Preparation method and application of coal gangue-based ultra-high performance concrete UHPC for wet joint

Abstract

The invention belongs to the technical field of concrete, and particularly relates to a preparation method and application of coal gangue-based ultra-high performance concrete UHPC for wet joints. Through composite gradient activation of calcination and ball milling and alkali-lithium salt synergistic excitation, efficient dissolution of active components of the coal gangue is achieved, the 3d compressive strength of the UHPC material is larger than or equal to 120 MPa, the 28d compressive strength of the UHPC material is larger than or equal to 150 MPa, and the UHPC material is improved compared with a traditional coal gangue-based material; meanwhile, through the synergistic effect of nano SiO2 / graphene oxide multi-scale reinforcement and steel fiber toughening, the interface bonding strength reaches 12-14 MPa, the chloride ion diffusion coefficient is smaller than 1.5 * 10 <-12 > m < 2 > / s, and the problems of wet joint interface debonding and durability degradation are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of concrete, and particularly relates to a preparation method and application of coal gangue-based ultra-high performance concrete (UHPC) for wet joints. Background Art

[0002] With the wide application of ultra-high performance concrete (UHPC) in the fields of prefabricated buildings, bridge wet joints, etc., its advantages such as high strength and high durability have significantly improved the safety and service life of engineering structures. However, the traditional UHPC technology still has the following key bottlenecks, which restrict its large-scale application in wet joint scenarios.

[0003] Current UHPC mainly relies on high-purity Portland cement, silica fume, quartz sand and other high-quality raw materials, resulting in high material costs. At the same time, the CO2 emissions generated during cement production and the exploitation of quartz sand cause ecological environment damage. Although some studies have tried to incorporate fly ash, slag and other solid wastes to replace cement, their low activity makes it difficult to meet the strength requirements of UHPC, and the solid waste content is generally less than 30%, with low resource utilization efficiency.

[0004] As a weak link in prefabricated structures, wet joints are prone to microcracks due to the shrinkage difference between new and old concretes. Although traditional UHPC improves the density by reducing the water-binder ratio, its high autogenous shrinkage rate poses a risk of interface debonding under restraint conditions. Existing technologies mostly use external curing or expansive agents to compensate for shrinkage, but external curing is difficult to penetrate deep into the joints, while expansive agents (such as CaO-based) are prone to cause a reduction in later strength, seriously threatening the durability of the structure.

[0005] As a solid waste associated with coal mining, coal gangue has the potential for gelling activity due to its Al2O3 and SiO2 components. However, in existing technologies, coal gangue is mostly treated by single calcination or mechanical grinding, and the resulting micro-powder has a low activity index, and the residual Fe2O3 and carbon impurities will hinder the hydration reaction and cause volume instability. Although existing technologies have proposed coal gangue-Portland cement composite cementitious materials, their coal gangue content is low, and the problem of weakening of the interfacial transition zone (ITZ) has not been solved, and the chloride ion permeability resistance is far lower than the UHPC standard.

[0006] Although traditional alkali activators (such as NaOH, water glass) can improve the activity of coal gangue, their strong alkalinity causes a sudden drop in the fluidity of the slurry and aggravates autogenous shrinkage.

[0007] Therefore, there is an urgent need to obtain a preparation method of coal gangue-based ultra-high performance concrete (UHPC) and apply it to wet joints of buildings. Summary of the Invention

[0008] (I) Technical Problems to be Solved In view of the above-mentioned disadvantages and deficiencies of the prior art, the present invention provides a preparation method and application of coal gangue-based ultra-high performance concrete (UHPC) for wet joints, which solves the technical problems of weakening of the interfacial transition zone (ITZ) and chloride ion permeability lower than the UHPC standard.

[0009] (II) Technical Solution In the first aspect, the present invention provides a preparation method of coal gangue-based ultra-high performance concrete (UHPC) for wet joints, comprising the following steps: S1. Dry-mix cement, coal gangue powder and silica fume until uniform to form a mixture; S2. Spray a composite nano-dispersion into the mixture and continue stirring to form a gelling material; the composite nano-dispersion is an aqueous dispersion containing active nano-SiO2; S3. Add a mixed activator containing sodium sulfate and lithium hydroxide to the gelling material; S4. Add an aggregate mixture to the gelling material, then sequentially add an aqueous solution containing a composite water reducer and a polyacrylic acid-based superabsorbent polymer (SAP), and stir at 100 - 150 rpm to form a concrete mixture, controlling its slump flow to reach 760 ± 20 mm.

