Strain hardening cement-based material taking coal gangue as aggregate and preparation method of strain hardening cement-based material

Abstract

The invention discloses a strain hardening cement-based material taking coal gangue as aggregate and a preparation method thereof, and the strain hardening cement-based material is prepared from the following raw materials in parts by mass: 800-1200 parts of a cementing material, 232-492 parts of coal gangue, 232-400 parts of water, 25-38 parts of a fiber material and 1-24 parts of a water reducing agent, the coal gangue comprises coal gangue sand with the particle size of 0.075 to 0.15 mm and / or coal gangue sand with the particle size of 0.15 to 0.3 mm. The coal gangue has a multi-edge or rough surface, so that the mechanical occlusion effect between aggregate and a cement matrix is improved, and meanwhile, the coal gangue with various different particle sizes is limited, so that particles with different particle sizes and irregular shapes can be mutually embedded and extruded and are complemented and compacted, the tensile property of the concrete is improved, and the service life of the concrete is prolonged. The impact toughness and the wear resistance of the concrete are greatly improved, and the concrete has a good application prospect.

Description

Technical Field

[0001] The present application belongs to the technical field of recycling and utilization of mining solid waste, and specifically relates to a strain-hardening cement-based material using coal gangue as aggregate and a preparation method thereof. Background Art

[0002] In recent years, my country has been undergoing a period of large-scale infrastructure construction, resulting in over-exploitation of river sand resources and severe ecological damage. Researchers and the construction industry at home and abroad are searching for alternative construction sands, such as sea sand, desert sand, and gangue sand, to replace river sand. Gangue, primarily composed of Al₂O₃ and SiO₂, possesses considerable strength, is lightweight and porous, and contains numerous internal defects, resulting in a water absorption rate far higher than that of ordinary river sand. Experimental studies have shown that strain-hardening cementitious materials prepared using gangue sand instead of quartz sand exhibit enhanced ductility and toughness, with superior tensile and flexural properties. Gangue, a solid waste generated during coal mining and washing, is a hard, black-gray rock with a low carbon content, low calorific value, and a hard texture. Gangue production accounts for approximately 10% of coal production. my country's current total gangue accumulation has reached over 7 billion tons, with the amount increasing annually, making it the largest industrial waste in terms of both stockpiling volume and annual growth, and occupying the most land. Gangue, which accumulates on the ground to form gangue heaps, not only occupies a large amount of land but also poses a significant threat to the environment, impacting coal mine production and the health of residents living near gangue heaps. Therefore, given the excellent mechanical properties of gangue and its overproduction, research on its treatment is essential.

[0003] Strain-hardening cementitious materials remove the coarse aggregate from traditional concrete and replace it with fine sand with a particle size of approximately 100 microns. By incorporating fine, short polyvinyl alcohol (PVA) or polyethylene (PE) fibers, the material achieves tensile strain hardening. Strain hardening refers to the phenomenon that when a material is subjected to a tensile load (especially after microcracks begin to expand), the tensile stress of the material does not decrease rapidly with the expansion of the cracks as in traditional brittle materials, but instead increases. During the tensile process, strain-hardening cementitious materials do not form a single macroscopic crack, but rather produce many tiny cracks. These cracks form a complex crack network within the material, thereby absorbing more energy and improving the overall performance of the material. Strain-hardening cementitious materials have excellent mechanical properties and durability, which help to improve the integrity, durability, and safety of building and infrastructure structures, especially in applications requiring high ductility and toughness. Therefore, this material has been used in many fields such as earthquake-resistant structures, bridge engineering, hydraulic structures, and repair and reinforcement.

[0004] However, the interface between gangue and strain-hardening cement matrix is ​​relatively weak, which makes it a weak link in the interface transition zone and the origin of cracks. When the matrix material is subjected to load, the irregular pores in the gangue may cause stress concentration at the crack tip, prompting the crack to start and expand. The fine particles of gangue sand 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 requirements on the particle size distribution, morphological characteristics and dosage of gangue.

