the organic reducing agent comprises oxalic acid. In some embodiments, an organic reducing agent can be added in a powder form to about 2% of total weight of the constituents. In some other embodiments, the organic reducing agent can be added based on the solubility of the organic acid in water, and the compressive strength as compared to mixtures without dissociating agent.

[0039] In some embodiments, the proportions of iron powder and other additives (including for example organic acids as dissolution agents) can influence the curing regime (based at least in part on the exposure of the mixture to CO2 and/or air). In some embodiments, the iron powder comprises about 88% iron and about 10% oxygen, along with trace quantities of copper, manganese, and calcium. In some embodiments, metallic iron powder sizes can range from about 5 µm to about 50 µm. For example, some embodiments comprise iron powder with a median particle size of about 19.03 µm. Further, in some embodiments, the selection of size ranges can facilitate reactivity. In some embodiments, the iron particles are elongated and angular in shape. In some embodiments, while influencing the rheological properties of the fresh mixture, the angular shape also provides benefits related to increased reactivity owing to the higher surface-to-volume ratio of the particles. In some embodiments, the iron powder can be obtained as a by-product of another industry process. For example, in some embodiments, the iron powder can be obtained from a shot-blasting facility.

[0040] Commercially available Type I/II OPC conforming to ASTM C 150 was used to prepare conventional cement pastes that were used as the baseline system to compare the properties of the novel iron-based binder systems. The chemical compositions of OPC, fly ash and metakaolin can be found in Vance K, Aguayo M, Oey T, Sant G, Neithalath N. Hydration and strength development in ternary Portland cement blends containing limestone and fly ash or metakaolin. Cem. Concr. Compos., 2013; 39:93-103, and Das S, Aguayo M, Dey V, Kachala R, Mobasher B, Sant G, et al. The fracture response of blended formulations containing limestone powder: Evaluations using two-parameter fracture model and digital image correlation. Cem. Concr, Compos., 2014; 53:316-26, the entire contents of which are incorporated by reference in their entirety. There is no restriction on the type and/or source of OPC, fly ash, or metakaolin, and any available conventional material can be used.

[0041] The particle size distributions (determined using dynamic light scattering) are shown in the plot 100 of FIG. 1 for iron powder (data line 110), fly ash (data line 115), metakaolin (data line 120), limestone (data line 125) and OPC (data line 130). The iron powder is coarser than all other ingredients used here. In some embodiments, the powder fraction of the iron-based binder mixture consists of 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin, and 2% organic acid by weight. This combination demonstrated the highest compressive strength and lowest porosity among a series of trial mixtures prepared as part of material design studies. These materials studies can be found in detail in Das S, Souliman B, Stone D, Neithalath N. Synthesis and Properties of a Novel Structural Binder Utilizing the Chemistry of Iron Carbonation. ACS Appl. Mater. Interfaces, 2014; 6(11):8295-304, the entire contents of which are incorporated by reference in their entirety.

[0042] In some embodiments, binder preparation includes a mixing procedure that involves initial dry mixing of all the starting materials, followed by the addition of water to obtain a substantially uniform cohesive mixture. Some embodiments of the invention can include a weight-based water-to-solids ratio (w/s) of 0.24 to attain a cohesive mix. In other embodiments, at least one of the powders forming the binder can be pre-mixed with water, and subsequently mixed with the remaining powders, or other pre-mixed water-powder mixtures.

[0043] Some embodiments include glass fiber reinforcement of the iron-based binder systems. In some embodiments, glass fiber can be added to improve the mechanical properties of the iron-based binder systems. For example, in some embodiments, fiber-reinforced binders can be prepared by adding about 0.5% and about 1.0% glass fibers by volume to the blends while mixing. In some embodiments, the glass fibers can be about 25 µm diameter and about 10 mm long). In some embodiments, the fiber reinforced iron-based and the OPC binders can be cured in the same way as their non-reinforced counterparts.

[0044] Table 1 provides a comparison of iron-based binder compositions of the invention with OPC compositions including compositions with and without fiber additions prepared as described above.

TABLE 1
Iron-based binder and OPC compositions
  Iron Carbonate  OPC
  Fiber vol. fraction (%)
  0  0.5  1  0  0.5  1

Weight  Iron powder  60  59.53  59.07  NA  NA  NA
(%)  Fly ash  20  19.84  19.69  NA  NA  NA
  limestone  8  7.94  7.88  NA  NA  NA
  metakaolin  10  9.92  9.84  NA  NA  NA
  Oxalic acid  2  1.98  1.97  NA  NA  NA
  OPC  NA  NA  NA  100  99.01  98.03
  Glass fiber  0  0.78  1.55  0  0.99  1.97
  Water-to-powder  0.24  0.24  0.24  0.4  0.4  0.4
  ratio

[0045] Prismatic specimens measuring about 127 mm (length), about 25.4 mm deep, and about 25.4 mm (width) were prepared in polypropylene molds and immediately placed inside clear plastic bags filled with 100% CO2 in room temperature inside a fume hood. The samples were de-molded after 1 day of carbonation in order to attain enough strength to strip the molds without specimen breakage. After de-molding, the beams were again placed in a 100% CO2 environment for another 5 days. The bags were refilled with CO2 every 12 hours or so to maintain saturation. After the respective durations of CO2 exposure, the samples were placed in air at room temperature to allow the moisture to evaporate for 4 days. These CO2 and moisture exposure durations were considered because the mechanical properties demonstrated insignificant changes beyond these curing times. For the specimen sizes evaluated here, it can be safely assumed that these durations result in kinetic carbonation limits, and further carbonation generally cannot be achieved without changes in process conditions (e.g., temperature or pressure). Companion OPC mixtures of the same size as mentioned above were prepared with a water-to-cement ratio (w/cm) of 0.40, which is common for moderate-strength concretes in many buildings and infrastructural applications. The OPC beams were de-molded after 1 day and were kept in a moist chamber (>98% RH and 23±2° C.) for a total of 28 days.

[0046] The flexural strengths of both iron-based and OPC binders were determined using standard center-point loading as per ASTM C293/293M-10, on beams having a span of 101.6 mm. The fracture properties, viz., the critical stress intensity factor (KIC<S>) and the critical crack tip opening displacement (hereinafter “CTODC”), were determined from three-point bend tests on notched beams using the two-parameter fracture model (herein after “TPFM”), described in Jenq Y, Shah S P. Two parameter fracture model for concrete. J Eng. Mech. 1985; 111(10):1227-41, and Shah S P. Fracture mechanics of concrete: applications of fracture mechanics to concrete, rock and other quasi-brittle materials. John Wiley & Sons; 1995. For each mixture, four replicate beams were tested. The notch depth was 3.8 mm (corresponding to a notch depth-to-beam depth ratio of 0.15). The beams were tested in a crack mouth opening displacement (hereinafter “CMOD”)-controlled mode (CMOD acting as the feedback signal) during the loading cycles and in a load-controlled mode during the unloading cycles.

[0047] Microstructural analysis was performed on small rectangular pieces (10×10 mm in size). The samples were from the interior portions of the beams. Prior to mounting, the sample was ultrasonically cleaned and rinsed with ethyl alcohol and dried with compressed air spray to remove debris from sectioning/handling. After drying, the sample was placed into a 32 mm two-part mounting cup, filled with a room-temperature setting epoxy, and subjected to 95 kPa of vacuum for 5 minutes to remove entrapped air. After hardening, the sample was polished using 600 grit and 800 grit Silicon Carbide (SiC) abrasive discs, and further ground using 3 µm and 1 µm diamond paste. Final polishing was accomplished with 0.04 µm colloidal silica suspension.

[0048] Digital Image Correlation (“DIC”) was used for the determination of fracture properties. DIC is a non-contact optical method to analyze digital images to extract the full displacement field on a specimen surface. The beam surface was painted with random black and white speckles to improve image correlation. A charge coupled device camera was used to record images every 5 seconds during a loading and unloading sequence, and image correlation performed to obtain the displacement fields on the specimen surface within a specific analysis region.

[0049] FIGS. 2A-2C illustrates micrographs showing the microstructure of iron-based binders. For example, FIG. 2A shows a lower magnification (150×) image 200 (scale bar corresponds to 100 µm), and FIG. 2B shows a higher magnification (1200×) image 225 showing an elongated iron particle and the surrounding regions (scale bar corresponds to 10 µm). Further, FIG. 2C shows a dissolution of Fe<+2 >from iron particle into the surrounding matrix (4300×) (image 250 where a scale bar corresponds to 1 µm). The images shown are for specimens cured for 6 days in a CO2 environment. FIG. 2A shows the general appearance of the material microstructure with bright (high density) iron particles along with the reaction products and pores. The unreacted iron particles are, in general, elongated. The dense reaction products (the grey phases in the microstructure) are formed from the carbonation of smaller iron particles and their complexation with the other minor ingredients in the mixture. This was confirmed from a thermal analysis study to be belonging to the carbonate-oxalate-cancrinite group, and described in Das S, Souliman B, Stone D, Neithalath N. Synthesis and Properties of a Novel Structural Binder Utilizing the Chemistry of Iron Carbonation. ACS. Appl. Mater. Interfaces 2014; 6(11):8295-304. A higher magnification image 225 is shown in FIG. 2B where an elongated iron particle 227 is at least partially surrounded by reaction product 227a, and the surrounding microstructure containing spherical fly ash particles is shown (annotated in the magnified image 250 of FIG. 2C as fly ash 275). The dark regions in this microstructure are the pores (annotated in FIG. 2C as pores 270), the volume fraction of which was found to be comparable to those of OPC-based systems as detailed in an extensive quantification work in the above described reference. FIG. 2C also shows the dissolution of iron into the matrix from the iron particle 260 and the formation of reaction products 265, where the iron carbonate binder (i.e., the reaction product 227a shown in FIG. 2B) can be seen at least partially surrounding the iron particle 260 as iron carbonate layer 265.

