Cementitious material based on coal slag and waste polypropylene fiber and preparation method thereof

Abstract

The present invention discloses a cementitious material based on coal slag and waste polypropylene fiber and a preparation method thereof. The preparation method comprises the following steps: mixing calcium oxide, calcium hydroxide and aluminum phosphate evenly to obtain a compound activator; mixing coal slag, waste polypropylene fiber and the compound activator evenly to obtain a mixture; grinding the mixture to obtain a precursor powder; mixing the precursor powder with water evenly to obtain a pure slurry; molding and curing the pure slurry to obtain a solidified cementitious material. The present invention utilizes mechanical grinding to act on coal slag and waste polypropylene fiber, so that the porous coal slag and waste polypropylene fiber with uneven size and difficult to disperse are squeezed and filled into the porous structure of the coal slag under the action of mechanical force, thereby achieving uniform mixing and filling of the two solid wastes without any modification treatment. The cementitious material prepared by the present invention has good compressive strength, impermeability and stability in a wet environment.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of cementitious materials, and particularly to a cementitious material based on coal cinder and waste polypropylene fiber and a preparation method thereof. Background Art

[0002] Geopolymer is a cementitious material with SiO 2 and Al 2 O 3 as the main chemical components, which is prepared by means of alkali activation to form a cementitious material with a three-dimensional network structure, and is commonly used in the building materials industry to optimize and replace cement with high CO 2 emissions. Common geopolymer preparation technologies require curing at normal temperature or even high temperature. For example, Chinese Patent CN202211698448.6 requires a curing temperature of 55-65°C, and Chinese Patent CN202310527147.5 requires curing at normal temperature. Due to the lack of heat in a low-temperature environment, the geopolymerization reaction is difficult to carry out, which greatly limits the application and development of geopolymers in low-temperature climates such as high mountains, plateaus, and cold regions in the north.

[0003] With the development of related technologies, the raw materials of geopolymers have gradually expanded to include industrial wastes such as slag, fly ash, desulfurized gypsum, and municipal solid waste incineration fly ash. However, these raw materials relatively have higher active silica and alumina components. At present, the application of low-activity products such as coal cinder after high-temperature sintering in geopolymer preparation technology is still a major problem. Coal cinder is the residue of coal combustion in industrial coal-fired boilers. Due to high-temperature calcination, this bulk solid waste has very low activity. The common treatment method is to use it as a material for filling soil, road base, and landfill to improve the stability and compressive strength of the soil. In addition, the silica and alumina components of coal cinder are fixed in the lattices of quartz, mullite, etc. A large amount of strong alkali activator is required to dissolve the silica and alumina components at high temperature, and more technical difficulties need to be overcome for comprehensive utilization in a low-temperature environment. Therefore, it is necessary to seek a method for large-scale utilization of coal cinder in a low-temperature climate. In addition, coal cinder contains a large amount of silica and alumina components, which makes it have the potential to become a raw material for geopolymers. However, due to its porous and brittle characteristics, it requires long-term grinding to reduce the porosity of the raw material particle structure, and the prepared geopolymer often contains a large number of pores in the microstructure, resulting in significant damage to the compressive strength in a humid environment.

[0004] Waste polypropylene fibers include waste materials in the production process of polypropylene filaments (such as transition filaments, etc.), 5%-10% of amorphous random polypropylene by-products generated during the production of polypropylene in chemical plants, fibers prepared by secondary recycling of waste woven bags, etc. The stock of waste polypropylene is large, the recovery rate is low, and the resource waste is serious. At the same time, polypropylene fibers are not hydrophilic, disperse poorly in concrete, and have weak bonding with concrete. Generally, high-cost surface modification treatment is required, which limits the popularization and use of polypropylene fibers. It is more difficult to utilize such solid waste as waste polypropylene fibers with high impurity content, unstable performance, and complex dimensions. In Chinese Patent CN 202211596834.4, by using fibers as anti-cracking and strengthening agents, only their toughness is used to inhibit the cracking of geopolymer materials caused by shrinkage, and the problem of difficult uniform dispersion of fibers has not been solved yet, and it is more inapplicable to waste fibers with poor physical properties and more difficult to utilize. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, and propose a cementitious material based on coal cinder and waste polypropylene fibers and its preparation method, so as to solve the technical problem that the compressive strength of coal cinder-based geopolymers is easily significantly damaged in a humid environment in the prior art.

[0006] In the first aspect, the present invention provides a preparation method of a cementitious material based on coal cinder and waste polypropylene fibers, including the following steps:

[0007] Prepare chemical agents: Mix calcium oxide, calcium hydroxide, and aluminum phosphate in proportion and uniformly to obtain a compound activator;

[0008] Mix raw materials: Mix coal cinder, waste polypropylene fibers and the compound activator uniformly to obtain a mixture;

[0009] Mechanical grinding: Grind the mixture to obtain a precursor powder;

[0010] Prepare neat paste: Mix the precursor powder and water uniformly to obtain neat paste;

[0011] Molding and curing: Carry out molding and curing on the neat paste to obtain a solidified and molded cementitious material based on coal cinder and waste polypropylene fibers.

