Superfine composite mineral admixture for tunnel engineering wet spraying concrete

Abstract

The invention discloses a superfine composite mineral admixture for tunnel engineering wet spraying concrete. The superfine composite mineral admixture comprises the following components in percentage by weight: 30-60 parts of dense silica fume; 40 to 70 parts of superfine slag powder; the weight of the dispersing agent is 0.03%-0.07% of the total weight of the dense silica fume and the superfine slag powder. According to the invention, industrial solid wastes such as silica fume, superfine slag powder and the like are used as raw materials, and the superfine composite mineral admixture for the wet-sprayed concrete with good dispersity is provided, so that cementing material particles tend to be closely stacked, contact points among powder particles are increased, the plastic viscosity and yield stress of fresh concrete are effectively increased, and the quality of the concrete is improved. The cohesiveness and the water-retaining property of fresh concrete are enhanced, and the rebound rate of wet-sprayed concrete is reduced.

Description

Technical Field

[0001] The invention relates to an admixture and a preparation method thereof, in particular to an ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering, belonging to the technical field of concrete admixtures. Background Art

[0002] Generally speaking, wet shotcrete is an important initial support material in modern tunnel construction. It quickly develops strength and, together with steel arches, steel mesh, and anchors, provides strong support for the surrounding rock, ensuring safety during subsequent construction and operation. However, wet shotcrete generally suffers from a high rebound rate during the spraying process, resulting in significant material waste and increased tunnel construction costs. Therefore, reducing the rebound rate of wet shotcrete is particularly important.

[0003] At present, in the existing technology, adding mineral admixtures (such as nanomaterials, silica fume, fly ash, slag, etc.) to improve the working performance of fresh concrete is an effective method to reduce the rebound rate of wet sprayed concrete. The larger the specific surface area of ​​the mineral admixture, the lower the rebound rate of wet sprayed concrete. Since the fine particles in the mineral admixture have a large specific surface area, they can absorb more water, thereby enhancing the thickening effect, improving the cohesion of the concrete, and improving its adhesion to the surrounding rock. At the same time, the smaller particle size helps to enhance the chemical reactivity of the material and promote the development of early adhesion. In addition, the addition of mineral admixtures can also improve the cohesion of concrete and enhance the wrapping of cement slurry on aggregates, thereby enhancing its integrity during the spraying process. As the consistency increases, the rebound energy required for concrete to hit the sprayed surface also increases, which is more conducive to reducing the rebound rate.

[0004] A search revealed a Chinese invention patent, CN 112441760 A, which discloses a composite admixture for shotcrete, its preparation method, and its application. The composite admixture consists of fly ash (50% to 70%), silica fume (15% to 25%), metakaolin (5% to 15%), plaster of Paris (0% to 5%), nano-sized α-Al2O3 (0% to 5%), and a surfactant (0% to 10%). When this composite admixture is used as one of the main cementitious materials in the preparation of shotcrete, the resulting concrete has a rebound rate of no more than 7%. This indicates that the addition of ultrafine mineral admixtures to shotcrete can indeed significantly reduce the rebound rate. However, the large amount of fly ash contained in this composite admixture, due to its low inherent activity, may have an adverse effect on the early strength development of shotcrete.

[0005] Another Chinese invention patent, published as CN 116969708 A, discloses a composite admixture, its preparation method, and application, as well as tunnel shotcrete. The composite admixture consists of silica fume (5-8 parts), nano-silica (0.1-1 part), nano-alumina (2-5 parts), nano-zirconium oxide (0.1-2 parts), glass powder (5-15 parts), silicate powder (0.5-3 parts), and aminocarboxylate (1-3 parts). Using this composite admixture in shotcrete can effectively control the rebound rate to within 8%. However, the high content of nanoscale components in this composite admixture may reduce the fluidity of fresh concrete, necessitating an increase in the amount of water reducer. Furthermore, the high content of glass powder in this admixture, due to its low activity, may adversely affect the early strength development of concrete. Although a small amount of sodium silicate has a certain alkali-stimulating effect, it may also accelerate the early hydration process of cement, thereby affecting the working life of fresh concrete.

