A low-cost admixture for shotcrete and preparation method thereof

Abstract

The invention provides a low-cost admixture for shotcrete and a preparation method thereof. The raw materials for preparing the admixture include the following components by weight percentage: 40% to 50% silica fume, 5% to 10% fast-hardening sulphoaluminate cement, 35% to 45% reinforcing agent, 2% to 4% dispersant, 1% to 2% shrinkage reducing agent, and 0.5% to 1% regulator. The raw materials for the shotcrete admixture are widely available, cheap and easy to obtain, can significantly improve the cohesiveness and pumpability of the shotcrete, shorten the setting time of the shotcrete, have high bonding strength with the rock base, reduce the rebound rate of the shotcrete, and greatly save the project construction cost.

Description

Technical Field

[0001] The invention relates to the field of concrete building materials, in particular to a low-cost admixture for shotcrete. The invention also relates to a method for preparing the admixture. Background Art

[0002] In the construction of tunnel projects, in order to ensure that the tunnel does not collapse, the surrounding rock needs to be supported and reinforced in time. Shotcrete construction technology does not require formwork support, has good molding conditions, fast concrete solidification and hardening, and fast construction progress. It is an effective measure for tunnel surrounding rock reinforcement. Shotcrete technology relies on the power of compressed air to quickly spray concrete mixed with accelerators onto the surface of the building or rock surface, and bond it together. At the same time, it fills the surface pits and cracks, reinforces the building or rock surface to form a complete, stable and strong structure, and then plays a role in strengthening and protecting the building or rock surface. In the near future and for some time to come, the demand for shotcrete in tunnel construction, coal mine reinforcement, urban roads and waterproofing facilities repair projects will continue to increase, which puts higher and higher requirements on the performance of shotcrete.

[0003] The alkali-free quick-setting agent widely used at present is an important component of the wet spraying process of shotcrete. During the construction process, it generally has problems such as high dosage, slow concrete setting time, insufficient early strength, and poor bonding strength with the base surrounding rock. Especially under unfavorable construction conditions such as tunnel seepage and soft surrounding rock, the rebound rate of shotcrete is further increased, too much concrete falls during construction, and the reuse rate of the fallen concrete is extremely low, resulting in a large amount of cost waste and seriously affecting the construction progress.

[0004] In order to solve the problems of poor cohesiveness, anti-sagging performance and high rebound rate of shotcrete, domestic and foreign scholars have conducted a lot of research on shotcrete admixtures and made certain progress, but the above problems have not been completely solved during the construction process, and the effect is not obvious. In addition, the current admixture price is generally more than double that of cement, and using it to replace cement will cause a certain increase in the cost of construction materials. The nano-scale shotcrete modified admixture of announcement number CN102826774B can make the rebound rate of shotcrete ≤8%, the setting time ≤2min, and the one-time spray layer thickness ≥35cm, but the amount of nano-silicon dioxide used in this patent is large and the price is too high. The nano-scale shotcrete modified admixture has limited effect on reducing rebound, and it needs to be added at a higher dosage to have a certain effect. The raw materials used in a rebound inhibitor for shotcrete with publication number CN115626792A are epoxy resin emulsion, cellulose ether and redispersible latex powder, all of which are organic substances, expensive, and used in large quantities, which is 6% of the mass of the cementitious material, which is not conducive to its promotion and use in practice. A rheological property regulator for wet shotcrete with publication number CN115108755A mainly reduces the friction resistance between wet shotcrete and pipelines, improves the fluidity and pumpability of concrete, and increases the bonding strength of concrete to achieve the purpose of reducing the amount of accelerator and cementitious material, thereby reducing costs. The materials used include air entraining components, bubble control components and rebound suppression components. Most of the raw materials are expensive, which has a great disadvantage in terms of cost. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a low-cost admixture for shotcrete and a preparation method thereof, which can not only effectively reduce the rebound rate, but also reduce the material cost, thereby greatly saving the project construction cost.

[0006] A low-cost admixture for shotcrete, wherein the raw materials for preparing the low-cost shotcrete admixture include the following components by weight: 40 to 50 parts of silica fume, 5 to 10 parts of rapid hardening sulphoaluminate cement, 35 to 45 parts of a reinforcing agent, 2 to 4 parts of a dispersant, 1 to 2 parts of a shrinkage reducing agent, and 0.5 to 1 part of a regulating agent.

[0007] Furthermore, the SiO2 content in the silica ash is more than 90%, and the fineness is 0.05μm~0.3μm.

