3D printable, lightweight, high strength, carbon capture, and carbon storage concrete

Abstract

A cementitious material, comprising: an amount of a porous biomineral, the porous biomineral optionally comprising diatomaceous earth (DE), the porous biomineral and cement being present at a weight ratio of at least about 0.05:0.95, optionally at least about 0.3:0.7; and an amount of a cement. A method, comprising effecting additive manufacturing of a structure with a cementitious material according to the present disclosure. A structural material, comprising an amount of a cured cementitious material according to the present disclosure. A structure, the structure comprising a structural material according to the present disclosure. A structure can be, for example, a building or even a portion of a building.

Description

3D PRINTABLE, LIGHTWEIGHT, HIGH STRENGTH,CARBON CAPTURE, AND CARBON STORAGE CONCRETERELATED APPLICATIONS

[0001] The present application claims priority to and the benefit of United States patent application no. 63 / 567,487, filed March 20, 2024. All foregoing applications are incorporated herein by reference in their entireties for any and all purposes.GOVERNMENT RIGHTS

[0002] This invention was made with government support under DE-AR0001631 awarded by the U.S. Department of Energy. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The present field relates to cementitious materials.BACKGROUND

[0004] Concrete, the world's second most widely used material after water, is primarily composed of cement, but its production process is carbon-intensive, contributing significantly to greenhouse gas emissions. Approximately 7% of global anthropogenic CO2 emissions result from cement production, exacerbating climate change and global warming. Efforts have been dedicated to achieving a carbon-zero goal by 2050, in line with the Paris Agreement, but substantial progress is still required. The cement and concrete industries have explored numerous strategies to mitigate their substantial carbon footprint, including low-emission secondary fuels, reduced clinker utilization, and carbon capture and storage.

[0005] One solution is carbon capture and storage within the concrete, wherein CO2 is transformed into a stable mineral carbonate form. This approach markedly enhances durability, reduces the carbon footprint of the final products, and distinguishes itself through cost-effectiveness and low energy consumption. But despite the significant research advancements in concrete carbonation, such as mixing processes, carbonation curing of cast concrete, and recycling waste aggregates, there are still some challenges thatneed to be addressed. These include relatively slow carbonation kinetics and difficulties in ensuring uniform carbonation in large or thick concrete structures.SUMMARY

[0006] In meeting the described long-felt needs, the present disclosure provides A cementitious material, comprising: an amount of a porous biomineral, the porous biomineral optionally comprising diatomaceous earth (DE), the porous biomineral and cement being present at a weight ratio of at least about 0.05:0.95, optionally at least about 0.3:0.7 ; and an amount of a cement.

[0007] Also provided is a method, comprising effecting additive manufacturing of a structure with a cementitious material according to the present disclosure.

[0008] Further provided is a structural material, comprising an amount of a cured cementitious material according to the present disclosure.

[0009] Further provided is a structure, the structure comprising a structural material according to the present disclosure. A structure can be, for example, a building or even a portion of a building. Such a structure can be at least partially formed by additive manufacture, but this is not a requirement.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In the drawings, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various aspects discussed in the present document. In the drawings:

[0011] FIG. 1. Concrete mixture with DE / Cement=0.3 through a 2mm nozzle.

[0012] FIG. 2. The SEM images of the pores that naturally form in the structure of DE.

[0013] FIG. 3. The porosity of concrete formulations with different DE / Cement ratios after being cured for 24 hours.

[0014] FIG. 4. The dry density of concrete formulations with different DE / Cement ratios after being cured for 24 hours.

[0015] FIG. 5. Surface area and pore size distribution of raw DE material.

[0016] FIG. 6. Pore volume and pore size distribution of raw DE material.

[0017] FIG. 7. The BET surface area of concrete formulations with different DE / Cement ratios after being cured for 24 hours.

[0018] FIG. 8. Surface area and pore size distribution of concrete formulations with different DE / Cement ratios after being cured for 24 hours.

[0019] FIG. 9. Compressive strength of concrete formulations with different DE / Cement ratios after being cured for 1 day and 28 days.

[0020] FIG. 10. Compressive strength of concrete with 70% Cement / 30% DE, 100% Cement, and 70% Cement / 30% SF with a water / binder ratio of 0.87 at various curing times.

[0021] FIG. 11. Compressive strength of DE / Cement ratio =0.5 concrete at various curing times.

[0022] FIG. 12. Static stress and time curves of 3D printable concrete formulation containing DE.

[0023] FIG. 13. The effect of different shear rates on the viscosity of 3D printable concrete formulations containing DE.

[0024] FIG. 14. The thixotropy of a 3D printable concrete formulation containing DE. The mixture was subjected to a shear rate of 0.1 s'1for 60 seconds, followed by a high shear rate of 100 s'1for 30 seconds, after which the shear rate was immediately reduced back to 0.1 s'1.

[0025] FIG. 15. The cross-sectional images of extruded concrete with and without DE from various nozzle sizes.

[0026] FIG. 16. The width-to-height (b / d) ratio of the extruded concrete with and without DE from various nozzle sizes.

[0027] FIG. 17. The elastic modulus of concrete with and without DE at different times after deposition on a substrate.

[0028] FIG. 18. The force displacement curves of concrete with and without DE at different times after deposition.

[0029] FIG. 19. 3D printed cylinder structure of the concrete with and without DE.

[0030] FIG. 20. 3D printed Triply Periodic Minimum Surface (TPMS) structures of the concrete with DE.

[0031] FIG. 21. Schematic of water migration between pores that are present between different printed layers.

[0032] FIG. 22. The interfacial bonding strength of the 3D-printed concrete cube with and without DE.

[0033] FIG. 23. Schematic and SEM images of the concrete with DE after prehydrated for 24 hours.

[0034] FIG. 24. Schematic and SEM images of the concrete with DE after cured in N2 for 7 days.

[0035] FIG. 25. BET surface area of the concrete with and without DE in CO2 and N2 environment for 1, 3, 5, and 7 days.

[0036] FIG. 26. Pore volume and pore width distribution of the concrete with and without DE in CO2 and N2 environment for 1 and 7 days.

[0037] FIG. 27. Schematic and SEM images of the concrete with DE after cured in CO2 for 7 days.

[0038] FIG. 28. Differential thermogravimetric (DTG) analysis of the concrete with DE in CO2 and N2 environment for 1, 3, 5, and 7 days.

[0039] FIG. 29. CO2 absorption per kilogram of cement in concrete over various days, comparing concrete with and without DE.

[0040] FIG. 30. Compressive strength of the concrete with DE in CO2 and N2 environment at various times.

[0041] FIGs. 31 A- 3 IE. Design of the 3D Printable Biomineral-infused Concrete. (FIG. 31 A to FIG. 3 IB) Illustrations of (FIG. 31 A) the bio-inspirations and (FIG. 3 IB) a floor design assembled from 3D printed TPMS carbon-absorbing concrete structures. (FIG. 31C) Effect of varying diatomaceous earth (DE) / binder mass ratios on the surface area distribution of the concrete, measured 1 day after being cured in the mold. (FIG. 3 ID) Effect of varying DE / binder mass ratios on the compressive strength of the concrete after being cured in saturated limewater for 28 days, with corresponding water / binder mass ratios. (FIG. 3 IE) Compressive strength of the concrete after being cured in saturated limewater at different time periods with a fixed water / binder mass ratio of 0.87, but with varying binder mass compositions (DE / binder mass ratio=0.3 and 0, silica fume (SF) / binder mass ratio=0.3). Error bars in the graph represent the standard deviation of 3 to 5 samples.

[0042] FIGs 32A - 32 J. CO2 Sequestration of DE-Infused Concrete with a DE / Binder Mass Ratio of 0.3. (FIGs. 32A, C, and E) Schematic illustrations of the possible products and the distribution of Ca2+ion concentration [Ca2+] from concrete with DE after being (FIG. 32A) pre-hydrated for 1 day, (FIG. 32C) cured in CO2, and (E) N2 environments for 7 days, respectively. [Ca2+]sat refers to the saturation concentration of Ca2+ions required for CaCCE formation. (FIGs. 32B, D, and F) Scanning electron microscope (SEM) images of the concrete with DE corresponding to (FIGs. 32A, C, and E). (FIG. 32G) CO2 sorption isotherm of the concrete with and without DE after prehydration for 1 day. (H) Effect of curing time on BET surface areas of the concrete with and without DE cured in CO2 and N2 environments, respectively. (FIG. 321) CO2 uptake of the concrete after being cured in a CO2 environment for different durations. (FIG. 32J) CO2 uptake at various depths in concrete after being cured in a sealed plastic tube with one end open in a CO2 environment for 7 days.

[0043] FIGs. 33 A-33D. Carbonation Efficiency of 3D Printed DE-Infused Structures with a DE / Binder Mass Ratio of 0.3. (FIG. 33 A) CO2 uptake measured at increasing depths from the surface to the core in both cast cube and 3D printed TPMS structures. (FIG. 33B) CO2 uptake efficiency of the cast cube and 3D printed TPMS structure. (FIG. 33C) CAD designs and corresponding photos of the 3D printed specimens of a solid cube and a TPMS cube, respectively. The solid and dashed line represents the bounding box of the structure. (FIG. 33D) CO2 concentration changes over 60 s in the test chamber containing (i) cast cube with 1 exposed face, (ii) cast cube with 5 exposed faces, and (iii) 3D-printed TPMS cube. The band indicates the error bar range. (FIG. 33E) Comparison of CO2 uptake rate per kg of cement. Error bars show the SD of 3 to 5 samples.

[0044] FIG. 34A-34I. Characterization of Diatomaceous Earth (DE). (FIGs. 34A to C) Scanning electron microscope (SEM) images of DE under different magnifications. (FIGs. 34D to F) Transmission electron microscopy (TEM) images of DE pores (FIG. 34D) and skeleton (FIGs. 34E to F). (G), N2 sorption isotherm curve of DE. (FIG. 34H) Surface area distribution of DE. (I) Pore volume distribution of DE.

[0045] FIG. 35. Comparison CO2 Sorption Isotherm Between DE and Silica Fume (SF). CO2 sorption isotherm curves of DE and silica fume (SF), respectively. Toevaluate DE’s unique CO2 sorption capacity relative to other supplementary cementitious materials, we analyzed it alongside SF, which also primarily comprises SiCE.

[0046] FIGs. 36A-36C. Characterization of 3D Printable Concrete with Various DE-to-binder Mass Ratios. (FIG. 36A) Optical images of cylinder specimens and extruded concrete filaments with different DE-to-binder mass ratios. (FIGs. 36B to C) Effect of varying DE-to-binder mass ratios on (FIG. 36B) the density of the concrete and (FIG. 36C) the porosity of the concrete. Materials in (FIG. 36B) and (FIG. 36C) were measured 1 day after curing the concrete in the mold. Error bars show the SD of 3 to 5 samples.

[0047] FIGs. 37A-37D. Influence of DE-to-Binder Mass Ratios on Pore Characteristics and Surface Area of Concrete. (FIGs. 37A to E) Effect of varying DE-to- binder mass ratios on (FIG. 37A) the pore volume distribution, (FIG. 37B) the cumulative pore volume distribution, (FIG. 37C) the cumulative pore area distribution, (FIG. 37D) N2 sorption isotherm curves, and (FIG. 37E) the BET surface area of the concrete. Materials were measured 1 day after curing of the concrete in the mold.

[0048] FIG. 38. Schematic Illustration of 3D Concrete Printing Setup and Stages.

[0049] FIGs. 39A-39B. Rheological Characterization of Fresh Concrete Inks. (A) Rheological characterization of the shear-thinning behavior of the fresh concrete ink with (DE / Binder=0.3) and without DE (DE / Binder=0). (FIG. 39B) Thixotropy behavior of the fresh concrete ink without DE, involving 3 steps: a low shear rate of 0.1 s'1for 60 s to mimic the initial resting state of the fresh concrete in the hopper, followed by a high shear rate of 100 s'1for 30 s to mimic the shearing and extruding process, and lastly a low shear rate of 0.1 s'1for 60 s to mimic the material resting on the printing stage.

[0050] FIGs. 40A-40C. Water Migration and Drying Behavior in 3D-Printed Concrete with DE-to-Binder Mass Ratios of 0 and 0.3. (FIG. 40A) Illustration of the migration of water and Ca2+ions between printed layers during the water evaporation pathway in the middle part of the DE -infused 3D printed concrete structure. (FIG. 40B) Photos showing a 3D printed cylinder with and without DE after 4 hours of printing. (FIG. 40C) Digital images of the 3D printed cylinders with and without DE at different drying states.

