120h ultra-slow setting waste base shotcrete and preparation process

Abstract

The present invention discloses a 120h ultra-slow setting waste-based shotcrete and a preparation process, including the raw materials of the following components: based on cement, cement 100%, soil and stone waste 400%, fly ash 15%-30%, mixing water 42-49%, compound retarder 2%-4%, quick setting agent 5%-8%, air entraining agent 0.015%-0.025%, early strength agent 1.5%-2.5%, defoamer 0.075%-0.125%. The compound retarder is a polycarboxylic acid water-reducing mother liquor, a polycarboxylic acid collapse-preserving mother liquor, sodium tripolyphosphate, sodium gluconate and water compounded in a certain proportion. The compound retarder of the present invention contains inorganic and organic substances at the same time, which prevents cement hydration together, and the effect is remarkable. The premixed wet material in the present invention has sufficient slow setting time and has a higher late strength after being made into shotcrete. Therefore, it can be ensured that the wet material transportation time is sufficient and the initial support of the underground project is good.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete preparation, and in particular relates to a 120h ultra-slow-setting waste-base shotcrete and a preparation process thereof. Background Art

[0002] In underground projects, the instability of the surrounding rock caused by excavation requires the use of shotcrete for initial support. At present, the most commonly used is tidal shotcrete, which is to add a certain amount of water to the aggregate to make it wet, then add cement and stir it, and then put it into the hopper of the sprayer, add the accelerator and output the mixture, and finally add water at the nozzle to spray it out. Tidal shotcrete has the advantages of better hydration, less dust and rebound than dry spraying, easier cleaning than wet spraying, and mature technology. However, there are still many defects: 1. Manual mixing before spraying leads to unstable ratio; 2. The moisture content of aggregate is difficult to control, which affects the strength of shotcrete; 3. The dust is large, which not only causes great harm to the health of the workers, but also pollutes the surrounding environment; 4. The slurry concentration is unstable, which affects the control of the rebound rate. At present, the latest super-slow setting concrete in the industry (patent publication number is CN112250387A) has a super-slow setting time of 108h and has sufficient late strength. On the other hand, due to the current shortage of sand and gravel resources, the present invention will replace sand and gravel with soil and stone waste on this basis, improve energy utilization and the profit of low value-added products, and develop a 120h super slow-setting soil and stone waste spraying material with longer slow-setting time and higher later strength. Summary of the invention

[0003] The purpose of the present invention is to utilize soil and stone waste materials with compositions similar to those of sand and stone, and after adding a compound retarder and other concrete admixtures, prepare a 120h super-slow-setting waste-based shotcrete, which can improve resource utilization, reduce the cost of underground shotcrete, simplify the underground shotcrete process, increase the underground transportation time, and enhance the later strength of the shotcrete.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A 120h ultra-slow-setting waste-base shotcrete comprises the following components in percentage by weight:

[0006] Taking cement as the benchmark, cement is 100%, soil and stone waste is 400%, fly ash is 15%~30%, mixing water is 42-49%, compound retarder is 2%~4%, accelerator is 5%~8%, air entraining agent is 0.015%~0.025%, early strength agent is 1.5%~2.5%, and defoaming agent is 0.075%~0.125%.

[0007] Furthermore, the 120h super-slow-setting waste-based shotcrete includes the following components in percentage by weight: 100% cement, 400% soil and stone waste, 17.5% fly ash, 45% mixing water, 3% compound retarder, 7% accelerator, 0.02% air entraining agent, 2% early strength agent, and 0.08% defoaming agent.

[0008] Furthermore, the compound retarder is prepared by compounding polycarboxylic acid water-reducing mother liquor, polycarboxylic acid slump-retaining mother liquor, sodium tripolyphosphate, sodium gluconate and water in a certain proportion, wherein the mass ratio of sodium gluconate: sodium tripolyphosphate: polycarboxylic acid water-reducing mother liquor: polycarboxylic acid slump-retaining mother liquor is 1:20:5.5:45.

