Preparation method and application of gangue-based ultra-high performance concrete (UHPC) for wet joints

Abstract

The present invention belongs to the field of concrete technology, and specifically relates to a preparation method and application of gangue-based ultra-high performance concrete (UHPC) for wet joints. The present invention achieves efficient dissolution of active components in gangue through composite gradient activation via calcination and ball milling, and synergistic activation with alkali-lithium salts. This results in UHPC materials with a 3d compressive strength of ≥120MPa and a 28d strength of ≥150MPa, both of which are higher than those of conventional gangue-based materials. Furthermore, the synergistic effect of multi-scale reinforcement via nano-SiO2 / graphene oxide and toughening via steel fibers results in an interfacial bonding strength of 12-14MPa and a chloride ion diffusion coefficient of <1.5×10 ‑12 m 2 / s, solving the problems of debonding and durability degradation at wet joint interfaces.

Description

Technical Field

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

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

[0003] Currently, UHPC relies primarily on high-quality raw materials such as high-purity Portland cement, silica fume, and quartz sand, resulting in high material costs. Furthermore, CO2 emissions from cement production and quartz sand mining cause ecological damage. Although some research has explored the use of solid wastes such as fly ash and slag as cement substitutes, these materials lack sufficient activity to meet UHPC strength requirements. Furthermore, the solid waste content is generally below 30%, resulting in low resource utilization efficiency.

[0004] Wet joints, a weak link in prefabricated structures, are prone to microcracks due to differential shrinkage between new and old concrete. While conventional UHPC improves density by reducing the water-cement ratio, its high autogenous shrinkage can lead to interfacial debonding under restraint conditions. Existing technologies often use external curing or expansive agents to compensate for shrinkage, but external curing methods struggle to penetrate deep into joints, while expansive agents (such as CaO) can easily cause later strength reduction, seriously threatening structural durability.

[0005] Gangue, a byproduct of coal mining, contains Al₂O₃ and SiO₂ components with potential for cementitious activity. However, existing technologies typically process gangue through simple calcination or mechanical grinding, resulting in a low powder activity index. Residual Fe₂O₃ and carbon impurities can hinder hydration and cause volume instability. While existing technologies have proposed gangue-cement composite cementitious materials, these materials often have low gangue content and fail to address the weakening of the interfacial transition zone (ITZ). Consequently, their chloride ion permeability resistance falls far below UHPC standards.

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

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

[0008] (1) Technical issues to be resolved

[0009] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a preparation method and application of gangue-based ultra-high performance concrete (UHPC) for wet joints, which solves the technical problems of weakening of the interface transition zone (ITZ) and lower chloride ion permeability than the UHPC standard.

[0010] (2) Technical solution

[0011] In a first aspect, the present invention provides a method for preparing gangue-based ultra-high performance concrete (UHPC) for wet joints, comprising the following steps:

[0012] S1. Dry-mix cement, coal gangue powder and silica fume until uniformly mixed to form a mixture;

[0013] S2, spraying the composite nano-dispersion liquid into the mixture and continuing to stir to form a gel material; the composite nano-dispersion liquid is an aqueous dispersion containing active nano-SiO2;

[0014] S3, adding a mixed activator containing sodium sulfate and lithium hydroxide to the gelling material;

[0015] S4. Add the aggregate mixture to the cementitious material, and then add the aqueous solution containing the composite water reducer and the polyacrylic acid super absorbent polymer (SAP) in sequence, and stir at 100-150 rpm to form a concrete mixture, controlling its expansion to 760±20 mm.

[0016] Optionally, in S1, the mixture includes, by weight, 40-60 parts of cement, 20-40 parts of coal gangue powder, and 10-30 parts of silica fume.