[0050] FIG. 3 illustrates a plot 300 showing the flexural strengths of plain (0% fiber) and fiber-reinforced (0.5% and 1%) iron carbonate binders after 6 days of carbonation and the corresponding OPC pastes after 28-days of hydration for comparison. The results presented here suggest that the iron carbonate binder (data bars 310) is about four-to-six times stronger than the traditional OPC paste in flexure (data bars 315). This can be attributed to a combination of the stronger carbonate matrix along with the presence of unreacted iron particles in the microstructure as shown in FIGS. 2A-2C. As illustrated, both binders are observed to exhibit increases in flexural strength with inclusion of fibers, with the iron-based system showing a much pronounced increase. While it has been proven that the addition of glass fiber in OPC systems results in an increase in toughness with only minor increase in flexural strength, the iron-based binder shows a different trend where the flexural strength is increased significantly with the incorporation of glass fibers into the matrix (e.g., see for example Sivakumar A, Santhanam M. Mechanical properties of high strength concrete reinforced with metallic and non-metallic fibers. Cem Concr Compos 2007; 29(8):603-8, and Altun F, Haktanir T, Ari K. Effects of steel fiber addition on mechanical properties of concrete and RC beams. Constr Build Mater 2007; 21(3):654-61, and Kwan W H, Ramli M, Cheah C B. Flexural strength and impact resistance study of fiber reinforced concrete in simulated aggressive environment. Constr Build Mater 2014; 63:62-71). An enhancement in flexural strength of about 50% is observed for the iron-based binder when 0.5% glass fibers by volume is incorporated, but further fiber addition does not appear to statistically enhance the material behavior, a behavior that is also observed for the Mode I fracture toughness of these binder systems.

[0051] The fracture parameters of the iron-based and OPC binder systems were studied using the TPFM. TPFM idealizes the pre-peak non-linear behavior in a notched specimen through an effective elastic crack approach. The beam sizes and the notch depth are same for both the systems, thereby rendering the comparisons of the fracture parameters free of size effects. The effect of fiber volume fractions on the fracture parameters were also evaluated in conjunction with the response of the matrix phase. In some further embodiments, the cyclic load-CMOD response of notched beams was analyzed. The representative load-CMOD responses are shown in FIGS. 4A-4C for the iron-based binder and the companion OPC-based binder with and without fiber reinforcement, and depict representative load-CMOD responses for iron carbonate binder and comparison with OPC paste. For example, FIG. 4A shows plot 400 with data for control materials. FIG. 4B shows plot 425 with data for 0.5% fiber volume for iron-carbonate based binder (data line 430) and OPC-based binder (data line 435). Further, FIG. 4C shows plot 450 with data for 1.0% fiber volume fraction, with iron-carbonate based binder (data line 455) and OPC-based binder (data line 460). Plot 400 of FIG. 4A shows the load-CMOD response for the control OPC (data line 415) and iron-based binder without fiber reinforcement (data line 410), and clearly illustrates the fundamental differences in the flexural response of these matrices. The significantly higher peak load and improved post peak response of the iron-based binder as compared to control OPC binder can be attributed to the presence of unreacted metallic iron particles (as described earlier and shown in FIGS. 2A-2C) which are inherently strong and ductile. In some embodiments, the iron-based binder contains higher amounts of larger pores (average size>0.2 µm) even though the total pore volumes are comparable. Consequently, some embodiments of the invention demonstrate compressive strength that is slightly lower than that of the OPC binder. However, the presence of strong and ductile phases in the microstructure dominates the flexural response, as shown earlier.

[0052] In some embodiments, the incorporation of fibers in an OPC matrix makes it ductile, as observed from the post-peak response and the larger CMODs for the fiber reinforced systems (as opposed to the unreinforced materials shown in FIGS. 4B and 4C). In some embodiments, both the peak load and the residual load are significantly higher for the iron carbonate binder, with and without fiber reinforcement (depicted in FIGS. 5A and 5B). For example, referring to FIG. 5A, iron-carbonate based binder (data line 510), and OPC-based binder (data line 515) is shown, and FIG. 5B, where iron-carbonate based binder (data line 530), and OPC-based binder (data line 535) is shown.

[0053] In some embodiments, the incorporation of glass fibers enhances the peak load of the iron-based binder much more than it does to the OPC binder, that can indicate the synergistic effect on flexural strength from the inclusion of the fiber in the iron carbonate matrix (including the unreacted iron particles). The residual load for the control binders was measured at a CMOD value of 0.12 mm, whereas a CMOD value of 0.25 mm was chosen for the binders with fiber reinforcement. In some embodiments, the residual loads provide an indication of the crack-tolerance and the post-peak response of these systems.

[0054] In some embodiments, an increase in fiber volume fraction is found to enhance the toughness of both the binder systems, and can be attributed to the crack-bridging effects of the fiber and the resultant increase in energy dissipation under load. For example, FIG. 6A shows a plot 600 of fracture toughness for iron carbonate-based binder (data bar 610), and OPC-based binders (data bar 615) in accordance with some embodiments of the invention, and FIG. 6B shows a plot 625 of critical crack tip opening displacements of iron carbonate-based binder (data bar 630) and OPC-based binders (data bar 635) in accordance with some embodiments of the invention. This data shows the two major fracture parameters of fracture toughness (“KIC<S>”) and CTODC derived using TPFM for both the binders, as a function of the fiber volume fraction. For example, FIG. 6A shows that the fracture toughness values of the iron-based binders are much higher than the control OPC binders (about 5-7 times higher) irrespective of the fiber volume fraction. In some embodiments, the KIC<S >values of the iron carbonate binder range from 30 MPa·mm<0.5 >to 50 MPa·mm<0.5>, which is approximately half of those of glass ceramics, polycrystalline cubic zirconia, SiN, alumina, and high-performance structural ceramics such as SiC, and about five times larger than the companion OPC binder. The ceramic systems mentioned earlier can be ten to thirty times more expensive than the iron-based binder.

[0055] In the unreinforced OPC matrix, the mechanism of strain energy dissipation can include crack extension. In some embodiments, the significantly higher KIC<S >of the iron-based binder, even for the unreinforced case, as compared to the OPC binder can be attributed to the crack bridging and/or deflection effects of the ductile, unreacted metallic iron particles in the matrix. As illustrated in FIGS. 2A-2C, many of the unreacted metallic iron particles are elongated. In some embodiments, these particles can function as a reinforcing phase that imposes a closing pressure on the crack. In some embodiments, this can bridge the cracks and the elastic incompatibility and de-bonding between the metallic particle-carbonate matrix interfaces can contribute to crack deflection.

[0056] In some embodiments of the invention, beyond a certain volume fraction of fibers, further toughness enhancement is negligible for the iron-based binders because the distribution of the unreacted iron particles and the fibers in the matrix is expected to be sufficient for crack bridging/deflection. The CTODC, which indicates the limit beyond which unstable crack propagation begins is shown in FIG. 6B as a function of the fiber volume fraction for both the binders. As shown, in some embodiments, a uniform increase in CTODC with fiber volume fraction can be observed for both the binders. Further, in some embodiments, the unstable crack propagation threshold limit (CTODC) for the unreinforced iron-based control binder is found to be about three times higher as compared to that of the corresponding OPC paste. The difference in CTODC between the two binder types reduces as fibers are incorporated. Further, in some embodiments, the KIC and CTODC values of the two binders indicate that the iron-based binder yields significantly improved crack resistance and ductility than the conventional OPC systems due to the presence of unreacted metallic iron powder surrounded by a carbonate matrix.

[0057] The KIC<S>-CTODC relationships of the two binders are compared in FIG. 7A, showing a plot 700 of fracture toughness-critical crack tip opening displacement relationship with change in fiber dosage for iron carbonate-based binder (data line 710) and OPC-based binder (data line 715) in accordance with some embodiments of the invention. In some embodiments, an increase in the fracture toughness is observed with an increase in the critical opening size of the crack. Further, while the increase in KIC<S >is proportional to an increase in CTODC for the OPC binders, in some embodiments, for the iron carbonate-based binder, the increase in KIC<S >is not prominent beyond a certain CTODc value (or fiber volume fraction since CTODC-fiber volume fraction relationships are linear for both the binder systems. This is illustrated in FIG. 7B, showing a plot 725 of variation in critical crack length with change in fiber dosage for iron carbonate-based binder (data line 730) and OPC-based binder (data line 735) in accordance with some embodiments of the invention. In some embodiments, the critical crack length increases with increase in fiber volume for both the binders. In unreinforced binders, the iron-based system has a higher critical crack length owing to the contribution from elongated, elastic iron particles. However, at a higher fiber volume fraction, the critical crack lengths for both the binders are comparable even though KIC<S >and CTODC are higher for the iron-based binder. This shows that in the iron-based systems, in some embodiments, beyond a certain fiber volume fraction, enhancement in fracture properties are negligible even though the performance is much better than the corresponding OPC systems.

