Coal gangue-based shotcrete and method for preparing the same

Abstract

The application relates to the technical field of anchor shotcrete, and particularly provides anchor shotcrete based on coal gangue and a preparation method thereof. The anchor shotcrete comprises the following components in parts by weight: cement 100-140 parts, coal gangue 135-150 parts, water 50-70 parts, admixture 15-20 parts, calcium formate 1-5 parts, water reducing agent 4-5 parts, quick setting agent 5-9 parts, nano zinc oxide 2-5 parts, nano calcium silicate 3-5 parts, nano silicon dioxide 1-5 parts, nano aluminum silicate 2-5 parts and nano titanium oxide 1-3 parts. The anchor shotcrete provided by the application still has better mechanical properties while using coal gangue as aggregate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete materials, and particularly relates to a coal gangue-based anchor shotcrete and a preparation method thereof. BACKGROUND

[0002] Anchor shotcrete is a building material commonly used to reinforce rock, underground caverns, tunnels, and other underground structures. Anchor shotcrete can prevent ground collapse to some extent, maintain the stability of the foundation, and increase the bearing capacity of underground structures. During construction, drilling is first required, then an anchor rod (usually made of steel) is inserted into the hole, and concrete is sprayed into the hole to form a layer of concrete protective layer closely attached to the rock surface. Because anchor shotcrete has good adhesion and compressive strength, it can maintain the integrity of the structure even if affected by geological disasters or earthquakes. Anchor shotcrete is an efficient, economical and environmentally friendly method of reinforcing underground structures, so it is increasingly used in engineering construction.

[0003] Coal gangue is a waste material separated during coal mining and washing, and is one of the largest industrial solid wastes discharged in China. For a long time, the main method of treating coal gangue in China has been to discard it by piling up, so some old mining areas have coal gangue piles as high as mountains. Large amounts of coal gangue stored in piles not only are a heavy burden for coal production, but also seriously pollute the environment. Therefore, scientific and rational utilization of coal gangue has become an important research topic for environmental protection and sustainable development.

[0004] Coal gangue refers to the waste or byproduct containing coal generated during the mining and processing of coal. It is one of the largest industrial solid wastes discharged in China. It is mainly composed of non-economic parts of coal seams, including broken coal, carbonaceous roof, rock debris, mudstone, and quartz. Coal gangue has a certain impact on the environment because it often appears in large quantities and contains a certain proportion of sulfur, ash, and other substances. During piling up or dumping, coal gangue may cause waste of land resources, pollute the surrounding soil and water. In addition, when coal gangue meets oxygen and water, it may form an acidic solution, causing acid mine drainage, which has a negative impact on the water environment and ecological system. In order to reduce the impact of coal gangue on the environment, some measures are often taken for treatment. For example, using coal gangue for backfilling, reclamation, or solid waste landfill; using advanced coal gangue coal preparation technology to recover coal resources from coal gangue; processing and treating coal gangue through physical, chemical, and other methods to make it more environmentally friendly. These measures aim to minimize the harm of coal gangue to the environment and achieve effective utilization of resources.

[0005] Coal gangue is a main solid waste of coal mining, which is widely used in preparing concrete in recent years to achieve the purpose of using solid waste and reducing the production cost of anchor shotcrete. However, coal gangue as a kind of weak aggregate will greatly weaken the strength of coal gangue concrete when mixed into the concrete. Therefore, how to use coal gangue as a weak aggregate in the concrete while not reducing the mechanical properties of the concrete has become a problem to be solved by the technical personnel in the field. SUMMARY

[0006] In order to solve the above problems, the embodiment of the present application provides a kind of anchor shotcrete based on coal gangue and its preparation method, the anchor shotcrete provided by the embodiment of the present application still has better mechanical properties while using coal gangue as aggregate.

[0007] Therefore, the embodiment of the present application adopts the following technical scheme:

[0008] In the first aspect, the present application provides a kind of anchor shotcrete based on coal gangue, comprising the following components by weight: cement 100-140 parts, coal gangue 135-150 parts, water 50-70 parts, admixture 15-20 parts, calcium formate 1-5 parts, water reducing agent 4-5 parts, accelerator 5-9 parts, nano zinc oxide 2-5 parts, nano calcium silicate 3-5 parts, nano silicon dioxide 1-5 parts, nano aluminum silicate 2-5 parts, nano titanium oxide 1-3 parts.