[0012] In the second aspect, the present invention provides a cementitious material based on coal cinder and waste polypropylene fibers, and this cementitious material based on coal cinder and waste polypropylene fibers is obtained by the preparation method of the cementitious material based on coal cinder and waste polypropylene fibers provided in the first aspect of the present invention.

[0013] Compared with the prior art, the beneficial effects of the present invention include:

[0014] The present invention realizes the uniform mixing and filling of two kinds of solid wastes by using mechanical grinding on coal cinder and waste polypropylene fibers, so that the porous coal cinder and the waste polypropylene fibers with uneven size and difficult dispersion are extruded and filled into the porous structure of the coal cinder under the action of mechanical force, without any modification treatment. The present invention has the characteristics of simplicity, safety, low cost, low energy consumption, high solid waste utilization rate, environmental friendliness and strong adaptability; the cementitious material prepared by the present invention has good compressive strength, impermeability and stability in a humid environment. Detailed implementation manners

[0015] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to 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.

[0016] In order to overcome the respective defects of two kinds of solid wastes, namely coal cinder and waste polypropylene fibers, the present invention realizes a "self-embedded dispersion system" by means of mechanical grinding, and solves the problems of large particle structure defects of coal cinder and uneven dispersion of waste polypropylene fibers.

[0017] Based on this, the present invention is proposed.

[0018] In a first aspect, the present invention provides a preparation method of a cementitious material based on coal cinder and waste polypropylene fibers, comprising the following steps:

[0019] S1. Prepare chemical agents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 uniformly in proportion to obtain a compound activator A;

[0020] S2. Mix raw materials: Mix coal cinder, waste polypropylene fibers and the compound activator A uniformly to obtain a mixture B;

[0021] S3. Mechanical grinding: Grind the mixture B to obtain a precursor powder;

[0022] S4. Prepare neat paste: Mix the precursor powder and water uniformly to obtain a neat paste;

[0023] S5. Molding and curing: Carry out molding and curing on the neat paste to obtain a cured and molded cementitious material based on coal cinder and waste polypropylene fibers.

[0024] In the present invention, coal gangue plays a role in providing silicon and aluminum raw materials for the reaction to form a cementitious material, and polypropylene fibers play a role in filling the geopolymer and reducing micro-defects. The introduction of these two solid wastes can achieve complementary defects. Through the synergistic utilization of two solid wastes, namely coal gangue and waste polypropylene fibers, the present invention realizes the complementary defects of the two solid wastes and makes the structure of the prepared geopolymer more dense. In view of the characteristics of porous and brittle coal gangue and slender and multi-sized polypropylene fibers, mechanical force is used in the grinding stage to embed the fibers into the coal gangue particles to form a "self-embedded dispersion system", which can not only quickly reduce the particle pores but also achieve a high degree of fiber dispersion, solving the problems of long grinding time of coal gangue, poor dispersion of fibers in concrete and easy agglomeration.

[0025] In some specific embodiments of the present invention, the main chemical components of coal gangue are: CO 2 The loss on ignition is 4 wt% - 10 wt%, SiO 2 The content is 43 wt% - 64 wt%, Al 2 O 3 The content is 20 wt% - 40 wt%, Fe 2 O 3 The content is 2 wt% - 6 wt%, and the CaO content is 1 wt% - 3 wt%; the initial particle size of coal gangue is 5 mesh and below.

[0026] In the present invention, by weight percentage, the compound activator A is composed of the following components: calcium oxide 30% - 60%, calcium hydroxide 20% - 50%, and aluminum phosphate 5% - 30%.

[0027] The present invention further promotes the dissolution and polymerization of silicon and aluminum components under low-temperature climate by means of combined calcium activation. The inventor found in the experimental process that traditional sodium hydroxide activation will release a large amount of heat instantaneously during the reaction, which is not sustainable under low-temperature climate and will cause a large amount of loss, and early cracking and bulging phenomena are likely to occur. However, through the inhibitory effect of calcium hydroxide and aluminum phosphate on the exothermic reaction of calcium oxide, the reaction heat in the process can be effectively regulated, enabling the geopolymerization reaction to proceed continuously under low-temperature environment, providing a development direction for the application of geopolymer under low-temperature climate. In the present invention, chemical activation of coal gangue is carried out in a multi-calcium system. Calcium oxide and calcium hydroxide, as the starting factors of chemical reactions, can provide a favorable environment for the occurrence of chemical reactions. Aluminum phosphate and calcium hydroxide are used as regulators. On the one hand, it can slow down the setting rate and prevent phenomena such as premature hardening, bulging and cracking. On the other hand, in a low-temperature environment, it can effectively slow down its heat loss, ensure that the heat required for the geopolymerization reaction is continuously released and utilized, and ensure that the geopolymerization reaction will not be negatively affected by aluminum phosphate. This synergistic activation effect of multiple components enriches the quantity and variety of the gel phase and inhibits the negative effects caused by calcification, ensuring the continuous supply of reaction heat.

