Method for capturing carbon in biocarbon

Abstract

Methods of capturing carbon in biochar are provided. The method includes mixing the biochar with an alkaline solution to form an intermediate mixture, and exposing the intermediate mixture to a CO2 source to precipitate calcium carbonate over and in the biochar to form a CO2 weathered biochar. In some cases, the method further includes injecting CO2 into the alkaline wastewater to sequestration / store CO2, which may then be used as mixed water for the production of cementitious composites. The method can be used for upgrading three waste streams, and the treated CO2 weathered biochar maintains the compressive strength of the obtained concrete when replacing part of the pre-cured cement and aggregate components. In addition, the treated CO2-weathered recycled aggregate maintains the mechanical strength of the obtained concrete when replacing part of the aggregate.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 488,440, filed March 3, 2023, and U.S. Provisional Patent Application No. 63 / 619,227, filed January 9, 2024, which are incorporated by reference herein as if fully set forth herein.

[0003] FEDERALLY SPONSORED RESEARCH

[0004] This invention was made with government support under Grant No. 69A3551947137 awarded by the U.S. Department of Transportation. The government has certain rights in the invention. TECHNICAL FIELD

[0005] The present disclosure relates to the use of spent alkaline solutions to treat biochar and optional recycled aggregates to increase carbon capture in cement-based composites. In addition, the present disclosure relates to carbonation of alkaline solutions for use as mixing water for further carbon capture in cement-based composites. BACKGROUND

[0006] Cement-based concrete structures remain an important part of the built environment, but existing methods and formulations are considered a major source of anthropogenic CO2 emissions, thereby threatening the sustainability of human society.

[0007] Biochar (B) is produced from pyrolysis of various feedstocks (e.g., biomass) and exhibits great potential in stabilizing and storing CO2. Biochar has been increasingly added to concrete applications to be used as supplementary cementitious materials (SCMs). Favorable utilization of biochar in cementitious materials is typically limited to no more than 5 wt% of cement, i.e., far from carbon neutrality. Beyond this ratio, the mechanical strength of the cementitious material is greatly reduced.

[0008] Despite recent progress in utilizing biochar to achieve net carbon neutral / carbon negative concrete, technical barriers remain, including: weak biochar strength, poor interfacial transition zone (TTZ) performance between biochar and cement matrix, and performance of biochar-modified cement-based composites not meeting regulations.

[0009] Accordingly, there is a need to adapt different types of biochar (produced from various feedstocks) for production of cement-based composites with different requirements in mechanical performance and durability for various building and construction applications. The present disclosure addresses this need. SUMMARY

[0010] The present disclosure provides a low-cost and simple method of capturing carbon in biochar to produce cement-based composites with greatly reduced carbon footprints, including carbon neutral and carbon negative concretes and other cement-based composites (e.g., strain hardening engineered cementitious composites, foamed concrete, shotcrete, 3D printable concrete, wood / concrete composites, and cement stabilized soil). Furthermore, the present disclosure combines similar carbonation strategies of recycled aggregates and alkaline solutions to further sequester / store CO2 and benefit carbon neutral / negative concretes.

[0011] One aspect of the present disclosure provides a method of capturing carbon in biochar, comprising mixing biochar with an alkaline solution to form an intermediate mixture; and exposing the intermediate mixture to a source of CO2 to precipitate calcium carbonate on and in the biochar to form CO2 weathered biochar. In some embodiments, CO2 is also injected into the alkaline solution to sequester / store CO2, and then the carbonated alkaline solution is used to mix the cementitious material when the pH of the solution reaches 7 or higher. In some embodiments, the method further comprises repeating the mixing and exposing steps to treat the intermediate mixture with additional amounts of the alkaline solution. In some embodiments, the alkaline solution comprises supernatant of concrete wash water. In some embodiments, the volume ratio of the alkaline solution to the biochar is 3: 1 to 1 : 1. In some embodiments, the source of CO2 is gaseous CO2 and / or carbonic acid. In some embodiments, the carbonation comprises exposure to air and / or injection of gaseous CO2 into the solution.

[0012] Another aspect of the present disclosure provides CO2 weathered biochar and / or recycled aggregates and / or carbonated alkaline solutions made by the methods described herein.

[0013] Another aspect of the present disclosure provides a method for capturing carbon in a cement-based composite, comprising mixing a biochar and / or recycled aggregate with an alkaline solution to form an intermediate mixture; exposing the intermediate mixture to a source of CO2 to precipitate calcium carbonate on and in the biochar to form a CO2-weathered biochar and / or recycled aggregate; and mixing the CO2-weathered biochar and / or recycled aggregate with cement and water to form the cement-based composite. Carbonation of the alkaline solution can comprise injecting gaseous CO2 into the alkaline solution until its pH reaches 7 or higher, which is then used as mixing water for production of the cement-based composite. In some embodiments, the biochar comprises particles having a size of 150 microns or less. In some embodiments, the CO2-weathered biochar replaces 1% to 80% by mass of the total dry intermixed amount of cement in the cement-based composite. In some embodiments, the CO2-weathered biochar replaces 1% to 40% by mass of the total dry intermixed amount of cement in the cement-based composite. In some embodiments, the biochar comprises particles having a size greater than 150 microns. In some embodiments, the cement-based composite further comprises aggregate, and the CO2-weathered biochar replaces 1% to 20% by mass of the total dry intermixed amount of aggregate in the cement-based composite. In some embodiments, the cement-based composite does not comprise any aggregate. In some embodiments, the biochar and / or water is carbonated. In some embodiments, the recycled aggregate (e.g., recycled concrete aggregate) is mixed with pure water instead of the alkaline solution to sequester / store CO2. In some embodiments, the carbonation comprises exposure to air and / or injection of gaseous CO2 into the solution. In some embodiments, the carbonated recycled aggregate is used to partially replace fine aggregate when its size ranges from 150 microns to 9.5 millimeters; to partially replace coarse aggregate when its size is greater than 9.5 millimeters; and as a filler and / or reactant for the cement-based composite when its size is less than 150 microns.

[0014] In some embodiments, the cement-based composite has increased compressive strength compared to a corresponding cement-based composite that does not contain the CO2-weathered biochar. In some embodiments, the cement-based composite is selected from the group consisting of concrete, paste, grout, mortar, and cement stabilized soil. In some embodiments, the method further comprises pretreating the biochar with a solution containing a nanomaterial prior to mixing the biochar with the alkaline solution. In some embodiments, the method further comprises pretreating the biochar with one or more oxidizing agents prior to mixing the biochar with the alkaline solution. In some embodiments, the biochar is a surface-modified biochar. In some embodiments, the cement-based composite further comprises a fibrous material.

[0015] Another aspect of the present disclosure provides a cement-based composite prepared by the methods described herein.

[0016] Additional features and advantages of the present application will be set forth in the description that follows, and in part will be apparent from the description, or can be learned by practice of the application. The present application will be realized and attained by the compositions and methods particularly pointed out in the written description and claims. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The process of concrete wash water and biochar synergistic capture of CO2 is shown.

[0018] Figure 2 Compressive strength of 7 days and 28 days of treated biochar paste samples are shown.

[0019] Figure 3A Thermogravimetric analysis / derivative thermogravimetric analysis (TGA / DTG) of raw biochar and treated biochar is shown.

[0020] Figure 3B Fourier transform infrared spectroscopy (FTIR) results of raw biochar and treated biochar are shown.

[0021] Figure 3C TGA / DTG of Portland limestone cement (PLC), PLC + 30 wt% biochar (B), and PLC + 30 wt% of CO2 weathered biochar (CWB) pastes are shown.

[0022] Figure 3D Representative microstructure of PLC-biochar pastes are shown. Inset shows precipitated calcium carbonate on the surface of CWB.

[0023] Figure 4 Flow chart for an exemplary embodiment of treating CWB for use as SCM.

[0024] Figure 5 Concrete compressive strength comparison of once treated biochar and three times treated biochar is shown.

[0025] Figure 6 Concrete compressive strength of different biochar dosages at 15 wt% replacement rate is shown.

[0026] Figure 7 Concrete compressive strength of different biochar dosages at 20 wt% replacement rate is shown.

[0027] Figure 8 Compressive strength of 5 wt% biochar replacement of cement is shown.

[0028] Figure 9 Compressive strength of 10 wt% biochar replacement of cement is shown.

[0029] Figure 10 The 28-day compressive strength of selected PLC pastes using various chemically treated biochar is shown.

[0030] Figure 11 The FTIR plot of selected biochar samples is shown.

[0031] Figure 12 The compressive strength and thermal conductivity of designed foam concrete is shown.

[0032] Figure 13A The compressive strength of biochar-modified samples is shown.

[0033] Figure 13B The total shrinkage of ECC samples over 50 days is shown.

[0034] Figure 14 The compressive strength of ECC samples containing biochar is shown.

[0035] Figure 15 The total shrinkage of ECC samples containing biochar is shown. DETAILED DESCRIPTION

[0036] In the description herein, the use of the singular includes the plural unless specifically contraindicated or clearly intended otherwise by the context. Further, it should be understood that any possible candidate or alternative for a given component or embodiment listed for that component can generally be used individually or in combination with each other unless specifically contraindicated or clearly intended otherwise by the context. Further, the drawings are not necessarily to scale, where some elements can be drawn larger or smaller than actual size for clarity. Further, reference numerals can be repeated in various drawings to show corresponding or analogous elements. Further, any such list of candidates or alternatives is merely illustrative and not limiting unless specifically contraindicated or clearly intended otherwise by the context. Further, unless otherwise indicated, numbers expressing quantities of components, compositions, reaction conditions, and the like used in the specification and claims are to be understood as being modified in all instances by the term “about.” This includes but does not necessarily encompass the precise quantitative values.

[0037] Accordingly, unless indicated to the contrary, numerate parameters listed in the specification and attached claims are approximations and can vary depending upon the desired properties to be obtained by the subject matter shown herein. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerate parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broadest scope of the subject matter shown herein are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

[0038] Various embodiments of carbon capture are described herein. In the following description, specific details of systems, components and operating procedures are included to provide a thorough understanding of certain embodiments of the disclosed technology. Persons skilled in the relevant art will also understand that the technology can have additional embodiments. The technology can also be implemented in a number of ways, not just the ones explicitly outlined below.

