Quick-hardening early-strength concrete mineral additive and preparation method thereof

Abstract

The invention discloses a quick-hardening early-strength concrete mineral additive and a preparation method thereof, and belongs to the technical field of building materials. The additive comprises the following components in parts by weight: 50-75 parts of a mineral active material (compounded by silica fume, slag powder and metakaolin), 15-30 parts of a composite activator (sodium silicate, lithium sulfate and triethanolamine synergistically), 5-10 parts of a sustained-release microcapsule (calcium sulphoaluminate coated with nano-silica) and 2-5 parts of an auxiliary thickening agent (compounded by HPMC and a water reducing agent). The preparation method comprises the steps of mineral activation, excitant reaction and mixing of the microcapsule and the thickening agent. After the additive is doped into concrete, the 3h compressive strength is greater than or equal to 15MPa, the initial setting time is less than or equal to 5min, and the additive has low resilience (less than or equal to 13%), high durability (impermeability is greater than or equal to P11) and environmental adaptability (-5 DEG C strength fluctuation ratio is less than or equal to 9%). And compared with the prior art, the cost is reduced by 40%, and the method has remarkable economic and social benefits.

Description

TECHNICAL FIELD

[0001] The application discloses a fast-hardening and early-strength concrete mineral additive and a preparation method thereof, and belongs to the technical field of building materials. BACKGROUND

[0002] In the field of construction engineering, with the continuous improvement of construction efficiency requirements and the increasing demand for engineering durability, fast-hardening and early-strength concrete technology has gradually become a key direction of research and application. However, while pursuing rapid hardening and high strength, existing technical solutions often fail to balance cost, environmental friendliness and construction performance, and have many technical bottlenecks.

[0003] Limitations of existing fast-hardening cement:

[0004] Currently, fast-hardening cement such as sulphoaluminate cement mainly relies on high-dose early-strength components (such as calcium sulphoaluminate) to achieve rapid hardening. Although this type of cement can achieve high strength in a short period of time, its production cost is high, and due to the high proportion of special components, it has poor versatility and is difficult to adapt to the needs of different engineering scenarios. For example, the high-early-strength cement system proposed in patent CN109160762A performs well under specific conditions, but its stringent requirements for raw materials and process conditions limit its large-scale popularization and application. To solve the contradiction between transportation and construction performance, some technologies use slow-release additives to inhibit early hydration. This type of technology balances the workability and strength development of concrete by regulating the release rate of the additive. However, as described in patent CN114920485A, slow-release additives often require complex in-situ polymerization processes and rely on organic solvents as carriers, which not only increases production costs but also poses environmental risks. In addition, the complex process flow also limits its popularity in actual engineering.

[0005] Traditional early-strength agents such as sodium sulfate can significantly improve the early strength of concrete, but their mechanism is single and can easily cause a large internal humidity gradient in the concrete, leading to shrinkage cracking and significantly reducing the durability of the concrete. In the application of shotcrete, traditional early-strength agents can also cause an increase in rebound rate and insufficient interfacial bond strength, affecting construction quality and efficiency. These problems are particularly pronounced in low-temperature environments, further limiting the application range of traditional early-strength agents.

[0006] And the demand for rapid construction and durability in current construction engineering is increasing, especially in scenarios such as emergency repair engineering, tunnel support, and bridge construction, there is an urgent need for a concrete additive that can achieve rapid hardening and high strength development while ensuring long-term durability and construction performance, while also considering cost and environmental friendliness. However, existing technologies are difficult to find a balance between fast-hardening and durability, construction performance, and are difficult to meet the complex and changing needs of engineering. SUMMARY

[0007] To solve the above-mentioned prior art problems, the application discloses a fast-hardening and early-strength type concrete mineral additive and a preparation method thereof, and the accelerated hydration reaction of mineral materials is realized by optimizing the proportioning of mineral active materials (silica fume, slag powder, and metakaolin) and introducing a composite activator (sodium silicate, lithium sulfate, and triethanolamine), so that the early strength of concrete is significantly improved.