[0017] Optionally, in S1, the preparation method of the coal gangue fine powder includes the following steps: feeding the crushed coal gangue particles into a magnetic separator, and the residual Fe2O3 after sorting is ≤0.8%; calcining the magnetically separated coal gangue at 800-900°C to obtain a calcined product of an active intermediate of γ-Al2O3 and amorphous SiO2; grinding the calcined product with zirconium oxide grinding balls at 200-300 rpm, and sieving to obtain coal gangue fine powder.

[0018] Optionally, in S2, the preparation method of the composite nano-dispersion includes the steps of: mixing amino-modified nano-SiO2 with propylene glycol, and ultrasonically dispersing until no visible agglomerates are formed to form a nano-SiO2 suspension; adding graphene oxide to deionized water, and mixing it with the nano-SiO2 suspension after ultrasonic treatment to form a composite nano-dispersion.

[0019] Optionally, in S4, the aggregate mixture is a combination of coal gangue machine-made sand, quartz sand and steel fiber.

[0020] Optionally, in S4, the composite water reducer is a copolymer water reducer of polycarboxylic acid-lignin sulfonate.

[0021] Optionally, in S4, the SAP is obtained by soaking dried SAP particles in deionized water, filtering, and then drying to a moisture content of 30%.

[0022] In the second aspect, the gangue-based ultra-high performance concrete UHPC obtained according to the preparation method of the first aspect is used in bridge closure sections, bridge deck pavement, expansion joints, and wet joints.

[0023] Optionally, the 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%.

[0024] (3) Beneficial effects

[0025] The preparation method of gangue-based ultra-high performance concrete (UHPC) of the present invention achieves efficient dissolution of active components of gangue through composite gradient activation of calcination and ball milling and synergistic excitation of alkali-lithium salt, so that the 3d compressive strength of the material is ≥120MPa and the 28d strength is ≥150MPa, which is higher than that of traditional gangue-based materials. At the same time, the multi-scale reinforcement of nano-SiO2 / graphene oxide and the toughening of steel fibers synergize to achieve an interfacial bonding strength of 12-14MPa and a chloride ion diffusion coefficient of <1.5×10 -12 m 2 / s, solving the problems of debonding and durability degradation at wet joint interfaces.

[0026] The preparation method of gangue-based ultra-high performance concrete (UHPC) of the present invention uses gangue as the core raw material, achieving a solid waste content of >85%, reducing cement usage and lowering carbon emissions compared to traditional UHPC; the calcination process simultaneously removes Fe2O3 and carbon impurities in the gangue to avoid secondary pollution. DETAILED DESCRIPTION

[0027] In order to better explain the present invention and facilitate understanding, the following specific implementation methods are described in detail.

[0028] The working principle and function of the coal gangue of the present invention are described as follows:

[0029] 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, converted into amorphous Al2O3 and SiO2, and the activity is greatly improved; the ultrafine powder fills the gaps between cement particles, reduces porosity, and improves the density of the cementitious system; and the carbon content of the residual carbon is reduced by oxidative combustion at high temperature, avoiding interference with the cementitious reaction.

[0030] The planetary ball mill crushes the calcined product to D50=1.2μm, increasing the specific surface area and exposing more reaction interfaces; at the same time, the mechanical force causes microcracks and bond breaks on the particle surface, promoting chemical bonding with the alkaline activator.

[0031] The coal gangue powder and nanomaterial (compound of nano-silicon dioxide and graphene oxide) of the present invention can enhance the interface transition zone, as described in detail below:

[0032] Through the amino functionalization of nano-SiO2 (-NH2) and Ca in the gel matrix 2+ Coordination bonding reduces the thickness of the interfacial transition zone (ITZ); nanoparticles act as nucleation sites for the gel, accelerating the volcanic ash reaction of the gangue micropowder (i.e., increasing the reaction rate); amino modification in amino-functionalized nano-SiO2 prevents nanoparticle agglomeration and ensures uniform distribution in the slurry.

[0033] The graphene oxide sheet structure (thickness <5nm) bridges microcracks through the "pulling effect", thereby improving the fracture toughness of the material; the graphene sheets form a three-dimensional conductive path, which can monitor the stress and strain state of the wet joint in real time (the resistance change rate is linearly related to the strain).

