Gangue-added cement and its preparation process

Abstract

The present application relates to the technical field of building materials, and specifically discloses a coal gangue-blended cement and its preparation process. The coal gangue-blended cement is prepared by including the following raw materials in parts by weight: 20-30 parts of activated coal gangue powder, 50-60 parts of cement clinker, 15-20 parts of slag powder, 1.5-2.5 parts of nano-calcium carbonate, 0.8-1.5 parts of calcium sulfoaluminate, 3-5 parts of a composite curing agent, 4-9 parts of a composite activator, 3-5 parts of water glass, and 0.5-1 part of a water reducer; the activated coal gangue powder is prepared by urea pretreatment, staged calcination, and acid salt activation; the composite curing agent includes silica fume and an organic acid; and the composite activator includes gypsum and triethanolamine. The coal gangue-blended cement prepared in the present application has relatively excellent compressive strength and flexural strength.

Description

Technical Field

[0001] The present application relates to the technical field of building materials, and more specifically, to a cement mixed with coal gangue and a preparation process thereof. Background Art

[0002] Gangue, a solid waste generated during coal mining and processing, has long been difficult to effectively treat. It not only occupies large amounts of land but also poses environmental risks such as spontaneous combustion and soil and water pollution. However, in-depth research has revealed that its primary components include oxides of silicon, aluminum, iron, calcium, and magnesium, along with smaller amounts of carbon, sulfur, and phosphorus. While the composition of gangue varies between regions and coal mines, silicon and aluminum oxides (SiO2 and Al2O3) typically account for over 60%, demonstrating its potential as a raw material for cementitious materials after activation.

[0003] At the same time, cement, a fundamental material in the construction industry, relies on high-temperature calcination of limestone in its production process, resulting in significant energy consumption and CO2 emissions, placing a heavy burden on the environment. Against this backdrop, incorporating coal gangue into cement production or directly preparing gangue-based cementitious materials not only provides efficient utilization of gangue waste, but also reduces energy consumption and CO2 emissions in cement production, achieving the dual goals of waste resource utilization and greening building materials. This has become a key area of ​​research and development in building materials technology.

[0004] The patent application document with publication number CN119263733A discloses a method for preparing a carbonized calcined gangue solid waste-based cementitious material, comprising the following steps: (1) weighing each raw material by weight, ball-milling the ready-mixed concrete waste slag and mixing it with the calcined gangue fine powder to obtain a solid mixture A; (2) soaking the solid mixture A with water, a surfactant, and an organic amine to obtain a solid-liquid mixture B; (3) introducing gas into the solid-liquid mixture B and stirring it, and then drying it to obtain a solid mixture C; (4) mixing the solid mixture C with the gypsum and cement to obtain the carbonized calcined gangue solid waste-based cementitious material.

[0005] In this scheme, when the calcined coal gangue fine powder and ready-mixed concrete waste slag are mixed and then subjected to wet carbonization treatment, the calcium carbonate generated by the reaction of CO2 with Ca(OH)2 in the system easily forms a dense calcium carbonate passivation layer on the surface of the particles, which physically blocks the contact area between the active SiO2 and Al2O3 in the calcined coal gangue fine powder and the subsequent cement hydration product Ca(OH)2, resulting in insufficient pozzolanic reaction; at the same time, after ball milling, a large amount of inert components still exist in the ready-mixed concrete waste slag, which has insufficient chemical compatibility with the cementitious matrix and weak interfacial bonding strength, thereby reducing the compressive strength of the material. Summary of the Invention

[0006] In order to further improve the compressive strength and flexural strength of cement, the present application provides a gangue-added cement and a preparation process thereof.

[0007] In the first aspect, the present application provides a coal gangue cement, which adopts the following technical solution:

[0008] A coal gangue cement is prepared by including the following raw materials in parts by weight:

[0009] 20-30 parts of activated coal gangue powder, 50-60 parts of cement clinker, 15-20 parts of slag powder, 1.5-2.5 parts of nano calcium carbonate, 0.8-1.5 parts of calcium sulfoaluminate, 3-5 parts of composite curing agent, 4-9 parts of composite activator, 3-5 parts of water glass and 0.5-1 part of water reducer;

[0010] The activated coal gangue powder is prepared by urea pretreatment, staged calcination and acid salt activation;

[0011] The composite curing agent includes silica fume and organic acid;

[0012] The composite activator comprises gypsum and triethanolamine.