[0005] Therefore, there is an urgent need for a component and preparation method that can use coal gangue as aggregate in strain-hardening cement-based materials, so that the coal gangue can be effectively combined with the cement matrix, ensuring the stability of the material and exerting its strain properties. Summary of the Invention

[0006] The technical problem to be solved by this application is to overcome the defects of the existing technology such as shortage of river sand resources, excess production of coal gangue waste, lack of effective means of utilizing coal gangue and cement matrix, increased increment and low utilization rate, and provide a strain-hardening cement-based material with coal gangue as aggregate and its preparation method. This application recycles and crushes coal gangue into machine-made sand for the production of strain-hardening cement-based materials. While improving the ductility and toughness of strain-hardening cement-based materials, it also effectively solves the problems of quantitative processing of coal gangue, environmental pollution, and land occupation of gangue mountains, makes up for the defects of small amount of coal gangue utilization and low utilization rate, alleviates the problem of aggregate shortage in the construction industry, promotes the comprehensive processing and utilization of coal gangue, turns waste into treasure, and reduces the production cost of strain-hardening cement-based materials.

[0007] This application adopts the following technical solutions to solve the above technical problems:

[0008] The present application provides a strain-hardening cement-based material using coal gangue as aggregate, which is composed of the following raw materials in parts by mass: 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] Wherein, the coal gangue includes: 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.

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

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

[0012] In some embodiments, when the coal gangue includes: the coal gangue sand with a particle size of 0.075 to 0.15 mm and the 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), preferably 1:1.2:1.96. In some embodiments, the cementitious material includes fine active mineral material and cement, and the mass ratio of the fine active mineral material 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, limestone powder, etc. Preferably, the fine active mineral material is fly ash.

[0015] The fly ash contains SiO2 at a content of 40% to 60%, Al2O3 at a content of 35% to 45%, and CaO at a content of 8% to 18%.

[0016] In some embodiments, the cement includes one or more of Portland cement, aluminate cement, and sulphoaluminate cement. Preferably, the cement is Portland 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 as raw material, and the polyethylene fiber is spun from polyethylene as raw material.

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

[0019] In some embodiments, the water reducing agent is a high-efficiency polycarboxylic acid water reducing agent, preferably, the high-efficiency polycarboxylic acid water reducing agent comprises polyhydroxy acid salt, preferably, the high-efficiency polycarboxylic acid water reducing agent is mainly composed of acrylic acid, methacrylic acid and maleic anhydride to link different side chain lengths of polyether.

[0020] In the formula, the acrylic acid, the methacrylic acid and the maleic anhydride are mainly used to link different side chain lengths of polyether, and the specific side chain length is designed and adjusted according to the actual application requirements in the conventional technology in the art.

[0021] In some embodiments, the coal gangue is crushed, ground, washed, dried and sieved to obtain the coal gangue sand according to the conventional technology in the art.

[0022] In the formula, the coal gangue is processed as follows:

[0023] In the first step, the existing coal gangue is washed to remove the coal dust, oil stains, soil and other impurities on the surface, and then classified according to the particle size and shape of the coal gangue to facilitate the subsequent crushing process.

[0024] In the second step, the coal gangue is preliminarily crushed by using a crusher (such as a jaw crusher) to remove large pieces of coal gangue and crush them into smaller pieces. The coarsely crushed coal gangue is further crushed by using a crusher (such as a cone crusher) to reduce the particle size and increase the roughness and irregularity of the particles. The medium crushed coal gangue is finely crushed by using a vertical impact crusher, a hammer crusher and other equipment to achieve the required particle size distribution. After this step, the particle size of most of the coal gangue reaches 4.75 mm or less.

[0025] In the third step, the coal gangue is finely ground by using a ball mill and other grinding equipment to improve the shape and surface properties of the particles. The grinding time should be strictly controlled, and the particle size should not be too fine. It is preferable that part of the coal gangue sand passes through a 0.15 mm sieve. Otherwise, it will affect the workability of the slurry material.

[0026] In the fourth step, new impurities may be generated during the crushing and grinding process, so the coal gangue needs to be washed again to ensure its cleanliness. The washed coal gangue is dried in a drying box to remove moisture. Preferably, the drying temperature is 105°C, and the drying time is 12 h.

[0027] In the fifth step, the sieving treatment is performed on the dried coal gangue, and the quality control test is performed on the coal gangue, including the particle size distribution, shape, surface properties, pore structure and the like, to ensure that the coal gangue has the characteristics of high ductility, multiple crack openings, high tensile strength, obvious strain hardening and high toughness, so as to meet the requirements of being used as a fine aggregate in strain hardening cement-based materials.

