Lightweight Geopolymer Material Containing Carbon Nanotube-Modified Hollow Microspheres and Preparation Method Thereof

Abstract

The present invention relates to the technical field of solid waste resource utilization, and particularly to a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres and a preparation method thereof. The material is composed of granulated blast furnace slag, silica fume, carbon nanotube-modified fly ash hollow microspheres, water, water glass, sodium hydroxide, and foam. Among them, carbon nanotubes are bridged to the surface of the fly ash hollow microsphere shell by a silane coupling agent to form a composite structure of carbon nanotube-modified fly ash hollow microspheres. Aiming at the problem that foam is easily damaged during the preparation process, the stirring blade adopted in the present invention has the function of flipping up and down, improving the slurry stirring process. The structure of the blade generates a gentle upward torque force on the slurry. This process of flipping and mixing simultaneously is more conducive to the mixing of foam and slurry, improving the stability of foam in the system.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste resource utilization, and particularly to a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres and a preparation method thereof. Background Art

[0002] With the development of the construction industry, energy consumption and environmental protection have received extensive attention. Lightweight thermal insulation geopolymer composites have attracted much attention. On the one hand, using granulated blast furnace slag and fly ash hollow microspheres as cementitious materials realizes the reuse of solid waste and reduces costs. On the other hand, compared with cement-based materials, the solid waste utilization reduces carbon emissions in construction projects and is environmentally friendly. Introducing voids into the geopolymer slurry is the main technical means to reduce the thermal conductivity and improve the thermal insulation performance, and can be used to prepare lightweight-thermal insulation geopolymer-based composites. Many researchers use physical foaming methods to introduce voids into cement / geopolymer to improve the thermal insulation performance of the materials. However, due to the instability of the foam in the slurry, the prepared lightweight composite materials are prone to problems such as bubble floating and rupture, which further cause collapse. From the perspective of the stability of the foam itself and the rheological properties of the slurry, the instability of the foam itself will undoubtedly lead to rupture, and the rheological properties of the slurry also play a key role in stability. If the yield stress and viscosity of the slurry are too low, the foam is prone to floating during the mixing process with the slurry; conversely, if the yield stress and viscosity are too high, it will cause damage to the foam. In addition, the preparation process of foam insulation materials should also be taken seriously. Traditional stirring blades are not suitable for fully mixing extremely low-density foam with the slurry evenly, and foam damage is prone to occur during the stirring process.

[0003] Chinese Patent Publication No.: CN111423160B discloses a lightweight geopolymer thermal insulation material and a preparation method thereof. The preparation method of the lightweight geopolymer thermal insulation material in this invention is as follows: Fly ash and metakaolin dry materials are stirred and mixed evenly, an alkali activator and water are added and stirred to obtain a geopolymer slurry, a foaming agent and a foam stabilizer are added to the slurry and rapidly stirred, and then lightweight aggregates are added and stirred and mixed evenly to obtain a geopolymer foam concrete slurry. Finally, it is cast into a mold, demolded, and cured at room temperature. This invention obtains green geopolymer foam concrete with relatively high strength, relatively light weight, and good thermal insulation performance, and solves the problems of poor durability, poor compressive strength, high cost, and non-environmental protection of the existing foam concrete and its preparation method. This invention consists of fly ash, metakaolin, sodium hydroxide, water glass, water, a foaming agent, a foam stabilizer, and lightweight aggregates. It can be seen that this invention has the following problems: The research on foaming agents in the market generally targets cement-based systems, and for the energy-saving and emission-reducing green alkali-activated cementitious material system, this invention does not consider the obvious inapplicability of foaming agents in this system. For example, the foam is unstable in the alkali-activated cementitious material, and problems such as bubble collapse are prone to occur during the preparation process. Summary of the Invention

[0004] To this end, the present invention provides a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres and a preparation method thereof, so as to overcome the problems that foams are unstable in alkali-activated cementitious materials and float, break and cause collapse during the preparation of lightweight geopolymers in the prior art.

[0005] To achieve the above object, on the one hand, the present invention provides a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres, and the material is composed of the following weight components: 17.65 - 18.75 parts of granular blast furnace slag, 1.47 - 1.56 parts of silica fume, 10.29 - 10.94 parts of carbon nanotube-modified fly ash hollow microspheres, 6.71 - 9.26 parts of water, 7.40 - 7.86 parts of water glass, 0.99 - 1.05 parts of sodium hydroxide, and 2.94 - 3.13 parts of foam.

[0006] Further, the main component of the granular blast furnace slag includes calcium oxide, and the calcium oxide content is greater than 35%.

[0007] Further, the silica fume contains 98% amorphous silica, and its average particle size is 0.3 - 10 μm;

[0008] The sodium hydroxide is a uniform granular or flaky solid with a purity greater than 96%;

[0009] The water glass is composed of 30% silica, 13.5% sodium peroxide and 56.5% water, and its modulus is 2.3.

