Carbon Nanotube Hybrid Material for Concrete Applications

Abstract

A carbon nanotube (CNT) hybrid material that includes a blend comprising a catalyst supported on at least one of a metal, metalloid, metal oxide or carbon support, and at least one material selected from the group of materials consisting of: cementitious materials, materials used in the production of cementitious materials, and materials used to enhance cementitious materials, and CNT on the blend.

Claims

1. A carbon nanotube (CNT) hybrid material, comprising: a blend comprising a catalyst supported on at least one of a metal, metalloid, metal oxide or carbon support, and at least one material selected from the group of materials consisting of: cementitious materials, materials used in the production of cementitious materials, and materials used to enhance cementitious materials; and CNT on the blend.

2. The material of claim 1, wherein the cementitious material comprises a hydraulic cement.

3. The material of claim 2, wherein the hydraulic cement comprises Portland cement.

4. The material of claim 1, wherein the cementitious material comprises a supplementary cementitious material (SCM).

5. The material of claim 4, wherein the SCM comprises fly ash.

6. The material of claim 1, wherein the catalyst is supported on nano-alumina particles.

7. The material of claim 1, wherein the CNT are grown on at least part of the blend in a rotary kiln reactor.

8. The material of claim 7, wherein the supported catalyst and the cementitious material are blended and then fed into the reactor wherein CNT are grown on this blend.

9. The material of claim 7, wherein the supported catalyst is fed into the reactor wherein CNT is grown on the supported catalyst to create a hybrid material, and then the hybrid material is blended with the cementitious material.

10. The material of claim 9, wherein the hybrid material is blended with the cementitious material by mechanical mixing of the two in powder form.

11. The material of claim 9, wherein the hybrid material is blended with the cementitious material by preparing a dispersion of the hybrid material in an aqueous solution and then mixing the dispersion with the cementitious material.

12. A carbon nanotube (CNT) hybrid material, comprising: a fly ash material comprising iron oxide and other metal oxides; and CNT on the fly ash.

13. The material of claim 12, wherein the CNT are grown on the fly ash in a rotary kiln reactor.

14. A carbon nanotube (CNT) hybrid material, comprising: a catalyst supported on alumina; and CNT grown at the catalyst sites on the alumina, wherein the CNT have an aspect ratio of over 1000.

15. The material of claim 14, wherein prior to CNT growth the alumina comprises agglomerations of elementary alumina particles that are smaller than about 1 micron in size.

16. The material of claim 15, wherein the CNT cause de-agglomeration of the elementary alumina particles in the CNT hybrid material.

17. The material of claim 14, wherein the nano-alumina particles are less than 70 microns in diameter.

18. The material of claim 14, wherein the catalyst active metal loading on the alumina is less than 1% by weight.

19. The material of claim 14, wherein the CNT are grown on the alumina particles in a rotary kiln reactor.

20. The material of claim 19, wherein the supported catalyst is fed into the reactor wherein CNT is grown on the supported catalyst to create a hybrid material, and then the hybrid material is blended with a second material selected from the group of materials consisting of: cementitious materials, materials used in the production of cementitious materials, and materials used to enhance cementitious materials.

21. The material of claim 20, wherein the hybrid material is blended with the second material by mechanical mixing of the two in powder form.

22. The material of claim 20, wherein the hybrid material is blended with the second material by preparing a dispersion of the hybrid material in an aqueous solution and then mixing the dispersion with the second material.

23. The material of claim 14, further comprising carbon black.

24. The material of claim 23, wherein carbon black is mixed with the supported catalyst before the CNT is grown.

25. The material of claim 24, wherein carbon black is present at levels of from about 10% to about 50% by weight of the supported catalyst.