[0028] The specific functions of each component in the chemical agents used in the present invention in the system are as follows:

[0029] Calcium oxide: During the geopolymer hydration process, calcium oxide releases heat. This heat not only promotes the progress of the reaction but also ensures the supply of the reaction heat required in low-temperature climates. At the same time, calcium hydroxide formed by the reaction of calcium oxide with water makes the aqueous solution alkaline when dissolved, which can accelerate the dissolution of active silica-aluminum components in coal cinder. Calcium hydroxide also has certain gelling properties, adding more useful chemical components and structural components to enhance the overall strength. The introduction of calcium ions can generate hydration products (C-S-H or C-(A)-S-H gel), causing the early strength to rise rapidly. At the same time, calcium ions provide nucleation sites for the formation of geopolymerization reaction products with higher polymerization degrees (N-A-S-H gel), further improving the properties such as the early strength, frost resistance, water absorption, and corrosion resistance of the geopolymer.

[0030] Calcium hydroxide: During the calcium activation process, calcium hydroxide is one of the main hydration products, which can promote the development of the early strength of the geopolymer. At the same time, calcium hydroxide is also the main product of the exothermic reaction of calcium oxide. Adding calcium hydroxide can inhibit the exothermic reaction of calcium oxide. Meanwhile, calcium hydroxide combines with active silica-aluminum components in the geopolymerization reaction and is gradually consumed, enabling the continuous forward progress of the exothermic reaction of calcium oxide, supplementing new calcium hydroxide and heat, and ensuring the stable progress of the geopolymerization reaction in low-temperature climates. Thus, the continuity of the heat during the reaction process is achieved instead of the loss caused by instantaneous heat release. At the same time, calcium hydroxide can replace calcium oxide according to different environmental temperatures to prevent negative phenomena such as expansion and cracking of the geopolymer material caused by excessive heat. Calcium hydroxide has strong alkalinity, which can promote the reaction of other minerals, affect their chemical properties and performance, and accelerate the development of the early strength of the geopolymer. In the early stage of the hardening of the geopolymer, calcium hydroxide forms hardening products through chemical reactions with minerals and water, enhancing the strength of the geopolymer mortar. An appropriate pH value can also affect the activity of other additives and components in the mortar.

[0031] Aluminum phosphate: The large introduction of calcium source significantly reduces the workability of the slurry, leading to the out-of-control hydration rate of C-S-H gel. A large number of inclusions hinder the later geopolimerization reaction. Aluminum phosphate can be used as a regulator in the geopolimerization reaction process. On the one hand, it can slow down the setting rate and prevent phenomena such as premature hardening, bulging, and cracking. On the other hand, aluminum phosphate can effectively slow down the rapid loss of heat in a low-temperature environment, ensuring the continuous supply of heat required for the geopolimerization reaction. The hydrolysis of aluminum phosphate makes the solution alkaline, providing a favorable environment for the dissolution of soluble silicon-aluminum components. Under the action of aluminum phosphate, aluminosilicate precursors can also be polymerized to form Si-Al-P gel, and at the same time, they can carry out polymerization reactions with the calcium source in the components to form a more complex gel phase. Aluminum phosphate can be used as a regulator of the water absorption performance of geopolymers, adjusting its water absorption rate, water absorption capacity, and water retention capacity, thus further improving the disadvantages that the heat release rate of calcium oxide absorption of water will not cause local overheating and the heat is rapidly generated and dissipated into the environment. In addition, the addition of aluminum phosphate can enhance the stability and durability of geopolimer gels. Aluminum phosphate interacts with the polymer chains in geopolymers to form a cross-linked structure, enhancing the structural stability of the gel and preventing its dehydration or decomposition. The introduction of phosphate groups endows geopolymers with the advantages of a smoother and denser gel structure, low efflorescence, and low dielectric loss, significantly improving the application performance of the cementitious material.

[0032] In some specific embodiments of the present invention, in the compound activator A, the mass ratio of calcium oxide to calcium hydroxide is 1:(0.4 - 1.5). In this process, the mass ratio of calcium oxide to calcium hydroxide can be adjusted to adapt to the low-temperature climate at different temperatures, and the proportion of calcium oxide increases with the decrease of the environmental temperature.

[0033] In some more specific embodiments of the present invention, in the compound activator A, the mass ratio of calcium oxide to calcium hydroxide is 1:(0.6 - 1).

[0034] In some more specific embodiments of the present invention, by weight percentage, the compound activator A is composed of the following components: 40% - 50% of calcium oxide, 30% - 40% of calcium hydroxide, and 10% - 20% of aluminum phosphate.

[0035] In the present invention, by weight percentage, the mixture B includes the following components: 70% - 80% of coal cinder, 1% - 6% of waste polypropylene fiber, and 18% - 25% of the compound activator A.

