A low-grade attapulgite-based active mineral admixture for sprayed concrete, and a preparation method and application thereof

Abstract

The application discloses a kind of low-grade attapulgite-based active mineral admixture for shotcrete and a preparation method and application thereof, and the mass fraction of each component is: 40-60 parts of active attapulgite, 10-20 parts of active rectorite, 5-20 parts of active montmorillonite, 5-15 parts of silica ash, 5-25 parts of metakaolin, 10-20 parts of fly ash, 0.5-6 parts of water reducing agent.The mineral reserves used in the application are abundant and low in price, providing a stable raw material source for shotcrete mineral admixtures.The shotcrete obtained on the basis of this active admixture has a significant reduction in falling block and rebound rate during construction, a significant increase in compressive strength, and good economic, environmental benefits and broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of concrete admixture materials, specifically to an active mineral admixture for low-grade attapulgite soil-based shotcrete and its preparation method. Background Technology

[0002] Shotcrete, due to its simple construction, strong adaptability, and high structural density, is widely used in civil engineering, tunnels, bridges, and other fields. However, in practical applications, shotcrete often faces problems such as construction sharding, high rebound rates, and reduced strength at later stages, seriously affecting the construction process. Furthermore, sharded and rebounded shotcrete hardens under the action of accelerators, resulting in material waste and environmental pollution. Therefore, designing and developing a low-cost material that can reduce shotcrete sharding and rebound rates and improve strength at all ages has become crucial for effectively improving the construction efficiency of shotcrete and enhancing the economic benefits of projects. Most inorganic minerals, such as fly ash, metakaolin, bentonite, and silica fume, can leverage their cementitious properties and filling properties to reduce construction sharding and rebound losses, accelerate cement hydration rates, and improve the strength of cement-based materials at all ages. Attapulgite's main chemical composition is similar to that of minerals such as fly ash and bentonite. Utilizing the fibrous structure of attapulgite, its active SiO2 and Al2O3 components, and its abundant reserves and low price, high-performance active admixtures for medium- and low-grade attapulgite-based shotcrete can be developed. This has both economic and environmental significance for reducing concrete costs, improving shotcrete properties, and expanding the application of attapulgite.

[0003] Chinese patent 202211141438.2 adds silica fume and attapulgite ore to the shotcrete formulation, but the process is relatively complex and no rebound test results are reported. Chinese patents 201810976597.1 and 201811636589.9 disclose a precast dry-mix shotcrete and a liquid alkali-free quick-setting agent to improve the cohesiveness of shotcrete, respectively. Both patents use attapulgite, resulting in a slight decrease in the rebound rate of the shotcrete, but the rebound loss is still relatively high, exceeding 11%, and the shotcrete construction requires high precision. Chinese patent 202210685126.1 discloses a thickener for shotcrete, its preparation method, and its application, composed of ultrafine mineral powder, fly ash, lignin fiber, resin fiber, and low-shrinkage additives. These admixtures are all high-molecular liquid materials, generally with high dosage and unit price. It is evident that a single inorganic mineral admixture cannot simultaneously meet the performance requirements of improving the high strength of shotcrete at all ages and reducing rebound rate and blockage.

[0004] Therefore, this patent utilizes silica fume with high active SiO2 content, metakaolin with high active SiO2 and Al2O3 content, fly ash, and attapulgite, palygorskite, and montmorillonite with high active SiO2 and Al2O3 content after activation treatment as active components. These are then mixed with an early-strength water-reducing agent powder to obtain an active mineral admixture for shotcrete. The total content of the active components SiO2 and Al2O3 in this admixture can reach 30-90%. The active mineral admixture prepared in this patent can not only effectively reduce sharding and rebound rates during construction but also improve compressive strength. Furthermore, the preparation method is simple and economical, and it has wider application value. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing shotcrete construction, such as slab breakage, high rebound rate, and high admixture cost. This invention provides a composite active mineral admixture based on active attapulgite, mixed with active attapulgite, active montmorillonite, silica fume, metakaolin, and water-reducing agent powder. Adding this active admixture can not only reduce slab breakage and rebound rate in shotcrete construction, but also save on project costs.