[0039] As disclosed herein, "biochar" refers to a product obtained by thermal decomposition or pyrolysis of a biomass material (e.g., a carbohydrate, a cellulose, a protein-containing material, and / or a fat-containing material, such as wood, agricultural residue, manure, etc.). The degree of combustion of the feedstock depends on the equivalence ratio of moles of oxygen fed to the reactor to the number of moles of carbon equivalents in the product during heating. Thus, if the equivalence ratio is zero, i.e., no oxygen in the reactor, the process is generally referred to as a "pyrolysis" process. If the equivalence ratio is less than about 0.15, such a process is generally referred to as "pyrolysis gasification" or "flame pyrolysis gasification"; while if the equivalence ratio is about 0.15 to about 0.3, such a process is generally referred to in the art as "gasification."

[0040] Cement refers to any inorganic cementitious material, wherein the material is capable of setting with water and hardening due to the interaction of water with the components of the material, thereby acting as a binder for the material.

[0041] As used herein, "concrete" refers to any type of construction material that includes aggregates embedded in a matrix (cement or binder) that fills the space between the aggregates and binds them together.

[0042] Concrete is generally a mixture of cement, water, and aggregate. For example, Portland cement is made by heating a mixture of limestone and clay that contains oxides of calcium, aluminum, silicon, and other metals and then pulverizing the material. The aggregate particles are typically sand and gravel and / or crushed stone. When the cement is mixed with water, a chemical reaction called hydration occurs, producing a glue-like substance that binds the aggregate together to form concrete. It is noted that after concrete is placed at a construction site, the chutes of concrete trucks and the hoppers of concrete pump trucks must be flushed to remove remaining concrete before it hardens, and this flushed material is a slurry comprising a supernatant that is considered concrete wash water and a sediment that is considered a high water cementitious paste.

[0043] Supernatant refers to the liquid that is above the solid residue after crystallization, sedimentation, centrifugation, or other treatment.

[0044] Basic solution refers to a solution having a pH greater than 7, for example a pH of at least greater than 7, for example at least 7.01, 8, 9, 10, 11, 12, or greater. The solution can be a basic aqueous solution. In some embodiments, the basic solution includes basic wastewater or solutions from food processing plants, concrete mixing plants, concrete wash water, paper mills, and basic water from other industrial processes. The basic solution can include supernatant and / or precipitate from such sources.

[0045] Recycled aggregate refers to solid materials having various size distributions. In some embodiments, recycled aggregate includes recycled concrete aggregate, demolished brick, recycled low-quality sandstone, gravel, sand, slag, topsoil, ballast, and geosynthetic aggregate. In some embodiments, recycled aggregate, for example carbonated recycled aggregate, is used to partially replace fine aggregate when its size range is 150 microns to 9.5 mm, to partially replace coarse aggregate when its size is greater than 9.5 mm, and to act as filler and / or reactant for cementitious composites when its size is less than 150 microns.

[0046] Detailed description

[0047] Embodiments of the present disclosure provide for the treatment of biochar with a basic solution to capture and sequester CO2, for example CO2 in the air or in industry, wherein calcium carbonate precipitated in / on the biochar provides a biochar that is considered CO2 weathered. The resulting carbon-negative cement paste incorporating CO2 weathered biochar is advantageous to achieve increased compressive strength, for example up to 30 MPa or higher.

[0048] Using biochar of fine size (e.g., 150 microns or less) to replace cement in a mass range of 1% to 40% and / or using biochar of coarse size (e.g., greater than 150 microns) to replace fine aggregate in a mass range of 1% to 20%, the methods disclosed herein can produce cementitious composites (e.g., paste, grout, mortar, concrete, or cement stabilized soil) having zero or negative CO2 emissions over their service life. This can adapt different types of biochar (produced from various feedstocks) for the production of cementitious composites having different requirements in mechanical performance and durability for various construction and construction applications, and can achieve performance enhancement through physical milling, surface modification, nano-modification, and CO2 curing, alone or in combination. For engineering applications with lower strength requirements, the disclosed methods can further increase the replacement rate of fine biochar to cement up to 80% and the replacement rate of coarse biochar to fine aggregate up to 100%.

[0049] Exemplary biochar feedstocks include, but are not limited to, biomass from forestry residues (e.g., woody biomass), municipal biosolids, animal-derived materials (e.g., manure), waste from paper and cellulose industries, recycled plastics or rubbers, forestry and economic crop residues, energy crops, bioprocessing waste, or biomass from other agricultural sources, such as coconut shells, rice hulls, and sugar cane bagasse, as well as other solid organic waste, such as sewage sludge, and the like.

[0050] The quality of biochar can depend on pyrolysis conditions (i.e., pyrolysis temperature, heating rate, pressure, residence time) and biomass feedstock. Generally, biochar is a stable carbon-rich material with a carbon content ranging from about 50% for high-ash feedstocks at low-temperature pyrolysis temperatures (about 350°C) to as high as 93% for low-ash feedstocks when pyrolyzed at high temperatures (about 800°C). The properties of biochar, such as surface area, pore structure, particle size, morphology, and pH, can be determined by pyrolysis conditions and milling parameters. These properties are interrelated and can further influence the properties of biochar that have a direct impact on concrete durability, including water retention capacity and cation exchange capacity.

[0051] In some embodiments, the pyrolysis temperature for preparing biochar ranges from about 250-1300°C, such as 300-800°C, the heating rate ranges from about 0.1-1,000°C / s, and the reaction time ranges from about 0.5-1,000 seconds. Preferably, the biochar has a surface area ranging from about 100 m 2 / g to about 600 m 2 / g. Using the method according to ASTM D1762-84 (105C), the biochar can have a bulk density ranging from about 0.01 Mg / m 3 to about 0.90 Mg / m 3 . The biochar can have pores of various sizes, such as pores having a size ranging from about 1 pm to 100 pm. The size of the biochar particles can range from about 10 nm to 1,000 pm or more.

[0052] Biochar with smaller particle sizes has a higher surface area, which can provide additional surface area for nucleation and growth of cement hydrates. Biochar can act as a “filler” to increase the packing density of cement-based composites, and fine biochar particles act as seeds to promote cement hydration and strength development. On the other hand, biochar-modified concrete requires more water-reducing agents to offset the water absorption of biochar and maintain the sustained workability of fresh mixtures. As colloids, biochar nanoparticles have a higher surface area per unit volume relative to biochar microparticles. The associated stronger van der Waals and electrostatic forces can lead to their re-agglomeration, which is detrimental to cement-based composites. Interestingly, biochar nanoparticles have less impact on the workability of cement mortars, which can be because there is more free water available to act as a lubricant to reduce inter-particle friction.

[0053] The roughness of the biochar appearance can promote the adhesion between biochar and cement paste, helping to avoid the early failure of cement-based composites. The flexural strength and fracture energy increased by up to 10% and 83%, respectively, after the addition of biochar in cement mortar. Angular biochar particles tend to reduce the fluidity of cement mixtures by inhibiting the movement of cement paste, but can bridge the aggregates and cement matrix at the interfacial transition zone (ITZ). Extensive milling and grinding promote the formation of fine angular biochar particles.

[0054] For the pore structure and density of biochar, increasing pyrolysis temperature leads to more release of volatile matter and pore formation, resulting in biochar with higher porosity and lower density. The density of biochar is only about 30% of OPC, making it a good candidate for producing lightweight concrete structures and insulating foam concrete. The water retention capacity of biochar is highly related to its pore structure, providing internal curing for biochar-modified concrete. It has been reported that biochar can promote the formation of calcium silicate hydrate (C-S-H) and calcium hydroxide (CH). In addition, biochar made from raw materials with high silica content (such as rice husk and pulp / paper mill waste) has been reported to have pozzolanic reactivity.

[0055] In some embodiments, the biochar used herein has a mineral content of about 10-80% by weight. Biochar with sufficient mineral content (e.g., at least 10%) can induce the formation of nanoscale carbonates by CO2 weathering of biochar. Without being bound by theory, the exemplary working mechanisms of the biochar described herein are as follows.

[0056] 1) Biochar (due to its high porosity) provides an “internal curing” mechanism, constantly providing moisture to the interior of the hardened concrete, promoting the formation of additional calcium silicate hydrate (C-S-H) gel, and increasing the degree of hydration of cement particles.

[0057] 2) Biochar (fine particles with a size similar to cement particles) provides additional surface area for the nucleation and growth of cement hydrates, i.e., the potential for higher strength gain rates.

[0058] 3) Some biochar acts as supplementary cementitious materials (SCMs) because of the presence of high levels of amorphous silicate phases in biochar (i.e., pozzolanic reactivity).

[0059] 4) The presence of some biochar in concrete can densify the microstructure of hardened concrete by filling action (i.e., increasing the packing density of the mixture), thereby increasing the strength and durability of the concrete.

[0060] Typically, biochar also reduces the density and "dead load" of the cementitious material itself. Biochar can also mitigate internal stress buildup in hardened concrete through biochar's built-in porosity, thereby mitigating damage from freeze-thaw cycling, chlorate formation, sulfate attack, alkali aggregate reaction, and various other deterioration mechanisms.

[0061] The biochar concrete described herein exhibits improved resistance to shrinkage cracking (up to 15%), as well as typically 20% to 50% better resistance to freeze-thaw and deicing salts, and 20% to 40% better resistance to external sulfate attack. Two additional working mechanisms are as follows.

[0062] 1) Biochar, as a lightweight aggregate, continuously provides moisture from within the hardened concrete matrix, thereby reducing the risk of shrinkage cracking.

[0063] 2) Biochar can improve the flexural and tensile properties of concrete through "enhancement effects" (i.e., bridging / deflecting cracks) and absorbing fracture energy.