[0036] In some specific embodiments of the present invention, by weight percentage, the mixture B includes the following components: 73% - 76% of coal cinder, 2% - 6% of waste polypropylene fiber, and 20% - 23% of the compound activator A.

[0037] In the present invention, the liquid-solid ratio of water to the precursor powder is 0.28 - 0.41 mL: 1 g, preferably 0.30 - 0.35 mL: 1 g.

[0038] In the present invention, the D90 particle size of the precursor powder is 300 mesh or less.

[0039] In some specific embodiments of the present invention, the grinding time is 2 - 4 min.

[0040] In the present invention, the forming method is: pouring the neat paste into a mold and vibrating it to form.

[0041] In the present invention, the curing method is: after sealing the mold containing the specimen after vibration forming, curing for 18 - 24 h and then demolding, and subsequently continuing to seal and cure until the specified age to obtain the cured and formed cementitious material based on coal gangue and waste polypropylene fibers.

[0042] In some preferred embodiments of the present invention, the specified age is 7 - 28 days.

[0043] The low-temperature climate referred to in the method of the present invention not only includes the environmental temperature, but also the temperature of the medium in the environment, that is, it is also applicable in the corresponding low-temperature water medium.

[0044] In some specific embodiments of the present invention, the water medium and the curing temperature are not lower than 0 °C to avoid the water from solidifying, more specifically 5 - 15 °C.

[0045] In the second aspect, the present invention provides a cementitious material based on coal gangue and waste polypropylene fibers, which is obtained by the preparation method of the cementitious material based on coal gangue and waste polypropylene fibers provided in the first aspect of the present invention.

[0046] To avoid repetition, the unified description of some raw materials involved in the following examples and comparative examples of the present invention is as follows:

[0047] Coal gangue refers to the residue after coal combustion in industrial coal-fired boilers. The main chemical components are: CO 2 The loss on ignition is 6.684 wt%, SiO 2 The content is 53.976 wt%, Al 2 O 3 The content is 30.310 wt%, Fe 2 O 3 The content is 4.204 wt%, and the CaO content is 1.769 wt%.

[0048] Waste polypropylene fibers include waste materials in the production process of polypropylene filaments (such as transition filaments, etc.), 5%-10% of non-crystalline random polypropylene by-products generated during the production of polypropylene in chemical plants, fibers prepared by secondary recycling of waste woven bags, etc. The diameter is generally between 10 and 50 μm, and the length varies from 30 to 150 mm.

[0049] Example 1

[0050] Example 1 provides a preparation method of a cementitious material based on coal cinder and waste polypropylene fibers, including the following steps:

[0051] (1) Prepare chemical reagents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 uniformly according to m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate)=3:2:1 to prepare a compound activator A;

[0052] (2) Mix raw materials: Place coal cinder (initial particle size less than 5 mesh) and waste polypropylene fibers in an oven, dry until the mass no longer changes, and after cooling to room temperature, mix them uniformly according to m(coal cinder):m(waste polypropylene fibers):m(compound activator A)=3.4:0.1:1 to obtain mixture B;

[0053] (3) Mechanical grinding: Put mixture B into a vibration mill and grind for 3 min until the D90 particle size is less than 300 mesh to obtain a precursor powder;

[0054] (4) Prepare neat paste: Add water at 5°C to the above-mentioned precursor powder and stir evenly to obtain a neat paste; the ratio of the volume (mL) of water to the mass (g) of the precursor powder is 0.30;

[0055] (5) Molding and curing: Pour the above-mentioned neat paste into a mold and vibrate to form a specimen. Then, seal the vibration-molded specimen with a self-sealing bag and cure it at a temperature of 5°C for 24 h and then demold. After demolding, continue to seal it in an environment temperature of 5°C and cure it until the 28th day to obtain a solidified and formed cementitious material.

[0056] Example 2

[0057] Example 2 provides a preparation method of a cementitious material based on coal cinder and waste polypropylene fibers, including the following steps:

[0058] (1) Prepare chemical reagents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 uniformly according to m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate)=3:2:1 to prepare a compound activator A;

[0059] (2) Mixed raw materials: Put coal cinder (initial particle size less than 5 mesh) and waste polypropylene fiber in an oven and dry until the mass no longer changes. After cooling to room temperature, mix them evenly according to m(coal cinder):m(waste polypropylene fiber):m(compound activator A) = 3.4:0.2:1 to obtain mixture B;

[0060] (3) Mechanical grinding: Put mixture B into a vibration mill and grind for 3 min until the D90 particle size is less than 300 mesh to obtain a precursor powder;

[0061] (4) Preparation of neat paste: Add water at 5 °C to the above-mentioned precursor powder and stir evenly to obtain a neat paste; the ratio of the volume of water (mL) to the mass of the precursor powder (g) is 0.34;

[0062] (5) Molding and curing: Pour the above-mentioned neat paste into a mold and vibrate to form a specimen. Then, seal the vibration-molded specimen with a self-sealing bag and cure it at 5 °C for 24 h and then demold. After demolding, continue to seal it and cure it in an environment at 5 °C until the 28th day to obtain a solidified and formed cementitious material.