26. The material of claim 24 comprising an aqueous dispersion of the hybrid material with carbon black.

27. The material of claim 26, wherein the aqueous dispersion is mixed with a cementitious material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Various aspects of at least one example are discussed below with reference to the accompanying figures, which are not intended to be drawn to scale. The figures are included to provide illustration and a further understanding of the various aspects and examples, and are incorporated in and constitute a part of this specification, but are not intended as a definition of the limits of the inventions. In the figures, identical or nearly identical components illustrated in various figures may be represented by a like reference character or numeral. For purposes of clarity, not every component may be labeled in every figure. In the figures:

[0035] FIG. 1 illustrates a rotary kiln catalytic reactor for the continuous production of CNT-Al.sub.2O.sub.3 hybrid material.

[0036] FIG. 2 illustrates variation of the mechanical properties as a function of the curing age for Sample 2.

[0037] FIGS. 3A-3C include TGA analyses of Portland cement before and after reaction, and Sample 1, respectively.

[0038] FIG. 4 includes SEM Images taken at low (25 K×) and high (100 K×) magnifications corresponding to Samples 1 and 2, with the Sample 1 images in the top row and Sample 2 images in the bottom row.

[0039] FIG. 5 is a cartoon representation of CNT-Al.sub.2O.sub.3 nanohybrid material and Portland cement with the CNT-Al.sub.2O.sub.3 nano-hybrid.

[0040] FIGS. 6A-6C include SEM images of CNTs/CF grown on fly ash particles.

[0041] FIG. 7 includes TGA analysis of CNT/CF grow on fly ash particles.

[0042] FIG. 8 illustrates variation of mechanical properties as a function of the curing age for Sample 4.

[0043] FIG. 9 illustrates conductivity properties of different CNT-Al.sub.2O.sub.3-cement samples.

[0044] FIGS. 10A and 10B illustrate piezo-resistivity response properties corresponding to Samples 4 and 5, respectively.

[0045] FIGS. 11A and 11B include SEM images taken at 10 K× and 50 K× magnification, respectively, showing MWCNT having high aspect ratio.

[0046] FIG. 12 illustrates conductivity properties of CNT-Al.sub.2O.sub.3-cement samples prepared using different mixing methods and CNT composition.

[0047] FIGS. 13A and 13B illustrate piezo-resistivity response of CNT-Al.sub.2O.sub.3-cement samples prepared using different mixing methods and CNT composition.

[0048] FIG. 14 illustrates piezo-resistivity response of a CNT-Al.sub.2O.sub.3-Carbon Black cement sample.

[0049] FIG. 15 illustrates piezo-resistivity response of a 60 wt. % CNT-Al.sub.2O.sub.3-cement hybrid material.

[0050] FIGS. 16A-16C includes SEM images taken at 5 K×, 10 K× and 25 K× magnifications, respectively, of several different CNT-Al.sub.2O.sub.3 hybrid materials.

DETAILED DESCRIPTION

[0051] Examples of the systems, methods and apparatuses discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The systems, methods and apparatuses are capable of implementation in other examples and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. In particular, functions, components, elements, and features discussed in connection with any one or more examples are not intended to be excluded from a similar role in any other examples.

[0052] Examples disclosed herein may be combined with other examples in any manner consistent with at least one of the principles disclosed herein, and references to “an example,” “some examples,” “an alternate example,” “various examples,” “one example” or the like are not necessarily mutually exclusive and are intended to indicate that a particular feature, structure, or characteristic described may be included in at least one example. The appearances of such terms herein are not necessarily all referring to the same example.

[0053] Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Any references to examples, components, elements, acts, or functions of the computer program products, systems and methods herein referred to in the singular may also embrace embodiments including a plurality, and any references in plural to any example, component, element, act, or function herein may also embrace examples including only a singularity. Accordingly, references in the singular or plural form are not intended to limit the presently disclosed systems or methods, their components, acts, or elements. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms.

[0054] FIG. 1 is a schematic representation of an exemplary rotary tube reactor system 10 that is configured to be used to accomplish hybrid material production processes of the present disclosure. The following description illustrates certain aspects of the disclosure but is not limiting of the scope of the disclosure.