[0051] FIGs. 41A-41D. Interfacial Bonding Strength of 3D-Printed Concrete with DE-to-Binder Mass Ratios of 0 and 0.3. (FIG. 41 A) Schematics of the 3-point bending test of a 3D printed cube. The cube's coordinates indicate the printing and testingdirection. (FIG. 4 IB) Load-displacement curves of a cast cube and a 3D printed cube from concrete with DE under a 3-point bending test. (FIG. 41C) Load-displacement curves of a cast cube and a 3D printed cube sample made of concrete without DE under a 3-point bending test. (FIG. 4 ID) The interfacial strength ratio of the 3D printed cubes with and without DE. Error bars show the SD of 3 to 5 samples.

[0052] FIGs. 42A-42H. Overhang analysis of diamond surfaces. (FIG. 42A) The original D surface with two-unit cells and a wavelength of 70 mm, thickened by 8 mm. (FIG. 42B) Sliced original D surface geometry with a layer height of 2.8 mm. (FIG. 42C) Overhang analysis of original D surface geometry. (FIG. 42D) Definition of the overhang. (FIG. 42E) Cumulative distribution of the overhang for the original and scaled D surfaces. (FIG. 42F) Scaled D surface, scaled by a factor of 2 in the z-direction. (FIG. 42G) Sliced Scaled D surface geometry with a layer height of 2.8 mm. (FIG. 42H) Overhang analysis of scaled D surface geometry.

[0053] FIG. 43. Flow chart of the steps for design and optimization of the diamond TPMS concrete canopy. (FIG. 43 A) Step 1 : Polyhedral Graphic Statics (PGS) Form-Finding. Base dimensions of the structure are established as the initial input / constraint. Boundary conditions and applied load locations are defined, and a force diagram is generated using a bar-node model. Blue bars indicate compression forces and red bars indicate tension forces. (FIG. 43B) Step 2: Embedding the TPMS into the Form Diagram. The diamond TPMS is embedded into the generated form diagram. (FIG. 43 C) Step 3: Volumetric Modeling and Overhang Analysis. Volumetric modeling adds thickness to the designed surfaces, using SDF. The design is segmented into unit cells, and each cell is analyzed for overhangs and 3D printability.

[0054] FIG. 44. CAD and geometry properties of the TPMS-based structures with identical-sized bounding boxes. A bounding box refers to the smallest rectangular geometry that completely encloses the structure.

[0055] FIGs. 45A-45C. Characterization of Microstructures of the DE -Infused Concrete with a DE-to-Binder Mass Ratio of 0 Under Various Curing Conditions. (FIG. 45A) SEM images of concrete with a DE / Binder=0 after being pre-hydrated for 1 day. (FIG. 45B) SEM images of concrete with a DE / Binder=0 after being cured in a CO2 environment for 7 days. (FIG. 45C) SEM images of concrete with a DE / Binder=0 after being cured in an N2 environment for 7 days.

[0056] FIGs. 46A-46B. Crystallographic Characterization of Concrete with DE- to-Binder Mass Ratios of 0 and 0.3 under CO2 and N2 Curing Conditions. (FIG. 46A) Powder X-ray diffraction (PXRD) spectra of the concrete with a DE / Binder=0.3 after being cured in CO2 and N2 environments for 7 days. (FIG. 46B) PXRD spectra of the concrete with a DE / Binder=0 after being cured in CO2 and N2 environments for 7 days.

[0057] FIG. 47. Pore Volume Distribution of Concrete with DE-to-Binder Mass Ratios of 0 and 0.3 Being Cured in CO2 and N2 Environment for Different Durations. From left to right, concrete with DE-to-Binder mass ratios of 0.3 being cured in a CO2 environment for 1 day and 7 days (corresponding to Figure 32C), concrete with DE-to- Binder mass ratios of 0.3 being cured in an N2 environment for 1 day and 7 days (corresponding to Figure 32E), concrete with DE-to-Binder mass ratios of 0 being cured in a CO2 environment for 1 day and 7 days (corresponding to Figure 45B), concrete with DE- to-Binder mass ratios of 0 being cured in a N2 environment for 1 day and 7 days (corresponding to Figure 45C).

[0058] FIGs. 48 A - 48B. Thermogravimetric Analysis (TGA) of Concrete with DE-to-Binder Mass Ratios of 0 and 0.3 Being Cured in CO2 and N2 Environments for Different Durations. (FIG. 48A) Derivative Thermogravimetric (DTG) curves of the concrete with DE-to-Binder mass ratios of 0.3 cured in CO2 and N2 environments for 1, 3, 5, and 7 days. (FIG. 48B) DTG curves of the concrete with DE-to-Binder mass ratios of 0 cured in CO2 and N2 environments for 1, 3, 5, and 7 days. DTG curves displayed distinct peaks within dehydration (30-300 °C), dehydroxylation (380-500 °C), and decarbonation (600-950 °C).

[0059] FIG. 49. CO2 Uptake Measurement Setup at Various Depths in Carbonated Concrete. Stepwise procedure for sampling at different depths of carbonated concrete sample.

[0060] FIGs. 50A - 50B. Compressive Strength of Concrete with DE-to-Binder Mass Ratios of 0 and 0.3 Being Cured Under Various Curing Conditions. (FIG. 50A) Compressive strength of the concrete with DE-to-Binder mass ratios of 0.3 after being cured in CO2 and N2 environments for different durations. (FIG. 50B) Compressive strength of the concrete with DE-to-Binder mass ratios of 0 after being cured in CO2 and N2 environments for different durations. Error bars in the graph show the SD of 3 to 5 samples.

[0061] FIGs. 51 A - 51C. Geometry and Properties of TPMS Cubes. (FIG. 51 A) Four TPMS surfaces as the walls of the TPMS cube. (FIG. 5 IB) TPMS cube formation by infilled mass inside the walls. (FIG. 51C) Surface area-to-volume ratio of the solid cube and the TPMS cube.

[0062] FIGs. 52A -52D. Comparison of mechanical properties between solid and TPMS concrete cubes. (FIG. 52A) Finite element analysis (FEA) simulation of the solid cube and the TPMS cube. (FIG. 52B) Normalized stiffness of the solid cube and TPMS cube derived from FEA simulations. (FIG. 52C) Compressive stress-strain curves for the solid cube and TPMS cube from physical testing. (FIG. 52D) Specific strength and specific stiffness of the solid cube and TPMS cube as measured in physical tests.

[0063] FIGs. 53 A - 53B. CO2Uptake Rate Test Setup. (FIGs. 53 A to B) Schematic illustration of the CO2 uptake rate testing: (FIG. 53 A) The setup using an automated CO2flux system, and (FIG. 53B) the measuring process. The test involves two stages: (1) the observation stage, where the chamber is closed to measure the change of CO2 concentration in the chamber, and (2) the purge stage, where the chamber is opened to allow fresh air to purge around the test area.

[0064] FIG. 54. Sample Images for CO2 Uptake Rate Test. Digital images of (i) cast cube with 1 exposed face, (ii) cast cube with 5 exposed faces, and (iii) 3D-printed TPMS cube.

[0065] FIG. 55. CO2 Uptake of the DE-Infused Concrete in Comparison with the State-of-the-Art Cementitious Materials. The state-of-the-art cementitious materials use ordinary Portland cement (OPC) as a binder, subjected to accelerated carbonation in a pure CO2 environment. Samples carbonized at the pressure of 2 bar or higher are highlighted within the gray dashed line region. Detailed calculations of the maximum theoretical CO2 uptake and the measured CO2 uptakes are provided in the Supplementary text. References cited in the figure correspond to Table 4.DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0066] The present disclosure may be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein.

[0067] 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. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0068] The singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0069] As used in the specification and in the claims, the term "comprising" can include the embodiments "consisting of' and "consisting essentially of.” The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named ingredients / steps and permit the presence of other ingredients / steps. However, such description should be construed as also describing compositions or processes as "consisting of' and "consisting essentially of' the enumerated ingredients / steps, which allows the presence of only the named ingredients / steps, along with any impurities that might result therefrom, and excludes other ingredients / steps.

[0070] As used herein, the terms “about” and “at or about” mean that the amount or value in question can be the value designated some other value approximately or about the same. It is generally understood, as used herein, that it is the nominal value indicated ±10% variation unless otherwise indicated or inferred. The term is intended to convey that similar values promote equivalent results or effects recited in the claims. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but can be approximate and / or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. In general, an amount, size, formulation, parameter or other quantity or characteristic is “about” or “approximate” whether or not expressly stated to be such. It is understood that where“about” is used before a quantitative value, the parameter also includes the specific quantitative value itself, unless specifically stated otherwise.

[0071] Unless indicated to the contrary, the numerical values should be understood to include numerical values which are the same when reduced to the same number of significant figures and numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0072] All ranges disclosed herein are inclusive of the recited endpoint and independently of the endpoints. The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value; they are sufficiently imprecise to include values approximating these ranges and / or values.

[0073] As used herein, approximating language can be applied to modify any quantitative representation that can vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially,” may not be limited to the precise value specified, in some cases. In at least some instances, the approximating language can correspond to the precision of an instrument for measuring the value. The modifier “about” should also be considered as disclosing the range defined by the absolute values of the two endpoints. For example, the expression “from about 2 to about 4” also discloses the range “from 2 to 4.” The term “about” can refer to plus or minus 10% of the indicated number. For example, “about 10%” can indicate a range of 9% to 11%, and “about 1” can mean from 0.9-1.1. Other meanings of “about” can be apparent from the context, such as rounding off, so, for example “about 1” can also mean from 0.5 to 1.4.

[0074] Further, the term “comprising” should be understood as having its open- ended meaning of “including,” but the term also includes the closed meaning of the term “consisting.” For example, a composition that comprises components A and B can be a composition that includes A, B, and other components, but can also be a composition made of A and B only. Any documents cited herein are incorporated by reference in their entireties for any and all purposes.

[0075] Any embodiment or aspect provided herein is illustrative only and does not limit the scope of the present disclosure or the appended claims. Any part or parts ofany one or more embodiments or aspects can be combined with any part or parts of any one or more other embodiments or aspects.

[0076] Here we report an innovative 3D-printable concrete material incorporating hierarchical porous biominerals, significantly reducing material waste and carbon footprint, enhancing the concrete's carbon absorption and storage capacity, and enabling intricate structures fabrication through 3D printing. One of the key viable supplementary cementing materials (SCMs) that can reduce the use of cement while providing carbon capture and storage is natural biomineral, diatomaceous earth (DE), characterized by its highly ordered, porous silica structures featuring hierarchical nano- to micro-sized pores. DE offers many advantages compared to other options of SCMs to replace cement.

[0077] It serves as a rheological modifier in the 3D printable concrete ink, facilitating the pumping and extrusion of fresh concrete. Consequently, it has the potential to significantly improve the material's printability. The printed concrete mixture deposited on the printing stage demonstrates remarkable shape retention when using nozzle sizes ranging from 2mm to 21mm. When under load, the fresh material with diatomaceous earth (DE) exhibits a distinctive strain-hardening behavior. This strain-hardening enables the extruded material to strengthen and harden during plastic deformation, empowering the printed material to withstand increased weight. This, in turn, facilitates the successful printing of additional layers.

[0078] The inherent hierarchical porosity of DE enables it to function as a water reservoir, storing water within the prints. This water can be transported between layers of the printed concrete ink, facilitating the dissolution of calcium-hydrated products between these layers. This mechanism serves a dual purpose: it maintains the hydration of the printed structures throughout the entire printing process and promotes strong bonding between adjacent layers. As a result, it effectively mitigates drying -induced shrinkage and cracking in the printed layers, particularly at the bottom of the print structures. This addresses a common limitation encountered in 3D-printed structures while simultaneously strengthening the overall print.

[0079] The incorporation of highly porous DE reduces the overall density of the concrete ink. This lightweight characteristic facilitates the stable stacking of up to 111print layers (200 mm) without collapsing. In comparison, the version without DE can only support less than 51 layers (98.6 mm), underscoring the buildability of our concrete recipe.

[0080] During the carbonation process, the negatively charged silica nanoparticles in DE binds calcium ions (Ca2+) within the pre-hydrated concrete, serving as active nucleation sites for the formation of calcium carbonate (CaCCE) that further strengthens the concrete compared to the hydration-cured concrete. This process depletes the local area around the DE of Ca2+and carbonate ions (CO32), inhibiting nucleation and ensuring that pores in other regions remain open for continuous CO2 capture. This enhanced CO2 sequestration efficiency of concrete outperforms the material without DE.

[0081] The features of DE in the disclosed technology advance sustainability in reducing greenhouse gas emissions. Further, the disclosed approach retains the high mechanical properties that are mandated for conventional concrete in construction.

[0082] Results and Discussion:

[0083] Material formulation

[0084] We present an innovative concrete formulation with distinctive characteristics, including 3D printability, lightweight properties, high porosity, low density, and highly efficient carbon absorption. To achieve these properties, we replace up to 50 wt.% of ordinary Portland cement (OPC) with the highly porous biomineral, diatomaceous earth (DE). Our material composition comprises OPC, DE, sand, hydroxypropyl methylcellulose (HPMC), and water.