[0013] In this scheme, activated coal gangue powder is pretreated with urea, calcined in stages, and activated with acid salts to form highly active components (activated alumina Lewis acid sites and high specific surface area nano-SiO2 gel), and enrich sulfate ions, laying the foundation for early catalysis and later enhancement. After mixing with cement clinker and other components: In the early stage, the activated alumina provides Lewis acid sites to adsorb water to generate H + , catalyzing the hydrolysis of C3S, the added nano-calcium carbonate acts as a heterogeneous nucleation site to accelerate the deposition of CSH, while triethanolamine and Ca 2+ The formation of complexes drives the rapid construction of CSH gel, accelerating early strength development. In the middle stage, water glass stimulates the dissociation of the silica-alumina phase in slag, which reacts with the activated gangue powder nano-SiO2 to form a low-calcium-silicon ratio CASH gel. The aluminum phases in the gypsum and cement clinker, as well as the added calcium sulfoaluminate, form needle-shaped ettringite and expansive ettringite crystals, respectively. These crystals, combined with the CASH gel, gradually fill the micron-sized pores, forming an interpenetrating, dense structure. In the later stage, unreacted sulfates in the system (such as gypsum, sodium sulfate, or their transformed phases) slowly dissolve, continuously releasing sulfate ions, driving the residual aluminum phase to form secondary ettringite. Simultaneously, the silica fume in the composite curing agent undergoes secondary hydration, forming CSH gel to seal the nanopores. These two interactions synergistically further densify the structure. Through the interfacial synergy and functional superposition of multiple components at different hydration stages, this system achieves a progressive improvement from early strength stimulation, mid-term structural densification, to late-stage performance enhancement, thereby achieving a synergistic improvement in both the early strength properties and long-term durability of cement-based materials.

[0014] Preferably, the mass concentration of the water glass is 20% to 30%, and the modulus is 2.0 to 2.5.

[0015] Preferably, the method for preparing the activated coal gangue powder comprises the following steps:

[0016] S1: After the coal gangue is crushed, it is evenly mixed with urea, hexamethylenetetramine and water, heated to 80-100°C, and mixed for 60-80 minutes to obtain the pretreated material;

[0017] S2: placing the pretreated material in a calcining furnace, first heating it to 180-220°C in an air atmosphere, keeping it warm for 30-50 minutes, then heating it to 280-350°C in a nitrogen atmosphere, keeping it warm for 60-90 minutes, then heating it to 650-750°C in a mixed atmosphere of ammonia and nitrogen, keeping it warm for 90-120 minutes, cooling it, and grinding it to obtain the calcined material;

[0018] S3: Evenly mix the calcined material with sodium sulfate and calcium sulfate, add water and mix evenly, adjust the pH to 4.0-5.0, heat to 150-170°C, activate for 120-180 minutes, and cool to obtain.

[0019] In this scheme, through the coordination of three stages of pretreatment, staged calcination and salt activation, in the pretreatment stage, urea hydrolysis and calcination initial decomposition products NH3 and HNCO assist in removing organic matter, hexamethylenetetramine pyrolysis under nitrogen atmosphere creates a reducing environment, promotes quartz surface etching, in a mixed atmosphere of ammonia and nitrogen at 650~750℃, the amorphous silicon aluminum phase formed by dehydroxylation of metakaolin undergoes ammonia surface modification, and subsequent hydrolysis can generate highly active, high specific surface area nano-SiO2 gel. In the subsequent salt activation stage, acidic hydrothermal conditions promote further dissolution of aluminum, and react with SO4 2- Combined to form an amorphous basic aluminum sulfate complex (activated alumina precursor), while the ammonium-modified silicon source is hydrolyzed into a high specific surface area nano-SiO2 gel, SO4 2- The activated gangue powder is enriched on the surface of the gel and aluminum phase through physical adsorption or hydrogen bonding. When the activated gangue powder is applied to the cement system, the nano-SiO2 gel acts as an efficient heterogeneous nucleation site to accelerate the precipitation of CSH in the early stage, and the activated alumina catalyzes the hydrolysis of C3S; in the middle stage, the nano-SiO2 reacts with the slag to form CASH gel, and the activated alumina and gypsum form ettringite to fill the pores; in the late stage, the residual sulfate in the system continuously releases SO4 2- , and generate secondary calcium aluminate with C3A, and cooperate with the secondary hydration products of silica fume to compact the structure, ultimately achieving the improvement of cement mechanical properties and durability.

[0020] Preferably, in step S1, the mass ratio of the coal gangue, urea, hexamethylenetetramine and water is 100:(5-8):(0.5-1):(10-15).

[0021] Preferably, in step S3, the mass ratio of the calcined material, sodium sulfate, calcium sulfate and water is 100:(2-3):(2-4):(10-15).

[0022] Preferably, the cement is Portland cement.

[0023] Preferably, the slag powder is blast furnace slag powder.

[0024] Preferably, in the composite activator, the mass ratio of gypsum to triethanolamine is (24-30): (1-1.5).

[0025] In this scheme, sulfate ions produced by the dissolution of gypsum react with C3A to form ettringite, which fills the pores while promoting the dissolution of aluminum ions in the coal gangue; triethanolamine complexes calcium ions, reduces the nucleation barrier of CSH gel, accelerates the hydrolysis of C3S, provides sufficient ions for the formation of ettringite, and synergizes with sulfate to regulate the morphology of CSH gel, making its structure denser.

[0026] Preferably, the composite activator further comprises sodium fluorosilicate, and the amount of the sodium fluorosilicate accounts for 4% to 6% of the total mass of the composite activator.

