Carbon nanotube hybrid materials and cementitious materials

Abstract

A carbon nanotube (CNT)-containing cementitious material with a CNT hybrid material comprising a cementitious material and cement. The CNT hybrid material is partially or fully deposited onto the cement after dry mixing, to develop the CNT-containing cementitious material.

Description

Carbon Nanotube Hybrid Materials and Cementitious MaterialsCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of the following Provisional Patent Applications, the disclosures of which are each incorporated by reference herein, and for all purposes: 63 / 541,412 filed on September 29, 2023; 63 / 544,061 filed on October 13, 2023; and 63 / 546,436 filed on October 30, 2023.BACKGROU ND OF THE I NVENTION

[0002] The concrete industry, like the energy sector, is facing significant technological challenges driven by environmental pressures. These pressures require a substantial reduction in CO2 emissions during cement production and economic incentives to improve construction materials performance, making structural components stronger, thinner, and lighter at lower costs. These demands, encompassing technical, environmental, and economic factors, will significantly impact production costs and, consequently, market prices.

[0003] In 2022, global cement production reached approximately 4.1 billion tons, constituting about 8.0% of the world's total CO2 emissions, which amounted to roughly 36.8 billion metric tons of emissions. China, India, and the United States contributed 2.17 billion MT, 370 million MT, and 95 million MT, respectively. In order to align with the Net Zero Emissions by 2050 (NZE) Scenario, the concrete sector must achieve a 4% reduction in CO2 intensity by the year 2030. Given accelerated economic and population growth, particularly in regions like Asia and the Middle East, it is projected that global cement production capacity will increase by about 5 billion metric tons by 2030.Currently, China leads worldwide cement production at approximately 52%, followed by India at approximately 10%.

[0004] During the cement manufacturing process, carbon dioxide is released when producing clinker, a key component of cement. In this process, calcium carbonate (CaCCh) is heated in a rotary kiln furnace, leading to a series of complex chemical reactions. CO2 is released as a by-product during calcination, which takes place in theupper, cooler end of the kiln or in a pre-calciner. This occurs at temperatures ranging between 600 and 900°C, resulting in the conversion of carbonates into oxides.

[0005] CaCO3+ Heat -> CaO (lime) + CO2

[0006] At higher calcination temperatures in the lower end of the kiln, the lime, the primary component of cement, reacts with materials containing silica, aluminum, and iron to produce minerals in the clinker (such as 2CaO-SiO2, 3CaO-SiO2, 3CaO-Al2O3, 4CaO-Al2O3-Fe2O3). The clinker, a multiphase calcium-silica compound, typically exhibits grain sizes ranging from micrometers to a few millimeters and serves as an intermediate product in cement manufacturing. After extraction from the kiln for cooling, it is ground into a fine powder and then combined with approximately 5 wt% of gypsum. This mixture results in the most common type of cement known as Portland cement. Masonry cement is generally the second most common type of cement. However, since Masonry cement requires more lime than Portland cement, its production generally leads to additional CO2emissions. An estimated factor of about 0.507 MT of CO2emissions per MT of clinker for Masonry type cement has been reported.

[0007] Calcium silicates, specifically 2CaO-SiO2(C2S, alite) and 3CaO-SiO2(C3S, belite), are responsible for cement's mechanical properties. In contrast, 3CaO-Al2O3(C3A, tricalcium aluminate) and 4CaO-Al2O3-Fe2O3(C4AF, brown millerite) promote the formation of the liquid phase during firing in the production of Portland cement. Various types of Portland cement exist, differing in their calcium and alumina silicate compositions. Type I is suitable for general use, Type II generates relatively low heat during hydration (an exothermic reaction), and Type III offers relatively high early strength.

[0008] Calcium silicate compounds have specific rates of reaction with water, producing various hydration products that intermesh and intercalate to create a dense and strong solid during the hydration process.