[0085] DE has demonstrated its value as a supplementary cementitious material (SCM), working in tandem with cement to act as a binder in concrete. This is attributed to its distinct physical and chemical properties, as well as its pozzolanic characteristics. Moreover, it possesses the capability to improve 3D printability, lower concrete density, and introduce porosity.

[0086] The sand-to-binder ratio in 3D printable concrete varies depending on the application, binder type, and desired properties. Typically, a common ratio is approximately 2: 1. In our formulation, we use all-purpose sand (Quikrete®), ensuring the sand size is smaller than 0.8mm by sieving. We maintain a sand-to-binder ratio of 2: 1 with the aim of reducing costs and preventing cured concrete from cracking and shrinking.

[0087] To enhance the viscosity and extrudability of the concrete mixture while maintaining stability and shape, we introduce 0.4 wt.% of HPMC as a viscosity -modifyingadmixture (VMA). The VMA-to-binder ratio in 3D printable concrete can range from 0.1 to 1 by weight and our inclusion of 0.4 ratio of HPMC ensures the fresh concrete remains extrudable and retains its desired shape.

[0088] Water plays a vital role in 3D concrete printing, serving as both an essential component in the concrete mixture and a key element in the curing process. It enables the material to be extruded, adhere to previous layers, and solidify into the desired shape. Diatomaceous earth (DE) is renowned for its remarkable water-absorption capacity, which can vary depending on the specific type, grade, and physical properties of DE. When the formulation does not include DE (Table 1 DE / Cement=0), the water-to-binder ratio is set at 0.5 to ensure the mixture can be extruded through a syringe with a nozzle of diameter of 2 mm (FIG. 1). As the DE / Cement ratio gradually increases in the formulation, the water-to-binder ratio also increases.Table 1. The material composition of 3D printable concrete with various DE / Cement ratios.

[0089] The water content in formulations containing DE can be calculated using the equation: Wwater = 0.5 * Wcement + 1.73 * WDE, where Wwater is the water weight in the mixture, Wcement is the cement weight, and WDE is the DE weight. The constants multiplying cement (0.5) and DE (1.73) may vary depending on the type or source. These values can be determined by assessing the extrudability of the mixture using a 2mm nozzle syringe. Details of the composition of various DE / Cement ratio mixtures are shown in Table 1.

[0090] Material properties

[0091] DE is distinguished by its highly porous structure, featuring nano- to micro-sized pores (FIG. 2). When DE is integrated into a concrete mixture, it introducessupplementary porosity to the material. As the DE / Cement ratio increased from 0 to 0.5, the porosity of 24-hour cured concrete exhibited increments of 7.9%, 10.6%, 14.9%, 18.9%, 23.6%, and 28.3% (FIG. 3). Correspondingly, as porosity increases, the dry density of the concrete decreases from 2091.9 tol906.6, 1767.2, 1701, 1590.1, and 1413.4 kilograms per cubic meter (kg / m3) (FIG. 4). These findings indicate that the gradual introduction of DE into the concrete formulation results in increased porosity within the concrete. The dry density range used to classify lightweight concrete falls between 1,600 to 1,900 kg / m3. In our case, formulations with 0.2 and 0.3 DE / Cement ratios fall within this category.

[0092] To quantitatively assess the impact of DE porosity within our concrete formulation, we conducted a Nitrogen adsorption-desorption analysis coupled with Brunauer-Emmett-Teller (BET) characterization. Employing BET analysis, we elucidated the specific surface area and porosity distribution of the solid materials under examination. The initial examination focused on the surface area of pure DE raw material, revealing a substantial BET surface area of 36.7709 m2 / g. FIG. 5 displays the surface area and pore size distribution, while FIG. 6 illustrates the pore volume and pore size distribution. The findings indicate that pores smaller than 20 nm significantly contribute to the overall surface area of DE. Subsequently, we investigated the surface area of concrete formulations with varying DE / Cement ratios. The BET surface area was observed to increase with a rising DE / cement ratio, as shown in FIG. 7. FIG. 8 expounds on the surface area and pore size distribution, revealing that in comparison to DE-absent concrete (DE / Cement=0), the introduction of DE in increasing ratios leads to a remarkable augmentation in the surface area of pores smaller than 20 nm. This evidence suggests that DE successfully introduces pores with dimensions as small as 2 nm into the concrete matrix, a feature not typically found in conventional concrete. We hypothesize that these pores could significantly enhance and contribute to the 3D printing and carbon capture and storage capabilities.

[0093] Water is an indispensable component in concrete, playing a pivotal role in the hydration reactions during the curing process. Managing water content effectively when working with concrete is crucial, as excessive dehydration can lead to a lack of structural integrity and the development of detrimental cracks. Conversely, a higher water- to-binder ratio generally leads to a decrease in mechanical strength, particularly in termsof compressive strength. The highly porous structure of DE not only provides the necessary porosity in concrete but also retains water without compromising mechanical strength. As depicted in FIG. 9, concrete compositions with varying DE ratios can achieve compressive strengths of up to 29.1 MPa after 28 days of curing. As the DE / Cement ratio increases, it introduces more porosity to the concrete, subsequently reducing its compressive strength. However, concrete with a 0.5 DE / Cement ratio still maintains a respectable compressive strength of 14.7 MPa after 28 days of curing.

[0094] To validate the DE porous scaffold's ability to retain water without sacrificing mechanical performance, we chose a composition with a DE / Cement ratio of 0.3, which achieved a compressive strength of 24 MPa at 28 days of curing. This meets the typical compressive strength range of Portland cement concrete, which usually falls between 20-40 MPa. We established two control groups with an identical water-to-binder ratio of 0.87, mirroring the conditions of the 0.3 DE / Cement concrete. The 0.3 DE / Cement concrete exhibited an impressive compressive strength of 30.5 MPa after 60 days of curing, reaching a plateau (FIG. 10). In contrast, the control group without DE but with the same water-to-binder ratio only reached a maximum compressive strength of 15.2 MPa after 90 days of curing.

[0095] As a point of comparison to DE, we substituted DE with a material of equivalent composition but lacking porosity, namely Silica Fume (SF). A mixture of 30% SF and 70% Cement resulted in a maximum strength of 11.1 MPa after 90 days of curing, attributed to the lower cement content and excess water in the material.

[0096] Comparing these results to the formulation without DE (DE / Cement=0) and featuring a water-to-binder ratio of 0.5, which achieved a maximum compressive strength of 32.9 MPa at 90 days (FIG. 11), the DE / Cement = 0.3 sample exhibited similar strength. This highlights the DE's ability to absorb excess water, preventing a decrease in strength and enabling the materials to meet the desired mechanical performance requirements for various structural applications.

[0097] To access the porosity for carbon absorption and the desired mechanical properties for structural applications, we selected the DE / Cement ratio =0.3 formulation for investigation of 3D printing performance and carbon absorption and storage capabilities. While we specifically opted for the DE / Cement=0.3 formulation for thisstudy, individuals can choose the DE / Cement ratio that suits their 3D printing requirements for different structures.

[0098] 3D printing performance

[0099] Concrete undergoes several stages during the 3D printing process, including pumping, extrusion, and layer deposition to form a 3D structure. The performance of 3D printing concrete is influenced by factors such as pumping pressure, the material's ability to maintain extruded geometry against self-weight, and the capability to stack successive layers.

[0100] We first initiate a rheological test to systematically characterize the material's properties for 3D printing. Rheological measurements offer insights into the concrete's flow and deformation. By understanding its behavior under various conditions, such as shear rate, we can fine-tune the mix for smooth pumping and extrusion through the 3D printer nozzle, ensuring the retention of the printed shape.

[0101] DE, besides providing porosity and retaining water, also functions as a rheological modifier in the mixture, enhancing material properties for continuous concrete 3D printing. To characterize these rheological properties, we conducted a comprehensive analysis, including static yield stress, dynamic yield stress, shear thinning, plastic viscosity, and thixotropy, using a rheometer (Discovery Hybrid Rheometer, HR-2, TA Instruments).

[0102] The static yield stress, indicating the stress required to initiate flow from a rest state, characterizes load-bearing capacity and shape retention. At a constant shear rate of 0.1 s’1, the concrete with DE (refers to DE / Cement = 0.3) displayed a static yield stress of 0.28 kPa, well within the typical range for 3D printing concrete (0.16-6.8 kPa) (FIG. 12). Dynamic yield stress represents the stress required to cease flow under shear and defines the material's response to high shear rates, as encountered during mixing, pumping, and extrusion. Through a systematic increase in shear rates applied to our freshly mixed materials with DE, we observed pronounced shear-thinning behavior. The mixture's viscosity decreased significantly from 2400 Pa-s to 7.4 Pa-s as the shear rate escalated from 0.1 to 150 s’1. This reduction in viscosity under high shear rates, known as shear-thinning properties, is particularly desirable in 3D printing concrete. It facilitates the smooth flow of the material during the 3D printing process, contributing to enhanced workability and precision in layer deposition (FIG. 13).

[0103] According to the Bingham model, our formulation features a dynamic yield stress of 0.756 kPa and a plastic viscosity of 7.203 Pa s. The slightly higher plastic viscosity exceeds the typical range (1.6-5.8 Pa s), indicating increased resistance to deformation. This is useful for shape retention, especially in overhanging sections, ensuring accurate and consistent geometry for stable 3D-printed structures. Lastly, thixotropy, representing the difference between dynamic and static yield stress, characterizes material recovery following high shear rates. Our formulation quickly regains its initial viscosity, achieving up to 100% recovery in less than a second (FIG. 14). This ensures the printed material can restore its original mechanical properties, useful for maintaining subsequent layer shapes. The results from the rheological tests indicate that the concrete formulation containing DE holds significant promise for 3D printing.

[0104] We next evaluate the material's ability to maintain its shape by extruding the concrete through various diameters of printer nozzles, ranging from 2mm to 22mm, and measuring the deformation of the extruded material's geometry. This choice of various nozzle diameters is intended for assessing printing capabilities across a spectrum, from small to large-scale robotic 3D concrete printers, which typically feature nozzle diameters around 20mm. Through the analysis of the cross-sectional area of the extruded material, we found that the width-to-height (b / d) ratio gradually rises as the nozzle diameter increases, attributed to gravity (FIG. 15). In the case of the concrete mixture without DE, the width-to-height ratio increases, resulting in significant deformation, reaching a ratio of 1.3 when the nozzle diameter reaches 21mm. In contrast, the concrete containing DE maintains a ratio of less than 1.1, even with a nozzle diameter of 21mm. This underscores the shape-retaining properties of the concrete formulation with DE, attributed to its high plastic viscosity and lower density (FIG. 16).

[0105] After being deposited on the printing stage, concrete must effectively support the stacking of successive layers, with the bottom layers playing a role in preventing collapse and structural failure. To quantify the load -bearing capacity, we conducted an indentation test at various time intervals, providing insights into the material's mechanical properties, including hardness and elastic modulus. The indentation test results indicated a consistent elastic modulus for both materials, with and without DE, over different time intervals (FIG. 17). However, a closer examination of the forcedisplacement curve revealed a distinctive strain-hardening behavior in the material withDE after 30 minutes of deposition on the substrate (FIG. 18). Strain-hardening, wherein a material becomes stronger and harder during plastic deformation, empowers the printed material to withstand increased weight, facilitating the successful printing of additional layers.

[0106] To analyze the load-bearing capacity of the materials, we conducted a buildability test, printing a cylinder structure with a 4.8 mm line width and a 1.8 mm layer height, totaling 111 layers (equivalent to 200 mm), without experiencing collapse or deformation. In contrast, the material without DE collapsed and buckled at the 43 layers, ultimately failing and causing cracks at the structure's bottom (FIG. 19). Demonstrating the printing performance of the material with DE, we successfully 3D printed two complex Triply Periodic Minimum Surface (TPMS) structures with large overhangs. This underscores the outstanding 3D printing performance of concrete by incorporating DE (FIG. 20).

[0107] Thanks to the high porosity contributed by the DE introduced in the concrete, water in the concrete after printing can migrate between the printed layers, effectively preventing drying -induced shrinkage by retaining and redistributing water between these layers (FIG. 21). Furthermore, the prehydrated products dissolved in the pore water have the capacity to migrate between the printed layers and enhance the interfacial bonding strength between layers. To verify this, we measured the interfacial bonding strength of a 3D-printed concrete cube and compared it to its identically sized cast cube. We observed that the concrete with DE resulted in a 178% improvement in interfacial bonding strength compared to concrete mixtures that do not incorporate DE (FIG. 22).