[0064] Biochar can be further modified to improve performance, as described herein. Types of biochar modification include, but are not limited to: physical milling, chemical weathering / surface modification / grafting, CO2 activation, and nano-modification.

[0065] Biochar can be pre-treated with one or more chemical reagents, such as an oxidizing agent (e.g., a strong acid, a peroxide, potassium permanganate, or a chlorate) or a high-energy beam (e.g., a laser) to produce graphene-oxide-like chemistry on the surface of the biochar. The amount of modified fine biochar can be 0-40% by weight of the total cement or more, and the amount of modified coarse biochar can be 0-20% by weight of the total fine aggregate or more. When mixing biochar with an alkaline solution, the temperature range can be from ambient (about 25°C) to 80°C, and the pressure range can be from 1 atm to 5 atm. The expected 28-day compressive strength range can be from 7,250 psi to 10,500 psi to meet various application requirements.

[0066] Surface modification of biochar includes chemical treatments such as oxidation and functional group grafting. For example, hydrogen peroxide (H2O2) or potassium permanganate (KMnO4) can be used to oxidize biochar, grafting -COOH or -OH groups, thereby introducing graphene-oxide-like chemistry on the surface of the biochar. Additionally, biochar can be pre-treated with sodium hydroxide (NaOH) to graft more -OH functional groups.

[0067] In further embodiments, a single or multiple types of nanomaterials can be used to fill or coat the fine or coarse biochar. The types of nanomaterials used can include those with nanosheet characteristics, such as: nanoclays (e.g., montmorillonite and halloysite) and graphene-derived materials (graphene, reduced graphene oxide, graphene oxide, surface functionalized graphene). Other nanomaterials can include nanoparticles or nanofibers: nanosilica, C-S-H (calcium silicate hydrate), nanohard cement, carbon nanotubes, carbon nanofibers, nanocellulose (cellulose nanocrystals, cellulose nanofibers, bacterial nanocellulose), chitin, nanocarbonates, nanoiron oxides, nanoboron, nanoalumina, and nanotitanium dioxide. These materials can work synergistically with the nanosheets mentioned above. The amount of nanomaterials used can be 0.05% to 2.0% of the total weight of the biochar, preferably 0.08% to 1.5%. First, the nanomaterials can be dispersed in water or water emulsion as much as possible by mechanical shearing force or ultrasonic force, and then mixed with the biochar.

[0068] As described herein, the biochar is mixed with an alkaline solution to form an intermediate mixture, and the intermediate mixture is exposed to a source of CO2, thereby precipitating calcium carbonate on and in the biochar to form a CO2-weathered biochar. In some embodiments, the method further comprises repeating the mixing and exposing steps to treat the intermediate mixture with additional amounts of the alkaline solution, e.g., the steps can be repeated an additional 1-50 times. In some embodiments, the volume ratio of the alkaline solution to the biochar is 10:1 to 1:1, e.g., 3:1 to 1:1. In some embodiments, the source of CO2 is gaseous CO2 (e.g., from air) and / or carbonic acid.

[0069] Further embodiments provide a CO2-weathered biochar prepared by the methods described herein.

[0070] Further embodiments provide a method of capturing carbon within a cement-based composite, comprising the mixing and exposing steps described above, and further mixing the CO2-weathered biochar with cement and water to form a cement-based composite.

[0071] Cement is a substance used in construction that sets, hardens, and adheres to other materials to bond them together. For example, cement can be used to bond aggregate (e.g., sand and gravel) together to form concrete. Cement used in construction is typically inorganic, often based on lime or calcium silicates. The methods of the present disclosure are compatible with any type of hydraulic or non-hydraulic cement. Cement can comprise a mixture of silicates and oxides. Suitable cements include, but are not limited to, Portland cement, blended Portland cement, pozzolan-lime cement, white cement, oil well cement, calcium aluminate cement, calcium sulfoaluminate cement, polymer-modified / impregnated cement, expansive cement, and cement for ultra-high performance concrete, among others. To further reduce the carbon footprint of cement-based composites, the methods described herein can also utilize unconventional cements, such as Portland limestone cement (e.g., containing 15 wt% ground limestone), supplementary cementitious materials (SCMs, such as fly ash, ground granulated blast furnace slag, silica fume, calcined clay, and natural pozzolans), calcium aluminate cement, magnesium phosphate cement, alkali-activated ash or slag, and geopolymeric binders, in place of cement.

[0072] In some embodiments, the CO2-weathered biochar having a size of 150 microns or less replaces 1% to 80% (e.g., 1% to 40%) by mass of the total dry mix of cement in the cement-based composite. In some embodiments, the cement-based composite further comprises aggregate, and the CO2-weathered biochar having a size greater than 125 microns replaces 1% to 20% by mass of the total dry mix of aggregate in the cement-based composite.

[0073] In some embodiments, the CO2-weathered recycled aggregate replaces 1% to 100% (e.g., 10-90%) by mass of the natural aggregate used in the cement-based composite, with size matching.

[0074] The composites described herein can or can not include aggregate. In some embodiments, the only aggregate present is coarse-sized biochar as described herein. Concrete aggregate is an inert filler in a concrete mixture. Exemplary concrete aggregates include, but are not limited to, recycled concrete aggregate, demolished brick, gravel, sand, recycled low-quality sandstone, slag, topsoil, ballast, and geosynthetic aggregate. Concrete aggregate can comprise 30-90% by weight of a concrete mixture.

[0075] In some embodiments, the compressive strength of the cement-based composite is increased compared to a corresponding cement-based composite that does not contain the CO2-weathered biochar. In some embodiments, the cement-based composite is selected from the group consisting of concrete, grout, cement paste, mortar, and cement stabilized soil. Aspects of the present disclosure provide cement-based composites made by the methods described herein.

[0076] Cement begins to set when mixed with water, which initiates a series of hydration chemical reactions. Water typically comprises 10-20% by weight of the mixture. The ingredients slowly hydrate and mineral hydrates set and harden. The interlocking of hydrates gives the cement its strength. Hydraulic cement cannot set by drying. Rather, proper curing requires maintaining the proper moisture content required for the hydration reactions to proceed during setting and hardening. If hydraulic cement is dried during the curing phase, the resulting product can be under-hydrated and significantly weakened. Suitable temperatures for curing are generally 5°C to 30°C. During curing, the concrete should be protected from water evaporation due to direct sun, high temperatures, low relative humidity, and wind.

[0077] The cement-based composite materials or mixtures described herein can also include one or more additional materials, such as concrete additives. For example, the mixtures can include siliceous or calcareous fly ash, slag cement, and / or silica fume. Such additives can be used in amounts of 0-10% by total weight of the solid ingredients.

[0078] In some embodiments, the cement-based composite material further comprises a fibrous material. In some embodiments, the content of recycled fibers (e.g., from textiles, carpets, composites, masks, etc.) is 0.5-2% by volume (if the diameter is a few millimeters) or 0.1-0.3% by volume (if the diameter is a few microns) to improve cohesiveness (e.g., in fresh shotcrete) and provide toughness (e.g., in hardened shotcrete). The shotcrete can be 3D printed. Nanomaterials (e.g., nanoclay, nanosilica, graphene oxide, etc.) can be used in amounts of 0.1-3.0% by weight of the biochar to ensure strength and achieve less rebound and better adhesion. The slump of the shotcrete can range from 7 cm to 12 cm.

[0079] In some embodiments, a combination of (a-olefin sulfonate sodium (AOS) + fatty alcohol polyoxyethylene ether (AEO) + Na3P04) is added: 0.1-5% by weight of cement, as a foaming agent and foam stabilizer.

[0080] In some embodiments, the composite material comprises: cement: biochar (both fine and coarse): AOS: AEO: Na3P04 = 30:70:1:2:0.75. The cement can be used in amounts of 20-60% by weight, and the biochar: 40-80% by weight. In a combination of fine biochar and coarse biochar, the content of coarse biochar can be 50% or more, which acts as built-in pores (bubbles).

[0081] The amounts of coarse and fine biochar, nanomaterials, and other raw materials can be adjusted to meet the requirements of different types of masonry mortars, such as N-type requiring 750 psi, O-type requiring 350 psi, S-type requiring 1,800 psi, typically between 2,300-3,000 psi, M-type requiring 2,500 psi, and K-type requiring 75 psi.

[0082] In some embodiments, the biochar, water, or concrete aggregate is carbonated prior to use in the methods described herein. Carbonation includes, but is not limited to, natural weathering carbonation in the atmosphere, or accelerated carbonation at set temperatures and CO2 concentrations. Recycled concrete aggregate (RCA; recycled concrete used as aggregate) or concrete demolition waste fines can be carbonated and used with biochar. The amount of biochar used can be 0-30% by weight of cement, the amount of RCA used can be 0-60% by weight of total aggregate, and the content of nanometer / micron carbonate can be 0-10% by weight of biochar.

[0083] In some embodiments, fine biochar is used to replace cement, up to 30% by weight of cement, and carbon-negative, strain-hardening engineered cementitious composites (ECC) are obtained with 28-day compressive strengths greater than 15,080 psi (104 MPa) and significantly reduced drying shrinkage. The tensile strength, initial cracking strength, and strain capacity of this biochar-ECC can reach 1,160 psi (8 MPa), 870 psi (6 MPa), and 4.8%, respectively.

[0084] As shown in the examples, a synergistic carbon capture strategy, i.e., using alkaline waste liquor together with biochar, has been demonstrated to achieve carbon-negative concrete and has been tested in the laboratory including mechanical strength and microstructural studies. This approach enables biochar to capture 22.85% or more of CO2 in the air, which precipitates calcium carbonate in / on the biochar. The 7-day and 28-day compressive strengths of carbon-negative cement pastes containing CO2 weathered biochar (CWB) and Portland limestone cement at a mass ratio of 30:70 reached 22.1 MPa and 27.6 MPa, respectively. Microstructural studies revealed the potential mechanisms of this biochar-modified concrete strength enhancement.