[0009] C3S + H2O -> C-S-H* + Ca(OH)2

[0010] C2S + H2O -> C-S-H* + Ca(OH)2

[0011] C3A + 18H2O -> C2AH8+ C4AH10

[0012] 2C3A + 32H2O + 3 Ca2+ SO42-> CeAS3H32

[0013] C6AS3H32+ 2C3A -> 3C4ASHI2

[0014] C4AF has an analogous reaction to C3A and produces Ce(A,F)S3H32.

[0015] C-S-H* is an amorphous hydrogel with a variable composition in terms of Ca / Si ratio and FfcO / SiCh ratios.

[0016] The reaction of C3A with water is exothermic and generates significant heat quickly, mainly contributing to early strength rather than ultimate strength. Longer-term strength primarily depends on calcium silicates, with C3S providing early strength and C2S offering better long-term contributions. The principal binding phase in Portland cements is the C-S-H*, which is the most significant hydration product in qualitative terms. Ferrite reactions fall between C3S and C2S in terms of rate but play a crucial role in long-term strength and durability.

[0017] Admixtures are solid or liquid ingredients added to a cement mix alongside cement, water, and aggregates. They aim to enhance the fluidity of the mix or improve certain properties of the resulting cured cement. Water-reducing agents are commonly used to enhance fluidity. Insufficient fluidity leads to relatively high porosity in cured cement due to incomplete water utilization in the hydration reaction. Silica fume, an admixture consisting of fine non-crystalline silica particles (finer than sand, as small as 0.1-0.2 pm), can refine the pore structure of cured cement, thus enhancing strength and modulus.

[0018] Numerous strategies have been employed to enhance concrete sustainability and develop green alternatives. These strategies include:

[0019] i) Reducing the clinker-to-cement ratio by adopting clinker substitutes.

[0020] ii) Incorporating recycled materials and waste from various sources such as industry, agriculture, and households.

[0021] iii) Optimizing mix designs.

[0022] iv) Reducing CO2 emissions by decreasing Portland cement content and partially substituting it with cementitious materials and binders like nano-alumina particles, fly ashes, silica fume, limestone, and blast furnace slag.

[0023] v) Enhancing concrete durability by using reinforcing materials such as carbon fibers (CFs), carbon nanotubes (CNTs), and steel fibers, thereby reducing long-term resource consumption and adopting low-impact construction methods.

[0024] vi) Continuously improving energy efficiency.

[0025] vii) Embracing low-carbon fuels.

[0026] viii) Implementing innovative technologies like Carbon Capture and Storage (CCS), which will play a pivotal role in achieving the emissions reduction goal.

[0027] Among the additives employed to enhance the mechanical properties of cementitious materials, nano-AECE particles have proven to be effective in increasing the modulus of elasticity in cement mortar. With approximately 5 wt.% of nano-AkOa particles, each having a size of hundreds of nanometers, the elastic modulus increased by 143% after 28 days of curing. During cement hydration, these particles filled the pores at the sand-paste interfaces, creating a denser interfacial transition zone (ITZ) with reduced porosity. This densification of the ITZ is responsible for the significant increase in the elastic modulus of the mortars.

[0028] The incorporation of carbon nanomaterials into the cementitious matrix offers a promising approach to achieving the performance objectives of concrete. Carbon nanotubes (CNTs) have gained significant attention due to their remarkable mechanical properties (Young's modulus of ITPa, tensile strength exceeding 60 GPa, and fracture deformation exceeding 12%), low density, unique physical and chemical characteristics, thermal and electrical conductivity, as well as piezoelectric properties. CNTs even exhibit a thermal conductivity at least twice that of diamond, and their negative coefficient of thermal expansion contributes to higher thermal stability. These properties make them valuable for enhancing the thermal stability of cement-based materials, positioning CNTs as ideal candidates for reinforcement in smart cement-based materials.