[0008] A fast-hardening and early-strength type concrete mineral additive, which comprises the following components in parts by weight:

[0009] Mineral active material 50-75 parts: composed of silica fume, slag powder, and metakaolin in a mass ratio of (2-4):(3-5):(1-2);

[0010] Composite activator 15-30 parts: composed of sodium silicate, lithium sulfate, and triethanolamine in a mass ratio of (5-7):(2-3):(1-1.5);

[0011] Slow-release microcapsule 5-10 parts: containing calcium sulfoaluminate particles coated with nanosilica, and the particle size of the microcapsule is 10-50 μm;

[0012] Auxiliary thickening agent 2-5 parts: a compound of hydroxypropyl methylcellulose (HPMC) and polycarboxylic acid water reducing agent in a mass ratio of (1:1).

[0013] Further, in the above fast-hardening and early-strength type concrete mineral additive, the specific surface area of the silica fume in the mineral active material is ≥15000 m 2 / kg, the activity index of the slag powder is ≥95%, and the Al2O3 content of the metakaolin is ≥35%.

[0014] Further, in the above fast-hardening and early-strength type concrete mineral additive, the preparation method of the slow-release microcapsule comprises:

[0015] The calcium sulfoaluminate powder and nanosilica are mixed in a mass ratio of (10:1), and a coating layer is formed at 200-300 DEG C through a spray drying method;

[0016] The coated particles are treated by low-temperature plasma to enhance the surface bonding force.

[0017] The application further discloses a preparation method of the additive, comprising the following steps:

[0018] S1: after the silica fume, slag powder, and metakaolin are mixed in proportion, they are ground in a ball mill to a specific surface area ≥800 m 2 / kg;

[0019] S2: Dissolve sodium silicate, lithium sulfate and triethanolamine in distilled water to form an activator solution, and stir the product of step S1 at 60-80 DEG C for 30-60 min.

[0020] S3: Add the slow-release microcapsule and auxiliary thickening agent, mix uniformly under vacuum, dry and crush to a particle size of less than or equal to 100 microns.

[0021] Further, in the above preparation method, the concentration of the activator solution in step S2 is 20-30 wt%, and the reaction temperature is controlled at 70 DEG C ± 2 DEG C.

[0022] The application also discloses an application method of the additive, and the mixing amount of the additive in the cementitious material is 5-20% of the total mass of the cementitious material, and the cementitious material is at least one of ordinary portland cement, fly ash and mineral powder.

[0023] Further, in the above application method, when the additive is applied to sprayed concrete, the mixing amount is 15-20%, and the compatibility with the quick-setting agent satisfies that the initial setting time is less than or equal to 5 min, and the final setting time is less than or equal to 10 min.

[0024] The application also discloses a concrete product containing the additive, and the concrete product comprises the following mass ratio:

[0025] Cement 300-450 kg / m 3 ;

[0026] Additive 15-90 kg / m 3 ;

[0027] Aggregate 1600-1800 kg / m 3 ;

[0028] Water-binder ratio 0.35-0.45.

[0029] Further, in the above concrete product, the 3h compressive strength of the concrete is greater than or equal to 15 MPa, the 24h compressive strength is greater than or equal to 35 MPa, and the 28d compressive strength is greater than or equal to 70 MPa.

[0030] Further, in the above concrete product, when the concrete is constructed in an environment of-5 DEG C to 40 DEG C, the 3h strength fluctuation rate is less than or equal to 10%.

[0031] Compared with the prior art, the application has the following outstanding beneficial effects:

[0032] The mineral additive for quick-hardening and early-strength concrete of the present application exhibits overall performance advantages, bringing revolutionary improvements to concrete engineering. Its quick-hardening and early-strength performance is particularly outstanding, with the concrete achieving a compressive strength of more than 15 MPa within 3 hours and a 24-hour strength of more than 35 MPa, significantly shortening the construction period and being particularly suitable for emergency scenarios such as repair and rescue; meanwhile, the 28-day strength is as high as 73 MPa, ensuring long-term structural stability. Through innovative slow-release microcapsule technology, the additive controls the concrete strength fluctuation rate within 9% in a wide temperature range of -5°C to 40°C, completely solving the technical bottleneck of low-temperature construction and ensuring construction quality under different climate conditions.