[0027] In this scheme, sodium fluorosilicate is hydrolyzed to release F - On the one hand, it selectively corrodes the slag glass, releasing active silicon-aluminum phase, providing sufficient material basis for subsequent hydration reaction; on the other hand, F - With Ca in the system 2+ Combined with CaF2, which is slightly soluble in water, these tiny CaF2 crystals are evenly distributed in the cement stone, acting as crystal nuclei and accelerating the nucleation and growth of CSH gel.

[0028] Preferably, in the composite curing agent, the mass ratio of the silica fume to the organic acid is (1-2): (0.5-1).

[0029] Preferably, the organic acid is selected from at least one of citric acid and tartaric acid.

[0030] In this scheme, silica fume fills the pores, and its amorphous SiO2 reacts with Ca(OH)2 to form CSH gel with low calcium-silicon ratio, which further reduces the porosity and optimizes the gel structure; organic acid reacts with Ca(OH)2 through carboxyl groups. 2+ Complexation delays the hydration rate of C3A, avoids early heat release concentration leading to plastic cracking, and provides sufficient time for the pozzolanic reaction of silica fume and the crack-blocking effect of whiskers, so that both can fully exert their filling and reinforcement effects.

[0031] Preferably, the composite curing agent further comprises zinc borate, and the amount of the zinc borate accounts for 2% to 4% of the total mass of the composite curing agent.

[0032] In this scheme, on the one hand, zinc borate can promote the densification construction of the CSH gel network and enhance the integrity and compressive strength of the cementitious system; on the other hand, it can regulate the crystal growth process of cement hydration products, inhibit the formation of coarse Ca(OH)2 crystals, and promote the uniform refinement of crystal size, thereby reducing the porosity of cement paste and improving structural density and impermeability.

[0033] Medium Zn 2+ The [SiO4] tetrahedral network embedded in the CSH gel forms a local [ZnO4] dense structure, which improves the microhardness; its BO3 3- It selectively adsorbs on the Ca(OH)2 crystal surface, inhibits the stacking of OH-layers through steric hindrance effect, and refines the crystal size.

[0034] Preferably, the composite curing agent further comprises sodium gluconate, and the amount of the sodium gluconate accounts for 5% to 7.5% of the total mass of the composite curing agent.

[0035] In this scheme, the hydroxyl and carboxyl groups in the sodium gluconate molecule can react with Ca 2+ The formation of a stable complex, in the early stage, together with the organic acid, delays the rapid hydration of C3A, avoids temperature cracks caused by local overheating, and creates a stable alkaline environment for the continuous hydrolysis of C3S; in the middle stage, as the hydration reaction proceeds, sodium gluconate gradually releases the complexed Ca 2+ , promoting the continuous growth of CSH gel and interweaving with the gel produced by the secondary hydration of silica fume, further filling the pores and improving the structural density.

[0036] Preferably, the coal gangue cement further comprises basalt fiber, and the amount of the basalt fiber is 2 to 4 parts by mass.

[0037] In this solution, the addition of basalt fiber bridges microcracks and disperses stress when subjected to stress, inhibiting crack expansion. During the hardening and shrinkage phase, the fibers offset shrinkage stress through physical constraints, reducing cracking. Furthermore, basalt fiber forms a composite reinforcement system with calcium sulfoaluminate. The calcium sulfoaluminate hydrates to form ettringite, which fills the pores. Its particles interweave with the CSH gel to provide rigid support. The basalt fiber, with its excellent flexibility and high toughness, absorbs energy when deformed under stress. The synergistic effect of these two factors significantly improves the flexural strength and impact resistance of the cement matrix, effectively reducing its brittleness.

[0038] In a second aspect, the present application provides a preparation process for the above-mentioned coal gangue cement, comprising the following steps:

[0039] After evenly mixing the activated coal gangue powder, cement clinker and slag powder, grind for 20 to 40 minutes, then add nano calcium carbonate, calcium sulfoaluminate and composite activator, continue grinding for 20 to 40 minutes, then add part of water glass, mix evenly, then add part of composite curing agent, mix evenly, then add the remaining water glass, mix evenly, then add water reducer and the remaining composite curing agent, mix for 15 to 25 minutes, sieve, and age to obtain the finished product.

[0040] In this scheme, the activated coal gangue powder, cement clinker and slag are first ground evenly, and the particle stacking state is optimized by matching the particle size gradient of different materials. At the same time, the slag glass structure is activated by mechanical force to expose more active sites. Then, nano-calcium carbonate, calcium sulfoaluminate, etc. are added and continued to grind, so that the highly active gel particles are evenly distributed to form a heterogeneous nucleation network, while avoiding hydration abnormalities caused by excessive grinding of calcium sulfoaluminate. When adding water glass and composite curing agent in steps, the first water glass added pre-wet the particle surface and preliminarily stimulates the activity of the slag, and cooperates with organic acid to regulate the early hydration rate of cement clinker; the second addition of water glass strengthens the aluminum phase excitation effect, and finally improves the rheological properties of the slurry through the synergistic effect of silica fume and water reducer. After aging treatment, the water glass penetrates into the pores of the particles to complete the pre-excitation reaction, and the water reducer reconstructs the adsorption layer on the particle surface.

[0041] Preferably, after adding the water reducing agent, the method further includes adding basalt fiber.