[0009] Furthermore, the specific preparation method of the compound retarder is as follows: taking a certain amount of water at room temperature, adding sodium gluconate and sodium tripolyphosphate into the water, stirring evenly until there is no white precipitate to obtain a mixed solution, and then sequentially adding polycarboxylic acid water-reducing mother solution and polycarboxylic acid collapse-preserving mother solution into the mixed solution and stirring evenly to prepare the compound retarder;

[0010] Furthermore, the amount of water used to prepare the mixed solution is 2.5% to 3.5% of the weight of the soil and stone waste, preferably 3%; the water used to prepare the mixed solution is deducted from the mixing water.

[0011] Furthermore, the quick-setting agent uses a low-alkali powdered quick-setting agent; the air-entraining agent uses triterpenoid saponin or K12; the defoaming agent uses a concrete defoaming agent; the early strength agent (also known as a coagulant) uses triethanolamine or other organic early strength agents such as calcium formate, and the soil and stone waste is soil and stone waste with a moisture content of 3%.

[0012] Another object of the present invention is to provide a preparation process for 120h ultra-slow-setting waste-based shotcrete, comprising the following steps:

[0013] (1) preparing wet material: taking a formula amount of cement, fly ash, and soil and stone waste with a moisture content of 3% and pouring them into a forced single-horizontal shaft concrete mixer to obtain a dry mixed aggregate, stirring the dry mixed aggregate for 5 to 10 minutes, adding a compound retarder during the stirring process to prepare wet material, and the wet material did not undergo obvious cement hydration after being left to stand for 120 hours;

[0014] (2) Preparation of concrete: After standing for 120 hours, add the wet material to mixing water at a water-cement ratio of (0.42-0.49):1, pour it into a forced single-horizontal shaft concrete mixer and stir for 2 minutes. First, add the defoamer and stir for 1-2 minutes to dissolve the invalid bubbles in the concrete. Then, add the air entraining agent and stir for 1-2 minutes to introduce dense small bubbles. Then, add the early strength agent and stir for 30 seconds. Finally, add the accelerator to the mixer and stir for 1-2 minutes to obtain the 120-hour ultra-slow-setting waste-based shotcrete.

[0015] Among them, the cement used conforms to the cement specified in Appendix A of GB 8076-2008 "Concrete Admixtures"; the fineness modulus of the soil and stone waste used belongs to the range of Class II sand, and the particle grading is good; the mixing water used conforms to the technical requirements of JGJ63-2006 "Standard for Water for Concrete", and the admixture testing complies with the specification GB 8076-2008 "Concrete Admixtures".

[0016] The function of the retarder is to prepare a composite retarder that can achieve a super retarding effect, ensure that the wet spray material is still in a wet state after being left to stand for 120 hours, and delay cement hydration. The composite retarder of the present invention contains both inorganic and organic substances, and cement hydration is prevented by the film formed by the inorganic retarder and the organic retarder on the surface of cement particles, with a significant effect.

[0017] The role of defoaming agent and air entraining agent: The defoaming agent is added first to eliminate harmful bubbles in the concrete through degassing and bubble breaking. At this time, the air content of the concrete is reduced, and air entraining agent needs to be added to introduce a large number of uniform, stable and closed tiny bubbles during the concrete mixing process, so as to achieve the purpose of improving the cohesion and appearance quality of the concrete.

[0018] The role of early strength agent: By adding organic early strength agent, the surface tension of cement particles in contact with water is reduced, its solubility is increased, and cement hydration is accelerated; at the same time, the early strength agent can reduce the concentration of cement hydrolysis products, promote the formation of hydration products such as gel, accelerate the coagulation and hardening of cement, and improve the early strength of super slow-setting soil and rock waste spraying materials to ensure the safety of the initial support of the tunnel.

