Active mineral admixture for low-grade attapulgite-based sprayed concrete as well as preparation method and application of active mineral admixture

Abstract

The invention discloses an active mineral admixture for low-grade attapulgite-based sprayed concrete as well as a preparation method and application of the active mineral admixture. The active mineral admixture comprises the following components in parts by mass: 40-60 parts of active attapulgite, 10-20 parts of active rectorite, 5-20 parts of active montmorillonite, 5-15 parts of silica fume, 5-25 parts of metakaolin, 10-20 parts of fly ash and 0.5-6 parts of a water reducing agent. Minerals used in the invention are rich in reserves and low in price, and a stable raw material source is provided for the mineral admixture for the sprayed concrete. When the sprayed concrete obtained on the basis of the active admixture is used for construction operation, the block falling rate and the rebound rate are greatly reduced, the compressive strength is greatly improved, and good economic and environmental benefits and wide application prospects are achieved.

Description

Technical Field

[0001] The invention relates to the field of concrete admixture materials, in particular to an active mineral admixture for low-grade attapulgite-based shotcrete and a preparation method thereof. Background Art

[0002] Shotcrete is widely used in civil engineering, tunnels, bridges and other fields due to its simple construction, strong adaptability and high structural density. However, in actual application projects, shotcrete often faces problems such as falling blocks, large rebound rate and reduced strength in the later stage, which seriously affect the construction process. In addition, the falling and rebounding shotcrete solidifies and hardens under the action of the accelerator, resulting in waste of raw materials and environmental pollution. Therefore, the design and development of a low-cost material that can reduce the falling blocks and rebound rate of shotcrete and improve the strength of each age has become the key to effectively improve the construction efficiency of shotcrete and improve the economic benefits of the project. Most inorganic minerals, such as fly ash, kaolin, bentonite, silica fume, etc., can play their advantages of cementitious properties and filling properties, reduce the loss of falling blocks and rebound during construction, accelerate the hydration rate of cement, and improve the strength of cement-based materials at each age. The main chemical composition of attapulgite is similar to that of fly ash, bentonite and other minerals. The fibrous structure and active SiO2 in the composition of attapulgite are used to improve the strength of cement-based materials at each age. 2 and Al 2 O 3 Due to its abundant reserves, low price and other characteristics, the development of high-performance medium and low-grade attapulgite-based active admixtures for shotcrete has both economic and environmental significance for reducing concrete costs, improving the properties of shotcrete and expanding the application of attapulgite.

[0003] Chinese Patent 202211141438.2 adds silicon micropowder and attapulgite ore to the shotcrete formula, but the process is relatively complicated and the rebound test results are not reported; Chinese Patent 201810976597.1 and Chinese Patent 201811636589.9 respectively disclose a prefabricated dry material shotcrete and a liquid alkali-free quick-setting agent for improving the cohesiveness of shotcrete. Both of the above patents use attapulgite, and the rebound rate of shotcrete has decreased, but the minimum rebound loss is above 11%, which is relatively high, and the requirements for shotcrete construction are relatively high. Chinese Patent 202210685126.1 discloses a viscosity enhancer for shotcrete and its preparation method and application, which is composed of ultrafine mineral powder, fly ash, lignin fiber, resin fiber, low shrinkage additives, etc. These admixtures are all polymer liquid materials, and the general dosage and unit price are high. It can be seen that a single inorganic mineral admixture cannot simultaneously meet the performance requirements of improving the high strength of shotcrete at all ages and reducing the rebound rate and falling blocks.

[0004] Therefore, this patent uses a high content of active SiO2 Silica fume with high content of active SiO 2 and Al 2 O 3 The components of metakaolin, fly ash and activated SiO 2 and Al 2 O 3 The active components are attapulgite, rectorite and montmorillonite, and the early strength water reducing agent powder is added and mixed to obtain an active mineral admixture for shotcrete. The active component SiO 2 With Al 2 O 3 The total content can reach 30-90%. The active mineral admixture prepared in this patent can not only effectively reduce the falling block and rebound rate during the construction process, but also improve the compressive strength. The preparation method is simple and economical, and has a wider application value. Summary of the invention

[0005] The purpose of the present invention is to provide a composite active mineral admixture obtained by mixing activated attapulgite as a base material, activated rectorite, activated montmorillonite, silica fume, metakaolin and water reducer powder, etc., in order to address the shortcomings of existing shotcrete construction, such as falling blocks, high rebound rate and high cost of admixtures. Adding the active admixture can not only reduce the falling blocks and rebound rate of shotcrete construction, but also save engineering costs.