[0033] In terms of construction performance, the additive reduces the rebound rate of shotcrete to below 13%, reduces material waste by more than 50% compared to traditional technology, and significantly improves the interfacial bonding strength between new and old concrete to more than 2.7 MPa, effectively avoiding the risk of structure delamination and falling off. In terms of durability, it has achieved a qualitative leap, with a freeze-thaw mass loss rate of less than 2.3%, a chloride ion permeation amount of only 45% of the traditional standard, an impermeability grade of P11, a long-term use shrinkage rate reduced by more than 50%, greatly extending the engineering life and reducing the risk of cracking.

[0034] What is worth noting is that the mineral active material accounts for more than 50% in the formulation of the additive, making full use of industrial waste, not only reducing the cost by 40%, but also completely abandoning organic solvents, in line with the development trend of green building materials. These comprehensive performance advantages enable the present application to achieve industry-leading levels in terms of rapid construction, environmental adaptation, quality control, cost control, and environmental benefits, setting a new technical benchmark for the field of concrete additives. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Comparison of the compressive strength of the concrete of Examples 1-5 and Comparative Examples 1-5;

[0036] Figure 2 Comparison of the temperature fluctuation rate (-5°C / 40°C) of the concrete of Examples 1-5 and Comparative Examples 1-5;

[0037] Figure 3 Comparison of the setting time of the concrete of Examples 1-5 and Comparative Examples 1-5;

[0038] Figure 4 Comparison of the shotcrete rebound rate (%) of the concrete of Examples 1-5 and Comparative Examples 1-5;

[0039] Figure 5 Comparison of the freeze-thaw cycle resistance (mass loss rate %) of the concrete of Examples 1-5 and Comparative Examples 1-5;

[0040] Figure 6Comparative of the concrete resistance to chloride ion penetration (Coulomb) of Examples 1-5 and Comparative Examples 1-5. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0042] The formula and preparation method of the examples and comparative examples are specifically defined as follows.

[0043] A fast-hardening and early-strength type concrete mineral additive comprises the following components in parts by weight:

[0044] 50-75 parts of mineral active material: composed of silica fume, slag powder and metakaolin in a mass ratio of (2-4):(3-5):(1-2);

[0045] 15-30 parts of composite activator: composed of sodium silicate, lithium sulfate and triethanolamine in a mass ratio of (5-7):(2-3):(1-1.5);

[0046] 5-10 parts of slow-release microcapsules: containing calcium sulfoaluminate particles coated with nanosilica, and the particle size of the microcapsules is 10-50 μm;

[0047] 2-5 parts of auxiliary thickening agent: compounded from hydroxypropyl methylcellulose (HPMC) and polycarboxylic acid water reducing agent in a mass ratio of (1:1).

[0048] The specific surface area of the silica fume in the mineral active material is ≥15000 m 2 / kg, the activity index of the slag powder is ≥95%, and the Al2O3 content of the metakaolin is ≥35%.

[0049] The preparation method of the slow-release microcapsules comprises:

[0050] The calcium sulfoaluminate powder and nanosilica are mixed in a mass ratio of (10:1), and a coating layer is formed at 200-300°C by spray drying;

[0051] The coated particles are treated by low-temperature plasma to enhance the surface bonding force.

[0052] The specific process is as follows

[0053] 1. Preparation and mixing of raw materials

[0054] Raw materials:

[0055] Calcium sulphoaluminate powder (particle size ≤ 50 μm, need to be dried in advance)

[0056] Nano-silica powder (particle size ≤ 30 nm, purity ≥ 99.5%)

[0057] Mixing process:

[0058] Calcium sulphoaluminate: nano-silica = 10:1 by mass ratio, add to the three-dimensional motion mixer.

[0059] Mixing speed 50 rpm, time 30 min, ensure that the nano-silica is evenly attached to the surface of the calcium sulphoaluminate.

[0060] 2. Spray drying method of coating

[0061] Equipment:

[0062] Centrifugal spray dryer (equipped with 1.0 mm nozzle, atomizing wheel speed ≥ 16000 rpm)

[0063] Process parameters:

[0064] Feeding speed: peristaltic pump speed 20 rpm, liquid flow rate 50 mL / min.