[0085] The pore structure and hydration products of biochar concrete can be controlled by appropriate timing and duration of CO2 curing, while increasing its sequestration of CO2. CO2 curing includes, but is not limited to, combinations of temperature, humidity, duration, and CO2 concentration. The temperature range for CO2 curing can be from ambient (e.g., about 25 °C) to 60 °C, the humidity range for CO2 curing can be from about 20% to 90%, the duration range for curing can be from about 30 minutes to 12 hours, the pressure range for CO2 curing can be from about 1 atm to 5 atm, and the CO2 concentration range can be from about 1% to 60%.

[0086] The present disclosure provides a durable, carbon-smart alternative for the construction and construction industry, which is increasingly scrutinized for its carbon footprint. The value-added application of biochar as a partial replacement of cement and / or fine aggregate can be a win-win strategy to reduce CO2 emissions and enhance carbon sequestration. The conversion of biomass to biochar can reduce CO2 emissions by about 0.4-1.2 tons per ton of dry feedstock.

[0087] For example, biochar concrete made by replacing 10% of cement and 10% of sand can be equivalent to 150% of the CO2 emissions equivalent in the manufacture of concrete. However, in many cases, the net climate offset is much greater because it depends on the alternative fate of the original waste biomass. The offset also varies with the time horizon considered, as the residence time of the greenhouse gases and aerosols (GHG / A) produced during the biomass conversion and decomposition in the atmosphere is different.

[0088] Although the application has been illustrated by a description of embodiments and specific examples, it is not the intention to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The application in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures can be made from such details without departing from the scope or spirit of applicant's general inventive concept.

[0089] It should be understood that the application is not limited to the particular embodiments described herein and, as such, many changes, modifications, variations and other uses will be suggested to those skilled in the art. The terms used herein are merely descriptive, but are not intended to be limiting.

[0090] When a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limit of that range is also contended herein. Furthermore, it is contemplated that any two values between the upper and lower limit of a range are also contemplated.

[0091] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Exemplary methods and materials are described herein; similar or equivalent methods and materials can also be used in the practice or testing of the present application.

[0092] All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the publications are cited.

[0093] The citation of any publication is for its disclosure prior to the filing date of this application. However, nothing herein is to be construed as an admission that the present application is not entitled to antedate such publication by virtue of prior application. Further, the dates of publication provided can be different from the actual publication dates which can need to be independently confirmed.

[0094] It should be noted that, as used herein and in the appended claims, the singular form "a", "an", and "the" include plural references unless the context clearly dictates otherwise. It should also be noted that the claims can be drafted to exclude any optional element. Accordingly, the specification is to be construed as supporting such exclusion unless it is explicitly stated to the contrary.

[0095] It will be apparent to those skilled in the art that each individual embodiment described and illustrated herein has discrete components and features which can be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present application. Any recited method can be conducted in the order of events recited or in any other order that is logically possible.

[0096] Examples

[0097] Example 1

[0098] The study used biochar from organic waste pyrolysis (Bioforce Tech, South San Francisco, CA) (e.g., OurCarbon TM ). Table 1 provides its chemical composition.

[0099] Table 1

[0100]

[0101]

[0102] As disclosed herein, an exemplary working embodiment was illustrated using ASTM C595 Type I Portland Limestone Cement (PLC, SAKRETE TM ) and 0.1 wt% of polycarboxylate based high range water reducer (HRWR, Master 7920, BASF). Concrete wash water (CW) was collected from previous experiments using Type I / II Portland cement, and the supernatant of the collected CW (e.g., pH value of 11.9) was used to treat the biochar at a volume ratio of, for example, 2:1. Figure 1 The beneficial carbon capture process disclosed herein was illustrated. Prior to mixing, such CO2 weathered biochar (denoted as CWB) and its counterpart (raw biochar, B) were pretreated, for example, by ball milling at a speed of 250 rpm and a material / sphere volume ratio of 1:2 for 1 hour. As used herein, ball milling particularly improved the physicochemical properties of, for example, the CO2 weathered biochar, such as the total surface and micropore surface of the material, which can enhance the adsorption capacity.

[0103] The maximum particle size of the biochar after milling was about 425 microns. To help understand the working embodiment, a control PLC and four types of PLC-biochar samples (PLC + 15 wt% B, PLC + 15 wt% CWB, PLC + 30 wt% B, and PLC + 30 wt% CWB) were manufactured. The PLC and CWB / B were first dry mixed for 3-5 minutes, water (water / total binder mass ratio of 0.35) was added for wet mixing for another 3 minutes, and then the cylindrical paste samples (D: 5 cm x H: 10 cm) were cast, wet cured, and tested according to ASTM C305, C511, and C39, respectively.

[0104] Microscopic studies were conducted on selected hardened paste samples to evaluate the CO2 capture level and reveal the enhancement mechanism of CO2 weathering on PLC-CWB composites. FEI QUANTA FEG 250 (FEI Company, USA) and VHX-7000 series optical microscope (Keyence Corp., USA) were employed to elucidate the microstructure. Fourier transform infrared (FTIR) analysis Nexus 8700, Therma Scientific, Waltham, MA) was conducted in the scanning range of 400-400 cm -1 at 4 cm -1at a heating rate of 10 °C / min from 50 °C to 1,000 °C to elucidate the changes in chemical bonds and components in the selected biochar and paste samples, respectively. TM at a heating rate of 10 °C / min from 50 °C to 1,000 °C to elucidate the changes in chemical bonds and components in the selected biochar and paste samples, respectively.

[0105] Compressive strength results

[0106] While the mixed biochar reduced the compressive strength of the PLC paste, the CO2 weathering of the biochar increased the 7-day (and 28-day) compressive strength of the 15(30)% biochar-PLC paste by 59.2% (15.5%) and 5.2% (15.3%), respectively, validating the initial thought process. For example, the compressive strength of PLC+30%CWB reached 22.1 MPa and 27.6 MPa at 7 days and 28 days, respectively, which was more than double what was previously reported. Figure 2 The observation that the mixed biochar reduced the compressive strength of the paste is in very good agreement with previous studies. The strength reduction is due to: 1) the weak strength of the biochar, which acts as an initiator of micro-defects under loading, 2) the poor ITZ between the biochar and the cementitious matrix, which promotes the propagation of cracks under loading, and 3) the heterogeneous microstructure induced by the biochar.

[0107] The synergistic carbon capture of the CW and biochar precipitated calcium carbonate onto / in the biochar (see inset Figure 3D ), which not only benefited the material strength of the biochar but also improved the ITZ between the biochar and the PLC paste through the compatibility between the calcium carbonate and the PLC hydrates. All these mechanisms further increased the mechanical strength of the paste with the CO2-weathered biochar.

[0108] Microscopic studies

[0109] Figure 3 provides the results of the microscopic studies (TGA / DTG, FTIR, SEM, and optical microscope imaging). Figure 3ATGA / DTG results of raw and treated biochar are shown, which have significant difference in thermal behavior (especially beyond 400°C). For raw biochar, the first mass loss at 50-100°C is mainly due to water evaporation, the second mass loss at 300-580°C can be attributed to the decomposition (or pyrolysis) of organic components, and the third mass loss at 600-700°C can be due to the decomposition of calcitic calcite. In contrast, the treated biochar shows less obvious pyrolysis and higher calcium carbonate content. The TGA data show that 100 grams of raw and treated biochar contain 1.55 g and 24.40 g of CO2, respectively (from decomposed calcium carbonate). The higher content of calcium carbonate (and lower content of organic components) explains the better thermal performance of the treated biochar. This result also indicates that the weathering process has captured 22.85 g of CO2 per 100 g of biochar.

[0110] Figure 3B FTIR results of raw and treated biochar are depicted. The main chemical bond in raw biochar is C=C, while the carbonate bond is more dominant in treated biochar due to the precipitation of captured CO2.

[0111] Figure 3C TGA / DTG results of PLC, PLC + 30 wt% B, and PLC + 30 wt% CWB pastes are depicted, respectively. The first mass loss is related to water evaporation and decomposition (or dehydration) of cement hydrates (e.g., C-S-H, C-A-S-H, and Aft). The second mass loss in PLC paste is due to the decomposition of portlandite (CH), while the second mass loss in PLC + 30 wt% B (CWB) can include both pyrolysis and decomposition of portlandite (including CH as PLC hydrate and uncarbonated CH from CW). The multiple mass loss peaks observed between 600-800°C are mainly due to the decomposition of carbonates, and the carbonate content in PLC + 30 wt% B (CWB) is much higher than that in PLC paste. This is not only due to the inherent calcium carbonate in biochar, but also due to carbonation caused by CO2 in air (note that CO2 can be provided by industrial CO2, such as carbonic acid) due to the porous microstructure of PLC-biochar pastes. Figure 3D ). The temperature range of the re-decomposition of carbonates in PLC + 30 wt% CWB paste is 750-950°C, which indicates that CO2 weathering has caused calcium carbonate to precipitate in different forms Figure 3D ).

[0112] Carbon footprint analysis

[0113] PLC typically contains 15% by weight of limestone and 85% by weight of ordinary Portland cement (OPC) to reduce the carbon footprint and energy consumption. The CO2 footprint of OPC is 0.9 kg / l kg OPC, so the CO2 footprint of PLC is 0.77 kg / l kg PLC (0.210 kg carbon / l kg PLC). In 1 kg PLC, the incorporation of 15% by weight of limestone sequesters an additional 0.066 kg CO2 (0.018 kg carbon), so the total carbon footprint is 0.192 kg. The carbon content of the original biochar is 32.86%, and 1 kg biochar captures 0.2285 kg CO2 (0.062 kg carbon). As such, 1 kg PLC + 30% CWB would emit 0.192 x 0.70 = 0.1344 kg carbon during the production of PLC, while the CWB itself reduces 0.3286 x 0.30 = 0.098 kg carbon and captures 0.062 x 0.30 = 0.0186 kg carbon. Figure 3C It is also shown that PLC + 30% CWB captures about 0.112 kg CO2 (0.0306 kg carbon) through its carbonation in air, which can increase over time. In total, the total carbon emissions of 1 kg PLC + 30% CWB are estimated to be -0.0128 kg = (0.1344 - 0.098 - 0.0186 - 0.0306) kg. The beneficial use of biochar in concrete also diverts carbon-rich biomass from other routes (e.g., slash pile burn and chip-and-spread). Thus, a considerable amount of avoided CO2 equivalent has not been considered in the analysis. Otherwise, the carbon negativity of the aforementioned biochar concrete would be even more pronounced.