[0034] In summary, mechanical grinding (ball milling) and high-temperature calcination can disrupt the structure of amorphous SiO2 in coal gangue, increasing its specific surface area and active sites. Furthermore, the added nano-SiO2, after amino functionalization, can be better dispersed and participate in the formation of CSH gel, acting as a nucleation agent. Furthermore, the alkaline environment provided by chemical activators (such as NaOH and Ca(OH)2) can promote the dissolution and reaction of SiO2.

[0035] The present invention introduces super absorbent polymer as an internal curing agent to reduce autogenous shrinkage, as described below:

[0036] The pre-absorbed SAP particles form a "micro-water reservoir" in the slurry, which gradually releases water as the ambient humidity decreases, prolonging the hydration reaction cycle; after dehydration, the SAP leaves behind closed pores of 20-50 μm, which not only compensates for shrinkage but also maintains impermeability (chloride ion diffusion coefficient <1.5×10 -12 m 2 / s).

[0037] The chemical activator obtained by sodium sulfate and lithium hydroxide further stimulates the activity of coal gangue, and sodium sulfate provides SO4 2- Al in coal gangue 3+ The reaction generates ettringite, which compensates for shrinkage and improves early strength; it can increase the liquid phase ion concentration, accelerate the depolymerization of the gangue glass network, and the dissolution rate of active SiO2 and Al2O3 is greater than 80%.

[0038] Lithium hydroxide provides a high pH environment (pH>13), destroying Si-O-Si and Al-O-Al bonds and releasing active monomers; Li + The activation energy of SiO2 dissolution is reduced by the "charge compensation effect", which reduces the activation energy of volcanic ash reaction; Li + Preferentially reacts with active SiO2 to form non-expandable lithium silicate, avoiding Na + / K + resulting in deterioration of durability.

[0039] The coal gangue aggregate and quartz sand of different particle sizes of the present invention improve density, and the specific functions are as follows:

[0040] The coarse particles of gangue machine-made sand (0.6-1.18mm) form a rigid skeleton that bears most of the compressive stress; the difference in thermal expansion coefficient between the gangue aggregate and the cementitious matrix is ​​reduced, reducing temperature stress; it directly replaces natural sand, reducing material costs and carbon emissions.

[0041] Fine particles of quartz sand (0.15-0.6mm) fill the gaps between coarse aggregates, making the aggregate system's bulk density greater than that of traditional UHPC. High-purity SiO2 does not react with the cementitious product, ensuring volume stability. The smooth surface reduces slurry flow resistance, and the expansion is stabilized at 760±20mm.

[0042] Steel fibers (2% by volume) significantly improve the fracture energy of UHPC through the fiber bridging effect; they form a "macro-meso-nano" synergistic reinforcement network with nano-SiO2 / graphene oxide; and the bonding strength between the epoxy-coated steel fibers and the matrix is ​​increased, avoiding interface slip.

[0043] Example 1

[0044] The preparation method of gangue-based ultra-high performance concrete (UHPC) of this embodiment includes the following steps:

[0045] The crushed gangue particles are fed into a magnetic separator, and the residual Fe2O3 content after separation is ≤0.8%; the magnetically separated gangue is calcined at 900°C for 2 hours to obtain a calcined product of active intermediates mainly composed of γ-Al2O3 and amorphous SiO2; the calcined product is ground with zirconia grinding balls at 300 rpm for 2 hours, and sieved to obtain gangue powder with D50=1.2μm.

[0046] 50 parts by mass of cement, 30 parts by mass of coal gangue powder and 20 parts by mass of silica fume were dry-mixed until uniform to form a mixture.

[0047] The amino-modified nano-SiO2 is mixed with glycerol and ultrasonically dispersed until no visible agglomerates are formed to form a nano-SiO2 suspension; graphene oxide is added to deionized water, and after ultrasonic treatment, is mixed with the nano-SiO2 suspension to form a composite nano-dispersion.