[0019] The role of the quick-setting agent: It has good adaptability with the early strength agent and can make the cementitious material solidify and harden in a short time. The low-alkali quick-setting agent used in the present invention can not only improve the early strength, but also has the advantages of good adhesion, low rebound rate, small dust volume, etc. The cost and environmental protection are also in place. However, the mid- and late-stage strength is still reduced to a certain extent. Therefore, it is necessary to introduce a certain amount of fly ash to improve the late strength of the super slow-setting soil and stone waste sprayed material.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] First, with the development of the construction industry and urbanization, natural sand and gravel resources are in short supply. Using soil and stone waste as aggregates to prepare sprayed materials has alleviated the supply pressure of sand and gravel aggregates to a certain extent and improved resource utilization.

[0022] Second, underground shotcrete spraying produces a lot of dust and a bad working environment, threatening the life and health of workers. The 120h super slow-setting soil and stone waste wet spraying material provided by the present invention can still keep the aggregate moist after 120h, greatly reducing the dust hazard and ensuring the safety of workers.

[0023] Third, using a twin-shaft trough mixer (manufacturer: Bahas-Sansohofen Machinery Co., Ltd.), the soil and stone waste and cement are prepared into a 120h super slow-setting soil and stone waste wet spraying material (can be bagged), which can achieve the purpose of improving the control accuracy of aggregate ratio, ensuring the strength of shotcrete, controlling the rebound rate, simplifying the underground spraying process, and improving the working environment.

[0024] Fourthly, the utilization of earth and stone waste in the present invention complies with the national industrial policy, and changes external purchase to internal supply, which not only increases the profit of low value-added products, but also plays a positive role in promoting the development of enterprises.

[0025] Fifth, the premixed wet material of the present invention has sufficient slow setting time and has high late strength after being made into shotcrete, so that sufficient wet material transportation time can be ensured and good initial support for underground engineering can be ensured.

[0026] Sixth, in the super retarder component compounded by the present invention, polycarboxylic acid water-reducing mother liquor can reduce the amount of water used; polycarboxylic acid slump-retaining mother liquor can ensure that the slump of shotcrete meets the specification requirements; sodium tripolyphosphate has a water-retaining effect (adding a water-retaining agent will affect the slump), belongs to an inorganic retarder, and has a poorer retarding effect than sugars; but sodium gluconate can enhance the retarding effect, and from a cost perspective, it has the highest cost-effectiveness. Therefore, the compounded retarder has the advantages of integrating the functions of water reduction, water retention, slump retention, and retarding. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the status diagram of the wet materials of test groups 1-4 after storage for 120 hours.

[0028] Figure 2 This is the status diagram of the wet materials of test groups 5-8 after storage for 120 hours. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention, and those skilled in the art in this field can make some non-essential improvements and adjustments based on the content of the above invention.

[0030] Among them, the sources of accelerators and compound retarders are as follows:

[0031] A new generation of accelerating setting agent produced by Hongfu Building Additives Factory in Dongying District;

[0032] Sodium tripolyphosphate produced by Hongyan Reagent Factory in Hedong District, Tianjin;

[0033] Food grade sodium gluconate produced by Henan Wanbang Industrial Co., Ltd.;

[0034] Collapse-resistant polycarboxylic acid water-reducing concentrate and high water-reducing polycarboxylic acid water-reducing concentrate produced by Hunan Zhongyan Building Materials Technology Co., Ltd.

[0035] The air entraining agent uses triterpenoid saponin from Jinan Shouyue Chemical Technology Co., Ltd.;

[0036] The defoamer used is the concrete defoamer produced by Jingqi Chemical;

[0037] The early strength agent (also known as accelerator) uses industrial-grade triethanolamine from Tianjin Zhonghe Shengtai Chemical Co., Ltd.

[0038] The soil and rock waste is soil and rock waste with a moisture content of 3% provided by Jiaozuo Qianye New Materials.