[0042] Preferably, the basalt fiber undergoes the following pretreatment steps before being added:

[0043] The basalt fiber is immersed in a silane coupling agent solution with a mass concentration of 0.5% to 1.0%, the pH is adjusted to 4 to 5, the temperature is raised to 80 to 100°C, the temperature is kept for 10 to 20 minutes, the solid-liquid separation is performed, the solution is washed, and the solution is dried to obtain the basalt fiber.

[0044] The silane coupling agent solution comprises a silane coupling agent, ethanol and water.

[0045] In summary, this application has the following beneficial effects:

[0046] 1. This application activates the gangue to generate nano-SiO2 gel and activated alumina, laying the foundation for early catalysis and later enhancement. Under the synergistic action of multiple components, nano-calcium carbonate and triethanolamine accelerate the deposition of CSH gel in the early stage, water glass and gypsum drive the secondary hydration of slag and gangue to fill the pores in the middle stage, and silica fume and activated gangue functional groups continue to compact the structure in the late stage, achieving synergistic growth of strength in the early, middle and late stages.

[0047] 2. This application prefers sodium fluorosilicate and zinc borate to regulate the early hydration rate, and citric acid and sodium gluconate to balance the setting time to avoid early cracking; basalt fiber bridges microcracks and restrains shrinkage, forming a rigid-flexible composite reinforcement system with calcium sulfoaluminate, significantly improving the subsequent flexural strength and toughness of the substrate. DETAILED DESCRIPTION

[0048] The present application is further described in detail below with reference to the embodiments.

[0049] Gangue: loss on ignition is about 12.75%, silicon dioxide 56.11%, aluminum oxide 16.03%, iron oxide 6.54%, calcium oxide 2.40%, magnesium oxide 3.12%;

[0050] Blast furnace slag powder: loss on ignition is about 1%, silicon dioxide 34.25%, aluminum oxide 14.53%, calcium oxide 41.02%, magnesium oxide 5.15%, iron oxide 0.67%, and manganese oxide 0.53%.

[0051] The particle size distribution of basalt fiber is 3~5mm.

[0052] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0053] Preparation Examples 1-3 Activated Gangue Powder

[0054] Preparation Example 1

[0055] The preparation method of activated coal gangue powder in this preparation example comprises the following steps:

[0056] S1: After the coal gangue is crushed, it is passed through an 80-mesh standard sieve, 800 g of the sieve residue is taken and placed in a reactor, and then a mixture of 40 g of urea, 4 g of hexamethylenetetramine and 80 g of water is added, and the mixture is stirred and mixed evenly. The mixture is heated to 80° C. and stirred and mixed for 80 minutes to obtain a pretreated material;

[0057] S2: placing the pretreated material in a calcining furnace, continuously introducing air at 5 L / min, and heating it to 180°C at 3°C / min, holding it for 50 minutes, then introducing nitrogen at 5 L / min for 5 minutes, keeping the nitrogen introduction rate unchanged, heating it to 280°C at 3°C / min, holding it for 90 minutes, then introducing a mixed gas of nitrogen and ammonia with a volume ratio of 95:5 at 5 L / min, and heating it to 650°C at 5°C / min, holding it for 120 minutes, naturally cooling it to room temperature, and grinding it until it completely passes through an 80-mesh standard sieve to obtain a calcined material;

[0058] S3: 600 g of the calcined material was placed in a high-pressure reactor, and a mixture of 12 g of sodium sulfate, 12 g of calcium sulfate and 60 g of water was added. After stirring and mixing evenly, the pH was adjusted to 5.0 with 10% by mass dilute sulfuric acid. The mixture was heated to 150°C and pressured to 0.6 MPa for activation for 180 min. The mixture was naturally cooled to room temperature, placed in a blast drying oven, dried to constant weight at 60°C, and ground to pass through a 100-mesh standard sieve to obtain activated coal gangue powder.

[0059] Preparation Example 2

[0060] The preparation method of activated coal gangue powder in this preparation example comprises the following steps:

[0061] S1: After the coal gangue is crushed, it is passed through an 80-mesh standard sieve, 800 g of the sieve residue is taken and placed in a reactor, and then a mixture of 64 g of urea, 8 g of hexamethylenetetramine and 120 g of water is added, and the mixture is stirred and mixed evenly. The mixture is heated to 100° C. and stirred and mixed for 60 minutes to obtain a pretreated material;

[0062] S2: placing the pretreated material in a calcining furnace, continuously introducing air at 5 L / min, and heating it to 220°C at 3°C / min, holding it for 30 minutes, then introducing nitrogen at 5 L / min for 5 minutes, keeping the nitrogen introduction rate unchanged, continuing to raise the temperature to 350°C at 3°C / min, holding it for 60 minutes, then introducing a mixed gas of nitrogen and ammonia with a volume ratio of 90:10 at 5 L / min, and heating it to 750°C at 5°C / min, holding it for 90 minutes, naturally cooling it to room temperature, and grinding it until it completely passes through an 80-mesh standard sieve to obtain a calcined material;

[0063] S3: 600 g of the calcined material was placed in a high-pressure reactor, and a mixture of 18 g of sodium sulfate, 24 g of calcium sulfate and 90 g of water was added. After stirring and mixing evenly, the pH was adjusted to 4.0 with 10% by mass dilute sulfuric acid. The mixture was heated to 170°C and pressured to 0.6 MPa for activation for 120 min. The mixture was naturally cooled to room temperature, placed in a blast drying oven, dried to constant weight at 60°C, and ground until it completely passed through a 100-mesh standard sieve to obtain activated coal gangue powder.

