Massive high-strength concrete suitable for underground structures and method for producing the same

Abstract

The application provides a mass high-strength concrete suitable for underground structures and a preparation method thereof, the mass high-strength concrete comprises the following components measured per cubic meter: 180-250 kg of low-heat portland cement, 90-120 kg of fly ash, 150-210 kg of slag powder, 900-1100 kg of coarse aggregate and 650-800 kg of fine aggregate, 6-15 kg of polycarboxylate superplasticizer, 0.5-1.5 kg of a retarder, 140-160 kg of water and a composite anti-cracking additive; the composite anti-cracking additive is formed by compounding calcium sulphoaluminate supported pyrene modified coal gangue and beta-cyclodextrin coated magnesium oxide microcapsules at a mass ratio of 1:1-2, and the amount is 6-10 wt% of the cementitious material. The high-strength concrete for underground structures provided by the application builds a shrinkage compensation and collaborative anti-cracking system by adding the composite anti-cracking additive, solves the double problems of early plastic cracks and insufficient mid-term shrinkage compensation of mass concrete, realizes the comprehensive improvement of the anti-cracking performance of mass concrete, and can meet the high impermeability, low shrinkage and high strength requirements under the complex constraint conditions of underground structures.

Description

Technical Field

[0001] This invention belongs to the field of building materials, specifically relating to a large-volume high-strength concrete suitable for underground structures and its preparation method. Background Technology

[0002] Mass concrete is widely used in underground structural engineering (such as basement floor slabs, side walls, roof slabs, and pile foundation caps), but its construction and service life face multiple technical challenges:

[0003] 1) Risk of hydration heat-induced cracks: Traditional large-volume concrete is prone to temperature stress cracks when the temperature difference between the inner and outer surfaces exceeds 25°C due to the concentrated release of hydration heat of cementitious materials. Especially in the early plastic stage (1 to 3 days after pouring), the tensile strength of concrete has not yet been formed, and the shrinkage stress caused by surface water loss exacerbates the initiation of cracks.

[0004] 2) Mismatch in shrinkage compensation: Existing magnesium oxide-based expansive agents rely on direct addition, and their hydration rate is significantly affected by ambient temperature, resulting in a mismatch between "temperature rise and expansion"—expansion is consumed prematurely during high-temperature periods, and shrinkage compensation is insufficient during low-temperature periods, which fails to meet the crack resistance requirements of GB 50496-2018 "Standard for Construction of Mass Concrete".

[0005] 3) Interfacial bonding failure problem: Although mineral admixtures such as fly ash and slag powder reduce the heat of hydration, the inert SiO2 layer on the particle surface results in weak interfacial bonding with the cement matrix, which easily forms crack propagation channels; fiber-reinforced materials have limited crack resistance due to stress concentration caused by uneven dispersion.

[0006] 4) Durability bottleneck: Single expansive agent or fiber reinforcement cannot simultaneously address early plastic crack resistance and mid-term shrinkage compensation, resulting in concrete impermeability grades generally lower than P8, and chloride ion diffusion coefficient > 3.0 × 10⁻⁶. -12 m 2 / s, which seriously affects its erosion resistance and structural life.

[0007] While existing technologies have attempted to improve performance through a combination of "low-heat cement + single expansive agent," the synergistic problem of controllable expansion rate and interface reinforcement remains unresolved, resulting in a still high risk of cracking in engineering applications. Therefore, there is an urgent need to develop a composite crack-resistant system that combines early interface strengthening, mid-term slow-release expansion, and long-term structural densification to meet the high-performance requirements of large-volume concrete in underground structures. Summary of the Invention

[0008] Based on the above problems, this section aims to provide a method for preparing large-volume high-strength concrete suitable for underground structures.