[0058] In some embodiments of the invention, the existence of unreacted, elongated iron particles and added fibers can influence and modify the fracture response. This can be examined using resistance curves (“R-curves”), by making use of the multiple loading-unloading cycles in the load-CMOD plots. For example, FIG. 8 illustrates resistance curves (data lines 805, 810, 815, 820, 825, 830) for the unreinforced and fiber reinforced iron-based and OPC binder systems in accordance with some embodiments of the invention. FIG. 8 shows the R-curves for both the binder systems at all levels of fiber reinforcements. For example, data lines 805, 810, 815 show OPC-based binder data at 0%, 0.5%, and 1% volume fraction of fiber reinforcement, and data lines 820, 825, 830 show iron-carbonate-based binder data at 0%, 0.5%, and 1% volume fraction of fiber reinforcement. “R” is defined as the strain energy rate required for crack propagation and it is an increasing and convex function for quasi-brittle materials. The contributions from both the elastic and inelastic strain energies are considered in the development of the R-curve. The elastic component can be calculated from the unloading compliances whereas the inelastic CMOD is used to calculate the inelastic strain energy release rate. Three parameters were obtained for each loading-unloading cycle including the compliance, the load at the initiation of the unloading, and inelastic CMOD, which is the residual displacement when the sample is unloaded. The R-curves comprise of a region where the resistance increases with crack length denoting the formation of a process zone and an energy plateau denoting steady-state crack extension. In some embodiments, the location of the transition point between the two regions depends on the matrix type and fiber volume. In some embodiments, the unreinforced OPC system shows almost negligible resistance whereas the corresponding iron-based system demonstrates some resistance to crack formation and growth, attributable to the reasons described elsewhere in this paper. Hence, in some embodiments, the use of fiber reinforcement improves the crack growth resistance of OPC systems, but the overall resistances are significantly lower than those of the iron-based binder systems.

[0059] The elastic and inelastic components of the strain energy release rate can be separated to obtain further insights on the relative influence of matrix (and the discrete phases in it), and the relative influence of matrix fiber reinforcement on the fracture response of these widely different material systems. The elastic component of the strain energy release rate corresponds to the energy release rate due to incremental crack growth whereas the inelastic component corresponds to effects such as permanent deformation caused due to crack-opening. For example, plot 900 of FIG. 9A illustrates elastic and inelastic components of crack growth resistance with varying crack extension for iron carbonate binder for different fiber dosage in accordance with some embodiments of the invention. For example, data lines 905, 910, 915 comprise elastic component response for iron-carbonate-based binder data at 0%, 0.5%, and 1% volume fraction of fiber reinforcement, and data lines 920, 925, 930 show the inelastic response for iron-carbonate-based binder data at 0%, 0.5%, and 1% volume fraction of fiber reinforcement. Further, plot 935 of FIG. 9B illustrates elastic and inelastic components of crack growth resistance with varying crack extension for OPC paste for different fiber dosage in accordance with some embodiments of the invention. For example, data lines 940, 945, 950 comprise elastic component response for iron-carbonate-based binder data at 0%, 0.5%, and 1% volume fraction of fiber reinforcement, and data lines 955, 960, 965 show the inelastic response for iron-carbonate-based binder data at 0%, 0.5%, and 1% volume fraction of fiber reinforcement. As indicated, in some embodiments, the contribution of the elastic component to the overall strain energy release rate is found to be higher than the inelastic component for the iron-based binder systems (both unreinforced and reinforced). However, for the OPC systems, the contribution of inelastic component is higher. Further, in some embodiments, both the elastic and the inelastic components increase with increase in crack extension for the fiber-reinforced iron-based system, However, for the fiber-reinforced OPC systems, the elastic component remains relatively constant with crack extension, and the increase in total strain energy is mainly due to increase in the inelastic component.

[0060] In some embodiments, the higher contribution of the elastic component in the iron-based systems can be attributed to the presence of a stronger matrix along with the presence of elastic metallic iron particles that provide crack growth resistance through the mechanisms described earlier. On the contrary, the brittle OPC matrix cracks easily, and consequently the load is carried almost completely by the fibers. The fibers bridge the crack, and energy dissipation is obtained through crack opening, which is reflected in the form of increased inelastic strain energy with increasing crack extension. The R-curve response is consistent with the values of fracture parameters (KIC<S >and CTODC) of these binders. In some embodiments, the fracture toughness of the iron-based systems was found to be much higher than the OPC systems whereas the CTODC values demonstrated less of a difference. The same trends are reflected in the R-curves: about an order of magnitude higher crack growth resistance (elastic contribution) observed for the iron-based systems than the OPC systems and comparatively lesser improvement (about 60% higher) in the crack-opening resistance (inelastic contribution).

[0061] Digital image correlation (“DIC”) can be used to determine KIC and CTODc of the binder systems. Two representative iron carbonate binders (0% and 1% fiber volume fraction) were examined for the extraction of fracture parameters through DIC. For example, FIG. 10A shows a load-CMOD response plot 1000 for iron carbonate binder with 1% fiber volume fraction in accordance with some embodiments of the invention, and FIG. 10B shows a horizontal (u) displacement field represented as a 3D surface plot 1025 for iron carbonate binder with 1% fiber in accordance with some embodiments of the invention. Referring to plot 1000 of FIG. 10A, the load-CMOD response for the fiber-reinforced iron-based binder can be seen as data line 1005, where the points P1, P2, P3 correspond to three different stages of crack extension (i.e., in the pre-peak, near-peak, and post-peak stages). The compliance value obtained by unloading at approximately 95% of the peak load in the post-peak region is used for the determination of KIC<S >and CTODC using TPFM, which is required in order to compare with the corresponding values obtained using the DIC technique. The horizontal u-displacement fields (along the crack opening direction) are obtained from image correlation. The plot 1025 of FIG. 10B shows crack opening behavior curve 1027, denoted by the horizontal displacement, and the crack extension, denoted by the jump in the displacement above the notch (extracted from the DIC data). As can be observed, in some embodiments, the CTOD and ?a values can be determined directly using the DIC method without instrumenting the crack for precise measurements. A threshold value of 0.005 mm is set to qualify the displacement-jump as contributing to crack extension. The crack extension corresponding to 95% of the peak load in the post-peak region is used to determine the DIC-based fracture toughness parameters using a set of simplified expressions as shown later.

[0062] FIGS. 11A-11F show horizontal 2D displacement fields and the 3D surface plots for unreinforced and reinforced (1% fiber volume fraction) iron-based binders in accordance with some embodiments of the invention. The plots correspond to: (a) and (b) pre-crack stage: P1 (CMOD: 0.0009 mm, Load: 91.4 N, =0 mm, CTOD=0 mm); (c) and (d) stable crack growth stage: P2 (CMOD: 0.0263 mm, Load: 1172 N, =3.95 mm, CTOD=0.0096 mm); (e) and (f) unstable crack-propagation stage: P3 (CMOD: 0.2019 mm; Load: 633.8 N; =18.58 mm; CTOD=0.156 mm) in accordance with some embodiments of the invention. As shown, the 2D displacement fields for the iron-based binder are shown for three different CTOD values which were selected as shown in FIG. 10A (“P1”, “P2”, and “P3”), where FIGS. 11A, 11C, and 11E show the 2D crack opening displacements, corresponding to the points P1, P2 and P3 of FIG. 10A. Further, FIGS. 11B, 11D, and 11F show the corresponding horizontal displacements as 3D surface plots 1120, 1160, 1190 for 2D surface regions 1105, 1145, and 1185 respectively. Plot 1100 of FIG. 11A corresponds to the case where only a very small load is applied to the specimen (point “P1” in FIG. 10A), and the values of both CTOD and crack extension are zero, as shown by the uniform horizontal displacement fields above the notch as well as a flat surface plot (#D plot 1125 of FIG. 11B). FIG. 11C corresponds to 95% of the peak load in the post-peak zone (Point “P2” in FIG. 10A). A displacement jump is clearly visible above the notch in both the 2D displacement field (FIG. 11C) and the 3D surface plot (3D plot 1165 of FIG. 11D). Beyond this point, the crack extension is found to be unstable (a large increase in CTOD and crack extension). FIG. 11E shows the displacement field corresponding to Point “P3” in FIG. 10A, and the 3D surface plot (3D plot 1195 of FIG. 11F). The CTOD and ?a values are very high in the post-peak zone.

[0063] CTODC and KIC values are shown Table 2 (obtained using calculated TPFM and DIC methods). For the iron-based binders, the data indicates a there is a correlation between the KIC and CTODc values obtained from the contact and non-contact methods.
TABLE 2
Comparison of the KIC and CTODc values determined using
  KIC (MPa · mm<0.5>)  CTODc (mm)
Specimen composition  TPFM  DIC  TPFM  DIC
Iron carbonate (Control)  31.40  33.56  0.0062  0.0040
Iron carbonate (Vf = 1.0%)  52.53  54.14  0.0089  0.0096

[0064] It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. Various features and advantages of the invention are set forth in the following claims.



Binder Compositions and Method of Synthesis
US2016075603
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Some embodiments of the invention include a method of producing iron carbonate binder compositions including providing a plurality of binder precursors including a powdered iron or steel, a first powdered additive comprising silica, a second powdered additive including calcium carbonate, and a powdered clay. The method includes mixing the plurality of binder precursors and a water additive to form an uncured product, and feeding at least a portion of the uncured product into a curing chamber. The curing chamber is fluidly coupled to a CO2 source so that some CO2 from the CO2 source reacts with the uncured product to form a cured iron carbonate containing product and at least one reaction byproduct, where at least some byproduct can be fed from the curing chamber to the CO2 source for use as a fuel by the CO2 source.

