A strain hardening cementitious material with coal gangue as aggregate and a preparation method thereof

Abstract

The application discloses a strain hardening cement-based material taking coal gangue as aggregate and a preparation method thereof, wherein the cement-based material is composed of the following raw materials in parts by mass: 800-1200 parts of cementitious material, 232-492 parts of coal gangue, 232-400 parts of water, 25-38 parts of fiber material and 1-24 parts of water reducing agent; the coal gangue comprises coal gangue sand with a particle size of 0.075-0.15 mm and / or coal gangue sand with a particle size of 0.15-0.3 mm. The coal gangue has a multi-angled or rough surface, which is helpful to improve the mechanical interlocking effect between the aggregate and the cement-based body, and meanwhile, a plurality of coal gangues with different particle sizes are limited, so that the particles with different particle sizes and irregular shapes can be embedded and densely filled with each other, thereby improving the tensile performance of the concrete, greatly improving the impact toughness and wear resistance of the concrete, and having a good application prospect.

Description

Technical Field

[0001] This application belongs to the field of recycling technology of mining solid waste, specifically relating to a strain-hardening cement-based material with coal gangue as aggregate and its preparation method. Background Technology

[0002] In recent years, researchers and engineers both domestically and internationally have been searching for alternative building sands to river sand, such as sea sand, desert sand, and coal gangue sand. Coal gangue, primarily composed of Al2O3 and SiO2, possesses certain strength, is lightweight and porous, and contains numerous internal defects, resulting in a much higher water absorption rate than ordinary river sand. Experiments have shown that strain-hardening cementitious materials prepared using coal gangue sand instead of quartz sand exhibit enhanced ductility and toughness, with superior tensile and flexural mechanical properties. Coal gangue, a solid waste generated during coal mining and washing, is a hard, dark gray rock with low carbon content and low calorific value. Coal gangue production accounts for approximately 10% of coal production, and my country's current total accumulated coal gangue has reached over 7 billion tons, with the amount increasing annually, making it the industrial waste with the largest accumulation and annual increase, and the largest land occupation in my country. Therefore, given the excellent mechanical properties and overproduction of coal gangue, research on its processing is essential.

[0003] Strain-hardening cementitious materials replace the coarse aggregate in traditional concrete with fine sand of approximately 100 micrometers in diameter. By incorporating fine, short polyvinyl alcohol (PVA) or polyethylene (PE) fibers, tensile strain hardening is achieved. Strain hardening refers to the phenomenon where, under tensile loads (especially after microcracks begin to propagate), the tensile stress in a material does not decrease rapidly with crack propagation as in traditional brittle materials, but rather increases. During tensile testing, strain-hardening cementitious materials do not form single macroscopic cracks, but rather numerous microcracks. These cracks form a complex crack network within the material, absorbing more energy and improving overall material performance. Strain-hardening cementitious materials possess excellent mechanical properties and durability, contributing to improved integrity, durability, and safety of building and infrastructure structures, especially in applications requiring high ductility and toughness. Therefore, this material is currently used in numerous fields such as seismic structures, bridge engineering, hydraulic structures, and repair and reinforcement.

[0004] However, the interface between coal gangue and strain-hardening cement matrix is ​​relatively weak, making it a weak link in the interface transition zone and the origin of cracks. When the matrix material is subjected to load, the irregularly shaped pores in the coal gangue may cause stress concentration at the crack tip, prompting crack initiation and propagation. Fine coal gangue sand particles may form a bridging effect at the crack tip, limiting the further opening of the crack and guiding the crack to form in a wider area. This places high demands on the particle size distribution, morphological characteristics, and dosage of coal gangue.

[0005] Therefore, there is an urgent need for a composition and preparation method that can use coal gangue as an aggregate in strain-hardening cementitious materials, so that the coal gangue can be effectively combined with the cement matrix, ensuring the stability of the material and giving full play to its strain performance. Summary of the Invention

[0006] The technical problem this application aims to solve is to overcome the shortcomings of existing technologies, such as the shortage of river sand resources, the overproduction of coal gangue waste, the lack of effective utilization methods for coal gangue and cementitious matrices, resulting in increased production volume and low utilization rate. This application provides a strain-hardening cementitious material using coal gangue as aggregate and its preparation method. This application recycles and crushes coal gangue into manufactured sand for the production of strain-hardening cementitious materials. While improving the ductility and toughness of the strain-hardening cementitious materials, it also effectively solves the problems of quantified coal gangue processing, environmental pollution, and land occupation caused by gangue piles. It compensates for the deficiencies of low coal gangue utilization and low utilization rate, alleviates the aggregate shortage problem in the construction industry, promotes the comprehensive treatment and utilization of coal gangue, turns waste into treasure, and reduces the production cost of strain-hardening cementitious materials.