[0065] Inlet air temperature: 250℃ (precisely controlled by electric heater, temperature fluctuation ≤ ±1℃).

[0066] Outlet air temperature: 120℃ (automatically adjusted by PID feedback to avoid inactivation of heat-sensitive materials).

[0067] Atomization pressure: compressed air 0.3 MPa (provides stable droplet size distribution, D50 ≈ 20 μm).

[0068] Coating mechanism:

[0069] High-temperature gas instantaneously evaporates water droplets, and nano-silica melts on the surface of calcium sulphoaluminate to form a glassy coating layer.

[0070] 3. Low-temperature plasma surface treatment

[0071] Equipment:

[0072] RF plasma treatment instrument (frequency 13.56 MHz, power 100 W)

[0073] Process parameters:

[0074] Working gas: oxygen (flow rate 50 sccm, providing active oxygen free radicals).

[0075] Treatment power: 100 W.

[0076] Treatment time: 5 min.

[0077] Vacuum: 30 Pa.

[0078] The preparation method of the additive comprises the following steps:

[0079] S1: After mixing the silica ash, slag powder and metakaolin in proportion, grind them in a ball mill to a specific surface area ≥800 m 2 / kg;

[0080] S2: Dissolve sodium silicate, lithium sulfate and triethanolamine in distilled water to prepare an activator solution, and stir the product of step S1 at 60-80°C for 30-60 min;

[0081] S3: Add slow-release microcapsules and auxiliary thickening agents, mix uniformly under vacuum, dry and crush to a particle size ≤100 μm.

[0082] Examples 1-5

[0083] The component ratio of the additive is shown in Table 1.

[0084] Table 1 Formulation of additive and corresponding concrete ratio of examples 1-5

[0085]

[0086]

[0087] 1. Preparation steps of the additive:

[0088] 1) Mineral activation: Mix silica ash (specific surface area ≥15000 m 2 / kg), slag powder (activity index ≥95%) and metakaolin (Al2O3 content ≥35%) in proportion, and ball mill to a specific surface area ≥800 m 2 / kg.

[0089] 2) Activator reaction: Dissolve sodium silicate, lithium sulfate and triethanolamine in distilled water (concentration 25 wt%), and stir the mineral active material at 70°C for 45 min.

[0090] 3) Mixing and coating: Add slow-release microcapsules (calcium sulfoaluminate coated with nano-silicon dioxide + plasma treatment) and auxiliary thickening agents, mix under vacuum, dry and crush to a particle size ≤100 μm.

[0091] 2. The preparation method of the slow-release microcapsules comprises:

[0092] Mix calcium sulfoaluminate powder and nano-silicon dioxide in a mass ratio of 10:1, and form a coating layer at 250°C by spray drying;

[0093] The coated particles are treated by low temperature plasma to enhance the surface binding force.

[0094] 3. Preparation steps of concrete:

[0095] According to the proportion, the cement, sand and gravel are weighed and added with additives and water, and stirred for 5 min until uniform;

[0096] Pour into 150mmx150mmx150mm test block, standard curing (20±2℃, RH≥95%).

[0097] Comparative Examples 1-5

[0098] (Comparison of prior art and missing key components)

[0099] Comparative Examples 1-5 are set, and the formula and process are shown in Table 2.

[0100] Table 2 Formulation and process of comparative examples

[0101]

[0102]

[0103] The concrete preparation and curing process is the same as in the examples.

[0104] Test Example 1

[0105] Compressive strength test

[0106] Test method:

[0107] Test piece preparation: according to GB / T 17671-1999 standard, 150mmx150mmx150mm concrete test block is formed, and standard curing (20±2℃, RH≥95%).

[0108] Loading rate: 0.5MPa / s uniform pressure to failure, record peak load.

[0109] Temperature fluctuation rate: the test block is cured in-5℃ and 40℃ environment respectively, and the difference percentage of 3h strength (|high temperature-low temperature| / normal temperature strengthx100%) is calculated.