[0029] However, effectively dispersing carbon nanotubes in construction materials presents a significant technological challenge due to their high hydrophobic nature, which causes CNTs to tend to form bundles or ropes in aqueous and organic suspensions. This characteristic impedes their efficient integration into the cementitious matrix. Cement particles typically range in size from 1 to 3pm, exhibiting a wide size distribution. Some studies have successfully combined chemical and mechanical dispersion techniques for CNTs, utilizing surfactants and ultrasonication to aid dispersion, as well as waterreducing additives to adjust the fluidity of CNT-cement mixtures. It has been reported that achieving an optimal CNT aspect ratio is necessary to enhance the electromechanicalproperties with minimal CNT loading in the concrete matrix. Unfortunately, ultrasonication and high shear mixing techniques are not scalable for commercial purposes and can potentially damage the CNTs, thereby reducing their effectiveness in enhancing mechanical strength, electrical and thermal conductivity, and piezoelectric response.

[0030] Handling CNT powders represents potential health and safety risks, and their high production cost makes them impractical for cost-sensitive construction materials markets. Therefore, the development of new-generation hybrid materials containing CNTs and techniques for integrating them into cement matrices using conventional mixing equipment becomes necessary. This approach aims to avoid the use of aqueous solutions containing surfactants and water-reducing agents. These new techniques for incorporating carbon nanotubes into cement must be efficient enough to ensure a significant improvement in mechanical properties, while also being safe and cost-effective to produce.SUMMARY OF THE I NVENTION

[0031] This invention introduces novel compositions and novel methods for safely integrating CNT-nano-AhOs hybrid materials into the cement matrix using conventional industrial mixing techniques. The CNT-nano-AhOs hybrid material is synthesized through the Catalytic Chemical Vapor Deposition (CCVD) method. The CNT synthesis takes place in fluidized bed or rotary tube reactors, utilizing active metal supported on alumina grains having primary particles sized in the hundreds of nanometers. During the CNTs synthesis conditions, the primary particles contained in the catalyst support grains tend to de-agglomerate and disperse into an open and expanded mesh formed by carbon nanotubes. When carbon nanotubes form an open and expanded mesh, less energy is required to de-bundle and disperse them.

[0032] The CNT-nano-AhCh hybrid material obtained in the synthesis is then ground to reduce the size of the expanded mesh of carbon nanotubes and optimize its aspect ratio to achieve better integration of the material into the cementitious matrix. The resulting fine powder, with particle sizes in the micron range, can then be shaped through granulation methods in the presence of a binder agent (such as colloidal silica, alumina, and / orpolymers) and blended with admixture materials (such as fume silica, fly ash, limestone, hydrogels, etc.) before being mechanically mixed with the cementitious material.

[0033] Also featured herein is a CNT-containing cementitious material that in some examples includes a CNT hybrid material comprising a cementitious material, a dispersant, and a defoamer. The components are mixed in a continuous high shear mixing equipment to develop the CNT-containing cementitious material.

[0034] In some examples the cementitious material comprises alumina. In some examples the dispersant comprises alkali lignin. In some examples the defoamer comprises an air-detraining admixture. In some examples this disclosure features a mortar comprising the CNT-containing cementitious material described above, water, cement, and sand.

[0035] In some examples the cementitious material comprises alumina. In some examples this disclosure features a mortar comprising the CNT-containing cementitious material described above, water, and sand.

[0036] Also featured herein is a CNT-containing cementitious material that in some examples includes a CNT hybrid material comprising a cementitious material and cement. The CNT hybrid material and the cement are dry mixed in a high-speed mixer to develop the CNT-containing cementitious material. The CNT hybrid material is partially or fully deposited onto the cement after the dry mixing process.

[0037] In some examples the cementitious material comprises alumina. In some examples this disclosure features a mortar comprising the CNT-containing cementitious material described above, water, and sand.

[0038] In one aspect a carbon nanotube (CNT)-containing cementitious material includes a CNT hybrid material comprising CNT and a cementitious material and cement. The CNT hybrid material is partially or fully deposited onto the cement after dry mixing to develop the CNT-containing cementitious material.