[0064] Preparation Example 3

[0065] The preparation method of activated coal gangue powder in this preparation example comprises the following steps:

[0066] S1: After the coal gangue is crushed, it is passed through an 80-mesh standard sieve, 800 g of the sieve residue is taken and placed in a reactor, and then a mixture of 50 g of urea, 6 g of hexamethylenetetramine and 100 g of water is added, and the mixture is stirred and mixed evenly. The mixture is heated to 90° C. and stirred and mixed for 70 minutes to obtain a pretreated material;

[0067] S2: The pretreated material is placed in a calcining furnace, air is continuously introduced at 5 L / min, and the temperature is increased at 3°C / min to 200°C, and the temperature is kept at this temperature for 40 minutes. Then, nitrogen is introduced at 5 L / min for 5 minutes, and the nitrogen introduction rate is kept constant. The temperature is further increased at 3°C / min to 300°C, and the temperature is kept at this temperature for 80 minutes. Then, a mixed gas of nitrogen and ammonia with a volume ratio of 90:10 is introduced at 5 L / min, and the temperature is increased at 5°C / min to 700°C, and the temperature is kept at this temperature for 110 minutes. The material is naturally cooled to room temperature and ground until it completely passes through an 80-mesh standard sieve to obtain a calcined material.

[0068] S3: 600 g of the calcined material was placed in a high-pressure reactor, and a mixture of 15 g of sodium sulfate, 18 g of calcium sulfate and 72 g of water was added. After stirring and mixing evenly, the pH was adjusted to 4.5 with 10% by mass dilute sulfuric acid. The mixture was heated to 160°C and pressured to 0.6 MPa for activation for 150 min. The mixture was naturally cooled to room temperature, placed in a blast drying oven, dried to constant weight at 60°C, and ground to pass through a 100-mesh standard sieve to obtain activated coal gangue powder.

[0069] Example 1

[0070] The coal gangue cement of this embodiment is prepared from the following raw materials:

[0071] 200g activated coal gangue powder, 500g Portland cement clinker, 150g blast furnace slag powder, 15g nano calcium carbonate, 8g calcium sulfoaluminate, 30g composite curing agent, 40g composite activator, 30g water glass and 5g polycarboxylate water reducer.

[0072] Activated coal gangue powder was obtained from Preparation Example 1;

[0073] The composite curing agent includes 20g of silica fume and 10g of citric acid;

[0074] The composite activator includes 38.4 g of gypsum and 1.6 g of triethanolamine;

[0075] The mass concentration of water glass is 20% and the modulus is 2.0;

[0076] Portland cement clinker and blast furnace slag powder should be passed through a 100-mesh standard sieve before use.

[0077] The preparation process of the coal gangue cement of this embodiment comprises the following steps:

[0078] After the activated coal gangue powder, silicate cement clinker and blast furnace slag powder are evenly mixed, they are added to the ball mill with a ball-to-material ratio of 3:1, a steel ball diameter distribution of 3~5mm, and a speed of 300rpm. Grind for 20min, then add triethanolamine, nano calcium carbonate, calcium sulfoaluminate and gypsum, continue grinding for 20min, move into the mixer, atomize and spray water glass (mix 15g of water glass with 5g of water and then atomize and spray). After the atomization is completed, first disperse it at a speed of 200rpm for 5min, then add citric acid, continue to disperse it for 5min, and then atomize and add the remaining water glass (mix 15g of water glass and 5g of water and then atomize and spray). After the atomization is completed, first disperse it at a speed of 200rpm for 5min, then add silica fume and polycarboxylate water reducer, and then adjust the speed to 80rpm, mix for 15min, pass through an 80-mesh standard sieve, take the undersize, seal and age for 6h to obtain the finished product.

[0079] Example 2

[0080] The coal gangue cement of this embodiment is prepared from the following raw materials:

[0081] 300g activated coal gangue powder, 600g Portland cement clinker, 200g blast furnace slag powder, 25g nano calcium carbonate, 15g calcium sulfoaluminate, 50g composite curing agent, 90g composite activator, 50g water glass and 10g polycarboxylate water reducer.

[0082] Activated coal gangue powder comes from Preparation Example 2;

[0083] The composite curing agent includes 33.3 g of silica fume and 16.7 g of citric acid;

[0084] The composite activator includes 85.7 g of gypsum and 4.3 g of triethanolamine;

[0085] The mass concentration of water glass is 30% and the modulus is 2.5;

[0086] Portland cement clinker and blast furnace slag powder should be passed through a 100-mesh standard sieve before use.