[0006] In order to solve the technical problem of the present invention, the technical scheme proposed is: a method for preparing an active mineral admixture for low-grade attapulgite-based shotcrete, wherein the mass fractions of each component in the active mineral admixture are: 40-60 parts of active attapulgite, 10-20 parts of active rectorite, 5-20 parts of active montmorillonite, 5-15 parts of silica fume, 5-25 parts of metakaolin, 10-20 parts of fly ash, and 0.5-6 parts of water reducer;

[0007] The preparation method comprises the following steps of first activating attapulgite ore, rectorite ore and montmorillonite ore, and then fully mixing the obtained activated attapulgite, activated rectorite and activated montmorillonite with silica fume, metakaolin and fly ash, and finally adding water reducing agent powder and fully dry mixing.

[0008] Preferably, the attapulgite ore, the rectorite ore and the montmorillonite ore are activated, and the specific steps are as follows:

[0009] (1) Activation treatment of attapulgite

[0010] The low- and medium-grade attapulgite ore is sieved and crushed to obtain 300-mesh attapulgite powder, and the attapulgite and acid solution are added into a container at a solid-liquid ratio of 1kg:3-8L, wherein the acid solution has a mass concentration of 10-20wt%, and stirred at 60-80°C for 3-6h. After the slurry is filtered, washed to neutrality, dried, crushed and sieved to obtain 300-mesh acidified attapulgite; the attapulgite and acidified attapulgite are calcined at 300-500°C for 1-3h to obtain activated attapulgite and activated acidified attapulgite;

[0011] (2) Activation treatment of rectorite

[0012] The rectorite ore is sieved and crushed to obtain 300-mesh montmorillonite ore powder, and the rectorite ore and acid solution are added into a container at a solid-liquid ratio of 1kg:2-10L, wherein the acid solution has a mass concentration of 10-15wt%, and stirred at 30-90°C for 3-6h. After the slurry is filtered, washed to neutrality, dried, crushed and sieved to obtain 300-mesh acidified rectorite; the rectorite ore and the acidified rectorite are calcined at 400-900°C for 1-2h to obtain activated rectorite ore and activated acidified rectorite;

[0013] (3) Activation treatment of montmorillonite

[0014] The low- and medium-grade montmorillonite ore is sieved and crushed to obtain 300-mesh montmorillonite raw soil powder, and the montmorillonite raw soil and acid solution are added into a container at a solid-liquid ratio of 1kg:5-10L, wherein the mass concentration of the acid solution is 10-25wt%, and stirred at 30-80℃ for 3-6h. After the end, the obtained slurry is filtered, washed to neutrality, dried, crushed and sieved to obtain 300-mesh acidified montmorillonite; the montmorillonite raw soil and the acidified montmorillonite are respectively calcined at 200-600℃ for 1-2h to obtain activated montmorillonite raw soil and activated acidified montmorillonite.

[0015] Preferably, the activated attapulgite, activated rectorite and activated montmorillonite are respectively one of the corresponding activated attapulgite original soil and activated acidified attapulgite, activated rectorite original soil and activated acidified rectorite, activated montmorillonite original soil and activated acidified montmorillonite; the silica fume particle size is less than 1 micron, the metakaolin particle size is less than 2 microns, and the fly ash particle size is less than 30 microns.

[0016] Preferably, the water reducing agent powder is one or more of ordinary water reducing agent powder and high performance water reducing agent powder.

[0017] Preferably, the water reducer powder is a combination of ordinary water reducer powder and high performance water reducer powder, wherein the ordinary water reducer powder is 2-3 parts and the high performance water reducer powder is 0.5-3 parts.

[0018] Preferably, the common water reducer powder is one of sodium lignin sulfonate, calcium lignin sulfonate, magnesium lignin sulfonate and potassium lignin sulfonate; and the high-performance water reducer powder is sodium polycarboxylate.

[0019] Preferably, in the acidification treatment of attapulgite, rectorite and montmorillonite, the acid is one of hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid, propionic acid and citric acid.