[0006] To solve the technical problem of this invention, the proposed technical solution is as follows: 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 active attapulgite, 10-20 parts active attapulgite, 5-20 parts active montmorillonite, 5-15 parts silica fume, 5-25 parts metakaolinite, 10-20 parts fly ash, and 0.5-6 parts water-reducing agent.

[0007] The preparation method is as follows: First, the raw attapulgite ore, attapulgite ore, and montmorillonite ore are activated. Then, the obtained activated attapulgite, activated attapulgite, and activated montmorillonite are fully mixed with silica fume, metakaolin, and fly ash. Finally, water-reducing agent powder is added and fully dry-mixed to form the final product.

[0008] Preferably, the attapulgite ore, palygorskite ore, and montmorillonite ore undergo activation treatment, and the specific steps are as follows:

[0009] (1) Activation treatment of attapulgite soil

[0010] Low-grade attapulgite ore is sieved and crushed to obtain 300-mesh attapulgite powder. The attapulgite powder and acid solution are added to a container at a solid-liquid ratio of 1 kg: 3-8 L, where the acid solution has a mass concentration of 10-20 wt%. The mixture is stirred at 60-80℃ for 3-6 hours. After stirring, the resulting slurry is filtered, washed until neutral, dried, crushed, and sieved to obtain 300-mesh acidified attapulgite. The attapulgite powder and acidified attapulgite are then calcined at 300-500℃ for 1-3 hours to obtain activated attapulgite powder and activated acidified attapulgite, respectively.

[0011] (2) Activation treatment of attapulgite

[0012] Ratorite ore is sieved and crushed to obtain 300-mesh montmorillonite ore powder. Ratorite ore and acid solution are added to a container at a solid-liquid ratio of 1 kg: 2-10 L, wherein the acid solution has a mass concentration of 10-15 wt%. The mixture is stirred at 30-90℃ for 3-6 hours. After stirring, the resulting slurry is filtered, washed until neutral, dried, crushed, and sieved to obtain 300-mesh acidified montmorillonite. Ratorite ore and acidified montmorillonite are calcined at 400-900℃ for 1-2 hours to obtain active montmorillonite ore and active acidified montmorillonite.

[0013] (3) Activation treatment of montmorillonite

[0014] Medium- and low-grade montmorillonite ore is sieved and crushed to obtain 300-mesh montmorillonite raw material. Montmorillonite raw material and acid solution are added to a container at a solid-liquid ratio of 1 kg: 5~10 L, wherein the mass concentration of the acid solution is 10~25 wt%. The mixture is stirred at 30~80℃ for 3~6 hours. After stirring, the resulting slurry is filtered, washed until neutral, dried, crushed and sieved to obtain 300-mesh acidified montmorillonite. Montmorillonite raw material and acidified montmorillonite are calcined at 200-600℃ for 1~2 hours to obtain activated montmorillonite raw material and activated acidified montmorillonite.

[0015] Preferably, the activated attapulgite, activated attapulgite, and activated montmorillonite are each one of the following: activated attapulgite soil and activated acidified attapulgite, activated attapulgite soil and activated acidified attapulgite, and activated montmorillonite soil and activated acidified montmorillonite; the silica fume has a particle size of less than 1 micrometer, the metakaolinite has a particle size of less than 2 micrometers, and the fly ash has a particle size of less than 30 micrometers.

[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-reducing agent powder is a combination of ordinary water-reducing agent powder and high-performance water-reducing agent powder, wherein there are 2-3 parts of ordinary water-reducing agent powder and 0.5-3 parts of high-performance water-reducing agent powder.

[0018] Preferably, the ordinary water-reducing agent powder is one of sodium lignosulfonate, calcium lignosulfonate, magnesium lignosulfonate, and potassium lignosulfonate; the high-performance water-reducing agent powder is sodium polycarboxylate.