[0009] In this embodiment, the mineral components in coal gangue are mainly composed of kaolin, quartz, montmorillonite, feldspar, illite, limestone, iron sulfide and aluminum oxide; the compounds in coal gangue are mainly composed of SiO2, Al2O3, K2O, Fe2O3, CaO, MgO, SO3 and P2O5 oxides, the content of SiO2 in coal gangue is between 40% and 70%, and the content of Al2O3 is between 15% and 30%. In the embodiment of the present application, coal gangue is used as aggregate to achieve effective utilization of solid waste and reduce the production cost of anchor shotcrete. The cement, admixture and additives can provide the binding property and workability of the concrete, so that the coal gangue is fully combined with other materials; specifically, the added calcium formate can improve the early strength of the anchor shotcrete, the water reducing agent can adjust the fluidity and compactness of the concrete, and improve the workability and mechanical properties of the anchor shotcrete. The accelerator can make the shotcrete quickly harden during construction.

[0010] The nano zinc oxide, nano calcium silicate, nano silicon dioxide, nano aluminum silicate and nano titanium oxide cooperate with each other to modify the shotcrete, which can enhance the mechanical properties and impermeability of the concrete, and improve the durability and stability of the shotcrete. The nano zinc oxide has catalytic effect and strengthening effect, can accelerate the cement hydration reaction, enhance the early strength development of the concrete, and improve the compressive strength and durability of the concrete. The nano calcium silicate can form dense hydration products by combining with calcium ions in water, fill the pores of the concrete, reduce the porosity and permeability, and improve the strength, durability and impermeability of the concrete. The nano silicon dioxide has fine particle size and high specific surface area, can fill the micro pores in the concrete, increase the interface contact area, improve the compactness and mechanical properties of the concrete, and improve the compressive strength and durability. The nano aluminum silicate can react with aluminum hydroxide in cement to generate gel, fill the internal pores of the concrete, increase the compactness and strength of the concrete, and also improve the durability and impermeability of the concrete. The nano titanium oxide can promote the cement hydration reaction in the concrete through catalytic effect, thereby increasing the strength and durability of the concrete.

[0011] The nano zinc oxide, nano calcium silicate, nano silicon dioxide, nano aluminum silicate and nano titanium oxide used in the present application are nanoscale materials, which can effectively fill the internal voids of the concrete, increase the structural compactness, thereby strengthening the mechanical properties and durability of the concrete. On the other hand, the above-mentioned nano materials also have pozzolanic activity, can react with calcium hydroxide to generate C-S-H gel, and appropriate addition can effectively promote the cement hydration, can make up for the low strength of the shotcrete caused by the addition of coal gangue, and improve the mechanical properties of the shotcrete.

[0012] As an implementable embodiment, the shotcrete comprises the following components in parts by weight: cement 100, coal gangue 135-140 parts, water 50-60 parts, admixture 18-20 parts, calcium formate 3-5 parts, water reducing agent 4-5 parts, accelerator 5-7 parts, nano zinc oxide 3-4 parts, nano calcium silicate 3-4 parts, nano silicon dioxide 3-5 parts, nano aluminum silicate 2-4 parts, and nano titanium oxide 1-2 parts.

[0013] As an implementable embodiment, the shotcrete comprises the following components in parts by weight: cement 100 parts, coal gangue 140 parts, water 60 parts, admixture 18 parts, calcium formate 3 parts, water reducing agent 4 parts, accelerator 7 parts, nano zinc oxide 3.5 parts, nano calcium silicate 4 parts, nano silicon dioxide 4 parts, nano aluminum silicate 3 parts, and nano titanium oxide 2 parts.

[0014] In this embodiment, the applicant has found that the anchor shotcrete with the above-mentioned proportion can give full play to the advantages of each component, so that the anchor shotcrete has better mechanical properties while using coal gangue as aggregate.

[0015] As an implementable embodiment, the continuous grading of the coal gangue is 0-15mm.

[0016] In this embodiment, the coal gangue is used to completely replace the coarse and fine aggregate in the anchor shotcrete. It has been verified that in the above-mentioned grading, the large particles form a skeleton by embedding each other, and a sufficient amount of fine aggregate fills the gap between the skeleton, thereby forming a continuous grading. After the addition of cementitious materials, the anchor shotcrete has a higher internal friction angle and a higher cohesion. Therefore, the above-mentioned reasonable continuous grading has better density, better bulk density, reduces the gap between particles, enhances the engagement effect between particles, can fully play the cementing effect of cement and the skeleton effect of aggregate, and is more obvious for increasing the strength of concrete. At the same time, the appropriate grading can improve the pumpability of the anchor shotcrete and reduce the rebound rate.