[0055] A catalyst feed system 16 can operate as follows. Catalyst particles in powder form are fed into the catalyst supply accumulation vessel 1. The air is subsequently removed from the catalyst supply accumulation vessel 1 using a flow of an inert gas. The inert gas can be preheated at temperatures between 60-150° C. to remove moisture from the catalyst during the purging process. The catalyst particles are then transferred to the second catalyst supply accumulation vessel 2 through a screw feeder. This equipment controls the amount of catalyst fed to the reactor 12. The catalyst and reaction gas feed system 14 can operate as follows. The catalyst particles contained in the second catalyst supply accumulation vessel are fed to the rotary tube reactor through a metal tube coupled to a vibrating catalyst particle feed system. The supply system is maintained in an inert gas atmosphere to inhibit unwanted reactions. When other material(s) are added along with the catalyst in order to produce CNT hybrid materials, these other material(s) can be fed together with the catalyst, or there can be a separate, parallel feed system for the other material(s). The second feed system (not shown) can be the same as the catalyst feed system, or otherwise configured to bring these material(s) to reaction temperature before they are fed into the reactor. In some examples the catalyst and other material(s) are pre-blended before being fed together into the reactor in the manner described above for the catalyst feed.

[0056] The tube that feeds catalyst/other materials into the reactor is long enough such that its end is located inside the rotary tube in the preheating zone of the furnace. In some examples the length of the inner tube is approximately ⅓ to ⅙ of the length of the rotary tube in the hot (reaction) zone of the furnace. In some examples the diameter of the inner tube is between ⅓ to ½ the diameter of the rotary tube. In some examples there are multiple heating zones of the reactor. In some examples the reactor is heated by gas or by electricity.

[0057] This arrangement results in the catalyst particles reaching the desired reaction temperature before coming into contact with the reaction gases. The inner tube is made of a special corrosion resistant steel, such as Inconel, titanium, etc. The length and diameter of the inner tube relative to the rotary tube is selected to ensure efficient heat transfer during the catalytic process.

[0058] The temperature of the process gas and the catalyst particles in the place where they enter in intimate contact is measured through a thermocouple introduced into a thermowell located in the inlet block of the reactor, indicated by a solid black line. Depending on the type of material to be synthesized, flyers or other mass-distribution structures (indicated schematically in FIG. 1) can be placed in the rotating tube to improve the transfer of mass and heat between the solid particles and the reaction gas. Flyers can also improve material flow within the rotating tube. The residence time of the catalyst within the reactor is controlled through the tube rotation speed and its inclination angle.

[0059] The product obtained is separated from the gas at the outlet of the reactor, for example using gas/solid separator 22. A system of valves discharges the product into containers (e.g., purge vessel 28) that have an inert gas injection to remove ethylene and hydrogen and cool the material before being packaged (e.g., in storage drum 30).

[0060] Liquid condenser 24 is used to remove undesired reaction by-products before hydrogen separation and recycling of reaction gases.

[0061] Unreacted ethylene (or other carbon-source reaction gas) and hydrogen are subsequently separated using a H.sub.2 membrane separator 26 that may comprise: organic polymers, nano-porous inorganic materials (ceramic, oxides, porous vycor glass, etc.), dense metal (Pd, and metal alloys), carbon and carbon-nanotubes based membranes, etc.

[0062] Unreacted carbon source is then recycled by recycle system 20, and the hydrogen can be used for other catalytic industrial processes, or for other purposes such as for power or heat generation or for transportation. The recycled gas can contain ethylene and hydrogen which facilitates the production reaction of carbon nanotubes and hybrid materials through improved heat transfer and catalyst activation. The amount of fresh ethylene to be fed to the reactor will depend on the level of ethylene conversion in the production of carbon nanotubes/hybrid materials.

[0063] The gas composition can be detected at several points as indicated in FIG. 1, using a mass spectrometer or other instrument. The composition data can be used for process control and for other purposes, such as for recording gas composition and quality. A controller (not shown in FIG. 1) is input with the gas composition data (and other variables) and controls valves, heaters, particle feeders and other process equipment (not all shown in FIG. 1) that is used to maintain desired process conditions.