[0007] This application adopts the following technical solution to solve the above-mentioned technical problems:

[0008] This application provides a strain-hardening cementitious material with coal gangue as aggregate, which is composed of the following raw materials in parts by weight: 800-1200 parts of cementitious material, 232-400 parts of coal gangue, 232-492 parts of water, 25-38 parts of fiber material, and 1-24 parts of water-reducing agent.

[0009] The coal gangue includes: coal gangue sand with a particle size of 0.075 to 0.15 mm and / or coal gangue sand with a particle size of 0.15 to 0.3 mm.

[0010] In some embodiments, the strain-hardening cementitious material with coal gangue as aggregate is composed of the following raw materials in parts by weight: 950-1050 parts cementitious material, 275-400 parts coal gangue, 275-400 parts water, 30-34 parts fiber material, and 2-20 parts water-reducing agent. Preferably, the strain-hardening cementitious material with coal gangue as aggregate is composed of the following raw materials in parts by weight: 1000 parts cementitious material, 350 parts coal gangue, 350 parts water, 32 parts polyvinyl alcohol fiber material, and 2.9 parts water-reducing agent.

[0011] In some embodiments, the strain-hardening cementitious material with coal gangue as aggregate is composed of the following raw materials in parts by mass: 1000 parts cementitious material, 350 parts coal gangue, 350 parts water, 32 parts polyvinyl alcohol fiber material, and 2.9 parts water-reducing agent;

[0012] In some embodiments, when the coal gangue comprises: coal gangue sand with a particle size of 0.075 to 0.15 mm and coal gangue sand with a particle size of 0.15 to 0.3 mm, the mass ratio of the two is 1:(0.8 to 0.15), preferably 1:0.11;

[0013] In some embodiments, when the coal gangue further includes coal gangue sand with a particle size of 0.3–0.6 mm, more preferably, when the coal gangue includes: coal gangue sand with a particle size of 0.075–0.15 mm, coal gangue sand with a particle size of 0.15–0.3 mm, and coal gangue sand with a particle size of 0.3–0.6 mm, the mass ratio of the three is 1:(0.8–1.5):(1.8–2.2), more preferably 1:1.2:1.96. In some embodiments, the cementitious material includes finely active mineral materials and cement, and the mass ratio of the finely active mineral materials to the cement is 1:(2–3).

[0014] In some embodiments, the fine active mineral material includes one or more of fly ash, slag powder, metakaolin, silica fume, and limestone powder, and preferably, the fine active mineral material is fly ash.

[0015] The fly ash contains 40%–60% SiO2, 35%–45% Al2O3, and 8%–18% CaO.

[0016] In some embodiments, the cement includes one or more of silicate cement, aluminate cement, and sulfoaluminate cement; preferably, the cement is silicate cement.

[0017] In some embodiments, the fiber material includes polyvinyl alcohol fiber and / or polyethylene fiber, wherein the polyvinyl alcohol fiber is spun from polyvinyl alcohol and the polyethylene fiber is spun from polyethylene.

[0018] When the polyvinyl alcohol fiber is used as the fiber material, the polyvinyl alcohol fiber has a diameter of 30-50 μm and a length of 9-15 mm. Preferably, the polyvinyl alcohol fiber has a diameter of 0.039 mm and a length of 12.0 mm.

[0019] In some embodiments, the water-reducing agent is a high-efficiency polycarboxylate water-reducing agent. Preferably, the high-efficiency polycarboxylate water-reducing agent includes polyhydroxy acid salts, and more preferably, it includes polyethers composed of acrylic acid, methacrylic acid, and maleic anhydride as the main linking links with different side chain lengths.

[0020] The acrylic acid, methacrylic acid, and maleic anhydride are polyethers with different side chain lengths as the main linkages. The specific side chain lengths are designed and adjusted according to the actual application requirements in conventional technologies in the field.

[0021] In some embodiments, the coal gangue is obtained by crushing, grinding, washing, drying, and screening in accordance with conventional methods in the art to obtain coal gangue sand.

[0022] The processing steps for the coal gangue are as follows:

[0023] The first step is to clean the existing coal gangue to remove surface coal dust, oil, mud and other impurities. Then, the coal gangue is classified according to its particle size and shape to facilitate subsequent crushing.