[0017] As an implementable embodiment, the admixture includes silica fume, fly ash and sodium bentonite in a weight ratio of 1-2:2-4:3-4.

[0018] In this embodiment, the addition of appropriate amounts of silica fume and fly ash can fill the pores of the concrete and improve the density and strength of the concrete. At the same time, the active ingredients in the silica fume and fly ash react with cement to form hardened gel, further filling the micro-pores and improving the durability of the concrete. Sodium bentonite can act as a catalyst in the cement hydration reaction, promoting the hydration reaction of cement, accelerating the crystal growth of concrete, and improving the early strength of concrete. Moreover, sodium bentonite has excellent water absorption thickening and suspension stability, and has water retention and thickening effect on concrete mortar, thereby improving the impermeability of concrete mortar. Silica fume, fly ash and sodium bentonite are mixed in the above-mentioned proportion to form cementitious materials with good bulk density, reduce the probability of concrete cracking, and improve the mechanical properties of concrete.

[0019] As an implementable embodiment, the anchor shotcrete further includes the following components in the following weight proportions: water-retention and anti-permeation agent 4-10 parts.

[0020] In this embodiment, the coal gangue has a high water demand. By adding a proper amount of the water-retaining and anti-permeable agent, the water retention of the anchor shotcrete can be effectively adjusted, the water penetration of the mortar and the water loss can be reduced, the flowability and workability of the mortar can be improved, and thus the workability and pumpability of the concrete mortar can be improved. Meanwhile, the water-retaining and anti-permeable agent can also reduce the permeability of the surface and the interior of the concrete, improve the anti-permeability of the concrete, and reduce the risk of cracks and damages of the concrete.

[0021] As an implementable embodiment, the water-retaining and anti-permeable agent comprises at least one of modified starch, nano-layered montmorillonite, and nano-layered mica.

[0022] In this embodiment, the modified starch, the nano-layered montmorillonite, and the nano-layered mica all have good dispersibility and adsorbability. After being uniformly dispersed in the concrete, they can absorb the water in the concrete and form stable water colloid, effectively reducing the water loss of the surface and the interior of the concrete. In this way, the drying speed of the concrete can be delayed, and sufficient time can be provided for the anchor shotcrete construction. Meanwhile, the addition of the modified starch, the nano-layered montmorillonite, and the nano-layered mica can fill the micro-pores of the concrete and reduce the permeability of the concrete. They can prevent the penetration and leakage of water and improve the anti-permeability of the concrete. The components in the modified starch, the nano-layered montmorillonite, and the nano-layered mica can react with the cement gel body to form stable hardened gel. This can fill the micro-defects in the concrete and improve the compactness and mechanical properties of the concrete. Meanwhile, they can also prevent the penetration of chloride ions and other harmful substances, reduce the diffusion coefficient of chloride ions in the concrete, and improve the durability and corrosion resistance of the concrete in high-salt environments.

[0023] As an implementable embodiment, the water-retaining and anti-permeable agent comprises modified starch, nano-layered montmorillonite, and nano-layered mica in a weight ratio of (1-4):(2-4):(1-2).

[0024] In this embodiment, the modified starch, the nano-layered montmorillonite, and the nano-layered mica have better compounding effects and better combination with the cementitious materials in the above-mentioned proportions, improve the relative humidity inside the concrete, reduce the possibility of cracks caused by self-shrinkage, and improve the anti-permeability of the concrete.

[0025] As an implementable embodiment, the modified starch is prepared by the following method:

[0026] 10-26 parts of starch and 1-2 parts of high-temperature amylase are added to 200-240 parts of deionized water, stirred and heated to 80-85℃, and subjected to a degradation gelatinization reaction for 1-2 hours. When the starch is colorless and transparent, a modified starch precursor is obtained.