[0009] On one hand, the present invention provides a large-volume high-strength concrete suitable for underground structures, comprising the following components measured per cubic meter:

[0010] 180–250 kg low-heat silicate cement, 90–120 kg fly ash, 150–210 kg slag powder, 900–1100 kg coarse aggregate and 650–800 kg fine aggregate, 6–15 kg polycarboxylate superplasticizer, 0.5–1.5 kg retarder, 140–160 kg water and composite crack-resistant admixture;

[0011] The composite crack-resistant admixture is composed of pyrene-modified coal gangue loaded with calcium sulfoaluminate and magnesium oxide microcapsules coated with β-cyclodextrin in a mass ratio of 1:1 to 2; the dosage is 6 to 10 wt% of the mass of the cementitious material.

[0012] π-π stacked pyrene-modified coal gangue can form a physical interlock with the hydration products of cementitious materials; calcium sulfoaluminate is anchored on the surface of coal gangue through dynamic covalent bonds of aldehyde-hydrazide, and the ettringite crystals generated by its hydration insert into the pores to form a dense interface, which improves the tensile strength of the interface and effectively inhibits early plastic cracks; at the same time, by delaying the hydration of calcium sulfoaluminate, early uncontrolled expansion is avoided; β-cyclodextrin-coated magnesium oxide microcapsules release magnesium under alkaline conditions. 2+ It compensates for mid-term expansion, forming a gradient compensation synergy of stability in the front and replenishment in the back, matching the mid-term temperature drop and shrinkage requirements of large-volume concrete, and avoiding the "expansion-temperature rise" mismatch problem of traditional expansion agents.

[0013] Furthermore, the low-heat silicate cement has a 3-day heat of hydration ≤240kJ / kg, a tricalcium aluminate content ≤7wt%, and a tricalcium silicate content of 40-50wt%; the coarse aggregate is continuously graded crushed stone with a particle size of 5-25mm, a mud content ≤0.5wt%, and a needle-like / flaky particle content ≤15wt%; the fine aggregate is medium sand with a fineness modulus of 2.5-3.0 and a mica content ≤2wt%.

[0014] Furthermore, the polycarboxylate superplasticizer has a water reduction rate of ≥25% and a solid content of 20-35 wt%; the retarder is sodium gluconate or citric acid.

[0015] Furthermore, the composite crack-resistant admixture has a particle size of 80–120 μm and a bulk density of 1.8–2.0 g / cm³. 3 Its preparation process is as follows:

[0016] Pyrene-modified coal gangue supported on calcium sulfoaluminate was mixed with β-cyclodextrin-coated magnesium oxide microcapsules and then fed into a fluidized bed at an air volume of 1.6–2.5 m³ / h. 3 Fluidize for 9-15 minutes at a temperature of 50-60℃ and an amplitude of 3-5mm; spray the surface with 3-5wt% methylcellulose binder solution to form a binder layer, and then dry and sieve to obtain composite crack-resistant admixture particles.

[0017] Furthermore, the preparation steps of the pyrene-modified coal gangue supported on calcium sulfoaluminate are as follows:

[0018] (1) Mix calcined coal gangue with an ethanol solution of 5-10 wt% pyrene-hydrazide modifier at a mass ratio of 1:1.5-2, and ultrasonically disperse for 1-1.5 h to obtain pyrene-modified coal gangue;

[0019] (2) Calcium sulfoaluminate was treated with 2.5-5 wt% ethanol solution of 3-aminopropyltriethoxysilane at 50-60°C for 3-4 h, and then 2.5-5 wt% glutaraldehyde solution was added and stirred at room temperature for 5-6 h to obtain surface aldehyde-modified calcium sulfoaluminate.

[0020] (3) Surface aldehyde-modified calcium sulfoaluminate and pyrene-modified coal gangue are mixed in a ball mill at a mass ratio of 1:2 to obtain calcium sulfoaluminate-loaded pyrene-modified coal gangue.

[0021] The specific surface area of ​​the calcium sulfoaluminate is ≥400 m². 2 / kg; the calcined coal gangue is the product of coal gangue after crushing, calcining at 900-1100℃, and ball milling, with a specific surface area ≥450m². 2 / kg.