[0087] The preparation process of the coal gangue cement of this embodiment comprises the following steps:

[0088] After the activated coal gangue powder, silicate cement clinker and blast furnace slag powder are evenly mixed, they are added to the ball mill with a ball-to-material ratio of 3:1, a steel ball diameter distribution of 3~5mm, and a speed of 300rpm. Grind for 40min, then add triethanolamine, nano calcium carbonate, calcium sulfoaluminate and gypsum, continue grinding for 40min, move into the mixer, atomize and spray part of the water glass (mix 25g of water glass with 8g of water and then atomize and spray). After the atomization is completed, first disperse it at a speed of 200rpm for 5min, then add citric acid, continue to disperse it for 5min, and then atomize and add the remaining water glass (mix 25g of water glass and 8g of water and then atomize and spray it), stir while spraying, and after the atomization is completed, first disperse it at a speed of 200rpm for 5min, then add silica fume and polycarboxylate water reducer, and then adjust the speed to 80rpm, mix for 25min, pass through an 80-mesh standard sieve, take the undersize, seal and age for 10h to obtain the finished product.

[0089] Example 3

[0090] The coal gangue cement of this embodiment is prepared from the following raw materials:

[0091] 260g activated coal gangue powder, 550g Portland cement clinker, 175g blast furnace slag powder, 20g nano calcium carbonate, 12g calcium sulfoaluminate, 40g composite curing agent, 65g composite activator, 40g water glass and 7g polycarboxylate water reducer.

[0092] Activated coal gangue powder is from Preparation Example 3;

[0093] The composite curing agent includes 27g silica fume, 10g citric acid, and 3g tartaric acid;

[0094] The composite activator includes 62.2 g of gypsum and 2.8 g of triethanolamine;

[0095] The mass concentration of water glass is 25% and the modulus is 2.2;

[0096] Portland cement clinker and blast furnace slag powder should be passed through a 100-mesh standard sieve before use.

[0097] The preparation process of the coal gangue cement of this embodiment comprises the following steps:

[0098] After the activated coal gangue powder, silicate cement clinker and blast furnace slag powder are evenly mixed, they are added to the ball mill with a ball-to-material ratio of 3:1, a steel ball diameter distribution of 3~5mm, and a speed of 300rpm. Grind for 30min, then add triethanolamine, nano calcium carbonate, calcium sulfoaluminate and gypsum, continue grinding for 30min, move into the mixer, and spray part of the water glass by atomization (mix 20g of water glass with 6g of water and spray it by atomization). After the atomization is completed, first disperse it at a speed of 200rpm for 5min, then add citric acid and tartaric acid, continue to disperse it for 5min, and then add the remaining water glass by secondary atomization (mix 20g of water glass and 6g of water and then spray it by atomization). Stir while spraying. After the atomization is completed, first disperse it at a speed of 200rpm for 5min, then add silica fume and polycarboxylate water reducer, and then adjust the speed to 80rpm, mix for 20min, pass through an 80-mesh standard sieve, take the undersize, seal and age for 8h to obtain the finished product.

[0099] Example 4

[0100] The difference between this embodiment and embodiment 3 is that:

[0101] The dosage of composite stimulant is 67.71g;

[0102] The composite activator includes 62.2 g of gypsum, 2.8 g of triethanolamine and 2.71 g of sodium fluorosilicate.

[0103] In the preparation process of this embodiment, sodium fluorosilicate is added after gypsum is added.

[0104] Other details are the same as in Example 3.

[0105] Example 5

[0106] The difference between this embodiment and embodiment 4 is that:

[0107] The dosage of composite stimulant is 69.15g;

[0108] The composite activator includes 62.2 g of gypsum, 2.8 g of triethanolamine and 4.15 g of sodium fluorosilicate.

[0109] The amount of composite curing agent used is 40.82g;

[0110] The composite curing agent includes 27g of silica fume, 10g of citric acid, 3g of tartaric acid and 0.82g of zinc borate.

[0111] In the preparation process of this embodiment, zinc borate is added after tartaric acid is added.

[0112] Other details are the same as in Example 4.

[0113] Example 6

[0114] The difference between this embodiment and embodiment 5 is that:

[0115] The amount of composite curing agent used is 43.96g;

[0116] The composite curing agent includes 27g of silica fume, 10g of citric acid, 3g of tartaric acid, 1.76g of zinc borate and 2.20g of sodium gluconate.

[0117] In the preparation process of this embodiment, sodium gluconate is added after adding silica fume.

[0118] Other details are the same as in Example 5.

[0119] Example 7

[0120] The difference between this embodiment and embodiment 6 is that:

[0121] The gangue cement also includes 20g of basalt fiber;

[0122] The amount of composite curing agent used is 45.20g;

[0123] The composite curing agent includes 27g of silica fume, 10g of citric acid, 3g of tartaric acid, 1.81g of zinc borate and 3.39g of sodium gluconate.

[0124] In the preparation process of this embodiment, basalt fiber is added after the polycarboxylate water-reducing agent is added.