[0020] Preferably, the method comprises the following steps:

[0021] Step 1: The attapulgite ore, rectorite and montmorillonite ore are crushed and sieved respectively to obtain 300-mesh attapulgite ore, 300-mesh rectorite ore and 300-mesh montmorillonite ore. The attapulgite ore, rectorite ore and montmorillonite ore and a 10wt% sulfuric acid solution are added to a container at a solid-liquid ratio of 1kg:5L, and stirred at 60°C for 2h, filtered and dried, crushed and sieved to obtain 300-mesh acidified attapulgite, acidified rectorite and acidified montmorillonite; the acidified attapulgite is heated at 500°C for 2h. o C for 1 h, and the acidified rectorite was heated at 850 o C for 1 h, and the acidified montmorillonite was heated at 450 o C for 1 h, and the activated attapulgite acid soil, activated rectorite acid soil and activated montmorillonite acid soil were obtained respectively;

[0022] Step 2: Mix 50 parts by weight of active attapulgite acid soil, 20 parts by weight of active rectorite acid soil, 5 parts by weight of active montmorillonite acid soil, 5 parts by weight of silica fume with a particle size distribution of 0.7-1 micron, 5 parts by weight of metakaolin with a particle size distribution of 1-2 microns, and 15 parts by weight of fly ash with a particle size distribution of 20-30 microns, then add 2 parts by weight of sodium lignin sulfonate and 2 parts by weight of sodium polycarboxylate water reducer powder, mix thoroughly and dry-mix to obtain an active mineral admixture.

[0023] In order to solve the technical problem of the present invention, another technical solution is proposed: the method for preparing active mineral admixtures for low-grade attapulgite-based shotcrete is applied in the field of concrete admixture materials, and the mass proportion of the active mineral admixture in each cubic meter of shotcrete mixture is 5.0-8.5 parts.

[0024] Preferably, the shotcrete comprises the following components in parts by weight: 400 parts of PO 42.5 ordinary Portland cement, 850 parts of natural fine aggregate, 850 parts of natural coarse aggregate, 7 parts of active mineral admixture, 23 parts of alkali-free liquid accelerating agent, and a water-cement ratio of 0.4.

[0025] The active mineral admixture for medium- and low-grade attapulgite-based shotcrete has an active component SiO 2 With Al 2 O 3 The total content can reach 30-90%.

[0026] Beneficial effects:

[0027] The present invention can improve the viscosity of shotcrete through the viscosity-increasing effect of attapulgite, rectorite and montmorillonite and the coupling effect of rod-shaped / layered structures, thereby solving the problems of falling blocks and rebound loss in shotcrete construction.

[0028] The active SiO in the ore is increased by acidifying and high-temperature roasting the medium- and low-grade attapulgite ore, rectorite ore and montmorillonite ore. 2 With Al 2 O 3 The content of iodine promotes the hydration of compounds with hydraulic cementing properties, thereby enhancing the strength of shotcrete.

[0029] The cost can be further reduced by using fly ash, metakaolin and silica fume, and utilizing their high content of active SiO 2 With Al 2 O 3 Further enhance the hydration effect, shorten the initial setting time of shotcrete, and improve early strength; improve the workability of shotcrete through water reducing agents, increase the fluidity of concrete, improve early strength, save cement, and further reduce costs.

[0030] Therefore, by adding powder water-reducing agent at the same time as active mineral admixture, the sprayed concrete prepared in this way can save cement, improve the workability, strength and durability of concrete, and significantly reduce the hydration heat of concrete. It can meet the construction requirements of sprayed concrete projects and has good economic benefits and broad application prospects.

[0031] According to the data of Examples 1-7 and Comparative Examples 1-9, the addition of active mineral admixtures improves the 7d compressive strength and 28d compressive strength of shotcrete, and reduces the rebound rate; according to the data of Examples 1-3, the optimal amount of active mineral admixture added is 7.0 parts; according to the data of Examples 1 and 4-5, the active mineral composition will affect the performance of shotcrete, and the mass ratio of the optimal combination is 10:4:1:1:1:3 for active attapulgite acid soil: active rectorite acid soil: active montmorillonite acid soil: silica fume: metakaolin: fly ash; according to the data of Example 1 and Comparative Examples 2-5, the type and amount of water reducer will also affect the performance of shotcrete, and the optimal condition is 2 parts. Sodium lignin sulfonate and 2 parts of sodium polycarboxylate water reducer powder; According to the data of Example 1 and Example 6-9, the effects of a single, two or three mineral mixture admixtures are not as good as the admixture effect of mixing active attapulgite, active rectorite, active montmorillonite, silica fume, metakaolin and fly ash together; According to the data of Example 1 and Example 6-7, the type of acid, the calcination temperature and the amount of active mineral admixture finally obtained for acidifying the mineral attapulgite, rectorite and montmorillonite have a significant effect on the performance of the shotcrete, especially on the rebound rate, among which the performance of the active mineral after the inorganic acid treatment is better than that after the organic acid treatment, and the optimal calcination temperature is 500℃ for the acidified attapulgite. o C, the acidified rectorite was calcined at 850 o C, acidified montmorillonite was calcined at 450 o In summary, Example 1 has the best performance, with a rebound rate of 4.8%, a slump of 120 mm, an early setting time of less than 3 minutes, a final setting time of less than 8 minutes, a 7d compressive strength of 28.6 MPa, and a 28d compressive strength of 44.6 MPa. DETAILED DESCRIPTION