[0110] The results are shown in Table 3 and Figures 1-2 .

[0111] Table 3 Compressive strength test

[0112]

[0113] From the above table data, it can be seen that:

[0114] All the 3h strength of Example 3h is ≥15MPa, 24h strength ≥35MPa, 28d strength ≥73MPa, significantly better than the comparative examples (e.g. 3h strength of Comparative Example 1 is only 10.7MPa). Example 3 performs best: 3h strength 17.1MPa, 28d strength 78.3MPa, 60% higher than Comparative Example 1 (Patent 1).

[0115] Key differences:

[0116] The role of slow-release microcapsules (Comparative Example 1 vs. Comparative Example 4): The 3h strength of Comparative Example 4 (without microcapsules) decreases by 13% (14.1MPa→16.5MPa), proving the contribution of microcapsules to the early strength by precisely releasing active components.

[0117] Mineral active material compounding (Comparative Example 1 vs. Comparative Example 3): The 3h strength of Comparative Example 3 (without metakaolin) is only 9.2MPa, indicating that the aluminum phase (Al2O3≥35%) of metakaolin is crucial for accelerating the hydration reaction.

[0118] Test Example 2

[0119] Setting time and construction performance

[0120] Test method:

[0121] Setting time: According to GB / T 1346-2011, the Vicat apparatus is used to determine the initial setting (penetration ≤4mm) and final setting (penetration ≤0.5mm) time.

[0122] Shot rebound rate: According to EN 14488-2-2006, simulate the shot construction of tunnel side wall, collect the mass percentage of fallen concrete.

[0123] The results are shown in Table 4 and Figures 3-4 .

[0124] Table 4 Setting time and construction performance

[0125] Group Initial setting time (min) Final setting time (min) Spraying rebound rate (%) Example 1 4 8 12 Example 2 5 9 13 Example 3 3 7 11 Example 4 4 8 12 Example 5 5 9 13 Comparative Example 1 15 30 25 Comparative Example 2 8 15 18 Comparative Example 3 20 40 30 Comparative Example 4 7 12 17 Comparative Example 5 25 45 35

[0126] From the results in Table 4, the initial setting time of the examples is ≤5min, and the final setting time is ≤9min, meeting the needs of rapid support for repair and shotcrete (the initial setting time of Comparative Example 1 is 15min, which cannot meet the urgent construction). Example 3 performs best: initial setting 3min, final setting 7min, rebound rate only 11%, 39% lower than Comparative Example 2 (Patent 2).

[0127] Key differences:

[0128] Synergistic effect of composite activator: In the examples, sodium silicate (inorganic activation) and triethanolamine (organic complexation) synergistically accelerate hydration, while Comparative Example 5 (only sodium sulfate) has an initial setting time of 25min.

[0129] Auxiliary thickening effect: HPMC complexed with water reducing agent to improve the cohesiveness of the paste, reducing the rebound of the spray (Example 1 rebound rate 12% vs. 25% of Comparative Example 1).

[0130] Test Example 3

[0131] Durability test

[0132] Test method description:

[0133] Freeze-thaw resistance: according to the rapid freezing method (GB / T 50082-2009), the test block is frozen at -20°C for 4h, and thawed in water at 20°C for 4h, and the mass loss rate is calculated after 50 cycles.

[0134] Chloride ion permeability: using ASTM C1202 electric flux method, the test block is tested under 60V direct current for 6h, the lower the total flux (Coulomb), the better the impermeability.

[0135] Impermeability grade: according to the step-by-step pressure method (0.1MPa / 8h increment), until the test block is permeated, record the highest pressure value (such as P12=1.2MPa).

[0136] The results are shown in Table 5 and Figures 5-6 .

[0137] Table 5 Durability test results

[0138]

[0139]

[0140] From the test results in Table 5, the advantages of the examples can be seen:

[0141] The mass loss rate of freeze-thaw resistance is ≤2.3%, the chloride ion permeability is ≤900C, and the impermeability grade is ≥P11, which is much better than the comparative examples (such as the impermeability of Comparative Example 1 is only P8). Example 3 has the best durability: impermeability grade P13 (1.3MPa), chloride ion permeability 800C, which is 300% higher than Comparative Example 1.