[0024] The second step involves using a crusher (such as a jaw crusher) to initially crush the coal gangue, removing large pieces and breaking them into smaller chunks. The coarsely crushed coal gangue is then further crushed using a crusher (such as a cone crusher) to reduce the particle size and increase the roughness and irregularity of the particles. Finally, the medium-crushed coal gangue is finely crushed using equipment such as a vertical impact crusher or a hammer crusher to achieve the desired particle size distribution. After this step, most of the coal gangue has a particle size of less than 4.75 mm.

[0025] The third step is to use grinding equipment such as ball mills to grind the particles to improve their shape and surface properties. The grinding time should be strictly controlled in this step, and the particle size should not be too fine. It is advisable to allow some of the coal gangue sand to pass through a 0.15mm sieve, otherwise it will affect the workability of the slurry material.

[0026] Fourth, during the crushing and grinding process, new impurities may be generated, so it is necessary to wash it again to ensure the cleanliness of the coal gangue. After washing, the coal gangue is placed in a drying oven for drying to remove moisture. Preferably, the drying temperature is 105°C and the drying time is 12 hours.

[0027] The fifth step involves screening the dried coal gangue and conducting quality control tests, including particle size distribution, shape, surface characteristics, and pore structure, to ensure that the coal gangue has high ductility, multiple cracks, high tensile strength, significant strain hardening, and high toughness, so as to meet the requirements for use as fine aggregate in strain hardening cement-based materials.

[0028] The maximum particle size of the coal gangue sand should generally not exceed 4.75 mm, and the coal gangue sand should pass a sieve test to ensure that its particle size distribution meets the following requirements: 100% pass through a 4.75 mm sieve, most particles (more than 50%) pass through a 0.60 mm sieve, the coarse particles (0.15 mm - 4.75 mm) of the fine aggregate should account for a certain proportion to ensure the skeleton effect, and the fine particles (0.075 mm - 0.15 mm) should also account for a certain proportion to fill the gaps between coarse particles and increase the density.

[0029] This application also provides a method for preparing a strain-hardening cementitious material using coal gangue as aggregate, which is prepared from the components described above, and the specific steps include:

[0030] (1) Mixing the base material: Dry mixing of the cementitious material and the coal gangue, then adding water for wet mixing, and then slowly adding water-reducing agent to obtain the base material;

[0031] (2) Incorporation of fibers: The fibers are mixed into the substrate and stirred to obtain a slurry;

[0032] (3) Pouring and curing: The slurry material is poured once, then poured a second time, and then cured.

[0033] In some embodiments, in step (1), the dry material is stirred at a speed of 140 rpm for 0.5 min.

[0034] In some embodiments, in step (1), the stirring speed of the wet material is 140 rpm and the stirring time of the wet material is 3 min.

[0035] In some embodiments, in step (1), the wet material is stirred until the substrate has the appropriate consistency.

[0036] In some embodiments, in step (2), the mixing is carried out in accordance with the conventional art, by reducing the stirring speed during the mixing process, sprinkling the fiber material into the slurry, and then stirring until it is evenly dispersed.

[0037] The mixing is conventional in the art and is carried out using a cement mortar mixer. The mixing speed is 130-150 rpm, preferably 140 rpm.

[0038] In some embodiments, in step (3), the single pouring is conventional in the art, pouring to half the volume of the mold in one go.

[0039] In some embodiments, step (3) further includes vibration after the first pouring, and the vibration is conventional in the art, using a vibration table for vibration.

[0040] When the vibration table is used for the vibration, the vibration time is 0.5 to 1.5 minutes, preferably 1 minute.

[0041] In some embodiments, half of the remaining volume of the secondary casting mold is used to cast the specimen in layers to ensure a dense molding.

[0042] In some embodiments, step (3) further includes vibration after the secondary pouring. The vibration is conventional in the art and is performed using a vibration table.

[0043] When the vibration table is used for the vibration, the vibration time is 0.5 to 1.5 minutes, preferably 1 minute.

[0044] In some embodiments, step (3) includes smearing and covering the surface after vibration.

[0045] The process involves smoothing the surface of the specimen using a trowel, and the process of covering the specimen with a polyethylene film to prevent moisture loss.

[0046] In some embodiments, the curing in step (3) is performed at room temperature.

[0047] In some embodiments, the curing time in step (3) is 12 to 48 hours, preferably 24 hours.

[0048] In some embodiments, step (3) includes a secondary maintenance after the initial maintenance.

[0049] The secondary curing involves moving the specimen to a standard curing room for curing. Preferably, the secondary curing time is 7 to 28 days.