[0064] Other details of the reactor and its uses are disclosed in U.S. patent application Ser. No. 17/954,899 filed on Sep. 28, 2022, the entire disclosure of which is incorporated herein by reference, for all purposes.

[0065] The following detailed description of examples illustrates but does not limit the scope of the present disclosure.

Example 1: Preparation of CNT-Cement Hybrid Materials

[0066] In this example, two CNT-Al.sub.2O.sub.3 hybrid materials were prepared as follows:

[0067] For the first material (Sample 1), fine powders of a MWCNT catalyst based on CoMoFe/MgO—Al.sub.2O.sub.3 (the catalyst is described in U.S. Pat. No. 9,855,551) were mechanically blended with Portland cement in a composition ratio of 20/80 wt. %, respectively, and then CNT synthesis was carried out on the blend in a rotary tube reactor at 600° C., in the presence of a flow of 80% V ethylene in hydrogen for 10-minute reaction time. The second material (Sample 2) was prepared by mechanically blending Portland cement powder with a previously-synthesized hybrid MWCNT-Al.sub.2O.sub.3 material, in a composition ratio of 20/80 wt. %, respectively. The compositions of both CNT-Al.sub.2O.sub.3-cement materials are shown in Table 2. In both cases, the alumina content is practically the same while the MWCNT content was 5 wt. % for sample 1 and 3 wt. % for sample 2. Mechanical performance test results are set forth in Table 3.

TABLE-US-00002 TABLE 2 Composition of the CNT-Al.sub.2O.sub.3-cement samples. MWCNT Cement Alumina content (wt. %) content (wt. %) content (wt. %) Sample 1 5.0 76.0 19.0 Sample 2 3.0 77.6 19.4

TABLE-US-00003 TABLE 3 Mechanical performance test of the CNT-Al.sub.2O.sub.3-cement samples Flexural Strength (MPa) Curing age (days) 3 7 28 Mortar-reference 4.32 5.29 5.91 Sample 1 5.14 6.53 9.02 Sample 2 5.85 7.38 9.76 Modulus of Elasticity (GPa) Curing age (days) 3 7 28 Mortar-reference 9.77 11.16 14.29 Sample 1 10.42 13.37 17.96 Sample 2 12.74 15.47 20.76 Compressive Strength (MPa) Curing age (days) 3 7 28 Mortar-reference 20.05 25.87 31.31 Sample 1 25.27 28.74 35.86 Sample 2 27.04 30.76 37.62

[0068] FIG. 2 illustrates variation of mechanical properties as a function of the curing age for Sample 2. Both flexural strength and modulus of elasticity increase progressively with the curing age, while the compressive strength decreases during the first 7 days and then remains constant. Sample 2 delivers +65%, 45% and 20% higher flexural, modulus of elasticity and compressive strength than a cement mortar reference after 28 days curing age. The observed values for Sample 1 were 53%, 24% and 15%, respectively.

[0069] FIGS. 3A and 3B show results of the thermogravimetric analysis (TGA) of Portland cement before and after being processed under reaction conditions in the presence of the ethylene+H.sub.2 gas mixture at 675° C. for 10 minutes residence time. As can be seen, important structural and composition changes of the cement occur after the reaction. These structural changes can significantly influence the mechanical, electrical and thermal conductivity properties of the concrete. This would explain the results obtained with Sample 1, where although the MWCNT content is higher than in Sample 2, the improvement in the mechanical properties of the cementitious material was inferior. FIG. 3C shows the TGA analysis of Sample 1 where a signal at 565° C. can be attributed to MWCNT.

[0070] FIG. 4 includes four SEM Images taken at low (25 K×) and high (100 K×) magnifications corresponding to Samples 1 and 2, with the Sample 1 images in the top row and Sample 2 images in the bottom row. The formation of short MWCNTs (<200 nm) and diameter approximately between 25 and 45 nm can be clearly seen in Sample 1. Some cement particles are observed that are not in contact with the nanotubes. On the contrary, in Sample 2, a mesh of long MWCNTs with a diameter between 10 and 15 nm can be seen surrounding and filling the spaces between the cement particles.

