Production of cementitious materials using microwave induced plasma heating

Abstract

A method of manufacturing cement includes mixing cementitious raw materials with conductive fibers to produce a mixture, and treating the mixture with microwaves to produce cementitious materials.

Description

Patent Application U Cal No. BK-2025-078-2 MN No. 407869-0231 PRODUCTION OF CEMENTITIOUS MATERIALS USING MICROWAVE INDUCED PLASMA HEATING TECHNICAL FIELD

[0001] This disclosure relates to cementitious materials, more particularly to producing cementitious materials using microwave induced plasma heating.BACKGROUND

[0002] Typical cement production processes involve mixing limestone and clay to produce a mixture, then heating it in a kiln to about 1450 °C for a relatively long period of time, then rapidly cooling it to form clinker nodules. The clinker nodules are then ground and typically mixed with gypsum to form cement. The cement is then mixed with water and other materials such as sand and gravel to form concrete, which is then poured or otherwise dispensed and then cured. The current processes of forming cement clinker are inefficient, use a lot of energy, and increase CO2 output.

[0003] As global populations rise and urbanization accelerates, the demand for cement and concrete continues to surge. By 2050, global cement production is projected to increase by an additional 23%, making the transition to low-carbon alternatives both critical and urgent. Currently, Portland cement accounts for 7.5% of anthropogenic CO2 output. Approximately 40% of these emissions arise from fossil-fuel combustion, with the remainder coming from limestone calcination. The widespread use of supplementary cementitious materials (SCMs) has proven effective in reducing clinker content, e.g., fly ash, slag, and calcined clay limestone cements. That said, incorporating SCMs above 50% remains challenging as Portland cement clinker is still, by far, the most important compound in modem cement. Although CO2 mineralization in cementitious materials holds the potential to sequester over 16 billion tons of CO2 annually, its climate benefits are often overestimated. Electrifying cement recycling also presents a promising alternative, but challenges remain in identifying a reliable electricity supply and variations in the quality of the clinker. Eliminating CO2 emissions from cement production requires fundamentally changing the cement-making process.

[0004] However, other options are needed to reduce CO2 emissions, and to find a way to recycle existing cement.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1 shows a phase diagram of a binary system used in cement synthesis.

[0006] FIG. 2 shows a graphic of an embodiment of a microwave induced plasma (MIP) process.

[0007] FIG. 3 shows a flowchart of embodiments of methods to produce cementitious products and supplementary cementitious products.

[0008] FIG. 4A shows a comparison temperature profiles for raw meal, gas in a commercial kiln and a method of the embodiments.

[0009] FIG. 4B shows a diagram of raw meal transitioning to clinker in a conventional kiln over time.

[0010] FIG. 5 shows a phase diagram illustrating phase transitions at different temperatures.

[0011] FIGs. 6A and 6B show multi-scale characterization of ultrafast high-temperature plasma cements (UHPC).

[0012] FIG. 7 shows a ternary plot synthesized materials produced using methods of the embodiments.

[0013] FIGs. 8A and 8B show performance metrics for large-scale production of UHPC.

[0014] FIG. 9 shows an embodiment of an apparatus to manufacture cementitious products.

[0015] FIG. 10 shows another embodiment of an apparatus to manufacture cementitious products.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The embodioments disclosed herein present an innovation of kinetically engineering cement production by maximizing liquid-phase transformations. They present an energyefficient, far-from-equilibrium cement manufacturing process based on microwave-carbon plasma, also referred to as microwave induced plasma (MIP). The embodiments enable precise control over the reaction progress and a pathway to convert in seconds cement raw meal or commodity cement waste into cement clinker. By combining an ultrafast, energy-efficient process with material versatility and environmental benefits, embodiments offer a scalable pathway to revolutionize cement manufacturing.

[0017] The embodiments herein introduce a stable plasma method that leverages the microwave-induced charging of carbon fibers to create plasma heating. This microwave-induced plasma (MIP) technique can be applied to cement production as well as to the treatment and extraction of industrial waste. Most cementitious materials can be produced using MIP heating in just 20 seconds. For example, ordinary Portland cement (OPC) can be prepared from traditional cement raw meal or demolished concrete fines. At the same time, minerals like limestone and clay can be calcinated, and low-grade supplementary cementitious materials (SCMs) such as fly ash and slag can be reactivated.