[0022] Furthermore, the synthesis steps of the pyrene-hydrazide modifier are as follows:

[0023] (1) Under a nitrogen atmosphere, bromopyrene and p-formylphenylboronic acid were reacted at a molar ratio of 1:1.1 to 1.2 in the presence of a catalyst and an alkaline reagent in a water bath at 80 to 90 °C for 12 to 15 h to obtain a pyrene-aldehyde intermediate; the catalyst was 2 to 5% of the molar amount of bromopyrene, which was Pd(PPh3)4, and the alkaline reagent was 2.5 to 3 times the molar amount of bromopyrene, which was sodium carbonate or potassium carbonate.

[0024] (2) Under a nitrogen atmosphere, the pyrene-aldehyde intermediate and thiourea were condensed at a molar ratio of 1:1 to 1.2 for 12 to 18 hours, and the pH of the reaction system was controlled at 6 to 7 with a phosphate-phosphate buffer solution to obtain the pyrene hydrazide modifier.

[0025] Furthermore, the β-cyclodextrin magnesium oxide microcapsules have a particle size of 50-100 μm and are obtained by stirring and mixing β-cyclodextrin coating liquid and magnesium oxide at a mass ratio of 1:1.5-2 and then spray drying.

[0026] The spray drying conditions are: inlet air temperature 80-90℃, atomization pressure 0.2-0.3MPa;

[0027] The concentration of the β-cyclodextrin coating solution is 5-10 wt%, and it also contains a dispersant and an auxiliary binder; the dispersant is 0.2-0.5 wt% sodium polyacrylate or sodium dodecyl sulfate, and the auxiliary binder is 1-2 wt% gelatin.

[0028] Furthermore, the dosage of the crack-resistant admixture is adjusted according to the application site:

[0029] For the top slab, the dosage is 6-7 wt% of the cementitious material;

[0030] Basement floor / sidewalls: 7-9 wt%;

[0031] The bedrock / pile foundation contact area is in a strongly confined environment of 9–10 wt%.

[0032] Another aspect of the present invention provides a method for preparing the above-mentioned large-volume, high-strength concrete, specifically comprising:

[0033] S1. Concrete mixing: First, put low-heat silicate cement, fly ash, and slag powder into the mixer and dry mix for 1-2 minutes. Then, add coarse aggregate and fine aggregate and continue dry mixing for 1-2 minutes. Next, add water, polycarboxylate superplasticizer, and retarder for 2-3 minutes. Finally, add composite crack-resistant admixture and continue mixing for 3-5 minutes to obtain the concrete mixture. The slump should be controlled at 140-160 mm.

[0034] S2. Moisture curing: The concrete mixture is poured into the mold, the surface is covered with a film and felt, and cured for 28 days at a humidity of ≥90%.

[0035] Beneficial effects:

[0036] This invention provides a high-strength concrete for underground structures. Through a composite design of pyrene-modified coal gangue loaded with calcium sulfoaluminate and magnesium oxide microcapsules coated with β-cyclodextrin, a dual-scale interface reinforcement and multi-stage shrinkage compensation synergistic crack-resistant system is constructed, significantly improving the performance of large-volume concrete and solving the dual problems of early-stage plastic cracking and insufficient mid-term shrinkage compensation in large-volume concrete. Furthermore, the low porosity of the pyrene-modified coal gangue, combined with the uniform dispersion of the microcapsules, densifies the concrete interior, significantly delaying chloride ion erosion and meeting the high durability requirements for long-term service of underground structures.

[0037] This invention also provides differentiated adaptation design for different levels of constraint in different parts (low constraint in the top slab, medium constraint in the bottom slab, and strong constraint in the pile foundation): by adjusting the dosage of crack-resistant admixtures, compensation can be achieved as needed. Attached Figure Description

[0038] Figure 1 The 1H NMR spectrum of the pyrene-hydrazide modifier. Detailed Implementation

[0039] The present invention is further illustrated below through specific embodiments, but is not limited to the embodiments described herein. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0040] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods; the materials and reagents used are conventional products that can be obtained commercially, unless otherwise specified.