[0039] In an example the cementitious material includes alumina. In an example the cement includes Portland cement. In an example the cement includes Type I or Type I / II Portland cement. In an example the CNT hybrid material includes from 15-72% CNT by weight. In some examples the CNT includes multi-wall CNT (MWCNT). In an example the CNT aspect ratio is from about 400 to about 700. In an example the CNT-containingcementitious material includes about 0.2wt% MWCNT. In an example the CNT- containing cementitious material includes fly ash. In an example the cementitious material includes alumina having particle sizes in the range of from about 500nm to about l,500nm. In an example the cement is part of a cement-fly ash admixture. In an example the mixing is accomplished using a high-speed mixer. Also featured is a mortar including the CNT-containing cementitious material, water, and sand. Also featured is a concrete including the CNT-containing cementitious material, water, sand, and gravel.

[0040] In another aspect a method of creating a carbon nanotube (CNT)-containing cementitious material includes dry mixing together a CNT hybrid material including CNT and a cementitious material and cement such that the CNT hybrid material is partially or fully deposited onto the cement by the dry mixing, to develop the CNT- containing cementitious material.

[0041] In an example the mixing is accomplished using a high-speed mixer. In an example the cementitious material includes alumina. In an example fly ash is also included. In an example the cementitious material includes alumina having particle sizes in the range of from about 500nm to about l,500nm. In an example the CNT hybrid material includes from 15-72% CNT by weight. Also featured is a mortar including the CNT-containing cementitious material, water, and sand. Also featured is a concrete including the CNT-containing cementitious material, water, sand, and gravel.BRI EF DESCRI PTION OF DRAWINGS

[0042] Figure 1 illustrates mechanical properties of mortar prepared using different CNT- nano-ALOs hybrids in cement.

[0043] Figure 2 includes scanning electron micrograph (SEM) images of the three CNT- nano-AEOs hybrid materials for which mechanical properties are illustrated in Figure 1.

[0044] Figure 3 illustrates mechanical properties of mortars prepared using different commercial Portland type cements and at different curing times.

[0045] Figure 4 illustrates mechanical strength properties of mortars prepared with 28 wt% and 72 wt% CNT in the hybrid materials.

[0046] Figure 5 includes SEM images of cement and CNT-nano-AhCE hybrid mixtures. Figure 5(a) 28 wt% CNT, Figure 5(b) 72 wt% CNT.

[0047] Figure 6 illustrates mechanical strength properties of the mortar prepared with the hybrid material and cement mixed with fly-ash.

[0048] Figure 7 includes SEM images of a cement and CNT-AI2O3 hybrid material powder mixture.

[0049] Figure 8 includes SEM images of the basal surface of the specimen containing CNT-A12O3 hybrid material and cement captured at different curing times.

[0050] Figure 9 includes SEM images of the edge surface of the specimen containing CNT-AI2O3 hybrid material and cement captured at different curing times.

[0051] Figure 10 shows four SEM images taken at 5K, 10K, and 14K magnifications of the CNT-cement mixtures prepared in both mixers

[0052] Figure 11 includes results of mechanical tests on the CNT-cement mixtures prepared in the mortar mixer and high-speed mixer at different curing times.DETAI LED DESCRIPTION OF TH E I NVENTION

[0053] This disclosure includes hybrid materials based on CNT (Carbon Nanotubes) and cementitious material such as alumina nanoparticles. In some examples the hybrid material can be used in advanced construction materials. This innovative material significantly enhances the electro-mechanical properties, along with reduced cement usage, in concrete, thereby helping to reduce CO2 emissions. Also disclosed are materials and methods for easily and safely integrating the CNT-nano-A12O3 hybrid material into the cementitious matrix using conventional mixing equipment.

[0054] In some examples the hybrid material is synthesized using a catalyst based on a combination of transition metal oxides (Co, Fe, Mo) supported on high specific surface area MgO-AhC (e.g., specific surface area in the range of 200-400 m2 / g). A catalyst preparation method was described in US Patent Application publication 2023 / 0116160 Al, the disclosure of which is incorporated herein by reference and for all purposes.

[0055] The CNT-nano-AECh hybrid material can be synthesized in a rotary tube reactor or fluidized bed reactor using a carbon source (such as ethylene, propylene, ethane, etc.) and hydrogen at a temperature between 600 and 750 °C, atmospheric pressure, and a residence time in the reactor between 5 and 20 minutes. CNT-alumina hybrid material synthesis is further described in US Patent Application publication 2023 / 0116160 Al.