[0063] Example 3

[0064] Example 3 provides a preparation method of a cementitious material based on coal cinder and waste polypropylene fiber, including the following steps:

[0065] (1) Preparation of chemical agents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 evenly according to m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate) = 2:2:1 to prepare compound activator A;

[0066] (2) Mixed raw materials: Put coal cinder (initial particle size less than 5 mesh) and waste polypropylene fiber in an oven and dry until the mass no longer changes. After cooling to room temperature, mix them evenly according to m(coal cinder):m(waste polypropylene fiber):m(compound activator A) = 3.5:0.2:1 to obtain mixture B;

[0067] (3) Mechanical grinding: Put mixture B into a vibration mill and grind for 3 min until the D90 particle size is less than 300 mesh to obtain a precursor powder;

[0068] (4) Preparation of neat paste: Add water at 15 °C to the above-mentioned precursor powder and stir evenly to obtain a neat paste; the ratio of the volume of water (mL) to the mass of the precursor powder (g) is 0.32;

[0069] (5)Molding and curing: Pour the above-mentioned neat paste into a mold and vibrate it to form a specimen. Then, seal the specimen after vibration molding with a self-sealing bag and cure it at a temperature of 15°C for 24 hours, and then demold it. After demolding, continue to seal it and cure it in an environment with a temperature of 15°C until the 28th day, and then a solidified and formed gelling material can be obtained.

[0070] Comparative Example 1

[0071] Compared with Example 1, the difference in Comparative Example 1 is only that the contents of each component in the compound activator A are inconsistent, specifically as follows:

[0072] Prepare chemical agents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 uniformly according to m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate)=0:2:1 to prepare the compound activator A.

[0073] Comparative Example 2

[0074] Compared with Example 1, the difference in Comparative Example 2 is only that the contents of each component in the compound activator A are inconsistent, specifically as follows:

[0075] Prepare chemical agents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 uniformly according to m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate)=10:2:1 to prepare the compound activator A.

[0076] Comparative Example 3

[0077] Compared with Example 1, the difference in Comparative Example 3 is only that the contents of each component in the compound activator A are inconsistent, specifically as follows:

[0078] Prepare chemical agents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 uniformly according to m(calcium oxide):m(calcium hydroxide):m(aluminum phosphate)=3:0:1 to prepare the compound activator A.

[0079] Comparative Example 4

[0080] Compared with Example 1, the difference in Comparative Example 4 is only that the contents of each component in the compound activator A are inconsistent, specifically as follows:

[0081] Prepare chemical agents: Mix calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3Mix 3 parts by mass of calcium oxide, 10 parts by mass of calcium hydroxide, and 1 part by mass of aluminum phosphate evenly to prepare compound activator A.

[0082] Comparative Example 5

[0083] Comparative Example 5 is different from Example 1 only in that the component contents in compound activator A are different, specifically as follows:

[0084] Prepare chemical agent: Put calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 Mix 3 parts by mass of calcium oxide, 2 parts by mass of calcium hydroxide, and 0 parts by mass of aluminum phosphate evenly to prepare compound activator A.

[0085] Comparative Example 6

[0086] Comparative Example 6 is different from Example 1 only in that the component contents in compound activator A are different, specifically as follows:

[0087] Prepare chemical agent: Put calcium oxide K 1 , calcium hydroxide K 2 , and aluminum phosphate K 3 Mix 3 parts by mass of calcium oxide, 2 parts by mass of calcium hydroxide, and 10 parts by mass of aluminum phosphate evenly to prepare compound activator A.

[0088] Comparative Example 7

[0089] Comparative Example 7 is different from Example 1 only in that sodium hydroxide is used to replace calcium oxide in Example 1 in compound activator A, specifically as follows:

[0090] Prepare chemical agent: Put sodium hydroxide K 4 , calcium hydroxide K 2 , and aluminum phosphate K 3 Mix 3 parts by mass of sodium hydroxide, 2 parts by mass of calcium hydroxide, and 1 part by mass of aluminum phosphate evenly to prepare compound activator A.

[0091] Comparative Example 8

[0092] Comparative Example 8 is different from Example 1 only in that the component ratios in mixture B are different, specifically as follows:

[0093] Mix raw materials: Put coal cinder (initial particle size below 5 mesh) and waste polypropylene fiber in an oven, dry until the mass no longer changes, and after cooling to room temperature, mix 5 parts by mass of coal cinder, 0.1 part by mass of waste polypropylene fiber, and 1 part by mass of compound activator A evenly to obtain mixture B.

[0094] Comparative Example 9

[0095] Comparative Example 9 is different from Example 1 only in that the component ratios in mixture B are different, specifically as follows:

[0096] Mixed raw materials: Put coal cinder (initial particle size less than 5 mesh) and waste polypropylene fiber in an oven, dry until the mass no longer changes, and after cooling to room temperature, mix evenly according to m(coal cinder):m(waste polypropylene fiber):m(compound activator A)=2:0.1:1 to obtain mixture B.