[0010] Optionally, in S1, by mass, the mixture comprises 40 - 60 parts of cement, 20 - 40 parts of coal gangue powder, and 10 - 30 parts of silica fume.

[0011] Optionally, in S1, the preparation method of the coal gangue powder comprises the following steps: Feed the crushed coal gangue particles into a magnetic separator, and after separation, the residual amount of Fe2O3 ≤ 0.8%; Calcinate the magnetically separated coal gangue at 800 - 900 °C to obtain a calcined product of γ-Al2O3 and amorphous SiO2 active intermediate; Grind the calcined product with zirconia grinding balls at 200 - 300 rpm and sieve to obtain coal gangue powder.

[0012] Optionally, in S2, the preparation method of the composite nano-dispersion comprises the steps of: Mix amino-functionalized nano-SiO2 and glycerol, and ultrasonically disperse until no visible agglomerates are formed to form a nano-SiO2 suspension; Add graphene oxide to deionized water, ultrasonically treat and then mix with the nano-SiO2 suspension to form a composite nano-dispersion.

[0013] Optionally, in S4, the aggregate mixture is a composition of coal gangue manufactured sand, quartz sand and steel fiber.

[0014] Optionally, in S4, the composite water reducer is a copolymer water reducer of polycarboxylic acid - lignosulfonate.

[0015] Optionally, in S4, the SAP is obtained by soaking dry SAP particles in deionized water, filtering, and then drying to a moisture content of 30%.

[0016] In a second aspect, the application of the coal gangue-based ultra-high performance concrete UHPC obtained by the preparation method according to the first aspect in the closure section of a bridge, the bridge deck paving, the expansion joint, and the wet joint.

[0017] Optionally, the coal gangue-based ultra-high performance concrete UHPC is suitable for an environment with a temperature of 10 - 40°C and a humidity of 50 - 85%.

[0018] (III) Beneficial effects The preparation method of the coal gangue-based ultra-high performance concrete UHPC of the present invention realizes the efficient dissolution of the active components of coal gangue through the composite gradient activation of calcination and ball milling and the synergistic excitation of alkali-lithium salts, so that the 3d compressive strength of the material is ≥120 MPa and the 28d strength is ≥150 MPa, which is improved compared with traditional coal gangue-based materials; at the same time, the multi-scale reinforcement of nano-SiO2 / graphene oxide and the synergistic toughening of steel fibers result in an interfacial bonding strength of 12 - 14 MPa and a chloride ion diffusion coefficient < 1.5×10 -12 m 2 / s, solving the problems of interfacial debonding and durability deterioration of wet joints.

[0019] The preparation method of the coal gangue-based ultra-high performance concrete UHPC of the present invention uses coal gangue as the core raw material, achieving a solid waste content > 85%, reducing the cement consumption and carbon emissions compared with traditional UHPC; the calcination process simultaneously removes Fe2O3 and carbon impurities in coal gangue, avoiding secondary pollution. Specific embodiments

[0020] In order to better explain the present invention for easy understanding, the following specific embodiments will describe the present invention in detail.

[0021] The principle of action and function of the coal gangue of the present invention are described as follows: The composite activation treatment of the coal gangue can improve its activity and fineness. Through high-temperature calcination at 850°C, layered silicate minerals such as kaolinite (Al2O3·2SiO2·2H2O) in the coal gangue are dehydrated and decomposed, transformed into amorphous Al2O3 and SiO2, and the activity is greatly improved; the ultra-fine powder fills the gaps between cement particles, reduces the porosity, and improves the density of the cementitious system; it oxidizes and burns at high temperature, reducing the carbon content of the residual carbon and avoiding interference with the cementitious reaction.

[0022] The planetary ball mill pulverizes the calcined product to D50 = 1.2 μm, increasing the specific surface area and exposing more reaction interfaces; at the same time, the mechanical force causes microcracks and broken bonds on the particle surface, promoting chemical bonding with the alkaline activator.