[0114] This approach not only captures and sequesters CO2, but also upgrades both types of waste (CW and B), and promotes the industrial application of carbon-negative concrete. After 14 days of weathering, the biochar treated with concrete wash water captures 22.85% by weight of CO2 in air, and this CO2-weathered biochar renders the paste carbon-negative when it occupies 30% by weight of Portland limestone cement.

[0115] Microscopic evidence confirms that the captured CO2 precipitates calcium carbonate into / on the biochar. This treatment increases the 7-day and 28-day compressive strengths of 15 (30) % by weight of biochar-Portland limestone cement paste by 59.2% (15.5%) and 5.2% (15.3%), respectively.

[0116] Example 2

[0117] Task 1: Achieving carbon-negative biochar concrete by replacing 10% of cement and 10% of sand

[0118] Task 3: Generating graphene-like chemical properties on the surface of biochar before it is used in cement-based composites

[0119] Task 4: Grafting certain functional groups onto biochar using chemical reagents at ambient temperature

[0120] Task 5: Developing carbon-negative foam concrete using biochar.

[0121] Materials: The experimental study employed ASTM C150 Type IL Portland Limestone cement and coarse aggregate with a maximum nominal size of 3 / 8 inch (9.5 mm). Coarse aggregate was provided by a local ready-mix concrete company, Premix-Inc, Pullman, WA, and commercial all-purpose sand was used as fine aggregate. The respective specific gravities (ASTM C127) and water absorptions (ASTM Cl28) of the coarse aggregate and sand were 2.69 (1.21%) and 2.65 (4.68%), respectively. Table 2 lists the particle size distribution of the coarse aggregate and fine sand based on sieve analysis according to ASTM C136. The apparent water-to-cementitious material ratio (w / cm) of the concrete mix was 0.4; the sand / cementitious binder mass ratio was 2.0; and the coarse-to-fine aggregate mass ratio was 1.75. OurCarbon TM Biochar used in this study was provided from pyrolysis of organic waste (Bioforce Tech). Note that the biochar was dried and sieved before mixing and the biochar passing the No. 100 sieve (finer than 150 microns) was used as cement replacement and the rest (ground to finer than 4 mm) was used as sand replacement. At the time of placement, the coarse aggregate was in a saturated surface-dry condition and the water content of the fine aggregate was 0.09%. A polycarboxylate-based high-range water-reducing admixture (HRWRA) Master 7920 produced by BASF Construction Chemicals, LLC was also used to achieve the required workability. The HRWRA content varied between 0.1% and 0.3% by weight of the cementitious materials to obtain a slump of at least 2.36 inches (60 mm).

[0122] Table 0. Particle size distribution of aggregate (cumulative percent passing)

[0123]

[0124]

[0125] Table 3. Concrete mix proportions (lb / yd 3 )

[0126]

[0127] Method: Biochar preparation. For Task 1 and 2, the biochar was first modified to enhance its performance as a building material, and then added to the concrete mix. The initial untreated biochar was soaked in concrete rinse water (2:1 by volume) for 1 hour. After that, the biochar was dried in an oven equipped with a fan at 60 °C for 11 hours. This 12-hour cycle was completed once for the once-treated biochar (1T) used in this study and three times for the thrice-treated biochar (3T) used in this study. After the drying stage, the biochar was ground using an industrial spice grinder for 10 seconds. After grinding, the fine fraction of the biochar that passed through a 100-mesh sieve was collected for use as a cement substitute. The coarse biochar that was retained on the 100-mesh sieve was collected for use as a sand substitute. Note that this coarse biochar passed completely through a 4-mesh sieve.

[0128] For Task 3 and Task 4, the main chemical functional groups of graphene oxide are -COOH or -OH. Therefore, both tasks employed similar technical solutions involving the use of hydrogen peroxide (H2O2) and potassium permanganate (KMnO4) to oxidize the biochar, grafting -COOH or -OH groups, thereby introducing graphene oxide-like chemical properties on the surface of the biochar. In addition, to differentiate the two tasks, we used sodium hydroxide (NaOH) to pretreat the biochar in Task 4 with the goal of grafting more -OH functional groups. Two types of biochar were selected: one (B1) was provided by OurCarbon TM and the other (B2) was a wheat straw-derived biochar produced by Qualterra, Spokane Valley, WA. All biochars were first ground to less than 125 pm before chemical treatment (e.g., oxidation and functional group grafting). The type, concentration, and treatment time are shown in Table 4. After chemical treatment, all biochars were washed multiple times until the pH of the wash water was close to 7.0. Subsequently, all treated biochars were dried before use, ready to substitute Portland Limestone Cement (PLC).

[0129] Table 4. Particle size distribution of aggregates (cumulative % passing)

[0130]

[0131] Note: H2O2, KMnO4, NaOH are denoted as HO, KM, and Na, respectively. For example, HO-C5-6 means treatment with 5% concentration of H2O2 for 6 hours.

[0132] For Task 5, the modification of biochar is similar to Task 1 and Task 2, but the weathering cycle is different. The 12-hour cycle is completed for 6 times. In addition, in order to guarantee the pore structure of the target foam concrete, no further grinding is carried out in this task.

[0133] Mixing procedure and sample preparation. For Task 1 and 2: First, the coarse aggregate is pre-soaked in water for at least 48 hours, then wiped dry with a towel to achieve a saturated surface dry (SSD) condition. Once the amount of material is weighed, the mixing water is divided into three parts. One part is used to pre-soak the fine biochar, ensuring that there is enough water to cover its surface. The second part of water is used to pre-soak the coarse biochar. Note that the water is added to the biochar for pre-soaking about 30 minutes before mixing. A small portion of the remaining water is mixed with the HRWRA, and the rest is added during the mixing stage. First, the coarse aggregate is placed in the mixing drum and stirred for a few rounds. Then, the HRWRA is added, followed by the sand, cement, and water. Finally, the pre-soaked biochar is added to the drum and stirred for five minutes. Then the concrete sample is poured with a diameter of 4 inches (100 mm) and a height of 8 inches (200 mm), cured in a saturated lime water bath, and tested according to ASTM C39 and C143, respectively.

[0134] For Task 3 and Task 4: The mixing ratio of all biochar-PLC pastes is biochar: PLC = 20:80 (mass), and the mass ratio of water to all solid materials is 0.40; polycarboxylate-based superplasticizer is used during mixing to achieve reasonable fluidity of the paste. Before mixing, the biochar is pre-saturated in water. The preparation of these biochar-PLC paste samples follows the specifications of ASTM C192, and fresh paste is poured into a cylindrical mold with dimensions of 5 cm (diameter) x 10 cm (height). After 24 hours of hydration and hardening, all hardened paste samples are demolded and cured in a standard environment for another 27 days for compressive strength testing according to ASTM C39.

[0135] For Task 5: According to our previous study (Li et al., 2017), foaming agent (a-olefin sulfonate: AOS) and foam stabilizer (sodium phosphate: Na3P04) were used in this task. The mixture design of the control PLC foamed paste was PLC:AOS:Na3P04=200:5:2, and the water-binder ratio was 0.3 by mass. Thirty percent by weight of biochar (carbonated or raw) was chosen to replace PLC to prepare PLC-biochar foamed paste. First, the weighed water, AOS, and Na3P04 were mixed to make a solution, and then the solution was divided into three parts and added to the dry binder every 2 minutes. After pouring all the solutions into the blender (4 minutes), the speed of the blender was adjusted to fast mode and blended for another 4 minutes to obtain fresh foamed paste. Then the paste was cast into cylindrical molds with a size of 5 cm (diameter) x 10 cm (height) for compressive strength testing and flat plate molds with a size of 2.5 cm (height) x 10 cm (width) x 10 cm (length) for thermal conductivity testing. After 28 days of curing, all samples were dried for 24 hours before testing. Table 5 provides the information of the designed foamed concrete.

[0136] Table 5. Design mixing ratio of foamed concrete (unit: g)

[0137]

[0138]

[0139] Results and Discussion

[0140] For Task 1 and Task 2: Carbon-negative biochar concrete was achieved by replacing cement and sand.

[0141] Throughout the discussion, the concrete mixtures containing untreated, once-treated, and thrice-treated biochar are denoted by the prefixes 0T, 1T, and 3T, respectively. Figure 5 An overview of the compressive strength of concrete containing 1T biochar and 3T biochar is shown. However, with two additional cycles of pretreatment (3T compared to 1T), the compressive strength of biochar concrete with cement replacement rates of 5% and 10% only increased slightly by 89 psi (1.20%) and 91 psi (1.27%), respectively. Therefore, only 1T biochar was used for comparison in the remaining part of this study.

[0142] Figure 6The compressive strength of various biochar concrete samples at 5% and 15% replacement rates is shown. Notably, the 1T compressive strength exceeds the 0T, indicating that the BC5%, BC15%, and BC5%-BS10% biochar concrete samples have an increase in compressive strength of 2.27%, 7.32%, and 9.94%, respectively. Furthermore, the data indicates that the concrete compressive strength is improved by 40.2% when replacing 5% of the cement with 1T fine biochar and 10% of the sand with 1T coarse biochar, compared to replacing 15% of the cement with fine biochar. This observation suggests that replacing both cement and sand with biochar can improve the potential for carbon neutrality. This can be primarily due to the large mass of sand in the concrete mix, resulting in a large amount of coarse biochar when replacing the sand. In this study, the coarse biochar (retained on the 150 pm sieve) is much finer than the sand particles. Therefore, replacing the sand with biochar increases the fine particles in the mix, resulting in better packing and higher strength. Furthermore, the biochar absorbs a significant amount of moisture, and since we did not perform moisture correction, this change significantly reduces the water / cementitious material ratio, further improving the strength.