[0027] Sodium bisulfite 1-2 parts and ammonium persulfate 3-6 parts are added to the modified starch precursor, after stirring for 20 min, acrylamide 35-90 parts and 2-acrylamide-2-methylpropane sulfonic acid 10-26 parts are added dropwise, respectively, stirring and heating to 60-70℃, pH regulator is added to maintain the pH value of the system at 6-7, the dropwise time is controlled at 1.5-2 hours, after the dropwise addition is completed, the reaction is continued for 3.5-5 hours to obtain a modified starch gel;

[0028] The obtained modified starch gel is soaked in anhydrous ethanol solution, washed, dried to constant weight, placed in an extractor, extracted with acetone as solvent for 8 hours to remove the homopolymer, and then the remaining material after extraction is freeze-dried and ground to obtain a modified starch with a particle size of less than 80 μm.

[0029] In this embodiment, the modified starch of the present application is based on the structure of natural high molecular material starch, the molecular structure size is controlled by degradation, and the hydrophilic amide group is introduced on the starch structure by graft polymerization, so that the prepared modified starch can form van der Waals force between water molecules in the capillary voids in the concrete, reduce the negative pressure tensile stress when the liquid surface in the capillary hole dries and migrates, and make the water in the concrete interior slowly diffuse from the concrete interior to the concrete surface, reduce the shrinkage rate of the concrete, and significantly improve the mechanical properties and durability parameters and performance of the concrete.

[0030] As an implementable embodiment, the starch is at least one of corn starch, wheat starch, and sweet potato starch.

[0031] As an implementable embodiment, the enzyme activity of the high-temperature amylase is 100000 u / mg, the applicable temperature range is 60-90℃, and the applicable pH range is 6-7.

[0032] As an implementable embodiment, the pH regulator is sodium hydroxide.

[0033] As an implementable embodiment, the cement is P.O42.5 ordinary portland cement.

[0034] In this embodiment, P.O42.5 ordinary portland cement is used as the main cementitious material of anchor spray concrete, which can ensure the mechanical properties, durability and construction quality of the concrete, and also has high economic benefit and practical value.

[0035] As an implementable embodiment, the water reducing agent is a polycarboxylic acid high-performance water reducing agent.

[0036] In the embodiment, since the aggregate in the application is coal gangue, the water demand of coal gangue is relatively large, in order to reduce the water-cement ratio, the polycarboxylate high-performance water reducing agent is added to reduce the water content in the concrete, while maintaining the fluidity and pumpability of the concrete, thereby improving the construction performance, strength and durability of the concrete.

[0037] In a second aspect, the application provides a preparation method of coal gangue-based anchor shotcrete, comprising the following steps:

[0038] According to the required proportion of raw materials, 100-140 parts of cement, 135-150 parts of coal gangue, 50-70 parts of water, 15-20 parts of admixture, 1-5 parts of calcium formate, 4-5 parts of water reducing agent, 2-5 parts of nano-zinc oxide, 3-5 parts of nano-calcium silicate, 1-5 parts of nano-silicon dioxide, 2-5 parts of nano-aluminum silicate, 1-3 parts of nano-titanium oxide are added, and then stirred uniformly, 5-9 parts of accelerator is added, and then stirred uniformly to obtain the anchor shotcrete.

[0039] In summary, the application has the following beneficial effects:

[0040] 1. In the embodiment of the application, coal gangue is used as aggregate, which realizes effective utilization of solid waste and reduces the production cost of anchor shotcrete;

[0041] 2. In the embodiment of the application, the nano-zinc oxide, nano-calcium silicate, nano-silicon dioxide, nano-aluminum silicate and nano-titanium oxide are mixed to modify the shotcrete, which can enhance the mechanical properties and impermeability of the concrete, improve the durability and stability of the coal gangue anchor shotcrete, and effectively guarantee the early strength and late strength of the anchor shotcrete;

[0042] 3. The modified starch, nano-layered montmorillonite and nano-layered mica in the embodiment of the application have excellent water-retention performance as water-retention and impermeability agents, which can reduce the permeation and leakage risk of the anchor shotcrete and improve the strength and durability of the anchor shotcrete. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the application will be described below.

[0044] It should be particularly pointed out that: except for the definition, the technical terms used in the following embodiments have the same meaning as generally understood by those skilled in the art to which the application belongs. The experimental reagents used in the following embodiments, unless otherwise specified, are conventional biochemical reagents; the raw materials, instruments and equipment used in the following embodiments, unless otherwise specified, can be purchased on the market or obtained by existing methods; the amount of the experimental reagents, unless otherwise specified, is the amount of reagents in conventional experimental operations; the experimental methods, unless otherwise specified, are conventional methods.