[0032] The following is a further description of the present invention, rather than a limitation of the present invention. Unless otherwise specified, the reagents, equipment and methods used in the present invention are conventional commercially available reagents, equipment and conventionally used methods in the art.

[0033] Embodiment 1:

[0034] The steps for preparing shotcrete are as follows:

[0035] Step 1: The attapulgite ore, rectorite and montmorillonite ore are crushed and sieved respectively to obtain 300-mesh attapulgite ore, 300-mesh rectorite ore and 300-mesh montmorillonite ore. The attapulgite ore, rectorite ore and montmorillonite ore and a 10wt% sulfuric acid solution are added to a container at a solid-liquid ratio of 1kg:5L, and stirred at 60°C for 2h, filtered and dried, crushed and sieved to obtain 300-mesh acidified attapulgite, acidified rectorite and acidified montmorillonite; the acidified attapulgite is heated at 500°C for 2h. o C for 1 h, and the acidified rectorite was heated at 850 o C for 1 h, and the acidified montmorillonite was heated at 450 o C for 1h to obtain active attapulgite acid clay, active rectorite acid clay and active montmorillonite acid clay respectively.

[0036] Step 2: Mix 50 parts by weight of active attapulgite acid soil, 20 parts by weight of active rectorite acid soil, 5 parts by weight of active montmorillonite acid soil, 5 parts by weight of silica fume with a particle size distribution of 0.7-1 microns, 5 parts by weight of metakaolin with a particle size distribution of 1-2 microns, and 15 parts by weight of fly ash with a particle size distribution of 20-30 microns, then add 2 parts by weight of sodium lignin sulfonate and 2 parts by weight of sodium polycarboxylate water reducer powder, mix thoroughly and dry-mix to obtain an active mineral admixture, and test the active SiO 2 With Al 2 O 3 The total content of.

[0037] Step 3: Put the cement, natural fine aggregate, natural coarse aggregate and active mineral admixture required for 3 cubic meters of shotcrete into the mixer according to the designed mix ratio, and mix them evenly. The preliminary shotcrete mix ratio design is calculated according to the current industry standard "Ordinary Concrete Mix Design Code" (JGJ / T55): in parts by weight, it includes the following components: 400 parts of P.O42.5 ordinary Portland cement, 850 parts of natural fine aggregate, 850 parts of natural coarse aggregate, 7 parts of active mineral admixture, 23 parts of alkali-free liquid accelerator (purchased from BASF Chemical Building Materials (China) Co., Ltd., model SA-160), and a water-cement ratio of 0.4.

[0038] Step 4: Add water to the mixture according to the water-cement ratio of shotcrete, stir for 2 minutes, then discharge from the mixer and pour onto an iron plate. Add 23 parts of the accelerator in step 3 by mass. After manual mixing twice, test the slump, setting time, compressive strength and other properties. The method standards are based on the "Standard for Test Methods for Performance of Concrete Mixtures" (GB / T 50080-2016), "Standard for Strength Test and Evaluation of Ordinary Concrete" (GBJ 107) and "Technical Code for Application of Shotcrete" (JGJT372-2016).

[0039] Step 5: Add water to the shotcrete mixture according to the water-cement ratio of shotcrete, stir for 2 minutes, add 23 parts of accelerator after transporting to the work site, stir for 2 minutes and then start the shotcrete operation, collect the fallen blocks and rebound concrete, weigh the rebound loss on site, and the specific experimental method standards are based on the "Standard for Experimental Methods for Performance of Concrete Mixtures" (GB / T 50080-2016) and the "Technical Code for Application of Shotcrete" (JGJT372-2016).

[0040] Embodiment 2:

[0041] The method is basically the same as Example 1, except that the active mineral admixture in step 3 is changed to 8.5 parts, and the other parts remain unchanged.

