High-early-strength low-resilience sprayed concrete and preparation method thereof

Abstract

The invention relates to the technical field of sprayed concrete, in particular to high-early-strength low-resilience sprayed concrete and a preparation method thereof, specifically, the sprayed concrete comprises the following raw materials: cement, gravel, sand, a water reducing agent, an admixture, water and an alkali-free accelerator, and the admixture is obtained by performing plasma enhanced mechanical force chemical treatment on silica fume and slag. According to the invention, the adopted admixture is the slag composite micro powder coated with the nano silica fume, so that the problems of agglomeration and non-uniform dispersion caused by directly adding the nano silica fume into the concrete are avoided. When being applied to sprayed concrete, the concrete modifier can improve the early-stage and later-stage compressive strength of the concrete and also can reduce the rebound rate of the sprayed concrete.

Description

Technical Field

[0001] The present invention relates to the technical field of shotcrete, and more specifically, to a high early-strength and low rebound shotcrete and a preparation method thereof. Background Art

[0002] Shotcrete technology plays an important role in underground construction and tunnel engineering. Shotcrete uses wind pressure to spray a certain proportion of the mixture at high speed onto the spraying surface. Compared with traditional cast-in-place concrete, shotcrete construction is more convenient, eliminating processes such as formwork support, pouring, and form removal, thus saving labor and shortening the construction period.

[0003] However, the current shotcrete has problems of low mechanical properties and poor compactness. Based on this, currently, it is mostly achieved by adding high-performance admixtures and mineral admixtures to improve strength and compactness. For example, silica fume, fly ash, etc. can effectively fill the pores between cements, improve the fluidity of the paste, and exhibit pozzolanic properties during the hydration of cement, thereby improving the material composition of the cementitious material. However, due to the low density of silica fume, there are certain difficulties in transportation, storage, and use. And most of the silica fume currently used in concrete production has been changed to densified silica fume, resulting in reduced dispersibility of silica fume and a decrease in the surface activity of the fine particles after agglomeration, causing a problem of reduced strength in shotcrete added with silica fume. Summary of the Invention

[0004] Technical problems to be solved by the present invention:

[0005] To solve the technical problems of reduced strength and high rebound rate in shotcrete due to poor plasticity of the concrete in the prior art.

[0006] Technical solutions adopted by the present invention:

[0007] In view of the above technical problems, the object of the present invention is to provide a high early-strength and low rebound shotcrete and a preparation method thereof. Specifically, that is:

[0008] First, the present invention provides a high early-strength and low rebound shotcrete, the raw materials of which include cement, crushed stone, sand, water reducer, admixture, water, and alkali-free accelerating agent, and the admixture is obtained by plasma-enhanced mechanochemical treatment of silica fume and slag.

[0009] According to some preferred embodiments, each component of the raw materials is calculated by weight, including 380 - 420 parts of cement, 820 - 870 parts of crushed stone, 750 - 800 parts of sand, 4 - 4.5 parts of water reducer, 20 - 45 parts of admixture, and 180 - 210 parts of water.

[0010] According to some preferred embodiments, in the preparation method of the admixture, the equipment for plasma-enhanced mechanochemical treatment is a plasma ball mill.

[0011] According to some preferred embodiments, in the preparation method of the admixture, in the plasma-enhanced mechanochemical treatment, the parameters are set as follows: the discharge current of the plasma is 190-240 mA, the discharge voltage is 4.5-5.0 kV, the discharge frequency is 9-10 kHz, and the atmosphere is air. Further preferably, the discharge current of the plasma is 230 mA, the discharge voltage is 4.8 kV, and the discharge frequency is 9.5 kHz.

[0012] According to some preferred embodiments, in the preparation method of the admixture, in the plasma-enhanced mechanochemistry, the parameters are set as the rotation speed of 900-1000 r / min and the time of 30-70 min. Further preferably, the rotation speed is 950 r / min and the time is 50 min.

[0013] According to some preferred embodiments, in the preparation method of the admixture, in the plasma-enhanced mechanochemistry, the addition amount of the dispersant accounts for 0.2-0.5% of the mass of the nano-silica fume, and more preferably 0.2%, 0.3%, 0.4%, 0.5%.