[0071] FIG. 5 is a simplified representation of the creation of the CNT-Al.sub.2O.sub.3 hybrid material, and the Portland cement additive with CNT-Al.sub.2O.sub.3 nanoparticles hybrid material. The catalyst contains primary or elementary nano-alumina particles, smaller than about 1 micron in size, which are typically agglomerated to form grains of sizes<100 microns. During the catalyst preparation, the active metals are deposited inside the pores as well as on their external surface of the elementary particles. During synthesis, the active metals catalyze the decomposition reaction of the carbon source into CNT+H.sub.2. CNTs growth in all directions causes de-agglomeration of elementary alumina particles. The hybrid CNT-Al.sub.2O.sub.3 material is formed. The integration of the CNT-Al.sub.2O.sub.3 nanohybrid in Portland cement is achieved through the deagglomeration of the nanohybrid particles during the aqueous dispersion preparation.

[0072] The same concept applies for other types of catalysts. For example, silica fumes are composed of elemental SiO.sub.2 particles of nanometric size. It has been observed that an addition of 10% nano-SiO.sub.2 with dispersing agents resulted in a 26% increase in compressive strength after 28 days of curing. The composite addition of nano-SiO.sub.2, and high volume of fly ash, and silica fume was found to be a very effective way to achieve good mechanical performance and an economic way to use both additives.

Example 2: Growth of CNTS on Fly Ash Particles

[0073] FIGS. 6A-6C are SEM images corresponding to the synthesis of CNTs and CFs on fly ash particles. Fly ash is a coal combustion product that is composed of fine particles of mainly metal oxides that are driven out of coal-fired boilers together with the flue gases. SiO.sub.2 (both amorphous and crystalline forms), Al.sub.2O.sub.3, Fe.sub.2O.sub.3 and CaO are the main chemical components present in fly ashes. Fly ash can replace some or most of the Portland cement in concrete production, leading to higher porosity at early age, and increases in mechanical strength, chemical resistance and durability.

[0074] The CNT synthesis was carried out in a rotary tube reactor at 650° C., in the presence of a flow of 80% V ethylene in hydrogen for 10-minute reaction time. The iron oxide particles contained in the fly ash act as a catalyst.

[0075] As can be seen in FIG. 6A, not all the particles show growth of CNT/CFs. A fly ash particle with CNT/CF is clearly shown in FIG. 6B. The image taken at highest magnification (FIG. 6C, 25 K×) shows the formation of braids of CNTs and CFs with lengths of approximately 1-1.5 microns and few hundred nm in diameter on the surfaces of the fly ash particles. The CNTs/CFs content on the fly ash particles, as determined by TGA analysis, is about 9 wt. % (FIG. 7).

Example 3: Influence of the CNT Aspect Ratio on Mechanical and Electrical Properties and Piezoelectric Response

[0076] In this example, three CNT-Al.sub.2O.sub.3 hybrid materials (samples 3, 4, and 5) were synthesized having differences in CNT content (15, 20, and 25 wt. % by weight of alumina as set forth in Table 4 below) by following the procedure described in example 1. The amount of carbon deposited on the Al.sub.2O.sub.3 nanoparticles depends on the reaction time, which varied between 3 and 10 minutes.

[0077] The CNT-Al.sub.2O.sub.3 hybrid materials powders were mechanically blended with Portland cement in such proportions that the MWCNT content in the samples were the same (0.15 wt. %). Table 4 shows the weight composition and aspect ratio properties of each sample. As the carbon yield increases, the length of the tubes progressively increases but their diameter remains unchanged (10+/−3 nm). Consequently, the CNT aspect ratio increases as a function of the increase in carbon yield during the synthesis of the CNT-Al.sub.2O.sub.3 hybrid material.