[0108] Carbonation of 3D printable concrete

[0109] Upon contact with water, concrete initiates a hydration reaction, wherein the primary cement ingredients, tricalcium silicate (3CaO • SiCE, C3S) and dicalcium silicate (2CaO • SiCh, C2S), react with water to form calcium silicate hydrate (C-S-H) gel and calcium hydroxide (Ca(OH)2). These reactions bind the concrete and influence its overall structure and properties. When exposed to CO2, the hydrated and unhydrated products, along with Ca(OH)2, react with CO2, leading to the formation of stable calcium carbonate (CaCCE) for permanent CO2 sequestration. With the high porosity and surfacearea contributed by DE in the concrete, we hypothesize that DE can maximize exposure to CO2 during carbonation, enhancing overall CO2 sequestration efficiency.

[0110] To test this hypothesis, we pre-hydrated the concrete material for 24 hours. During pre-hydration, C3S, C2S, and Ca(OH)2 release calcium ions (Ca2+) and silicate ions (SiO ') into the pore solution within the concrete. SEM images of the 24h pre-hydrated sample revealed pores on the DE surrounded by pre-hydrated substances (FIG. 23). The concentration gradient established during pre-hydration drove the migration of ions, particularly Ca2+, facilitated by water in the concrete pores. In the concrete material with DE, this process intensifies due to two reasons. First, DE pores, during mixing and printing, hold a substantial amount of water, creating a greater ion concentration gradient. Second, negatively charged silica nanoparticles in DE bind Ca2+on the surface (FIG. 23).

[0111] We then introduced the pre-hydrated material to CO2 and N2 environments at atmospheric pressure, ambient temperature, and 80% relative humidity (RH). In the N2 environment, continuous curing occurred through the hydration reaction, with SEM images showing hydration products closing up pores on the DE (FIG. 24). The surface area of the material with DE decreased by 36.5% after 7 days of curing in the N2 environment (FIG. 25). A similar trend was observed in concrete without DE, with a 38.5% decrease in surface area (FIG. 25). Pore volume - pore width distribution curves indicated a drastic reduction in pores smaller than 4nm after 7 days of curing in the N2 environment (FIG. 26).

[0112] When the 24-hour pre-hydrated material is exposed to a CO2 environment, the prehydrated substances begin to react with the CO2 to produce CaCCE. SEM images reveal that the pores on the DE became clear and opened up again, with rhombohedral calcium carbonate formed adjacent to the DE (FIG. 27). With the pores reopening, the material with DE maintains a high surface area and pore volume, establishing a continuous channel for CO2 to flow in and carbonate with the concrete. While the material without DE in a CO2 environment shows a similar trend of minimal change in surface area, the DE material exhibits a 240% higher surface area than the material without DE, even after 7 days of carbonation (FIG. 25 and 26). The mechanism of pores reopening and remaining open is attributed to DE acting as active nucleation sites for prehydration products attached to the DE, forming CaCCh. This nucleation processdepletes the local area around the DE of Ca2+and CO2-, inhibiting nucleation around the site and allowing continuous CO2 capture.

[0113] To quantify CO2 sequestration, we employ the thermogravimetric analysis (TGA) and analyze it with differential thermogravimetric (DTG). DTG curves of DE material cured in N2 and CO2 environments displayed distinct peaks within three main sections, including dehydration (30-300 °C), dehydroxylation (380-500 °C), and decarbonation (600-950 °C) (FIG. 28). For CCE-cured material, mass loss from CO2 in the decarbonation range increased with curing days, confirming CO2 absorption and sequestration as CaCCE. Material with DE sequestered 477.8g of CO2 per 1kg of cement, which is 145% more than concrete without DE at 1 day of carbonation (FIG. 29). This enhanced CO2 sequestration efficiency of the material with DE continued to outperform the material without DE for up to 7 days.

[0114] As CO2 is sequestered in the stable form of CaCCE, it enhances the mechanical properties, with compressive test results consistently showing higher strength in CCE-cured samples compared to N2-cured concrete over various curing times (FIG. 30).

[0115] Summary

[0116] The presented technology provides a revolutionary 3D-printable concrete material addressing challenges in the construction industry. This innovation involves incorporating diatomaceous earth (DE), a natural biomineral, to create a concrete that is lightweight, possesses high strength, and actively captures and stores carbon dioxide (CO2). Features of particular note include:

[0117] 1. Carbon Capture and Storage (CCS) in Concrete:

[0118] The concrete composition actively captures and stores CO2 through a carbonation process, converting CO2 into stable calcium carbonate (CaCCE).

[0119] This approach not only reduces the carbon footprint of the final product but also enhances durability and distinguishes itself in terms of cost-effectiveness and low energy consumption.

[0120] 2. 3D Printability and Structural Strength:

[0121] DE serves as a rheological modifier in the 3D printable concrete ink, improving pumpability and extrudability.

[0122] The material exhibits remarkable shape retention and strain-hardening behavior under load, enabling the successful printing of intricate structures with increased weight-bearing capacity.

[0123] A lightweight characteristic facilitates stacking up to 111 layers (200 mm) without collapsing, showcasing buildability.

[0124] 3. Hierarchical Porosity and Water Retention:

[0125] DE's inherent hierarchical porosity acts as a water reservoir, preventing drying-induced shrinkage and cracking.

[0126] The material's ability to redistribute water and pre-hydrated substance between printed layers enhances hydration during the printing process and ensures uniform carbonation.

[0127] 4. Material Composition and Properties:

[0128] The concrete formulation replaces up to 50 wt.% of ordinary Portland cement with DE, contributing to reduced material waste and improved sustainability.

[0129] DE's porosity and physical properties introduce supplementary porosity, reducing overall density and without sacrificing compressive strength.

[0130] 5. 3D Printing Performance:

[0131] Rheological tests demonstrate the material's suitability for 3D printing, featuring desirable properties such as shear-thinning behavior and thixotropy.

[0132] The material consistently maintains shape across various nozzle diameters, showcasing shape retention and reduced deformation.

[0133] 6. Carbonation and CO2 Sequestration Efficiency:

[0134] The concrete efficiently captures and stores CO2, outperforming materials without DE in terms of surface area and pore volume.

[0135] DE's role as an active nucleation site enhances CO2 sequestration efficiency, with the material achieving 145% more CO2 absorption than concrete without DE.

[0136] In conclusion, the disclosed 3D-printable concrete material addresses environmental concerns, enhances construction efficiency, and opens new possibilities for sustainable building practices. The integration of DE provides a multifaceted solution that not only improves material properties but also contributes to the global effort to mitigate carbon emissions in the construction industry.

[0137] Additional Disclosure

[0138] As explained elsewhere herein, the integration of diatomaceous earth, a highly accessible biomineral with hierarchical porosity, facilitates CaCCh nucleation and mitigates carbonation resistance, achieving a maximum CO2 absorption of 488.7 gCCh per kg cement in 7 days, a 142% increase over conventional concrete. Geometric optimization enables uniform carbonation, reduces material usage by 78%, and enlarges the surface- area-to-volume ratio by 515%, increasing CO2 uptake by 30% compared to solid structures. This approach offers a scalable, sustainable solution without compromising structural integrity.

[0139] Here, we demonstrate 3D printing of CCS concrete in diamond TPMS structures by replacing cement with abundantly available biomineral, diatomaceous earth (DE) of hierarchical porosity, and optimize the design and printing tool path to realize large overhangs. By leveraging the material properties of DE and the geometric design of diamond-based TPMS structures, we achieve uniform CO2 uptake throughout the bulk, while maintaining structural integrity. DE, derived from remains of fossilized diatom with 80-90% SiC>2, is a naturally abundant porous material with a global production of 2.6 million tons in 2023. Its hierarchical pore structure (2-100 nm) FIG. 34) enhances nutrient absorption, gas exchange, and structural support (26). Integration of DE imparts many advantages, including shear-thinning rheology for smooth extrusion, rapid structural recovery for self-supporting prints, water retention and redistribution to mitigate shrinkage-induced cracking during drying, and reduced density that useful to realize TPMS structures in concrete with a large overhang angle, 0, up to 45° (FIG. 3 IB). The TPMS design reduces material usage by 78%, while increasing the surface -area-to-volume ratio by 515%. Meanwhile, gas adsorption analysis confirms that DE exhibits superior CO2 sorption capacity compared to silica fume (SF), a commonly used SiCh-based SCM (FIG. 35). Through the interactions with CaO hydration products, DE further reduces carbonation resistance and promotes nucleation and growth of CaCCh crystals for increased compressive strength. Leveraging both the material benefits of DE and the geometric advantages of TPMS, the 3D-printed CCS concrete structures exhibit a 30% higher CO2 conversion and a 32% greater CO2 uptake rate than conventional solid cubes.

[0140] Design and Characterization of 3D Printable Biomineral -infusedConcrete.

[0141] The hierarchical pores in DE (micron-sized pores in the skeleton and nanopores in silica) are anticipated to enhance CO2 absorption efficiency, s we systematically increase the DE / binder mass ratio (binder refers to the combined mass of cement and DE), a linear relationship is observed between the reduction of concrete density and the increase in porosity (FIG. 3 IB and FIG. 36). Brunauer-Emmett-Teller (BET) analysis confirms increased pore sizes (2-10 nm) as the DE / binder ratio is over 0.3, resulting in a high BET surface area (>11.6 m2 / g) (FIG. 31C and FIG. 37). The porous scaffold of DE can retain a substantial amount of water, preventing premature drying of the printed concrete (FIG. 3 ID) without compromising the concrete ink viscosity (FIG. 36A). Proper water management during 3D printing is essential to maintain the desired rheological properties and prevent crack formation caused by uneven dehydration across printed layers. A high water / binder ratio may weaken mechanical strength, while a low ratio could increase the risk of nozzle clogging. Upon curing, hydration reactions occur as tricalcium silicate (3CaO SiCh, C3S) and dicalcium silicate (2CaO SiO2, C2S) react with water to form calcium silicate hydrate (3CaO SiO2 31420, C-S-H) gel and calcium hydroxide (Ca(OH)2), which governs structural integrity and mechanical properties. Therefore, the DE / binder mass ratio = 0.3 is chosen in our experiments to balance the needs for CO2 uptake and mechanical integrity. A compressive strength of 23.4 ± 0.12 MPa is obtained after 28 days in saturated limewater, comparable to conventional OPC concrete (20-40 MPa) (28) (FIG. 3 IE and fig. S5). For comparison, concrete cured from pure cement and SF samples with the same water / binder mass ratio exhibit lower strengths, 13.4 ± 0.69 MPa and 8.27 ± 0.11 MPa, respectively, attributed to excess water in the mixture, generating larger pore volumes (FIG. 3 IE). Interestingly, the DE-enhanced concrete continues strengthening over 90 days due to pozzolanic reaction forming additional C-S-H gel, while the control samples without DE plateau at 28 days.

[0142] Design and 3D Concrete Printing of Triply Periodic Minimum Surfaces

[0143] 3D concrete printing is a multifaceted process that needs to consider pumping efficiency, extrusion quality, shape retention, layer stacking ability, and material integrity post-printing and curing (FIG. 38). Concrete printing also involves a complex shear scenario across various printing stages. We subject the fresh concrete inks to varying shear rates to simulate the 3D printing stages. Although both the concrete inks with and without DE demonstrate shear-thinning behaviors (FIG. 39 A), the DE-infused ink rapidlyrestores its initial viscosity and yield stress within a second at 100 s ', ensuring extrusion stability and effective layer stacking (Fig. 2A). In contrast, the control ink recovers only 76% (FIG. 39). We next examine the ink's ability to retain its shape when extruded through nozzles of different diameters. Nozzles larger than 20 mm are commonly used in mid and large-scale robotic concrete printing. DE-infused ink consistently maintains a width / height (b / d) ratio <1.1 across nozzle diameters up to 21 mm, attributed to its lower density (1,700 kg / m3) (Fig. 2B and fig. S8). The control ink, with a density of 2,100 kg / m3, reaches b / d = 1.2 for nozzle diameters above 6.8 mm due to gravity effects.

[0144] The load-bearing capacity of the printed concrete ink relates to its stacking height. Once the concrete is deposited, it reaches a stable state, while the hydration reactions continue, gradually increasing its strength over time. To investigate the change in the strength of the concrete ink post-extrusion, we perform micro-indentation onto the freshly printed concrete inks at various time intervals after they are stabilized from the high shear rates. The DE-infused concrete has nearly identical stiffness to the control ink over an hour, despite using less cement and more water. After setting for 30 min, DE-infused concrete exhibits strain-hardening due to enhancing interparticle cohesion and yield stress. Conversely, the concrete without DE exhibits a drastic drop in post-yield strength after reaching its yield point, making it highly susceptible to catastrophic failure. In buildability tests by continuously printing a single-wall cylinder, the DE-infused concrete sustains stacking up to 111 layers till exhausting the ink, reaching an aspect ratio of 42, while the control ink fails after 43 layers due to uneven drying and high density (FIG. 19). In fact, the exposed lower layers experience early hydration reactions, leading to shrinkage, cracks, and structural instability. In contrast, water can migrate through DE’s hierarchical porosity, preventing differential drying across printed layers in DE-infused concrete, and retaining moisture in the lower layers for up to 20 hours under ambient conditions (FIG. 40). We hypothesize that hydrated products (e.g., Ca2+, OFF) can also migrate along with water between layers, enhancing interfacial bonding, which is typically a weak point that compromises the mechanical performance of 3D-printed structures. To test this hypothesis, we measure the interfacial bonding strength of 3D-printed and cast concrete cubes, with and without DE. The DE-infused, printed concrete exhibits a 178% increase in interfacial strength ratio (vs. the cast sample) compared to that printed from the conventional concrete (FIG. 41).