[0010] Further, the composition mass ratio of each component of the carbon nanotube-modified fly ash hollow microspheres is:

[0011] Silane coupling agent: carbon nanotube: fly ash hollow microsphere = 1:1:97;

[0012] Among them, the purity of the silane coupling agent is greater than 98%.

[0013] Further, the preparation method of the carbon nanotube-modified fly ash hollow microspheres includes:

[0014] Step S01, combining a silane coupling agent with carbon nanotubes;

[0015] Step S011, mixing the silane coupling agent and an ethanol aqueous solution in a mass ratio of 1:80 to obtain a mixed solution A, and magnetically stirring it at 60°C for 3 h to fully hydrolyze it to obtain solution A;

[0016] Step S012, ultrasonically dispersing 1 g of carbon nanotubes in 500 ml of deionized water for 2 h to obtain a uniform solution B;

[0017] Step S013: Mix solution A and solution B, and ultrasonically stir for 1 h to make them evenly mixed to obtain solution C;

[0018] Step S02: Pretreat fly ash cenospheres. Select fly ash cenospheres with a particle size of 80 - 120 μm and ultrasonically treat them in acid for 30 min to obtain a fly ash acid solution. Filter out the particles in the fly ash acid solution and wash them repeatedly 2 times with deionized water. Place the washed particles in a vacuum drying oven at 105 °C and dry for 3 h;

[0019] Step S03: Graft carbon nanotubes onto the surface of fly ash cenospheres through a silane coupling agent to modify the fly ash cenospheres;

[0020] Step S031: Add the pretreated fly ash cenospheres in Step S02 to solution C, and magnetically stir at 60 °C for 3 h to obtain solution D;

[0021] Step S032: Filter out the carbon nanotube cenospheres in solution D and wash them with deionized water and absolute ethanol respectively. After washing, place the carbon nanotube cenospheres in an oven at 105 °C and dry for 6 h to obtain carbon nanotube - modified fly ash cenospheres;

[0022] Wherein, the acid includes a 10% dilute hydrochloric acid solution, and the absolute ethanol is an ethanol solution with a purity of 99.6%.

[0023] Further, the foam is formed by mixing dodecyldimethylbetaine and water in a mass ratio of 1:50 and slowly stirring for 2 min;

[0024] Wherein, the dodecyldimethylbetaine is an amphoteric surfactant with an active substance content of 30%, and it is a light - yellow transparent liquid with a density of 1.04 g / mL.

[0025] On the other hand, the present invention also provides a preparation method of a lightweight geopolymer material containing carbon nanotube - modified hollow microspheres, including the following steps:

[0026] Step S1: Prepare an alkali activator, and the alkali activator includes the sodium hydroxide, the sodium silicate and water;

[0027] Step S2: Weigh granular blast furnace slag, carbon nanotube - modified fly ash cenospheres, silica fume and an alkali activator by weight using an electronic scale;

[0028] Step S3: Mix the granular blast furnace slag, carbon nanotube - modified fly ash cenospheres, silica fume and an alkali activator in Step S2 evenly in a stirring pot to prepare a dry material;

[0029] Step S4, slowly add the alkali activator solution to the dry materials in the mixing pan and stir for 3 min using a conventional mortar mixer at a stirring rate of 140 r / min until a paste is formed.

[0030] Step S5, add the foam to the surface of the paste and mix the foam and the paste evenly by stirring to prepare a foam geopolmer-based composite paste.

[0031] Step S6, perform post-treatment using the foam geopolmer-based composite paste to obtain a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres.

[0032] Among them, the post-treatment includes forming, curing, and maintenance.

[0033] Further, step S3 includes:

[0034] Step S31, add the carbon nanotube-modified fly ash hollow microspheres and the silica fume to the mixing pan and stir for 3 min until the two dry materials are mixed evenly.

[0035] Step S32, add the granulated blast furnace slag to the two dry materials that have been evenly mixed in step S31 and stir for 1.5 - 4 min until the three dry materials are mixed evenly.

[0036] Further, in step S5, the stirring blades used are stirring blades that can be flipped up and down, and the flipping and stirring time is 2 min, and the stirring rate is 60 - 200 r / min.

[0037] Further, in step S5, the judgment method for determining that the foam and the paste are mixed evenly includes:

[0038] The color uniformity of the mixture of the foam and the paste meets the standard, and / or the volume change of the mixture of the foam and the paste meets the standard.

[0039] Compared with the prior art, the beneficial effect of the present invention is that when preparing a lightweight geopolymer material by bridging carbon nanotubes to the surface of fly ash hollow microspheres through a silane coupling agent, the carbon nanotubes hydrolyze in an alkaline environment to generate O2 - , and are adsorbed to the cations on the surface of the foam through the action of Coulomb force, improving the stability of the foam in the system.

[0040] Further, bridging the carbon nanotubes to the surface of the fly ash hollow microspheres and introducing them into the slurry to play a synergistic effect with the foam can, to a certain extent, avoid phenomena such as the fusion and fragmentation of bubbles, optimize the pore structure characteristics of the foam slurry, and the uniformly distributed pore structure helps to improve the compressive strength of the specimen.