[0143] Figure 7 The compressive strength of different biochar concrete samples at 10% and 20% biochar replacement rates is shown. Notably, the once-treated biochar exhibits superior compressive properties compared to the untreated biochar, showing an increase of 1.33%, 4.64%, and 14.1% for the BC10%, BC20%, and BC10%-BS10% samples, respectively. Furthermore, it is evident that the concrete compressive strength is improved by 68.1% when replacing 10% of the cement with 1T fine biochar and 10% of the cement with 1T coarse biochar (total of 20%), compared to replacing 20% of the cement with fine biochar. This further confirms the observation that replacing both cement and sand with biochar can improve performance while achieving carbon neutrality. Similar reasons, as explained in …, error, reference not found, can influence this behavior.

[0144] Figure 8 The change in compressive strength of concrete samples with 5% biochar replacement rate based on the weight of cement is shown. Overall, the addition of biochar, whether treated or untreated, enhances the compressive strength of the samples. Notably, in this experiment, the moisture content of the mixtures of different types of biochar (0T, 1T, and 3T) remains constant, while the workability is adjusted through HRWRA. Despite the differences in water absorption rates, the biochar is not moisture-corrected.

[0145] The effect of untreated biochar on workability was more pronounced than 1T and 3T biochar. At day seven, the 0T-BC5%-BS10% sample had a 32.6% increase in compressive strength compared to the control (100% cement sample). However, the 0T sample had only a 2.84% increase in 28-day compressive strength over the corresponding 28-day compressive strength of concrete.

[0146] In contrast, 1T-BC5%-BS10% had a 7.69% and 13.1% increase in strength at day 7 and day 28, respectively, compared to the control mortar sample. The 0T sample exhibited higher compressive strength at seven days compared to the 1T sample, but lower strength at 28 days. The higher initial strength of the 0T sample can be attributed to the high water retention capacity of untreated biochar in early-age concrete, effectively reducing the water / cement ratio of the mixture and increasing the compressive strength. However, over time, the gradual release of water (internal curing mechanism) can decrease the relative compressive strength after 28 days. For the 1T sample, the main factor affecting strength is calcium carbonate (solid) that increases the strength of biochar concrete. Figure 8 It was also shown that adding 10% biochar as a sand substitute decreases the 28-day compressive strength of biochar concrete by 10.4% and 2.61% compared to the corresponding BC5% and BC10% samples.

[0147] The target values for the 7-day and 28-day compressive strength of biochar concrete samples were 3,950 psi and 5,010 psi, respectively. However, the experimental 7-day and 28-day compressive strengths were measured to be 5,978 psi and 6,591 psi, which were 51.3% and 31.6% over the expected values, respectively. This large variation can be due to the lack of moisture correction for the added fine or coarse biochar during the mixing process, which can have led to a decrease in the water / binder ratio and an increase in strength.

[0148] Figure 9 The change in compressive strength at 7 days and 28 days is shown for a biochar cement replacement rate of 10% by weight. Similar to previous findings, untreated biochar performed better than 1T biochar at seven days, with a 2.81% and 6.14% increase for BC10%-BS10% and BC10% samples, respectively. However, after 28 days, the strength of the untreated (0T) sample BC10%-BS10% decreased by 5.17% compared to the control, while the strength of BC10% increased by 1.58%. In contrast, the 1T samples of BC10%-BS10% and BC10% had a 14.1% and 1.33% increase in compressive strength, respectively.

[0149] The target compressive strength for the combined 10% fine biochar and 10% coarse biochar at day 7 and day 28 was 5,640 psi and 6,050 psi, respectively. According to the experimental results, Figure 9, biochar concrete achieved this goal with 6.0% and 8.9% higher compressive strength at 7 days and 28 days, respectively, compared to the expected values. To further improve the mechanical properties of biochar concrete, about 10% of silica fume by weight of cementitious materials was added to the mix to achieve the expected 28-day compressive strength of 8,200 psi.

[0150] For Task 3 and Task 4: Changing the surface properties of biochar through chemical treatment for cement-based composites.

[0151] Figure 10 The 28-day compressive strength of selected PLC pastes using biochar with various chemical treatments is shown. While the introduction of biochar in PLC pastes resulted in a decrease in compressive strength, chemical treatment helped to improve the strength compared to using untreated biochar. The compressive strength results show that the longer the treatment time and the higher the chemical solution concentration, the higher the strength increase. This is likely due to the higher content of grafted functional groups (-COOH and -OH) as a result of longer treatment time and higher solution concentration. These grafted functional groups act as growth templates, accelerating the hydration process and controlling the formation of more uniform hydrates. All these benefits enhance the performance of the weak interfacial transition zone between biochar and PLC pastes.

[0152] In Figure 11 , the Fourier Transform Infrared Spectroscopy (FTIR) plot of selected biochar samples proved the existence of grafted functional groups, which provided the basis for the above-mentioned strength enhancement mechanism. Interestingly, chemical treatment also improved the workability of biochar-PLC pastes. For example, when hydrophobic B2 was used, more HRWRA was needed to ensure that workability met practical requirements. However, after treatment, the grafted -COOH and -OH transformed the biochar surface to be hydrophilic, achieving ideal workability without the need for additional HRWRA.

[0153] For Task 5: Carbon-negative foam concrete with added biochar.

[0154] Figure 12The 28-day compressive strength and thermal conductivity of the prepared foam concrete are shown. Sample 3 stands out among all the prepared foam concrete, exhibiting acceptable strength and the lowest thermal conductivity, while Sample 5 stands out among all the foam concrete with biochar admixture, as it has the highest strength and acceptable thermal conductivity. These performances also meet the general requirements of building insulation materials. Compared with traditional organic insulation materials, this biochar-PLC exhibits higher fire resistance due to its inorganic nature and built-in porosity, translating into safety and flexibility advantages in the event of a fire. By adjusting the foaming time, the foam concrete can be customized for various applications, such as backfilling roadbeds, foundation pits, and mining pits, which are traditionally done with soil and concrete. In addition to the carbon credit accumulated in the biochar foam concrete, the use of foam concrete can also avoid the subsidence risk brought by soil filling techniques and is more cost-effective than using traditional concrete.

[0155] Example 3

[0156] Carbon-negative biochar concrete can be obtained by replacing 10% of cement and 10% of sand. The mass ratio of water / cementitious binder is 0.40; the mass ratio of sand / cementitious binder is 2.0; and the mass ratio of coarse aggregate to fine aggregate is 1.75. Please note that the biochar is dried and sieved before mixing; the biochar passing through a No. 120 sieve (i.e., finer than 125 microns) is used as a cement replacement, and the rest (ground to finer than 4 mm) is used as a sand replacement.

[0157] Depending on the type of biochar used, the 7-day and 28-day compressive strengths of the biochar concrete can reach up to 5,640 psi and 6,050 psi, respectively, i.e., 45-110% and 75-110% of the control group (without biochar), respectively. If the biochar is pretreated with limewater and / or with other materials, the 28-day compressive strength of the concrete containing 10% biochar fine aggregate can reach 8,200 psi.

[0158] The amount of fine biochar (finer than 125 microns) is controlled in the range of 1-20% by weight of cement, and the amount of coarse biochar is controlled in the range of 0-20% by weight of fine aggregate.

[0159] Nano-materials (e.g., 1% by weight of nano-clay) and supplementary cementitious materials (e.g., 15% by weight of fly ash) can be used to pretreat the biochar, along with limewater, so that the resulting biochar overcomes its original weak strength limitation and becomes a strong fine aggregate (comparable to ordinary fine aggregate).

[0160] Example 4

[0161] Carbon neutral biochar concrete was obtained by replacing 5% of cement and 10% of sand. The mass ratio of water to cementitious binder was 0.40; the mass ratio of sand to cementitious binder was 2.0; and the mass ratio of coarse aggregate to fine aggregate was 1.75. Note that the biochar was dried and sieved before mixing; the biochar that passed through a 120 mesh sieve (i.e., finer than 125 microns) was used as a cement replacement, and the remainder was used as a sand replacement.

[0162] Biochar was soaked in concrete wash water, then captured C02 in air and formed nano- and micro-sized carbonate precipitates on or in the biochar, which was then mixed into fresh concrete. This strategy not only upcycles both wastes to develop sustainable construction materials, but also reduces the C02 footprint of the final product. In one example, cement pastes containing 15 wt% C02 weathered biochar achieved 7-day and 28-day compressive strengths of up to 3,950 psi and 5,010 psi, respectively, meeting the requirements of some application scenarios.

[0163] Example 5

[0164] Before using biochar in cement-based composites, we generated graphene-like chemistry on the surface of biochar using high temperature (or ambient temperature), high pressure, and oxidizing agents. We oxidized biochar with single or simultaneous / sequential combinations of oxidizing agents, followed by washing several times until the pH of the wash water reached 7. Fine biochar treated with acid replaced 20 wt% of cement in ordinary Portland cement pastes (water to cementitious binder mass ratio of 0.40), which exhibited comparable 28-day compressive strength (6,816 psi) relative to the original cement pastes.

[0165] Example 6

[0166] We used various chemical reagents or high-energy beams at ambient temperature to graft certain functional groups (-COOH, -OH) onto the surface of biochar, thereby enhancing the interface between biochar and the cement matrix. Surface-modified fine biochar was used to replace 10 wt% of cement in ordinary Portland cement pastes (water to cementitious binder mass ratio of 0.40), which exhibited comparable 28-day compressive strength (7,250 psi) relative to the original cement pastes.

[0167] Example 7

[0168] We used a small amount of nanomaterials to modify the surface or interior of biochar to enhance the performance of biochar concrete. For example, nano-modification of biochar (with 2 wt% montmorillonite nanoclay) compensated for the deficiencies of original biochar, and concrete incorporating 20% of fine biochar by weight of cement achieved a 28-day compressive strength of 7,000 psi, comparable to the control concrete without any biochar.