[0097] Comparative Example 10

[0098] Comparative Example 10 is different from Example 1 only in that the component ratios in mixture B are different, specifically as follows:

[0099] Mixed raw materials: Put coal cinder (initial particle size less than 5 mesh) and waste polypropylene fiber in an oven, dry until the mass no longer changes, and after cooling to room temperature, mix evenly according to m(coal cinder):m(waste polypropylene fiber):m(compound activator A)=3.4:1:1 to obtain mixture B.

[0100] Comparative Example 11

[0101] Comparative Example 11 is different from Example 1 only in that the component ratios in mixture B are different, specifically as follows:

[0102] Mixed raw materials: Put coal cinder (initial particle size less than 5 mesh) and waste polypropylene fiber in an oven, dry until the mass no longer changes, and after cooling to room temperature, mix evenly according to m(coal cinder):m(waste polypropylene fiber):m(compound activator A)=3.4:0:1 to obtain mixture B.

[0103] Comparative Example 12

[0104] Comparative Example 12 is different from Example 1 only in that the water temperature for preparing the neat paste and the ambient temperature for forming and curing are different, specifically as follows:

[0105] Preparation of neat paste: Add water at 35°C to the precursor powder and stir evenly to obtain the neat paste; the ratio of the volume of water (mL) to the mass of the precursor powder (g) is 0.32.

[0106] Forming and curing: Pour the above neat paste into a mold and vibrate to form a specimen. Then, seal the vibrated specimen with a self-sealing bag and cure it at a temperature of 35°C for 24 h and then demold. After demolding, continue to seal and cure it at an ambient temperature of 35°C until the 28th day to obtain the solidified and formed cementitious material.

[0107] Comparative Example 13

[0108] Comparative Example 13 is different from Example 1 only in that the waste polypropylene fibers do not participate in mechanical grinding, but are added and stirred with water during the preparation of the neat paste, as follows:

[0109] Mixed raw materials: Put the coal cinder (initial particle size less than 5 mesh) in an oven and bake until the mass no longer changes. After cooling to room temperature, mix evenly according to m(coal cinder):m(compound activator A)=3.4:1 to obtain mixture B;

[0110] Mechanical grinding: Put mixture B into a vibration mill and grind for 3 min until the D90 particle size is less than 200 mesh to obtain a precursor powder;

[0111] Preparation of neat paste: Add waste polypropylene fibers (m(waste polypropylene fibers):m(compound activator A)=0.2:1) and water at 5°C to the above-mentioned precursor powder, stir evenly to obtain a neat paste; where the ratio of the volume of water (mL) to the total mass (g) of the precursor powder and waste polypropylene fibers is 0.34.

[0112] Test group

[0113] The performance of the cementitious materials based on coal cinder and waste polypropylene fibers obtained in Examples 1-3 and Comparative Examples 1-13 above was tested using the test standards specified in "GB 175-2007 General Portland Cement" and "GB 50164-2011 Concrete Quality Control Standard", and the results are shown in Table 1.

[0114] Table 1

[0115]

[0116]

[0117] It can be seen from the data in Table 1 that by using the methods in Examples 1-3 of the present invention, cementitious materials based on coal cinder and waste polypropylene fibers can be prepared under low-temperature climates, and the prepared cementitious materials have good compressive strength and low dry-wet strength change rate, and can be applied to building cementitious materials under low-temperature climates.

[0118] Compared with Example 1, the compressive strength of the specimen without calcium oxide in the compound activator A in Comparative Example 1 decreased significantly. This is because calcium oxide is the main body of the activator. Relying only on the action of calcium hydroxide and aluminum phosphate, on the one hand, it cannot provide a sufficient alkaline environment to dissolve the silicon-aluminum components in coal slag. On the other hand, the lack of calcium oxide leads to insufficient heat supply, and it is difficult to undergo a hydration reaction in a low-temperature climate. The gel structure that provides strength cannot be formed, and the compressive strength of the material is almost completely lost. In Comparative Example 2, the compressive strength of the specimen with excessive calcium oxide in the compound activator A decreased significantly. This is because although excessive incorporation of calcium oxide can increase the degree of early geopolymerization reaction, the too-fast reaction rate and too-high local reaction heat result in a large number of pores and structural defects in the cementitious material, causing a significant decrease in the strength of the geopolymer. In the later curing in a low-temperature climate, it also shows inadaptability, that is, the pores and cracks in the cementitious material further expand, leading to easy cracking of the specimen.

[0119] Compared with Example 1, the compressive strength of the specimen without calcium hydroxide in the compound activator A in Comparative Example 3 decreased. Calcium hydroxide itself is a hydration product and has certain cementitious properties, which can effectively promote the development of the early strength of the calcium-activated system of geopolymer. The lack of calcium hydroxide reduces the alkalinity of the reaction environment and the amount of hydration products generated, thus reducing the compressive strength of the reaction products. In Comparative Example 4, the compressive strength of the specimen with excessive calcium hydroxide in the compound activator A decreased significantly. Under the condition of a certain amount of introduced calcium ions, excessive incorporation of calcium hydroxide will cause a linear decrease in the relative content of calcium oxide. Without the continuous heat release of calcium oxide in a low-temperature climate, various chemical reactions are difficult to proceed, and the properties of the prepared geopolymer are poor.