[0045] The cement in the embodiments of the present application is P.O 42.5 ordinary portland cement; the water reducing agent is polycarboxylic acid high performance water reducing agent, and the water reducing rate thereof is 35%; the accelerator is JYS154 accelerator produced by Wuhan Jiyesheng Chemical Co., Ltd. The enzyme activity of the thermostable amylase is 100000 u / mg, the applicable temperature range is 60-90℃, and the applicable pH range is 6-7, which is purchased from Guangdong Wengjiang Chemical Reagent Co., Ltd. with the article number PB95971.

[0046] Preparation Example 1

[0047] The modified starch is prepared by the following method:

[0048] Starch 20 parts and thermostable amylase 1 part are added into 200 parts of deionized water, stirred and heated to 80℃, and a degradation gelatinization reaction is performed for 1.5 hours. When the starch is colorless and transparent, a modified starch precursor is obtained;

[0049] Sodium bisulfite 1 part and ammonium persulfate 3 parts are added into the modified starch precursor, stirred for 20 min, and then acrylamide 70 parts and 2-acrylamide-2-methylpropanesulfonic acid 20 parts are added dropwise, respectively. Stirring and heating to 65℃, a pH regulator is added to maintain the pH value of the system at 6-7, and the dropwise adding time is controlled to be 1.5-2 hours. After the dropwise adding is completed, the reaction is continued for 4 hours to obtain a modified starch gel;

[0050] The obtained modified starch gel is soaked in anhydrous ethanol solution, washed, dried to constant weight, and then placed in an extractor. Acetone is used as a solvent to extract for 8 hours to remove homopolymers. Then, the remaining material after extraction is freeze-dried, and after pulverization, a modified starch with a particle size of less than 80μm is obtained.

[0051] Example 1

[0052] A coal gangue-based anchor shotcrete includes the following components in parts by weight: cement 100 parts, coal gangue 135 parts, water 50 parts, admixture 15 parts, calcium formate 1 part, water reducing agent 4 parts, accelerator 5 parts, nano-zinc oxide 2 parts, nano-calcium silicate 3 parts, nano-silicon dioxide 1 part, nano-aluminum silicate 5 parts, and nano-titanium oxide 3 parts. The coal gangue is divided into coal gangue aggregates of different particle size ranges of 0-2.5mm, 2.5-5mm, 5-10mm, and 10-15mm, and the weight percentages of the coal gangue aggregates of different particle size ranges are 0-2.5mm: 34.5%, 2.5-5mm: 17.1%, 5-10mm: 26.2%, and 10-15mm: 22.2%, respectively. The admixture includes silica fume, fly ash, and sodium-based bentonite in a weight ratio of 1:2:3.

[0053] The above anchor shotcrete is prepared by the following method:

[0054] According to the required proportion of the above raw materials, cement, coal gangue, water, admixture, calcium formate, water reducing agent, nano zinc oxide, nano calcium silicate, nano silicon dioxide, nano aluminum silicate, nano titanium oxide, stirring uniformly, adding accelerator, stirring uniformly to obtain anchor spray concrete.

[0055] Example 2

[0056] A coal gangue-based anchor spray concrete, compared with example 1, the only difference is that it comprises the following components in parts by weight: cement 120 parts, coal gangue 140 parts, water 60 parts, admixture 18 parts, calcium formate 3 parts, water reducing agent 4.5 parts, accelerator 7 parts.

[0057] Example 3

[0058] A coal gangue-based anchor spray concrete, compared with example 1, the only difference is that it comprises the following components in parts by weight: cement 140 parts, coal gangue 150 parts, water 70 parts, admixture 20 parts, calcium formate 5 parts, water reducing agent 5 parts, accelerator 9 parts.

[0059] Example 4

[0060] A coal gangue-based anchor spray concrete, compared with example 1, the only difference is that it comprises the following components in parts by weight: nano zinc oxide 4 parts, nano calcium silicate 4 parts, nano silicon dioxide 3 parts, nano aluminum silicate 4 parts, nano titanium oxide 2 parts.

[0061] Example 5

[0062] A coal gangue-based anchor spray concrete, compared with example 1, the only difference is that it comprises the following components in parts by weight: nano zinc oxide 5 parts, nano calcium silicate 5 parts, nano silicon dioxide 5 parts, nano aluminum silicate 2 parts, nano titanium oxide 1 part.