[0125] Before use, basalt fiber undergoes the following processing steps:

[0126] Immerse 20 g of basalt fiber in 100 mL of a silane coupling agent solution with a mass concentration of 0.5%, stir and mix evenly, adjust the pH to 4 with 5% dilute sulfuric acid, heat to 80°C, keep warm for 20 minutes, filter, wash twice with deionized water, transfer to a 60°C forced air drying oven, and dry to constant weight to obtain the obtained product.

[0127] The silane coupling agent includes silane coupling agent KH550, ethanol and water, and the volume ratio of ethanol to water is 1:1.

[0128] Other details are the same as in Example 6.

[0129] Example 8

[0130] The difference between this embodiment and embodiment 7 is that:

[0131] The gangue cement also includes 40g of basalt fiber;

[0132] Before use, basalt fiber undergoes the following processing steps:

[0133] 40 g of basalt fiber was immersed in 200 mL of a silane coupling agent solution with a mass concentration of 1%. After stirring and mixing evenly, the pH was adjusted to 5 with 5% dilute sulfuric acid, and the temperature was raised to 80°C and kept warm for 10 minutes. The fiber was filtered, washed twice with deionized water, and transferred to a 60°C forced air drying oven and dried to constant weight.

[0134] The silane coupling agent includes silane coupling agent KH550, ethanol and water, and the volume ratio of ethanol to water is 1:0.8.

[0135] Other details are the same as in Example 7.

[0136] Comparative Example 1

[0137] The difference between this comparative example and Example 1 is:

[0138] No calcium sulfoaluminate was added;

[0139] Other details are the same as in Example 1.

[0140] Comparative Example 2

[0141] The difference between this comparative example and Example 1 is:

[0142] The preparation method of activated coal gangue powder comprises the following steps:

[0143] S1: After the coal gangue is crushed, it is passed through an 80-mesh standard sieve, 600 g of the sieve residue is taken, and placed in a reactor. Then, a mixture of 30 g of urea, 3 g of hexamethylenetetramine and 60 g of water is added, and the mixture is stirred and mixed evenly. The mixture is heated to 80° C. and stirred and mixed for 80 minutes to obtain a pretreated material;

[0144] S2: The pretreated material is placed in a calcining furnace, air is continuously introduced at 5 L / min, and the temperature is increased to 180°C at 3°C / min, and kept warm for 50 minutes. Then, nitrogen is introduced at 5 L / min for 5 minutes, and the nitrogen introduction rate is kept unchanged. The temperature is increased to 280°C at 3°C / min, and kept warm for 90 minutes. Then, a mixed gas of nitrogen and ammonia with a volume ratio of 95:5 is introduced at 5 L / min, and the temperature is increased to 650°C at 5°C / min, and kept warm for 120 minutes. Naturally cool to room temperature, grind until it completely passes through a 100-mesh standard sieve, and obtain activated coal gangue powder.

[0145] Other details are the same as in Example 1.

[0146] Comparative Example 3

[0147] The difference between this comparative example and Example 1 is:

[0148] The preparation method of activated coal gangue powder comprises the following steps:

[0149] After the coal gangue is crushed, it is passed through an 80-mesh standard sieve. 600 g of the sieve residue is taken and placed in a calcining furnace. Air is continuously introduced at 5 L / min, and the temperature is increased to 180°C at 3°C / min, and kept warm for 50 minutes. Then, nitrogen is introduced at 5 L / min for 5 minutes, and the nitrogen introduction rate is kept unchanged. The temperature is increased to 280°C at 3°C / min and kept warm for 90 minutes. Then, a mixed gas of nitrogen and ammonia with a volume ratio of 95:5 is introduced at 5 L / min, and the temperature is increased to 650°C at 5°C / min. The temperature is kept warm for 120 minutes. The mixture is naturally cooled to room temperature and ground until it completely passes through a 100-mesh standard sieve to obtain activated coal gangue powder.

[0150] Other details are the same as in Example 1.

[0151] Comparative Example 4

[0152] The difference between this comparative example and Example 1 is:

[0153] The composite curing agent is 30g of silica fume;

[0154] Other details are the same as in Example 1.

[0155] Comparative Example 5

[0156] The difference between this comparative example and Example 1 is:

[0157] The composite activator is 40g of gypsum;

[0158] Other details are the same as in Example 1.

[0159] Performance testing

[0160] The properties of the gangue cements prepared in Examples 1 to 8 and Comparative Examples 1 to 5 were tested according to the following method:

[0161] Compressive strength and flexural strength: According to GB / T 17671-2021 "Test method for strength of cement mortar (ISO method)", cement mortar was prepared with a water-cement ratio of 0.5 (cement: standard sand = 1:3). The mortar fluidity was controlled at 155 mm. The specimens were formed into 40 mm × 40 mm × 160 mm prisms and cured to the test age.

[0162] Initial setting time: Tested in accordance with GB / T 1346-2011 "Test methods for water consumption, setting time and soundness of cement at standard consistency", and the water consumption at standard consistency is recorded simultaneously (accurate to 0.1mL);

[0163] Porosity: The pore structure of 28-day-old specimens was determined using mercury intrusion porosimetry at a pressure of 330 MPa. The specimens were prepared by grinding the crushed pieces to a particle size no greater than 2 mm and then drying them at 50°C in a vacuum oven to constant weight.