[0023] The coal gangue micro-powder and nano-materials (the compound of nano-silica and graphene oxide) of the present invention can enhance the interfacial transition zone, and the specific description is as follows: Through the coordination bonding of the amino group (-NH2) in the amino-functionalized nano-SiO2 with Ca in the cementitious matrix, the thickness of the interfacial transition zone (ITZ) is decreased; the nano-particles serve as the nucleation sites of the gel, accelerating the pozzolanic reaction of the coal gangue micro-powder (i.e., the reaction rate is increased); the agglomeration of the nano-particles is prevented by the modification of the amino group in the amino-functionalized nano-SiO2, ensuring uniform distribution in the slurry. 2+ The graphene oxide sheet structure (thickness < 5 nm) bridges micro-cracks through the "pulling effect", increasing the fracture toughness of the material; the graphene sheets form a three-dimensional conductive path, which can monitor the stress and strain states of the wet joint in real time (the change rate of resistance is linearly related to the strain).

[0024] In short, for the amorphous SiO2 in the coal gangue, its structure can be destroyed by mechanical grinding (ball milling) and high-temperature calcination, increasing the specific surface area and active sites; while the added nano-SiO2 can be better dispersed and participate in the formation of C-S-H gel after amino-functionalization, playing a nucleation effect. At the same time, the alkaline environment provided by chemical activators (such as NaOH, Ca(OH)2) can promote the dissolution and reaction of SiO2.

[0025] The present invention introduces a superabsorbent polymer as an internal curing agent to reduce autogenous shrinkage, and the specific description is as follows:

[0026] The pre-absorbed SAP particles form "miniature reservoirs" in the slurry, gradually releasing water as the environmental humidity decreases, prolonging the hydration reaction period; the closed pores with a diameter of 20 - 50 μm left after the dehydration of SAP not only compensate for shrinkage but also maintain impermeability (chloride ion diffusion coefficient < 1.5×10 m -12 m 2 / s).

[0027] The chemical activator obtained from sodium sulfate and lithium hydroxide in the present invention further activates the activity of the coal gangue. Sodium sulfate provides SO4 2- to react with Al in the coal gangue to generate ettringite, compensating for shrinkage and enhancing the early strength; it can increase the liquid-phase ion concentration, accelerating the depolymerization of the coal gangue vitreous network, and the dissolution rates of active SiO2 and Al2O3 > 80%. 3+ Lithium hydroxide provides a high pH environment (pH > 13), breaking the Si-O-Si and Al-O-Al bonds and releasing active monomers; Li

[0028] decreases the activation energy of SiO2 dissolution through the "charge compensation effect", reducing the activation energy of the pozzolanic reaction; Li + + ​React preferentially with reactive SiO2 to form non-expansive lithium silicate, avoiding the durability deterioration caused by Na + / K + caused by K.

[0029] The coal gangue aggregates and quartz sand with different particle sizes in the present invention improve the density, and the specific functions are as follows: The coarse particles of coal gangue manufactured sand (0.6 - 1.18 mm) form a rigid skeleton, bearing most of the compressive stress; the difference in the thermal expansion coefficients between the coal gangue aggregates and the cementitious matrix is reduced, reducing the temperature stress; it directly replaces natural sand, reducing the material cost and carbon emissions.

[0030] The fine particles of quartz sand (0.15 - 0.6 mm) fill the gaps between the coarse aggregates, making the bulk density of the aggregate system greater than that of traditional UHPC; high-purity SiO2 does not react with the cementitious products, ensuring volume stability; the smooth surface reduces the flow resistance of the paste, and the slump flow is stable at 760 ± 20 mm.

[0031] Steel fibers (volume fraction 2%) greatly increase the fracture energy of UHPC through the fiber bridging effect; form a "macro - meso - nano" synergistic strengthening network with nano - SiO2 / graphene oxide; the bonding strength between the epoxy - coated steel fibers and the matrix increases, avoiding interface slip.

[0032] Example 1

[0033] The preparation method of the coal gangue - based ultra - high - performance concrete (UHPC) in this example includes the following steps: Send the crushed coal gangue particles into a magnetic separator, and after separation, the residual amount of Fe2O3 ≤ 0.8%; calcine the magnetically separated coal gangue at 900 °C for 2 h to obtain a calcined product of active intermediates mainly composed of γ - Al2O3 and amorphous SiO2; grind the calcined product with zirconia grinding balls at 300 rpm for 2 h, and sieve to obtain coal gangue fine powder with D50 = 1.2 μm.