[0063] Example 6

[0064] A coal gangue-based anchor spray concrete, compared with example 1, the only difference is that it comprises the following components in parts by weight: nano zinc oxide 3 parts, nano calcium silicate 4 parts, nano silicon dioxide 4 parts, nano aluminum silicate 3 parts, nano titanium oxide 2 parts.

[0065] Example 7

[0066] A coal gangue-based anchor spray concrete, compared with example 1, the only difference is that it further adds water-retaining and anti-permeability agent 4 parts; wherein the water-retaining and anti-permeability agent is the modified starch in preparation example 1.

[0067] Example 8

[0068] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: 7 parts of a water-retaining impermeability agent is further added; wherein the water-retaining impermeability agent is a nano-layered montmorillonite.

[0069] Example 9

[0070] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: 10 parts of a water-retaining impermeability agent is further added; wherein the water-retaining impermeability agent is a nano-layered mica.

[0071] Example 10

[0072] A coal gangue-based anchor shotcrete, compared with Example 8, only differs in that: the water-retaining impermeability agent comprises modified starch, nano-layered montmorillonite and nano-layered mica at a weight ratio of 4:2:1; wherein the modified starch is the modified starch prepared in Preparation Example 1.

[0073] Example 11

[0074] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: the water-retaining impermeability agent comprises modified starch, nano-layered montmorillonite and nano-layered mica at a weight ratio of 3:3:2; wherein the modified starch is the modified starch prepared in Preparation Example 1.

[0075] Example 12

[0076] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: the water-retaining impermeability agent comprises modified starch, nano-layered montmorillonite and nano-layered mica at a weight ratio of 1:4:1; wherein the modified starch is the modified starch prepared in Preparation Example 1.

[0077] Comparative Example 1

[0078] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: no nano-zinc oxide is added.

[0079] Comparative Example 2

[0080] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: no nano-zinc oxide and nano-calcium silicate are added.

[0081] Comparative Example 3

[0082] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: no nano-zinc oxide, nano-calcium silicate and nano-silicon dioxide are added.

[0083] Comparative Example 4

[0084] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: no nano-zinc oxide, nano-calcium silicate, nano-silicon dioxide, nano-aluminum silicate and nano-titanium oxide is added.

[0085] Comparative Example 5

[0086] A coal gangue-based anchor shotcrete, compared with Example 1, only differs in that: no nano-zinc oxide, nano-calcium silicate, nano-silicon dioxide, nano-aluminum silicate and nano-titanium oxide is added.

[0087] Performance detection of anchor shotcrete

[0088] According to the requirements of Appendix B in JGJ / T 372-2016 “Technical Specification for Application of Shotcrete”, the anchor shotcrete test piece is prepared, and the performance of the anchor shotcrete test piece is tested according to the following method:

[0089] 1. Slump: The slump of the concrete mixture at room temperature (20±5) ℃ is tested according to the slump test in GB / T50080-2016 “Standard Test Methods for Properties of Fresh Ordinary Concrete”.

[0090] 2. Compressive strength: The standard test block is made according to the method in GB / T50081-2016 “Standard Test Methods for Mechanical Properties of Fresh Ordinary Concrete”, and the compressive strength of the standard test block after 1d, 7d and 28d curing is measured.

[0091] 3. Chloride ion diffusion coefficient: The chloride ion diffusion coefficient of the standard test block is tested according to the RCM method in GB / T50082-2009 “Standard Test Methods for Long-Term Performance and Durability of Ordinary Concrete”.

[0092] 4. Water permeability resistance: The water penetration depth of the standard test block is tested according to the step-by-step pressure method in GB / T50082-2009 “Standard Test Methods for Long-Term Performance and Durability of Ordinary Concrete”.

[0093] Table 1 Performance detection results of anchor shotcrete in Examples 1-12 and Comparative Examples 1-5

[0094]

[0095] According to Examples 1-3 and in combination with Table 1, it can be seen that the preferred raw material ratio in the preparation of the anchor shotcrete in the examples is preferred, the slump of the prepared coal gangue-based anchor shotcrete is suitable, has better fluidity, and still has better compressive strength even in the case of adding coal gangue aggregate, and even improves the working performance and mechanical properties of the anchor shotcrete to a certain extent.