BACKGROUND

[0003] Anthropogenic emission of CO2 is accepted as being responsible for changes in global climate and potentially irreversible damaging impacts on ecosystems and societies. Various technologies designed to reduce the amount of greenhouse gases such as CO2 in the atmosphere is an active research area through the developed and developing world. The sequestration of CO2 offers the potential to prevent CO2 from entering the atmosphere (i.e., by removal of the CO2 from an industrial waste stream), or a potential route to extraction of CO2 that is already present in the atmosphere. Physical trapping of CO2, such as injection of CO2 into depleted natural gas reservoirs under the seabed or into the deep ocean has not yet been proven to be a leak-proof technology option. Chemical sequestration on the other hand offers the potential to trap the CO2 virtually permanently. The use of mineral rocks (especially alkaline-earth oxide bearing rocks) as a feedstock for reaction with CO2 is one of the promising routes for reduction of concentration of CO2 in the atmosphere. CO2 is passed through the rock, and chemically sequestered through mineral carbonation. See for example, Klein, E.; Lucia, M. D.; Kempka, T.; Kühn, M. Evaluation of Long-term Mineral Trapping at the Ketzin Pilot Site for CO2 Storage: An Integrative Approach Using Geochemical Modeling and Reservoir Simulation. Int. J. Greenhouse Gas control 2013, 19, 720-730, and Xu, T.; Apps, J. A.; Pruess, K.; Yamamoto, H. Numerical Modeling of Injection and Mineral Trapping of CO2 with H2S and SO2 in a Sandstone Formation. Chem. Geol. 2007, 242, 319-346, and Naganuma, T.; Yukimura, K.; Todaka, N.; Ajima, S. Concept and Experimental Study for a New Enhanced Mineral Trapping System by Means of Microbially Mediated Processes. Energy Procedia 2011, 4, 5079-5084.

[0004] Many industrial processes produce metal and metal oxide wastes that require disposal. For example, particulate waste that includes some metallic iron or steel powder can be generated in significant amounts as bag-house dust waste during the Electric Arc Furnace (EAF) manufacturing process of steel and from the shot-blasting operations of structural steel sections. The traditional means of disposing EAF and shot-blasting dust is landfilling as it is not economically feasible to recycle the iron from the dust. Several million tons of such waste material is being landfilled at great costs all over the world. It is known that secondary carbonate rocks formed during mineral trapping demonstrate mechanical strength, which suggests the possibility of using mineral trapping in conjunction with a binder for the development of a sustainable construction material.

[0005] Several studies on iron carbonate formation by CO2 corrosion of steel have been reported (see for example, Wu, S. L.; Cui, Z. D.; He, F.; Bai, Z. Q.; Zhu, S. L.; Yang, X. J. Characterization of the Surface Film Formed from Carbon Dioxide Corrosion on N80 Steel. Mater. Lett. 2004, 58, 1076-1081, and Nordsveen, M.; Ne{hacek over (s)}ic, S.; Nyborg, R.; Stangeland, A. A Mechanistic Model for Carbon Dioxide Corrosion of Mild Steel in the Presence of Protective Iron Carbonate Films—Part 1: Theory and Verification. Corros. Sci. 2003, 59, 443-456, and Nesic, S.; Postlethwaite, J.; Olsen, S. An Electrochemical Model for Prediction of Corrosion of Mild Steel in Aqueous Carbon Dioxide Solutions. Corros. Sci. 1996, 52, 280-294, and Sun, J. B.; Zhang, G. A.; Liu, W.; Lu, M. X. The Formation Mechanism of Corrosion Scale and Electrochemical Characteristic of Low Alloy Steel in Carbon Dioxide-saturated Solution. Corros. Sci. 2012, 57, 131-138. In addition to iron oxidation, dissolved CO2 is also capable of reacting with iron. A dense layer of iron carbonate can form which adheres strongly to the substrate. For example, CO2 can react with iron as outlined in the following reaction equations (1), (2):

Fe+2CO2+2H2O?Fe<2+>+2HCO3<->+H2?  (1)

Fe<2+>+2HCO3<->?FeCO3+CO2+H2O  (2)

[0006] The net reaction then can be defined by the following reaction equation (3):

Fe+CO2+H2O?FeCO3+H2?  (3)

[0007] However the kinetics of the reaction and the rate of product formation are often very slow. To be of any use for beneficial industrial applications, a promoter including one or more reducing agents can be added to increase the rate of reaction. However the handling and processing properties of the mixtures of powders can prevent optimal mixing of materials, thereby preventing homogeneous reaction and compositional development.

SUMMARY OF THE INVENTION

[0008] Some embodiments of the invention include a method of producing iron carbonate binder compositions comprising providing a plurality of binder precursors including a powdered iron or steel, a first powdered additive comprising silica, a second powdered additive comprising calcium carbonate, and a powdered clay. The method includes providing a curing chamber including a first fluid coupling between a first end of the curing chamber and a first end of a CO2 source, and a second fluid coupling between a second end of the curing chamber and a second end of the CO2 source. The method further includes mixing the plurality of binder precursors and a water additive to form an uncured product, and feeding at least a portion of the uncured product into a curing chamber. Further, the method includes using CO2 at least partially from the CO2 source, curing at least a portion of the uncured product to form a cured iron carbonate containing product and at least one reaction byproduct.

[0009] In some embodiments, the first powdered additive further comprises alumina. In some further embodiments, the powdered clay comprises at least one of kaolinite and metakaolin. In some embodiments, the water additive comprises at least one of effluent water and seawater. In some further embodiments of the invention, the plurality of binder precursors includes at least one organic reducing agent comprising at least one carboxylic acid additive. In some other embodiments, the at least one carboxylic acid additive comprises oxalic acid.

[0010] Some embodiments include a second powdered additive that comprises limestone. In some further embodiments, the first powdered additive is derived from fly ash. In some embodiments, the powdered iron or steel comprises powdered iron or steel recycled from at least one industrial process.

[0011] In some embodiments of the invention, the curing chamber is coupled to or integrated with an existing industrial process comprising the CO2 source. In some further embodiments, the CO2 source comprises a furnace of the existing industrial process. In some further embodiments, the CO2 source comprises at least one of a furnace, a boiler, a reactor or process vessel, a power station or generator, an oil or gas well or field, a natural or synthetic CO2 aquifer, a CO2 sequestration apparatus, and the atmosphere or environment.

[0012] In some embodiments, the CO2 from the CO2 source is fed to the curing chamber by the second fluid coupling. In some embodiments, the flow rate of the CO2 is determined by at least one meter and is controlled by at least one valve. In some embodiments, the at least one reaction byproduct is fed from the curing chamber to the CO2 source by the first fluid coupling.

[0013] In some embodiments of the invention, at least one reaction byproduct is hydrogen gas. In some further embodiments, the at least one reaction byproduct is CHxOy, where x=0-4 and y=0-2.

[0014] In some embodiments, the flow rate of the at least one byproduct is determined by at least one meter and is controlled by at least one valve. In some embodiments, at least some of the carbonate of the iron carbonate containing product is formed from CO2 from the CO2 source. In some embodiments, the CO2 from the CO2 source is produced by an exothermic reaction driven at least in part by the at least one reaction byproduct.

DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 illustrates a schematic of a method of synthesis and processing of binder compositions using a recycled reaction products integrated within a conventional furnace process in accordance with some embodiments of the invention.

[0016] FIG. 2 provides an illustrative view of a scanning electron micrograph of iron particles according to one embodiment of the invention.

[0017] FIG. 3A shows a plot of particle size distribution of metallic iron powder, OPC, fly ash, metakaolin, which is the clay source and limestone powder in accordance with at least one embodiment of the invention.

[0018] FIG. 3B illustrates a table of compositions comprising mixtures of iron powder, fly ash, limestone and a clay source such as metakaolin and/or kaolinite in accordance with at least one embodiment of the invention.

[0019] FIG. 4A illustrates a plot of compressive strength values of mixtures after 3 days in CO2 and 2 days in air in accordance with various embodiments of the invention.

[0020] FIG. 4B illustrates a plot of compressive strength values of mixtures showing 7-day compressive strengths of plain and modified OPC mixtures for comparison with 4-day carbonated iron-carbonate (mixture 2: 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) in accordance with various embodiments of the invention.

[0021] FIG. 5A illustrates a plot of the effect of fly ash content on the compressive strength of iron carbonate binders in accordance with some embodiments of the invention.

[0022] FIG. 5B illustrates a plot of the effect of limestone content on the compressive strength of iron carbonate binders in accordance with some embodiments of the invention.

[0023] FIG. 5C illustrates a plot of the effect of metakaolin content on the compressive strength of iron carbonate binders in accordance with some embodiments of the invention.

[0024] FIG. 6A illustrates a response surface plot showing the statistical influence of amounts of fly ash and metakaolin in accordance with some embodiments of the invention.

[0025] FIG. 6B illustrates a response surface plot showing the statistical influence of amounts of fly ash and limestone in accordance with some embodiments of the invention.

[0026] FIG. 6C illustrates a response surface plot showing the statistical influence of amounts of limestone and metakaolin in accordance with some embodiments of the invention.

[0027] FIG. 7 shows a bar graph of the comparison of compressive strength of mixture 1 (comprising 64% iron powder, 20% fly ash, 8% limestone, 6% metakaolin) and mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) under different curing conditions in accordance with some embodiments of the invention.

[0028] FIG. 8A illustrates a surface plot of the effect of curing procedure and curing duration in accordance with some embodiments of the invention.

[0029] FIG. 8B shows a bar graph of the effect of air-curing duration on compressive strength of mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin), and carbonated for 4 days in accordance with some embodiments of the invention.

[0030] FIG. 9 illustrates a graph showing variations in average pore diameter with varying carbonation durations for mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) in accordance with some embodiments of the invention.