[0042] Embodiment 3:

[0043] It is basically the same as Example 1, except that the active mineral admixture in step 3 is changed to 5.0 parts, and the other parts remain unchanged.

[0044] Embodiment 4:

[0045] It is basically the same as Example 1, except that the composition of the active mineral admixture in step 2 is changed to: 60 parts of active attapulgite acid soil, 10 parts of active rectorite acid soil, 5 parts of active montmorillonite acid soil, 10 parts of silica fume with a particle size distribution of 0.7-1 micron, 10 parts of kaolin with a particle size distribution of 1-2 microns, and 10 parts of fly ash with a particle size distribution of 20-30 microns are mixed evenly, and the other parts remain unchanged.

[0046] Embodiment 5:

[0047] It is basically the same as Example 1, except that the composition of the active mineral admixture in step 2 is changed to: 40 parts of active attapulgite acid soil, 15 parts of active rectorite acid soil, 20 parts of active montmorillonite acid soil, 5 parts of silica fume with a particle size distribution of 0.7-1 micron, 25 parts of kaolin with a particle size distribution of 1-2 microns, and 20 parts of fly ash with a particle size distribution of 20-30 microns are mixed evenly, and the other parts remain unchanged.

[0048] Embodiment 6:

[0049] The same as Example 1, except that the calcination temperature of the acidified soil in step 1 is changed to the calcination temperature of the acidified attapulgite at 400 o C for 1 h, and the acidified rectorite was heated at 700 o C for 1 h, and the acidified montmorillonite was heated at 350 o C for 1h.

[0050] Embodiment 7:

[0051] The method is basically the same as Example 1, except that the 10wt% sulfuric acid solution in step 1 is replaced with 10wt% acetic acid, and the other contents remain unchanged.

[0052] Comparative Example 1:

[0053] It is basically the same as Example 1, except that no active mineral admixture is added, and the other conditions remain unchanged.

[0054] Comparative Example 2:

[0055] The method is basically the same as Example 1, except that the water reducing agent is changed to 3 parts by weight of calcium lignin sulfonate, and the other parts remain unchanged.

[0056] Comparative Example 3:

[0057] The method is basically the same as Example 1, except that the water reducing agent is changed to 0.5 parts of sodium polycarboxylate, and the other parts remain unchanged.

[0058] Comparative Example 4:

[0059] The method is basically the same as Example 1, except that the water reducer is changed to 3 parts of sodium lignin sulfonate and 3 parts of sodium polycarboxylate water reducer powder, and the other parts are unchanged.

[0060] Comparative Example 5:

[0061] The method is basically the same as Example 1, except that the water reducer is changed to 2 parts of sodium lignin sulfonate and 0.5 parts of sodium polycarboxylate water reducer powder, and the other parts remain unchanged.

[0062] Comparative Example 6:

[0063] It is basically the same as Example 1, except that the active mineral admixture is changed to silica fume, and the other parts remain unchanged.

[0064] Comparative Example 7:

[0065] It is basically the same as Example 1, except that the active mineral admixture is changed to activated acidified attapulgite, and the other parts remain unchanged.

[0066] Comparative Example 8:

[0067] It is basically the same as Example 1, except that the active mineral admixture is changed to activated acidified attapulgite and activated rectorite, the mass ratio of the two is 5:2, and the other parts remain unchanged.

[0068] Comparative Example 9:

[0069] It is basically the same as Example 1, except that the active mineral admixture is changed to activated acidified attapulgite, metakaolin and fly ash, and the mass ratio of the two is 10:1:3, and the other parts remain unchanged.