[0041] Furthermore, the present invention adsorbs carbon nanotubes on the surface of fly ash cenospheres, solving the problems of easy agglomeration and difficult dispersion of carbon nanotubes in cementitious materials. Uniformly dispersed carbon nanotubes are more conducive to interacting with ions on the surface of the foam. Therefore, uniformly dispersed carbon nanotubes on fly ash cenospheres are more conducive to improving the stability of the foam.

[0042] Furthermore, the preparation method provided by the present invention adjusts the rheological properties of the slurry by changing the ratio of the alkaline solution to the cementitious material. Appropriate yield stress and viscosity are beneficial to the force balance of the foam in the slurry, playing a role in fixing the foam.

[0043] Furthermore, the preparation method provided by the present invention improves the rotating blades of the mixer, selects blades that can turn the slurry up and down, and determines the optimal conditions for the fully uniform mixing of foam with extremely low density and slurry with relatively high density by controlling the stirring rate.

[0044] Furthermore, the present invention selects granulated blast furnace slag and a small amount of silica fume as solid waste cementitious materials, combines physical foaming to reduce the density of the mixture, and the prepared thermal insulation material can effectively improve the utilization rate of industrial solid waste. At the same time, it greatly reduces the emissions of greenhouse gases. The carbon dioxide emissions of producing one ton of geopolymers are reduced by 70 - 80% compared with producing one ton of cement. It is a new type of low-carbon, green and environmentally friendly green building material. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the chemical reaction of carbon nanotube modified fly ash cenospheres in the embodiment of the present invention;

[0046] Figure 2 It is a preparation flow chart of a lightweight geopolymer material containing carbon nanotube modified cenospheres in the embodiment of the present invention;

[0047] Figure 3 It is a schematic diagram of the stirring blade in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0048] In order to make the objectives and advantages of the present invention clearer, the present invention will be further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0049] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and do not limit the protection scope of the present invention.

[0050] It should be noted that in the description of the present invention, the terms indicating the direction or positional relationship such as "upper", "lower", "left", "right", "inner", "outer", etc. are based on the direction or positional relationship shown in the drawings. This is only for convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0051] In addition, it should also be noted that in the description of the present invention, unless otherwise clearly specified and defined, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0052] The present invention provides a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres, which is composed of the following weight components: 17.65 - 18.75 parts of granular blast furnace slag, 1.47 - 1.56 parts of silica fume, 10.29 - 10.94 parts of carbon nanotube-modified fly ash hollow microspheres, 6.71 - 9.26 parts of water, 7.40 - 7.86 parts of water glass, 0.99 - 1.05 parts of sodium hydroxide, and 2.94 - 3.13 parts of foam.

[0053] The main component of the granular blast furnace slag used in the present invention includes calcium oxide, and the calcium oxide content is greater than 35%.

[0054] Specifically, the high calcium content of the slag makes the vitreous body more easily disintegrate, with higher activity. The amorphous phase participates in the reaction with the alkali activator to form more calcium aluminosilicate hydrate, which helps the development of the matrix strength.

[0055] The silica fume used in the present invention contains 98% amorphous silica, and its average particle size is 0.3 - 10 μm, and the density and specific surface area are 560 - 720 kg / m 3 , 19 - 26 m 2 / g; the sodium hydroxide is a white translucent uniform granular or flaky solid with a purity greater than 96%, which is easily soluble in water, with a pH value of 12.7, a melting point of 318.4 °C, a boiling point of 1390 °C, and a density of 2.93 g / cm 3 ; the water glass is composed of 30% silica, 13.5% sodium peroxide, and 56.5% water, and is in the state of a transparent viscous liquid, with a density of 1526 - 1559 kg / m 3 , the chemical composition has a SiO2 content of 30%, a Na2O content of 13.5%, a water content of 56.5%, and a modulus of 2.3.

[0056] Specifically, there are two reasons for choosing silica fume with a particle size of 0.3 - 10 μm in the present invention: on the one hand, the silica fume with a particle size of 0.3 - 10 μm has a fine particle size and excellent micro-filling effect, which can improve the compactness of the geopolymer matrix and is beneficial to the development of its strength; on the other hand, reactive amorphous silica is easily involved in the reaction to form calcium silicate hydrate in an alkaline environment, filling part of the micro-pores.

[0057] The present invention prepares a lightweight geopolymer material by bridging carbon nanotubes to the surface of fly ash hollow microspheres through a silane coupling agent. The composition ratio of each component of the carbon nanotube-modified fly ash hollow microspheres is 1 g of silane coupling agent, 1 g of carbon nanotubes, and 97 g of fly ash hollow microspheres. The silane coupling agent is silane coupling agent KH-560, with a purity greater than 98%, which is a colorless or slightly yellow transparent liquid, having a density of 1065 - 1072 kg / m 3 at 25 °C, a boiling point of 286 - 293 °C, and a flash point of 109 - 113 °C.