[0048] The composite nano-dispersion liquid, which accounts for 1% of the mass of the coal gangue powder, is sprayed into the mixture, and the mixture is continuously stirred to form a gelling material.

[0049] An activator in an amount of 2% by mass of the total mass of the mixture is added to the gelling material, wherein the activator is prepared by mixing sodium sulfate and lithium hydroxide in a mass ratio of 4:1.

[0050] The dried SAP particles were soaked in deionized water, filtered, and then dried to a moisture content of 30% to obtain SAP.

[0051] An aggregate mixture is added to the cementitious material, followed by an aqueous solution containing a composite water reducer and a polyacrylic acid-based superabsorbent polymer (SAP). The mixture is stirred at 150 rpm to form a slurry, with the slurry expansion controlled to 760 ± 20 mm. The aggregate mixture comprises 50 wt% coal gangue sand, 45 wt% quartz sand, and 5 wt% steel fiber. The composite water reducer is a polycarboxylic acid-lignin sulfonate copolymer water reducer with a mass ratio of 4:1. The slurry is then poured into the wet joints. Finally, the newly poured concrete is cured.

[0052] The slurry of this embodiment includes 20wt% cement, 12wt% coal gangue powder, 8wt% silica fume, 0.8wt% activator, 24wt% coal gangue machine-made sand, 21.6wt% quartz sand, 2.4wt% steel fiber, 0.12wt% composite nano-dispersion, 0.12wt% polyacrylic acid super absorbent polymer SAP, 0.5wt% composite water reducer and 10.5wt% water.

[0053] Example 2

[0054] The preparation method of gangue-based ultra-high performance concrete (UHPC) of this embodiment includes the following steps:

[0055] The crushed gangue particles are fed into a magnetic separator, and the residual Fe2O3 content after separation is ≤0.8%; the magnetically separated gangue is calcined at 850°C for 2h to obtain a calcined product of active intermediates mainly composed of γ-Al2O3 and amorphous SiO2; the calcined product is ground with zirconia grinding balls at 250rpm for 2h, and sieved to obtain gangue powder with D50=1.2μm.

[0056] 40 parts by mass of cement, 40 parts by mass of coal gangue powder and 20 parts by mass of silica fume were dry-mixed until uniformly mixed to form a mixture.

[0057] The amino-modified nano-SiO2 is mixed with glycerol and ultrasonically dispersed until no visible agglomerates are formed to form a nano-SiO2 suspension; graphene oxide is added to deionized water, and after ultrasonic treatment, is mixed with the nano-SiO2 suspension to form a composite nano-dispersion.

[0058] The composite nano-dispersion liquid, which accounts for 1% of the mass of the coal gangue powder, is sprayed into the mixture, and the mixture is continuously stirred to form a gelling material.

[0059] An activator in an amount of 2% by mass of the total mass of the mixture is added to the gelling material, wherein the activator is prepared by mixing sodium sulfate and lithium hydroxide in a mass ratio of 4:1.

[0060] The dried SAP particles were soaked in deionized water, filtered, and then dried to a moisture content of 30% to obtain SAP.

[0061] An aggregate mixture was added to the cementitious material, followed by an aqueous solution containing a composite water reducer and a polyacrylic acid-based superabsorbent polymer (SAP). The mixture was stirred at 130 rpm to form a slurry, with the slurry expansion controlled to 760 ± 20 mm. The aggregate mixture comprised 60 wt% coal gangue sand, 35 wt% quartz sand, and 5 wt% steel fiber. The composite water reducer was a polycarboxylic acid-lignin sulfonate copolymer water reducer with a mass ratio of 4:1. The slurry was then poured into the wet joints. Finally, the newly poured concrete was cured.