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

[0020] Preferably, it includes the following steps:

[0021] Step 1: Crush and sieve the raw attapulgite, palygorskite, and montmorillonite ore separately to obtain 300-mesh raw attapulgite, 300-mesh palygorskite, and 300-mesh montmorillonite. Add the raw attapulgite, palygorskite, and montmorillonite ore to a 10wt% sulfuric acid solution at a solid-liquid ratio of 1 kg: 5 L in a container. Stir thoroughly at 60°C for 2 hours, filter, dry, crush, and sieve to obtain sulfuric acid-acidified 300-mesh acidified attapulgite, acidified palygorskite, and acidified montmorillonite. Then, immerse the acidified attapulgite in a 500-mesh solution. o Calcination at C for 1 hour, followed by acidified attapulgite at 850°C o Roasted at C for 1 hour, then acidified montmorillonite was placed at 450°C. o Calcination at C for 1 h yielded active attapulgite acid soil, active attapulgite acid soil, and active montmorillonite acid soil, respectively.

[0022] Step 2: Mix 50 parts by weight of activated attapulgite, 20 parts by weight of activated attapulgite, 5 parts by weight of activated montmorillonite, 5 parts by weight of silica fume with a particle size distribution of 0.7-1 micrometer, 5 parts by weight of metakaolin with a particle size distribution of 1-2 micrometer, and 15 parts by weight of fly ash with a particle size distribution of 20-30 micrometer evenly. Then add 2 parts by weight of sodium lignosulfonate and 2 parts by weight of sodium polycarboxylate superplasticizer powder, and mix thoroughly to obtain the active mineral admixture.

[0023] To solve the technical problem of the present invention, another technical solution is proposed: the method for preparing low-grade attapulgite soil-based shotcrete active mineral admixtures is applied in the field of concrete admixture materials, wherein the mass ratio of the active mineral admixture in each cubic meter of shotcrete mix is ​​5.0-8.5 parts.

[0024] Preferably, the sprayed concrete 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 quick-setting agent, and a water-cement ratio of 0.4.

[0025] The active mineral admixture for medium- and low-grade attapulgite soil-based shotcrete described above has a total content of 30-90% of active components SiO2 and Al2O3.

[0026] Beneficial effects:

[0027] This invention improves the viscosity of shotcrete by utilizing the cohesive properties of attapulgite, montmorillonite, and montmorillonite, as well as the bonding effect of rod-shaped / layered structures, thereby solving the problems of sharding and rebound loss during shotcrete construction.

[0028] By acidifying and high-temperature roasting medium- and low-grade attapulgite, attapulgite, and montmorillonite ores, the content of active SiO2 and Al2O3 in the ores is increased, promoting the hydration of compounds with hydraulic cementitious properties, thereby enhancing the strength of shotcrete.

[0029] Costs can be further reduced by using fly ash, metakaolin, and silica fume, and their high content of active SiO2 and Al2O3 can be used to further enhance hydration, shorten the initial setting time of shotcrete, and improve early strength. Water-reducing agents can be used to improve the workability of shotcrete, increase the fluidity of concrete, improve early strength, save cement usage, and further reduce costs.

[0030] Therefore, by adding active mineral admixtures along with powdered water-reducing agents, the resulting shotcrete can save cement, improve the workability, strength, and durability of concrete, and significantly reduce the heat of hydration. It can meet the construction requirements of shotcrete projects and has good economic benefits and broad application prospects.