[0039] Unless otherwise specified, other raw materials are commercially available products.

[0040] The experimental design is shown in Table 1:

[0041] Table 1 Test design mix ratio

[0042]

[0043]

[0044] (1) Preparation of wet material:

[0045] According to the formula in Table 1, cement, fly ash, and soil and stone waste with a moisture content of 3% are poured into a forced single-horizontal shaft concrete mixer and the dry-mixed aggregate is stirred for about 5 minutes. During the mixing process of the aggregate, the compounded super retarder is added, and the wet material is prepared and left to stand for 120 hours to observe its retarding effect.

[0046] In the tests listed in Table 1, Groups 1, 2, 3, and 4 changed the fly ash dosage and the water used to prepare the solution to determine the best ratio. Among them, Groups 1 and 3 changed the water used to prepare the solution, and Groups 2 and 4 changed the fly ash dosage to determine the optimal water used to prepare the solution and the fly ash dosage, respectively. Group 5 is a control group test for fly ash, which mainly tests whether the uniaxial compressive strength meets the standard when fly ash is not added. Group 6 removed sodium gluconate from the compound retarder combination to observe its retarding effect. Group 7 removed sodium tripolyphosphate from the compound retarder combination to observe its retarding effect. Group 8 observed the effect of placing the wet material for seven days without adding a compound retarder.

[0047] In the tests listed in the above table, groups 1, 2, 3, and 4 changed the fly ash dosage and retarder moisture content (water used to prepare the solution) to determine the best ratio, among which groups 1 and 3 changed the retarder moisture content, and groups 2 and 4 changed the fly ash dosage to respectively determine the optimal retarder moisture content and fly ash dosage. Group 5 is a control group test for fly ash, which mainly tests whether the uniaxial compressive strength meets the standard when no fly ash is added. The compound retarder in group 6 does not contain sodium gluconate, and its retarding effect is observed. The compound retarder in group 7 does not contain sodium tripolyphosphate, and its retarding effect is observed. Group 8 observes its storage state without adding compound retarder. The state of each group of wet materials after storage for 120 hours is as follows: Figure 1 and Figure 2 shown.

[0048] pass Figure 1 and Figure 2 It can be seen that after 120 hours of storage, tests 1-4 showed no caking and were still moist; after 120 hours of storage, tests 5-7 showed some caking, some cement hydrated, the damp material gradually became dry, and some moisture was lost; after 120 hours of storage, test 8 had completely caked, the cement was completely hydrated, and could not be put into use.

[0049] (2) Preparation of concrete: The wet material after standing for 120 hours is poured into a forced single-horizontal shaft concrete mixer at a water-cement ratio (mass ratio of mixing water to cement) = (0.42-0.49):1 and stirred for 2 minutes. A defoamer is first added and stirred for 1-2 minutes to dissolve the invalid bubbles in the concrete. Then, an air entraining agent is added and stirred for 1-2 minutes to introduce a certain amount of dense small bubbles. Then, an early strength agent is added and stirred for 30 seconds. Finally, an accelerator is added to the mixer and stirred for 1-2 minutes to obtain shotcrete.

[0050] (3) Preparation of compression test blocks: Pour the mixed concrete slurry, cast into molds, and make test blocks. Curing is carried out under standard conditions of temperature of 20±2℃ and relative humidity of 95%, and then demolding is carried out with a spray gun and compressive strength test is carried out using a pressure testing machine. The preparation of the above compression test blocks and the compressive strength test are carried out in accordance with GB 50086-2015 "Technical Specifications for Geotechnical Anchors and Sprayed Concrete Support Engineering" and GB / T50081-2019 "Standard for Test Methods for Physical and Mechanical Properties of Concrete". The final compressive strength of each group of test blocks is shown in Table 2.