[0006] Another Chinese invention patent, patent publication number CN 115849764 B, discloses a shotcrete admixture, its preparation method, and application. The admixture consists of a redispersible copolymer rubber powder (8-15 parts), an early strength enhancer (10-20 parts), composite mineral micropowder (40-60 parts), a modified composite fiber (0.5-3 parts), a water reducer (0.1-1.5 parts), and polyamide wax powder (0.05-0.5 parts). The addition of this admixture can effectively improve the early strength of shotcrete, reduce rebound rate, and mitigate adverse properties such as shrinkage. This type of composite admixture typically contains a thickening component, an early strength component, a water-reducing component, and a shrinkage-reducing and anti-cracking component, and is composed of a combination of multiple organic and inorganic components. However, it may have poor compatibility with cement and alkali-free accelerators, and may also cause abnormalities in the cement hydration process, thereby affecting the regulation of the workability of fresh concrete.

[0007] In summary, it can be seen that ultrafine mineral admixtures can significantly reduce the rebound rate of shotcrete, while the use of highly active mineral admixtures can help improve its early strength. Mineral admixtures usually have good environmental adaptability and compatibility with admixtures, and can maintain stable performance under different temperature and humidity conditions, thereby avoiding problems that may arise when using organic-inorganic composite materials. At the same time, the resource utilization of industrial solid waste such as silica fume and slag is in line with the development direction of the country's "dual carbon strategy". However, due to the small particle size of silica fume and ultrafine mineral admixtures, they are very prone to agglomeration, which affects their dispersion effect in fresh concrete, and thus has an adverse effect on the flow properties of fresh concrete and the density of hardened concrete, which often brings many inconveniences in practical applications.

[0008] Therefore, it is necessary to develop an ultrafine mineral admixture for wet shotcrete in tunnel engineering to optimize the composition of the mineral admixture and improve its dispersion performance, which is the key to solving the above technical problems. Summary of the Invention

[0009] In view of the many defects and shortcomings in the above-mentioned background technology, the present invention has made improvements and innovations thereto, with the aim of providing an ultrafine composite mineral admixture for wet sprayed concrete, which uses industrial solid waste such as silica fume and ultrafine slag powder as raw materials and has good dispersibility, so that the cementitious material particles tend to be densely packed, the contact points between the powder particles are increased, the plastic viscosity and yield stress of the fresh concrete are effectively increased, the cohesiveness and water retention of the fresh concrete are enhanced, and the rebound rate of the wet sprayed concrete is reduced.

[0010] To solve the above problems and achieve the above objectives, the present invention provides an ultrafine composite mineral admixture for wet sprayed concrete in tunnel engineering by adopting the following design structure and the following technical solutions:

[0011] An ultrafine composite mineral admixture for wet shotcrete in tunnel engineering, comprising the following components in percentage by weight:

[0012] Add 30-60 parts of silica fume;

[0013] 40-70 parts of ultrafine slag powder;

[0014] Dispersant, the weight of the dispersant is 0.03% to 0.07% of the total weight of the densified silica fume and the ultrafine slag powder.

[0015] Preferably, the densified silica fume is a by-product or co-product of producing ferrosilicon alloy or industrial silicon in an electric arc furnace, and its main component is glassy SiO2, its particle size is 10 to 500 nm, and its bulk density is 500 to 700 kg / m 3 .

[0016] Preferably, the ultrafine slag powder is a powder obtained by mechanically grinding industrial solid waste granulated blast furnace slag, wherein the median particle size (D 50 )<8μm.

[0017] Preferably, the dispersant is sodium hexametaphosphate.

[0018] Preferably, the weight of the dispersant is 0.05% of the total weight of the densified silica fume and the ultrafine slag powder.

[0019] Preferably, the densified silica fume is 43.5 parts; the ultrafine slag powder is 56.5 parts.

[0020] Preferably, the preparation method comprises:

[0021] The densified silica fume, ultrafine slag powder and dispersant are added into a ball mill and ground and dispersed together to obtain ultrafine composite mineral admixture for wet spraying concrete of tunnel engineering.

[0022] Preferably, the rotation speed of the ball mill is 48 r / min, and the grinding time is 10 to 30 min.

[0023] Preferably, the grinding time is 20 min.

[0024] The beneficial effects of the present invention compared with the prior art are:

[0025] 1. The silica fume and ultrafine slag powder in the ultrafine composite mineral admixture of the present invention have good dispersibility. When added to concrete, they form a sequential filling between silica fume, ultrafine slag powder, and cement particles, causing the cementitious material particles to tend to be densely packed, increasing the contact points between the powder particles, effectively increasing the plastic viscosity and yield stress of the fresh concrete, enhancing the cohesiveness and water retention of the fresh concrete, and reducing the rebound rate of the wet-sprayed concrete.