[0096] According to the embodiments 1, 4-6 and comparative examples 1-5 and Table 1, in the embodiments of the present application, the modification of the shotcrete by the mutual cooperation of nano-zinc oxide, nano-calcium silicate, nano-silicon dioxide, nano-aluminum silicate and nano-titanium oxide can enhance the mechanical properties and impermeability of the concrete, improve the durability and stability of the shotcrete based on coal gangue, and the absence of any of the substances has no obvious effect. The possible reason is that the nano-zinc oxide, nano-calcium silicate, nano-silicon dioxide, nano-aluminum silicate and nano-titanium oxide as nano-scale materials can effectively fill the internal voids of the concrete, increase the structural density, thereby enhancing the mechanical properties and durability of the concrete. On the other hand, the above nano-materials also have pozzolanic activity, can react with calcium hydroxide to generate C-S-H gel, and appropriate incorporation can effectively promote cement hydration, can make up for the low strength of the shotcrete caused by the incorporation of coal gangue, and improve the mechanical properties of the shotcrete. In the embodiment 6, when 3 parts of nano-zinc oxide, 4 parts of nano-calcium silicate, 4 parts of nano-silicon dioxide, 3 parts of nano-aluminum silicate and 2 parts of nano-titanium oxide are added, the slump of the shotcrete is 93 mm, the 1d compressive strength is 9.2 Mpa, the 7d compressive strength is 43.5 Mpa, the 28d compressive strength is 61.1 Mpa, the chloride ion diffusion coefficient is 1.19 x 10 -12 m 2 / s, and the water penetration depth is 3.3 mm.

[0097] According to the embodiments 7-12 and Table 1, in the embodiments of the present application, the water-retaining and impermeability agent is added when preparing the shotcrete, and the water-retaining and impermeability agent is selected from the compounding of modified starch, nano-layered montmorillonite and nano-layered mica. The prepared shotcrete has a certain degree of improvement in slump and compressive strength, and the chloride ion diffusion coefficient and water penetration depth are reduced. The water-retaining and impermeability agent is compounded from modified starch, nano-layered montmorillonite and nano-layered mica in a specific ratio, which can help to improve the compressive strength and impermeability of the shotcrete based on coal gangue to a certain extent, and improve the slump, making it easier to meet the construction requirements. Compared with the absence of any of the water-retaining and impermeability agents of modified starch, nano-layered montmorillonite and nano-layered mica, the mechanical properties and construction performance of the prepared shotcrete are reduced to a certain extent, that is, on the basis of ensuring the mechanical properties, the water-retaining and impermeability agent compounded from modified starch, nano-layered montmorillonite and nano-layered mica has better effect in improving the impermeability of the shotcrete. In the embodiment 11, the slump of the shotcrete is 115 mm, the 1d compressive strength is 9.2 Mpa, the 7d compressive strength is 43.1 Mpa, the 28d compressive strength is 60.6 Mpa, the chloride ion diffusion coefficient is 0.85 x 10 -12 m 2 / s, and the water penetration depth is 2.0 mm, and the performance is better.

[0098] The anchor shot concrete in Example 11 having a rebound of 3.6% was sprayed on the construction surface by a SPJ2010 wet sprayer.

[0099] Finally, it should be pointed out that the above examples are only used to illustrate the technical solutions of the present application. Those skilled in the art should understand that although the present application has been described in detail with reference to the foregoing examples, the technical solutions recorded in the foregoing examples can still be modified, or some technical features can be replaced by equivalent features. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions in the embodiments of the present application.