[0142] Key differences:

[0143] Compact filling of mineral active materials: silica fume (specific surface area ≥15000m 2 / kg) and slag powder fill the pores, reduce permeability. Long-term protection of slow-release microcapsules: nanosilica-coated calcium sulfoaluminate delays the invasion of harmful ions, and the impermeability grade of Comparative Example 4 (without microcapsules) is only P10.

[0144] Test Example 4

[0145] Long-term shrinkage test (GB / T 50082-2009)

[0146] Specimen curing: standard curing to 28d and 90d, measure length change (precision 0.001mm), calculate shrinkage (AL / L0x10 6 )

[0147] Results are shown in Table 6.

[0148] Table 6 Long-term shrinkage test results

[0149] Group 28d shrinkage (x10 -6 )]]> 90d shrinkage (x10 -6 )]]> Example 1 320 420 Example 2 335 440 Example 3 310 400 Example 4 325 430 Example 5 330 435 Comparative Example 1 580 750 Comparative Example 2 500 650 Comparative Example 3 620 800 Comparative Example 4 450 600 Comparative Example 5 700 900

[0150] From the above Table 6, the advantages of the embodiments of the application can be seen:

[0151] 28d shrinkage ≤330x10 -6 , 90d ≤435x10 -6 , significantly lower than the comparative examples (such as 700x10 -6 of Comparative Example 5). The shrinkage of Example 3 is the lowest: 28d 310x10 -6 , 90d 400x10 -6 , which proves that the high-activity mineral system reduces drying shrinkage.

[0152] Key differences:

[0153] Composite activator inhibits shrinkage: triethanolamine complex calcium ions, reduces the crystallization expansion stress of hydration product Ca(OH)2. The shrinkage of Comparative Example 3 (without metakaolin) is as high as 620x10 -6 , which shows that the pozzolanic reaction of metakaolin is crucial to volume stability.

[0154] Test Example 5

[0155] Bond strength test (JGJ / T 70-2009)

[0156] Test method description:

[0157] New and old concrete interface is brushed with interface agent, and after spraying or pouring, it is cured for 28d, and the bond strength is tested by using a puller (loading rate 0.05MPa / s).

[0158] Results are shown in Table 7

[0159] Table 7 Bond strength test results

[0160] Group New and old concrete bonding strength (MPa) Example 1 2.8 Example 2 2.7 Example 3 3.0 Example 4 2.9 Example 5 2.7 Comparative Example 1 1.5 Comparative Example 2 1.8 Comparative Example 3 1.2 Comparative Example 4 2.0 Comparative Example 5 1.0

[0161] Advantages of the embodiments:

[0162] Bond strength ≥ 2.7 MPa (3.0 MPa for Example 3), meeting the requirement of JGJ / T 70-2009 (≥ 2.5 MPa is excellent), while Comparative Example 5 is only 1.0 MPa.

[0163] Key differences:

[0164] Interface enhancement of mineral active materials: silica fume forms C-S-H gel with cement paste, improving interface density (SEM shows no cracks at interface of Example 1).

[0165] Comparative Example 2 (Patent 2 technology) has only 1.8 MPa of interface bond strength due to poor compatibility of traditional slow-release agent with cement.

[0166] Example 6

[0167] Application example

[0168] 1. Additive for shotcrete and construction

[0169] Formulation and process parameters

[0170] Additive formulation:

[0171] Mineral active materials (silica fume: slag powder: metakaolin = 3.5:4:1.5, total amount 65 parts);

[0172] Composite activator (sodium silicate: lithium sulfate: triethanolamine = 6:2.5:1.2, total amount 20 parts);

[0173] Slow-release microcapsules (8 parts, particle size 15 μm);

[0174] Auxiliary thickening agent (HPMC: water reducing agent = 1:1, 4 parts).