[0041] P·LH 42.5 type low-heat silicate cement, specific surface area 290m² 2 / kg, 7d heat of hydration 240kJ / kg, 28d compressive strength 42.5MPa, 28d flexural strength 6.8MPa, Asia Cement Holdings Limited; its mineral composition is shown in Table 1.

[0042] Table 1 (Unit: wt.%)

[0043] <![CDATA[Mineral composition [注] > <![CDATA[C3S]]> <![CDATA[C2S]]> <![CDATA[C4AF]]> <![CDATA[C3A]]> <![CDATA[CaSO4·2H2O]]> other content 41.36 31.9 15.47 3.46 4.5 3.31

[0044] Note: C3S is tricalcium silicate (3CaO·Al2O3), C2S is dicalcium silicate (2CaO·Al2O3), C3A is tricalcium aluminate (3CaO·Al2O3), and C4AF is tetracalcium aluminoferrite (4CaO·Al2O3·Fe2O3).

[0045] Class I fly ash from power plants, with a specific surface area of ​​440 m². 2 / kg, density 2.4g / cm³ 3 Water demand ratio 103%, Qiangdong Mineral Products Processing Plant, Lingshou County, Hebei Province;

[0046] S95 slag powder, specific surface area 450m² 2 / kg, density 2.6g / cm³ 3 7-day activity index 83%, Shengbang Mineral Products Processing Plant, Lingshou County, Hebei Province.

[0047] The chemical compositions of the three cementing materials are summarized in Table 2.

[0048] Table 2 (Unit: wt.%)

[0049] chemical composition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> f-CaO other Low-heat silicate cement 20.04 3.97 58.64 4.69 4.87 3.37 0.82 0.15 0.47 2.98 fly ash 49.33 22.41 4.49 13.87 0.81 0.66 0.12 1.83 / 6.48 Slag powder 32.81 10.55 37.04 3.66 8.95 0.08 0.03 0.02 / 6.86

[0050] Grade 72.5 calcium sulfoaluminate, specific surface area 420 m² 2 / kg, 7d compressive strength 75MPa, 7d flexural strength 9.0MPa, Tangshan Arctic Bear Building Materials Co., Ltd.

[0051] Coal gangue from a coal mine in Xi'an was crushed and ground into coal gangue powder with a fineness of 20±1% and an 80µm particle size. After static calcination in a high-temperature furnace at 950℃ for 2 hours, it was removed and allowed to cool naturally. After ball milling, the specific surface area was 520m². 2 / kg, with a particle size (D50) of 37.24μm.

[0052] The chemical composition of calcium sulfoaluminate and coal gangue raw materials is shown in Table 3.

[0053] Table 3 (Unit: wt.%)

[0054] chemical composition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> <![CDATA[P2O5]]> <![CDATA[TiO2]]> other Coal gangue 49.05 22.90 1.25 3.76 0.88 0.37 1.83 0.75 0.19 1.02 18.0 Calcium sulfoaluminate 6.12 40.13 37.46 1.87 2.76 7.56 0.12 1.23 / 1.37 1.38

[0055] The coarse aggregate is a 5-25mm continuously graded Class I crushed stone for construction, washed and dried, with a mud content of 0.4wt%; the fine aggregate is a continuously graded medium sand with a fineness modulus of 2.8, a mud content of 0.2wt%, and a mica content of 1.8wt%.

[0056] D-JSS1 type polycarboxylate superplasticizer (35% solids content) was purchased from Guangzhou Dashengshi Building Materials Co., Ltd. Its product specifications are shown in Table 4.

[0057] Table 4 (Unit: %)

[0058] Testing items Water reduction rate Perfusion rate gas content 7d compressive strength ratio 28d compressive strength ratio 28-day shrinkage ratio Water reducing agent 28 45 5.0 160 150 100

[0059] Sodium gluconate retarder, conforming to standard Q / 1626SXW 005, density 1.763 g / cm³ 3 Shandong Xiwang Sugar Industry Co., Ltd.