[0062] The slurry of this embodiment includes 16wt% cement, 16wt% coal gangue powder, 8wt% silica fume, 0.8wt% activator, 28.8wt% coal gangue machine-made sand, 16.8wt% quartz sand, 2.4wt% steel fiber, 0.12wt% composite nano-dispersion, 0.12wt% polyacrylic acid super absorbent polymer SAP, 0.5wt% composite water reducer and 10.5wt% water.

[0063] Comparative Example 1 (without adding SAP)

[0064] The preparation method of the gangue-based ultra-high performance concrete UHPC of this comparative example comprises the following steps:

[0065] The crushed gangue particles are fed into a magnetic separator, and the residual Fe2O3 content after separation is ≤0.8%; the magnetically separated gangue is calcined at 900°C for 2 hours to obtain a calcined product of active intermediates mainly composed of γ-Al2O3 and amorphous SiO2; the calcined product is ground with zirconia grinding balls at 300 rpm for 2 hours, and sieved to obtain gangue powder with D50=1.2μm.

[0066] 50 parts by mass of cement, 30 parts by mass of coal gangue powder and 20 parts by mass of silica fume were dry-mixed until uniform to form a mixture.

[0067] The amino-modified nano-SiO2 is mixed with glycerol and ultrasonically dispersed until no visible agglomerates are formed to form a nano-SiO2 suspension; graphene oxide is added to deionized water, and after ultrasonic treatment, is mixed with the nano-SiO2 suspension to form a composite nano-dispersion.

[0068] The composite nano-dispersion liquid, which accounts for 1% of the mass of the coal gangue powder, is sprayed into the mixture, and the mixture is continuously stirred to form a gelling material.

[0069] An activator in an amount of 2% by mass of the total mass of the mixture is added to the gelling material, wherein the activator is prepared by mixing sodium sulfate and lithium hydroxide in a mass ratio of 4:1.

[0070] An aggregate mixture was added to the cementitious material, followed by an aqueous solution containing a composite water reducer. The mixture was stirred at 130 rpm to form a slurry, with the slurry expansion controlled to 760 ± 20 mm. The aggregate mixture comprised 50 wt% coal gangue sand, 45 wt% quartz sand, and 5 wt% steel fiber. The composite water reducer was a polycarboxylic acid-lignin sulfonate copolymer water reducer with a mass ratio of 4:1. The slurry was then poured into the wet joints. Finally, the newly poured concrete was cured.

[0071] The internal moisture distribution of the slurries at different ages was measured by NMR. Compared with Example 1, it was proved that SAP can continuously release moisture and prolong the hydration reaction.

[0072] The slurry of this embodiment includes 20wt% cement, 12wt% coal gangue powder, 8wt% silica fume, 0.8wt% activator, 24wt% coal gangue machine-made sand, 21.6wt% quartz sand, 2.4wt% steel fiber, 0.12wt% composite nano-dispersion liquid, 0.5wt% composite water reducer and 10.6wt% water.

[0073] Comparative Example 2 (without adding composite nano-dispersion liquid)

[0074] The preparation method of the gangue-based ultra-high performance concrete UHPC of this comparative example comprises the following steps:

[0075] The crushed gangue particles are fed into a magnetic separator, and the residual Fe2O3 content after separation is ≤0.8%; the magnetically separated gangue is calcined at 900°C for 2 hours to obtain a calcined product of active intermediates mainly composed of γ-Al2O3 and amorphous SiO2; the calcined product is ground with zirconia grinding balls at 300 rpm for 2 hours, and sieved to obtain gangue powder with D50=1.2μm.

[0076] 50 parts by mass of cement, 30 parts by mass of coal gangue powder and 20 parts by mass of silica fume were dry-mixed until uniform to form a mixture.

[0077] An activator in an amount of 2% by mass of the total mass of the mixture is added to the gelling material, wherein the activator is prepared by mixing sodium sulfate and lithium hydroxide in a mass ratio of 4:1.

[0078] The dried SAP particles were soaked in deionized water, filtered, and then dried to a moisture content of 30% to obtain SAP.