[0056] The carbon nanotube content in the hybrid material ranges from 15 to 85 wt%, preferably between 20 and 75 wt%. The content of MgO-AhCh support in the catalyst varies between 96.6 and 98.5 wt%, and the active metal (e.g., Co and Fe) content ranges from 1.45 to 2.9 wt%. The catalyst contains micron-sized elementary nano-alumina particles which are agglomerated to form catalyst grains that have a particle size of less than 500 pm, preferably less than 150 pm when a rotary tube reactor is used and between 150-500 pm when a fluidized bed reactor is used. The active metal is deposited on the catalyst grains. The elementary nano-alumina particles typically have sizes ranging from 600 to 1500 nm. During the initial stage of the catalytic reaction, the growth of CNTs causes de-agglomeration of the elementary particles that form the catalyst grains. As the reaction progresses, these elementary particles are dispersed in a three-dimensional open mesh of carbon nanotubes. The morphological properties of the support (shape and size of the particles) as well as the composition of the active phase in the catalyst determine the structure and morphology of the three-dimensional mesh of carbon nanotubes. The more open and less tangled the carbon nanotube mesh is, the easier it is to disperse with less energy usage in mixing equipment.

[0057] Example 1: Proof of concept of mechanical blending CNT-AI2O3 powder and cement.

[0058] In this example, CNT -nano- AI2O3 hybrid materials were synthesized with different contents of multi -wall CNT (MWCNT) (15 wt%, 20 wt%, and 25 wt% MWCNT) and mixed with commercial Portland Type I cement, so that the CNT content in the cement for all samples was 0.15 wt%. Mixing of the CNT hybrid and commercial Portland Type I cement powder took place in a high-speed mixer at 1200 rpm for 2 minutes.

[0059] Mortars were prepared by mixing the cement containing the hybrid material, a plasticizer agent, sand, and water, and their mechanical properties were measured after 3, 7, and 28 curing days. Flexural Strength and Young's Modulus were determined following ASTM C348-20 standards, while Compressive Strength and Young's Modulus properties were determined through ASTM C349-18 standards.

[0060] Figure 1 illustrates the results of the mechanical properties determined for the mortars prepared with these different synthesized CNT-nano-AhCh materials (15 wt%,20 wt%, and 25 wt% MWCNT from left to right in the Figure, respectively). The percentage improvement of the mechanical properties, in terms of Flexural Strength, Modulus of Elasticity, and Compressive Strength of the mortar as a function of curing time is perhaps best for the sample containing 20wt% CNT in the hybrid material.

[0061] The morphological properties of the synthesized CNTs-nano-AhCh hybrid materials were analyzed using scanning electron microscopy (SEM), as shown in Figure 2 (15 wt%, 20 wt%, and 25 wt% MWCNT from left to right in the Figure, respectively). The images, captured at 7.5 KX magnification, reveal carbon nanotubes and alumina particles in sizes ranging from 500 to 1500 nm. Additionally, bundles and individual carbon nanotubes are observed with lengths of 3.0 to 5.0 pm for the 15wt% CNT sample, 4.0 to 6.0 pm for the 20 wt% CNT sample, and 6 to 8 pm for the 25wt% CNT sample. The average CNT diameter for all samples is approximately 10 nm, which corresponds to 6-8 walls, resulting in aspect ratios (L / D) of around 400, 500, and 700 for the 15wt%, 20wt%, and 25wt% CNT samples, respectively.

[0062] When these hybrid materials are mixed with cement particles, the open and loosely entangled structure of the CNTs formed on the catalyst particles and low aspect ratio allows for greater integration with less mechanical energy usage compared to conventional carbon nanotubes which form a compact and tangled mesh similar to cotton balls, bird nests, rods, etc.

[0063] Example 2. Influence of the type of Portland cement.

[0064] In this example, two types of commercial Portland cement were used (Portland type I and Portland type I / II), and mechanical blends were prepared with a CNT-nano- AI2O3 hybrid material containing 28 wt% MWCNT. The percentage of MWCNT in the cement was 0.20 wt%.