[0058] Please refer to Figure 1 shown, which is a schematic chemical reaction diagram of carbon nanotube-modified fly ash hollow microspheres in an embodiment of the present invention. The method for preparing carbon nanotube-modified fly ash hollow microspheres in this embodiment includes the following steps:

[0059] Step S01, combining the silane coupling agent with carbon nanotubes. The -Si-OR group of the silane coupling agent undergoes hydrolysis to form -Si-OH groups. The silane molecules aggregate with each other through intermolecular forces to form long chains. At the same time, the silane coupling agent containing -Si-OH groups forms hydrogen bonds with the -OH groups on the surface of the carbon nanotubes and undergoes a condensation reaction, finally forming a silicon-oxygen network structure containing -Si-O-Si- chemical bonds;

[0060] Step S011, mixing the silane coupling agent and an ethanol aqueous solution in a mass ratio of 1:80 to obtain a mixed solution A, and magnetically stirring it at 60 °C for 3 h to fully hydrolyze it to obtain solution A;

[0061] Step S012, ultrasonically dispersing 1 g of carbon nanotubes in 500 ml of deionized water for 2 h to obtain a uniform solution B;

[0062] Step S013, mixing solution A and solution B, and ultrasonically stirring for 1 h to make them evenly mixed to obtain solution C;

[0063] Step S02, pre-treating fly ash hollow microspheres. Select fly ash hollow microspheres with a particle size of 80 - 120 μm and ultrasonically treat them in acid for 30 min to obtain a fly ash acid solution. Filter out the particles in the fly ash acid solution and wash them repeatedly 2 times with deionized water. Place the washed particles in a vacuum drying oven at 105 °C and dry them for 3 h;

[0064] Step S03: graft carbon nanotubes onto the surface of fly ash hollow microspheres through a silane coupling agent to modify the fly ash hollow microspheres. Among them, the hydroxyl groups on the surface of the fly ash hollow microspheres treated with an acid solution undergo a condensation reaction with the hydroxyl groups of the silane coupling agent, bridging the carbon nanotubes onto the surface of the fly ash hollow microspheres to form a composite structure of fly ash hollow microspheres modified with carbon nanotubes;

[0065] Step S031: Add the pretreated fly ash hollow microspheres in Step S02 to Solution C and magnetically stir at 60 °C for 3 h to obtain Solution D;

[0066] Step S032: Filter out the carbon nanotube hollow microspheres in Solution D and wash them with deionized water and absolute ethanol respectively. After washing, place the carbon nanotube hollow microspheres in an oven at 105 °C and dry for 6 h to obtain carbon nanotube-modified fly ash hollow microspheres;

[0067] Among them, the acid includes a 10% dilute hydrochloric acid solution, and the absolute ethanol is an ethanol solution with a purity of 99.6%. At room temperature, the density is 0.81 g / cm 3 , the melting point is -113 °C, and the boiling point is 78 °C.

[0068] Under the above modification mechanism, grafting carbon nanotubes onto the surface of fly ash hollow microspheres solves, on the one hand, the problem that nanomaterials (carbon nanotubes) are prone to agglomeration and difficult to disperse uniformly in the slurry. On the other hand, carbon nanotubes hydrolyze to generate O2- in an alkaline environment, while the surface of the foam presents positive ions, and the two are adsorbed to each other through the action of Coulomb force. This effect is beneficial in the following aspects: First, it prevents the water secretion of the foam; Second, it increases the viscoelasticity of the foam liquid film; Third, it inhibits the thinning of the foam wall, thereby improving the stability of the foam. This uniformly dispersed carbon nanotube is more conducive to interacting with the ions on the surface of the foam, achieving the effect of stabilizing the foam.

[0069] The foam used in the present invention is formed by mixing dodecyldimethylbetaine and water according to a mass ratio of 1:50 and stirring at a low speed for 2 min;

[0070] Among them, the dodecyldimethylbetaine is an amphoteric surfactant with an active substance content of 30%, and it is a light yellow transparent liquid with a density of 1.04 g / mL.

[0071] Please refer to Figure 2 as shown. It is a flowchart for the preparation of a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres according to an embodiment of the present invention. This embodiment provides a preparation method for a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres, including the following steps:

[0072] Step S1: Prepare an alkali activator, and the alkali activator includes the sodium hydroxide, the water glass and water;

[0073] Step S2, weigh granular blast furnace slag, carbon nanotube-modified fly ash cenospheres, silica fume and an alkali activator by weight using an electronic scale;

[0074] Step S3, mix the granular blast furnace slag, carbon nanotube-modified fly ash cenospheres, silica fume and alkali activator in step S2 evenly in a mixing pan to prepare dry materials;

[0075] Step S4, slowly add the alkali activator solution to the dry materials in the mixing pan and stir with a conventional mortar mixer for 3 min to form a paste, and the stirring rate of the mixer is 140 r / min;

[0076] Step S5, add the foam to the surface of the paste and mix the foam and the paste evenly by stirring to prepare a foam geopolmer-based composite paste;

[0077] Step S6, perform post-treatment using the foam geopolmer-based composite paste to obtain a lightweight geopolymer material containing carbon nanotube-modified cenospheres;

[0078] Among them, the post-treatment includes shaping, curing and maintenance.