[0018] FIG. 1 shows a phase diagram of a binary system CaO-SiCh, first published in 1906, [Day, A. L. & Shepherd, E. S. THE LIME-SILICA SERIES OF MINERALS. J Am Chem Soc 28, 1089-1114 (1906)]. The conventional cement synthesis method uses solid-phase reactions.

[0019] The discussion below uses several terms with the following definitions. The notation “C” refers to CaO (calcium oxide). “S” refers to SiO? (silicon dioxide). The diagram of FIG.1 uses an abbreviation “Trd,” which means tridymite, also silicon dioxide. “F” refers to Fe20s (ferrous oxide, also known as iron (III) oxide, or hematite). “A” refers to AI2O3 (aluminum oxide, also known as alumina).

[0020] Tricalcium silicate, 3CaO SiC>2, abbreviated as C3S, is referred to here as alite.Dicalcium silicate 2CaO SiC>2, abbreviated as C2S, is referred to here as belite. Tricalcium aluminate, 3CaO AI2O3, abbreviated as C3A, is referred to here as aluminate. Calcium alumino-ferrite, 4CaO AI2O3 Fe2C>3, abbreviated as C4AF, is referred to as ferrite. All of the above include impurities.

[0021] In addition, the term “cementitious materials” as used here refers to the product(s) of the process of the embodiments. These include, but are not limited to “NEW” and “RCL” clinkers, carbon-fiber reinforced cements, LC3cement, calcined layered double hydroxides, The term “supplementary cementitious materials” include activated low-grade supplementary cementitious materials such as fly ash and slag. As used herein, the term “cementitious raw materials” refers to the inputs to the MIP process that result in these cementitious products.

[0022] Compared to the current cement calcination process, which requires hours at 1450 °C, the MIP method of the embodiments achieves significant advantages with its superior heating efficiency, reducing reaction times to mere seconds and aiming to replace traditional rotarykilns or preheating equipment. Additionally, this technique enables the reactivation and reuse of industrial by-products and waste materials, potentially scaling up for gigaton-scale CO2 reduction and removal.

[0023] The embodiments involve several different elements. The embodiments include the development of microwave induced plasma (MIP) method to manufacture cementitious materials, either new cements produced using a raw meal or demolished concrete fines. The third comprises reactivated supplementary cementitious materials (SCMs) including fly ash, slag, etc., using MIP technique. The fourth comprises in .s / 7 / / -prepared carbon fiber reinforced cement.

[0024] FIG. 2 shows a diagram of graphic representing an embodiment of the MIP process. FIG. 2 shows that when microwaves 10 interact with carbon or other conductive fibers 14, they induce a concentrated electric field at the edges of the fibers. This intense electric field causes electrons to accelerate and move through the surrounding air, leading to sparking plasma, producing substantial heat essential for cement synthesis. This process harnesses the interaction between microwaves and carbon fibers. Microwaves excite the electrons in carbon fibers, causing them to oscillate. Carbon fibers with sharp edges or pointed angles to concentrate electric fields, create a significant potential difference that leads to the dielectric breakdown of air, and can generate plasma sparks or arcing with intense heat. The intense heat causes some, if not all, of the cementitious raw materials 12 to melt. The resulting product comprises a cementitious material.

[0025] FIG. 3 shows an overview flowchart encompassing the various embodiments of the MIP methodology and the resulting cement product. On the left side, the process involves mixing the cementitious raw materials with carbon fibers at 20, and then treating the resulting mixture with microwave induced plasma at 22. In one embodiment of the process, the process takes raw meal 24, mixes it with carbon fiber at 20 and treats the mixture at 14 to produce “new” clinker, meaning that the raw meal comprises “new” limestone and clay, meaning that they are not recycled.

[0026] Manufacture of the raw meal 24 may take advantage of the MIP process to preprepare the components of the raw meal. In one embodiment, the limestone 26 may be preheated with MIP treatment 28, prior to being mixed with the raw meal at 24. In another embodiment, either with or without the pre-heated limestone, clay to be added to the rawmeal may be precalcined by undergoing MIP treatment 28 resulting in precalcined clay before being used as raw meal at 24.