[0169] Example 8

[0170] Biochar-modified concrete and other biochar cement-based composites can be cured at early stages (e.g., 0.5 to 4 hours) at ambient temperature in the presence of concentrated CO2(e.g., 20% to 40%) for a certain period of time (e.g., 30 minutes) to induce the formation of nano / micro-sized carbonates and to improve the strength and durability of the materials. Depending on the type of biochar used, the 7-day and 28-day compressive strengths of biochar-modified concrete are improved by 15% to 25% through the CO2curing process. The strength improvement is more significant, in the range of 25% to 50%, if the biochar cement-based composite is pervious concrete or foam concrete.

[0171] Example 9

[0172] Table 6. Carbon-negative, strain-hardening engineered cementitious composites (ECC)

[0173]

[0174] Relative to the control (Ref.-ECC), Figure 13A It is shown that the 28-day compressive strengths of the biochar-modified samples are all slightly higher, although their 3-day compressive strengths are reduced by 10% to 40%. Figure 13B The total shrinkage of the ECC samples at 50 days is shown, with the sample that replaced 10% cement with fine biochar showing the largest reduction (20% reduction). Note that the water-cement ratio of the ECC is 0.195, i.e., autogenous shrinkage is the main factor of total shrinkage. These results confirm the effectiveness of biochar for internal curing of ECC.

[0175] Example 10

[0176] Carbon-negative foam concrete is an economical and sustainable method for backfilling roadbeds, foundation pits, and mining pits, which can replace soil backfilling or concrete backfilling. Foam concrete is produced by using one or more foaming agents, with the characteristics of lightweight and porous. Depending on the specific mix design (with CO2curing if needed), foam concrete with 28-day compressive strengths ranging from 145 psi (1 MPa) to 1,450 psi (10 MPa) can be produced, and the foam concrete does not significantly sink when it comes into contact with water, meeting the requirements of a filling material. The thermal conductivity of foam concrete can range from 0.05 W / mK to 0.25 W / mK, meeting the requirements of an insulating material. Foam concrete can also be used for sound insulation, such as sound barriers and fireproof materials.

[0177] Example 11

[0178] Carbon neutral shotcrete can be produced by adding biochar to the fresh mix. This specialty concrete is useful for repairing and reinforcing both cut and full slopes and retaining walls. We mixed modified biochar into fresh shotcrete, and this 20% biochar cement concrete achieved 28-day compressive strengths of up to 4,950 psi (35 MPa) with no significant rebound and good adhesion.

[0179] An exemplary control mix design for shotcrete is as follows. Cement: fine aggregate = 1 : 3.5-4.5, water-cement ratio = 0.42-0.50, and an amount of viscosity modifier and / or fibers.

[0180] Example 12

[0181] Low carbon footprint, vegetation growing shotcrete can be produced by adding biochar to the fresh mix. This specialty concrete is useful for repairing damaged ecosystems. We filled some nutrients and plant seeds into biochar, then mixed the biochar into fresh concrete, which was then used for vegetation growth. We utilized vacuum to absorb the solution containing necessary nutrients and seeds into coarse biochar, which was then mixed with cement, fine biochar (raw or modified), and admixtures (or fibers) to make vegetation foam shotcrete. This 50% biochar cement foam concrete achieved 28-day compressive strengths of up to 2,175 psi (15 MPa) and can be used as a growth bed for alkali tolerant plant species.

[0182] Example 13

[0183] Carbon neutral 3D printable concrete can be produced by adding biochar to the fresh mix. This specialty concrete is useful for pre-cast concrete parts, in-situ cast new structures, or repairing / reinforcing aged concrete structures. We mixed modified biochar into fresh 3D printable concrete. This 20% biochar cement concrete achieved 28-day compressive strengths of up to 4,950 psi (35 MPa) and met the plasticity requirements.

[0184] An exemplary control mix design for 3D printable concrete is as follows. Cement: fine sand = 1 : 1.5-2.5, SCM: cement = 0-1.5: 2.5, water-cement ratio = 0.15-0.25, and an amount of viscosity modifier, nanomaterials, and / or fibers. The SCM can be fly ash, silica fume, calcined clay, limestone powder, or waste glass powder.

[0185] Example 14

[0186] Carbon neutral buildings contain wood-concrete composites that can be produced by adding biochar to the concrete portion. This specialty concrete is useful for casting on wood floors, providing protection and enhancing the integrity of the composite structure under external loads (e.g., earthquakes and wind). We will incorporate modified biochar into the concrete. This 40% biochar cement foam concrete has a 28-day compressive strength of up to 2,175 psi (15 MPa) and can be used for wood-concrete composites.

[0187] An exemplary control mix design for concrete is as follows. Cement: fine aggregate = 1 : 3.5-4.5, fine aggregate: coarse aggregate = 1 : 2-4, water-cement ratio = 0.42-0.50, and as necessary amounts of SCMs, concrete admixtures, nanomaterials (as admixtures), and / or fibers.

[0188] Example 15

[0189] Carbon neutral mortar for masonry can be produced by adding biochar to fresh mortar mixtures. We will incorporate modified biochar into fresh mortar, and this 30% biochar cement mortar has a 28-day compressive strength of up to 3,115 psi (21.5 MPa) and can be customized for use in all types of mortar.

[0190] An exemplary control mix design for masonry mortar is as follows. Cement: fine aggregate = 1 : 3.0-4.0, SCM: cement = 0-l : 2.0, water: cement = 2.5-3.5 : 1, and as necessary amounts of SCMs, concrete adaptive chemistry / nano admixtures, and / or fibers.

[0191] Example 16

[0192] Carbon neutral biochar cement can be used to alter the original structure of soft soils such as expansive soils, collapsible soils, and the like, and then to strengthen / stabilize them. We will incorporate modified biochar-cement into soft soils, and 5% cement containing 40% biochar by weight reduces swelling of expansive soils by 60% and settlement of collapsible soils by 50%, respectively.

[0193] An exemplary control mix design for paste is as follows. Water: cement = 2.5-3.5 : 1, and as necessary amounts of SCMs, concrete adaptive chemistry / nano admixtures, and / or fibers.

[0194] Example 16

[0195] Multiple carbonation processes

[0196] Carbonated biochar: Mix dry biochar with the precipitate of a waste concrete wash slurry (cement paste), add and mix additional wash supernatant, then inject CO2 gas until the pH reaches neutrality (pH = 7). Dry and grind before use.

[0197] Carbonated recycled concrete aggregate (RCA) (both fine and coarse): RCA was soaked in pure water and stirred, CO2 was introduced to the mixture while stirring until the pH of the solution became neutral (7), then dried for later use.

[0198] Carbonated water (waste rinse water): CO2 was injected into the collected rinse water until the pH reached neutrality, and used after ultrasonic dispersion (e.g., to mix micron / nano CaCO3 solution). Note: The rinse water can be replaced by other alkaline waste liquid.

[0199] Carbon capture estimation

[0200] After estimation and calculation, (60% Portland limestone cement + 40% raw biochar) + (30% carbonated fine RCA + 70% raw fine RCA) + carbonated alkaline water can produce carbon-negative mortar, with a carbon footprint of -0.007124 tons per ton of mortar.

[0201] (60% Portland limestone cement + 40% raw biochar) + (30% carbonated fine RCA + 70% raw fine RCA) + (30% carbonated coarse RCA + 70% raw coarse RCA) + carbonated alkaline water can produce carbon-negative concrete, with a carbon footprint of -0.00645 tons per ton of concrete.

[0202] Example 17

[0203] Experiment

[0204] Materials

[0205] Given the limited supply of Type I / II ordinary Portland cement (OPC) and the huge CO2 emission, Portland limestone cement (PLC: 85 wt% OPC + 15 wt% limestone) was used in this study to mitigate the CO2 footprint of the cement / concrete industry. The fine natural aggregate used in this study was obtained from Bonsal American Inc. (Charlotte, NC) and purchased from a local building supplier. The biochar used was provided by OurCarbon TM and its chemical components were analyzed by XRF, as detailed in Table 7. Recycled concrete aggregate (RCA) was obtained from our previous waste OPC paste sample (OPC: water = 1:0.5 mass ratio) with the purpose of partially replacing the natural fine aggregate. In addition, this study also designated to upgrade another byproduct of the concrete industry, rinse paste slurry, to further promote the sequestration of CO2. To ensure the repeatability of the experiment, we simulated the rinse slurry in the laboratory with a fixed raw material ratio as follows.

[0206] Table 7. OurCarbon TMChemical composition of the biochar provided.

[0207]

[0208] Multiple carbonation process

[0209] This study investigates a multiple carbonation process involving biochar, alkaline wastewater, RCA, and CO2-cured carbonation for the production of mortar samples. The process mainly utilizes the added or inherent alkali and CO2 gas for carbonation, ultimately achieving the goal of carbon negativity. To ensure consistency and repeatability of the experiment, we use a fixed mass ratio of 1 :5 of the simulated concrete industry waste by-product, wash paste slurry, with water.

[0210] The supernatant and sediment of the simulated wash paste slurry are collected for various uses. After approximately 12 hours of sedimentation, the supernatant is extracted from the slurry and prepared for carbonation as mixing water. A plastic tube connects the supernatant in a sealed container to a CO2 gas tank, and carbonation is considered complete when the pH of the supernatant goes from 12 to 7 (neutral). Prior to use, the carbonated supernatant is subjected to 10 minutes of ultrasonic dispersion to obtain a mixed nano / micro CaCO3 suspension, which is expected to enhance the performance of the hardened samples, as widely reported in nano-engineered cement-based composites.

[0211] The slurry sediment is mixed with biochar, which captures and sequesters CO2 using its high alkalinity, which is also expected to enhance the fragile structure of the biochar. The mass ratio of dry biochar to dry paste sediment is fixed at 2:1, and the water content of the slurry sediment is determined by measurement. Subsequently, additional supernatant is thoroughly mixed with dry biochar at a volume ratio of 3:1, and CO2 gas is injected using the same strategy as for the preparation of carbonated supernatant until the pH reaches 7 (neutral). During the underwater carbonation process, the biochar sediment mixture must be stirred regularly to ensure adequate contact between CO2 and alkali. The biochar sediment mixture is subjected to preliminary air drying, followed by oven drying at 100°C for 24 hours to ensure complete dehydration. Prior to the preparation of mortar / concrete samples, the dried mixture is ball-milled at 250 rpm for 1 hour, with a volume ratio of material to balls of approximately 1:2.