[0026] 2. The silica fume and ultrafine slag powder in the ultrafine composite mineral admixture of the present invention react with calcium hydroxide, a cement hydration product, in concrete to produce a volcanic ash reaction to form a hydrated calcium silicate gel, which further densifies the microstructure of the concrete, improves the interface transition zone, and thus enhances the mechanical properties and impermeability of the hardened concrete.

[0027] 3. Compared with organic-inorganic multi-component composite admixtures, the main raw materials of the ultrafine composite mineral admixture of the present invention are inorganic mineral industrial solid waste, which meets the "green and low-carbon" development requirements of my country's transportation industry; in addition, the ultrafine composite mineral admixture has good compatibility with cement and other concrete admixtures, the preparation method is simple, and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0029] Figure 1 It is a scanning electron microscope image of the densified silica fume, ultrafine slag powder and ultrafine composite mineral admixture involved in the present invention. DETAILED DESCRIPTION

[0030] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the technical solutions of the present invention are further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other unless there is a conflict. The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

[0031] According to the theory of close particle packing, ultrafine slag powder (micron-sized particles) can effectively fill the gaps between cement particles. At the same time, silica fume (nano-sized particles) is further filled between the ultrafine slag powder particles, thereby forming a denser stacking structure in the composite cementitious material system and significantly enhancing the cohesive properties of the slurry. Moreover, the close packing of particles will release excess water in the gaps of the cement slurry, which helps the flow properties of the concrete. According to the calculation results of the Fuller close packing model, the optimal mass ratio of silica fume (particle size <1μm) to ultrafine slag powder (particle size 1-8μm) is 4.35:5.65. Taking into account the errors that may exist in the actual preparation process, the present invention appropriately relaxes the mass ratio range of silica fume to ultrafine slag powder, where the proportion of silica fume is in the range of 30% to 60%, and the proportion of ultrafine slag powder is in the range of 40% to 70%.

[0032] In the present invention, in order to effectively improve the economy of storage and transportation, silica fume is usually treated with compressed air to promote particle agglomeration, thereby increasing its bulk density, which is called densified silica fume.

[0033] The densified silica fume in the present invention can be silica fume currently available on the market, which is obtained by processing.

[0034] The present invention also proposes a method for preparing the ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering, comprising the following steps: adding densified silica fume, ultrafine slag powder, and a dispersant to a ball mill for grinding and dispersing at a speed of 48 rpm for 10 to 30 minutes, preferably 20 minutes, to obtain the ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering. Scanning electron microscope images of the densified silica fume, ultrafine slag powder, and ultrafine composite mineral admixture are shown in FIG. Figure 1 The silica fume particles in the ultrafine composite mineral admixture are adsorbed on the surface of the ultrafine slag powder particles, and its dispersibility is greatly improved compared with the dense silica fume.

[0035] according to Figure 1 It can be concluded that the particles of densified silica fume are relatively coarse, and these coarse particles are formed by the agglomeration of nanoscale particles. Using the preparation method provided by the present invention, the coarse particles in the ultrafine composite mineral admixture are significantly reduced, and the nanoscale silica fume particles are uniformly adsorbed on the surface of the ultrafine slag powder, thereby greatly improving the dispersibility of the silica fume. This characteristic ensures that the ultrafine composite mineral admixture prepared by the present invention has a good dispersion effect in cement, achieving a step-by-step filling between the silica fume, ultrafine slag powder, and cement particles, effectively improving the flow properties of concrete.

[0036] In summary, the present invention will be further described in detail below with reference to specific examples:

[0037] Example 1

[0038] In this embodiment, ultrafine composite mineral admixture for wet spraying concrete of tunnel engineering is prepared according to the following steps and proportions:

[0039] Step 1: Weigh 30 parts of densified silica fume and 70 parts of ultrafine slag powder into a ball mill, and then add a dispersant at a total weight of 0.05% of the total weight of silica fume and ultrafine slag powder;

[0040] Step 2: After the addition is completed, the ball mill is turned on and ground for 20 minutes to evenly disperse the silica fume and ultrafine slag powder to obtain an ultrafine composite mineral admixture for wet shotcrete in tunnel engineering.