[0145] Compared with simple geometry such as cylinders with 0 = 0°, complex highly porous structures with 0 > 45° for high surface-area-to-volume ratios are much more delicate and face new challenges especially when printed in concrete: extensive support structures are typically required but removing them could break the brittle concrete prints. Here, we employ a post-tension design and optimization strategy (18, 30) that transforms the self-supporting diamond TPMS into the desired forms, followed by post-slicing overhang analysis to assess printability (FIGS. 42, 43). Diamond TPMS is selected as the basis for our design due to its superior mechanical strength and loadbearing capacity (30). Its periodic anticlastic surfaces and straight lines simplify the 3D printing process and minimize the need for support. These features also enable geometric transformations, such as rotation, scaling, and mirroring, without compromising structural integrity, allowing for efficient adaptation to design requirements with improved load distribution, reduced overhangs, and optimized printability. To validate our approach, we print two TPMS-based structures using DE-infused concrete with a maximum 0 = 450without any support. Figure 2e shows a printed scaled diamond TPMS unit cell with two periodicities, achieving 66% reduction in material usage and 274% increase in surface area-to-volume ratio compared to the identical bounding box of the smallest rectangular geometry that completely encloses the structure (FIG. 44 A). We further print a unit of a post-tensioned concrete canopy, resulting in 78% reduction in material usage and 515% increase in surface area-to-volume ratio compared to its identical bounding box (Fig. 2F and FIG. 44B). These optimized structures, along with the improved concrete printing performance, can withstand large overhangs (up to 45°) without layer collapse during printing.

[0146] CO2 Sequestration and Carbonation Mechanism in DE-Infused Concrete

[0147] To evaluate the CO2 sequestration efficiency, we pre-hydrate the concrete with and without DE for 24 h. This process facilitates the release of Ca2+and SiO42' from C3S, C2S, and Ca(OH)2 into water retained in the pores of DE and concrete mixtures, driven by the ion concentration gradient (33) (Fig. 32A). Limited prehydration could cause CaCCE to encase the unhydrated cement, hindering the binding effect and limiting the carbonation reactions (27). As seen from the scanning electron microscopy (SEM) images (FIG. 32B), after 24 h of prehydration, an acicular Type I C-S-H (needlelike ettringite structure) is formed within the concrete and on the DE surface. Waterretained within the DE pores facilitates the ion migration process, thereby amplifying the ion concentration gradient and promoting interactions between Ca2+and the negatively charged DE. Type I C-S-H and prism-like calcium hydroxide crystals (Ca(0H)2) are also present randomly in the concrete without DE (FIG. 45). The prehydrated samples are subsequently introduced to a pure CO2 environment under ambient pressure and 75% relative humidity (RH). High-purity CO2 accelerates the concrete carbonation rate and increases the degree of carbonation. Thus, it is commonly used in the concrete carbonation process. Furthermore, high concentration CO2 from industrial waste flue gases is readily available. Careful control of RH is essential for optimizing the concrete carbonation reactions; excessive moisture can block the pores and hinder CO2 diffusion (35). The CO2 adsorption isotherm shows that after 24 h of prehydration, DE -infused concrete achieves higher adsorption of CO2 compared to concrete without DE (FIG. 32G). After 7 days of carbonation, DE surface was cleared up. Instead, stable calcite crystals exhibiting a characteristic rhombohedral morphology are formed in the adjacent regions (FIG. 32C and D, FIG. 45 and 46). The re-emergence of pores on DE leads to a surface area (20.5 m2 / g), 240% higher than that of concrete without DE (8.57 m2 / g), primarily attributed to micropores (pores < 2 nm) (FIG. 32H and FIG. 47).

[0148] Typically, the carbonation product (CaCCE) has a higher molar volume than Ca(OH)2 and C-S-H, resulting in a significant decrease in porosity. However, in this case, the large surface area and increased pore size / pore volume benefit the continuous carbonation process. To further understand the mechanism, we compare the carbonated concrete to a control group exposed to an N2 environment, representing continuous curing through hydration (FIG. 32E and FIG. 45). SEM images reveal the continuous formation of ettringite clusters resulting in occluding pores on DE in the concrete after 7 days of curing under N2 (FIG. 32F), and reduction in surface area over time (FIG. 32H and FIG. 47). During prehydration, the pozzolanic reaction of DE promotes the early formation of C-S-H around the DE particles. When set in an N2 environment, the reaction continues, promoting further formation of C-S-H and occluding the pores on DE. The high surface area of DE allows for numerous sites for nucleation and growth of CaCCE. In contrast, when exposed to CO2, CO2 molecules diffuse into the concrete pores through DE, dissolve in water, and form carbonate ions. Carbonation reaction promotes the dissolution of hydration products and their reactions with the prehydrated products. Meanwhile, masstransport depletes Ca2+and CCE2' ions locally over the DE surface, creating undersaturation, leading to the formation of calcite crystals outside of DE and re- emergence of pores on DE surface (FIG. 32B), in agreement with literature.

[0149] The capacity of CO2 stored in carbonated concrete is quantified by thermogravimetric analysis (TGA) (FIG. 321 and FIG. 48). DE-infused concrete stores up to 488.7 gCO2kgcement'1after 7 days of carbonation, a 142% increase over concrete without DE (FIG. 321). This enhanced carbonation efficiency is attributed to DE's ability to mitigate carbonation resistance in concrete and the inherent reduction in cement content. To reveal how DE-infused concrete may improve CO2 diffusion, we cast samples with and without DE in 10 cm tubes, exposing only one surface to CO2 over 7 days. We then drill the tubes stepwise (FIG. 49) and measure CO2 uptake across depths. While CO2 uptake, in general, decreases with sample depth, it ceases beyond a depth of 20 mm in the concrete without DE. In contrast, even at depths of 20-30 mm, the DE-infused concrete retained 65% of the CO2 uptake at its surface layer (0-5 mm) (FIG. 32J). Efficient CO2 diffusion assists the growth of stable calcite, enhancing early strength and durability: compressive tests consistently show higher strength in CCE-cured samples compared to N2-cured ones over the first 96 hours (FIG. 50).

[0150] Carbonation Efficiency of the 3D Printed TPMS Structures

[0151] We next assess the contribution of TPMS geometry to CO2 uptake enhancement beyond the material’s effect. A 3D printed diamond TPMS structure and a cast solid cube with the same bounding box volume are placed in a CO2 chamber for 7 days after 24 h of pre-hydration (FIG. 33A and FIG. 44). Stepwise sample collection and TGA results show that the TPMS structure achieves CO2uptake of 423.7 ± 3.6 gCO2kgcement'1at the surface and 393.2 ± 4.5 gCO2kgcement'1at the core layer (only a 7.2% drop). In contrast, CO2 uptake in the solid cube drops by 81% from 344.1 ± 8.3 gCCE kgcement'1at the surface to 64.8 ± 2.9 gCO2kgcement'1at the core. Notably, within the same surface depth range (0-10 mm), the TPMS structure exhibits 122% higher CO2 uptake than the cast cube, attributed to the corrugated surface of the TPMS geometry, which further enhances the surface area for carbonation. Using the maximum CO2 uptake of DE-infused concrete (FIG. 321) as a reference for 100% uptake efficiency, we estimate total CO2 uptake based on mass and layer-by-layer analysis. The TPMS structure with a DE / bindermass ratio of 0.3 achieves an uptake efficiency of 85% vs. 55% for the cube, highlighting the geometric advantage of a 274% higher surface area-to-volume ratio (FIG. 33B).

[0152] To explore TPMS structural benefits, we transform four flat surfaces of a standard ASTM Cl 09 cube into diamond TPMS surfaces and thickened them to form walls. Considering the potential buckling of the thin-walled TPMS structure, we reinforce it by offsetting contour surfaces inward and filling the internal cavities (FIG. 33C, FIG. 51). This approach increases material usage but still reduces overall material volume by 11% while achieving a 27% higher surface area-to-volume ratio than the bulk cube (FIG. 51). We note in meter-scale floor assemblies, adhesives, rebar, and support structures can be used to enhance the overall strength, which is ongoing. Here, we focus on the material assessment of individual TPMS units. Finite element analysis of stress distribution under compression reveals stress concentrations along the edges and walls of the solid cube, whereas in the TPMS cube, stress is more pronounced at the edges due to boundary effects (FIG. 52). Compression tests show a 10.5% lower compressive strength than the solid cube; however, specific strength and stiffness are minimally reduced by 0.02% and 2.3%, respectively.

[0153] To evaluate the geometry effect on CO2 uptake rate, we continuously measure CO2 concentration in a closed chamber for 60 s for both cast solid cube and printed TPMS cube under ambient conditions (450-480 ppm CO2), utilizing an automated CO2 flux system (FIG. 53). Over 5 cycles, the cast solid cube with five open surfaces absorbs four times more CO2 than the single-surface cube (FIG. 33D(ii) and FIG. 54). The non-linear CO2 uptake vs. surface area may result from competition for CO2 among adjacent surfaces, therefore, reducing the overall absorption efficiency. Nevertheless, the 3D printed TPMS cube demonstrates a further 9% reduction in CO2 concentration within the observation period compared to the cast cube (FIG. 33D(iii)). After normalizing the CO2 uptake rate by the total cement usage in each structure, the TPMS cube achieves a 32% higher uptake rate than the cast cube (FIG. 33E).

[0154] Conclusion

[0155] In this disclosure, we present a sustainable and 3D-printed CCS concrete by replacing cement with naturally abundant biomineral, DE, featuring hierarchical porosity, and the optimal design of self-supported, highly porous diamond TPMS structures. DE provides the necessary rheology for printing intricate TPMS structures,prevents non-uniform dehydration during printing, and enables a maximum CO2 absorption of 488.7 gCCh kgcement'1within 7 days — a 142% increase compared to conventional concrete. DE-infused concrete allows for deeper and more uniform carbonation throughout the structure. We further elucidate the role of DE beyond being simply a porous material for carbonation. We show that DE reduces carbonation resistance, allowing the re-emergence of pores for continuous carbonation, and promotes nucleation and growth of CaCCE crystals for increased compressive strength.

[0156] The TPMS design reduces material usage by 78%. Together, the highly porous geometry and the use of DE lead to 30% improvement of the CO2 uptake efficiency compared to a solid cube of the same volume. The continuous monitoring of CO2 concentration changes reveals that the optimized TPMS design improves the CO2 uptake rate by 32%. Our concrete design outperforms the state-of-the-art OPC-based concrete in carbonation efficiency, approaching the theoretical CO2 uptake maximum within just 7 days (FIG. 55, Tables S3, S4). Here, through optimized geometry that minimizes material waste, and understanding various roles of highly accessible, nature’s products, DE, in concrete 3D printing, we offer insights that advance sustainable, scalable, and high-performing next-generation infrastructures.

[0157] Materials and Methods

[0158] Material composition and preparation

[0159] The concrete ink formulation first started with the dry mixing of ASTM C-150 type I Portland cement (Quikrete, USA) and natural diatomaceous Earth (DE) (DiatomaceousEarth.com) at a weight ratio of 7:3 to serve as the binder. Subsequently, all- purpose sand (Quikrete, USA) was sifted through a No. 20 sieve (ASTM El 1 Test Sieve) and dry-mixed with the binder in a 2: 1 weight ratio. For enhancing extrudability during 3D printing, hydroxypropyl methylcellulose (HPMC) was incorporated as a viscositymodifying admixture (VMA) at a concentration of 0.4 wt% relative to the binder. Following the dry material homogenization at medium speed for 2 minutes using a stainless-steel mixer (KitchenAid Classic Stand mixer), 0.87 wt% of deionized (DI) water corresponding to the binder was introduced into the mixer. The mixing process involved initial low-speed blending for 60 seconds, followed by medium-speed mixing for 120 seconds, with intermittent manual scraping to ensure thorough incorporation and prevent material adherence to the sides. Throughout the mixing, the mixer was covered to avoidwater loss. The mixed fresh concrete was utilized within 3 minutes for subsequent 3D printing and characterization. The chemicals were used as purchased without further purifications. In the case of various DE / binder ratio concrete mixtures, the ratios of sand to binder and VMA to binder remained consistent. The water / binder ratio varied based on the DE / binder ratio, determined by the equation: W water = 0.5 * Wcement + 1.73 * WDE, where W water is the water weight, Wcement is the cement weight, and WDE is the DE weight. It is crucial to note that the constants (0.5 and 1.73) may be adjusted based on material sources, with the final values determined through the assessment of mixture extrudability using a 2 mm nozzle syringe. To evaluate the impact of microstructure variations — specifically, the presence or absence of pores - on the mechanical strength of concrete under high water content conditions, DE is replaced with an equivalent weight of ASTM C-1240 silica fume (Sikacrete - 950DP, Sika) and all other parameters are kept the same.