[0070] Summary: According to the data of Examples 1-7 and Comparative Examples 1-9, the addition of active mineral admixtures improves the 7d compressive strength and 28d compressive strength of shotcrete, and reduces the rebound rate; According to the data of Examples 1-3, the optimal amount of active mineral admixture added is 7.0 parts; According to the data of Examples 1 and 4-5, the active mineral composition will affect the performance of shotcrete, and the mass ratio of the optimal combination is active attapulgite acid soil: active rectorite acid soil: active montmorillonite acid soil: silica fume: metakaolin: fly ash is 10:4:1:1:1:3; According to the data of Example 1 and Comparative Examples 2-5, the type and amount of water reducer will also affect the performance of shotcrete, and the optimal condition is 2 parts of sodium lignin sulfonate and 2 parts of sodium polycarboxylate water reducer powder; according to the data of Example 1 and Examples 6-9, the effects of a single, two or three mineral mixture admixtures are not as good as the admixture effect of mixing active attapulgite, active rectorite, active montmorillonite, silica fume, metakaolin and fly ash together; according to the data of Examples 1 and 6-7, the type of acid for acidifying the mineral attapulgite, rectorite and montmorillonite, the calcination temperature and the amount of the active mineral admixture finally obtained all have a significant effect on the performance of the shotcrete, especially on the rebound rate, among which the performance of the active mineral after the inorganic acid treatment is better than that after the organic acid treatment, and the optimal calcination temperature is 500 for the acidified attapulgite. o C, the acidified rectorite was calcined at 850 o C, acidified montmorillonite was calcined at 450 o In summary, Example 1 has the best performance, with a rebound rate of 4.8%, a slump of 120 mm, an early setting time of less than 3 minutes, a final setting time of less than 8 minutes, a 7d compressive strength of 28.6 MPa, and a 28d compressive strength of 44.6 MPa (see Table 1).

[0071] Table 1 Active content of active mineral admixtures and results of on-site shotcrete test

[0072]

[0073] Example 8

[0074] The steps for preparing shotcrete are as follows:

[0075] Step 1: The attapulgite ore, rectorite ore and montmorillonite ore were crushed and sieved respectively to obtain 300-mesh attapulgite ore, 300-mesh rectorite ore and 300-mesh montmorillonite ore. o C for 1 h, and the rectorite raw soil was heated at 850 o C for 1 h, and the montmorillonite was calcined at 450 oC for 1 h to obtain activated attapulgite, activated rectorite and activated montmorillonite respectively.

[0076] Step 2: Mix 50 parts of active attapulgite, 20 parts of active rectorite, 5 parts of active montmorillonite, 5 parts of silica fume with a particle size distribution of 0.7-1 microns, 5 parts of metakaolin with a particle size distribution of 1-2 microns, and 15 parts of fly ash with a particle size distribution of 20-30 microns, then add 2 parts of sodium lignin sulfonate and 1 part of sodium polycarboxylate water reducer powder, mix thoroughly and dry mix to obtain active mineral admixture, and test the active SiO 2 With Al 2 O 3 The total content of.

[0077] Step 3: Put the cement, natural fine aggregate, natural coarse aggregate and active mineral admixture required for 3 cubic meters of shotcrete into the mixer according to the designed mix ratio, and mix them evenly. The preliminary shotcrete mix ratio design is calculated according to the current industry standard "Ordinary Concrete Mix Design Code" (JGJ / T55): in parts by weight, it includes the following components: 400 parts of P.O42.5 ordinary Portland cement, 850 parts of natural fine aggregate, 850 parts of natural coarse aggregate, 7 parts of active mineral admixture, 23 parts of alkali-free liquid accelerator (purchased from BASF Chemical Building Materials (China) Co., Ltd., model SA-160), and a water-cement ratio of 0.4.

[0078] Step 4: Add water to the mixture according to the water-cement ratio of shotcrete, stir for 2 minutes, unload from the mixer, pour onto an iron plate, add 23 parts of accelerating agent, and test the slump, setting time, compressive strength and other properties after manual mixing twice, according to the same method standard as in Example 1.

[0079] Step 5: Add water to the shotcrete mixture according to the water-cement ratio of the shotcrete, stir for 2 minutes, add 23 parts of accelerator after transporting to the work site, stir for 2 minutes and then perform the shotcrete operation, collect the fallen blocks and rebound concrete, and weigh the rebound loss on site. The specific experimental method standard is the same as that in Example 1.

[0080] Embodiment 9:

[0081] The same as Example 8, except that the calcination temperature of the original soil in step 1 is changed to calcining the original attapulgite at 500 o C for 1 h, and the rectorite raw soil was heated at 900 o C for 1 h, and the montmorillonite was calcined at 450 o C for 1 h, and all other conditions remain unchanged.

[0082] Embodiment 10:

[0083] It is basically the same as Example 8, except that the active mineral admixture in step 3 is changed to 8.5 parts, and the other parts remain unchanged.

[0084] Embodiment 11:

[0085] It is basically the same as Example 8, except that the active mineral admixture in step 3 is changed to 5.0 parts, and the other parts remain unchanged.

[0086] Comparative Example 10:

[0087] It is basically the same as Example 8, except that the active mineral admixture is changed to active attapulgite original soil, and the other parts remain unchanged.

