Patent Application
20160264466
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.
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The particle size distributions (determined using dynamic light scattering) are shown in the plot 100 of
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.
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.
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.
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.
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 (KICS) 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.
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.
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.
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
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
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.
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,
In the unreinforced OPC matrix, the mechanism of strain energy dissipation can include crack extension. In some embodiments, the significantly higher KICS 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
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
The KICS-CTODC relationships of the two binders are compared in
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,
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
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 (KICS 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).
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,
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.
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.
This application claims priority from U.S. Provisional Application No. 62/131,799, filed on Mar. 11, 2015, the entire contents of which are incorporated herein by reference.
Some research conducted for conception and development of at least one embodiment of the invention described herein was made using Federal funds awarded by the National Science Foundation under Grant No. 1353170. The U.S. Federal Government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62131799 | Mar 2015 | US |