[0031] According to data from Examples 1-7 and Comparative Examples 1-9, the addition of active mineral admixtures improved the 7-day and 28-day compressive strength of shotcrete while reducing the rebound rate. According to data from Examples 1-3, the optimal amount of active mineral admixture added was 7.0 parts. According to data from Examples 1 and 4-5, the composition of active minerals affects the performance of shotcrete, with the optimal mass ratio being 10:4:1:1:1:3 for active attapulgite, active montmorillonite, silica fume, metakaolinite, and fly ash. According to data from Examples 1 and Comparative Examples 2-5, the type and amount of water-reducing agent also affect the performance of shotcrete, with the optimal condition being 2 parts. Sodium lignosulfonate and 2 parts of sodium polycarboxylate superplasticizer powder; according to the data of Examples 1 and 6-9, the effect of admixtures of one, two, or three minerals alone is not as good as that of admixtures that mix activated attapulgite, activated attapulgite, activated montmorillonite, silica fume, metakaolin, and fly ash together; according to the data of Examples 1 and 6-7, the type of acid used for acidification treatment of minerals such as attapulgite, attapulgite, and montmorillonite, the calcination temperature, and the amount of the final activated mineral admixture added all have a significant impact on the performance of shotcrete, especially on the rebound rate. Among them, the performance of activated minerals treated with inorganic acids is better than that treated with organic acids. The optimal calcination temperature is 500°C for acidified attapulgite. o Calcined at C, acidified attapulgite at 850°C o Calcination at C, acidified montmorillonite at 450°C o Firing at C. In summary: Example 1 exhibits 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 7-day compressive strength of 28.6 MPa, and a 28-day compressive strength of 44.6 MPa. Detailed Implementation

[0032] The following is a further description of the present invention, but not a limitation thereof. Unless otherwise specified, the reagents, equipment and methods used in the present invention are commercially available reagents, equipment and methods conventionally used in this technical field.

[0033] Example 1:

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

[0035] Step 1: Crush and sieve the raw attapulgite, palygorskite, and montmorillonite ore separately to obtain 300-mesh raw attapulgite, 300-mesh palygorskite, and 300-mesh montmorillonite. Add the raw attapulgite, palygorskite, and montmorillonite ore to a 10wt% sulfuric acid solution at a solid-liquid ratio of 1 kg: 5 L in a container. Stir thoroughly at 60°C for 2 hours, filter, dry, crush, and sieve to obtain sulfuric acid-acidified 300-mesh acidified attapulgite, acidified palygorskite, and acidified montmorillonite. Then, immerse the acidified attapulgite in a 500-mesh solution. o Calcination at C for 1 hour, followed by acidified attapulgite at 850°C o Roasted at C for 1 hour, then acidified montmorillonite was placed at 450°C. o Calcination at C for 1 h yielded activated attapulgite acid soil, activated attapulgite acid soil, and activated montmorillonite acid soil, respectively.

[0036] Step 2: Mix 50 parts by weight of activated attapulgite, 20 parts by weight of activated attapulgite, 5 parts by weight of activated montmorillonite, 5 parts by weight of silica fume with a particle size distribution of 0.7-1 micrometer, 5 parts by weight of metakaolin with a particle size distribution of 1-2 micrometer, and 15 parts by weight of fly ash with a particle size distribution of 20-30 micrometer evenly. Then add 2 parts by weight of sodium lignosulfonate and 2 parts by weight of sodium polycarboxylate superplasticizer powder, mix thoroughly and dry mix evenly to obtain the active mineral additive, and test the total content of active SiO2 and Al2O3.

[0037] Step 3: Add the cement, natural fine aggregate, natural coarse aggregate, and active mineral admixture required for 3 cubic meters of shotcrete to the mixer according to the designed mix proportion, and dry mix evenly. The preliminary shotcrete mix proportion design is calculated according to the current industry standard "Specification for Mix Proportion Design of Ordinary Concrete" (JGJ / T55): 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 quick-setting agent (purchased from BASF Chemicals 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 the shotcrete, stir for 2 minutes, then discharge it from the mixer and pour it onto the iron plate. Add 23 parts by weight of the quick-setting agent from Step 3. After manually mixing twice, test the slump, setting time, compressive strength and other properties. The method and standard are based on the comprehensive "Standard for Test Method of Performance of Concrete Mixture" (GB / T 50080-2016), "Standard for Strength Testing and Evaluation of Ordinary Concrete" (GBJ 107), and "Technical Specification for Application of Shotcrete" (JGJT372-2016).