[0034] Dry - mix 50 parts by mass of cement, 30 parts by mass of coal gangue fine powder and 20 parts by mass of silica fume until uniform to form a mixture.

[0035] Mix amino - modified nano - SiO2 and glycerol, and ultrasonically disperse until no visible agglomerates are formed to form a nano - SiO2 suspension; add graphene oxide into deionized water, and after ultrasonic treatment, mix it with the nano - SiO2 suspension to form a composite nano - dispersion.

[0036] Spray 1% of the composite nano - dispersion based on the mass of the coal gangue fine powder into the mixture, and continue to stir to form a cementitious material.

[0037] Add an activator accounting for 2% of the total mass of the mixture to the cementitious material. The activator is prepared by mixing sodium sulfate and lithium hydroxide at a mass ratio of 4:1.

[0038] Soak the dry SAP particles in deionized water, filter, and then dry to a moisture content of 30% to obtain SAP.

[0039] Add an aggregate mixture to the cementitious material, then successively add an aqueous solution containing a composite water reducer and polyacrylic acid-based superabsorbent polymer SAP, and stir at 150 rpm to form a slurry, controlling the slump flow of the slurry to reach 760 ± 20 mm; wherein, the aggregate mixture includes 50 wt% coal gangue manufactured sand, 45 wt% quartz sand, and 5 wt% steel fibers; the composite water reducer is a copolymer water reducer of polycarboxylic acid-lignosulfonate at a mass ratio of 4:1. Subsequently, pour the slurry into the wet joint; finally, cure the newly cast concrete.

[0040] The slurry in this example includes 20 wt% cement, 12 wt% coal gangue powder, 8 wt% silica fume, 0.8 wt% activator, 24 wt% coal gangue manufactured sand, 21.6 wt% quartz sand, 2.4 wt% steel fibers, 0.12 wt% composite nano-dispersion, 0.12 wt% polyacrylic acid-based superabsorbent polymer SAP, 0.5 wt% composite water reducer, and 10.5 wt% water.

[0041] Example 2

[0042] The preparation method of the coal gangue-based ultra-high performance concrete UHPC in this example includes the following steps: Send the crushed coal gangue particles into a magnetic separator, and after separation, the residual amount of Fe2O3 is ≤ 0.8%; calcine the magnetically separated coal gangue at 850 °C for 2 h to obtain a calcined product of active intermediates mainly composed of γ-Al2O3 and amorphous SiO2; grind the calcined product with zirconia grinding balls at 250 rpm for 2 h, and sieve to obtain coal gangue powder with D50 = 1.2 μm.

[0043] Dry-mix 40 parts by mass of cement, 40 parts by mass of coal gangue powder, and 20 parts by mass of silica fume until uniform to form a mixture.

[0044] Mix the amino-functionalized nano-SiO2 and glycerol, and ultrasonically disperse until no visible agglomerates are formed to obtain a nano-SiO2 suspension; add graphene oxide to deionized water, ultrasonically treat it, and then mix it with the nano-SiO2 suspension to form a composite nano-dispersion.

[0045] Spray 1% of the composite nano-dispersion based on the mass of the coal gangue powder into the mixture, and continue to stir to form a cementitious material.

[0046] Add an activator accounting for 2% of the total mass of the mixture to the cementitious material, where the activator is prepared by mixing sodium sulfate and lithium hydroxide at a mass ratio of 4:1.

[0047] Soak the dry SAP particles in deionized water, filter, and then dry to a moisture content of 30% to obtain SAP.

[0048] Add the aggregate mixture to the cementitious material, and then successively add an aqueous solution containing a composite water reducer and polyacrylic acid-based superabsorbent polymer SAP, and stir at 130 rpm to form a slurry, controlling the slump flow of the slurry to reach 760 ± 20 mm; wherein, the aggregate mixture includes 60 wt% coal gangue manufactured sand, 35 wt% quartz sand, and 5 wt% steel fibers; the composite water reducer is a copolymer water reducer of polycarboxylic acid - lignosulfonate with a mass ratio of 4:1. Subsequently, pour the slurry into the wet joint; finally, cure the newly cast concrete.