[0120] Compared with Example 1, in Comparative Example 5, obvious cracks appeared in the specimen of the compound activator A without aluminum phosphate during the demolding process, and the strength test results also showed that the specimen had weak compressive ability. The lack of aluminum phosphate led to a lack of regulation of calcium oxide in the early exothermic reaction, and the early hydration reaction was too rapid, resulting in large heat loss. In a low-temperature climate, premature hardening is likely to occur, causing the geopolymer reaction to terminate prematurely and crack. At the same time, the lack of aluminum phosphate makes the hydration products change into C-S-H gel, lacking a denser gel structure, and its stability decreases. In Comparative Example 6, with excessive incorporation of aluminum phosphate in the compound activator A, calcium oxide and calcium hydroxide, which are the main components playing an activating role, are greatly reduced. It is difficult to initiate the geopolymerization reaction only by the salt regulator aluminum phosphate, so its compressive strength drops sharply.

[0121] Compared with Example 1, in Comparative Example 7, sodium hydroxide was used to replace calcium oxide in the compound activator A, and obvious efflorescence occurred. In addition, the compressive strength of the specimen obtained by activating with traditional sodium hydroxide in a low-temperature climate was significantly insufficient, because the occurrence and continuous progress of the geopolymerization reaction were inhibited at low temperatures.

[0122] Compared with Example 1, in Comparative Example 8, the ratio of coal gangue to compound activator A was significantly increased. This led to insufficient relative dosage of compound activator A, and a large amount of coal gangue could not be activated, resulting in failure to dissolve active silica and alumina components and a significant reduction in the amount of gel products formed. In Comparative Example 9, the ratio of coal gangue to compound activator A was significantly decreased. This led to a significant reduction in the amount of activated coal gangue raw materials and a significant shortage of active silica and alumina components that could be formed. While the amount of gelling products formed decreased, the excessive concentration of compound activator A led to many defects in the geopolymers, thus affecting the performance of the geopolymers.

[0123] Compared with Example 1, in Comparative Example 10, the ratio of coal gangue to waste polypropylene fibers was significantly decreased, which led to an excessive relative dosage of waste polypropylene fibers, exceeding the demand for "self-inlaid dispersion" that can be generated during mechanical grinding. Therefore, the excessive waste polypropylene showed local aggregation and uneven dispersion inside the specimen, affecting the compressive strength of the specimen. In Comparative Example 11, no waste polypropylene fibers were added, which led to a decrease in the compactness of the geopolymers and a slight decrease in the compressive strength of the prepared specimens. It should be noted that the deterioration was significant in terms of the performance of wet and dry strength. The compressive strength of the geopolymer specimen after soaking decreased by 15%, and a large amount of water caused by the increase in microstructural defects could penetrate into the specimen to cause damage.

[0124] Compared with Example 1, in Comparative Example 12, the water temperature for preparing the neat paste and the ambient temperature for molding and curing were further increased from 5°C to 35°C. The increase in ambient temperature was theoretically more suitable for the progress of the geopolymer reaction. However, since the addition amount of calcium oxide was not adjusted correspondingly, local overheating occurred, and obvious structural defects such as cracking and bulging appeared in the specimen. Therefore, the compressive strength of the prepared gelling material decreased significantly instead.

[0125] Compared with Example 1, in Comparative Example 13, the waste polypropylene fibers and water were added together for stirring. Without participating in mechanical grinding, obvious characteristics of poor hydrophilicity and poor dispersibility appeared. The aggregation of waste polypropylene fibers could also be observed on the internal cross-section of the geopolymers prepared after curing. Therefore, the compressive strength of the prepared gelling material decreased significantly.

[0126] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0127] (1) The present invention prepares a cementitious material from coal gangue and waste polypropylene fibers, which can efficiently recycle these two types of solid wastes, namely coal gangue and waste polypropylene fibers, on a large scale, reduce waste emissions and dependence on natural resources. At the same time, it can reduce the potential harm of coal gangue and waste polypropylene fibers to the environment, solidify harmful substances in the cementitious material, and reduce the release risk to the environment. There is no need for calcination or high-temperature curing, and environmentally friendly chemical reactions are used to replace traditional physical processes, thereby reducing energy consumption during the preparation process.

[0128] (2) The present invention successfully overcomes the respective defects of the two solid waste raw materials during the mechanical grinding stage, including the porous and brittle nature of coal gangue and the high impurity content, unstable performance, and complex dimensions of waste polypropylene fibers. During the short grinding process, due to the slender and diverse dimensions of waste polypropylene fibers, they are easily embedded into the pores of coal gangue particles and then fixed and dispersed in the coal gangue powder under the high-intensity extrusion of mechanical force. This enables the uniform distribution of waste polypropylene fibers without any modifiers and pretreatment, while reducing the structural defects of coal gangue. It significantly improves the grinding effect and the compactness of geopolymer specimens and reduces production costs.