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

[0029] The present application also provides a method for preparing a strain-hardening cement-based 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 the cementitious material and the coal gangue, then adding the water to wet-mix the cementitious material, and then slowly adding the water reducing agent to obtain the base material;

[0031] (2) Incorporating fibers: mixing fibers into the substrate and stirring to obtain a slurry;

[0032] (3) Casting and curing: Cast the slurry material once, cast it a second time, and then perform curing.

[0033] In some embodiments, in step (1), the rotation speed of the dry material stirring is 140 rpm, and the stirring time of the dry material is 0.5 min.

[0034] In some embodiments, in step (1), the wet material is stirred at a rotation speed of 140 rpm, and the wet material is stirred for 3 minutes.

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

[0036] In some embodiments, in step (2), the mixing is performed according to conventional techniques in the art, the stirring speed is reduced during the mixing process, the fiber material is sprinkled into the slurry, and then the stirring is performed until the slurry is evenly dispersed.

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

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

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

[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 test piece in layers to ensure dense molding.

[0042] In some embodiments, in step (3), vibration is further included 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, in step (3), the vibration further includes the operations of plastering and coating.

[0045] The surface finishing is to smooth the surface with a spatula to obtain a test piece, and the coating is to cover the test piece with a layer of polyethylene film to prevent water loss.

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

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

[0048] In some embodiments, in step (3), after the curing, secondary curing is also included.

[0049] Wherein, the secondary curing is to move the plant to a standard curing room for curing. Preferably, the secondary curing time is 7 to 28 days;

[0050] Wherein, the temperature of the secondary curing is 18-22°C, more preferably 20°C.

[0051] During the research, the present applicant found that coal gangue has a multi-angle or rough surface. Such a shape helps to improve the mechanical bite between the aggregate and the cement matrix. The irregularly shaped particles can be embedded in each other and complement each other densely. The rough surface characteristics of the coal gangue particles can provide more anchor points and enhance the bonding with the cement matrix. The surface should be as clean as possible, without dirt, oil or other harmful substances to avoid affecting the reaction and bonding with the cement.

[0052] During the research, the present applicant found that by adding PVA fibers or PE fibers to the material, the fibers embedded in the matrix span the cracks, forming the so-called "crack bridging" effect. During the crack propagation process, the fibers will experience debonding slippage, tensile hardening and tensile deformation. This process requires energy consumption. The mechanical process of the PVA fibers or PE fibers used (their own scraping damage, interface slip hardening) can absorb part of the energy caused by external forces and reduce the destructive effect of energy on the matrix.

[0053] Through research, the present application has found that the PVA fiber or PE fiber incorporated in the present application, at a specific fiber size, fiber content and excellent slip performance of the fiber-coal gangue sand matrix interface, can ensure the improvement of the fiber bridging residual energy, which makes the material have the characteristics of strain hardening (the above-mentioned energy criterion); when the specimen material is subjected to a tensile load, as the strain increases, the specimen material exhibits higher and higher stress, that is, the specimen material gradually hardens during the stretching process. The greater the fiber bridging residual energy in the specimen material, the greater the potential for the development of multi-crack cracks, and the better the ductility of the specimen material. Experiments have shown that the coal gangue sand and fiber in the specimen material complement each other and work together to make the material have the characteristics of low initial cracking and high ductility.

[0054] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present application.

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

[0056] The positive progressive effect of this application is that it can consume a large amount of coal gangue waste, save energy and reduce emissions, and protect the environment, and it can give full play to the high ductility, high toughness and good deformation ability of strain-hardening cement-based materials, improve the tensile properties of concrete, and greatly improve the impact toughness and wear resistance of concrete, promote the application of coal gangue in the field of strain-hardening cement-based materials, and lay the foundation for the use of coal gangue sand to prepare strain-hardening cement-based materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The present application may be better understood by referring to the following description in conjunction with the accompanying drawings. The accompanying drawings, together with the following detailed description, are incorporated into and form a part of this specification and are used to further illustrate preferred embodiments of the present application and to explain the principles and advantages of the present application, wherein:

[0058] Figure 1 It is a cube compression test instrument;

[0059] Figure 2 It is the cube loading method;

[0060] Figure 3 It is the clamping method for uniaxial tensile test;

[0061] Figure 4 This is the failure form of uniaxial tensile test;

[0062] Figure 5 It is a three-point bending test loading method;

[0063] Figure 6 This is the bending failure form of the three-point bending test. DETAILED DESCRIPTION

[0064] The present application is further illustrated below by way of examples, but the present application is not limited to the scope of the examples. Experimental methods without specific conditions in the following examples may be performed according to conventional methods and conditions, or selected according to the product instructions.