[0160] Rheological characterization

[0161] The rheological properties of the fresh concrete were tested using a temperature-controlled rheometer (DHR-3, TA Instruments) with a 40-mm-diameter parallel plate. The measurements were carried out at 23 °C with an 8000 pm gap and began immediately after material preparation. The concrete mixture was pre-sheared at a rate of 100 s'1for 60 seconds and then left to rest for 60 s before each test. The thixotropy test included 3 steps. Firstly, the sample was sheared by a constant shear rate of 0.1 s'1for 60 s. Secondly, the sample was sheared by a constant shear rate of 100 s'1for 30 s. Lastly, the sample was sheared by a constant shear rate of 0.1 s'1for 60 seconds. Shear-thinning was evaluated from 0.1 s ' to 150 s ' within 120 s and then decreased from 150 s ' to 0.1 s ' in 120 s.

[0162] Mechanical testing

[0163] Cubes (5x5x5 cm, ASTM Cl 09) and cylinders (diameter: 15 mm, height: 30 mm) were used for compressive strength testing. For the compressive strength of the hydrated cured sample, the material was cast in the mold for 24 hours at room temperature (23 °C) and then fully immersed in saturated limewater at room temperature (23 °C) until the desired curing age (3 days, 7 days, 14 days, 28 days, 60 days, and 90 days). Subsequently, the samples were wiped free of surface water and tested using a mechanical tester (Instron 4206) with a 1 mm / min loading rate until failure. For the compressive strength of the carbonated samples, testing occurred immediately after thecarbonation process at different carbonation times (6 h, 1 day, 2 days, 3 days, and 4 days). The interfacial bonding strength of the 3D printed structures was measured through the three-point bending test. 3D printed cubes (5x5x5 cm) were manufactured with the same printing parameters as outlined in the 3D printing section and were loaded onto a mechanical tester with a supporting span of 4 cm and a loading rate of 1 mm / min, testing until failure. The upper anvil was positioned between two printed layers at the center of the specimen. The force-displacement curve and Young’s modulus of the concrete mixture at different setting times were determined by compacting wet concrete in a petri dish (height: 20.3 mm, diameter: 50 mm) and using a round-flat end cylinder indenter with radius R=0.5 mm loaded onto the Instron mechanical tester to indent the center of the sample by applying force F to a certain indentation depth 6. Young’s modulus was calculated as E=F(l-u2) / 2R5, where u =0.5 is the Poisson ratio of the fresh concrete. The interfacial strength ratio is defined as the maximum strength of a 3D printed cube under a 3-point bending test divided by the strength of a cast cubic sample of the same size.

[0164] Physical properties

[0165] The dry density of materials with various DE / binder mass ratios was determined by drying the samples in a vacuum chamber at 80 °C for 24 hours until a constant weight was achieved. The dry density was calculated by dividing the dry mass of the concrete sample by its volume. The porosity of materials with various DE / binder mass ratios was determined by fully immersing the sample in water and sonicating it for 1 h. The sample was then wiped to remove surface water, and the weight was measured. The absorbed water weight was used to calculate the pore volume of the sample, and the porosity was determined by dividing the pore volume by the total volume of the sample.

[0166] 3D Printing

[0167] To conduct printing tests, an in-house-developed desktop concrete 3D printer with a 25x25x25 cm printing volume is used. The printer adapted a multiple-step extrusion method that is composed of a nozzle with an embedded auger and a 2L syringelike material hopper. The printer is equipped with two extra stepper motors in addition to the three motors driving the gantry in the XY and Z directions. Of the two additional motors, one controls the auger that is embedded in the nozzle to provide a shear force on the concrete through the spinning to achieve shear-thinning and enhance the extrudability of the concrete; the other stepper motor paired with a 1:20 reducer gearbox and drive alinear piston moving linearly to compress the concrete from the material hopper to nozzle through PVC hose (FIG. 38). The rotational speed, direction, torque, and power supply of both stepper motors are numerically controlled through the programmable logic controller and are set to the same parameters for all the printing described in this disclosure.

[0168] Printing characterization

[0169] The extrudability and shape retainability of the concrete inks were characterized using the 3D printing system. Various diameters of nozzle heads (2, 4.8, 6.8, 11, 16, and 21 mm) were installed on the printing head to assess whether the fresh concrete could be successfully extruded. The extruded material was printed into a straight line with a layer height 1.2 times that of the nozzle diameter, which prevented the nozzle from squeezing the deposited material. The printed lines from different nozzle sizes were then cured in a humidity chamber (RH > 95%) for 24 hours. Subsequently, a sharp blade was used to cut the printed lines at different locations, and a micro-camera combined with the image processing tool (ImageJ) was employed to measure the width and height of the cut cross-section. The material buildability was characterized by printing a 10 cm diameter cylinder structure with a 4.8 mm line width and a 1.8 mm layer height, continuously printing to 111 layers (equivalent to 200 mm) or until failure.

[0170] Carbonation

[0171] Cylinder samples (Diameter: 15mm, Height: 30mm) were prepared for the carbonation test. The concrete material was initially cast (pre-hydrated) in the mold for 24 hours at room temperature (23 °C). The sample was then de-molded and transferred to a 1 -gallon airtight sealed bag. Pure humid CO2 was injected into the carbonation bag at one atmospheric pressure every 6 hours, and the relative humidity in the carbonation bag was maintained at 75% using a saturated sodium chloride solution. For the control group, pure humid N2 was injected instead of CO2. The samples were removed from the carbonation bag after various carbonation times (6h, 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, and 7 days) and stored immediately in a vacuum desiccator until characterization.

[0172] Carbonation characterization

[0173] The quantity of absorbed CO2 was characterized by a thermogravimetric analyzer (TGA-DSC SDT650, TA Instruments). The material was ground and sifted through a No. 20 sieve (ASTM El l Test Sieve). The material was then loaded into an aluminum pan. The furnace was heated from 30°C to 1000 °C with a ramp rate of 10°C / min under a constant N2 flow of 100 mL / min. The derivative thermogravimetry (DTG) curves were then obtained by taking the first derivative of the weight signal with time and plotting it as a function of temperature. Powder X-ray diffraction (XRD) diagrams were collected using a Rigaku Smartlab high-resolution diffractometer with Cu Ka radiation ( = 1.5416 A, 30 mA, and 40 kV) with a parallel beam setting in the 0-29 geometry. The 29 range is screened between 20 and 800with data points collected every 0.05° (29) using a scan speed of 35 s per step. CO2 and N2 adsorption-desorption isotherms were collected using a surface area and porosity analyzer (TriStar II Plus-3030, Micromeritics Inc., USA). CO2 as the adsorbate was performed at 273 K, and N2 as the adsorbate was completed at 77 K. Prior to the experiment, samples were degassed at 105 °C for 24 h under vacuum. The adsorption-desorption isotherms were evaluated to give the pore size distribution and cumulative volume based on non-local density functional theory (NLDFT) from the absorption isotherm, as well as Brunauer-Emmett-Teller (BET) surface areas.

[0174] Image analysis

[0175] SEM micrographs were collected using environmental scanning electron microscopy (FEI Quanta 600 ESEM). TEM micrographs were collected using a JEOL 1400 microscope operated at 120 kV. The TEM was calibrated using a MAGICAL TEM calibration standard.

[0176] Sample Preparation for CO2 Uptake Measurement at Various Depths

[0177] To assess CO2 uptake at different depths, a stepwise drilling approach was implemented on carbonated concrete samples (FIG. 49). A concrete sample was cast in a plastic tube (3 cm in diameter, 10 cm in length) and carbonated for 7 days with only the top surface exposed, with the sides sealed using Parafilm to restrict carbonation to a single surface (Step 1). A 3 / 16” drill bit was first used to collect powder samples from the target depth (Step 2). To minimize cross-contamination, a 1 / 2” drill bit was then used to clear the surrounding material at the same depth (Step 3). This process was repeated for deeper layers, alternating between the 3 / 16” and 1 / 2” drill bits to ensure precise sampling at each designated depth (Step 4). For comparing CO2 uptake efficiency between the 3D printed TPMS structure and a solid cast cube with the same bounding volume, both structures underwent a 1-day pre-hydration followed by 7-day carbonation in a CO2 chamber.

[0178] CO2uptake rate

[0179] The CO2uptake rate was measured using an automated long-term chamber with a 20 cm collar (8100-104, LI-COR Biosciences), a multiplexer to link the chamber to the gas analyzers (LI-8150, LI-COR Biosciences), and an automated Soil CO2 flux system to measure CO2 concentrations (LL8100A, LI-COR Biosciences). The 3D- printed and cast samples were stored and cured in a humidity chamber (>95%) with pure humid N2filled for 24 hours before measuring the CO2uptake. The samples were introduced into the testing chamber for 5 cycles. In each cycle, the chamber opened with a 45-second pre-purge of fresh air, then closed for a 1 -minute observation period to measure CO2 concentration. The 1 -minute observation period was selected to allow sufficient time for detecting changes in CO2 concentration while minimizing excessive CO2 depletion within the chamber. Following the observation period, a 45-second post-purge reset the chamber to ambient CO2 levels, which is essential for maintaining accuracy and consistency across measurements.

[0180] Finite element analysis (FEA)

[0181] In the FEA simulation (Abaqus / Standard), the concrete corresponding to solid and TPMS cubes are modeled as linear elastic, isotropic material with the measured Young’s modulus of 3.5 GPa and Poisson’s ratio of 0.2. The built geometric are imported into Abaqus CAE as STL files and are meshed to solid quadratic tetrahedral elements (C3D10). A mesh refinement study was conducted to verify the accuracy and convergence of the solution. Static analysis is performed for compression. The minimum time step is set to 10-12 to ensure the accuracy.

[0182] Effect of Water Retention by Diatomaceous Earth on Concrete Strength Development

[0183] To evaluate how the water-retaining ability of DE affects concrete’s mechanical performance, we select a composition with a DE-to-binder mass ratio of 0.3 as the model material. This composition demonstrates a compressive strength of 23.4 ± 0.12 MPa after curing in the saturated limewater for 28 days, within the range of a typical OPC concrete (20 - 40 MPa) (FIG. 3 IE and fig. S5). For comparison, two control groups are formulated: one consists of pure cement as the binder, that is DE-to-binder mass ratio = 0, the other uses SF to replace cement with an SF-to-binder mass ratio = 0.3. The water-to- binder mass ratio is kept the same, 0.87, as that of the 0.3 DE / binder formulation. Afterbeing cured in the saturated limewater for 28 days, the cement-only sample reaches a compressive strength of 13.4 ± 0.69 MPa, while the sample containing SF achieves a strength of 8.27 ± 0.11 MPa (FIG. 3 IE). Additionally, the 0.3 DE / binder concrete sample continues to gain strength and reaches a peak compressive strength of 30.5 ± 0.57 MPa after being cured for 90 days, due to the pozzolanic effect, where the silica in DE reacts with Ca(OH)2 to form C-S-H. In contrast, the compressive strengths of the two control groups plateau after 28 days. The lower strength of the two control samples can be attributed to the excess water in the mixture with a water -to-binder ratio of 0.87, which is higher than 0.4-0.6 for conventional cast concrete, thus, generating a large pore volume after concrete curing and drying. The excess water retained by DE, however, is essential to formulate the printable concrete ink. The sample containing SF exhibits the weakest compressive strength, which could be due to the lowest binder content among the three. We hypothesize that during curing, DE’s hierarchical porous structures generate a concentration gradient of pre-hydration products released from the cement, such as calcium ions (Ca2+) and silicate ions (SiO '), and facilitate the chemical reactions between the free lime, Ca(OH)2, and DE, resulting in the formation of additional C-S-H gel. This gel acts as a binder, providing significant and continuous increases in compressive strength for the concrete containing DE.