[0031] FIG. 10A illustrates a plot showing a logarithmic increase of flexural strength with increase in carbonation duration, where mixture 1 comprises 64% iron powder, 20% fly ash, 8% limestone, 6% metakaolin, and mixture 2 comprises 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin in accordance with some embodiments of the invention.

[0032] FIG. 10B illustrates a plot showing the interaction between bulk density and flexural strength for the mixtures of FIG. 10A in accordance with some embodiments of the invention.

[0033] FIG. 11A shows a plot including thermogravimetric and differential thermogravimetric curves corresponding to the core and surface of mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin), carbonated for 3 days in accordance with some embodiments of the invention.

[0034] FIG. 11B shows a plot including thermogravimetric and differential thermogravimetric curves corresponding to the core and surface of mixture 6 (comprising 65% iron powder, 15% fly ash, 8% limestone, 10% metakaolin), carbonated for 3 days in accordance with some embodiments of the invention.

[0035] FIG. 12A illustrates thermal analysis results of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 1 day, where samples were exposed to air for 3 days after carbonation in accordance with some embodiments of the invention.

[0036] FIG. 12B illustrates thermal analysis results of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 2 days, where samples were exposed to air for 3 days after carbonation in accordance with some embodiments of the invention.

[0037] FIG. 12C illustrates thermal analysis results of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 3 days, where samples were exposed to air for 3 days after carbonation in accordance with some embodiments of the invention.

[0038] FIG. 12D illustrates thermal analysis results of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 4 days, where samples were exposed to air for 3 days after carbonation in accordance with some embodiments of the invention.

[0039] FIG. 13A illustrates a plot of the effect of carbonation duration on mass loss in the 250-400° C. range in thermogravimetric analysis in accordance with some embodiments of the invention.

[0040] FIG. 13B illustrates a plot of the effect of carbonation duration on the amount of CaCO3 remaining in the 250-400° C. range in thermogravimetric analysis in accordance with some embodiments of the invention.

DETAILED DESCRIPTION

[0041] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

[0042] The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures, in which like elements in different figures have like reference numerals. The figures, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives and fall within the scope of embodiments of the invention.

[0043] Some embodiments of the invention include various compositions and synthesis methods of a structural binder utilizing the chemistry of iron carbonation. In some embodiments, a structural binder can be formed by reaction of iron with carbon dioxide (herein referred to as CO2). In some embodiments, the CO2 can be waste CO2 obtained from one or more industrial processes. Some embodiments include methods to form a sustainable binder system for concretes through carbonation of iron dust. For example, in some embodiments, iron can react with aqueous CO2 under controlled conditions to form complex iron carbonates which have binding capabilities. Further, some embodiments can include additives comprising silica and alumina. In some embodiments, silica and/or alumina additives can facilitate iron dissolution, which in some embodiments can provide beneficial rheological characteristics and properties. In some embodiments, the binder system can rely on the effects of corrosion of iron particles to form a binding matrix. In this instance, binder formation can result in the consumption and trapping of CO2 from an industrial operation and subsequent carbonate formation by conversion of at least a portion of the iron particles. Further, the binder formation can provide a means to reduce the overall ordinary Portland cement production (which is itself a significant emitter of CO2) through the use of carbonated metallic iron powder as the binder material for concrete. As used herein, the term metallic iron powder can include powders or particulate compositions comprising iron powder, steel powder, mixtures of iron and steel powder, fine particulates containing 10% or more reduced or metallic iron, or mixtures thereof.

[0044] In some embodiments, dissolution agents (such as organic acids) can be added to enhance the corrosion rate of iron. Further, in some embodiments, the rheological behavior (flowability and castability) and early strength development can be improved using one or more additives. For example, additives common to Portland cement concretes such as class F fly ash, powdered limestone, and metakaolin can be used as minor ingredients along with metallic iron powder to form pastes with adequate binding capabilities. In some embodiments, fly ash can be added as a source of silica to potentially facilitate iron silicate complexation. Further, in some embodiments, limestone powder can be added to provide additional nucleation sites. Some embodiments include one or more “powdered” clays having a layered structure which retains water and which can be used to improve the rheological properties. For example, in some embodiments, a clay source such as kaolinite and/or metakaolin can be added to provide cohesiveness as the iron-based mixtures are prepared.

[0045] Some embodiments provide compositions comprising fly ash, limestone, and a clay source such as metakaolin and/or kaolinite in various proportions. In some embodiments, the proportions of iron powder and other additives (including for example organic acids as dissolution agents) can influence the curing regime (based at least in part on the exposure of the mixture to CO2 and/or air). In some embodiments, the iron powder comprises about 88% iron and about 10% oxygen, along with trace quantities of copper, manganese, and calcium. In some embodiments, a binder composition can include class F fly ash. In some further embodiments, the composition can comprise metakaolin conforming to ASTM C 618.

[0046] In further embodiments, the binder composition can comprise limestone powder. In some embodiments, the limestone powder can comprise a median particle size of about 0.7 µm conforming to ASTM C 568. In some embodiments, limestone can be added with a particle size that can range from a median size of about 0.7 µm to about 20 µm. In some embodiments, the fineness determines its nucleation ability.

[0047] Some embodiments of the invention include compositions comprising metallic iron powder with median particle size of about 19 µm. In some embodiments, metallic iron powder sizes can range from about 5 µm to about 50 µm. Further, in some embodiments, the selection of size ranges can facilitate reactivity. In some embodiments, the iron powder can be obtained from a shot-blasting facility. In some embodiments, the iron powder can be derived from waste steel dust (such as so-called “bag house dust” from a shot blasting operation). In some embodiments, the waste dust comprises fine residue from blasting structural steel components such as I-beams with steel shot (round) or grit (angular). In this example, the shot and grit break down during numerous cycles of being blasted against steel targets. Other sources of the iron or steel powder can be from brake drum turnings, mill scale (if containing >10% metallic iron), machine shop shavings, finely chopped sheet steel and other waste ferrous scrap, and other sources of fine particulates containing particles of <50 um in size and containing about 10% or more of metallic iron. In some further embodiments, synthesized pure metallic iron powder can be used such as electrolytic iron powder and hydrogen-reduced iron powder.

[0048] In some embodiments of the invention, the curing of the binder composition can be integrated into a conventional furnace process to take advantage of the use of CO2 emitted from the convention process, and from the potential to recycle energy, reduce waste, and potentially lower costs by recycling gases from binder reaction and curing processes described above. For example, in some embodiments, CO2 from a conventional process can be used to provide a source of reactant in equation (1) or (3) described earlier. Further, in some embodiments of the invention, H2 emitted from the reactions (1) or (3) can be used within at least one reaction and/or process of the convention process.

[0049] FIG. 1 illustrates a schematic of a method of synthesis and processing of binder compositions using a recycled reaction products integrated within a source of CO2 (such as a conventional furnace process) in accordance with some embodiments of the invention. In some embodiments of the invention, binder components 105 can be prepared and fed using a delivery process 107 into a mixing process 110. In some embodiments, the binder components 105 can be mixed using the mixing process 110 to produce any of the binder mixtures described herein. The mixing process can comprise any conventional mixing process including ball-milling, low-shear mixing, high-shear mixing, rotary-blade mixing, acoustic mixing, extrusion mixing, shaker-mixing, or any other conventional binder mixing process. In some embodiments, binder components 105 can be mixed until a binder mixture is produced that is generally homogenous. The mixing time can be dependent on the mixer and the binder components 105 may be mixed for longer or shorter periods based on the composition and the mixer type.

[0050] In some embodiments, a mixture 112 can be transferred to a form or mold 120. In some embodiments, water and/or seawater 114 can be added and an uncured aggregate can be formed into a form or mold 120. In some embodiments, uncured forms 130 can be transferred (transfer process 116) from the form or mold 120 and assembled and/or prepared for transfer 132 to a curing chamber 140.

[0051] In some embodiments of the invention, the curing chamber 140 can be fluidly coupled to a CO2 source (such as a conventional reactor or furnace 175). For example, in some embodiments, at or adjacent to or proximate to a first end 140a of the curing chamber 140, a fluid coupling 187 can be coupled at one end and coupled to a first end 175a of the conventional furnace 175. Further, for example, in some embodiments, at or adjacent to or proximate to a second end 140b of the curing chamber 140, a fluid coupling 177 can be coupled at one end and coupled to a second end 175b of the conventional furnace 175. In some other embodiments, the CO2 source can comprise other sources of CO2 including, but not limited to, an existing industrial process comprising the CO2 source such as a furnace of the existing industrial process, a furnace, a boiler, a reactor or process vessel, a power station or generator, an oil or gas well or field, a natural or synthetic CO2 aquifer, a CO2 sequestration apparatus, and/or the atmosphere or environment.

[0052] In some embodiments, the fluid couplings 177, 187 can include at least one meter for metering a fluid flow and/or at least one valve for altering or adjusting a fluid flow. For example, in some embodiments, the fluid coupling 177 can comprise a fluid valve 181. In some further embodiments, the fluid coupling 187 can comprise a fluid valve 183. In some further embodiments, the fluid coupling 187 can comprise a fluid meter 185. In some other embodiments, the fluid coupling 177 can comprise a fluid meter 179.

[0053] In some embodiments of the invention, the fluid valve 181 can at least partially restrict or stop fluid flow in the fluid coupling 177 between the conventional furnace 175 and the curing chamber 140. In some further embodiments of the invention, the fluid valve 183 can at least partially restrict or stop fluid flow in the fluid coupling 187 between the conventional furnace 175 and the curing chamber 140.