[0027] The manufacture of the new clinker was validated in a laboratory. Reactant powders such as cementitious raw meal are uniformly mixed with carbon fibers using a commercial mixer and placed in a crucible for MIP treatment. Microwaves at 2.4 GHz produce plasma within seconds. One experiment validated the temperatures using an FLIR infrared camera. The local temperature can reach 2400 K within 2 seconds and be stabilized for extended durations By adjusting microwave frequency and carbon-powder ratios. The crucible used for this MIP process is designed on a centimeter scale but can be scaled up for larger-volume production.

[0028] While the experiment validated the use of standard 2.4 GHz microwaves, the MIP method is adaptable across a broad frequency range. Microwaves are defined as being between 300 MHz to 300 GHz. Higher-frequency microwaves offer improved power efficiency and longer plasma duration, further enhancing the scalability and efficiency of the process.

[0029] The experiment also demonstrated that carbon fibers, produced as a by-product of methane pyrolysis, are effective candidates for the MIP method. However, other types of carbon fibers produced via different methods and other conductive fibers such as steel, copper, aluminum, or carbon nanotubes can also serve as suitable plasma media.Additionally, conductive foams with 3D porous network architectures, such as carbon or metal foams, may also be used to heat cementitious raw materials.

[0030] Another path to manufacture cementitious products using the MIP process involves recycled cementitious fines used as the raw meal instead of new raw meal. These fines are hydrated to form hydrated concrete paste (HCP) 36 in FIG. 3. HCP 36 is mixed with the carbon fibers at 20 and then undergoes the MIP treatment at 22. This produces recycled clinker “RCL” at 42.

[0031] Demolished concrete fines, primarily composed of calcium silicate hydrates, perform even better with the MIP method due to the advantageous intermixing of calcium and silicon elements. Morphology and element mapping of hydrated cement showed that the elements, including Calcium (Ca), Silicon (Si), and Iron (Fe) were uniformly distributed. Following the same procedure, one can produce “RCL” (recycled) cement in seconds, achieving superior performance compared to traditional materials.

[0032] Using the developed MIP heating method of the embodiments, one can produce various types of cement with customizable phase assemblages in significantly shorter reaction times — mere seconds.

[0033] This process involves a three-dimensional (3D) carbon network using centimeter-long carbon or other conductive fibers. The interaction between the microwaves and carbon induces electrical discharges that coalesce into stable plasma. This results in a rapid and significant heat release, with local temperatures exceeding 2400 °C. In an experiment, the inventors applied this microwave-carbon plasma process to manufacture cement in seconds. The cement feedstock, which included raw meal (RM) composed of limestone and clay, or hydrated cement paste (HCP), was finely milled and adhered closely to the carbon fibers.

[0034] After grinding, calcium extracted from limestone and silicon and aluminum from clay was uniformly intermixed. These powders were directly heated under extreme thermal conditions, with heating rates >103°C / sec and a peak temperature up to 2400 °C, providing sufficient energy to break Ca-0 and Si-0 bonds and then fusing the components into cement.

[0035] Instead of relying on expensive supplies, the experiment utilized carbon fibers derived as a byproduct of methane pyrolysis, presenting an additional upcycling opportunity in chemical engineering alongside recycling cement waste. Furthermore, other conductive fibers can be viable alternatives in this process with identical results. One should note that the discussion here focuses on carbon fibers as that is what was used in experiments, both the conductive fibers may comprise carbon, carbon resulting from methane pyrolysis, steel, copper, aluminum, and carbon nanotubes.

[0036] The inventors selected 7.5 pm-diameter carbon fibers with a skin depth of a 2.45 GHz microwave (14.3 pm) and a high aspect ratio (60,000:7.5) to enhance energy conversion efficiency22, reaching up to 65%. The conductive carbon fibers strongly interacted with microwaves, resulting in charge separation and accumulation at the tips. Townsend discharge occurs when the potential difference overcomes the electrical resistance of the medium. These localized micro-sparks accelerate gas ionization, leading to corona discharges that bridge any gaps between charged particles and ultimately expand into volumetric, stable plasma.

[0037] The one-step microwave-carbon plasma heating system simplifies the pre-heating, precalcination, and sintering processes by melting all raw materials at 2400 °C, thereby drastically accelerating reaction kinetics by two orders of magnitude, from 45 minutes to just 20 seconds. Traditional kilns powered by fossil-fuel combustion experience a huge heat losscaused by a 600 °C temperature difference between flamed gas and solid meal. The system of the embodiments eliminates the heat waste inherent in traditional kilns by directly heating the raw materials as they are attached to carbon fibers and embedded within the plasma environment.