[0039] Step 5: Add water to the shotcrete mixture according to the water-cement ratio, stir for 2 minutes, transport to the work site, add 23 parts of quick-setting agent, stir for 2 minutes, and then carry out the shotcreting operation. Collect the dropped and rebounded concrete, and weigh the rebound loss on site. The specific test method standards are combined with the "Standard for Test Methods of Concrete Mixture Performance" (GB / T 50080-2016) and the "Technical Specification for Application of Shotcrete" (JGJT372-2016).

[0040] Example 2:

[0041] It is basically the same as Example 1, except that the active mineral additive in step 3 is changed to 8.5 parts, and everything else remains the same.

[0042] Example 3:

[0043] It is basically the same as Example 1, except that the active mineral additive in step 3 is changed to 5.0 parts, and everything else remains the same.

[0044] Example 4:

[0045] The process is basically the same as in Example 1, except that the composition of the active mineral additive in step 2 is changed to: 60 parts of active attapulgite, 10 parts of active attapulgite, 5 parts of active montmorillonite, 10 parts of silica fume with a particle size distribution of 0.7-1 micrometer, 10 parts of metakaolin with a particle size distribution of 1-2 micrometer, and 10 parts of fly ash with a particle size distribution of 20-30 micrometer are mixed evenly, while all other aspects remain unchanged.

[0046] Example 5:

[0047] The process is basically the same as in Example 1, except that the composition of the active mineral additive in step 2 is changed as follows: 40 parts of active attapulgite, 15 parts of active attapulgite, 20 parts of active montmorillonite, 5 parts of silica fume with a particle size distribution of 0.7-1 micrometer, 25 parts of metakaolin with a particle size distribution of 1-2 micrometer, and 20 parts of fly ash with a particle size distribution of 20-30 micrometer are mixed evenly, while all other aspects remain unchanged.

[0048] Example 6:

[0049] This is basically the same as Example 1, except that the calcination temperature of the acidified soil in step 1 is changed to 400°C for the acidified attapulgite soil. o Calcined at C for 1 hour, then acidified attapulgite at 700°C o Roasted at C for 1 hour, then acidified montmorillonite was placed at 350°C. o Roast at C for 1 hour.

[0050] Example 7:

[0051] It is basically the same as Example 1, except that the 10wt% sulfuric acid solution in step 1 is replaced with 10wt% acetic acid, and everything else remains the same.

[0052] Comparative Example 1:

[0053] It is basically the same as Example 1, except that no active mineral additives were added, and everything else remains the same.

[0054] Comparative Example 2:

[0055] It is basically the same as Example 1, except that the water-reducing agent is changed to calcium lignosulfonate with a mass fraction of 3 parts, while the rest remains the same.

[0056] Comparative Example 3:

[0057] It is basically the same as Example 1, except that the water-reducing agent is changed by 0.5 parts of sodium polycarboxylate, while everything else remains the same.

[0058] Comparative Example 4:

[0059] It is basically the same as Example 1, except that the water-reducing agent is changed to 3 parts sodium lignosulfonate and 3 parts sodium polycarboxylate water-reducing agent powder, and everything else remains the same.

[0060] Comparative Example 5:

[0061] The method is basically the same as in Example 1, except that the water-reducing agent is changed to 2 parts sodium lignosulfonate and 0.5 parts sodium polycarboxylate water-reducing agent powder, while everything else remains the same.

[0062] Comparative Example 6:

[0063] It is basically the same as Example 1, except that the active mineral additive is changed to silica fume, while everything else remains the same.

[0064] Comparative Example 7:

[0065] It is basically the same as Example 1, except that the active mineral additive is changed to active acidified attapulgite, while everything else remains the same.

[0066] Comparative Example 8:

[0067] The method is basically the same as Example 1, except that the active mineral additive is changed to active acidified attapulgite and active attapulgite, with a mass ratio of 5:2, while other aspects remain unchanged.

[0068] Comparative Example 9:

[0069] The example is basically the same as Example 1, except that the active mineral additive is changed to active acidified attapulgite, metakaolin and fly ash, with a mass ratio of 10:1:3, and the rest remains the same.