[0054] In some embodiments of the invention, the fluid meter 179 can measure or monitor a fluid flow in the fluid coupling 177 between the conventional furnace 175 and the curing chamber 140. In some further embodiments of the invention, the fluid meter 185 can measure or monitor fluid flow in the fluid coupling 187 between the conventional furnace 175 and the curing chamber 140.

[0055] In some embodiments of the invention, with uncured forms 130 entering and/or moving, and/or stationary within the curing chamber, fluids including H2 and/or CHxOy (where x can be between zero and four, and y can be between zero and two) can pass from the curing chamber 140 through the fluid coupling 187 into the conventional reactor or furnace 175. Further, in some embodiments, CO2 producing within the conventional reactor or furnace 175 can flow from the conventional reactor or furnace 175 to the curing chamber 140. In some embodiments, the flow of CO2 can be measured or monitored with the fluid meter 179. In some further embodiments, the flow of CO2 from the conventional reactor or furnace 175 to the curing chamber 140 can be modified or halted using the fluid valve 181.

[0056] In some embodiments, the flow of fluids from the curing chamber 140 to the conventional reactor or furnace 175 including H2 and/or CHxOy can be measured or monitored with the fluid meter 185. In some further embodiments, the flow of fluids including H2 and/or CHxOy from the curing chamber 140 to the conventional reactor or furnace 175 can be modified or halted using the fluid valve 183.

[0057] In some embodiments of the invention, the flow of fluids including H2 and/or CHxOy from the curing chamber 140 to the conventional reactor or furnace 175 is based at least in part on a cure reaction (e.g., from a reaction shown in equation 1) of the uncured products 130 during conversion to a cured product 150 that can exit the curing chamber 140 through a process 142. Further, in some embodiments of the invention, at least a portion of the curing and conversion of the uncured products 130 to cured product 150 can be dependent at least in part on CO2 delivered from one or more reactions or processes of the conventional reactor or furnace 175.

[0058] FIG. 2 provides an illustrative view of a scanning electron micrograph 200 of iron particles (where the scale bar corresponds to 20 µm) according to one embodiment of the invention. As shown, the iron powder can include elongated and plate-like particles. In some embodiments, the elongated and plate-like particles can influence the rheological properties of the mixture. Further, in some embodiments, the larger surface area-to-volume ratio of this shape as compared to spherical shaped particles can improve reactivity of the iron powder. In some embodiments, fly ash can be used to provide a silica source for the reactions (and to potentially facility iron silicate complexation). In some embodiments, added limestone powder can provide nucleation sites for one or more cure reactions within the binder composition. In some embodiments, added water can be reduced in chemical reactions within any of the disclosed binder compositions (however it does not form part of the binder). In some embodiments, to minimize water demand, while maintaining binder consistency and cohesiveness, added metakaolin can be added to the binder composition. In some further embodiments, an organic reducing agent/chelating agent of metal cations can be included in the binder composition.

[0059] In some embodiments, various iron-based binder compositions were prepared and compared with commercially available type I/II ordinary Portland cement (hereinafter “OPC”). For example, in some embodiments, OPC conforming to ASTM C 150 was used to prepare conventional cement pastes, and the compressive strengths of the iron-based binder compositions were compared with those of the traditional OPC-based systems. In some embodiments, OPC was also partially replaced by class F fly ash and blast furnace slag up to about 40% and about 50% respectively by mass for comparison purposes. Fly ash generally contains about 60% by mass of SiO2, whereas the siliceous content of metakaolin is about 50%. In some embodiments, the limestone powder used comprises a nominally pure calcium carbonate (about 97% by mass).

[0060] FIG. 3A shows a plot 300 of particle size distribution (obtained from a laser diffraction-based particle size analyzer) of metallic iron powder (data plot 305), OPC (data plot 309), fly ash (data plot 307), metakaolin (data plot 311) and limestone powder (data plot 313) in accordance with at least one embodiment of the invention. In some embodiments, binder composition preparation methods can include dry mixing of all materials (iron powder, fly ash, limestone powder, a clay source such as metakaolin and/or kaolinite, and an organic reducing agent). In some embodiments, water can be added to some of the dry ingredients and the other ingredients can then mixed in order to obtain a uniform cohesive mixture. In some embodiments, the mass-based water-to-solids ratio (hereinafter “w/s”) was varied between about 0.22 and about 0.25 depending upon the proportions of the constituents in the mixtures to attain a cohesive mix. As described earlier, since the carbonation process of iron does not incorporate water in the reaction product, the w/s used can be primarily based on the criteria of obtaining desired workability, casting behavior, and ability to strip the cured composition from molds without specimen breakage.

[0061] In some embodiments of the method, the mixture was transferred to cylindrical molds (about 32.5 mm diameter and about 65 mm long) in a Harvard miniature compaction apparatus (ASTM D 4609—Annex A1) in five layers to fill the mold completely. In some embodiments, the specimens were de-molded immediately using a specimen ejector for the compaction apparatus, and placed inside clear plastic bags filled with 100% CO2 at room temperature (between about 18° C. and about 22° C.) inside a fume hood for 1 to 4 days. In some embodiments, the bags were refilled with CO2 every 12 hours so as to maintain saturation inside the chamber. In some embodiments, after the respective durations of CO2 exposure, the samples were placed in air at room temperature (between about 18° C. and about 22° C.) to allow the moisture to evaporate for 1 to 30 days. In some embodiments, the OPC-based samples were cast in 50 mm cube molds and moist-cured (>98% RH and 23±2° C.) for 7 days before compressive strength testing. In some embodiments, the water-to-cementitious materials ratio (hereinafter “w/cm”) adopted for the OPC-based mixtures was about 0.40, which is the most common w/cm used for moderate strength (20-35 MPa) concretes.

[0062] As described earlier, some embodiments comprise binder compositions including various mixture proportions of iron powder, and at least one of fly ash, limestone powder, a clay source such as kaolinite and/or metakaolin, and one or more organic reducing agents. Further, in some embodiments, binder compositions can be cured using various curing procedures. For example, different mixtures with varying iron powder, fly ash, limestone, and a clay source such as metakaolin and/or kaolinite contents can be proportioned to select one or more compositions based on compressive strength of the cured binder composition. For example, some binder compositions include an iron powder content that ranged from about 58 to about 69% by mass. In some embodiments, the fly ash content was maintained at about 15% or about 20%. Further, in some embodiments, a limestone content of about 8% to about 10% was used. Further, some embodiments included a metakaolin content of about 6% to about 10%. In some embodiments, the w/s ratios varied between about 0.22 and about 0.25. These preliminary proportions were arrived at based on several trial proportions that used iron powder from about 50 to about 100% of the total binder content. Moreover, the binder composition included other ingredients at multiple levels beyond the ranges described above, and several w/s ratios in the range of about 0.15 to about 0.30.

[0063] FIG. 3B illustrates a table (375) of compositions comprising mixtures of iron powder, fly ash, limestone and metakaolin in accordance with at least one embodiment of the invention. The proportions of the eight short-listed mixtures are shown, and were chosen based on the homogeneous nature of the mixture, their ability to be compacted into molds, and their ability to be demolded without breakage. As shown, in some embodiments, the binder composition can comprise about 64% iron powder, about 20% fly ash, about 8% limestone, and about 6% metakaolin (“mixture 1” marked as 380). In some further embodiments, the binder composition can comprise about 60% iron powder, about 20% fly ash, about 8% limestone, and about 10% metakaolin (“mixture 2” marked as 382). In some other embodiments, the binder composition can comprise about 62% iron powder, about 20% fly ash, about 10% limestone, and about 6% metakaolin (“mixture 3” marked as 384). Some embodiments include a binder composition that comprises about 58% iron powder, about 20% fly ash, about 10% limestone, and about 10% metakaolin (“mixture 4” marked as 386). In some embodiments, the binder composition can comprise about 69% iron powder, about 15% fly ash, about 8% limestone, and about 6% metakaolin (“mixture 5” marked as 388). In some other embodiments, the binder composition can comprise about 65% iron powder, about 15% fly ash, about 8% limestone, and about 10% metakaolin (“mixture 6” marked as 390). In some further embodiments, the binder composition can comprise about 67% iron powder, about 15% fly ash, about 10% limestone, and about 6% metakaolin (“mixture 7” marked as 392). Some further embodiments of the invention include a binder composition comprising about 63% iron powder, about 15% fly ash, about 10% limestone, and about 10% metakaolin (“mixture 8” marked as 394). In some embodiments of the invention, the binder components 105 can comprise any of the mixtures 380, 382, 384, 386, 388, 390, 392.

[0064] In some embodiments, the organic reducing agent comprises an acid. In some embodiments, the organic reducing agent comprises oxalic acid. In some embodiments, the acid can comprise at least one carboxylic acid group. In some embodiments, an organic reducing agent can be added in a powder form to about 2% of total mass of the constituents. In some other embodiments, the organic reducing agent can be added based on the solubility of the organic acid in water, and the compressive strength as compared to mixtures without dissociating agent. In some embodiments of the invention, the binder components 105 can comprise any of the mixtures 380, 382, 384, 386, 388, 390, 392 that also comprise 2 wt % of an organic acid including, but not limited to oxalic acid or any organic carboxylic acid.

[0065] In some embodiments, binder composition samples were kept in a 100% CO2 atmosphere for 3 days immediately after casting and de-molding, and cured in air for 2 days before they were tested in uniaxial compression. In some embodiments, in order to determine the optimal combination of CO2 and air-curing durations, the CO2 curing exposure duration was varied from 1 to 4 days, and the air curing duration varied from 1 to 3 days. In some embodiments, the upper limit of the carbonation duration was chosen based on the thermo-gravimetric analysis which showed similar degrees of carbonation in the core and surface of the cylindrical samples after 4 days of carbonation. In some embodiments, air-curing was extended to 30 days, but no appreciable changes in compressive strengths were found after 3 days.