[0008] Furthermore, the rapid hardening sulphoaluminate cement has a grade of 525.

[0009] Furthermore, the reinforcing agent is prepared by mixing lithium slag, aluminum slag and stone powder in a ratio of 6:3:1, grinding the mixture, calcining the mixture at 1000-1200°C for 3 hours, and then adding triethanolamine and sodium silicate to the calcined product for ball milling after the product is cooled to obtain a reinforcing agent having a specific surface area of ​​400 m2 / kg-450 m2 / kg.

[0010] Furthermore, the ratio of triethanolamine to sodium silicate is 1:1, and the two account for 2.5% to 4% of the mass of the calcined product.

[0011] Furthermore, the dispersant is at least one of a powdered carboxylic acid water reducer and a naphthalene-based water reducer.

[0012] Furthermore, the shrinkage reducing agent is magnesium oxide waste residue that has been dried at 105° C., cooled, and ground.

[0013] Furthermore, the specific surface area of ​​the magnesium oxide waste slag is 300 m2 / kg to 400 m2 / kg.

[0014] Furthermore, the regulator is at least one of citric acid, boric acid and tartaric acid.

[0015] The present invention also proposes a method for preparing the above-mentioned admixture for shotcrete, which comprises the following steps:

[0016] Mix silica fume, rapid hardening sulphoaluminate cement, reinforcing agent, dispersant, shrinkage reducing agent and regulating agent evenly.

[0017] The low-cost admixture for shotcrete of the present invention can significantly improve the cohesiveness and pumpability of shotcrete, shorten the setting time of shotcrete, increase the bonding strength with the rock base, reduce the rebound rate of shotcrete, and greatly save the project construction cost by compounding silica fume, fast-hardening sulphoaluminate cement, a reinforcing agent, a dispersant, a shrinkage reducing agent and a regulating agent.

[0018] The silica fume used in the above admixture has a large specific surface area, strong chemical reaction activity, and surface adsorption. After being added to concrete, it can absorb more free water, thereby increasing the cohesiveness of the concrete, and can effectively improve the divergence problem of concrete during the spraying process from the nozzle of the wet spraying machine to the surface of the surrounding rock. At the same time, it can improve the bonding force between the sprayed concrete and the base surrounding rock, which is beneficial to reducing the rebound rate. At the same time, silicon dioxide has a "ball bearing" effect, which is beneficial to increase the fluidity and pumpability of the slurry. The aluminum hydrogen silicate in the silica fume can play a volcanic ash activity effect, and can react with the calcium oxide in the cement to generate hydrated calcium silicate and hydrated calcium sulfoaluminate, so that the early strength of the sprayed concrete is improved, and it can also react with the hydration reaction product to produce a secondary hydration reaction, which promotes the growth of the later strength of the sprayed concrete. In addition, the silica fume particle size is very small, which can fill the gel pores inside the concrete, increase the density, and further improve the later strength of the sprayed concrete. The addition of silica fume can also reduce the cracks caused by the rapid hydration of cement and concrete, which is beneficial to improve the impermeability and durability of the concrete.

[0019] Compared with ordinary Portland cement, fast-hardening sulphoaluminate cement has an extremely fast hydration rate, which can significantly shorten the setting time of shotcrete, improve its early strength, and greatly reduce the rebound rate of shotcrete.

[0020] The lithium slag and aluminum slag in the reinforcing agent work together, and the proportion of Al2O3 in the composite is greatly increased. After adding it to the shotcrete, it can quickly solidify and harden. At the same time, the content of CaO, MgO, Na2O and K2O in the lithium slag reaches 15%, which acts as flux oxides during the combustion process, can reduce the sintering temperature and save energy. The composite action of sodium silicate and triethanolamine can stimulate the dissolution and hydration of the mineral phases of lithium slag and aluminum slag, increase the formation rate of hydration products, and promote the increase of the early strength of concrete. Triethanolamine can promote the secondary hydration reaction of SiO2 and Al2O3 with CH, continuously forming CSH gel, making the concrete structure more compact and further increasing the strength in the later stage.