[0070] Summary: Based on the data from Examples 1-7 and Comparative Examples 1-9, the addition of active mineral admixtures improved the 7-day and 28-day compressive strength of shotcrete while reducing the rebound rate. Based on the data from Examples 1-3, the optimal amount of active mineral admixture added was 7.0 parts. Based on the data from Examples 1 and 4-5, the composition of active minerals affected the performance of shotcrete, with the optimal mass ratio being 10:4:1:1:1:3 for active attapulgite, active montmorillonite, silica fume, metakaolinite, and fly ash. Based on the data from Examples 1 and Comparative Examples 2-5, the type and amount of water-reducing agent also affected the performance of shotcrete, with the optimal condition being 2... Two parts sodium lignosulfonate and two parts sodium polycarboxylate superplasticizer powder were used. According to data from Examples 1 and 6-9, the effect of admixtures consisting of one, two, or three mineral mixtures alone was not as good as admixtures made by mixing activated attapulgite, activated attapulgite, activated montmorillonite, silica fume, metakaolin, and fly ash together. According to data from Examples 1 and 6-7, the type of acid used for acidification of attapulgite, attapulgite, and montmorillonite, the calcination temperature, and the final amount of activated mineral admixture all significantly affected the performance of shotcrete, especially the rebound rate. The performance of activated minerals treated with inorganic acids was better than those treated with organic acids. The optimal calcination temperature for acidified attapulgite was 500°C. o Calcined at C, acidified attapulgite at 850°C o Calcination at C, acidified montmorillonite at 450°C o Firing at C. 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 7-day compressive strength of 28.6 MPa, and a 28-day compressive strength of 44.6 MPa (see Table 1).

[0071] Table 1. Activity content of active mineral admixtures and experimental results of shotcrete in the field.

[0072]

[0073] Example 8

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

[0075] Step 1: Crush and sieve the raw attapulgite, palygorskite, and montmorillonite ore separately to obtain 300-mesh raw attapulgite, 300-mesh palygorskite, and 300-mesh montmorillonite. Then, sieve the raw attapulgite ore at a 500-mesh screen. o Calcination at C for 1 hour, followed by calcination of the original clay at 850°C. o Calcination at C for 1 hour, then montmorillonite at 450°C oCalcination at C for 1 hour yielded activated attapulgite soil, activated attapulgite soil, and activated montmorillonite soil, respectively.

[0076] Step 2: Mix 50 parts of activated attapulgite soil, 20 parts of activated attapulgite soil, 5 parts of activated montmorillonite soil, 5 parts of silica fume with a particle size distribution of 0.7-1 micrometer, 5 parts of metakaolin with a particle size distribution of 1-2 micrometer, and 15 parts of fly ash with a particle size distribution of 20-30 micrometer evenly. Then add 2 parts of sodium lignosulfonate and 1 part of sodium polycarboxylate superplasticizer powder, mix thoroughly and dry mix evenly to obtain the active mineral additive, and test the total content of active SiO2 and Al2O3.

[0077] Step 3: Add the cement, natural fine aggregate, natural coarse aggregate, and active mineral admixture required for 3 cubic meters of shotcrete to the mixer according to the designed mix proportion, and dry mix evenly. The preliminary shotcrete mix proportion design is calculated according to the current industry standard "Specification for Mix Proportion Design of Ordinary Concrete" (JGJ / T55): 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 quick-setting agent (purchased from BASF Chemicals 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 the sprayed concrete, stir for 2 minutes, then discharge it from the mixer and pour it onto the iron plate. Add 23 parts of quick-setting agent, and manually mix twice to test the slump, setting time, compressive strength and other properties. The method and standard are the same 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, transport it to the work site, add 23 parts of quick-setting agent, stir for 2 minutes, and then carry out the shotcreting operation. Collect the fallen blocks and rebound concrete, and weigh the rebound loss on site. The specific test method and standard are the same as in Example 1.

[0080] Example 9:

[0081] This is basically the same as Example 8, except that the calcination temperature of the raw soil in step 1 is changed to 500°C for the raw attapulgite soil. o Calcination at C for 1 hour, followed by calcination of the original clay at 900°C. o Calcination at C for 1 hour, followed by calcination of the montmorillonite raw soil at 450°C o Roast at C for 1 hour, with all other conditions remaining unchanged.