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

[0066] The raw materials in the following examples are all commercially available.

[0067] Example 1

[0068] The raw material mix ratio of the strain hardening cement-based material using coal gangue as aggregate in this embodiment is shown in Table 1.

[0069] Table 1

[0070]

[0071] A method for preparing a strain-hardening cement-based material using coal gangue as aggregate comprises the following steps:

[0072] (1) Mixing the base material: First, put the cementitious material and coal gangue sand into the mixer and stir for 2 minutes to mix the dry materials evenly. Then slowly add water, and then slowly add acrylic acid high-efficiency polycarboxylate water reducer and continue stirring for 2 minutes to obtain a uniform flowing slurry. During the mixing process, be careful to clean the solid materials stuck to the mixer wall.

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

[0074] (3) Casting and curing: Cast to half of the mold volume at one time, vibrate on a vibration table for 1 minute, then cast the remaining half for a second time, vibrate again and smooth the surface with a spatula, cover the smoothed surface with a layer of polyethylene film to prevent water loss, perform a first curing at room temperature for 24 hours, then remove the mold, and then perform a second curing on the specimen, and move it to a standard curing room (temperature 20±2℃, relative humidity>95%) for a second curing.

[0075] Example 2

[0076] The raw material mix ratio of the strain hardening cement-based material using coal gangue as aggregate in this embodiment is shown in Table 2.

[0077] Table 2

[0078]

[0079] A method for preparing a strain-hardening cement-based material using coal gangue as aggregate comprises the following steps:

[0080] (1) Mixing the base material: First, put the cementitious material and coal gangue sand into the mixer and stir for 2 minutes to mix the dry materials evenly. Then slowly add water, and then slowly add acrylic acid high-efficiency polycarboxylate water reducer and continue stirring for 2 minutes to obtain a uniform flowing slurry. During the mixing process, be careful to clean the solid material stuck to the mixer wall;

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

[0082] (3) Casting and curing: Cast to half of the mold volume at one time, vibrate on a vibration table for 1 minute, then cast the remaining half for a second time, vibrate again and smooth the surface with a spatula, cover the smoothed surface with a layer of polyethylene film to prevent water loss, perform a first curing at room temperature for 24 hours, then remove the mold, and then perform a second curing on the specimen, and move it to a standard curing room (temperature 20±2℃, relative humidity>95%) for a second curing.

[0083] Example 3

[0084] The raw material mix ratio of the strain hardening cement-based material using coal gangue as aggregate in this embodiment is shown in Table 3.

[0085] Table 3

[0086]

[0087] A method for preparing a strain-hardening cement-based material using coal gangue as aggregate comprises the following steps:

[0088] (1) Mixing the base material: First, put the cementitious material and coal gangue sand into the mixer and stir for 2 minutes to mix the dry materials evenly. Then slowly add water and then slowly add acrylic acid high-efficiency polycarboxylate water reducer and continue stirring for 2 minutes to obtain a uniform flowing slurry. During the mixing process, care should be taken to clean the solid materials adhering to the mixer wall.

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

[0090] (3) Casting and curing: Cast to half of the mold volume at one time, vibrate on a vibration table for 1 minute, then cast the remaining half for a second time, vibrate again and smooth the surface with a spatula, cover the smoothed surface with a layer of polyethylene film to prevent water loss, perform a first curing at room temperature for 24 hours, then remove the mold, and then perform a second curing on the specimen, and move it to a standard curing room (temperature 20±2℃, relative humidity>95%) for a second curing.

[0091] Example 4

[0092] The raw material mix ratio of the strain hardening cement-based material using coal gangue as aggregate in this embodiment is shown in Table 4.

[0093] Table 4

[0094]

[0095] A method for preparing a strain-hardening cement-based material using coal gangue as aggregate comprises the following steps:

[0096] (1) Mixing the base material: First, put the cementitious material and coal gangue sand into the mixer and stir for 2 minutes to mix the dry materials evenly. Then slowly add water and then slowly add acrylic acid high-efficiency polycarboxylate water reducer and continue stirring for 2 minutes to obtain a uniform flowing slurry. During the mixing process, care should be taken to clean the solid materials adhering to the mixer wall.