[0060] Preparation Example 1

[0061] Synthesis of pyrene-hydrazide modifier:

[0062] (1) 0.02 mol of bromopyrene and 0.024 mol of p-formylphenylboronic acid were dissolved in a toluene / ethanol mixture (3:1, v / v). 0.4 mmol of Pd(PPh3)4 and 0.06 mol of Na2CO3 were added to obtain the reaction system, which was then deoxygenated under nitrogen. The reaction system was stirred for 12 h under a nitrogen atmosphere and in an 80°C water bath. The product was subjected to silica gel column chromatography (petroleum ether / ethyl acetate = 8:1) to obtain pyrene-p-formylbenzene as a white solid, with a yield of 89.5%.

[0063] (2) 0.015 mol of pyrene-p-formylbenzene and 0.018 mol of aminothiourea were dissolved in an ethanol / water solution with a volume ratio of 1:1. The pH was controlled at 6.5–7 with phosphate buffer solution, and the reaction was stirred at room temperature for 15 h. The product was washed with diethyl ether to obtain a pale yellow solid of pyrene-hydrazide modifier with a yield of 87.4%. Its 1H NMR spectrum is shown below. Figure 1 .

[0064] Preparation Example 2

[0065] Preparation of composite crack-resistant admixtures:

[0066] (1) Pyrene-modified coal gangue was obtained by mixing calcined coal gangue at a mass ratio of 1:2 with an ethanol solution of 8 wt% pyrene-hydrazide modifier obtained in Preparation Example 1 and ultrasonically dispersing for 1 h. Calcium sulfoaluminate powder was added to an ethanol solution of 4 wt% 3-aminopropyltriethoxysilane and treated at 60 °C for 4 h; then 5 wt% glutaraldehyde solution was added and stirred at room temperature for 6 h to obtain surface-aldehyde-modified calcium sulfoaluminate. Surface-aldehyde-modified calcium sulfoaluminate and pyrene-modified coal gangue were mixed in a ball mill at a mass ratio of 1:2 to obtain pyrene-modified coal gangue supported on calcium sulfoaluminate with a particle size of 69 μm.

[0067] (2) Prepare an 8 wt% β-cyclodextrin coating solution (containing 0.5 wt% sodium polyacrylate and 1.5 wt% gelatin); add magnesium oxide powder of twice the mass of β-cyclodextrin to the coating solution, mechanically stir at 800 rpm for 1 h to obtain a mixed solution, and spray dry (inlet air temperature of 90℃, atomization pressure of 0.3 MPa) to obtain β-cyclodextrin-coated magnesium oxide microcapsules with a particle size of 75 μm.

[0068] (3) Pyrene-modified coal gangue loaded with calcium sulfoaluminate and magnesium oxide microcapsules coated with β-cyclodextrin were added to a mixer at a mass ratio of 3:5 and stirred at 20 rpm for 20 min. The premix was then transferred to a fluidized bed reactor and the temperature was set at 60℃ and the air volume at 2.0 m³ / min. 3 / (kg·h, amplitude of 3mm, fluidized treatment for 10min; spray 5wt% methylcellulose ethanol-water (v:v=7:3) solution to form a binder layer, dry at 50℃ and screen with a vibrating screen to obtain composite crack-resistant admixture particles.

[0069] The relevant performance tests were conducted on the composite crack-resistant admixture, and the results are shown in Table 5.

[0070] Table 5

[0071]

[0072] Example 1

[0073] A type of high-strength concrete for basement floor slabs, comprising the following raw materials (per cubic meter):

[0074] The following mixture was prepared: 220 kg of P·LH 42.5 low-heat silicate cement, 100 kg of Grade I fly ash, 180 kg of S95 slag powder, 1000 kg of crushed stone, 750 kg of medium sand, 150 kg of water, 8 kg of polycarboxylate superplasticizer, 1.0 kg of retarder, and 40 kg of the composite crack-resistant admixture obtained in Preparation Example 2 (containing 15 kg of pyrene-modified coal gangue and 25 kg of β-cyclodextrin-coated magnesium oxide microcapsules). The preparation was carried out according to the following steps:

[0075] (1) Dry mix the three cementitious materials, namely low-heat silicate cement, fly ash and slag powder, for 1.5 min. Add crushed stone and medium sand and continue to dry mix for 1.5 min. Then, add water, polycarboxylate superplasticizer and retarder and wet mix for 3 min. Finally, add composite anti-cracking admixture and stir for 4 min to obtain concrete mixture with a slump of 150 mm.