[0079] An aggregate mixture was added to the cementitious material, followed by an aqueous solution containing a composite water reducer and a polyacrylic acid-based superabsorbent polymer (SAP). The mixture was stirred at 130 rpm to form a slurry, with the slurry expansion controlled to 760 ± 20 mm. The aggregate mixture comprised 50 wt% coal gangue sand, 45 wt% quartz sand, and 5 wt% steel fiber. The composite water reducer was a polycarboxylic acid-lignin sulfonate copolymer water reducer with a mass ratio of 4:1. The slurry was then poured into the wet joints. Finally, the newly poured concrete was cured.

[0080] The slurry of this embodiment includes 20wt% cement, 12wt% coal gangue powder, 8wt% silica fume, 0.8wt% activator, 24wt% coal gangue machine-made sand, 21.6wt% quartz sand, 2.4wt% steel fiber, 0.12wt% polyacrylic acid super absorbent polymer SAP, 0.5wt% composite water reducer and 10.6wt% water.

[0081] Test example

[0082] The 3d / 28d compressive strength of the examples and comparative examples were tested according to ISO 679 standard;

[0083] The interfacial bonding strength of the examples and comparative examples was measured using the Z-type test piece method according to ASTM C882. The results are shown in Table 1.

[0084] Table 1: Performance index results of gangue-based UHPC of the embodiments of the present invention and the comparative example

[0085]

[0086] The preparation method of the gangue-based ultra-high performance concrete UHPC of the embodiment of the present invention uses composite gradient activation of calcination and ball milling and synergistic excitation of alkali-lithium salt to make the material's 3d compressive strength ≥120MPa and 28d strength ≥150MPa, which are improved compared with traditional gangue-based materials; at the same time, the multi-scale reinforcement of nano-SiO2 / graphene oxide and the toughening of steel fibers synergistically achieve an interface bonding strength of 12-14MPa.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing gangue-based ultra-high performance concrete (UHPC) for wet joints, characterized in that: The following steps are involved: S1. Dry-mix cement, coal gangue powder and silica fume until uniformly mixed to form a mixture; The preparation method of the coal gangue fine powder comprises the following steps: The crushed gangue particles are fed into a magnetic separator, and the residual Fe2O3 content after separation is ≤0.8%; The magnetically separated coal gangue is calcined at 800-900°C to obtain a calcined product containing an active intermediate of γ-Al2O3 and amorphous SiO2; The calcined product is ground with zirconium oxide grinding balls and sieved to obtain coal gangue fine powder; S2, spraying the composite nano-dispersion liquid into the mixture and continuing to stir to form a gel material; the composite nano-dispersion liquid is an aqueous dispersion containing active nano-SiO2, and the preparation method of the composite nano-dispersion liquid comprises the following steps: The amino-modified nano-SiO2 is mixed with glycerol and ultrasonically dispersed until no visible agglomerates are formed to form a nano-SiO2 suspension; graphene oxide is added to deionized water, and after ultrasonic treatment, is mixed with the nano-SiO2 suspension to form a composite nano-dispersion; S3, adding a mixed activator containing sodium sulfate and lithium hydroxide to the gelling material; S4. Add the aggregate mixture to the cementitious material, and then add the aqueous solution containing the composite water reducer and the polyacrylic acid super absorbent polymer (SAP) in sequence, and stir at 100-150 rpm to form a concrete mixture, controlling its expansion to 760±20 mm.

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

3. The preparation method according to claim 1, wherein: In S4, the aggregate mixture is a combination of coal gangue machine-made sand, quartz sand and steel fiber.

4. The preparation method according to claim 1, wherein: In S4, the composite water reducer is a copolymer water reducer of polycarboxylic acid-lignin sulfonate.

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

6. Use of gangue-based ultra-high performance concrete (UHPC) obtained according to the preparation method according to any one of claims 1 to 5 in bridge closure sections, bridge deck pavement, expansion joints, and wet joints.

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