TABLE-US-00004 TABLE 4 Properties of Samples 3, 4 and 5. MWCNT MWCNT CNT Alumina content content diameter content in CNT-Al.sub.2O.sub.3 in cement aspect ratio in cement (wt. %) (wt. %) (L/D) (wt. %) Sample 3 15 0.15 435 0.85 Sample 4 20 0.15 570 0.60 Sample 5 25 0.15 730 0.45

[0078] Mechanical performance tests (flexural, modulus of elasticity and compressive strength) were performed for samples 3, 4 and 5. The results are shown in Table 5. As the aspect ratio (L/D) increases, the mechanical properties of the cement improve significantly.

[0079] FIG. 8 shows the variation of the mechanical properties as a function of the curing age for Sample 4.

[0080] As the curing age increases, the percentage increase in flexural properties and the modulus of elasticity becomes greater with respect to the mortar reference. In the case of compressive strength, the percentage tends to decrease from 36% to 19% during the first 7 days and then tends to stabilize. After 28 hours of curing age, flexural strength, the modulus of elasticity and the compressive strength values were 81%, 50% and 22%, respectively. These results represent an improvement of the flexural strength and modulus of elasticity properties with respect to the samples prepared in example 1, whose MWCNT content in the cement was 5 and 3 wt. % for samples 1 and 2, vs 0.15 wt. % for samples 3 and 4, respectively.

TABLE-US-00005 TABLE 5 Mechanical performance test of the CNT-Al.sub.2O.sub.3-cement prepared samples Flexural Strength (MPa) Curing age (days) 3 7 28 Mortar-reference 4.32 5.29 5.91 Sample 3 6.06 7.56 10.13 Sample 4 6.19 7.75 10.31 Sample 5 6.44 7.88 10.56 Modulus of Elasticity (GPa) Curing age (days) 3 7 28 Mortar-reference 9.23 11.15 14.30 Sample 3 12.50 14.72 19.72 Sample 4 12.57 15.00 19.72 Sample 5 12.78 15.28 20.00 Compressive Strength (MPa) Curing age (days) 3 7 28 Mortar-reference 20.05 25.87 31.31 Sample 3 27.03 30.47 37.50 Sample 4 27.19 30.63 37.81 Sample 5 27.34 30.94 37.97

[0081] Electrical conductivity properties at different curing ages corresponding to samples 3, 4 and 5 are shown in FIG. 9. The most conductive material was Sample 5 which has the highest CNT aspect ratio (730).

[0082] Piezo-resistivity response test results corresponding to the samples 4 and 5 are shown in FIGS. 10A and 10B, respectively. Sample 5 shows the greatest changes in resistivity (Δρ/ρ.sub.o) when the sample was submitted to different stress level.

Example 4: Influence of the CNT-Al.SUB.2.O.SUB.3.-Cement Preparation Method

[0083] In this example, a MWCNT-Al.sub.2O.sub.3 hybrid material having 35 wt. % MWCNT and L/D>1000 was employed. FIGS. 11A and 11B are SEM images taken at different magnifications (10 K× and 50 K×, respectively) of the MWCNT-Al.sub.2O.sub.3 hybrid material. Long MWCNTs of more than 10 microns in length, and alumina nanoparticles of approximately 500 nm in diameter can be observed.

[0084] An aqueous suspension was prepared by mixing using 350 ml H.sub.2O, 0.10 or 0.15 wt. % MWCNT-Al.sub.2O.sub.3 hybrid material in cement and 0.4% superplasticizer of cement. The dispersions were prepared by using ultrasonication or intensive mixer equipment. In the intensive mixer, the MWCNT-Al.sub.2O.sub.3 hybrid material in dry form, and the mixing water was placed in the bowl and mixed for 10 minutes using a speed of 285 rpm. The dry materials (cement and sand) were added in the mix for the preparation of mortar specimens.