[0082] Example 10:

[0083] It is basically the same as Example 8, except that the active mineral additive in step 3 is changed to 8.5 parts, and everything else remains the same.

[0084] Example 11:

[0085] It is basically the same as Example 8, except that the active mineral additive in step 3 is changed to 5.0 parts, and everything else remains the same.

[0086] Comparative Example 10:

[0087] It is basically the same as Example 8, except that the active mineral additive is changed to active attapulgite soil, while everything else remains the same.

[0088] Comparative Example 11:

[0089] This is basically the same as Example 8, except that the active mineral additive is changed to active attapulgite soil, active attapulgite soil and active montmorillonite soil, with a mass ratio of 10:4:1, and other aspects remain unchanged.

[0090] Comparative Example 12:

[0091] This is basically the same as Example 8, except that the active mineral additive is changed to active attapulgite clay, metakaolin, and fly ash in a mass ratio of 10:1:3, while other aspects remain unchanged.

[0092] Summary: Based on the data from Examples 1, 8, and Comparative Example 1, the performance of shotcrete with active mineral admixtures made from acid-treated attapulgite, attapulgite, and montmorillonite is superior to that with admixtures made from native soil-based active mineral admixtures. Based on the data from Examples 8 and 10-11, the optimal dosage of the active mineral admixture is 7.0 parts. Based on the data from Examples 8-9, the calcination temperature of the native mineral soil also affects the activity of the active minerals, with 500°C being the optimal temperature for the attapulgite native soil. o Calcination at C: 900°C o Calcination at C, 450g of montmorillonite raw soil o The minerals obtained by C roasting treatment have better properties; according to the data of Example 8 and Comparative Examples 1 and 10-12, for the original soil-based active mineral admixture, the effect of admixtures of one, two or three mineral mixtures alone is not as good as the effect of admixtures that mix active attapulgite, active attapulgite, active montmorillonite, silica fume, metakaolinite and fly ash together; (see Table 1).

[0093] As can be seen from the above experimental data, the active mineral admixture for low-grade attapulgite soil-based shotcrete prepared by the present invention has a total content of 30-90% of active components SiO2 and Al2O3. It can significantly reduce the slab breakage and rebound rate of ordinary shotcrete construction, shorten the initial setting time to less than 3 minutes, shorten the final setting time to less than 10 minutes, and improve the 7-day and 28-day compressive strength.

[0094] The present invention is not limited to the specific technical solutions described in the above embodiments. All technical solutions formed by equivalent substitutions are within the scope of protection claimed by the present invention.

Claims

1. A method for preparing an active mineral admixture for low-grade attapulgite soil-based shotcrete, characterized in that: The mass fractions of each component in the active mineral admixture are: 40-60 parts active attapulgite, 10-20 parts active attapulgite, 5-20 parts active montmorillonite, 5-15 parts silica fume, 5-25 parts metakaolinite, 10-20 parts fly ash, and 0.5-6 parts water-reducing agent. The preparation method is as follows: First, the raw attapulgite ore, attapulgite ore, and montmorillonite ore are activated. Then, the obtained activated attapulgite, activated attapulgite, and activated montmorillonite are fully mixed with silica fume, metakaolin, and fly ash. Finally, water-reducing agent powder is added and fully dry-mixed to form the final product.