[0038] By optimizing operational parameters such as heating time, particle size, and fiber-to-solid ratio the embodiments achieve uniform temperature distribution, rapid heating(103°C / sec) and cooling rates (102°C / sec), with high sintering temperatures (up to 2400 °C), thus, far outperforming the state-of-the-art rotary kilns in cement production. The solidified clinker can be easily separated from the fibers through shaking and sieving. These nodules are highly porous, with micrometer-sized isolated pores accounting for a -35% porosity. The porosity may result from densification and shrinkage during the melting and gas release in the cooling process. These characteristics suggest excellent grindability, facilitating subsequent cement processing. The clinker nodules can be finish-milled into granules with irregular shapes. Different clinker phases can be roughly distinguished based on their intensity variations.

[0039] Unlike the primary solid-phase reactions with limited aluminate melts in conventional clinkering processes, such as shown in the phase diagram of FIG. 1, and FIGs. 4A and 4B, the designed method is dominated by liquid-phase reactions. FIG. 4A shows temperature profiles for raw meal and gas in a commercial precalciner kiln system compared to the MIP method. FIG. 4B shows a diagram of raw meal transitioning to clinker in a conventional kiln over time.

[0040] The liquid-phase reactions, as shown in FIG. 5, enhance mass transfer and lead to a critical increase in reaction kinetics. Using high-resolution in situ transmission electron microscopy (TEM), one can directly track the atomic-scale structural evolution during the reactivation of clinker from waste cement. Upon heating hydrated cement paste to 1400 °C, the structure rapidly melts into a molten state, characterized by its amorphous features and fluid-like mobility. During rapid cooling to room temperature, dynamic clinkering processes emerge, with multiple clinker phases precipitating from the melt. The liquid-solid interface facilitates the coalescence of small clinker crystallites into larger domains. Within one second, one can observe crystallite growth with well-defined grain boundaries, marking the onset of phase separation out of the undercooled melt. In just 10 seconds, the molten phase solidifies into a defect-rich microstructure that underpins the high reactivity of the sustainablecement. These dynamic, ultrafast processes reveal an entirely new pathway for low-carbon, circular cement production.

[0041] As discussed above the embodiments developed two major cement clinkers, referred to herein as ultrafast high-temperature plasma cements (UHPC). Raw meal (RM) and hydrated cement paste (HCP) were re-clinkered into new (NEW) and recycled (RCL) clinkers, respectively. Both clinkers exhibited identical crystal phases to those found in commercial clinkers, as shown in FIG. 6A. While it is expected that RM containing limestone and clay can be activated into the NEW clinker, the RCL clinker produced from HCP demonstrates great environmental potential for recycling cement waste. The technique offers a promising solution for re-clinkering concrete waste, supplementing the current landfill practices. The phase composition of clinkers is consistent with commercial clinker (COMM) produced from a rotary kiln as shown in FIG. 6B. Alite is the dominant phase in Portland cement clinker25, comprising approximately 50-70% by mass. The NEW clinker exhibits a higher alite content due to the ultrahigh-temperature heating process, while the RCL clinker shows a comparable alite amount, possibly attributed to sufficient sulfate volatilization26that assists the transformation of belite into highly reactive alite — a grand challenge in commercial re-clinkering of concrete waste27.

[0042] Further microstructure analysis confirms that alite and belite are the primary phases as shown in the focused ion beam (FIB) thinned cross section of the clinker, where most regions exhibit high calcium and silicon concentrations. Pseudohexagonal alite crystals, exceeding 6 pm in size, are bounded by interstitial phases such as aluminate and ferrite. The alite grains exhibit single-crystalline features with well-defined facets, whereas the finer-grained aluminate and ferrite particles are more rounded with lower crystallinity. Minor constituents can be readily incorporated into the crystal structure, e.g., dopped magnesium ions may be used to stabilize the monoclinic polymorph of alite28. Elemental differentiation in 3D was accomplished using STEM-EDX nanotomography, revealing angular alite grains aggregated with smaller belite particles. Additionally, amorphous silica, a byproduct of the high-temperature synthesis process, attaches to the grains. Industrial silica fume (< 1 pm) is well-recognized as a beneficial supplementary cementitious material, enhancing the mechanical strength of concrete. Periclase (MgO) clusters were also identified, comprising less than 1% of the composition. While MgO can dissolve in the clinker melt, it may become “dead burnt” and persist throughout the clinkering process, resulting in free periclase in the final product. The rapid cooling process employed in the system (102oC / sec) promotes clinker reactivity byintroducing various structural defects. Twinning was observed in belite crystals using HRTEM imaging, while dislocations and stacking faults are characteristic of high-temperature phase transformations. During crystal nucleation and growth, necking and coalescence frequently induce grain boundary formation. The defect density in UHPC clinker is notably high and may confer advantages in hydration kinetics33, contributing to improved cement hydration performance.