[0021] The dispersant preferably includes at least one of a powder carboxylic acid water reducer and a naphthalene water reducer. The dispersant can promote the mutual dispersion of cement particles, effectively improve the fluidity and cohesiveness of the concrete mixture, and ensure that the concrete state can meet the on-site requirements and the continuity of construction. The shrinkage reducer uses the waste residue after magnesium oxide desulfurization in the power plant, which can react with the cement hydration product to generate crystals with increased volume, fill the internal pores of the concrete, compensate for the cracks caused by the shrinkage of the shotcrete, and improve the crack resistance of the concrete. The regulator uses a relatively low-priced organic acid. Organic retarders are mostly surfactants, which have a strong active effect on the surface of cement particles, can be adsorbed on the surface of cement particles, and inhibit the coagulation of cement particles. At the same time, the surfactant can also be adsorbed on the newly generated hydration product, which can delay the formation process of the hydration product to a certain extent. In addition, the hydroxyl active group in the organic acid can effectively complex Ca 2+ , lowering Ca 2+ The concentration delays the formation of crystal nuclei and has a good retarding effect, which can ensure that the shotcrete is in a good working condition before spraying construction.

[0022] The low-cost admixture for shotcrete of the present invention can significantly improve the cohesiveness and pumpability of concrete, shorten the setting time of concrete, increase the bonding strength with the rock base, and reduce the rebound rate of shotcrete, which can be controlled within 5%, greatly saving the project construction cost. The thickness of one shotcrete can be increased from 30cm to more than 50cm, and the construction progress can be improved by more than 50%. The 8h compressive strength of shotcrete using this product can reach more than 15MPa, and the 28d compressive strength ratio is greater than 110%, with good mechanical properties and support effects.

[0023] The present invention uses waste materials such as lithium slag, aluminum slag and magnesium oxide waste slag as raw materials. The raw materials are widely available, cheap and easy to obtain. The industrial waste slag used accounts for nearly 50% of the total raw material usage. While reducing the cost of raw materials, the purpose of treating solid waste can also be achieved, and it has good economic value and social value. DETAILED DESCRIPTION

[0024] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0025] The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from conventional biochemical reagent stores unless otherwise specified. In addition, except for special instructions in this example, the terms and processes involved in this example are understood according to the general knowledge and conventional methods in the prior art.

[0026] A low-cost admixture for shotcrete. The raw materials for preparing the admixture include the following components by weight percentage: 40 to 50 parts of silica fume, 5 to 10 parts of rapid hardening sulphoaluminate cement, 35 to 45 parts of reinforcing agent, 2 to 4 parts of dispersing agent, 1 to 2 parts of shrinkage reducing agent, and 0.5 to 1 part of regulating agent. Embodiment 1

[0027] The following components are mixed in percentage by mass, specifically including: 50 parts of silica fume, 5 parts of rapid hardening sulphoaluminate cement, 40 parts of reinforcing agent, 4 parts of powder carboxylic acid water reducer, 0.5 parts of magnesium oxide waste slag with a specific surface area of ​​300㎡ / kg~400㎡ / kg, and 0.5 parts of tartaric acid. The reinforcing agent is lithium slag, aluminum slag and stone powder mixed in a ratio of 6:3:1, ground, calcined at 1000~1200℃ for 3h, and triethanolamine and sodium silicate are added to the calcined product after cooling for ball milling, wherein the ratio of triethanolamine to sodium silicate in the reinforcing agent is 1:1, and the two account for 2.5% of the mass fraction of the calcined product. Embodiment 2

[0028] The following components are mixed in percentage by mass, specifically including: 45 parts of silica fume, 10 parts of rapid hardening sulphoaluminate cement, 39 parts of reinforcing agent, 4 parts of naphthalene water reducer, 1 part of magnesium oxide waste slag with a specific surface area of ​​300㎡ / kg~400㎡ / kg, and 1 part of citric acid. The reinforcing agent is lithium slag, aluminum slag and stone powder mixed in a ratio of 6:3:1 and ground, and then calcined at 1000~1200℃ for 3h. After the calcined product is cooled, triethanolamine and sodium silicate are added thereto for ball milling, wherein the ratio of triethanolamine to sodium silicate in the reinforcing agent is 1:1, and the two account for 4% of the mass fraction of the calcined product. Embodiment 3

[0029] The following components are mixed in percentage by mass, specifically including: 40 parts of silica fume, 10 parts of rapid hardening sulphoaluminate cement, 45 parts of reinforcing agent, 2.5 parts of powder carboxylic acid water reducer, 1.5 parts of magnesium oxide waste slag with a specific surface area of ​​300㎡ / kg~400㎡ / kg, and 1 part of boric acid. The reinforcing agent is lithium slag, aluminum slag and stone powder mixed in a ratio of 6:3:1 and ground, and then calcined at 1000~1200℃ for 3h. After the calcined product is cooled, triethanolamine and sodium silicate are added thereto for ball milling, wherein the ratio of triethanolamine to sodium silicate in the reinforcing agent is 1:1, and the two account for 3% of the mass fraction of the calcined product. Embodiment 4