2. The method for preparing the active mineral admixture for low-grade attapulgite soil-based shotcrete according to claim 1, characterized in that: The activation treatment of the attapulgite ore, palygorskite ore, and montmorillonite ore is carried out through the following specific steps: (1) Activation treatment of attapulgite soil Low-grade attapulgite ore is sieved and crushed to obtain 300-mesh attapulgite powder. The attapulgite powder and acid solution are added to a container at a solid-liquid ratio of 1 kg: 3-8 L, where the acid solution has a mass concentration of 10-20 wt%. The mixture is stirred at 60-80℃ for 3-6 hours. After stirring, the resulting slurry is filtered, washed until neutral, dried, crushed, and sieved to obtain 300-mesh acidified attapulgite. The attapulgite powder and acidified attapulgite are then calcined at 300-500℃ for 1-3 hours to obtain activated attapulgite powder and activated acidified attapulgite. (2) Activation treatment of attapulgite Ratorite ore is sieved and crushed to obtain 300-mesh montmorillonite raw material. Ratorite ore and acid solution are added to a container at a solid-liquid ratio of 1 kg: 2-10 L, wherein the mass concentration of the acid solution is 10-15 wt%. The mixture is stirred at 30-90℃ for 3-6 hours. After stirring, the resulting slurry is filtered, washed until neutral, dried, crushed and sieved to obtain 300-mesh acidified montmorillonite. Ratorite raw material and acidified montmorillonite are calcined at 400-900℃ for 1-2 hours to obtain active montmorillonite raw material and active acidified montmorillonite. (3) Activation treatment of montmorillonite Medium- and low-grade montmorillonite ore is sieved and crushed to obtain 300-mesh montmorillonite raw material. Montmorillonite raw material and acid solution are added to a container at a solid-liquid ratio of 1 kg: 5~10 L, wherein the mass concentration of the acid solution is 10~25 wt%. The mixture is stirred at 30~80℃ for 3~6 hours. After stirring, the resulting slurry is filtered, washed until neutral, dried, crushed and sieved to obtain 300-mesh acidified montmorillonite. Montmorillonite raw material and acidified montmorillonite are calcined at 200-600℃ for 1~2 hours to obtain activated montmorillonite raw material and activated acidified montmorillonite.

3. The method for preparing the active mineral admixture for low-grade attapulgite soil-based shotcrete according to claim 1, characterized in that: The activated attapulgite, activated attapulgite, and activated montmorillonite are each one of the following: activated attapulgite soil and activated acidified attapulgite, activated attapulgite soil and activated acidified attapulgite, and activated montmorillonite soil and activated acidified montmorillonite; the silica fume has a particle size of less than 1 micrometer, the metakaolinite has a particle size of less than 2 micrometers, and the fly ash has a particle size of less than 30 micrometers.

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

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

7. The method for preparing the active mineral admixture for low-grade attapulgite soil-based shotcrete according to claim 2, characterized in that: Acidification treatment of attapulgite, attapulgite, and montmorillonite, wherein the acid solution is 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 soil-based shotcrete according to claim 1, characterized in that: Includes the following steps: Step 1: Crush and sieve the raw attapulgite, palygorskite, and montmorillonite ore separately to obtain 300-mesh raw attapulgite, 300-mesh palygorskite, and 300-mesh montmorillonite. Add the raw attapulgite, palygorskite, and montmorillonite ore to a 10wt% sulfuric acid solution at a solid-liquid ratio of 1 kg: 5 L in a container. Stir thoroughly at 60°C for 2 hours, filter, dry, crush, and sieve to obtain sulfuric acid-acidified 300-mesh acidified attapulgite, acidified palygorskite, and acidified montmorillonite. Then, immerse the acidified attapulgite in a 500-mesh solution. o Calcination at C for 1 hour, followed by acidified attapulgite at 850°C o Roasted at C for 1 hour, then acidified montmorillonite was placed at 450°C. o Calcination at C for 1 h yielded active attapulgite acid soil, active attapulgite acid soil, and active montmorillonite acid soil, respectively. Step 2: Mix 50 parts by weight of activated attapulgite, 20 parts by weight of activated attapulgite, 5 parts by weight of activated montmorillonite, 5 parts by weight of silica fume with a particle size distribution of 0.7-1 micrometer, 5 parts by weight of metakaolin with a particle size distribution of 1-2 micrometer, and 15 parts by weight of fly ash with a particle size distribution of 20-30 micrometer evenly. Then add 2 parts by weight of sodium lignosulfonate and 2 parts by weight of sodium polycarboxylate superplasticizer powder, and mix thoroughly to obtain the active mineral admixture.

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

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