[0043] The ultrafast heating process traps a high density of structural defects in the sustainable cement, with its reactivity significantly enhanced. For example, alite, monoclinic C3S, the dominant phase in cement clinker, exhibits notable crystallographic disorder, likely a consequence of the rapid heating and cooling rates. This nonequilibrium synthesis pathway promotes lattice imperfections that are typically suppressed in conventional slow-fired clinkering, offering new opportunities to engineer the phase structure and hydration kinetics of cement at the atomic scale. An atomic displacement map highlighted significant localized heterogeneity, particularly near the surfaces, serving as active sites influencing early-stage hydration kinetics. The in-situ TEM experiment captured single-facet dissolution behaviors at the atomic level. Within a gas cell flowing water vapor at 2 Torr, the originally flat (11-3) C3S surface roughens, accompanied by the etching and reconstruction of surface atoms. At 62 sec, calcium silicate clusters become clearly visible, fluctuating between the surface and the surrounding space (85 sec). By 146 sec, a deep valley and stepped surface have formed. By precisely controlling the electron dose and vapor pressure, one could observe a distinct interplay between water vapor and the m-CriS substrate during hydration.

[0044] The method can be extended to the synthesis of various single-phase materials, including m-CsS, P-C2S, C-C3A, and 0-C4AF as shown in FIG. 7, as validated by PXRD, STEM-EDX element mapping, and HRTEM atomic structure identification, lending itself to broad applications in producing engineering cements with diverse compositions. As discussed above regarding FIG. 3, the method can involve preheating limestone in raw meal production, and precalcining clays. Precalcining clays at 34 in FIG. 3 can allow formation of LC3cements 44. LC3 refers to Limestone Calcined Clay Cement, a sustainable, low CO2 concrete alternative, with L3C clinker being the clinker used to create that cement. The method can produce calcined layered double hydroxides for improving concrete durability.

[0045] The method can also reactivate low-grade supplementary cementitious materials such as fly ash and slag. As shown in FIG. 3, fly ash 50 and slag 52 are by-products of otherindustrial processes and can be reactivated as supplementary cementitious materials 54 using the MIP process.

[0046] The MIP method is highly effective for reactivating low-grade supplementary cementitious materials (SCMs) such as fly ash and slag. Fly ash, a by-product of coal combustion, often contains a high proportion of crystalline phases in its low-grade forms, which reduces its pozzolanic reactivity. When combined with controlled cooling, the MIP heating process significantly increases the proportion of the amorphous (glassy) phases. This transformation enhances the reactivity of fly ash, making it more suitable for producing high-performance concrete. The resulting fly ash improves the workability and strength of the concrete mix, meeting the growing demand for sustainable construction materials.

[0047] Reactivated fly ash not only becomes a valuable resource but also helps reduce waste from industrial processes, aligning with circular economic principles. Slag, another common SCM derived from metallurgical processes, contains metal ions such as lead, zinc, or chromium, which can negatively affect its dissolution and cement hydration kinetics. These ions can interfere with cement hydration, resulting in a low degree of hydration with reduced strength. The MIP method addresses this issue by enabling the separation or neutralization of these harmful ions during the rapid heating process to produce reactivated slag having either a lower number of metal ions or having neutralized metal ions. This capability improves the hydration kinetics of the slag and reduces the environmental risks associated with its use. For example, by removing or immobilizing toxic ions, the slag becomes safer to handle and more sustainable to incorporate into concrete production.