[0088] Comparative Example 11:

[0089] It is basically the same as Example 8, except that the active mineral admixture is changed to activated attapulgite, activated rectorite and activated montmorillonite, the mass ratio of the three is 10:4:1, and the other parts remain unchanged.

[0090] Comparative Example 12:

[0091] It is basically the same as Example 8, except that the active mineral admixture is changed to active attapulgite, metakaolin and fly ash, the mass ratio of the three is 10:1:3, and the other parts remain unchanged.

[0092] Summary: According to the data of Example 1, Example 8 and Comparative Example 1, the performance of the shotcrete mixed with active mineral admixtures of attapulgite, rectorite and montmorillonite after acidification is better than that mixed with original soil-based active mineral admixtures; According to the data of Example 8 and Examples 10-11, the optimal dosage of the active mineral admixture is 7.0 parts; According to the data of Examples 8-9, the roasting temperature of the original mineral soil also has an effect on the activity of the active mineral, among which the original attapulgite soil of 500 o C, the raw rectorite was calcined at 900 o C, calcined at 450 o The mineral obtained by roasting treatment of C has better performance; according to the data of Example 8 and Comparative Examples 1 and 10-12, for the original soil-based active mineral admixtures, the effects of a single, two or three mineral mixture admixtures are not as good as the admixtures mixed with active attapulgite, active rectorite, active montmorillonite, silica fume, kaolin and fly ash; (see Table 1).

[0093] It can be seen from the above experimental data that the active mineral admixture for low-grade attapulgite-based shotcrete prepared by the present invention has an active component SiO 2 With Al 2 O 3The total content can reach 30-90%, which can greatly reduce the falling and rebound rate of ordinary shotcrete construction operations, shorten the initial setting time to less than 3 minutes, shorten the final setting time to less than 10 minutes, and improve the 7d and 28d compressive strengths.

[0094] The present invention is not limited to the specific technical solutions described in the above embodiments, and all technical solutions formed by equivalent replacement are within the protection scope required by the present invention.

Claims

1. A method for preparing an active mineral admixture for low-grade attapulgite-based shotcrete, characterized in that: The mass proportions of the components in the active mineral admixture are: 40-60 parts of active attapulgite, 10-20 parts of active rectorite, 5-20 parts of active montmorillonite, 5-15 parts of silica fume, 5-25 parts of metakaolin, 10-20 parts of fly ash, and 0.5-6 parts of water reducer; The preparation method comprises the following steps of first activating attapulgite ore, rectorite ore and montmorillonite ore, and then fully mixing the obtained activated attapulgite, activated rectorite and activated montmorillonite with silica fume, metakaolin and fly ash, and finally adding water reducing agent powder and fully dry mixing.

2. The method for preparing the active mineral admixture for low-grade attapulgite-based shotcrete according to claim 1, characterized in that: The attapulgite ore, rectorite ore and montmorillonite ore are activated, and the specific steps are as follows: (1) Activation treatment of attapulgite The low- and medium-grade attapulgite ore is sieved and crushed to obtain 300-mesh attapulgite powder, and the attapulgite and acid solution are added into a container at a solid-liquid ratio of 1kg:3-8L, wherein the acid solution has a mass concentration of 10-20wt%, and stirred at 60-80°C for 3-6h. After the slurry is filtered, washed to neutrality, dried, crushed and sieved to obtain 300-mesh acidified attapulgite; the attapulgite and acidified attapulgite are calcined at 300-500°C for 1-3h to obtain activated attapulgite and activated acidified attapulgite; (2) Activation treatment of rectorite The rectorite ore is sieved and crushed to obtain 300-mesh montmorillonite ore powder, and the rectorite ore and acid solution are added into a container at a solid-liquid ratio of 1kg:2-10L, wherein the acid solution has a mass concentration of 10-15wt%, and stirred at 30-90°C for 3-6h. After the slurry is filtered, washed to neutrality, dried, crushed and sieved to obtain 300-mesh acidified rectorite; the rectorite ore and the acidified rectorite are calcined at 400-900°C for 1-2h to obtain activated rectorite ore and activated acidified rectorite; (3) Activation treatment of montmorillonite The low- and medium-grade montmorillonite ore is sieved and crushed to obtain 300-mesh montmorillonite raw soil powder, and the montmorillonite raw soil and acid solution are added into a container at a solid-liquid ratio of 1kg:5-10L, wherein the mass concentration of the acid solution is 10-25wt%, and stirred at 30-80℃ for 3-6h. After the end, the obtained slurry is filtered, washed to neutrality, dried, crushed and sieved to obtain 300-mesh acidified montmorillonite; the montmorillonite raw soil and the acidified montmorillonite are respectively calcined at 200-600℃ for 1-2h to obtain activated montmorillonite raw soil and activated acidified montmorillonite.