[0066] Physical characterization was performed on one or more of the cured binder compositions described above. For example, flexural strength tests were carried out on mixtures under compression. Paste beams, 250 mm×25 mm×25 mm in size were prepared and cured in a 100% CO2 environment for 2-6 days. The air exposure time was maintained constant at 3 days. Three-point bending tests were conducted at a displacement rate of 0.375 mm/min until the samples failed. Thermo-gravimetric analysis was performed using a Perkin Elmer STA 6000 simultaneous thermal analyzer. The analyzer was programmed to increase the temperature from 30° C. to 995° C. at a rate of 15° C./minute in a N2 environment. The samples were obtained from cylindrical samples that were cured for the compressive strength tests. Samples from both surface as well as core of the cylindrical specimens were analyzed in order to assess the influence of CO2 penetration on the degree of reaction. Mercury intrusion porosimetry was adopted to study the pore structure. The samples for MIP tests were taken from the core of the cylindrical sample. The MIP test was done in two steps: (i) evacuation of gases, filling the sample holder with mercury, and increasing the pressure up to 345 kPa, and (ii) intrusion of the mercury into the sample at high pressures (up to 414 MPa). The contact angle and surface tension of Hg used for the analysis was 0.485 N/m. In the absence of a better understanding of the contact angle between Hg and the iron carbonate binder, the common value used for OPC-based pastes (130°) was used here. The pore diameters were evaluated using the Washburn equation based on the assumption that the pores are of cylindrical shape. A minimum pore diameter of 0.003 µm can be evaluated using MIP. The average pore diameter (da) can be estimated for varying carbonation durations using the total volume of mercury intruded (V, cm<3>/g) and the pore surface area (A, cm<2>/g) obtained from MIP as shown below:

da=(4V/A)

[0067] In some embodiments, the compressive strength of one or more of the binder compositions measured to determine the behavior of compressive strength for a specific curing duration and procedure. In some embodiments, binder composition samples were kept in a CO2 environment for 3 days and then cured in air for 2 days at 23±2° C. to get a comparative measure of the compressive strengths of one or more compositions. For example, FIG. 4A illustrates a plot of compressive strength values of mixtures after 3 days in CO2 and 2 days in air in accordance with various embodiments of the invention. The results show compressive strength bars 401, 402, 403, 404, 405, 406, 407, 408 corresponding to the mixtures shown in table 375, including 380, 382, 384, 386, 388, 390, 392, and 394 respectively. Further, FIG. 4B illustrates a plot of compressive strength values of mixtures showing 7-day compressive strengths of plain and modified OPC mixtures for comparison with 4-day carbonated iron-carbonate (mixture 2: 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) in accordance with various embodiments of the invention.

[0068] The influence of various constituents on compressive strength is illustrated in FIGS. 5A-5C. For example, FIG. 5A illustrates a plot 500 of the effect of fly ash content on the compressive strength of iron carbonate binders in accordance with some embodiments of the invention. FIG. 5B illustrates a plot 525 of the effect of limestone content on the compressive strength of iron carbonate binders, and FIG. 5C illustrates a plot 550 of the effect of metakaolin content on the compressive strength of iron carbonate binders in accordance with some embodiments of the invention. The results illustrated in FIG. 5A implies that the samples with 20% fly ash (shown as 501, 502) were significantly stronger than the samples with 15% fly ash, irrespective of the contents of limestone and metakaolin. In this instance, the best performing mixtures (mixture 1 shown as 501, and mixture 2 shown as 502) contained 20% fly ash by mass. These mixtures also demonstrated the lowest porosity (determined from mercury intrusion porosimetry), possibly due to the combined effect of particle packing and increased reaction product formation. From FIG. 5B, it can be seen that in some embodiments, the limestone content exerts negligible influence on compressive strength at lower fly ash contents, but at higher fly ash contents, a lower amount of limestone powder is preferable. Further, in some embodiments, the compressive strength is relatively insensitive to variations in metakaolin content for the samples containing 20% fly ash. Thus, in some embodiments, the synergistic effect of silicates and cohesive nature of metakaolin can ensure a denser matrix. In some embodiments of the invention, with a binder comprising a lower fly ash content, an increase in the metakaolin content is associated with significant decrease in the compressive strength values. In some embodiments, this can be attributed to the increased water retention by metakaolin, and the lack of quantity of fly ash to enhance the workability and produce a consistent and defect-free mixture.

[0069] In some embodiments, the statistical influence of the amounts of fly ash, metakaolin and limestone on the compressive strength and the relative sensitivity of strength to these factors can be determined using a 2<3 >factorial analysis. For example, FIG. 6A illustrates a response surface plot 600 showing the statistical influence of amounts of fly ash and metakaolin in accordance with some embodiments of the invention. Further, FIG. 6B illustrates a response surface plot 625 showing the statistical influence of amounts of fly ash and limestone in accordance with some embodiments of the invention, and FIG. 6C illustrates a response surface plot 650 showing the statistical influence of amounts of limestone and metakaolin in accordance with some embodiments of the invention. It is confirmed that fly ash is the dominant factor influencing the compression strength. The sensitivity of compressive strength to variations in the amount of limestone and metakaolin is relatively low. As described earlier, metakaolin is used as a rheology modifier (modifying the overall cohesiveness of the binder mixture), and the limestone can function as a nucleation site for the reaction products.

[0070] The range of amount of limestone used in the compositions described herein (about 8-10%) does not significantly impact the strength, however thermogravimetric analysis indicates some consumption of limestone in the reaction to form a carbonate-containing complex reaction product. As discussed earlier, the data illustrated in FIG. 2A does not indicate significant differences in compressive strengths between mixtures 1 and 2 under the chosen curing condition (in a CO2 environment for 3 days and air-cured for 2 days). To observe whether changes in curing conditions would elicit varied response from these mixes, the cylindrical specimens were carbonated for 3 or 4 days and air-cured for 1 or 3 days. FIG. 7 shows a bar graph 700 of the comparison of compressive strength of mixture 1 (comprising 64% iron powder, 20% fly ash, 8% limestone, 6% metakaolin) and shown as 710, and mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) shown as 720, under different curing conditions in accordance with some embodiments of the invention. Here the number before ‘C’ represents the days of carbonation whereas the number before ‘A’ represents the air exposure time in days. Therefore, as an example, “3C-1A” represents three days of carbonation and one day of air exposure time.

[0071] The effects of curing procedure and duration on compressive strengths of the iron carbonate binders are shown in FIGS. 8A and 8B. For example, FIG. 8A illustrates a surface plot 800 of the effect of curing procedure and curing duration in accordance with some embodiments of the invention. Further, FIG. 8B shows a bar graph 825 of the effect of air-curing duration on compressive strength of mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin), and carbonated for 4 days in accordance with some embodiments of the invention. In some embodiments, the samples were cured in CO2 for 1 to 4 days and in air for 1 to 3 days thereafter. Referring to FIG. 8A, the strength values are shown in a response surface plot as function of CO2 and air-curing durations. As illustrated, in some embodiments, the influence of CO2 curing duration shows low compressive strength values for the samples cured in CO2 for 1 day only (due to the very low degree of carbonation). In some embodiments, the carbonation provides mechanical strength in the binder compositions. Moreover, in some embodiments, there is no discernible strength increase when the moisture leaves the system through air exposure. This can be seen where for 1 day of carbonation, increasing the air exposure duration from 1 to 3 days does not impact the compressive strength positively. However, the effect of air-curing is evident when the carbonation duration is increased. In some embodiments, a significant increase in strength is observed for specimens carbonated for a longer duration when the air curing time was increased. This can be attributed to the fact that the average pore sizes decrease with increased carbonation duration as shown in FIG. 9, which illustrates plot 900 showing variations in average pore diameter with varying carbonation durations for mixture 2 (60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin).

[0072] In some embodiments, the average pore size of the 1-day carbonated samples is larger, which in some embodiments can consequently exert less internal moisture pressure under a compression test (pressure is inversely proportional to the pore size). Therefore, in some embodiments, the loss of moisture through air exposure does not have a larger effect on internal pressure (and thus the compressive strength). Further, in some embodiments, the pore sizes of samples carbonated for a longer duration are lower due to increased reaction product formation, which in some embodiments, results in an increased sensitivity of compressive strength to the loss of moisture.

[0073] In order to further illustrate the effect of air exposure, FIG. 8B plots the compressive strengths as a function of air exposure duration after the samples were carbonated for 4 days. As illustrated, in some embodiments, the first three days of exposure to air results in an enhancement in the compressive strength. Further, as the moisture dries out completely, there is no significant change in compressive strength which signifies that the reaction product is passive and stable in air, and does not cause deterioration when exposed to air for longer time periods. Thus, in some embodiments, the air exposure duration (which is dependent on the pore structure that can allow moisture to escape from the bulk of the material) can influence the compressive strength at longer carbonation durations.