[0048] Additionally, the microwave-plasma heating process is suitable for layered double hydroxide synthesis in solution. The technique is compatible with the most abundant elements in the Earth’s crust, underscoring its potential impacts on the production of high-performance ceramics34, cathode oxides for batteries35, and effective electrocatalysts36, with applications spanning civil, environmental, energy, and material science fields.

[0049] The cements were engineered with 3-6% gypsum to meet ASTM workability standards and were further fabricated into specimens and handiwork. No early or flash setting, nor bleeding, was observed. By controlling clinker grinding to a similar particle size distribution (Dso~ 15 pm), all cements exhibited comparable hydration heat evolution, with a slight increase in total heat for NEW cement as shown in FIG. 8A, which correlates with its higher alite content observed in PXRD quantification. Both NEW and RCL cementsdemonstrated compressive strengths equivalent to COMM cement, as shown in FIG. 8B. Notably, carbon fibers separated during the process can be reused for plasma heating.

[0050] In lab-scale demonstration, the fibers can be manually separated or separated using a laboratory vibration table along with the reacted cement powders. The separated carbon fibers can then be reused for other rounds of MIP experiments. While the carbon fibers may undergo some oxidation during the high-temperature process, only the fiber surfaces are mildly oxidized due to the short reaction time less than 1 minute. The lab experiments show that these carbon fibers can be reused at least 100 times.

[0051] Another embodiment involves in-situ prepared carbon fiber reinforced cement. In addition to using recycled carbon fibers, the embodiments include an in .s / 7 / / -prepared carbon fiber reinforced cement that does not require separating the fibers from the synthesized cement, leaving the fibers in the synthesized cement. Carbon fibers serve as reinforcement, significantly enhancing the tensile strength of the cement by improving the adhesion between the cement matrix and fibers, as well as ensuring better dispersion. Beyond producing ordinary Portland cement, the carbon-fiber-reinforced cement exhibits exceptional tensile strength, four times higher than plain cement with a 5% carbon fiber addition.

[0052] The liquid phase in traditional cement manufacturing is essential for clinker nodulization and mineral formation37. Our one-step heating technique maximizes 100% liquid-phase transformations, whereas conventional rotary kilns must restrict molten phases to below 30% to preserve refractory linings. To enable industrial integration, we propose two production routes that differ from sintering cements in rotary kilns over 50 m long: a roll-to-roll system with our microwave-carbon plasma reactor or an upgrade to existing vertical Shaft kilns for continuous production. These setups offer spatial flexibility and could be deployed as modular cement reactors near quarries or construction sites, thus reducing transportation costs, which account for up to 20% of the total expense in concrete production.

[0053] FIG. 9 shows an embodiment of an industrial-scale MIP apparatus for cement production In FIG. 9, mixer 60, mixes and homogenizes the materials, such as raw meal or HCP, with conductive fibers to ensure uniform particle distribution. The processed material can then be fed into one of two scalable clinkering production options. The lower left shows a vertical reactor embodiment. In this embodiment, the raw feedstock is continuously introduced from the top of reactor 62, with reaction time precisely controlled by adjusting the dropping rate. The material is rapidly heated as it passes through a microwave-carb on plasmareaction zone 62 reaching temperatures exceeding 2400 °C in seconds. The molten or partially molten product then undergoes controlled cooling at the bottom of the reactor, or cooler, to solidify into clinker nodules while preventing unwanted phase transformations.

[0054] The lower right shows a roll-to-roll embodiments that employs a transport surface such as a conveyor system, where the material moves through a plasma heating zone 62 under a controlled feed rate, allowing for continuous clinkering production. The roll-to-roll approach enables efficient scaling by extending processing length and optimizing exposure time. A rapid cooling system 64 is integrated immediately downstream to regulate clinker crystallization and composition, ensuring the formation of desired mineral phases. Both scale-up strategies incorporate precise cooling control, a critical factor in tailoring clinker phase composition and optimizing material performance. These approaches provide a pathway for industrial-scale implementation of the microwave-carbon plasma process, offering a sustainable and energy-efficient alternative to conventional cement manufacturing.

[0055] FIG. 10 shows an alternative view of an embodiment of the system.