[0085] FIG. 12 shows the variation of the electrical conductivity of the samples prepared according to different mixing techniques and CNT content in the cement as a function of curing age. By increasing the CNT content in the cement from 0.10 to 0.15 wt. %, the resistivity of the material decreases by about 39%. For the samples containing 0.15% CNT in the cement, no significant differences in electrical conductivity are observed when using ultrasonication or intensive mixer equipment. No significant differences are observed in piezoelectric response between the samples prepared using different mixing equipment. See FIGS. 13A and 13B (ultrasonication and intensive mixing, respectively). These results clearly demonstrate that the CNT-Al.sub.2O.sub.3 material can be easily dispersed using conventional mixing equipment.

Example 5: CNT-Al.SUB.2.O.SUB.3.-Carbon Black Hybrid Material for Smart Concrete

[0086] As mentioned above, carbon black (CB) has been used as an additive to enhance the electrical conductivity properties and piezoelectric response in the manufacture of smart concrete. In this example (Sample 6), catalyst powder was mixed with carbon black in a certain proportion (40% by weight of catalyst) and the CNT synthesis was carried in a rotary tube reactor under the reaction conditions described in example 1. Subsequently, an aqueous dispersion was prepared with the hybrid material CNT-Al.sub.2O.sub.3—CB and then mixed with the cement powder following the same procedure used in example 4.

[0087] Table 6 shows the composition by weight of the hybrid material CNT-Al.sub.2O.sub.3—CB and in the cement mixture. The total conductive carbon composition is 0.13 wt. % (MWCNT=0.08 wt. % and CB: 0.05 wt. %) which is comparable with the MWCNT content in samples 3 to 5 (cement). Note that the composition of MWCNT is lower than samples 3 to 5.

TABLE-US-00006 TABLE 6 Composition of Sample 6 of cement MWCNT-Al.sub.2O.sub.3- Carbon MWCNT in CB in Nano-Al.sub.2O.sub.3 Black in cement cement cement in cement (wt. %) (wt. %) (wt. %) (wt. %) Sample 6 0.15 0.08 0.05 0.02

TABLE-US-00007 TABLE 7 Electrical conductivity and mechanical properties of Sample 6. Curing age (days) 3 7 28 Resistivity (K .Math. Ω .Math. cm) 1.6 4.5 6.8 Flexural Strength (MPa) 5.7 7.1 10.3 Young Modulus (GPa) 12.0 14.6 22.1 Compressive strength (MPa) 21.1 25.8 32.7 Flexural Strength (%) 32% 34% 74% Young Modulus (%) 30% 31% 55% Compressive strength (%)  5%  0%  4%

[0088] Table 7 shows the electrical and mechanical conductivity properties of the Sample 6 hybrid material (CNT-Al.sub.2O.sub.3-Carbon Black) in the cement as a function of curing time. An improvement in the conductive properties of cement is observed when compared with the results obtained for Sample 5. The Piezoelectric response of sample 6 (FIG. 14) also increased significantly (from 3.9% to 7.82%).

[0089] Table 7 also lists improvements in mechanical properties (in %) as compared to a mortar reference. Flexural strength and modulus of elasticity properties also improved significantly by approximately 74% and 55%, respectively, with respect to the mortar reference after 28 days of curing time. The compressive strength increased 4%.

Example 6

[0090] In this example, a MWCNT-Al.sub.2O.sub.3 hybrid material having 60 wt. % MWCNT was prepared and a series of experiments were conducted by combining Portland cement with the CNT hybrid material and 30 wt. % fly ash. Table 8 includes changes in the mechanical properties of the different prepared samples obtained after 28 days curing age (as compared to the Portland cement reference). Table 8 also lists improvements in mechanical properties (in %) as compared to a mortar reference. The mechanical strength properties slightly increased after adding 30% of fly ash to the mortar. When 0.1 wt. % of CNT-Al.sub.2O.sub.3 hybrid material was added to the mortar, flexural strength, the modulus of elasticity and the compressive strength increased by about 88%, 82% and 11%, respectively. This material also showed the highest piezoelectric response value (FIG. 15). The addition of 30 wt. % fly ash and 0.1 wt. % CNT-Al.sub.2O.sub.3 hybrid material to the mortar caused an improvement of about 11% in the compressive strength property while, the flexural strength and the elasticity modulus values increased by about 28% and 25%, respectively.