[0014] According to some preferred embodiments, in the preparation method of the admixture, in the plasma-enhanced mechanochemistry, the dispersant includes at least one of ethylene glycol, polycarboxylate, lignosulfonate, and sodium stearate.

[0015] According to some preferred embodiments, in the preparation method of the admixture, in the plasma-enhanced mechanochemistry, the ball milling medium is zirconium bead sand, and the ball-to-material ratio is 5-10:1.

[0016] According to some preferred embodiments, in the admixture, the mass ratio of silica fume to slag is 1:3-5, preferably 1:4.

[0017] According to some preferred embodiments, in the admixture, the silica fume is selected from semi-dense silica fume after densification treatment in the metal silicon industrial smelting process; the semi-dense silica fume is subjected to high-speed air flow crushing and depolymerization treatment, and the D50 of the depolymerized silica fume is 0.254 μm.

[0018] According to some preferred embodiments, in the admixture, the slag is selected as commercial slag powder, and the quality coefficient K is 1.587, D50 = 10.369 μm.

[0019] According to some preferred embodiments, a conventional polycarboxylate water reducer can be selected as the water reducer.

[0020] Second, the present invention provides a preparation method of the aforementioned high-early-strength and low-elasticity rebound shotcrete, including the following steps:

[0021] Weigh the raw materials in proportion to obtain a mixture, and then use a wet concrete spraying machine to mix and spray the mixture and an alkali-free accelerating agent, thus obtaining high-early-strength and low-rebound sprayed concrete.

[0022] Technical mechanism and beneficial effects adopted in the present invention:

[0023] By adding treated admixtures to the sprayed concrete, the present invention can improve the early strength and late strength of the sprayed concrete, and save construction time at the same time. Specifically, by using plasma + mechanochemical treatment, in a sealed container, a cold-field discharge plasma forms a non-thermal plasma, and a high-energy non-equilibrium plasma is formed by the gas in the sealed container under near-atmospheric pressure. Then, in combination with mechanochemical treatment, silica fume and slag are refined, activated in activity, and subjected to chemical reactions, etc. Considering the particle size difference between silica fume and slag, the obtained admixture forms a structural form with silica fume coating slag. In this form, due to the high activity of the plasma, adsorption is likely to occur, thus enhancing its surface activity, and combined with the fresh and numerous defects introduced in the mechanochemical treatment, the activity of the obtained admixture is further enhanced. The formation of the coating structure in the admixture is conducive to the regulation of the interfacial bonding between the binder and the aggregate in the concrete and the improvement of the density. Description of the drawings

[0024] Figure 1 SEM images of silica fume and slag;

[0025] Figure 2 SEM image of the admixture obtained in Example 1 (×5000 times);

[0026] Figure 3 SEM image of the admixture obtained in Example 1 (×50000 times);

[0027] Figure 4 SEM image of the admixture obtained in Example 1 (×100000 times);

[0028] Figure 5 SEM images of mortars obtained with admixtures of different dosages (left - reference sample, upper left - 10μm, lower left - 1μm; middle - dosage of 6% in Example 1, upper middle - 10μm, lower middle - 2μm; right - dosage of 8% in Example 2, upper right - 10μm, lower right - 2μm). Detailed implementation manners

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0030] Embodiment

[0031] This embodiment provides a shotcrete, and the components of the raw materials are shown in Table 1.

[0032] Table 1 Mix Ratio Table of Components of Raw Materials for C25 Shotcrete (kg / m 3 )

[0033] Type Cement Crushed stone Sand Water reducing agent Mineral admixture Water Reference sample 470 838 733 4.72 0 218 Example 1 404 846 780 4.3 26 194 Example 2 395.6 846 780 4.4 34.4 198

[0034] In Table 1, the specific settings of the components of the raw materials are as follows:

[0035] The water reducing agent uses a polycarboxylate water reducing agent.

[0036] The cement is P·O 42.5 grade ordinary Portland cement produced by Southwest Cement Factory. The fineness modulus of the aggregate is 2.6, the stone powder content is 3%, and the methylene blue is 0.7.