Claims

1. An anchor shotcrete based on coal gangue, characterized in that: The invention comprises the following components in parts by weight: 100-140 parts of cement, 135-150 parts of coal gangue, 50-70 parts of water, 15-20 parts of admixture, 1-5 parts of calcium formate, 4-5 parts of water reducer, 5-9 parts of accelerating agent, 2-5 parts of nano zinc oxide, 3-5 parts of nano calcium silicate, 1-5 parts of nano silicon dioxide, 2-5 parts of nano aluminum silicate, and 1-3 parts of nano titanium oxide; The anchor shotcrete further comprises the following components in parts by weight: 4-10 parts of a water-retaining and anti-seepage agent, wherein the water-retaining and anti-seepage agent comprises modified starch, nano-layered montmorillonite, and nano-layered mica in a weight ratio of (1-4): (2-4): (1-2); Wherein, the modified starch is prepared by the following method: Add 10-26 parts of starch and 1-2 parts of high-temperature amylase to 200-240 parts of deionized water, stir and heat to 80-85°C, and perform degradation and gelatinization reaction for 1-2 hours. When the starch becomes colorless and transparent, a modified starch precursor is obtained; Add 1-2 parts of sodium bisulfite and 3-6 parts of ammonium persulfate to the modified starch precursor, stir for 20 minutes, then dropwise add 35-90 parts of acrylamide and 10-26 parts of 2-acrylamide-2-methylpropanesulfonic acid, stir and heat to 60-70°C, add a pH adjuster to maintain the pH value of the system at 6-7, control the dropwise addition time to 1.5-2 hours, and continue to heat and react for 3.5-5 hours after the dropwise addition is completed to obtain a modified starch gel; The obtained modified starch gel is soaked in an anhydrous ethanol solution, washed, dried to constant weight, placed in an extractor, and extracted with acetone as a solvent for 8 hours to remove homopolymers. The residue after extraction is then freeze-dried and ground to obtain modified starch with a particle size of less than 80 μm.

2. The anchor shotcrete according to claim 1, characterized in that The invention comprises the following components in parts by weight: 100 parts of cement, 135-140 parts of coal gangue, 50-60 parts of water, 18-20 parts of admixture, 3-5 parts of calcium formate, 4-5 parts of water reducer, 5-7 parts of accelerating agent, 3-4 parts of nano zinc oxide, 3-4 parts of nano calcium silicate, 3-5 parts of nano silicon dioxide, 2-4 parts of nano aluminum silicate and 1-2 parts of nano titanium oxide.

3. The anchor shotcrete according to claim 2, characterized in that: The invention comprises the following components in parts by weight: 100 parts of cement, 140 parts of coal gangue, 60 parts of water, 18 parts of admixture, 3 parts of calcium formate, 4 parts of water reducer, 7 parts of accelerating setting agent, 3.5 parts of nano zinc oxide, 4 parts of nano calcium silicate, 4 parts of nano silicon dioxide, 3 parts of nano aluminum silicate and 2 parts of nano titanium oxide.

4. The anchor shotcrete according to any one of claims 1 to 3, characterized in that: The continuous gradation of the coal gangue is 0-15 mm.

5. The anchor shotcrete according to any one of claims 1 to 3, characterized in that: The admixture includes silica fume, fly ash and sodium bentonite in a weight ratio of 1-2:2-4:3-4.

6. A method for preparing anchor shotcrete based on coal gangue as claimed in claim 1, characterized in that: The following steps are involved: According to the required ratio of raw materials, 100-140 parts of cement, 135-150 parts of coal gangue, 50-70 parts of water, 15-20 parts of admixture, 1-5 parts of calcium formate, 4-5 parts of water reducer, 2-5 parts of nano zinc oxide, 3-5 parts of nano calcium silicate, 1-5 parts of nano silicon dioxide, 2-5 parts of nano aluminum silicate, 1-3 parts of nano titanium oxide, 4-10 parts of water-retaining and anti-seepage agent are mixed evenly, and then 5-9 parts of accelerator are added and mixed evenly to obtain anchor shotcrete; The water-retaining and anti-seepage agent comprises modified starch, nano-layered montmorillonite, and nano-layered mica in a weight ratio of (1-4): (2-4): (1-2); Wherein, the modified starch is prepared by the following method: Add 10-26 parts of starch and 1-2 parts of high-temperature amylase to 200-240 parts of deionized water, stir and heat to 80-85°C, and perform degradation and gelatinization reaction for 1-2 hours. When the starch becomes colorless and transparent, a modified starch precursor is obtained; Add 1-2 parts of sodium bisulfite and 3-6 parts of ammonium persulfate to the modified starch precursor, stir for 20 minutes, then dropwise add 35-90 parts of acrylamide and 10-26 parts of 2-acrylamide-2-methylpropanesulfonic acid, stir and heat to 60-70°C, add a pH adjuster to maintain the pH value of the system at 6-7, control the dropwise addition time to 1.5-2 hours, and continue to heat and react for 3.5-5 hours after the dropwise addition is completed to obtain a modified starch gel; The obtained modified starch gel is soaked in an anhydrous ethanol solution, washed, dried to constant weight, placed in an extractor, and extracted with acetone as a solvent for 8 hours to remove homopolymers. The residue after extraction is then freeze-dried and ground to obtain modified starch with a particle size of less than 80 μm.

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