[0065] Figure 3 illustrates the mechanical properties: flexural strength, top left chart, compressive strength bottom left chart, and modulus of elasticity top right chart, results of mortars prepared with a mixture of CNT -nano- AI2O3 hybrid material and two types of commercial Portland cement at 3, 7, and 28 days, as indicated in Figure 3. The percentage of improvement in Flexural, Modulus of Elasticity and Compressive Strength over the curing days is similar for both cement types.

[0066] Example 3. Influence of the CNT composition in the hybrid material.

[0067] In this example, a hybrid material CNT-nano-AECh was synthesized with a CNT content of approximately 28wt% and 72 wt%. The synthesized material was ground before mixing with Portland type I / I I cement particles using the same mixing conditions as in Example 1. The CNT content in the cement was about 0.20 wt%.

[0068] Figure 4 illustrates the mechanical property results (the same as in Figure 3) determined at 3, 7, and 28 curing days for two mortars prepared with hybrid materials containing 28 wt% (the right-side graph) and 72 wt% (the left-side graph) MWCNT. After 3 curing days, the mortar prepared with the hybrid material containing 72% CNT shows greater improvements in flexural properties and modulus of elasticity. However, this material exhibits a significantly lower improvement in compressive strength compared to the mortar with 28 wt% CNT.

[0069] At 7 curing days, the mortar prepared with the sample containing 72 wt% CNT in the hybrid material demonstrates a moderately greater improvement in all three mechanical properties compared to the results obtained from the mortar with 28 wt% CNT in the hybrid material.

[0070] After 28 curing days, the improvement percentages in all three mechanical properties in both mortars prepared with hybrid materials are similar.

[0071] Figure 5 (images labeled a and b) includes two SEM images of the mechanical mixture of 28% CNT-nano-AhCh hybrid material and cement taken at 4KX (image a), and 72% CNT-nano-A12O3 hybrid material and cement taken at 2KX (image b). The SEM labeled “a” depicts the formation of a mesh of carbon nanotubes, approximately 17 microns long, in contact with a cement particle. In this sample, the size of the carbon nanotube mesh and cement particles ranged from 10 to 40 pm.

[0072] In the SEM image taken at 2 KX magnification (“b”) shows elongated bundles of the hybrid material containing 72 wt% CNTs, with lengths ranging approximately from 10 to 30 pm, mixed with cement particles of similar sizes.

[0073] Example 4: Effect of fly ash added to the cement.

[0074] Adding fly ash to cement offers multiple benefits, including improved workability, increased long-term strength and durability, reduced heat during curing (beneficial for large structures), lower permeability, environmental friendliness (utilizingcoal combustion waste), and cost savings due to its cement-replacing pozzolanic properties.

[0075] In this example, a commercial Portland type I cement was used, which has approximately 30 wt% fly-ash admixture, and prepared a mortar by mixing it with the hybrid material containing 28 wt% CNT. The CNT content in the cement and fly ash was 0.20 wt%.

[0076] Figure 6 illustrates the results of the improvement in mechanical properties (the same three properties reported for Figure 4) of the mortar prepared with the hybrid material and cement mixed with fly-ash, at 3, 7, and 28 days. It is noted that the percentage increases in flexural properties, modulus of elasticity, and compressive strength are lower compared to cements without fly ash (Figures 3 and 4). However, the values obtained for the improvement in flexural properties and modulus of elasticity, which are around 28% after 28 days of curing, justify the use of the CNT-nano-AhCh hybrid material combined with admixtures as a viable alternative to reduce cement usage in construction materials, contributing to a decrease in CO2 emissions. The compressive strength performance improved by 8% at 28 curing days.

[0077] Example 5: SEM Analysis of CNT-hybrid and cement specimen at various curing times.

[0078] In this example, specimens of 5 mm thickness and 6 cm diameter were prepared, containing Portland cement type VII and CNT-hybrid material with 0.20 wt% MWCNT. The MWCNT content in the hybrid material is 72 wt%. This material was previously ground before mixing it with the cement powder in a high-speed mixer equipment under the same mixing conditions as set forth in Example 1.