[0037] The admixture includes silica fume and slag. Specifically:

[0038] Silica fume is semi-dense silica fume collected by encrypting high-temperature flue gas during the smelting of industrial silicon. After the semi-dense silica fume is pulverized and depolymerized by high-speed airflow, the chemical composition is shown in Table 2, and the physical properties are shown in Table 3. Among them, the D50 of silica fume is 0.254 μm, and the microscopic morphology is in a particle agglomerated state, as shown in Figure 1 (a).

[0039] Slag uses commercial slag powder from Kunming Iron and Steel Co., Ltd. The chemical composition is shown in Table 2, the quality coefficient K is 1.587, and the physical properties are shown in Table 3. The D50 is 10.369 μm, and the particle morphology is angular, as shown in Figure 1 (b).

[0040] Table 2 Chemical Composition Table of Raw Materials of Silica Fume and Slag (wt%)

[0041] Component CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> FeO MgO MnO <![CDATA[TiO2]]> P <![CDATA[SO3]]> C Silica fume 0.22 94.0 0.47 0.21 0.19 - - - - 2.55 Slag 37.52 31.05 11.82 1.74 7.50 0.36 4.4 0.017 0.81 -

[0042] Table 3 Physical Property Table of Silica Fume and Slag

[0043]

[0044] In the foregoing, the preparation method of the admixture is

[0045] Put the slag and silica fume into a plasma ball mill, add a dispersant and conduct ball milling treatment. The ball milling medium is zircon sand, and the ball-to-material ratio is 6:1. Control the rotation speed at 950 r / min and the time at 50 min, and at the same time set the relevant parameters of the plasma. The atmosphere is air to obtain the admixture.

[0046] In the above, the specific operation parameters are shown in Table 4.

[0047] Table 4 Operation Parameter Table

[0048]

[0049] Take the admixture prepared in Example 1-1 as the sample and conduct the determination of the microscopic morphology of the sample. The results are as Figures 2 to 4 shown.

[0050] From Figures 2 to 4 it can be seen that the powder morphology of the admixture obtained in Example 1-1 indicates that the agglomerated structure of spherical nano-silica fume is destroyed, mainly covered by single-layer spherical nanoparticles and stacked disorderly, thus greatly improving the dispersibility of silica fume, further increasing the active sites of slag, and thus being able to improve the hydration activity index.

[0051] The preparation method of shotcrete is to weigh and blend the raw material components in proportion to obtain the mixture, and then use a wet concrete spraying machine to mix the mixture with an alkali-free accelerating agent (Jiangsu Aolait, SL-16, solid content of 53.9%, and the dosage of the alkali-free accelerating agent accounts for 7% of the cementitious material).

[0052] Comparative Example

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 1-1 is that only silica fume is used.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 1-1 is that the silica fume and slag are subjected to ball milling treatment. A planetary ball mill is selected for ball milling, the ball milling medium is zircon sand, the ball-to-material ratio is 7:3, the ball milling time is 1 h, and the rotation speed is 900 r / min.

[0057] Test Example

[0058] Take the concrete prepared in Example 1-2 and Comparative Example 1-2 as samples and conduct relevant tests on the concrete.

[0059] Determine the influence of cement hydration heat release, and the results are shown in Table 5.

[0060] Table 5

[0061]

[0062] As can be seen from the results in Table 5, the admixture prepared by the present technology can effectively increase the early hydration heat release rate, shorten the induction period, increase the heat release peak value, and promote the cement hydration process.

[0063] The hydration products of the 3d neat paste were measured, and the results are shown in Table 6.

[0064] Table 6 Peak intensity of neat paste hydration products (3d)

[0065]

[0066] As can be seen from the results in Table 6, after adding the admixture prepared by the present technology, the CH content decreased significantly, and the content of cementitious materials (C-S-H and AFt) increased significantly, which is beneficial to the densification of the concrete interface structure and the increase of early strength.

[0067] The microtopographies of the mortars of the reference sample, Example 1, and Example 2 were further measured, and the results are as Figure 5 shown.