[0051] Table 2

[0052]

[0053] In test 8, no retarder was added, and the material completely agglomerated after 120 hours, and the uniaxial compressive test could not be carried out. The uniaxial compressive strengths of test groups 1, 2, 3, and 4 all reached the strength index of more than 7MPa. Among them, the second group with a lower water content of the retarder (less water was used to prepare the solution) and a larger amount of fly ash had the best compressive strength effect.

[0054] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for preparing 120h ultra-slow setting waste-based shotcrete, characterized in that The following steps are involved: (1) Preparation of wet material: Pour the formulated amount of cement, fly ash, and soil and stone waste with a moisture content of 3% into a forced single-horizontal shaft concrete mixer to obtain dry mixed aggregate. Stir the dry mixed aggregate for 5 to 10 minutes, add a compound retarder during the stirring process to prepare wet material. After the wet material was left to stand for 120 hours, no obvious cement hydration occurred. (2) Preparation of concrete: Add the wet material after standing for 120 hours to mixing water at a water-cement ratio of (0.42-0.49):1 into a forced single-horizontal shaft concrete mixer and stir for 2 minutes. First, add the defoamer and stir for 1-2 minutes to dissolve the invalid bubbles in the concrete. Then, add the air entraining agent and stir for 1-2 minutes to introduce dense small bubbles. Then, add the early strength agent and stir for 30 seconds. Finally, add the accelerator and stir for 1-2 minutes to obtain the 120-hour ultra-slow-setting waste-based shotcrete. The 120h ultra-slow setting waste-based shotcrete comprises the following components in percentage by weight: Taking cement as the benchmark, cement is 100%, soil and stone waste is 400%, fly ash is 15%~30%, mixing water is 42-49%, compound retarder is 2%~4%, accelerator is 5%~8%, air entraining agent is 0.015%~0.025%, early strength agent is 1.5%~2.5%, and defoaming agent is 0.075%~0.125%.

2. The method for preparing 120h ultra-slow setting waste-based shotcrete according to claim 1, characterized in that It includes the following components in percentage by weight: 100% cement, 400% soil and stone waste, 17.5% fly ash, 45% mixing water, 3% compound retarder, 7% accelerator, 0.02% air entraining agent, 2% early strength agent and 0.08% defoaming agent.

3. The method for preparing 120h ultra-slow setting waste-based shotcrete according to claim 1, characterized in that: The compound retarder is prepared by compounding polycarboxylic acid water-reducing mother liquor, polycarboxylic acid slump-retaining mother liquor, sodium tripolyphosphate, sodium gluconate and water in a certain proportion, wherein the mass ratio of sodium gluconate:sodium tripolyphosphate:polycarboxylic acid water-reducing mother liquor:polycarboxylic acid slump-retaining mother liquor is 1:20:5.5:

45.

4. The method for preparing 120h ultra-slow setting waste-based shotcrete according to claim 3, characterized in that: The specific preparation method of the compound retarder is as follows: taking a certain amount of water at room temperature, adding sodium gluconate and sodium tripolyphosphate into the water, stirring evenly until there is no white precipitate to obtain a mixed solution, and then sequentially adding polycarboxylic acid water-reducing mother liquid and polycarboxylic acid collapse-preserving mother liquid into the mixed solution and stirring evenly to prepare the compound retarder.

5. The method for preparing 120h ultra-slow setting waste-based shotcrete according to claim 4, characterized in that: The amount of water used to prepare the mixed solution is 2.5%~3.5% of the weight of the earth and stone waste, and the water used to prepare the mixed solution is deducted from the mixing water.

6. The method for preparing 120h ultra-slow setting waste-based shotcrete according to claim 1, characterized in that: The accelerator is a low-alkali powdered accelerator; the air entraining agent is triterpenoid saponin or K12; the defoamer is a concrete defoamer; the early strength agent is triethanolamine or other organic early strength agents, and the soil and stone waste is soil and stone waste with a moisture content of 3%.

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