[0079] Specifically, step S3 includes:

[0080] Step S31, add the carbon nanotube-modified fly ash cenospheres and the silica fume to the mixing pan and stir for 3 min until the two dry materials are mixed evenly;

[0081] Step S32, add the granular blast furnace slag to the two dry materials that have been evenly mixed in step S31 and stir for 1.5 - 4 min until the three dry materials are mixed evenly.

[0082] Specifically, the powdery materials are added in two batches because of their large density difference. If they are mixed together, as the stirring progresses, the dry materials with a larger density are likely to sink to the bottom. Therefore, in the process of mixing and stirring the dry materials in the present invention, first mix the carbon nanotube-modified fly ash cenospheres with a relatively low density and the silica fume evenly, and then add the granulated blast furnace slag with a larger density to the surface, and start the mixer to stir for 1.5 - 4 min, then the state of uniform mixing of the three dry materials can be achieved;

[0083] Among them, if the stirring time is greater than 4 min, it is easy for the high-density materials to sink to the bottom, and if the stirring time is less than 1.5 min, it is easy for the dry materials to be insufficiently mixed.

[0084] Please refer to Figure 3As shown, it is a schematic diagram of the stirring blade in the embodiment of the present invention. The stirring blade used in step S5 of the preparation method provided by the present invention is a stirrable-up-and-down blade, and its stirring time is 2 min, and the stirring rate is 60-200 r / min.

[0085] Specifically, the conventional stirring blade has a large shearing force, which is easy to cause foam breakage; at the same time, it does not have the torque force to turn the slurry up and down, and it is very difficult to mix materials with large density differences such as foam and slurry evenly; while the turning and stirring is mainly based on a gentle force, and a torsional effect is generated during the stirring process, which can make the slurry better wrap a large amount of foam. The present invention selects the turning and stirring time to be 2 min because there is a certain relationship between the turning and mixing time and foam defoaming. A time longer than 2 min will cause some foam to break. At the same time, the stirring rate also needs to be strictly controlled, and there is a certain correlation between the rate and the slurry viscosity and the degree of foam mixing uniformity.

[0086] Therefore, the embodiment of the present invention explores the influence of the stirring rate on its performance, and the selected stirring rates are 60, 100, and 200 r / min. According to the performance results, the preferred stirring rate is 60-100 r / min.

[0087] Specifically, in the step S5, the judgment methods for judging whether the foam and the slurry are mixed evenly include:

[0088] The color uniformity of the mixture of foam and slurry meets the standard, and / or the volume change of the mixture of foam and slurry meets the standard.

[0089] Specifically, observe the color of the mixture: place the mixture under a light source and check whether the colors at each position of the mixture are evenly distributed; if the colors are evenly distributed, it is judged that the foam and the slurry are mixed evenly. During the stirring and mixing process of the foam and the slurry, the volume change curve of the mixture is obtained through experiments, and combined with the judgment criteria for mixing evenly (color uniformity, composition homogeneity), the corresponding relationship between the volume of the evenly mixed mixture and the initial volume is obtained. Thus, according to the volume change relationship of the mixture of foam and slurry, a preset standard volume change range is determined. When the volume change amount of the evenly mixed mixture in the preparation reaches the preset volume change amount, it is judged that the foam and the slurry are mixed evenly. Measure the volume of the mixture: measure a certain amount of the mixture of foam and slurry and record its initial volume. After standing or stirring for a certain period of time, measure the volume of the mixture again. According to the preset standard volume change range, judge whether the volume change of the mixture is within an acceptable range; if the volume change meets the standard range, it can be considered that the foam and the slurry are mixed evenly. The stirring time of the above judgment methods should be within the stirring threshold time. The present invention selects the turning and stirring threshold time to be 2 min because there is a correlation between the turning and mixing time and foam defoaming. A time longer than 2 min will cause some foam to break.

[0090] In addition, in the embodiment of the present invention, the viscosity of the slurry is determined by adjusting the ratio of the alkali activator solution to the cementitious material, so that the foam is in a balanced force state and stably exists in the system. When the ratio of the alkali activator to the cementitious material is less than 0.4, the viscosity of the slurry is relatively high, greater than 1.6 Pa·s. Since the strength of the foam is extremely low, it is subject to a large resistance when stirred in a slurry with a relatively high viscosity and is prone to breakage; when the ratio of the two is greater than 1, the viscosity of the slurry is relatively low, less than 0.5 Pa·s. Since the foam is extremely light in weight, it is prone to floating, merging, and uneven dispersion under the action of buoyancy in a slurry with a relatively low viscosity, which is not conducive to the development of the pore structure. Therefore, in the present invention, through the adjustment of the mix ratio, the viscosity of the foam geopolmer-based slurry is controlled within the range of 0.5 - 1.6 Pa·s.