[0079] For specimen preparation, a water / cement plus hybrid material ratio of 0.5 / 1.0 by weight was used. The cement and CNT-hybrid material and water were mixed in a 4- quart stainless steel bowl capacity laboratory planetary mixer following the ASTM standard C 305-06 procedure. The specimens were kept under controlled temperature and humidity conditions for 7 days. SEM and ED AX analysis were performed at 1, 2 and 3 curing days on both edge and basal surfaces of the specimen.

[0080] Figure 7 includes SEM analyses at 2KX, 3.5KX, 10KX, and 25KX (four images, left to right) magnifications of the cement powder and CNT-A12O3 hybrid materialmixture. Cement particles ranging from 10 to 40 microns in size and bundles of carbon nanotubes approximately 10 to 30 microns in length and 1 to 2 microns in diameter are observed. The carbon nanotube diameter is approximately 10 + / - 3 nm.

[0081] Figure 8 includes SEM images taken at magnifications ranging from 5KX to 50KX of the basal surface of the specimen containing CNT-AI2O3 hybrid material and cement after 1, 2, and 3 days of curing time.

[0082] On the first day of curing (the top row of four SEM images taken at 10, 15, 25, and 50KX, from left to right), significant amounts of carbon nanotubes form an open mesh on the basal surface, separated by cementitious material particles. By the second day (the middle row of four SEM images taken at 5, 10, 25, and 30KX, from left to right), very few carbon nanotubes meshes were visible. On the third day of curing (bottom row, both SEMs taken at 5KX), no carbon nanotubes were observed on the basal surface; they were covered by the cementitious matrix.

[0083] EDAX analysis indicated that the basal surface was primarily composed of hydrated calcium silicates (C-S-H), calcium hydroxide (amorphous particles), as well as hydrated calcium aluminate (C-A-H), calcium sulfate, calcium aluminates, magnesium, and iron.

[0084] Figure 9 includes nine SEM images taken at magnifications ranging from 10 KX to 50 KX of the edge surface of the specimen containing CNT-AI2O3 hybrid material and cement after 1 day (top row of three SEM images taken at 10, 25, and 50KX from left to right) , 2 days (middle row of three SEM images taken at 15, 25, and 25KX from left to right), and 3 days (bottom row of three SEM images taken at 15, 25, and 50KX from left to right) of curing time.

[0085] Carbon nanotube meshes are clearly observed on the edge surface of the cementitious matrix specimen. As curing time increases, the carbon nanotube bundles untangle, forming meshes that progressively expand due to the formation and growth of hydrated calcium silicate and aluminate crystals and amorphous calcium hydroxide. Individual nanotubes become visible in the images. The hydrated calcium silicate and aluminate crystals increase in size as the hydration reaction of the precursor 3CaO.SiC>2, 2CaO.SiO2 and 3CaO.AhO3 species progresses. The initial stage of the hydration reaction of the calcium aluminate and silicate phases that make up the clinker may beimportant, as it can influence the degree of dispersion and entanglement of carbon nanotube bundles in the cementitious matrix, thereby determining the extent of improvement in the electro-mechanical properties of the cement.

[0086] The SEM images in this example support the hypothesis that the cementitious materials penetrate into the porous CNT bundles of about 1 micron diameter, disentangling the CNTs to a significant extent as the cement cures, which enhances the reinforcing effectiveness of the nanoscale CNTs.

[0087] The images also allow for observation of the CNT bundles and CNTs in cement paste (vs. mortar, which contains a high loading of sand particles) and to observe morphology at various (short) curing times.

[0088] Example 6:

[0089] In this example, CNT-cement mixtures were prepared using a mortar mixer and a high-speed mixer. In a conventional mortar mixer with a four cubic foot capacity polyethylene drum, 2.5 kilograms of both CNT and cement powders (0.20 wt% CNT) were mixed for 30 minutes at a constant rotation rate of approximately 24 rpm. In the high-speed mixer, 200 grams of the CNT-cement powder were placed in a 0.5 kg capacity container and mixed at 1,000 rpm for 1 minute.