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

[0098] (3) Casting and curing: Cast to half of the mold volume at one time, vibrate on a vibration table for 1 minute, then cast the remaining half for a second time, vibrate again and smooth the surface with a spatula, cover the smoothed surface with a layer of polyethylene film to prevent water loss, perform a first curing at room temperature for 24 hours, then remove the mold, and then perform a second curing on the specimen, and move it to a standard curing room (temperature 20±2℃, relative humidity>95%) for a second curing.

[0099] Example 5

[0100] The raw material mix ratio of the strain hardening cement-based material using coal gangue as aggregate in this embodiment is shown in Table 5.

[0101] Table 5

[0102]

[0103]

[0104] A preparation method of a strain hardening cement-based material taking coal gangue as aggregate, according to the following steps:

[0105] (1) Base material stirring: first, the cementitious material and coal gangue sand are put into the stirrer, stirred for 2 min, and the dry materials are uniformly mixed, then water is slowly added, and the acrylic high-efficiency polycarboxylic acid water reducing agent is slowly added and continuously stirred for 2 min to obtain a uniformly flowing slurry; during the stirring process, attention should be paid to cleaning the solid materials adhered to the stirrer wall;

[0106] (2) Incorporate polyvinyl alcohol fiber: control the low-speed operation of the stirrer, slowly sprinkle the polyvinyl alcohol fiber into the flowing slurry, and fully stir to ensure uniform dispersion of the fiber;

[0107] (3) Pouring and curing: pour once to half of the mold volume, vibrate the table for 1 minute, then pour the remaining half, vibrate again, then use a spatula to smooth the surface, cover a layer of polyethylene film on the smooth test piece to prevent water loss, and then remove the mold after 24h of primary curing at room temperature, then the test piece is subjected to secondary curing, and is moved to a standard curing room (temperature 20±2℃, relative humidity >95%) for secondary curing.

[0108] Comparative Example 1

[0109] Comparative Example 1 and Example 1 differ in that the mass ratio of the two particle sizes of coal gangue is different, and the raw material mixing ratio of the strain hardening cement-based material taking coal gangue as aggregate in Comparative Example 1 is shown in Table 6.

[0110] Table 6

[0111]

[0112] A preparation method of a strain hardening cement-based material taking coal gangue as aggregate, according to the following steps:

[0113] (1) Base material stirring: first, the cementitious material and coal gangue sand are put into the stirrer, stirred for 2 min, and the dry materials are uniformly mixed, then water is slowly added, and the acrylic high-efficiency polycarboxylic acid water reducing agent is slowly added and continuously stirred for 2 min to obtain a uniformly flowing slurry; during the stirring process, attention should be paid to cleaning the solid materials adhered to the stirrer wall;

[0114] (2) Incorporate polyvinyl alcohol fiber: control the low-speed operation of the stirrer, slowly sprinkle the polyvinyl alcohol fiber into the flowing slurry, and fully stir to ensure uniform dispersion of the fiber;

[0115] (3) Casting and curing: Cast to half of the mold volume at one time, vibrate on a vibration table for 1 minute, then cast the remaining half for a second time, vibrate again and smooth the surface with a spatula, cover the smoothed surface with a layer of polyethylene film to prevent water loss, perform a first curing at room temperature for 24 hours, then remove the mold, and then perform a second curing on the specimen, and move it to a standard curing room (temperature 20±2℃, relative humidity>95%) for a second curing.

[0116] Comparative Example 2

[0117] The difference between Comparative Example 2 and Example 1 is that the amount of coal gangue with a particle size of 0.075 to 0.15 mm added is greater. The raw material proportion of the strain hardening cement-based 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 cement-based material using coal gangue as aggregate comprises the following steps:

[0121] (1) Mixing the base material: First, put the cementitious material and coal gangue sand into the mixer and stir for 2 minutes to mix the dry materials evenly. Then slowly add water and then slowly add acrylic acid high-efficiency polycarboxylate water reducer and continue stirring for 2 minutes to obtain a uniform flowing slurry. During the mixing process, care should be taken to clean the solid materials adhering to the mixer wall.

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

[0123] (3) Casting and curing: Cast to half of the mold volume at one time, vibrate on a vibration table for 1 minute, then cast the remaining half for a second time, vibrate again and smooth the surface with a spatula, cover the smoothed surface with a layer of polyethylene film to prevent water loss, perform a first curing at room temperature for 24 hours, then remove the mold, and then perform a second curing on the specimen, and move it to a standard curing room (temperature 20±2℃, relative humidity>95%) for a second curing.