[0076] (2) Pour the concrete mixture into the mold, cover it with polyethylene film and two layers of 5cm thick industrial felt, and place it in a curing box with a humidity of 95±2% for 28 days.

[0077] Example 2

[0078] A type of high-strength concrete for basement roof slabs is prepared using the same steps as in Example 1, except for the amount of raw materials used (per cubic meter):

[0079] The following ingredients were prepared: 180 kg of P·LH 42.5 low-heat silicate cement, 120 kg of Grade I fly ash, 200 kg of S95 slag powder, 1050 kg of crushed stone, 700 kg of medium sand, 140 kg of water, 6 kg of polycarboxylate superplasticizer, 0.8 kg of retarder, and 35 kg of the composite crack-resistant admixture obtained in Preparation Example 2.

[0080] Example 3

[0081] A type of high-strength, large-volume concrete for underground bedrock is prepared using the same steps as in Example 1, except for the amount of raw materials used (per cubic meter):

[0082] 250 kg of P·LH 42.5 low-heat silicate cement, 120 kg of Grade I fly ash, 210 kg of S95 slag powder, and 58 kg of the composite crack-resistant admixture obtained in Preparation Example 2.

[0083] Comparative Example 1

[0084] The difference from Example 1 is that the composite crack-resistant admixture used does not contain pyrene-modified coal gangue, and 40 kg of β-cyclodextrin-coated magnesium oxide microcapsules (per cubic meter) are added.

[0085] Comparative Example 2

[0086] The difference from Example 1 is that the composite anti-cracking admixture raw material used does not contain β-cyclodextrin-coated magnesium oxide microcapsules, and 40 kg of pyrene-modified coal gangue (per cubic meter) is added.

[0087] Comparative Example 3

[0088] The difference from Example 1 is that the coal gangue in the composite anti-cracking admixture raw material is not modified with pyrene, and is compounded with magnesium oxide microcapsules coated with β-cyclodextrin (per cubic meter).

[0089] Performance tests were conducted on the different underground structures of Examples 1-3 and Comparative Examples 1-3 using large-volume high-strength concrete, and the results are shown in Table 6.

[0090] Table 6

[0091]

[0092]

[0093] Table 6 shows that the large-volume high-strength concrete in Examples 1-3 also exhibits excellent early plastic stage crack resistance (expansion rate of 1.6-2.2 × 10⁻⁶ days from 1 to 3 days). -4 Mid-term contraction compensation (7–14 days expansion rate 2.3–4.5 × 10⁻⁶) -4 ) and long-term structural density (365-day shrinkage rate of 7–9 × 10⁻⁶) -4 The chloride ion diffusion coefficient is ≤2.0×10⁻⁶. -12 m 2 / s). In the composite crack-resistant admixture, the dense interface formed by pyrene-modified coal gangue loaded with calcium sulfoaluminate through π-π stacking can be used for early interface reinforcement, improving impermeability (P9-P12) and interfacial pull-out strength (≥2MPa); calcium sulfoaluminate is anchored to the surface of pyrene-modified coal gangue through dynamic covalent bonds of aldehyde-hydrazide, delaying its hydration rate. β-cyclodextrin-coated magnesium oxide microcapsules provide sustained-release Mg in the middle stage. 2+ It can be used to compensate for shrinkage during medium-term expansion and prevent through cracks. Compared with the conventional underground structure concrete in Example 1, the concrete in Example 2 is used in an underground roof structure, which is a low-confinement area. Therefore, with a lower anti-cracking agent dosage (6wt%), the 28-day restricted expansion rate of the concrete can reach 1.8×10⁻⁶. -4 The bedrock concrete in Example 3 is used in a service environment under strong confinement; therefore, the dosage of the composite crack-resistant admixture needs to be appropriately increased to 10 wt% to achieve an expansion rate of 4.5 × 10⁻⁶ days over 7–14 days. -4 .