[0091] The embodiment of the present invention uses the prepared geopolymer slurry for the following several performance tests:

[0092] (1) Pour the slurry into a graduated cylinder with a diameter of 6.5 cm and a height of 36 cm, and record the settlement distance after the slurry hardens to further evaluate the stability index of the foam in this system: The stability index is determined by the settlement distance of the slurry. The larger the settlement distance, the worse the stability of the foam in this system.

[0093] (2) Use a rotational viscometer Vi skomat NT to record the change of the slurry torque with the rotation speed, and test the rheological properties of the slurry, that is, the viscosity.

[0094] (3) Pour the slurry into a mold of 50 mm×50 mm×50 mm, seal the film to prevent water evaporation, demold after curing at room temperature for 24 h; put the demolded specimen into a standard curing room and cure for 3 - 28 days. The conditions of the curing room are 20 - 25 °C and the humidity is above 95%.

[0095] (4) After the specimen is cured, test the compressive strength of the sample within the specified time.

[0096] (5) After the specimen is dried in an oven, test the dry density and thermal conductivity of the sample. The drying conditions are 105 °C and the time is 48 h.

[0097] (6) Use the ultrasonic method UPV to detect the pore uniformity in the specimen material. When the test result is greater than 1800 m / s, the pores are evenly distributed.

[0098] Example 1:

[0099] In this example, a foam geopolymer containing modified fly ash hollow microspheres is prepared. By weight, its components are as follows: 18.75 parts of granulated blast furnace slag, 1.56 parts of silica fume, 10.94 parts of carbon nanotube fly ash hollow microspheres, 6.71 parts of water, 7.86 parts of water glass, 1.05 parts of NaOH, and 3.13 parts of foam.

[0100] The ratio of the alkali activator to the cementitious material in step S1 of the preparation method provided by the present invention is limited to 0.50;

[0101] The stirring rate of the stirring blade in step S5 is set to 60 r / min.

[0102] Example 2:

[0103] This example prepares a foamed geopolymers containing modified fly ash hollow microspheres. By weight, its components are as follows: 17.65 parts of granulated blast furnace slag, 1.47 parts of silica fume, 10.29 parts of carbon nanotube fly ash hollow microspheres, 9.26 parts of water, 7.40 parts of water glass, 0.99 part of NaOH, and 2.94 parts of foam.

[0104] The difference from Example 1 is that the ratio of the alkali activator to the cementitious material is different, and the ratio of the alkali solution to the cementitious material is limited to 0.60.

[0105] Example 3:

[0106] This example prepares a foamed geopolymers containing modified fly ash hollow microspheres. By weight, its components are as follows: 17.65 parts of granulated blast furnace slag, 1.47 parts of silica fume, 10.29 parts of carbon nanotube fly ash hollow microspheres, 9.26 parts of water, 7.40 parts of water glass, 0.99 part of NaOH, and 2.94 parts of foam.

[0107] The difference from Example 1 is that the ratio of the alkali activator to the cementitious material is different, and the ratio of the alkali solution to the cementitious material is limited to 1.0.

[0108] Example 4:

[0109] This example prepares a foamed geopolymers containing modified fly ash hollow microspheres. By weight, its components are as follows: 18.75 parts of granulated blast furnace slag, 1.56 parts of silica fume, 10.94 parts of carbon nanotube fly ash hollow microspheres, 6.71 parts of water, 7.86 parts of water glass, 1.05 part of NaOH, and 3.13 parts of foam.

[0110] The difference from Example 1 is that the rate of stirring and mixing the slurry is different, and the stirring rate of the stirring blade in step S5 is set to 100 r / min.

[0111] Example 5:

[0112] In this embodiment, a foamed geopolymer containing modified fly ash hollow microspheres is prepared. By weight, its components are as follows: 18.75 parts of granular blast furnace slag, 1.56 parts of silica fume, 10.94 parts of carbon nanotube fly ash hollow microspheres, 6.71 parts of water, 7.86 parts of water glass, 1.05 parts of NaOH, and 3.13 parts of foam.

[0113] The difference between this embodiment and Embodiment 1 is the rate of stirring and mixing the slurry. The stirring rate of the stirring blade in Step S5 is set to 200 r / min.

[0114] Embodiment 6:

[0115] This embodiment is a comparative example. The difference between this embodiment and Embodiment 1 is that carbon nanotubes are not bridged to the surface of fly ash hollow microspheres, that is, unmodified fly ash hollow microspheres are used. By weight, its components are as follows: 18.75 parts of granular blast furnace slag, 1.56 parts of silica fume, 10.94 parts of fly ash hollow microspheres, 6.71 parts of water, 7.86 parts of water glass, 1.05 parts of NaOH, and 3.13 parts of foam;

[0116] The comparison with Embodiment 1 is that unmodified fly ash hollow microspheres are weighed in Step S2.