[0124] Effect Example 1

[0125] The mechanical properties test method is as follows:

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

[0127] ② Uniaxial tensile test: The tensile test specimens of the embodiment and comparative example were dog-bone type specimens with a tensile gauge length of 80 mm, a width of 30 mm, and a thickness of 14 mm. Six specimens were formed in each group. The specimens were clamped with a homemade fixture on an MTS microcomputer-controlled electronic universal testing machine (maximum capacity 300 kN). Loading was carried out in a displacement control mode of 0.15 mm / min. Extensometers with a gauge length of 80 mm were installed on both sides of the specimen to measure the tensile strain, as shown in FIG. Figure 3 As shown, Figure 4 It is one of the forms of destruction.

[0128] ③ Three-point bending test: The bending test was carried out on an MTS microcomputer-controlled electronic testing machine. The tensile test specimens of the embodiment and the comparative example were set as 160mm×40mm×40mm rectangular parallelepiped 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. The three-point bending test device was used, as shown in FIG. Figure 5 As shown in the figure, during the loading process, the computer automatically collects data such as mid-span deflection, load and time, so as to analyze the flexural mechanical properties of the coal gangue sand strain hardening cement-based material. Figure 6 These are several bending failure modes of the specimen material.

[0129] The mechanical properties of the products obtained in the examples and comparative examples obtained by this method after a secondary curing time of 7 days are shown in Table 8 below.

[0130] Table 8

[0131]

[0132]

[0133] The results show that after 7 days of secondary curing, Examples 1-4 exhibited superior compressive strength and ultimate flexural load compared to Comparative Examples 1-2. In terms of both compressive and flexural performance, Examples 1-4 were significantly superior to Comparative Examples 1-2. It is speculated that Comparative Example 1 suffers from an excessive amount of 0.15-0.3mm coal gangue sand, resulting in poor gradation and reduced mechanical properties of the product. Comparative Example 2 suffers from a high amount of 0.075-0.15mm fine particles, which prevent intergranular interaction and result in decreased compressive strength and ultimate flexural load, leading to reduced mechanical properties. The mechanical properties of the products obtained from the Examples and Comparative Examples obtained using this method after a secondary curing period of 28 days are shown in Table 9 below.

[0134] Table 9

[0135]

[0136] The results show that after 28 days of secondary curing, the compressive strength parameters of Examples 1 to 4 are significantly improved. Compared with Comparative Examples 1 to 2, the difference in compressive strength between Examples 1 to 4 and Comparative Examples 1 to 2 is greater.

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

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

Claims

1. A strain-hardening cement-based material using coal gangue as aggregate, characterized in that: The raw materials are as follows: 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. 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.

2. The strain-hardening cement-based material with coal gangue as aggregate according to claim 1, characterized in that: The composition is composed of the following raw materials in parts by mass: 950-1050 parts of cementitious material, 275-400 parts of coal gangue, 275-400 parts of water, 30-34 parts of fiber material, and 2-20 parts of water reducing agent.

3. The strain-hardening cement-based material with coal gangue as aggregate according to claim 2, characterized in that: The strain-hardening cement-based material with coal gangue as aggregate satisfies at least one of the following conditions: The strain-hardening cement-based material with coal gangue as aggregate is composed of the following raw materials in parts by mass: 1000 parts of cementitious material, 350 parts of coal gangue, 350 parts of water, 32 parts of polyvinyl alcohol fiber material, and 2.9 parts of water reducing agent; When the gangue includes the gangue sand with a particle size of 0.075 to 0.15 mm and the 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); When the coal gangue further includes coal gangue sand with a particle size of 0.3-0.6 mm, the coal gangue sand with a particle size of 0.075-0.15 mm, the coal gangue sand with a particle size of 0.15-0.3 mm and the 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); The gelling material comprises fine active mineral material and cement, and the mass ratio of the fine active mineral material to the cement is 1:(2-3).