[0050] The temperature for the secondary curing is 18–22°C, more preferably 20°C.

[0051] The study found that coal gangue has a multi-faceted or rough surface. Such a shape helps to improve the mechanical interlocking between the aggregate and the cement matrix. Irregularly shaped particles can interlock and complement each other to achieve compaction. The rough surface of coal gangue particles can provide more anchoring points and enhance the bond with the cement matrix. The surface should be as clean as possible, free of dirt, oil or other harmful substances, to avoid affecting the reaction and bond with cement.

[0052] In this study, it was found that when PVA or PE fibers are incorporated into the material, the fibers embedded in the matrix cross the cracks, forming a so-called "crack bridging" effect. During the crack propagation process, the fibers undergo debonding slip, pull-out hardening, and tensile deformation. This process requires energy. The mechanical processes of the PVA or PE fibers used (their own scraping damage and interfacial slip hardening) can absorb some of the energy caused by external forces, reducing the destructive effect of energy on the matrix.

[0053] This application, through research, has discovered that the PVA or PE fibers incorporated in this application, with specific fiber sizes, fiber content, and excellent slip properties at the fiber-coal gangue sand matrix interface, can ensure the enhancement of fiber bridging residual energy, thus enabling the material to exhibit strain hardening characteristics (the aforementioned energy criterion). When the specimen material is subjected to tensile load, with the increase of strain, the specimen material exhibits increasingly higher stress, i.e., the specimen material gradually hardens during the tensile process. The greater the fiber bridging residual energy in the specimen material, the greater the potential for multi-crack development, and the better the ductility of the specimen material. Experiments have shown that the coal gangue sand and fibers in the specimen material complement each other and work together, giving the material the characteristics of low initial cracking and high ductility.

[0054] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of this application.

[0055] All reagents and raw materials used in this application are commercially available.

[0056] The positive and progressive effects of this application are as follows: This application can consume a large amount of coal gangue waste, save energy and reduce emissions, and protect the environment. It can also give full play to the characteristics of high ductility, high toughness and good deformation capacity of strain-hardening cement-based materials, improve the tensile properties of concrete, and greatly improve the impact toughness and wear resistance of concrete. It promotes the application of coal gangue in the field of strain-hardening cement-based materials and lays the foundation for the preparation of strain-hardening cement-based materials using coal gangue sand. Attached Figure Description

[0057] This application can be better understood by referring to the description given below in conjunction with the accompanying drawings. These drawings, together with the detailed description below, are incorporated in and form part of this specification, and are used to further illustrate preferred embodiments of the application and explain the principles and advantages of the application, wherein:

[0058] Figure 1 This is a cube compression testing instrument;

[0059] Figure 2 This is a cube loading method;

[0060] Figure 3 For uniaxial tensile testing clamping method;

[0061] Figure 4 The failure mode is uniaxial tensile test.

[0062] Figure 5 The loading method is a three-point bending test.

[0063] Figure 6 The bending failure mode is shown in the three-point bending test. Detailed Implementation

[0064] The present application is further illustrated below by way of embodiments, but this does not limit the present application to the scope of the embodiments described. Experimental methods in the following embodiments that do not specify specific conditions are performed according to conventional methods and conditions, or according to the product instructions.

[0065] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0066] All raw materials used in the following examples are commercially available.

[0067] Example 1

[0068] The raw material mix proportions of strain-hardening cementitious materials using coal gangue as aggregate in this embodiment are shown in Table 1.

[0069] Table 1

[0070]

[0071] A method for preparing a strain-hardening cementitious material using coal gangue as aggregate, comprising the following steps:

[0072] (1) Substrate mixing: First, put the cementitious material and coal gangue sand into the mixer and mix for 2 minutes to make the dry materials evenly mixed. Then slowly add water, and then slowly add acrylic high-efficiency polycarboxylate superplasticizer and continue mixing for 2 minutes to obtain a uniformly flowing slurry. During the mixing process, attention should be paid to cleaning the solid materials adhering to the mixer wall.

[0073] (2) Adding polyvinyl alcohol fiber: Control the mixer to run at low speed, slowly sprinkle polyvinyl alcohol fiber into the flowing slurry, and stir thoroughly to ensure that the fiber is evenly dispersed.

[0074] (3) Pouring and curing: Pour the first batch of the mold to half its volume, vibrate it for 1 minute on a vibrating table, then pour the remaining half in the second batch, vibrate it again, and smooth the surface with a trowel. Cover the smoothed specimen with a layer of polyethylene film to prevent moisture loss. After curing at room temperature for 24 hours, remove the mold and then perform a second curing on the specimen. Move the specimen to a standard curing room (temperature 20±2℃, relative humidity >95%) for a second curing.