[0041] The prepared ultrafine composite mineral admixture was added to the concrete in an amount of 6% by weight instead of cement, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0042] Example 2

[0043] In this embodiment, ultrafine composite mineral admixture for wet spraying concrete of tunnel engineering is prepared according to the following steps and proportions:

[0044] Step 1: Weigh 43.5 parts of densified silica fume and 56.5 parts of ultrafine slag powder into a ball mill, and then add a dispersant at a total weight of 0.05% of the total weight of the silica fume and ultrafine slag powder;

[0045] Step 2: After the addition is completed, the ball mill is turned on and ground for 20 minutes to evenly disperse the silica fume and ultrafine slag powder to obtain an ultrafine composite mineral admixture for wet shotcrete in tunnel engineering.

[0046] The prepared ultrafine composite mineral admixture was added to the concrete in an amount of 6% by weight instead of cement, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0047] Example 3

[0048] In this embodiment, ultrafine composite mineral admixture for wet spraying concrete of tunnel engineering is prepared according to the following steps and proportions:

[0049] Step 1: Weigh 60 parts of densified silica fume and 40 parts of ultrafine slag powder and add them into a ball mill, and then add a dispersant with a total weight of 0.05% of the total weight of silica fume and ultrafine slag powder;

[0050] Step 2: After the addition is completed, the ball mill is turned on and ground for 20 minutes to evenly disperse the silica fume and ultrafine slag powder to obtain an ultrafine composite mineral admixture for wet shotcrete in tunnel engineering.

[0051] The prepared ultrafine composite mineral admixture was added to the concrete in an amount of 6% by weight instead of cement, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0052] Example 4

[0053] The ultrafine composite mineral admixture prepared in Example 2 was added to concrete in an amount of 3% by weight instead of cement, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0054] Example 5

[0055] The ultrafine composite mineral admixture prepared in Example 2 was added to concrete in an amount of 9% by weight instead of cement, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0056] Example 6

[0057] The ultrafine composite mineral admixture prepared in Example 2 was added to concrete in an amount of 12% by weight instead of cement, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0058] Comparative Example 1

[0059] A kind of dense silica fume with SiO2 content of 93% and specific surface area of ​​21100m 2 / kg.

[0060] Add equal weight of densified silica fume to concrete instead of cement at a dosage of 6%, and prepare wet sprayed concrete according to the mix proportion in Table 1.

[0061] Comparative Example 2

[0062] An ultrafine slag powder with a specific surface area of ​​709m 2 / kg, median particle size D 50 It is 4.8μm.

[0063] Ultrafine slag powder was added to the concrete in an amount of 6% instead of cement by weight, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0064] Comparative Example 3

[0065] An organic polymer viscosity increasing agent polyacrylamide.

[0066] Polyacrylamide accounting for 0.2‰ of the cement mass was added to the concrete, and wet sprayed concrete was prepared according to the mix ratio in Table 1.

[0067] Comparative Example 4

[0068] An organic polymer viscosity increasing agent: hydroxypropyl methylcellulose.

[0069] Hydroxypropyl methylcellulose accounting for 0.3‰ of the cement mass was added to the concrete, and wet sprayed concrete was prepared according to the mix proportion in Table 1.

[0070] The plastic viscosity and yield stress of fresh concrete were tested using a concrete rheometer. The slump, rebound, and compressive strength of wet shotcrete were tested in accordance with JGJ / T 372-2016, "Technical Specification for the Application of Shotcrete." The mix proportions for wet shotcrete are shown in Table 1. The alkali-free liquid accelerator was added at the spray nozzle at a rate of 7% of the total cementitious material. The results of the on-site wet shotcrete tests are shown in Table 2.

[0071] As shown in Table 1 below, Table 1 shows the mix ratio of wet sprayed concrete.

[0072] Table 1C25 wet shotcrete mix ratio (kg / m 3 )

[0073]

[0074]

[0075] Table 2 below is the test results of on-site C25 wet shotcrete:

[0076] Table 2 Test results of on-site C25 wet shotcrete

[0077]

[0078]