4. The strain-hardening cement-based material with coal gangue as aggregate according to claim 3, characterized in that: The strain-hardening cement-based material with coal gangue as aggregate satisfies at least one of the following conditions: the fine active mineral material includes one or more of fly ash, slag powder, metakaolin, silica fume, limestone powder, etc.; The cement includes one or more of Portland cement, aluminate cement, and sulphoaluminate cement; The fiber material includes polyvinyl alcohol fiber and / or polyethylene fiber; the water reducer is a high-efficiency polycarboxylate water reducer; When the coal gangue includes the coal gangue sand with a particle size of 0.075 to 0.15 mm and the coal gangue sand with a particle size of 0.15 to 0.3 mm, the mass ratio of the two is 1:0.11; The coal gangue also includes coal gangue sand with a particle size of 0.3-0.6 mm. The mass ratio of the coal gangue sand with a particle size of 0.075-0.15 mm, the coal gangue sand with a particle size of 0.15-0.3 mm and the coal gangue sand with a particle size of 0.3-0.6 mm is 1:1.2:1.

96.

5. The strain-hardening cement-based material with coal gangue as aggregate according to claim 4, characterized in that: The strain-hardening cement-based material with coal gangue as aggregate satisfies at least one of the following conditions: The fine active mineral material is fly ash; The cement is Portland cement; The polyvinyl alcohol fiber is made by spinning polyvinyl alcohol as raw material; The polyethylene fiber is produced by spinning polyethylene as a raw material.

6. The strain-hardening cement-based material with coal gangue as aggregate according to claim 4, characterized in that: The strain-hardening cement-based material with coal gangue as aggregate satisfies at least one of the following conditions: When the polyvinyl alcohol fiber is used as the fiber material, the diameter of the fiber material is 30 to 50 μm and the length is 9 to 15 mm; When the polyethylene fiber is used as the fiber material, the diameter of the polyethylene fiber is 30 to 50 μm, for example, 40 μm; When the polyethylene fiber is used as the fiber material, the length of the polyethylene fiber is 9 to 15 mm, for example, 12 mm; The high-efficiency polycarboxylate water-reducing agent includes polyhydroxy acid salt.

7. A method for preparing a strain-hardening cement-based material using coal gangue as aggregate according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: (1) Mixing the base material: dry-mixing the cementitious material and the coal gangue, then adding the water to wet-mix the cementitious material, and then adding the water reducing agent to obtain the base material; (2) Incorporating fibers: mixing fibers into the substrate and stirring to obtain a slurry; (3) Casting and curing: Cast the slurry material once, cast it a second time, and then perform curing.

8. A method for preparing a strain-hardening cement-based material using coal gangue as aggregate according to claim 7, characterized in that: The method for preparing the strain-hardening cement-based material using coal gangue as aggregate satisfies at least one of the following conditions: In step (1), the rotation speed of the dry material stirring is 140 rpm, and the stirring time of the dry material is 0.5 min; In step (1), the wet material is stirred at a speed of 140 rpm and for a time of 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 performed until it is evenly dispersed; in step (3), the casting is performed to one-half of the mold volume; In step (3), the first pouring further includes vibrating, and the vibrating is performed using a vibration table; In step (3), half of the remaining volume of the secondary casting mold is used to cast the test piece in layers to ensure dense molding; In step (3), the vibrating step further includes the operations of plastering and coating; In step (3), the curing is carried out at room temperature; In step (3), the curing time is 12 to 48 hours; In step (3), after the curing, secondary curing is also included.

9. A method for preparing a strain-hardening cement-based material using coal gangue as aggregate according to claim 8, characterized in that: The method for preparing the strain-hardening cement-based material using coal gangue as aggregate satisfies at least one of the following conditions: In step (1), the stirring is carried out using a cement mortar mixer, and the stirring speed is 130 to 150 rpm; when the vibration table is used for the vibration, the vibration time is 0.5 to 1.5 minutes; In step (3), the secondary pouring further includes vibrating, and the vibrating is performed using a vibrating table; when the vibrating is performed using the vibrating table, the vibrating time is 0.5 to 1.5 minutes; In step (3), the coating is a polyethylene film to prevent water loss; In step (3), the curing time is 24 hours; In step (3), the secondary curing is to move the product to a standard curing room for curing; In step (3), the secondary curing time is 7 to 28 days; In step (3), the temperature of the secondary curing is 18-22°C.

10. A strain-hardening cement-based material using coal gangue as aggregate, characterized in that: The material is prepared by the method for preparing a strain hardening cement-based material using coal gangue as aggregate according to any one of claims 7 to 9.

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