[0075] Example 2

[0076] The raw material mix proportions of strain-hardening cementitious materials using coal gangue as aggregate in this embodiment are shown in Table 2.

[0077] Table 2

[0078]

[0079] A method for preparing a strain-hardening cementitious material using coal gangue as aggregate, comprising the following steps:

[0080] (1) Substrate mixing: First, put the cementitious material and coal gangue sand into the mixer and mix for 2 minutes to ensure the dry materials are evenly mixed. Then, slowly add water, followed by slowly adding the high-efficiency polycarboxylate superplasticizer and continue mixing for 2 minutes to obtain a uniformly flowing slurry. During the mixing process, pay attention to cleaning any solid materials adhering to the mixer wall;

[0081] (2) Adding polyvinyl alcohol fiber: Control the mixer to run at low speed, slowly sprinkle polyvinyl alcohol fiber into the flowing slurry, and stir thoroughly to ensure that the fiber is evenly dispersed.

[0082] (3) Pouring and curing: Pour the first batch of the mold to half its volume, vibrate it for 1 minute on a vibrating table, then pour the remaining half in the second batch, vibrate it again, and smooth the surface with a trowel. Cover the smoothed specimen with a layer of polyethylene film to prevent moisture loss. After curing at room temperature for 24 hours, remove the mold and then perform a second curing on the specimen. Move the specimen to a standard curing room (temperature 20±2℃, relative humidity >95%) for a second curing.

[0083] Example 3

[0084] The raw material mix proportions of strain-hardening cementitious materials using coal gangue as aggregate in this embodiment are shown in Table 3.

[0085] Table 3

[0086]

[0087] A method for preparing a strain-hardening cementitious material using coal gangue as aggregate, comprising the following steps:

[0088] (1) Substrate mixing: First, put the cementitious material and coal gangue sand into the mixer and mix for 2 minutes to make the dry materials evenly mixed. Then slowly add water and then slowly add acrylic high-efficiency polycarboxylate superplasticizer and continue mixing for 2 minutes to obtain a uniformly flowing slurry. During the mixing process, attention should be paid to cleaning the solid materials adhering to the mixer wall.

[0089] (2) Adding polyvinyl alcohol fiber: Control the mixer to run at low speed, slowly sprinkle polyvinyl alcohol fiber into the flowing slurry, and stir thoroughly to ensure that the fiber is evenly dispersed.

[0090] (3) Pouring and curing: Pour the first batch of the mold to half its volume, vibrate it for 1 minute on a vibrating table, then pour the remaining half in the second batch, vibrate it again, and smooth the surface with a trowel. Cover the smoothed specimen with a layer of polyethylene film to prevent moisture loss. After curing at room temperature for 24 hours, remove the mold and then perform a second curing on the specimen. Move the specimen to a standard curing room (temperature 20±2℃, relative humidity >95%) for a second curing.

[0091] Example 4

[0092] The raw material mix proportions of strain-hardening cementitious materials using coal gangue as aggregate in this embodiment are shown in Table 4.

[0093] Table 4

[0094]

[0095] A method for preparing a strain-hardening cementitious material using coal gangue as aggregate, comprising the following steps:

[0096] (1) Substrate mixing: First, put the cementitious material and coal gangue sand into the mixer and mix for 2 minutes to make the dry materials evenly mixed. Then slowly add water and then slowly add acrylic high-efficiency polycarboxylate superplasticizer and continue mixing for 2 minutes to obtain a uniformly flowing slurry. During the mixing process, attention should be paid to cleaning the solid materials adhering to the mixer wall.

[0097] (2) Adding polyvinyl alcohol fiber: Control the mixer to run at low speed, slowly sprinkle polyvinyl alcohol fiber into the flowing slurry, and stir thoroughly to ensure that the fiber is evenly dispersed.

[0098] (3) Pouring and curing: Pour the first batch of the mold to half its volume, vibrate it for 1 minute on a vibrating table, then pour the remaining half in the second batch, vibrate it again, and smooth the surface with a trowel. Cover the smoothed specimen with a layer of polyethylene film to prevent moisture loss. After curing at room temperature for 24 hours, remove the mold and then perform a second curing on the specimen. Move the specimen to a standard curing room (temperature 20±2℃, relative humidity >95%) for a second curing.

[0099] Example 5

[0100] The raw material mix proportions of strain-hardening cementitious materials using coal gangue as aggregate in this embodiment are shown in Table 5.