[0094] Comparative Example 1 lacked pyrene-free coal gangue, resulting in insufficient interfacial bonding strength, increased cracking, and a drop in impermeability grade to P6. Comparative Example 2 lacked β-cyclodextrin magnesium oxide microcapsules, leading to a lack of mid-term expansion and an expansion rate of only 5.0 × 10⁻⁶ days from 7 to 14 days. -4 Contraction intensified, with the 365-day shrinkage rate increasing to 1.8 × 10⁻⁶. -4 The impermeability was further reduced, with an impermeability grade of only P5. In Comparative Example 3, the coal gangue, without activation and pyrene modification, could not form dynamic acylhydrazone bonds with calcium sulfoaluminate for anchoring, leading to interfacial bonding failure and a significant reduction in interfacial bonding strength. Calcium sulfoaluminate particles were freely dispersed in the slurry and rapidly hydrated upon contact with water, causing uncontrolled early expansion (expansion rate reached 3.8 × 10⁻⁶ in 1-3 days). -4 The interfacial pull-out strength drops sharply to 1.1 MPa, which increases the risk of cracking in the plastic stage of concrete. Comparative Example 3 has the lowest impermeability grade (P4).

[0095] This invention utilizes the synergistic design of pyrene-modified coal gangue and β-cyclodextrin magnesium oxide slow release to synergistically exert early plastic crack inhibition and mid-term shrinkage compensation effects, thereby achieving a comprehensive improvement in the crack resistance of large-volume concrete and meeting the requirements of high impermeability, low shrinkage and high strength under complex constraints of underground structures.

[0096] 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 it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A type of high-strength concrete for large-volume underground structures, characterized in that, Includes the following components measured per cubic meter: 180~250kg low-heat silicate cement, 90~120kg fly ash, 150~210kg slag powder, 900~1100kg coarse aggregate and 650~800kg fine aggregate, 6~15kg polycarboxylate superplasticizer, 0.5~1.5kg retarder, 140~160kg water and composite crack-resistant admixture; The composite crack-resistant admixture is composed of pyrene-modified coal gangue supported on calcium sulfoaluminate and magnesium oxide microcapsules coated with β-cyclodextrin in a mass ratio of 1:1~2, and the dosage is 6~10 wt% of the cementitious material. The preparation steps of the pyrene-modified coal gangue supported on calcium sulfoaluminate are as follows: (1) Mix calcined coal gangue with an ethanol solution of 5-10 wt% pyrene-hydrazide modifier at a mass ratio of 1:1.5-2, and ultrasonically disperse for 1-1.5 h to obtain pyrene-modified coal gangue; (2) Calcium sulfoaluminate was treated with an ethanol solution of 2.5-5 wt% 3-aminopropyltriethoxysilane at 50-60°C for 3-4 h, and then 2.5-5 wt% glutaraldehyde solution was added and stirred at room temperature for 5-6 h to obtain surface aldehyde-modified calcium sulfoaluminate. (3) Surface aldehyde-modified calcium sulfoaluminate and pyrene-modified coal gangue are mixed in a ball mill at a mass ratio of 1:2 to obtain calcium sulfoaluminate-loaded pyrene-modified coal gangue. The synthesis steps of the pyrene-hydrazide modifier are as follows: (1) Under a nitrogen atmosphere, bromopyrene and p-formylphenylboronic acid were reacted at a molar ratio of 1:1.1~1.2 in the presence of a catalyst and an alkaline reagent in a water bath at 80~90℃ for 12~15h to obtain a pyrene-aldehyde intermediate; the catalyst was 2~5% of the molar amount of bromopyrene Pd(PPh3)4 and the alkaline reagent was 2.5~3 times the molar amount of bromopyrene sodium carbonate or potassium carbonate; (2) Under a nitrogen atmosphere, the pyrene-aldehyde intermediate and thiourea were condensed at a molar ratio of 1:1~1.2 for 12~18h, and the pH of the reaction system was controlled at 6~7 with a phosphate-phosphate buffer solution to obtain the pyrene-hydrazide modifier. The β-cyclodextrin-coated magnesium oxide microcapsules were obtained by mixing β-cyclodextrin coating solution and magnesium oxide at a mass ratio of 1:1.5~2 and then spray drying. The preparation process of the composite crack-resistant admixture is as follows: The calcium sulphoaluminate loaded pyrene modified coal gangue is mixed with β-cyclodextrin coated magnesium oxide microcapsules, and then is put into a fluidized bed under stirring, and is fluidized for 9-15 min under the conditions of air flow of 1.6-2.5 m 3 / (kg·h), temperature of 50-60 ℃, and vibration amplitude of 3-5 mm; the surface is sprayed with 3-5 wt% methyl cellulose binder solution, and the composite anti-cracking additive particles are obtained after drying and screening.