[0164] The specific test results are shown in Table 1 below.

[0165] Table 1 Performance test data of coal gangue cement prepared in Examples 1 to 8 and Comparative Examples 1 to 5

[0166]

[0167] Combined with the performance test data in Table 1, analysis of Examples 1 to 8 and Comparative Examples 1 to 5 shows that:

[0168] From Examples 1 to 8 and Comparative Examples 1 to 5, it can be seen that the addition of calcium sulfoaluminate rapidly hydrates to form an interwoven framework of calcium sulfate, which synergistically accelerates the early hydration process with the triethanolamine in the composite activator, forming a solid strength base. After pretreatment, staged calcination, and activation with an acidic salt solution, the internal silicon-aluminum phase of the coal gangue is converted into highly active nano-SiO2 gel and amorphous basic aluminum sulfate complex, which together with the silica fume in the composite curing agent provide active sites for continuous hydration. In the alkaline environment of the composite activator, it promotes the uniform formation of CSH gel and densification of the network structure, achieving a synergistic improvement in strength at all ages. Sodium fluorosilicate regulates the size of hydration products by forming calcium fluoride crystal nuclei and refines the CSH gel network. Zinc borate inhibits chloride ion penetration and alkali-aggregate reaction, maintaining a stable hydration environment and improving durability. Sodium gluconate, as a retarder, delays the peak time of hydration exotherm, reduces temperature stress, and promotes the orderly deposition and optimized crystal growth of CSH gel. The compounded basalt particles improve the development path of microcracks through the bridging effect. While improving the flexural strength, it enhances the structural density through the filling effect without significantly diluting the concentration of the cementitious material, ensuring the stability of the compressive strength.

[0169] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A cement mixed with coal gangue, characterized in that: The invention is prepared by comprising the following raw materials in parts by weight: 20-30 parts of activated coal gangue powder, 50-60 parts of cement clinker, 15-20 parts of slag powder, 1.5-2.5 parts of nano calcium carbonate, 0.8-1.5 parts of calcium sulfoaluminate, 3-5 parts of composite curing agent, 4-9 parts of composite activator, 3-5 parts of water glass and 0.5-1 part of water reducer; The steps of preparing activated coal gangue powder include: S1: crushing the coal gangue, mixing it evenly with urea, hexamethylenetetramine and water, heating it to 80-100°C, and mixing it for 60-80 minutes to obtain a pretreated material; S2: placing the pretreated material in a calcining furnace, first heating it to 180-220°C in an air atmosphere, keeping it warm for 30-50 minutes, then heating it to 280-350°C in a nitrogen atmosphere, keeping it warm for 60-90 minutes, then heating it to 650-750°C in a mixed atmosphere of ammonia and nitrogen, keeping it warm for 90-120 minutes, cooling it, and grinding it to obtain a calcined material; S3: mixing the calcined material with sodium sulfate and calcium sulfate, adding water and mixing it evenly, adjusting the pH to 4.0-5.0, heating it to 150-170°C, activating it for 120-180 minutes, and cooling it to obtain activated coal gangue powder; The composite curing agent includes silica fume and organic acid; The composite activator comprises gypsum and triethanolamine.

2. The coal gangue cement according to claim 1, characterized in that: In step S1, the mass ratio of the coal gangue, urea, hexamethylenetetramine and water is 100:(5-8):(0.5-1):(10-15).

3. The coal gangue cement according to claim 1, characterized in that: In step S3, the mass ratio of the calcined material, sodium sulfate, calcium sulfate and water is 100:(2-3):(2-4):(10-15).

4. The coal gangue cement according to claim 1, characterized in that: The composite activator further comprises sodium fluorosilicate, and the amount of the sodium fluorosilicate accounts for 4% to 6% of the total mass of the composite activator.

5. The coal gangue cement according to claim 1, characterized in that: The organic acid is selected from at least one of citric acid and tartaric acid.

6. The coal gangue cement according to claim 1, characterized in that: The composite curing agent further comprises zinc borate, and the amount of the zinc borate accounts for 2% to 4% of the total mass of the composite curing agent.

7. The coal gangue cement according to claim 1, characterized in that: The coal gangue cement further comprises basalt fiber, and the amount of the basalt fiber is 2 to 4 parts by mass.

8. A process for preparing cement blended with coal gangue according to any one of claims 1 to 7, characterized in that: The steps include: After evenly mixing the activated coal gangue powder, cement clinker and slag powder, grind for 20 to 40 minutes, then add nano calcium carbonate, calcium sulfoaluminate and composite activator, continue grinding for 20 to 40 minutes, then add part of water glass, mix evenly, then add part of composite curing agent, mix evenly, then add the remaining water glass, mix evenly, then add water reducer and the remaining composite curing agent, mix for 15 to 25 minutes, sieve, and age to obtain the finished product.

9. The process for preparing cement blended with coal gangue according to claim 8, characterized in that: After adding the water reducing agent, the process also includes the step of adding basalt fiber.

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