[0068] From Figure 5 the results, it can be seen that the reference sample ( Figure 5 left) is the microtopography diagram (SEM diagram) of pure cement. It can be observed that the lamellar Ca(OH)2, needle-like AFt, and flocculent C-S-H gels in the reference sample are intertwined with each other and fill the pores of the aggregate particles, but obvious pores can be observed between the needle-like products. Figure 5 In the middle is the microtopography diagram (SEM diagram) of Example 1. It can be observed that the number of needle-like AFt increases significantly after adding Admixture 1, and there are no obvious pores at the mortar-interface. The microtopography of the specimen of Example 2 is as Figure 5 shown on the right. It can be observed that Ca(OH)2 is scattered in the matrix, with a smaller quantity and volume. The C-S-H gels overlap to form a network, compressing the growth space of Ca(OH)2, reducing the volume of Ca(OH)2, and promoting the densification of the mortar-interface. However, too high an admixture content will reduce the fluidity of the paste, resulting in a decrease in the local water-binder ratio, a reduction in the amount of hydration products, and an increase in the pores in the interface instead.

[0069] The strength and rebound rate of C25 shotcrete were measured respectively, and the measurement results are shown in Table 7.

[0070] Table 7 Measurement results of C25 shotcrete

[0071] Sample 3d strength (MPa) 7d strength (MPa) Comprehensive rebound rate (%) Reference sample 28.3 34.7 26.12 Example 1-1 32.9 41.4 8.26 Example 1-2 30.6 36.7 13.87 Example 1-3 31.1 37.8 13.24 Example 1-4 32.3 39.5 10.08 Example 1-5 31.8 39.2 9.97 Example 1-6 30.6 36.9 13.79 Example 2 34.5 44.6 7.44 Comparative example 1 25.2 35.8 20.42 Comparative example 2 26.6 36.1 18.15

[0072] As can be seen from the results in Table 7, the concrete formulation prepared by the present technology can improve the early strength and late strength of C25 shotcrete, thereby saving construction time and significantly reducing the rebound rate.

[0073] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high early strength and low rebound shotcrete, characterized in that The raw materials include cement, crushed stone, sand, water reducer, admixture, water, and non-alkali accelerating agent. The admixture is obtained by subjecting silica fume and slag to plasma-enhanced mechanochemical treatment.

2. The high-early-strength and low-elasticity rebound shotcrete according to claim 1, wherein, By weight, the components of the raw materials include 380 - 420 parts of cement, 820 - 870 parts of crushed stone, 750 - 800 parts of sand, 4 - 4.5 parts of water reducer, 20 - 45 parts of admixture, and 180 - 210 parts of water.

3. The high-early-strength and low-elasticity rebound shotcrete according to claim 1 or 2, characterized in that, In the preparation method of the admixture, the equipment for plasma-enhanced mechanochemical treatment is a plasma ball mill.

4. The high-early-strength and low-elasticity rebound shotcrete according to claim 3, wherein, In the plasma-enhanced mechanochemical treatment, the parameters are set as follows: the discharge current of the plasma is 190 - 240 mA, the discharge voltage is 4.5 - 5.0 kV, the discharge frequency is 9 - 10 kHz, and the atmosphere is air.

5. The high-early-strength and low-elasticity rebound shotcrete according to claim 4, wherein The discharge current of the plasma is 230 mA, the discharge voltage is 4.8 kV, and the discharge frequency is 9.5 kHz.

6. The high-early-strength and low-elasticity rebound shotcrete according to claim 3, wherein, In the plasma-enhanced mechanochemistry, the parameters are set as the rotation speed of 900 - 1000 r / min and the time of 30 - 70 min.

7. The high-early-strength and low-elasticity rebound shotcrete according to claim 6, characterized in that, The rotation speed is 950 r / min and the time is 50 min.

8. The high-early-strength and low-elasticity rebound shotcrete according to claim 3, characterized in that, The mass ratio of silica fume to slag is 1:3 - 5.

9. The high-early-strength and low-elasticity rebound shotcrete according to claim 3, wherein In the admixture: the D50 of silica fume is 0.254 μm; the mass coefficient K of slag is 1.587, and D50 is 10.369 μm.

10. A method for preparing high-early-strength and low-elasticity rebound shotcrete according to any one of claims 1 to 9, characterized in that, It includes the following steps: Weigh the raw materials in proportion to obtain a mixture, and then use a wet concrete spraying machine to mix the mixture and the non-alkali accelerating agent and spray them out to obtain high-early-strength and low-rebound shotcrete.

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