[0212] Carbonation of RCA follows a similar approach. RCA is soaked in pure water at a volume ratio of 1:4 and stirred regularly for 24 hours. CO2 gas is then injected into the mixture until the pH of the solution reaches 7 (neutral). Again, regular stirring of the RCA-water mixture is crucial during the underwater carbonation process to ensure adequate contact between CO2 and the alkali leached from the RCA. Prior to use, the carbonated RCA is air-dried, then oven-dried at 100°C for 24 hours to ensure complete dehydration.

[0213] Preparation of mortar and concrete samples

[0214] The manufacturing process of these new mortar samples is detailed as follows. The natural aggregates and carbonated RCA were dry mixed for 5 minutes, then PLC and carbonated biochar were added and mixed into the aggregates until a homogeneous mixture was obtained. Meanwhile, carbonated alkaline water was ultrasonically dispersed for 10 minutes at 50% amplitude to obtain a mixed nano / micro CaC03 suspension, which was then poured into the dry mixture and mixed thoroughly for 5 minutes to achieve the desired fluidity and consistency. The fresh mortar mixture was cast into cylindrical molds with dimensions of 50.8 mm (diameter) x 101.6 mm (height) and covered with plastic lids for 24 hours to avoid any water evaporation. After demolding, all mortar cylinders were moved to standard curing conditions (22 ± 1 °C, relative humidity 95 ± 3%) and cured for 6 days and 27 days for testing the 7-day and 28-day compressive strength, respectively. The mixture combinations of the mortar samples are shown in Table 8.

[0215] Table 8. Mixture combinations (wt%) of mortar samples.

[0216] Sample No. 1 2 2(C) 4 5 6 7 PLC 100 70 70 70 60 60 60 CBiochar / 30 30 / 40 / / Biochar / / / 30 / 40 40 Natural aggregate (F) 300 240 240 240 210 210 210 CRCA (F) / 60 60 60 90 90 / RCA (F) / / / / / / 90 Tap water 50 / / 50 / / 50 CWater / 50 50 / 50 50 /

[0217] Note: CBiochar, CRCA, and CWater represent carbonated biochar, RCA, and alkaline water, respectively; 2(C) represents sample No. 2 cured with CO2; (F) represents fine aggregates.

[0218] The manufacturing process of the concrete samples was similar to that of the mortar samples, but with the addition of coarse aggregates. In addition, the water to binder ratio of the concrete samples was fixed at 0.35 to meet the requirements of chloride-containing concrete mixtures in cold regions. Based on the results of the mortar samples, all RCAs were carbonated before use. To ensure good workability, a high-range water reducer (HRWR) was used during the concrete manufacturing process. Table 9 gives the mixture combinations of various concrete samples.

[0219] Table 9. Mixture combinations (kg / m3) of concrete samples. 3 ).

[0220]

[0221]

[0222] Note: CBiochar, CRCA, and CWater represent carbonated biochar, RCA, and alkaline water, respectively. In addition, (C) and (F) represent coarse and fine aggregates, respectively.

[0223] Experimental tests

[0224] Mechanical properties

[0225] The compressive strength of the mortar / concrete samples was tested using a multi-station system following the ASTM C1231 / C1231M standard test method. A two-stage loading procedure was used: the first stage had a loading rate of 2 mm / min until 2,500 lbs was reached, aimed at accelerating the testing process, while the second stage had a loading rate of 0.5 mm / min until the sample failed, aimed at obtaining more reliable results. The peak load was recorded to calculate the strength, and the final compressive strength was calculated by averaging the results of three samples.

[0226] Quantification of carbonation

[0227] Two methods were proposed to quantify carbonation for solid and liquid samples, respectively. For solid samples (i.e., carbonated biochar, carbonated RCA, and CO2-cured samples), thermogravimetric analysis was used to evaluate the carbonate content, thus quantifying the sequestered CO2. The initial and final temperatures for thermogravimetric analysis in this study were set at 50 °C and 1000 °C, respectively, with a heating rate of 10 °C / min. All samples were dehydrated with absolute ethanol prior to analysis. For liquid samples (i.e., carbonated supernatant of flushed slurry), the sequestered CO2 could be estimated from the change in pH from 12 to 7. To simplify the estimation, all hydroxide ions (OH - ) were considered to be neutralized by CO2, generating bicarbonate ions at the same molar concentration. The ionization of bicarbonate ions (HCO3 - ) was not considered, and this simplification slightly underestimated the sequestered CO2 content.

[0228] Results and discussion

[0229] Mechanical performance

[0230] Preliminary CO2 footprint estimation for mortar samples

[0231] The sequestered CO2 content in each raw material component was estimated according to the methods discussed above and is provided in Table 10. In addition, the CO2 content emitted during the production of PLC and natural aggregates was also listed in Table 10 to estimate the total CO2 footprint.

[0232] Table 10. Sequestered carbon content and CO2 equivalent content (kg / kg) for each raw material component.

[0233]

[0234] Note: CBiochar, CRCA, and CWater represent carbonated biochar, RCA, and alkaline water, respectively.

[0235] Example 18

[0236] To explore high replacement rates, we investigated engineered cementitious composites (ECC) with 5 wt%, 10 wt%, 20 wt%, 30 wt% of biochar replacing 37% of the OPC by weight. The remaining ingredients in the ECC mix included 22% Class C fly ash, 6% silica fume, 20% sand, 13% water, and about 1% each of high-range water reducer and polypropylene fibers. We measured the compressive strength at 3 days, 7 days, and 28 days, and the drying shrinkage at 50 days.

[0237] The 3-day compressive strength of the biochar-modified samples was 10-40% lower than the control sample, but the 28-day compressive strength of all biochar-modified samples was slightly higher than the control sample Figure 14 ). This result can be attributed to the delayed pozzolanic reaction in the biochar-modified samples, which does not occur in the early stages of hydration. The sample with 10% OPC replacement showed a maximum reduction of 20% in total shrinkage Figure 15 . Notably, the water to binder ratio was 0.195, which means that autogenous shrinkage is a major component of the total shrinkage. These results confirm the effectiveness of biochar for internal curing.

[0238] It is to be understood that the embodiments and examples of the present invention described above are merely illustrative of the only possible ways in which the present invention can be practiced. Numerous modifications and adaptations will be apparent to those skilled in the art without departing from the spirit and scope of the present invention. All such modifications and adaptations are intended to be included within the scope of the disclosure and the present invention, which is set forth in the following claims.

Claims

1. A method for capturing carbon in biochar, comprising: Biochar is mixed with an alkaline solution to form an intermediate mixture; and The intermediate mixture is exposed to a CO2 source to cause calcium carbonate to precipitate on and within the biochar to form CO2-weathered biochar.

2. The method of claim 1, further comprising repeating the mixing and exposure steps to treat the intermediate mixture with an additional amount of alkaline solution.

3. The method according to claim 1, wherein the alkaline solution comprises the supernatant of concrete flushing water.

4. The method according to claim 1, wherein the volume ratio of the alkaline solution to the biochar is 10:1 to 1:

1.

5. The method according to claim 1, wherein the CO2 source is gaseous CO2 and / or carbonic acid.

6. The method of claim 1, wherein the alkaline solution is carbonized prior to the mixing step.

7. A CO2-weathered biochar prepared by the method of claim 1.

8. A method for capturing carbon in a cement-based composite material, comprising: Biochar is mixed with an alkaline solution to form an intermediate mixture; The intermediate mixture is exposed to a CO2 source to cause calcium carbonate to precipitate on and within the biochar to form CO2-weathered biochar. and The CO2-weathered biochar is mixed with cement and an aqueous solution to form the cement-based composite material.

9. The method of claim 8, wherein the biochar comprises particles with a size of 150 micrometers or smaller.

10. The method of claim 9, wherein the total amount of cement in the CO2-weathered biochar-replaced cement-based composite material is 1% to 80% by mass.

11. The method of claim 10, wherein the CO2-weathered biochar replaces 1% to 40% by mass of the total amount of cement in the cement-based composite material.

12. The method of claim 8, wherein the biochar comprises particles with a size greater than 150 micrometers.

13. The method of claim 12, wherein the cement-based composite material further comprises aggregate, and wherein the CO2-weathered biochar replaces 1% to 20% by mass of the total amount of aggregate in the cement-based composite material.

14. The method of claim 12, wherein the cement-based composite material does not contain any aggregate.

15. The method of claim 12, wherein the cement-based composite material comprises recycled aggregate.

16. The method of claim 15, wherein the recycled aggregate is carbonated.

17. The method of claim 16, wherein the recycled aggregate is carbonated via the following step: The recycled aggregate is mixed with a second alkaline solution to form a second intermediate mixture; and The second intermediate mixture is exposed to a CO2 source to cause calcium carbonate to precipitate on and within the recycled aggregate to form CO2-weathered recycled aggregate.

18. The method of claim 8, wherein the biochar is carbonized.

19. The method according to claim 8, wherein the aqueous solution is a carbonated alkaline aqueous solution.

20. The method of claim 8, wherein the compressive strength of the cement-based composite material is increased compared to the corresponding cement-based composite material of biochar without CO2 weathering.

21. The method of claim 8, wherein the cement-based composite material is selected from concrete, paste, cement slurry, mortar, and cement-stabilized soil.

22. The method of claim 8, further comprising pretreating the biochar with a solution containing nanomaterials before mixing the biochar with the alkaline solution.

23. The method of claim 8 further comprises pretreating the biochar with one or more oxidizing agents before mixing the biochar with the alkaline solution.

24. The method according to claim 8, wherein the biochar is surface-modified biochar.

25. The method of claim 8, wherein the cement-based composite material further comprises a fiber material.

26. A cement-based composite material prepared by the method of claim 8.

Images