[0184] Geometrical Design and Optimization of Triply Periodic Minimal Surfaces

[0185] The complex structures of the triply periodic minimal surfaces (TPMS) present significant challenges during 3D concrete printing, which requires substantial overhangs. Unlike typical fused deposition modeling (FDM) materials, such as thermoplastics, which solidify immediately upon extrusion, concrete requires time to harden and attain its full strength. This lag complicates the printing of intricate TPMS geometries, particularly on an architectural scale, necessitating extensive support structures in conventional concrete casting. Removal of the supports is laborious, causes material and energy waste, and requires significant post -processing. Therefore, we transform the TPMS geometry to achieve a high surface area and self-supporting structure suitable for 3D concrete printing. To elucidate our design principle, we use the diamond (D) TPMS unit cell as a case study and analyze the overhangs. We design a D surface composed of two-unit cells with a wavelength of 70 mm (FIG. 42A). The surface isthickened by 8 mm to create a printable volume. The geometry is then sliced with a layer height of 2.8 mm (FIG. 42B) for overhang analysis (FIG. 42C). The overhang at a specific point on the toolpath is defined as the horizontal offset relative to the previous layer, divided by the layer height (FIG. 42D). An overhang value of 1 corresponds to a 45° local inclination, generally acceptable for most 3D printable materials without additional support structures. The cumulative distribution of overhangs (FIG. 42C and E) shows that the original TPMS structure has 18% of points with overhangs greater than 1, suggesting the high probability of printing failure due to layer collapse. To mitigate this issue, we scale the original D surface by a factor of 2 in the z direction, followed by the same overhang analysis (FIG. 42F to H). The cumulative distribution reveals that the proportion of overhangs greater than 1 is reduced to less than 2% (FIG. 42E). This adjustment ensures adequate contact between layers, thereby preventing potential layer collapse during printing. The scaled TPMS structure is successfully 3D printed using concrete infused with diatomaceous earth (DE) (Fig. 2E). The material's high printing accuracy validates the structural integrity instigated by the design, which effectively addresses the challenges associated with 3D concrete printing of TPMS geometries at the unit cell level. The transformation using scaling is a simple example of how geometry adjustments can affect overhangs and improve printability.

[0186] Next, we present a more complex example of designing a 3D printable concrete beam using the D surface. The beam is composed of 9 modules of concrete structures and incorporates continuous channels that facilitate the integration of posttensioning cables aligned with the tensile force requirements of the structure. This design ensures that prefabricated 3D printed concrete structures can be assembled after printing.

[0187] To illustrate the design and optimization process, we present a flow chart in FIG. 43. Step 1, the Polyhedral Graphic Statics (PGS) form-finding process, involves establishing the geometry of the load paths that minimize the bending moment in the system, setting the base dimensions, and defining the boundary conditions, including the desired loads and support locations (FIG. 43 A). This initial setup serves as a constraint for the system, providing the foundation for further design. A force diagram of graphic statics shows the equilibrium of forces as closed polyhedral cells that are topologically dual to the form diagram represented as a bar-node model. The structural form is derived from the force diagram based on their reciprocal relationship in a process that is calledstructural form finding. The form of the structure is a network of bars (to carry forces) connected by nodes. The internal flow of forces can be further optimized by manipulating the force diagram. In FIG. 43 A, the blue bars indicate compression forces, while the red bars indicate tension forces. By ensuring equilibrium, a range of equilibrated structural forms can be generated, accommodating both tension and compression forces. In the example of a concrete beam design, constant tension forces are maintained in the lower bars of the system. This approach prevents higher stress concentrations at specific points in the beam system and allows for even load distribution. Given the anisotropic nature of concrete, characterized by its high compressive strength but low tensile strength, the constant tension force determined from graphic statics can be utilized as the posttensioning force for cables running through the beam, ideally producing consistent compression. Once the bar-node model is established, the desired structure form is defined.

[0188] Step 2, embedding the TPMS into the generated form diagram (FIG. 43B). We select the D surface because it exhibits high mechanical strength and loadbearing capacity compared to other common TPMS geometries, such as Gyroid (G) and Primitive (P) surfaces, making it suitable for applications requiring robust structural integrity. Besides, the implicit function defining the D surface, cos cos x cos cos y cos cos z = sin sin x sin sin y sin sin z, inherently contains straight lines. The linear segments reduce the complexity of the 3D printing process, decreasing the need for support structures and mitigating structural collapse. Additionally, our design requires a continuous force path to integrate post -tensioning cables for assembling the 3D printed modules. The straight lines within the D surface facilitate the implementation of these force paths, aligning well with the bar-node model used in the PGS form-finding process (FIG. 43B). In the TPMS embedding process, geometric transformations of the D surface are performed, including rotation, translation, scaling, and mirroring. The D surface’s periodic anticlastic surfaces, defined by the centers of curvature on opposing sides forming a hyperbolic paraboloid, permit the application of mirroring, rotation, and translation without compromising structural integrity. The transformation of the D surface not only aligns the force path but also reduces overhangs, as demonstrated in the single unit of the D surface example in FIG. 42. In addition, the introduction of mirror symmetry in the D surface enhances mechanical performance bydeflecting the cracks and regulating the deformation behavior, thus preventing catastrophic failure due to stress concentration. By leveraging these transformations, we ensure that the TPMS geometry is integrated seamlessly with the desired form diagram, enhancing both the mechanical performance and printability of the final structure.

[0189] Step 3, employing the volumetric modeling to add thickness to the designed surfaces, creating a tangible 3D structure (FIG. 43C). The Signed Distance Function (SDF) is used for this purpose. An SDF describes a shape by providing the shortest distance from any point in space to the nearest point on the shape's surface. The SDF value is positive for points outside the shape, negative for points inside, and zero on the surface. This technique allows for precise definition and manipulation of geometric forms, enabling the uniform assignment of thickness to the designed surfaces and the seamless integration of these surfaces into a coherent volumetric model. Following the volumetric modeling of the structure, the design is segmented into 9 unit cells. Each unit cell is then analyzed to assess the presence of large overhangs and their suitability for 3D printing, using the same process shown in FIG. 42. This evaluation ensures that the final printed structure is self-supported. Through this design process, we can create a 3D- printed concrete beam and apply similar principles to customize other TPMS geometries based on specific structural and functional requirements. We successfully print one module of the beam using carbon-absorbing concrete, showcasing the successful realization of the design with the intended geometric features and structural integrity (Fig. 2F and FIG. 43 C).

[0190] In the design of the TPMS cube unit shown in Figure 6a, our goal is to create a cube structure with a larger surface area for CO2 absorption while maintaining compressive strength comparable to the standard solid cube specimen (5x5x5 cm, ASTM C109). To achieve this, we kept the top and bottom surfaces flat to avoid generating curved surfaces. This design choice is intended to prevent stress concentration during the compression test. We transform the four side surfaces of the standard cube into a D surface, which is then thickened by 8 mm to form walls (FIG. 51 A). Because a thin-walled TPMS structure is prone to buckling under compressive load, we address this issue by recursively offsetting the contour surfaces inward and completely filling the internal voids (FIG. 33C, FIG. 5 IB). This approach ensures the TPMS cube has the necessary strength while maintaining a high surface area-to-volume ratio. In all the 3D-printed geometriesdiscussed in this paper, overhangs are kept below 45° by refining the shape during the slicing process. This ensures that the contact surface between layers is sufficient to support the subsequent layers, preventing potential collapse during printing. This careful management of overhangs allows for the successful realization of complex designs with high surface area-to-volume ratios and high stiffness using 3D concrete printing techniques.

[0191] Carbonation Reactions of Unhydrated and Hydrated Cement Phases inDE-Infused Concrete

[0192] Upon exposure to CO2, both the unhydrated (Eq. (SI) and (S2)) and hydrated (Eq. (S3) and (S4)) products react as follows (45, 46):3CaO ■ S1O2(C3S) + 3CO2+ nH20 - S1O2■ nH20 + 3CaCO3(SI)2CaO ■ S1O2(C2S) + 2CO2+ nH20 -+ S1O2■ nH20 + 2CaCO3(S2)3CaO ■ 2S1O2■ 3H2O + 3CO2-+ 3CaCO3+ 2S1O2■ 3H2O (S3)Ca(OH)2+ CO2-+ CaCO3+ H2O (S4)

[0193] In Eq. (SI), the unhydrated tricalcium silicate (3CaO ■ S1O2or C3S) reacts with CO2and water produce calcium carbonate (CaCO3) and amorphous silica gel (S102- nH20).

[0194] In Eq. (S2), dicalcium silicate (2CaO ■ S1O2or C2S), another main component of unhydrated cement, undergoes a similar carbonation process. It reacts with CO2and water to form CaCO3and S1O2■ nH20.

[0195] In Eq. (S3), the hydrated calcium silicate (3CaO ■ 2S1O2■ 3H2O), or Type I C-S-H, reacts with CO2forms CaCO3.

[0196] In Eq. (S4), calcium hydroxide (Ca(OH)2), also known as portlandite, readily reacts with CO2to form CaCO3and water.

[0197] Calculation of CO2 Uptake

[0198] CO2 uptake in the concrete samples with and without DE over different time periods is determined by a therm ogravimetric analyzer (TGA-DSC SDT650, TA Instruments). The carbonated samples are ground and sifted through a No. 20 sieve (ASTM El 1 Test Sieve) before loaded into an aluminum pan. The furnace is heated from 30°C to 1000 °C at a ramp rate of 10 °C / min under a constant N2 flow of 100 mL / min. The CO2 uptake is calculated according to (47):, gco2OU2, uptake / o (“ - gcement

[0199] where MTGA 600oCis the mass at 600°C of the concrete sample measured during the thermogravimetric analysis (TGA) tests, MTGA 950oCis the mass at 950°C of the concrete sample measured during the TGA tests. Mdryingredient is the mass of the dry concrete ingredients (excluding water), which includes ordinary Portland cement (OPC), DE, sand, hydroxypropyl methylcellulose (HPMC). Mcementis the mass of the cement in the Mdry ingredient- The mass loss from 600°C to 950°C during TGA is considered the decarbonization range, where the mass loss represents the CO2 being captured in the concrete during the carbonation reaction. The obtained value is then divided by the mass of the test material at 950°C. This first part of the equation represents the CO2 uptake of all the dry ingredients in the concrete. To determine the CO2 uptake of the binder (in this case, OPC), the second part of the equation is applied. The mass loss percentage of concrete with and without DE at different carbonation times is listed in Table 1 and Table

[0200] Eq. S5 can be simplified and represented as: geo, Mass of reacted CO2(S6)CO2, uptake % - - ) = - x 100% geement Mass of cement

[0201] where the mass of reacted CO2 can be evaluated by TGA or other methods.

[0202] Calculation of The Theoretical Maximum CO2 Uptake

[0203] To calculate the theoretical maximum CO2 uptake of our concrete sample, we use the Steinour formula. This formula estimates the maximum amount of CO2 that can be sequestered by cement-based materials based on their chemical composition. The Steinour formula is expressed as (27, 48y.CO2(%) = 0.785(CaO - 0.7S03) + 1.09Na20 + 0.93K20 (S7)

[0204] The Steinour formula is ideal for evaluating the CO2 uptake potential of concrete made with ordinary Portland cement (OPC). In this equation, CaO (calcium oxide), Na2O (sodium oxide), and K2O (potassium oxide) are the primary oxides that react with CO2 to form carbonates. The formula accounts for the available CaO after subtracting the fraction associated with SO3 (sulfur trioxide), which has a negative effect on carbon sequestration potential. Other oxides, such as silica, are inert to carbonation. By inserting the oxide content values of our cement into this equation, we can determine the theoretical maximum CO2 uptake capacity of our concrete.

[0205] To determine the chemical composition, specifically the contents of CaO, SO3, Na2O, and K2O, of the cement we use in our concrete system. The X-ray fluorescence spectroscopy (XRF) results of commercial Portland cement (Type I / II) manufactured by Quikrete (USA) from literature are summarized in table 3. Based on the chemical content of the OPC used in our concrete, we can calculate that the theoretical maximum CO2 uptake of the cement in our material system falls within the range of 50.39 ± 3.6%. This implies that for every g of OPC cement, there is a maximum CO2 uptake capacity of 0.5039 ± 0.036g of CO2.