[0175] Shotcrete formulation (kg / m 3 ):

[0176] Cement (42.5 ordinary portland cement) 420;

[0177] Additive (Example 6 self-made) 25;

[0178] Sand (medium sand, fineness modulus 2.6) 750;

[0179] Stone (5-10 mm continuous gradation) 1050;

[0180] Water-binder ratio 0.36;

[0181] Accelerator (alkali-free type) dosage 4% (total mass of cementitious materials).

[0182] Preparation and construction process:

[0183] Additive preparation: Same as the process of Example 1, ensuring the slow-release microcapsules enhance surface stability after plasma treatment.

[0184] Concrete mixing: Dry cement, sand, and gravel were mixed for 1 min, then the additive and 80% water were added and mixed for 2 min, and finally the accelerator and the remaining water were added and mixed until uniform.

[0185] Spraying construction:

[0186] Equipment: Zhongtie Yanfeng wet sprayer, nozzle diameter 50 mm;

[0187] Spraying parameters: air pressure 0.5 MPa, spraying distance 1.2 m, spraying angle 80°-90°;

[0188] Layered spraying: the first layer was 50 mm thick, and the second layer was sprayed 10 min later to a total thickness of 150 mm.

[0189] Test items and results

[0190] 2. Workability and rebound rate (EN 14488-2-2006)

[0191] Test method:

[0192] Slump flow: initial slump flow of fresh concrete and retained value after 30 min;

[0193] Rebound rate: sprayed 1 m 2 Area, the mass ratio of the fallen concrete was collected.

[0194] Results are shown in Table 8

[0195] Table 8 Workability and rebound rate

[0196] Group Expansion (mm) 30 min expansion loss rate Rebound rate (%) Example 6 260 ≤5％ 10 Comparative Example 2 240 15％ 18 Comparative Example 5 200 30％ 35

[0197] Conclusion:

[0198] Example 6 due to the inhibition of early hydration by slow-release microcapsules, the slump loss rate was only 5%, and the rebound rate was as low as 10%, which was significantly better than Comparative Example 2 (Patent 2 technology).

[0199] 3. Setting time and early strength (GB / T 35159-2017)

[0200] Test method:

[0201] Setting time: tested immediately after simulated spraying;

[0202] Strength test block: standard curing after spraying molding, test 8h, 24h strength.

[0203] Results are shown in Table 9

[0204] Table 9 Setting time and early strength

[0205]

[0206] The 8h strength of Example 6 reached 18.5MPa, meeting the immediate load bearing requirement of tunnel support (industry requirement ≥8MPa), and increased by 83% compared to Comparative Example 2.

[0207] 4. Interfacial bond strength and durability (JGJ / T 70-2009)

[0208] Test method:

[0209] Bond strength: interfacial pull-out test of sprayed layer and existing concrete;

[0210] Freeze-thaw resistance: 50 times of quick freeze cycles (-20℃~20℃);

[0211] Permeability resistance grade: no leakage under step-by-step pressurization to 1.4MPa.

[0212] Results are shown in Table 10.

[0213] Table 10 Interfacial bond strength and durability

[0214]

[0215]

[0216] Example 6 reached a bond strength of 3.2MPa and a permeability resistance grade of P14 due to the pore filling of mineral active materials, far exceeding Comparative Example 2 (P9).

[0217] The above examples and test examples are summarized as follows:

[0218] 1. Outstanding fast hardening and early strength performance:

[0219] 3h compressive strength ≥15MPa (up to 17.1MPa), 24h strength ≥35MPa, and 28d strength ≥73MPa, increased by more than 90% compared to traditional early strength agents (Comparative Example 5).

[0220] Initial setting time ≤5min and final setting time ≤9min, meeting the immediate support requirement of repair and rescue and sprayed concrete.

[0221] 2. Excellent environmental adaptability:

[0222] The slow-release microcapsules (calcium sulphoaluminate coated with nano-silicon dioxide) precisely control the release of active components, with a strength fluctuation rate of ≤9% in the environment of -5℃~40℃, solving the low-temperature construction problem (low-temperature failure of Comparative Patent 1).

[0223] 3. Excellent construction performance:

[0224] Spraying rebound rate ≤ 13% (only 11% in Example 3), reduced by 56% compared with traditional technology (rebound rate 25% in Comparative Example 1), reducing material waste.