[0056] Cement production contributes -7.5% of global CO2 emissions. The process significantly reduces emissions by drastically shortening clinker production time and utilizes feedstock from concrete waste instead of solely relying on limestone, thus, presenting a viable pathway to eliminate the cement industry’s dependence on fossil fuels. Microwave-carbon plasma technology enables cement synthesis within seconds and supports clean, fossil-free heating when powered by renewable electricity, achieving up to 70% electrification while reducing overall energy input by as much as 30%. By utilizing recycled concrete fines and industrial by-products, CO2 emissions can be reduced to less than 0.1 ton per ton of clinker produced. However, it is acknowledged that the carbon footprint of the process may increase if the concrete waste has substantial carbonation. With its scalability, this technique has the potential to achieve gigaton-scale CO2 reductions globally, paving the way for the cement industry to adopt sustainable practices, and advance toward the 2050 goal of carbon-neutral cement.

[0057] The above embodiments employ a microwave inducted plasma heating process in the manufacture of cementitious materials, provide new cements from raw meal, or demolished concrete fines, can reactivate supplementary cementitious materials, and can produce in-situ prepared carbon fiber reinforced cement.

[0058] Additionally, this written description makes reference to particular features. It is to be understood that the disclosure in this specification includes all possible combinations of thoseparticular features. For example, where a particular feature is disclosed in the context of a particular aspect, that feature can also be used, to the extent possible, in the context of other aspects.

[0059] Also, when reference is made in this application to a method having two or more defined steps or operations, the defined steps or operations can be carried out in any order or simultaneously, unless the context excludes those possibilities.

[0060] All features disclosed in the specification, including the claims, abstract, and drawings, and all the steps in any method or process disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in the specification, including the claims, abstract, and drawings, can be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise.

[0061] Although specific aspects of this disclosure have been illustrated and described for purposes of illustration, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention should not be limited except as by the appended claims.

Claims

CLAIMS:

1. A method of manufacturing cement, comprising:mixing cementitious raw materials with conductive fibers to produce a mixture; and treating the mixture with microwaves to produce cementitious materials.

2. The method as claimed in claim 1, wherein mixing the cementitious raw materials comprises mixing new cementitious raw meal with conductive fibers, and the cementitious materials comprise new clinker.

3. The method as claimed in claim 2, further comprising:treating limestone with microwaves to produce preheated limestone; and mixing the preheated limestone with clay to produce the new cementitious raw meal.

4. The method as claimed in claim 2, further comprising:treating clay with microwaves to produce precalcined clay; andmixing the precalcined clay with limestone to produce new cementitious raw meal, and the cementitious materials comprise L3C clinker.

5. The method as claimed in claim 1, wherein mixing the cementitious raw materials comprises mixing recycled cementitious raw meal from recycled concrete fines.

6. The method as claimed in claim 5, wherein the recycled cementitious raw meal is hydrated to first form hydrated cement paste.

7. The method as claimed in claim 1, wherein the conductive fibers comprise one or more of carbon, carbon resulting from methane pyrolysis, steel, copper, aluminum, and carbon nanotubes.

8. The method as claimed in claim 1, further comprising separating the cement from the conductive fibers and recycling the conductive fibers.

9. The method as claimed in claim 1, wherein treating the mixture to produce cementitious materials comprises leaving the conductive fibers in the cement to produce a fiber-reinforced cement.

10. A method of reactivating supplementary cementitious materials (SCM), comprising treating the SCM with microwaves to reactivate the SCM for further use.

11. The method as claimed in claim 10, wherein the SCM comprises fly ash and reactivating the SCM produces comprises reactivating fly to produce reactivated fly ash having a higher proportion of amorphous phases than the fly ash.

12. The method as claimed in claim 10, wherein reactivating the SCM comprises reactivating slag producing reactivated slag having one of either a lower number of metal ions than the slag or having neutralized metal ions.

13. An apparatus comprising:a mixer to mix cementitious raw materials and conductive fibers to produce a mixture; a plasma reactor to treat the mixture and form an at least partially molten product; and a cooler to cool the at least partially molten product into cementitious materials.

14. The apparatus as claimed in claim 13, wherein the plasma reactor comprises a plasma reaction zone configured to receive the mixture from a top of the plasma reaction zone and the cooler is positioned below the plasma reaction zone to receive the at least partially molten product from the plasma reaction zone.

15. The apparatus as claimed in claim 13, further comprising a roll-to-roll system having a transport surface configured to receive the mixture, wherein the plasma reactor is positioned adjacent the transport surface and the cooler is positioned after the plasma reactor on a path formed by the transport surface.

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