2. The large-volume high-strength concrete according to claim 1, characterized in that, The low-heat silicate cement has a 3-day heat of hydration ≤240kJ / kg, a tricalcium aluminate content ≤7wt%, and a tricalcium silicate content of 40~50wt%. The coarse aggregate is continuously graded crushed stone with a particle size of 5~25mm, a mud content ≤0.5wt%, and a needle-like and flaky particle content ≤15wt%. The fine aggregate is medium sand with a fineness modulus of 2.5~3.0 and a mica content ≤2wt%.

3. The large-volume high-strength concrete according to claim 1, characterized in that, The polycarboxylate superplasticizer has a water reduction rate of ≥25% and a solid content of 20~35wt%; the retarder is sodium gluconate or citric acid.

4. The large-volume high-strength concrete according to claim 1, characterized in that, The composite crack-resistant admixture has a particle size of 80~120μm and a bulk density of 1.8~2.0g / cm³. 3 .

5. The large-volume high-strength concrete according to claim 1, characterized in that, The specific surface area of ​​the calcium sulfoaluminate is ≥400 m². 2 / kg; the calcined coal gangue is the product of coal gangue after crushing, calcining at 900~1100℃, and ball milling, with a specific surface area ≥450m². 2 / kg.

6. The large-volume high-strength concrete according to claim 1, characterized in that, The β-cyclodextrin-coated magnesium oxide microcapsules have a particle size of 50~100μm; The spray drying conditions are: inlet air temperature 80~90℃, atomization pressure 0.2~0.3MPa; The concentration of the β-cyclodextrin coating solution is 5-10 wt%, and it also contains a dispersant and an auxiliary binder; the dispersant is 0.2-0.5 wt% sodium polyacrylate or sodium dodecyl sulfate, and the auxiliary binder is 1-2 wt% gelatin.

7. The large-volume high-strength concrete according to claim 1, characterized in that, The dosage of the composite crack-resistant admixture is adjusted according to the application site: The top slab consists of 6-7 wt% cementitious material. Basement floor / sidewalls, 7~9 wt%; The bedrock / pile foundation contact area is a strongly confined environment with a concentration of 9~10 wt%.

8. The method for preparing large-volume high-strength concrete according to any one of claims 1 to 7, characterized in that, Specifically, it includes: S1. Concrete mixing: First, put low-heat silicate cement, fly ash, and slag powder into the mixer and dry mix for 1-2 minutes. Then, add coarse aggregate and fine aggregate and continue dry mixing for 1-2 minutes. Next, add water, polycarboxylate superplasticizer, and retarder and wet mix for 2-3 minutes. Finally, add composite crack-resistant admixture and continue mixing for 3-5 minutes to obtain the concrete mixture. The slump should be controlled at 140-160 mm. S2. Moisture curing: The concrete mixture is poured into the mold, the surface is covered with a film and felt, and cured for 28 days at a humidity of ≥90%.

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