3. The method for preparing the active mineral admixture for low-grade attapulgite-based shotcrete according to claim 1, characterized in that: The activated attapulgite, activated rectorite and activated montmorillonite are respectively one of the corresponding activated attapulgite original soil and activated acidified attapulgite, activated rectorite original soil and activated acidified rectorite, activated montmorillonite original soil and activated acidified montmorillonite; the silica fume particle size is less than 1 micron, the metakaolin particle size is less than 2 microns, and the fly ash particle size is less than 30 microns.

4. The method for preparing the active mineral admixture for low-grade attapulgite-based shotcrete according to claim 1, characterized in that: The water reducing agent powder is one or more of ordinary water reducing agent powder and high performance water reducing agent powder.

5. The method for preparing the active mineral admixture for low-grade attapulgite-based shotcrete according to claim 2, characterized in that: The water reducing agent powder is a combination of common water reducing agent powder and high performance water reducing agent powder, wherein the common water reducing agent powder is 2-3 parts and the high performance water reducing agent powder is 0.5-3 parts.

6. The method for preparing the active mineral admixture for low-grade attapulgite-based shotcrete according to claim 5, characterized in that: The common water reducing agent powder is one of sodium lignin sulfonate, calcium lignin sulfonate, magnesium lignin sulfonate and potassium lignin sulfonate; the high performance water reducing agent powder is sodium polycarboxylate.

7. The method for preparing the active mineral admixture for low-grade attapulgite-based shotcrete according to claim 2, characterized in that: The acid treatment of attapulgite, rectorite and montmorillonite is carried out by using one of hydrochloric acid, sulfuric acid, nitric acid, formic acid, acetic acid, propionic acid and citric acid.

8. The method for preparing the active mineral admixture for low-grade attapulgite-based shotcrete according to claim 1, characterized in that: The following steps are involved: Step 1: The attapulgite ore, rectorite and montmorillonite ore are crushed and sieved respectively to obtain 300-mesh attapulgite ore, 300-mesh rectorite ore and 300-mesh montmorillonite ore. The attapulgite ore, rectorite ore and montmorillonite ore and a 10wt% sulfuric acid solution are added to a container at a solid-liquid ratio of 1kg:5L, and stirred at 60°C for 2h, filtered and dried, crushed and sieved to obtain 300-mesh acidified attapulgite, acidified rectorite and acidified montmorillonite; the acidified attapulgite is heated at 500°C for 2h. o C for 1 h, and the acidified rectorite was heated at 850 o C for 1 h, and the acidified montmorillonite was heated at 450 o C for 1 h, and the activated attapulgite acid soil, activated rectorite acid soil and activated montmorillonite acid soil were obtained respectively; Step 2: Mix 50 parts by weight of active attapulgite acid soil, 20 parts by weight of active rectorite acid soil, 5 parts by weight of active montmorillonite acid soil, 5 parts by weight of silica fume with a particle size distribution of 0.7-1 micron, 5 parts by weight of metakaolin with a particle size distribution of 1-2 microns, and 15 parts by weight of fly ash with a particle size distribution of 20-30 microns, then add 2 parts by weight of sodium lignin sulfonate and 2 parts by weight of sodium polycarboxylate water reducer powder, mix thoroughly and dry-mix to obtain an active mineral admixture.

9. The active mineral admixture for preparing low-grade attapulgite-based shotcrete according to any one of claims 1 to 8 is used in the field of concrete admixture materials, characterized in that: The mass proportion of active mineral admixtures in each cubic meter of shotcrete mixture is 5.0-8.5 parts.

10. The active mineral admixture for preparing low-grade attapulgite-based shotcrete according to the method of claim 9 is used in the field of concrete admixture materials, characterized in that: The shotcrete comprises the following components by weight: 400 parts of PO 42.5 ordinary Portland cement, 850 parts of natural fine aggregate, 850 parts of natural coarse aggregate, 7 parts of active mineral admixture, 23 parts of alkali-free liquid accelerating agent, and a water-cement ratio of 0.4.

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