[0129] (3) The compound activator A prepared by the present invention can effectively improve the reaction activity, play a complementary role among the components in the geopolymerization reaction, synergistically activate and cooperate with each other, enabling the reaction process to be accurately regulated and obtaining better quality and performance of the cementitious material. The alkaline environment after the dissolution of the compound activator A helps the dissolution of active silicon-aluminum components, forming complex multi-phase hydration products. The exothermic hydration reaction of calcium oxide accelerates the formation of the gel phase in cold climates. Aluminum phosphate can prevent the uncontrolled hydration rate, delay heat loss, and prevent premature hardening and optimize the gel structure. While calcium hydroxide synergistically inhibits the exothermic hydration of calcium oxide with aluminum phosphate, it also provides calcium ions and an alkaline environment, avoiding the inhibition of the geopolymerization reaction by aluminum phosphate and enabling the rapid adjustment of the optimal compound activator A according to the ambient temperature.

[0130] (4) The compressive strength of the cementitious material prepared by the present invention using coal gangue in cold climates reaches the 32.5R grade specified in "GB 175-2007 General Portland Cement", providing new ideas for the application of geopolymer materials in cold climates and broadening the application scenarios of geopolymers as cement substitutes.

[0131] (5) The cementitious material based on coal gangue and waste polypropylene fibers prepared by the present invention can be applied to the simple preparation and rapid forming of building materials in cold climates. The ratio and dosage of the composite activator can be adjusted according to the ambient temperature to meet industrial requirements. By adjusting the proportion of the compound activator A, the rapid initiation and continuous progress of the geopolymerization reaction in cold climates can be promoted.

[0132] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a gelling material based on coal slag and waste polypropylene fibers, characterized in that: The following steps are involved: Preparation of chemical agents: Mix calcium oxide, calcium hydroxide and aluminum phosphate in proportion to obtain a compound activator; Mixing raw materials: Evenly mixing coal slag, waste polypropylene fiber and the compound activator to obtain a mixture; Mechanical grinding: grinding the mixed material to obtain precursor powder; Preparing a pure slurry: mixing the precursor powder and water evenly to obtain a pure slurry; Forming and curing: forming and curing the clean slurry to obtain a solidified gelling material based on coal slag and waste polypropylene fibers; Wherein, the composite activator is composed of the following components by weight percentage: 30% to 60% calcium oxide, 20% to 50% calcium hydroxide, and 5% to 30% aluminum phosphate.

2. The method for preparing a gelling material based on coal ash and waste polypropylene fibers according to claim 1, characterized in that: The composite activator is composed of the following components by weight: 40% to 50% calcium oxide, 30% to 40% calcium hydroxide, and 10% to 20% aluminum phosphate.

3. The method for preparing a cementitious material based on coal ash and waste polypropylene fibers according to claim 1, characterized in that: Calculated by weight percentage, the mixture includes the following components: 70% to 80% of coal slag, 1% to 6% of waste polypropylene fiber, and 18% to 25% of a compound activator.

4. The method for preparing a cementitious material based on coal ash and waste polypropylene fibers according to claim 1, characterized in that: The liquid-to-solid ratio of the water to the precursor powder is 0.28-0.41 mL: 1 g.

5. The method for preparing a cementitious material based on coal ash and waste polypropylene fibers according to claim 1, characterized in that: The D90 particle size of the precursor powder is 300 mesh or less.

6. The method for preparing a cementitious material based on coal ash and waste polypropylene fibers according to claim 1, characterized in that: The main chemical components of the coal ash are: CO2 loss on ignition is 4wt%~10wt%, SiO2 content is 43wt%~64wt%, Al2O3 content is 20wt%~40wt%, Fe2O3 content is 2wt%~6wt%, and CaO content is 1wt%~3wt%; the initial particle size of the coal ash is 5 mesh or less.

7. The method for preparing a cementitious material based on coal ash and waste polypropylene fibers according to claim 1, characterized in that: The grinding time is 2 to 4 minutes; the molding method is: pouring the clean slurry into a mold for vibration molding; the curing method is: sealing the mold containing the vibration-molded sample, demolding after curing for 18 to 24 hours, and then continuing to seal and cure to a specified age to obtain a solidified gelling material based on coal ash and waste polypropylene fiber.

8. The method for preparing a cementitious material based on coal ash and waste polypropylene fibers according to claim 1, characterized in that: The water and curing temperature should not be lower than 0℃.

9. A cementitious material based on coal slag and waste polypropylene fibers, characterized in that: The gelling material based on coal ash and waste polypropylene fibers is obtained by the preparation method of the gelling material based on coal ash and waste polypropylene fibers according to any one of claims 1 to 8.

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