[0225] New and old concrete interface bonding strength ≥ 2.7 MPa (up to 3.0 MPa in Example 3), avoiding the risk of delamination and falling off.

[0226] 4. Overall improvement of durability:

[0227] Anti-freeze mass loss rate ≤ 2.3% (≤ 5% according to national standard), chloride ion permeability ≤ 900C (≤ 2000C according to national standard), impermeability grade ≥ P11, life cycle extended by more than 30%.

[0228] Long-term shrinkage rate ≤ 435 × 10 -6 (900 × 10 -6 in Comparative Example 5), significantly reducing the risk of cracking.

[0229] 5. Economical and environmentally friendly:

[0230] Mineral active material (silica fume, slag powder, metakaolin) ratio ≥ 50%, using industrial waste to reduce cost by 40%, and no organic solvent pollution.

[0231] The above are only a few preferred embodiments of the present application, which are described in more detail and in more detail, but should not be construed as limiting the scope of the present patent. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application.

Claims

1. A rapid-hardening, early-strength concrete mineral additive, characterized in that, The following components are included by weight: 50-75 parts of mineral active material: composed of silica fume, slag powder and metakaolin in a mass ratio of (2-4):(3-5):(1-2); 15-30 parts of composite activator: composed of sodium silicate, lithium sulfate, and triethanolamine in a mass ratio of (5-7):(2-3):(1-1.5); 5-10 parts of sustained-release microcapsules: containing calcium sulfoaluminate particles coated with nano-silica, with a microcapsule particle size of 10-50 μm; 2-5 parts of auxiliary thickener: a mixture of hydroxypropyl methylcellulose (HPMC) and polycarboxylate superplasticizer in a mass ratio of 1:

1.

2. The additive according to claim 1, characterized in that, The specific surface area of ​​silica fume in the mineral active material is ≥15000 m². 2 / kg, the activity index of slag powder is ≥95%, and the Al2O3 content of metakaolin is ≥35%.

3. The additive according to claim 1, characterized in that, The method for preparing the sustained-release microcapsules includes: Calcium sulfoaluminate powder and nano-silica were mixed at a mass ratio of 10:1 and a coating layer was formed at 200-300°C by spray drying. The coated particles are treated with low-temperature plasma to enhance surface adhesion.

4. A method for preparing the additive according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Mix silica fume, slag powder, and metakaolin in a certain proportion, then grind them in a ball mill until the specific surface area is ≥800m². 2 / kg; S2: Dissolve sodium silicate, lithium sulfate, and triethanolamine in distilled water to prepare an activator solution, and react it with the product of step S1 at 60-80°C for 30-60 min. S3: Add sustained-release microcapsules and auxiliary thickener, mix evenly under vacuum conditions, dry and then pulverize to a particle size ≤100μm.

5. The preparation method according to claim 4, characterized in that, In step S2, the concentration of the activator solution is 20-30 wt%, and the reaction temperature is controlled at 70℃±2℃.

6. A method of applying the additive according to any one of claims 1 to 3, characterized in that, The dosage in concrete cementitious materials is 5% to 20% of the total mass of cementitious materials, and the cementitious materials are at least one of ordinary Portland cement, fly ash, and mineral powder.

7. The application method according to claim 6, characterized in that, When applied to shotcrete, the dosage is 15-20%, and the compatibility with accelerators must meet the following requirements: initial setting time ≤ 5 min, final setting time ≤ 10 min.

8. A concrete product containing the additive according to any one of claims 1 to 3, characterized in that, Includes the following mass ratios: Cement 300~450kg / m 3 ; Additives 15-90 kg / m 3 ; Aggregate 1600~1800kg / m 3 ; Water-to-binder ratio: 0.35–0.

45.

9. The concrete product according to claim 8, characterized in that, The concrete has a 3-hour compressive strength ≥15MPa, a 24-hour compressive strength ≥35MPa, and a 28-day compressive strength ≥70MPa.

10. The concrete product according to claim 8, characterized in that, When the concrete is constructed in an environment of -5℃ to 40℃, the strength fluctuation rate over 3 hours is ≤10%.

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