TABLE-US-00008 TABLE 8 Mechanical performance test of the CNT- Al.sub.2O.sub.3-Fly cement prepared samples Compressive Flexural Elasticity Strength (MPa) Strength (MPa) Modulus (GPa) Mortar 31.31 5.91 14.30 Mortar + Fly Ash 34.64 6.26 14.77 Mortar + CNT-hybrid 34.19 11.1 26.06 Mortar + CNT- 34.85 7.59 17.86 hybrid + Fly Ash Mortar + Fly Ash  9%  6%  3% Mortar + CNT-hybrid 11% 88% 82% Mortar + CNT- 11.%  28% 25% hybrid + Fly Ash

[0091] Comparing the results obtained when using MWCNT-Al.sub.2O.sub.3—CB (Example 5) vs CNT-Al.sub.2O.sub.3(Example 6) it can be clearly seen that the CNT-Al.sub.2O.sub.3 delivers superior performance benefits in mechanical reinforcement, electrical conductivity and piezoelectric properties, despite the difference in total carbon content in cement (0.13% in MWCNT-Al.sub.2O.sub.3—CB vs 0.08 wt. % in the CNT-Al.sub.2O.sub.3 hybrid material).

Example 7

[0092] In this example, CNT-Al.sub.2O.sub.3 hybrid materials having different CNT compositions were synthesized by mechanically blending fine alumina powder with fine CoMoFe/MgO-Al.sub.2O.sub.3 catalyst powder employed in Example 1. The composition of the alumina powder in the blends varied from 0 to 95 wt. %. The particle size of both materials, as determined through the laser scattering technique, varied between 1 to 10 microns in diameter (Mean=3 to 4μ). The CNT synthesis was carried out in a rotary tube reactor at 650° C. temperature, in the presence of a gas flow that comprise 80% V ethylene and 20% V hydrogen for 10-minutes reaction time.

[0093] Table 9 shows the results of the synthesis of CNT-Al.sub.2O.sub.3 hybrid materials obtained from different catalyst-alumina blends. The results clearly show that by diluting the catalyst particles by 20% with alumina powder, the CNT yield remains above 80 wt. %. Increasing the alumina composition in the blend, the CNT yield tends to decrease progressively until reaching a CNT composition in the hybrid material of 27% for 95% Al.sub.2O.sub.3 and 5 wt. % catalyst blends.

TABLE-US-00009 TABLE 9 Composition of the CNT-Al.sub.2O.sub.3 hybrid material obtained with different catalyst-alumina blends. Catalyst (wt. %) Alumina (wt. %) MWCNT (wt. %) 100 0 84.0 80 20 81.2 60 40 77.9 40 60 71.8 20 80 56.2 10 90 40.5 5 95 27.0

[0094] SEM Images taken at different (5K, 10K and 25 K) magnifications of the CNT-Al.sub.2O.sub.3 hybrid materials of Table 9 are shown in FIGS. 16A to 16C, respectively, for alumina composition in the blend between 0% to 90 wt. % (0%, 20%, 40%, 60%, 80%, and 90%). When no alumina is blended with the catalyst particles, the formation of a compact mesh is observed where the CNTs are found highly entangled. When alumina powder is progressively blended with the catalyst particles, the formation of CNTs structures in rods-shapes are observed. These CNT rods are separated from each other when the alumina content in the blend increases. The CNTs become longer while their diameter remains unchanged for all the samples analyzed (8-13 nm). Alumina and catalyst particles having sizes of approximately 0.5 to 2 microns were observed in greater proportion for samples that contain greater than 80 wt. % alumina. FIG. 16C shows clear evidence of the formation of an open mesh of CNTs when the alumina content in the blend is greater than 20 wt. %. These tubes are easier to disentangle and would require less energy to disperse. Compared to prior art, this material can be easily integrated into the cement particles in suspension, powder, or granulated forms.

[0095] Having described above several aspects of at least one example, it is to be appreciated 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.