[0117] Embodiment 7:

[0118] This embodiment is a comparative example. The difference between this embodiment and Embodiment 1 is that carbon nanotubes are added separately to the foamed geopolymer without bridging them to the surface of fly ash hollow microspheres. By weight fraction, its components are as follows: 18.75 parts of granular blast furnace slag, 1.56 parts of silica fume, 1.36 parts of carbon nanotubes, 6.71 parts of water, 7.86 parts of water glass, 1.05 parts of NaOH, and 3.13 parts of foam;

[0119] The comparison with Embodiment 1 is that in Step S2, carbon nanotubes and unmodified fly ash hollow microspheres need to be weighed by weight fraction, and in Step S3 when preparing the dry material, carbon nanotubes and unmodified fly ash hollow microspheres are mixed together with silica fume and blast furnace slag.

[0120] Embodiment 8:

[0121] This embodiment is a comparative example. The difference between this embodiment and Embodiment 1 is that a conventional stirring method is used without using the improved stirring blade that can be turned up and down. By weight, its components are as follows:

[0122] 18.75 parts of granular blast furnace slag, 1.56 parts of silica fume, 10.94 parts of carbon nanotube fly ash hollow microspheres, 6.71 parts of water, 7.86 parts of water glass, 1.05 parts of NaOH, and 3.13 parts of foam;

[0123] The difference between this example and Example 1 is that in step S5, a traditional stirring blade is used to prepare the foam geopolymers containing modified fly ash hollow microspheres, and the stirring time and rate remain unchanged at 2 minutes and 60 r / min respectively.

[0124] The material composition ratios of Examples 1-8 and the test results of the geopolymer composites prepared with the material compositions of Examples 1-8 are shown in Table 1 and Table 2 respectively;

[0125] Among them, in Table 1, FAC represents carbon nanotube-modified fly ash hollow microspheres.

[0126] Table 1 Design results of the mix proportions of the geopolymer composites of Examples 1-8

[0127]

[0128] Table 2 Test results of the geopolymer composites of Examples 1-8

[0129]

[0130] From the performance test results of Examples 1-3, it can be seen that when preparing the lightweight geopolymer materials containing carbon nanotube-modified hollow microspheres, changing the ratio of the alkali activator to the cementitious material will affect the stability of the foam. When this ratio is 0.5, the sedimentation distance is the smallest, the stability of the foam in the material is the highest, the compressive strength of the material is the largest, the thermal conductivity and dry density are the smallest, and the pore distribution is the most uniform.

[0131] From the performance test results of Examples 1, 4, and 5, it can be seen that when preparing the lightweight geopolymer materials containing carbon nanotube-modified hollow microspheres, changing the stirring rate of the stirring blade will also affect the stability of the foam. When the stirring rate is 60 r / min, the sedimentation distance is the smallest, the stability of the foam in the material is the highest, the compressive strength of the material is the largest, the thermal conductivity and dry density are the smallest, and the pore distribution is the most uniform.

[0132] From the performance test results of Example 1 and Example 6, it can be seen that using carbon nanotube-modified fly ash hollow microspheres and using unmodified fly ash hollow microspheres have a very large impact on the performance of the materials when preparing lightweight geopolymers: when preparing the geopolymer materials with carbon nanotube-modified fly ash hollow microspheres, the sedimentation distance of its slurry is only one-ninth of that of Example 6, its pores are more uniform, making the strength of its material three times that of the control example 6. At the same time, the geopolymer materials prepared with carbon nanotube-modified fly ash hollow microspheres have lower thermal conductivity and better heat insulation effect.

[0133] From the performance test results of Example 1 and Example 7, it can be seen that there are significant differences in the properties of the geopolymer materials prepared by using carbon nanotube-modified fly ash hollow microspheres and by directly adding fly ash without carbon nanotube modification into the dry materials: when directly adding carbon nanotubes into the dry materials to prepare the materials, the foam distribution will be uneven, resulting in a sedimentation distance three times that of the example, and it will also have a very large impact on the compressive strength of the prepared geopolymer materials, with its compressive strength being only one-fourth of that of Example 1.

[0134] From the performance test results of Example 1 and Example 8, it can be seen that using blades that can be flipped up and down can make the foam distribution more uniform than conventional blades, thereby improving the compressive strength and heat preservation performance of the geopolymer materials, and also reducing the weight of the geopolymer materials.