[0049] The slurry in this example includes 16 wt% cement, 16 wt% coal gangue micro-powder, 8 wt% silica fume, 0.8 wt% activator, 28.8 wt% coal gangue manufactured sand, 16.8 wt% quartz sand, 2.4 wt% steel fibers, 0.12 wt% composite nano-dispersion, 0.12 wt% polyacrylic acid-based superabsorbent polymer SAP, 0.5 wt% composite water reducer, and 10.5 wt% water.

[0050] Comparative Example 1 (without adding SAP) The preparation method of the coal gangue-based ultra-high performance concrete UHPC in this comparative example includes the following steps: Send the crushed coal gangue particles into a magnetic separator, and after separation, the residual amount of Fe2O3 ≤ 0.8%; calcine the magnetic-separated coal gangue at 900 °C for 2 h to obtain a calcined product of an active intermediate mainly composed of γ-Al2O3 and amorphous SiO2; grind the calcined product with zirconia grinding balls at 300 rpm for 2 h, and sieve to obtain coal gangue micro-powder with D50 = 1.2 μm.

[0051] Dry-mix 50 parts by mass of cement, 30 parts by mass of coal gangue micro-powder, and 20 parts by mass of silica fume until uniform to form a mixture.

[0052] Mix the amino-functionalized nano-SiO2 and glycerol, and ultrasonically disperse until no visible agglomerates are formed to obtain a nano-SiO2 suspension; add graphene oxide to deionized water, and after ultrasonic treatment, mix with the nano-SiO2 suspension to form a composite nano-dispersion.

[0053] Spray 1% of the composite nano-dispersion based on the mass of the coal gangue micro-powder into the mixture, and continue to stir to form a cementitious material.

[0054] Add an activator accounting for 2% of the total mass of the mixture to the cementitious material, where the activator is prepared by mixing sodium sulfate and lithium hydroxide at a mass ratio of 4:1.

[0055] Add an aggregate mixture to the cementitious material, then add an aqueous solution containing a composite water reducer, and stir at 130 rpm to form a slurry, controlling the slump flow of the slurry to reach 760 ± 20 mm; wherein, the aggregate mixture includes 50 wt% coal gangue manufactured sand, 45 wt% quartz sand, and 5 wt% steel fiber; the composite water reducer is a copolymer water reducer of polycarboxylic acid - lignosulfonate with a mass ratio of 4:1. Subsequently, pour the slurry into the wet joint; finally, cure the newly cast concrete.

[0056] Measure the internal moisture distribution of the slurry at different ages by NMR. Compared with Example 1, it is proved that SAP can continuously release moisture and prolong the hydration reaction.

[0057] The slurry in this example includes 20 wt% cement, 12 wt% coal gangue powder, 8 wt% silica fume, 0.8 wt% activator, 24 wt% coal gangue manufactured sand, 21.6 wt% quartz sand, 2.4 wt% steel fiber, 0.12 wt% composite nano - dispersion, 0.5 wt% composite water reducer, and 10.6 wt% water.

[0058] Comparative Example 2 (without adding composite nano - dispersion) The preparation method of the coal gangue - based ultra - high - performance concrete UHPC in this comparative example includes the following steps: Send the crushed coal gangue particles into a magnetic separator, and after separation, the residual amount of Fe2O3 ≤ 0.8%; calcine the magnetically separated coal gangue at 900 °C for 2 h to obtain a calcined product of active intermediates mainly composed of γ - Al2O3 and amorphous SiO2; grind the calcined product with zirconia grinding balls at 300 rpm for 2 h, and sieve to obtain coal gangue powder with D50 = 1.2 μm.

[0059] Dry - mix 50 parts by mass of cement, 30 parts by mass of coal gangue powder, and 20 parts by mass of silica fume until uniform to form a mixture.

[0060] Add an activator accounting for 2% of the total mass of the mixture to the cementitious material, where the activator is prepared by mixing sodium sulfate and lithium hydroxide at a mass ratio of 4:1.

[0061] Soak the dry SAP particles in deionized water, filter, and dry to a moisture content of 30% to obtain SAP.