[0101] Table 5

[0102]

[0103]

[0104] A method for preparing a strain-hardening cementitious material using coal gangue as aggregate, comprising the following steps:

[0105] (1) Substrate mixing: First, put the cementitious material and coal gangue sand into the mixer and mix for 2 minutes to make the dry materials evenly mixed. Then slowly add water and then slowly add acrylic high-efficiency polycarboxylate superplasticizer and continue mixing for 2 minutes to obtain a uniformly flowing slurry. During the mixing process, attention should be paid to cleaning the solid materials adhering to the mixer wall.

[0106] (2) Adding polyvinyl alcohol fiber: Control the mixer to run at low speed, slowly sprinkle polyvinyl alcohol fiber into the flowing slurry, and stir thoroughly to ensure that the fiber is evenly dispersed.

[0107] (3) Pouring and curing: Pour the first batch of the mold to half its volume, vibrate it for 1 minute on a vibrating table, then pour the remaining half in the second batch, vibrate it again, and smooth the surface with a trowel. Cover the smoothed specimen with a layer of polyethylene film to prevent moisture loss. After curing at room temperature for 24 hours, remove the mold and then perform a second curing on the specimen. Move the specimen to a standard curing room (temperature 20±2℃, relative humidity >95%) for a second curing.

[0108] Comparative Example 1

[0109] Compared with Example 1, Comparative Example 1 differs in the different mass ratios of coal gangue with two particle sizes. The raw material mix ratio of strain-hardening cementitious material with coal gangue as aggregate in Comparative Example 1 is shown in Table 6.

[0110] Table 6

[0111]

[0112] A method for preparing a strain-hardening cementitious material using coal gangue as aggregate, comprising the following steps:

[0113] (1) Substrate mixing: First, put the cementitious material and coal gangue sand into the mixer and mix for 2 minutes to make the dry materials evenly mixed. Then slowly add water and then slowly add acrylic high-efficiency polycarboxylate superplasticizer and continue mixing for 2 minutes to obtain a uniformly flowing slurry. During the mixing process, attention should be paid to cleaning the solid materials adhering to the mixer wall.

[0114] (2) Adding polyvinyl alcohol fiber: Control the mixer to run at low speed, slowly sprinkle polyvinyl alcohol fiber into the flowing slurry, and stir thoroughly to ensure that the fiber is evenly dispersed.

[0115] (3) Pouring and curing: Pour the first batch of the mold to half its volume, vibrate it for 1 minute on a vibrating table, then pour the remaining half in the second batch, vibrate it again, and smooth the surface with a trowel. Cover the smoothed specimen with a layer of polyethylene film to prevent moisture loss. After curing at room temperature for 24 hours, remove the mold and then perform a second curing on the specimen. Move the specimen to a standard curing room (temperature 20±2℃, relative humidity >95%) for a second curing.

[0116] Comparative Example 2

[0117] Compared with Example 1, Comparative Example 2 differs in that it contains more coal gangue with a particle size of 0.075-0.15 mm. The raw material mix ratio of the strain-hardening cementitious material with coal gangue as aggregate in Comparative Example 2 is shown in Table 7.

[0118] Table 7

[0119]

[0120] A method for preparing a strain-hardening cementitious material using coal gangue as aggregate, comprising the following steps:

[0121] (1) Substrate mixing: First, put the cementitious material and coal gangue sand into the mixer and mix for 2 minutes to make the dry materials evenly mixed. Then slowly add water and then slowly add acrylic high-efficiency polycarboxylate superplasticizer and continue mixing for 2 minutes to obtain a uniformly flowing slurry. During the mixing process, attention should be paid to cleaning the solid materials adhering to the mixer wall.

[0122] (2) Adding polyvinyl alcohol fiber: Control the mixer to run at low speed, slowly sprinkle polyvinyl alcohol fiber into the flowing slurry, and stir thoroughly to ensure that the fiber is evenly dispersed.

[0123] (3) Pouring and curing: Pour the first batch of the mold to half its volume, vibrate it for 1 minute on a vibrating table, then pour the remaining half in the second batch, vibrate it again, and smooth the surface with a trowel. Cover the smoothed specimen with a layer of polyethylene film to prevent moisture loss. After curing at room temperature for 24 hours, remove the mold and then perform a second curing on the specimen. Move the specimen to a standard curing room (temperature 20±2℃, relative humidity >95%) for a second curing.