[0135] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

[0136] The above are only the preferred embodiments of the present invention and are not used to limit the present invention; for those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lightweight geopolymer material containing carbon nanotube-modified hollow microspheres, characterized in that, The material consists of the following components by weight: 17.65 - 18.75 parts of granular blast furnace slag, 1.47 - 1.56 parts of silica fume, 10.29 - 10.94 parts of carbon nanotube modified fly ash hollow microspheres, 6.71 - 9.26 parts of water, 7.40 - 7.86 parts of sodium silicate, 0.99 - 1.05 parts of sodium hydroxide, and 2.94 - 3.13 parts of foam; The foam is formed by mixing dodecyldimethylbetaine and water in a mass ratio of 1:50 and stirring at a low speed for 2 min; Among them, the dodecyldimethylbetaine is an amphoteric surfactant with an active substance content of 30%, and it is a light yellow transparent liquid with a density of 1.04 g / mL; The preparation method of the carbon nanotube modified fly ash hollow microspheres includes the following steps: Step S01, combining a silane coupling agent with carbon nanotubes; Step S011, mixing the silane coupling agent and an ethanol aqueous solution in a mass ratio of 1:80 to obtain a mixed solution A, and magnetically stirring it at 60 °C for 3 h to fully hydrolyze it to obtain solution A; Step S012, ultrasonically dispersing 1 g of carbon nanotubes in 500 mL of deionized water for 2 h to obtain a uniform solution B; Step S013, mixing solution A and solution B, and ultrasonically stirring for 1 h to mix them evenly to obtain solution C; Step S02, pre-treating fly ash hollow microspheres, selecting fly ash hollow microspheres with a particle size of 80 - 120 μm, ultrasonically treating them in acid for 30 min to obtain a fly ash acid solution, filtering out the particles in the fly ash acid solution and washing them repeatedly 2 times with deionized water, and placing the washed particles in a vacuum drying oven at 105 °C for 3 h; Step S03, grafting carbon nanotubes onto the surface of fly ash hollow microspheres through a silane coupling agent to modify the fly ash hollow microspheres; Step S031, mixing the pre-treated fly ash hollow microspheres in step S02 and solution C in a mass ratio of 1:6, and magnetically stirring at 60 °C for 3 h to obtain solution D; Step S032, filtering out the carbon nanotube hollow microspheres in solution D and washing them with deionized water and absolute ethanol respectively, and drying the carbon nanotube hollow microspheres in an oven at 105 °C for 6 h to obtain carbon nanotube modified fly ash hollow microspheres; Among them, the acid includes a 10% dilute hydrochloric acid solution, and the absolute ethanol is an ethanol solution with a purity of 99.6%.

2. The lightweight geopolymer material containing carbon nanotube-modified hollow microspheres according to claim 1, characterized in that, The main component of the granular blast furnace slag includes calcium oxide, and the calcium oxide content is greater than 35%; 3. The lightweight geopolymer material containing carbon nanotube-modified hollow microspheres according to claim 1, characterized in that, The silica fume contains 98% amorphous silica, and its average particle size is 0.3 - 10 μm; The sodium hydroxide is a uniform granular or flaky solid with a purity greater than 96%; The sodium silicate consists of 30% silica, 13.5% sodium peroxide, and 56.5% water, and its modulus is 2.3; 4. The lightweight geopolymer material containing carbon nanotube-modified hollow microspheres according to claim 1, wherein, The composition mass ratio of the components of the carbon nanotube modified fly ash hollow microspheres is: Silane coupling agent: Carbon nanotubes: Fly ash hollow microspheres = 1:1:97; Among them, the purity of the silane coupling agent is greater than 98%.

5. The lightweight geopolymer material containing carbon nanotube-modified hollow microspheres according to claim 1, characterized in that, The preparation method of a lightweight geopolymer material containing carbon nanotube modified hollow microspheres includes the following steps: Step S1: Prepare an alkali activator, which includes sodium hydroxide, water glass, and water. Step S2: Weigh granulated blast furnace slag, carbon nanotube-modified fly ash hollow microspheres, silica fume, and the alkali activator by weight. Step S3: Mix the granulated blast furnace slag, carbon nanotube-modified fly ash hollow microspheres, silica fume, and the alkali activator in Step S2 evenly in a mixing pot to prepare a dry material. Step S4: Slowly add the alkali activator solution to the dry material in the mixing pot and stir with a mortar mixer for 3 min until a paste is formed. The stirring rate of the mixer is 140 r / min. Step S5: Add foam to the surface of the paste and mix the foam and the paste evenly by stirring to prepare a foam geopolmer-based composite paste. Step S6: Perform post-treatment on the foam geopolmer-based composite paste to obtain a lightweight geopolymer material containing carbon nanotube-modified hollow microspheres. Among them, the post-treatment includes shaping, curing, and maintenance.

6. The preparation method according to claim 5, wherein, Step S3 includes: Step S31: Add the carbon nanotube-modified fly ash hollow microspheres and the silica fume to the mixing pot and stir for 3 min until the two dry materials are mixed evenly. Step S32: Add the granulated blast furnace slag to the two dry materials that have been mixed evenly in Step S31 and stir for 1.5 - 4 min until the three dry materials are mixed evenly.

7. The preparation method according to claim 5, wherein In Step S5, the stirring blade used is a stirring blade that can be flipped up and down, and its flipping and stirring time is 2 min, and the stirring rate is 60 - 200 r / min.

8. The preparation method according to claim 5, characterized in that, In Step S5, the judgment method for determining that the foam and the paste are mixed evenly includes: The color uniformity of the mixture of the foam and the paste meets the standard, and / or the volume change of the mixture of the foam and the paste meets the standard.

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