[0206] Characterization of TPMS Cube Mechanical Properties

[0207] To assess whether the TPMS surface affects the mechanical performance of the cube, we conduct finite element analysis (FEA) simulation to analyze the stress distribution of both cube structures (FIG. 33C) under compression force. FEA results indicate stresses concentrate at the edges and walls of a standard cube, but more at the edge of the TPMS cube due to boundary effects (FIG. 52A). The TPMS cube has 11.4% lower stiffness than the solid cube (FIG. 52B). To validate this, we perform compression tests on the cast standard solid cubes and 3D printed TPMS cubes with the same bounding box dimensions (5x5x5cm according to ASTM Cl 09). The compressive stress-strain curve shows that the 3D printed TPMS cube has 10.5% lower compressive strength than the solid cast cube (FIG. 52C), in agreement with FEA simulation. This could be due to stress concentration on the walls of the structure, as observed in the FEA, and that the testing surface (top surface) is not as flat as the cast concrete due to the corrugated printing textures, causing additional stress concentration. We note that the TPMS cube has a smaller volume within the bounding box, resulting in a lower structural density for the TPMS cube (1520.3 kg / m3) compared to the solid cube (1700 kg / m3). Therefore, the TPMS cube only experiences a 0.02% reduction in its specific strength and a 2.3% reduction in its specific stiffness (strength or stiffness divided by the structural density of the cube) compared to the cast solid cube (FIG. 52D). This highlights that the TPMS cube can maintain its structural strength while reducing material usage and increasing the structure's surface area.Table 1. Thermogravimetric analysis of concrete with DE at different carbonation times.Table 2. Thermogravimetric analysis of concrete without DE at different carbonation times.Table 3. Chemical composition of type I / II Portland Cement manufactured by Quikrete (USA) measured by X-ray fluorescence spectroscopy (XRF) (49- 51).Table 4. Summary of CO2 uptake in cementitious materials under various carbonation conditions reported in the literature.a. The cement pastes were made of two types of OPC with varying alkali and AI2O3 contents.b. CO2 uptake was measured by the powders taken from the outer surface layer (thickness 0.2 mm).c. 10 wt.% of OPC was replaced with Class I fly ash.d. The powder, after being mixed with water, was directly introduced into a carbonation chamber. The sample was carbonated for 1 hour, then milled for 2-3 minutes at 40°C, and the process was repeated for 5 cycles.

[0208] Aspects

[0209] The following Aspects are illustrative only and do not limit the scope of the present disclosure or the appended claims. Any part or parts of any one or more Aspects can be combined with any part or parts of any one or more other Aspects.

[0210] In one Aspect, the present disclosure provides a cementitious material, comprising: an amount of a porous biomineral, the porous biomineral optionally comprising diatomaceous earth (DE); and an amount of a cement. The porous biomineralcan define a hierarchical porosity. The porous biomineral and cement can be present, for example, at a weight ratio of at least about 0.05:0.95, optionally at least about 0.25:0.75, and optionally at least about 0.3:0.7.

[0211] The cementitious material can achieve uniform CO2 uptake in the bulk of the cementitious material, although this is not a requirement. As described elsewhere herein the cementitious material can be utilized in an additive manufacturing process, such as 3D printing. This is not a requirement, however, as the disclosed cementitious material can be used in other manufacturing processes, including processes applicable to traditional cementitious materials.

[0212] In some Aspects, the cementitious material further comprises any one or more of sand, water, and a viscosity modifier. The viscosity modifier can comprise, for example, a polysaccharide. The polysaccharide can comprise, for example, cellulose, such as methylcellulose and hydroxypropylcellulose (HPC).

[0213] In some Aspects, the polysaccharide comprises a methylcellulose.

[0214] In some Aspects, the methylcellulose comprises a methyl cellulose derivative, for example, methyl cellulose (HPMC) and hydroxyethyl methyl cellulose (HEMC).

[0215] In some Aspects, the cement comprises Portland cement.

[0216] In some Aspects, the cementitious material exhibits a static yield stress of from about 0.3 to about 0.7 kPa at a constant shear rate of 0.1 s'1. The cementitious material can, in some Aspects, exhibit a static yield stress is 0.16 - 6.8 kPa when subjected to shear rate of 0. Is'1.

[0217] In some Aspects, the cementitious material exhibits a viscosity of from about 2700 to about 6600 Pa-s at a constant shear rate of about 0.1 s'1and a viscosity of from about 6 to about 12.1 Pa-s at a constant shear rate of about 100 s'1.

[0218] In some Aspects, the cementitious material exhibits a dynamic yield stress of from about 0.7 to about 0.825 kPa. In some Aspects, the cementitious material exhibits a dynamic yield stress of 0.05 to 0.76 kPa.

[0219] In some Aspects, the cementitious material exhibits a plastic viscosity of from about 4.5 to about 7.2 Pa-s, for example from about 1.6 to about 5.8 Pa-s.

[0220] In some Aspects, the cementitious material (1) exhibits a first viscosity at a shear rate of 0.1 s’1, and (2) regains the first viscosity within about 1 second of returning to a shear rate of 0.1 s’1following shearing at a rate of 100 s’1.

[0221] In some Aspects, the biomineral and cement are present in a weight ratio of from 0.01 :0.99 to 0.5:0.5. In some Aspects, the weight ratio of biomineral to binder is 0.3 or greater, for example, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46, 0.48, 0.5, 0.52, 0.54, 0.56, 0.58, 0.60, 0.62, 0.64, 0.66, 0.68, 0.70, 0.72, 0.74, 0.76, 0.78, 0.80, 0.82, 0.84, 0.86, 0.88, or greater. The biomineral to binder ratio can also be a sub-range of the foregoing, for example from about 0.3 to about 0.7, from about 0.3 to about 0.5, and all intermediate values and sub-ranges.

[0222] As mentioned elsewhere herein, the biomineral can be diatomaceous earth (DE).

[0223] In some Aspects, the cementitious material exhibits a compressive strength of from about 15 to about 30 MPa following curing for 28 days.

[0224] In some Aspects, the cementitious material exhibits a compressive strength of from about 28 to about 33 MPa following curing for 60 days.

[0225] In some Aspects, the cementitious material exhibits strain hardening with printing. The disclosed cementitious material can exhibit a width to height ratio of no greater than 1.1 when additively manufactured through a nozzle of a diameter of up to 21 mm. The disclosed cementitious material can have a density of, for example, from about 1500 to about 1800 kg / m3, for example from about 1700 to about 1800 kg / m3. The disclosed cementitious material can, when additively manufactured as a single-wall cylinder, achieve an aspect ratio of up to about 42.

[0226] In some Aspects, the disclosed technology provides a method, comprising effecting additive manufacturing of a structure with a cementitious material according to the present disclosure.

[0227] In some Aspects, the present disclosure provides a structural material, comprising an amount of a cured cementitious material according to the present disclosure.

[0228] In an Aspect, the present disclosure provides a structural material, comprising: an amount of diatomaceous earth (DE); and an amount of concrete. Such astructural material can be, for example, an amount of a cured cementitious material according to the present disclosure.

[0229] In some Aspects, the structural material further comprises a viscosity modifying admixture, the viscosity modifying admixture optionally comprising a polysaccharide.

[0230] In some Aspects, the polysaccharide comprises a cellulose.

[0231] In some Aspects, the structural material exhibits a dry density of from about 1400 to about 2100 kg / m3.

[0232] In some Aspects, the structural material exhibits a porosity of from about 5 to about 30%. This is not a requirement, however, as the structural material can exhibit a porosity of or greater than about 55%, for example, 55%, 57%, 60%, 62%, 65%, 68%, 70%, 73%, 76%, 79%, 82%, 85%, 88%, 91%, 94%, and above. The porosity can be in the range, of, for example, from about 60% to about 95%, from about 62% to about 90%, from about 65% to about 85%, from about 68% to about 82%, from about 70% to about 77%, or even from about 72% to about 74%. The porosity can also be any intermediate range and / or subrange from about 60% to about 95%, for example from about 61% to about 72%.

[0233] The structural material can be, as an example, be present in an additively-manufactured structure, though the structural material cab be present in structures that are formed via manufacture other than additive manufacture. The structural material can be present in a structure that can be characterized as including a triply periodic minimum surface (TPMS) region, although this is not a requirement. The structure can be self-supporting.

[0234] In some Aspects, the structural material exhibits a hierarchical pore structure. Without being bound to any particular theory or embodiment, the biomineral can comprise a hierarchical pore structure.

[0235] In some Aspects, the disclosed technology provides a structure, the structure comprising a structural material according to the present disclosure. A structure can be, for example, a building or even a portion of a building.

[0236] The structure can exhibit an even level of carbonation through the thickness of the structure. As an example, the structure can comprise a section that comprises a plurality of layers of material according to the present disclosure, and thatsection can exhibit a level of carbonation (CO2 uptake) that is constant or within, for example, 10% of the maximum carbonation in the depth of that section. As an example, if the CO2 uptake at the surface of the region is X, the CO2 uptake at any other depth of the section is no less than 0.95X.

[0237] The level of carbonation at two separate points in the depth of the structure can also vary by, for example, less than 5%. As an example, the structure can exhibit a CO2 uptake at its surface layer and exhibit a CO2 uptake at a depth of 20 mm or even 30 mm of at least about 60% of the CO2 uptake at the surface layer. See, for example, FIG. 32J for an example, non-limiting illustration of the foregoing.

[0238] In some Aspects, the structure defines at least one overhang. The overhang can define an angle up to about 45°, for example from about 5° to about 45°, from about 10° to about 40°, from about 15° to about 35°, or even from about 20° to about 25°. Such a structure can include a TMPS region.

[0239] In some Aspects, the structure comprises a plurality of superposed layers of the structural material, the plurality of superposed layers optionally comprising from about 50 to about 120 layers.

Claims

What is Claimed:

1. A cementitious material, comprising: an amount of a porous biomineral, the porous biomineral optionally comprising diatomaceous earth (DE), the porous biomineral and cement being present at a weight ratio of at least about 0.05:0.95, optionally at least about 0.3:0.7; and an amount of a cement.

2. The cementitious material of claim 1, further comprising any one or more of sand, water, and a viscosity modifier.

3. The cementitious material of claim 2, wherein the viscosity modifier comprises a cellulose.

4. The cementitious material of claim 1, wherein the cementitious material exhibits a static yield stress of from about 0.3 to about 0.7 kPa at a constant shear rate of 0.1 s'1.

5. The cementitious material of claim 1, wherein the cementitious material exhibits a viscosity of from about 2700 to about 6600 Pa-s at a constant shear rate of about0.1 s'1and a viscosity of from about 6 to about 12.1 Pa-s at a constant shear rate of about 100 s'1.

6. The cementitious material of claim 1, wherein the cementitious material exhibits a dynamic yield stress of from about 0.70 to about 0.85 kPa.

7. The cementitious material of claim 1, wherein the cementitious material exhibits a plastic viscosity of from about 4.5 to about 7.2 Pa-s.

8. The cementitious material of claim 1, wherein the cementitious material (1) exhibits a first viscosity at a shear rate of 0.1 s'1, and (2) regains the first viscosity within about 1 second of returning to a shear rate of 0.1 s'1following shearing at a rate of 100 s'1.

9. The cementitious material of claim 1, wherein the biomineral and cement are present in a weight ratio of from 0. 1 :0.9 to 0.5:0.5, optionally from 0.3:0.7 to 0.5:0.5.

10. The cementitious material of claim 1, wherein the cementitious material exhibits a compressive strength of from about 15 to about 30 MPa following curing for 28 days.

11. The cementitious material of claim 1, wherein the cementitious material exhibits a compressive strength of from about 28 to about 33 MPa following curing for 60 days.

12. The cementitious material of claim 1, wherein the cementitious material exhibits strain hardening with printing.

13. The cementitious material of claim 1, wherein cementitious material exhibits a width-to-height ratio of no greater than 1.1 when additively manufactured through a nozzle of a diameter 21 mm or less.

14. The cementitious material of claim 1, wherein the cementitious material has a density of from about 1400 to about 2100 kg / m3, optionally from about 1500 to about 1800 kg / m3.

15. The cementitious material of claim 1, wherein the cementitious material, when additively manufactured as a single-wall cylinder, achieves an aspect ratio of about 40.

16. The cementitious material of claim 1, wherein the cementitious material exhibits an interfacial strength between portions of from 150 to 190% of a comparable cementitious material free of the biomineral.

17. A method, comprising effecting additive manufacturing of a structure with a cementitious material according to claim 1.

18. A structural material, comprising: an amount of diatomaceous earth (DE); and an amount of concrete.

19. The structural material of claim 18, further comprising a viscosity modifying admixture, the viscosity modifying admixture optionally comprising a polysaccharide.

20. The structural material of claim 18, wherein the structural material exhibits a dry density of from about 1400 to about 2100 kg / m3.

21. The structural material of claim 18, wherein the structural material exhibits a porosity of from about 5 to about 90%, optionally from about 60% to about 75%.

22. A structure, the structure comprising a structural material according to claim 18.

23. The structure of claim 22, wherein the structure defines at least one overhang.

24. The structure of claim 23, wherein the overhang defines an angle of up to 45°.

25. The structure of claim 24, wherein the overhang defines an angle of from 5 to 45°.

26. The structure of claim 25, wherein the overhang defines an angle of from 30 to 45°.

27. The structure of claim 22, wherein the structure comprises a plurality of superposed layers of the structural material, the plurality of superposed layers optionally comprising from about 50 to about 120 layers.

28. The structure of claim 22, wherein the structure comprises a triply periodic minimum surface (TPMS) region.

29. The structure of claim 23, wherein the structure comprises a section that exhibits a level of CO2 uptake that is within 10% of the maximum level of CO2 uptake in the depth of the section.

0. The structure of claim 23, wherein the structure exhibits a CO2 uptake at its surface layer and exhibits a CO2 uptake at a depth of 20 mm that is at least about 60% of the CO2 uptake at the surface layer.

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