[0124] Example 1

[0125] The mechanical property testing methods are as follows:

[0126] ① Cube compression test: The products of the examples and comparative examples were prepared into cube specimens of 70.7mm × 70.7mm × 70.7mm, with 3 specimens per set. During the test, an MTS microcomputer-controlled electro-hydraulic servo pressure testing machine with a capacity of 3000kN was used. Figure 1As shown, a displacement control mode was used for loading, with a loading rate of 0.5 mm / min. Figure 2 As shown.

[0127] ② Uniaxial tensile test: The tensile specimens of the examples and comparative examples were dog-bone type specimens, with a tensile gauge length of 80 mm, a width of 30 mm, and a thickness of 14 mm, with 6 specimens per group. The specimens were held in a self-made fixture on an MTS microcomputer-controlled electronic universal testing machine (maximum capacity 300 kN), and a displacement control mode of 0.15 mm / min was applied. Extensometers with an 80 mm gauge length were installed on both sides of the specimen to measure the tensile strain. Figure 3 As shown, Figure 4 This is one form of destruction.

[0128] ③ Three-point bending test: The bending test was conducted on an MTS microcomputer-controlled electronic testing machine. The tensile specimens of the examples and comparative examples were set as 160mm×40mm×40mm cuboid specimens, with 3 specimens in each group. The loading method was three-point bending, with a span of 100mm and a loading rate of 1.5mm / min. A three-point bending test device was used, such as... Figure 5 As shown, during the loading process, the computer automatically collects data such as mid-span deflection, load, and time to analyze the flexural mechanical properties of the coal gangue sand strain-hardening cementitious material. Figure 6 These are several modes of bending failure of the specimen material.

[0129] The mechanical properties of the products prepared according to this method in the examples and comparative examples with a secondary curing time of 7 days are shown in Table 8 below.

[0130] Table 8

[0131]

[0132]

[0133] The results showed that after 7 days of secondary curing, Examples 1-4 exhibited superior compressive strength and ultimate flexural load compared to Comparative Examples 1-2. Examples 1-4 were significantly better than Comparative Examples 1-2 in both compressive and flexural performance. It is speculated that Comparative Example 1 suffered from poor gradation due to excessive coal gangue sand with a particle size of 0.15-0.3 mm, resulting in reduced mechanical properties. Comparative Example 2, with its higher content of 0.075-0.15 mm fine-particle sand, failed to achieve proper interlocking, leading to decreased compressive strength and ultimate flexural load, thus reducing some mechanical properties. The mechanical properties of the products obtained by the examples and comparative examples after 28 days of secondary curing are shown in Table 9 below.

[0134] Table 9

[0135]

[0136] The results showed that after 28 days of secondary curing, the compressive strength parameters of Examples 1-4 were significantly increased. Compared with Comparative Examples 1-2, the difference in compressive strength between Examples 1-4 and Comparative Examples was greater.

[0137] Finally, it should be noted that the terms “comprising,” “including,” or any other variations thereof in this application are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0138] Although this application has been disclosed above through the description of specific embodiments, it should be understood that those skilled in the art can devise various modifications, improvements, or equivalents to this application within the spirit and scope of the appended solutions. Such modifications, improvements, or equivalents should also be considered to be included within the scope of protection claimed in this application.

Claims

1. A strain-hardening cementitious material using coal gangue as aggregate, characterized in that, Composed of the following raw materials by weight: 800-1200 parts cementitious material, 232-400 parts coal gangue, 232-492 parts water, 25-38 parts fiber material, and 1-24 parts water-reducing agent; The coal gangue comprises: coal gangue sand with a particle size of 0.075~0.15mm and coal gangue sand with a particle size of 0.15~0.3mm, in a mass ratio of 1:0.11; or, the coal gangue comprises: coal gangue sand with a particle size of 0.075~0.15mm, coal gangue sand with a particle size of 0.15~0.3mm, and coal gangue sand with a particle size of 0.3~0.6mm, in a mass ratio of 1:(0.8~1.5):(1.8~2.2). The cementitious material includes fine active mineral materials and cement, and the mass ratio of the fine active mineral materials to the cement is 1:(2~3).

2. The strain-hardening cementitious material with coal gangue as aggregate as described in claim 1, characterized in that, The product is composed of the following raw materials in parts by weight: 950-1050 parts cementitious material, 275-400 parts coal gangue, 275-400 parts water, 30-34 parts fiber material, and 2-20 parts water-reducing agent; the fiber material includes polyvinyl alcohol fiber and / or polyethylene fiber.