[0074] FIG. 10A shows graph 1000 showing the variation in flexural strength of iron carbonate binders (for mixtures 1, shown as plot 1010 and mixture 2, shown as plot 1020) with an increase in carbonation duration. As shown, in some embodiments, the flexural strengths are very similar for both the mixtures, which is consistent with the trends for compressive strength. Further, a carbonation duration of six days can result in a relatively high flexural strength of about 8 MPa. In comparison, typical OPC-based systems demonstrate a flexural strength of 3-4 MPa. Therefore, in some embodiments of the invention, the increased flexural strength of the binder compositions provides options for several applications that require improved flexural properties (such as beams, pavement slabs, and the like). FIG. 10B shows a graph 1050 with the relationship between flexural strength and density for mixture 1 (shown as plot 1052) and mixture 2 (shown as 1051). In some embodiments, higher carbonation durations results in more reaction product formation and increased density as the reaction product fills the pores more efficiently. Further, in some embodiments, the iron-based binder paste is only about 20-25% denser that common Portland cement-based pastes. In some embodiments, concretes that contain about 70% aggregates by volume, the density differences drops down to about 10%.

[0075] In some embodiments, thermo-gravimetric analysis was performed on powdered samples extracted from the surface and core of cylindrical specimens prepared from various binder compositions disclosed herein to investigate the degree of reaction responsible for differences in mechanical properties. The thermal analysis results of mixtures 2 and 6 were compared in order to understand the differences in product constitution between samples with the best and worst compressive strength. FIG. 11A shows a plot 1100 including thermogravimetric and differential thermogravimetric (DTG) curves corresponding to the core and surface of mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin), carbonated for 3 days. For example, plot 1105 shows data for the surface of mixture 2, and plot 1110 shows the data for the core of mixture 2. The corresponding DTG curves are shown as plots 1107, 1112. Further, FIG. 11B shows a plot 1150 including thermogravimetric and differential thermogravimetric curves corresponding to the core and surface of mixture 6 (comprising 65% iron powder, 15% fly ash, 8% limestone, 10% metakaolin), carbonated for 3 days in accordance with some embodiments of the invention. For example, plot 1155 shows data for the surface of mixture 2, and plot 1160 shows the data for the core of mixture 2. The corresponding DTG curves are shown as plots 1157, 1162.

[0076] A comparison of FIGS. 11A and 11B suggests that the total weight loss for mixture 2 is significantly higher than that for mixture 6, indicating that in some embodiments, the overall degree of reaction and product formation is lower under the chosen carbonating conditions for the starting material combination of mixture 6. Further, in some embodiments, the total weight loss of the sample from the surface of mixture 6 cylinder is slightly lower than the weight loss from the core sample of mixture 2. This shows that the constitution of mixture 6 is not reactively sensitive to desirable levels of carbonation and product formation, which reflects in the compressive strength of the binder. This observation also indicates that in some embodiments, the carbonation efficiency and mechanical properties of iron carbonate binders are very sensitive to the overall starting material composition. From a compositional viewpoint, the differences between mixtures 2 and 6 are not very large (the range of iron powder contents that provided reasonable strengths were between about 60% and about 69%). In some embodiments, the DTG curves include three distinct peaks for the binder samples. In some embodiments, the peak at around 110° C. can be attributed to evaporable water, and the peak at around 300° C. can be attributed to products belonging to the carbonate-oxalate-cancrinite group. In some embodiments, and the peak at around 740° C. can be attributed to calcium carbonate. The DTG curve for mixture 2 shows a strong, distinct peak at about 300° C. (for samples from both the core and the surface) whereas the intensity of the peak reduces for samples from mixture 6. The peak is almost non-existent for the sample from the core of mixture 6, indicating that in some embodiments, the carbonation efficiency for that mixture constitution is low.

[0077] Further, in some embodiments, the effect of carbonation duration on reaction product formation can be evaluated for one or more of the binder compositions described herein. For example, FIG. 12A illustrates thermal analysis results 1200 of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 1 day, where samples were exposed to air for 3 days after carbonation. For example, plot 1205 shows thermogravimetric data for surface, and plot 1210 shows thermogravimetric data for core, with DTG plots shown as 1207, 1212 respectively.

[0078] FIG. 12B illustrates thermal analysis results 1225 of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 2 days, where samples were exposed to air for 3 days after carbonation in accordance with some embodiments of the invention. For example, plot 1230 shows thermogravimetric data for surface, and plot 1235 shows thermogravimetric data for core, with DTG plots shown as 1232, 1237 respectively.

[0079] FIG. 12C illustrates thermal analysis results 1250 of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 3 days, where samples were exposed to air for 3 days after carbonation. For example, plot 1255 shows thermogravimetric data for surface, and plot 1260 shows thermogravimetric data for core, with DTG plots shown as 1257, 1262 respectively.

[0080] FIG. 12D illustrates thermal analysis results 1275 of samples from mixture 2 (comprising 60% iron powder, 20% fly ash, 8% limestone, 10% metakaolin) carbonated for 4 days, where samples were exposed to air for 3 days after carbonation in accordance with some embodiments of the invention. For example, plot 1280 shows thermogravimetric data for surface, and plot 1285 shows thermogravimetric data for core, with DTG plots shown as 1282, 1287 respectively. In some embodiments, the peak at 110° C. in the thermal analysis plot (due to evaporation of water) reduces in magnitude with increases in carbonation duration (especially after 2 days of carbonation), whereas the peak at 300° C. (attributable to carbonate-oxalate cancrinite group materials) increases in magnitude significantly when the carbonation period is increased. Further, it can be observed that the difference in final weight loss between surface and core reduces as the carbonation duration is increased. In some embodiments, this indicates that CO2 diffusion extends to the core with an increase in exposure duration as expected. After 4 days (the data shown in FIG. 12D), it can be observed that there is virtually no difference in the thermogravimetric and differential thermogravimetric signatures between the core and the surface indicating that complete carbonation can be achieved in these samples. These results are a function of specimen size, constitution, and the carbonating environment. While the thermal signatures indicate similar levels of carbonation in the core and surface of these samples, in some embodiments, the iron particles are not completely converted into iron carbonates. Moreover, as the reaction products form around these particles and the moisture content in the specimens drop, the ionic diffusion coefficient decreases and the reaction becomes extremely slow.

[0081] Carbonation duration-dependent mass loss patterns can be further examined in FIGS. 13A and 13B. For example, FIG. 13A illustrates a plot 1300 of the effect of carbonation duration on mass loss in the 250-400° C. range in thermogravimetric analysis with core data 1310 and surface data 1305, and FIG. 13B illustrates a plot 1350 of the effect of carbonation duration on the amount of CaCO3 remaining in the 250-400° C. range in thermogravimetric analysis with surface data 1355 and core data 1360. In some embodiments, the carbonation degree is shown to increase with carbonation duration, with a significant increase in reaction product formation in the specimen core between 2 and 3 days of CO2 exposure. In some embodiments, the mass loss observed in the 650-800° C. range corresponds to thermal decomposition of calcium carbonate (from the added limestone) into calcium oxide. In some embodiments, the amount of calcium carbonate remaining in the system can be calculated based on the stoichiometry of the thermal decomposition reaction of calcium carbonate. In some embodiments, the percentage of unreacted calcium carbonate present in the system for various carbonation durations (shown in FIG. 13B) illustrates a significant difference in the amount of unreacted CaCO3 between the core and the surface in the first two days of carbonation. However, in some embodiments, this difference is reduced as the carbonation period is increased to 3 to 4 days. In some embodiments, the amount of unreacted CaCO3 is generally the same at the specimen surface at all carbonation durations as can be observed from FIG. 13B. In some embodiments, as carbonation proceeds, the amount of CaCO3 remaining in the core drops because of the consumption of some limestone in the reaction product formation. In some embodiments of the invention, between two and three days, there is a reduction in the amount of calcium carbonates present in the core, which corresponds to the increase in the amount of carbonate complex (shown in FIG. 13A). Thus in some embodiments, it can be inferred that some portion of calcium carbonate is utilized to form the carbonate-oxalate complex, and the remaining unreacted limestone is decomposed in that temperature range. In some embodiments, this can be evidenced by the fact that the thermal analysis study confirms a substantially similar degree of carbonation of core and surface after 4 days of carbonation, restricting the upper limit of carbonation duration to 4 days.

[0082] As evidenced by the results described herein, in some embodiments, the compressive strength of binder compositions described herein can be significantly influenced by the fly ash content. In some embodiments, while limestone in the chosen range did not influence the strength at lower fly ash contents, synergistic effects were evident at higher fly ash contents. Further, in some embodiments, metakaolin primarily influenced the processing of the binder by providing cohesion to the mixtures, and generally improving the process rheology. Moreover, in some embodiments, CO2 exposure duration and air curing duration were also found to be influential on the mechanical properties of the one or more binder compositions. In some embodiments, the effect of air exposure time on compressive strength was found to be negligible at lower levels of carbonation (1-2 days), although the sensitivity increased significantly at higher carbonation durations (3-4 days). Thermo-gravimetric analysis showed that in some embodiments, the carbonation efficiency of iron carbonate binders is very sensitive to the overall starting material composition. Further, in some embodiments, the difference in mass loss between surface and core reduced significantly as the CO2 diffusion is extended to the core with an increase in carbonation duration. In some embodiments, the distinct differential thermogravimetric analysis peak at 300° C., common for carbonate-oxalate cancrinite group materials, was evident in the signals from one or more of the disclosed binder compositions. Further, in some embodiments, the mass loss in the temperature range of 250-400° C. increased as the carbonation duration increased, indicating the formation of more carbonate-bearing binding products. Further, in some embodiments, calcium carbonate content in the specimen core decreased when the carbonation was increased, that in some embodiments, indicates the consumption of limestone in reaction product formation. Moreover, the results indicate that reaction product formation increases as the carbonation progresses, which in some embodiments, can result in a denser structure that can possess improved mechanical properties.

[0083] It will be appreciated by those skilled in the art that while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein. Various features and advantages of the invention are set forth in the following claims.




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