[0062] An aggregate mixture is added to the gelling material, and then an aqueous solution containing a composite water reducer and a polyacrylic acid-based superabsorbent polymer SAP are added in sequence. Stir at 130 rpm to form a slurry, and control the slump flow of the slurry to reach 760 ± 20 mm; wherein, the aggregate mixture includes 50 wt% coal gangue manufactured sand, 45 wt% quartz sand and 5 wt% steel fiber; the composite water reducer is a copolymer water reducer of polycarboxylate-lignosulfonate with a mass ratio of 4:1. Subsequently, the slurry is poured into the wet joint; finally, the newly poured concrete is cured.

[0063] The slurry in this example includes 20 wt% cement, 12 wt% coal gangue powder, 8 wt% silica fume, 0.8 wt% activator, 24 wt% coal gangue manufactured sand, 21.6 wt% quartz sand, 2.4 wt% steel fiber, 0.12 wt% polyacrylic acid-based superabsorbent polymer SAP, 0.5 wt% composite water reducer and 10.6 wt% water.

[0064] Test Example Test the 3d / 28d compressive strength of the examples and comparative examples according to the ISO 679 standard; According to ASTM C882, the Z-shaped specimen method is used to measure the interfacial bond strength of the examples and comparative examples. The results are shown in Table 1.

[0065] Table 1: Results of various performance indicators of coal gangue-based UHPC of the examples and comparative examples of the present invention

[0066] The preparation method of the coal gangue-based ultra-high performance concrete UHPC of the examples of the present invention uses the composite gradient activation of calcination and ball milling and the synergistic excitation of alkali-lithium salts, so that the 3d compressive strength of the material ≥ 120 MPa and the 28d strength ≥ 150 MPa, which is improved compared with the traditional coal gangue-based materials; at the same time, the multi-scale enhancement of nano-SiO2 / graphene oxide and the synergistic toughening of steel fibers result in an interfacial bond strength of 12 - 14 MPa.

[0067] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of coal gangue-based ultra-high performance concrete UHPC for wet joints, characterized in that, It includes the following steps: S1. Dry-mix cement, coal gangue micro-powder and silica fume until uniform to form a mixture; S2. Spray the composite nano-dispersion into the mixture and continue stirring to form a cementitious material; the composite nano-dispersion is an aqueous dispersion containing active nano-SiO₂; S3. Add a mixed activator containing sodium sulfate and lithium hydroxide to the cementitious material; S4. Add an aggregate mixture to the cementitious material, then sequentially add an aqueous solution containing a composite water reducer and a polyacrylic acid-based superabsorbent polymer SAP, and stir at 100 - 150 rpm to form a concrete mixture, controlling its slump flow to reach 760 ± 20 mm.

2. The preparation method according to claim 1, characterized in that: In S1, by mass, the mixture includes 40 - 60 parts of cement, 20 - 40 parts of coal gangue micro-powder, and 10 - 30 parts of silica fume.

3. The preparation method according to claim 1, characterized in that: In S1, the preparation method of the coal gangue micro-powder includes the following steps: Feed the crushed coal gangue particles into a magnetic separator, and after separation, the residual amount of Fe₂O₃ ≤ 0.8%; Calcine the magnetically separated coal gangue at 800 - 900 °C to obtain a calcined product of γ-Al₂O₃ and amorphous SiO₂ active intermediate; Grind the calcined product with zirconia grinding balls at 200 - 300 rpm and sieve to obtain coal gangue micro-powder.

4. The preparation method according to claim 1, characterized in that: In S2, the preparation method of the composite nano-dispersion includes the steps: Mix amino-functionalized nano-SiO₂ with glycerol and ultrasonically disperse until no visible agglomerates are formed to form a nano-SiO₂ suspension; add graphene oxide to deionized water, ultrasonically treat and then mix with the nano-SiO₂ suspension to form a composite nano-dispersion.

5. The preparation method according to claim 1, characterized in that: In S4, the aggregate mixture adopts a composition of coal gangue manufactured sand, quartz sand and steel fiber.

6. The preparation method according to claim 1, characterized in that: In S4, the composite water reducer is a copolymer water reducer of polycarboxylic acid - lignosulfonate.

7. The preparation method according to claim 1, characterized in that: In S4, the SAP is obtained by soaking dry SAP particles in deionized water, filtering and then drying to a moisture content of 30%.

8. Application of the coal gangue-based ultra-high performance concrete UHPC obtained by the preparation method according to any one of claims 1 - 7 in bridge closure sections, bridge deck paving, expansion joints, and wet joints.

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