3. The strain-hardening cementitious material with coal gangue as aggregate as described in claim 2, characterized in that, The strain-hardening cementitious material with coal gangue as aggregate is composed of the following raw materials in parts by mass: 1000 parts cementitious material, 350 parts coal gangue, 350 parts water, 32 parts polyvinyl alcohol fiber material, and 2.9 parts water-reducing agent.

4. The strain-hardening cementitious material with coal gangue as aggregate as described in claim 2, characterized in that, The strain-hardening cementitious material using coal gangue as aggregate satisfies at least one of the following conditions: The fine active mineral materials include one or more of the following: fly ash, slag powder, metakaolin, silica fume, and limestone powder. The cement includes one or more of silicate cement, aluminate cement, and sulfoaluminate cement; The water-reducing agent is a high-efficiency polycarboxylate water-reducing agent; The mass ratio of the coal gangue sand with a particle size of 0.075~0.15mm, the coal gangue sand with a particle size of 0.15~0.3mm, and the coal gangue sand with a particle size of 0.3~0.6mm is 1:1.2:1.

96.

5. The strain-hardening cementitious material with coal gangue as aggregate as described in claim 2, characterized in that, The strain-hardening cementitious material using coal gangue as aggregate satisfies at least one of the following conditions: The fine active mineral material is fly ash; The cement is silicate cement; The polyvinyl alcohol fiber is obtained by spinning polyvinyl alcohol as a raw material. The polyethylene fiber is obtained by spinning polyethylene as raw material.

6. The strain-hardening cementitious material with coal gangue as aggregate as described in claim 4, characterized in that, The strain-hardening cementitious material using coal gangue as aggregate satisfies at least one of the following conditions: The diameter of the polyvinyl alcohol fiber material is 30~50μm, and the length of the polyvinyl alcohol fiber material is 9~15mm; The polyethylene fiber has a diameter of 30~50μm and a length of 9~15mm.

7. The strain-hardening cementitious material with coal gangue as aggregate as described in claim 4, characterized in that, The polyethylene fiber has a diameter of 40 μm and a length of 12 mm.

8. A method for preparing a strain-hardening cementitious material using coal gangue as aggregate as described in any one of claims 1 to 7, characterized in that, The preparation method includes the following steps: (1) Mixing the base material: Dry mixing of the cementitious material and the coal gangue, then adding water for wet mixing, and then adding water-reducing agent to obtain the base material; (2) Incorporation of fibers: The fibers are mixed into the substrate and stirred to obtain a slurry; (3) Pouring and curing: The slurry material is poured once, then poured a second time, and then cured.

9. A method for preparing a strain-hardening cementitious material using coal gangue as aggregate as described in claim 8, characterized in that, The method for preparing the strain-hardening cementitious material using coal gangue as aggregate satisfies at least one of the following conditions: In step (1), the stirring speed of the dry material is 140 rpm, and the stirring time of the dry material is 0.5 min; In step (1), the stirring speed of the wet material is 140 rpm, and the stirring time of the wet material is 3 min; In step (2), the stirring speed is reduced during the mixing process, the fiber material is sprinkled into the slurry, and then the stirring is carried out until it is evenly dispersed; In step (3), the pouring is carried out once to half the volume of the mold; In step (3), the first pouring is followed by vibration, which is performed using a vibrating table. In step (3), half of the remaining volume of the secondary casting mold is used to cast the specimen in layers to ensure that the molding is dense; In step (3), the vibration process also includes the operations of smearing and covering with a film; In step (3), the curing is carried out at room temperature; In step (3), the curing time is 12~48h; In step (3), after the initial maintenance, a secondary maintenance is also included.

10. A method for preparing a strain-hardening cementitious material using coal gangue as aggregate as described in claim 9, characterized in that, The method for preparing the strain-hardening cementitious material using coal gangue as aggregate satisfies at least one of the following conditions: In step (1), the mixing is carried out using a cement mortar mixer, and the mixing speed is 130~150 rpm; when the vibration table is used for compaction, the compaction time is 0.5~1.5 min. In step (3), the secondary pouring is followed by vibration, which is performed using a vibrating table; when the vibrating table is used for vibration, the vibration time is 0.5~1.5min. In step (3), the coating is a layer of polyethylene film to prevent moisture loss; In step (3), the curing time is 24 hours; In step (3), the secondary curing involves moving the specimen to a standard curing room for curing. In step (3), the secondary curing time is 7~28 days; In step (3), the temperature for the secondary curing is 18~22℃.

11. A strain-hardening cementitious material using coal gangue as aggregate, characterized in that, It is prepared by the method for preparing strain-hardening cementitious materials with coal gangue as aggregate as described in any one of claims 8 to 10.

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