[0090] Figure 10 shows four SEM images taken at 5KX, 10KX, and 14KX magnifications of the CNT-cement mixtures prepared in both mixers. The SEMs labeled (a) and (b) (the left column) are from a mortar mixer and taken at 5KX and 10KX, respectively. The SEMs labeled (c) and (d) (the right column) are from a high-speed mixer and taken at 5KX and 14KX, respectively. In both cases, individual bundles of carbon nanotubes longer than 10 pm and 1 to 3 pm in diameter were observed on the cement particles. No significant differences were found between the mixtures made in the two mixing equipment.

[0091] Figure 11 presents the results of mechanical tests on the CNT-cement mixtures prepared in the mortar mixer and high-speed mixer at different curing times. The values of mechanical strength obtained for both the reference mortar and the mixtures from both machines are shown. The percentage improvement in flexural properties, modulus of elasticity, and compressive strength (in the three graphs, from left to right respectively) of the cement progressively increases with curing time (3 days, 7 days, and 28 days). Bothmixing methods exhibit similar results in enhancing the three mechanical properties mentioned at various curing times, and the observed differences in mechanical strength values expressed in MPa and percentage are insignificant.

[0092] Having described above several aspects of at least one example, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way of example only, and the scope of the invention should be determined from proper construction of the appended claims, and their equivalents.

Claims

Claims1. A carbon nanotube (CNT)-containing cementitious material, comprising: a CNT hybrid material comprising CNT and a cementitious material; and cement; wherein the CNT hybrid material is partially or fully deposited onto the cement after dry mixing to develop the CNT-containing cementitious material.

2. The CNT-containing cementitious material of claim 1, wherein the cementitious material comprises alumina.

3. The CNT-containing cementitious material of claim 1, wherein the cement comprises Portland cement.

4. The CNT-containing cementitious material of claim 1, wherein the cement comprises Type I or Type I / II Portland cement.

5. The CNT-containing cementitious material of claim 1, wherein the CNT hybrid material comprises from 15-72% CNT by weight.

6. The CNT-containing cementitious material of claim 1, wherein the CNT comprises multiwall CNT (MWCNT).

7. The CNT-containing cementitious material of claim 6, wherein the CNT aspect ratio is from about 400 to about 700.

8. The CNT-containing cementitious material of claim 6, wherein the CNT-containing cementitious material comprises about 0.2wt% MWCNT.

9. The CNT-containing cementitious material of claim 1, further comprising fly ash.

10. The CNT-containing cementitious material of claim 1, wherein the cementitious material comprises alumina having particle sizes in the range of from about 500nm to about l,500nm.

11. The CNT-containing cementitious material of claim 1, wherein the cement is part of a cement-fly ash admixture.

12. The CNT-containing cementitious material of claim 1, wherein the mixing is accomplished using a high-speed mixer or a mortar mixer.

13. A mortar comprising the CNT-containing cementitious material of claim 1 , water, and sand.

14. A concrete comprising the CNT-containing cementitious material of claim 1, water, sand, and gravel.

15. A method of creating a carbon nanotube (CNT)-containing cementitious material, comprising: dry mixing together a CNT hybrid material comprising CNT and a cementitious material and cement; such that the CNT hybrid material is partially or fully deposited onto the cement by the dry mixing, to develop the CNT-containing cementitious material.

16. The method of claim 15, wherein the mixing is accomplished using a high-speed mixer or a mortar mixer.

17. The method of claim 15, wherein the cementitious material comprises alumina.

18. The method of claim 15, further comprising also dry mixing fly ash.

19. The method of claim 15, wherein the cementitious material comprises alumina having particle sizes in the range of from about 500nm to about l,500nm.

20. The method of claim 15, wherein the CNT hybrid material comprises from 15-72% CNT by weight.

21. A mortar comprising the CNT-containing cementitious material made by the method of claim 15, water, and sand.

22. A concrete comprising the CNT-containing cementitious material made by the method of claim 15, water, sand, and gravel.

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