[0079] It can be seen from Examples 1 to 6 and Comparative Examples 1 to 2 that the addition of ultrafine composite mineral admixtures, silica fume and ultrafine slag powder can increase the plastic viscosity and yield stress of fresh concrete, thereby improving its cohesiveness and water retention, while reducing the slump and reducing the rebound rate of wet sprayed concrete. The improvement of the plastic viscosity and yield stress of fresh concrete helps to enhance its cohesiveness and water retention, thereby effectively reducing the rebound rate of wet sprayed concrete. However, the reduction in slump will increase pumping resistance and affect the construction efficiency of wet sprayed concrete. As the dosage of ultrafine composite mineral admixture gradually increases from 3% to 12%, the slump of wet sprayed concrete continues to decrease, while the plastic viscosity and yield stress gradually increase; compared with the blank group, its rebound rate is reduced by 39.0%, 54.5%, 58.0% and 60.0%, respectively. Compared with the use of silica fume or ultrafine slag powder alone, ultrafine composite mineral admixtures can achieve step-by-step filling of silica fume, ultrafine slag powder and cement particles in concrete due to their good dispersion properties, significantly increasing the number of contact points between particles, thereby further improving the plastic viscosity and yield stress of the slurry, and effectively reducing the rebound rate of wet sprayed concrete.

[0080] Taking into account the performance and workability, the appropriate dosage of ultrafine composite mineral admixture is about 6%. Without significantly affecting the pumping efficiency, the rebound rate of wet sprayed concrete can be controlled within 10%.

[0081] Furthermore, the addition of ultrafine composite mineral admixtures can improve the compressive strength of hardened concrete. These admixtures exert filling, nucleation, and pozzolanic effects in concrete, promoting the early hydration of cement. By consuming calcium hydroxide, a cement hydration product, they generate more CSH gel, effectively densifying the concrete's microstructure and the interface transition zone between aggregate and paste. Compared to using silica fume or ultrafine slag powder alone, ultrafine composite mineral admixtures exhibit more pronounced filling, nucleation, and pozzolanic effects in concrete due to their superior dispersion properties, further enhancing the concrete's mechanical properties.

[0082] Comparative Examples 3 and 4 show that incorporating an appropriate amount of an organic viscosity enhancer (such as polyacrylamide and hydroxypropyl methylcellulose) can significantly increase the plastic viscosity of fresh concrete and slightly increase its yield stress, with minimal effect on slump. It can also significantly reduce the rebound rate of wet-sprayed concrete, keeping it below 10%. However, the incorporation of an organic viscosity enhancer can, to a certain extent, reduce the early and late compressive strength of hardened concrete, which may have an adverse effect on initial support engineering.

[0083] In summary, the ultrafine composite mineral admixture prepared in the embodiment of the present invention can not only significantly reduce the rebound rate of wet sprayed concrete, but also improve its compressive strength, thereby achieving the dual effects of cost reduction and support performance improvement in engineering applications.

[0084] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and does not constitute any other limitation thereto. Any person skilled in the art may utilize the above-disclosed technical content to modify or modify the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and modifications to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention remain within the scope of protection of the present invention.

Claims

1. An ultrafine composite mineral admixture for wet shotcrete in tunnel engineering, characterized in that: The composition comprises the following components in percentage by weight: Add 30-60 parts of silica fume; 40-70 parts of ultrafine slag powder; Dispersant, the weight of the dispersant is 0.03% to 0.07% of the total weight of the densified silica fume and the ultrafine slag powder.

2. The ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to claim 1, characterized in that: The densified silica fume is a by-product or co-product of producing ferrosilicon alloy or industrial silicon in an electric arc furnace. Its main component is glassy SiO2, its particle size is 10-500nm, and its bulk density is 500-700kg / m 3 .

3. The ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to claim 1, characterized in that: The ultrafine slag powder is a powder obtained by grinding industrial solid waste granulated blast furnace slag through mechanical grinding, and its average particle size (D 50 )<8μm.

4. The ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to claim 1, characterized in that: The dispersant is sodium hexametaphosphate.

5. The ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to claim 1 or 4, characterized in that: The weight of the dispersant is 0.05% of the total weight of the densified silica fume and the ultrafine slag powder.

6. The ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to claim 1, characterized in that: The densified silica fume is 43.5 parts; the ultrafine slag powder is 56.5 parts.

7. The method for preparing ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to any one of claims 1 to 6, characterized in that: The preparation method comprises: The densified silica fume, ultrafine slag powder and dispersant are added into a ball mill and ground and dispersed together to obtain ultrafine composite mineral admixture for wet spraying concrete of tunnel engineering.

8. The method for preparing ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to claim 7, characterized in that: The rotation speed of the ball mill is 48 r / min, and the grinding time is 10 to 30 minutes.

9. The method for preparing ultrafine composite mineral admixture for wet spraying concrete in tunnel engineering according to claim 7, characterized in that: The grinding time is 20 min.

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