[0030] The following components are mixed in percentage by mass, specifically including: 48 parts of silica fume, 8 parts of rapid hardening sulphoaluminate cement, 37.5 parts of reinforcing agent, 3.5 parts of powder carboxylic acid water reducer, 2 parts of magnesium oxide waste slag with a specific surface area of ​​300㎡ / kg~400㎡ / kg, and 1 part of tartaric acid. The reinforcing agent is lithium slag, aluminum slag and stone powder mixed and ground in a ratio of 6:3:1, calcined at 1000~1200℃ for 3h, and triethanolamine and sodium silicate are added to the calcined product after cooling for ball milling, wherein the ratio of triethanolamine to sodium silicate in the reinforcing agent is 1:1, and the two account for 3.5% of the mass fraction of the calcined product.

[0031] According to the requirements of JGJ / T372-2016 "Technical Specifications for the Application of Shotcrete", C30 shotcrete was used for performance testing. The concrete mix ratio was: Lafarge cement 480kg / m 3 ; Medium sand 912kg / m 3 , fineness modulus 3.0; 5-10mm crushed stone 836kg / m 3 , water 172kg / m 3 , GK-3000 polycarboxylic acid high performance water reducing agent 4.8kg / m produced by Shijiazhuang Changan Yucai Building Materials Co., Ltd. 3 ; GK-3B alkali-free liquid accelerating agent 28.8kg / m produced by Shijiazhuang Changan Yucai Building Materials Co., Ltd. 3 .

[0032] The low-cost admixture for shotcrete prepared in the above Examples 1-4 was used to replace the same amount of cement at 10% of the mass of cement, and was added to prepare shotcrete. The shotcrete without replacing the low-cost admixture of the present invention was used as a blank group. The material of the low-cost admixture for shotcrete of the present invention is easy to obtain, and the process is simpler than that of cement. Compared with using cement entirely, the cost of replacing 10% of the admixture is lower. The performance of the above embodiments and the blank group was tested, and the results are shown in the following table:

[0033] Table 1 Comparative test results of low-cost shotcrete admixtures

[0034]

[0035] As can be seen from the test results in Table 1, the admixture for shotcrete prepared by the present invention can significantly improve the cohesiveness and pumpability of shotcrete, shorten the setting time of shotcrete, have high bonding strength with the rock base, and can reduce the rebound rate of shotcrete from 20% to less than 5%, greatly saving construction costs. The thickness of a single shotcrete can be increased from 30cm to more than 50cm, and the construction progress can be increased by more than 50%. The 8h compressive strength of the shotcrete using this product can reach more than 15MPa, and the 28d compressive strength ratio is greater than 110%, with good mechanical properties and support effects. The present invention uses wastes such as lithium slag and magnesium oxide waste slag as raw materials, and the industrial waste slag used accounts for nearly 50% of the total raw material consumption. Using it instead of cement can further reduce the cost of shotcrete, and also achieve the purpose of recycling solid waste. Using the admixture of the present invention for tunnel construction, the comprehensive cost per meter of construction distance can be saved by more than 15%, with good economic value and social value.

[0036] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0037] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A low-cost admixture for shotcrete, characterized in that: The raw materials for preparing the low-cost shotcrete admixture include the following components by weight: 40 to 50 parts of silica fume, 5 to 10 parts of rapid hardening sulphoaluminate cement, 35 to 45 parts of reinforcing agent, 2 to 4 parts of dispersant, 1 to 2 parts of shrinkage reducing agent, and 0.5 to 1 part of regulating agent; The reinforcing agent is prepared by mixing lithium slag, aluminum slag and stone powder in a ratio of 6:3:1, grinding the mixture, calcining the mixture at 1000-1200°C for 3 hours, adding triethanolamine and sodium silicate to the mixture after the calcined product is cooled, and ball milling is performed to obtain the reinforcing agent, wherein the specific surface area of ​​the reinforcing agent is 400 m2 / kg-450 m2 / kg; The regulator is at least one of citric acid, boric acid and tartaric acid.

2. The admixture for shotcrete according to claim 1, characterized in that: The SiO2 content in the silica ash is more than 90%, and the fineness is 0.05μm~0.3μm.

3. The admixture for shotcrete according to claim 1, characterized in that: The rapid hardening sulphoaluminate cement is labeled 525.

4. The admixture for shotcrete according to claim 1, characterized in that: The ratio of triethanolamine to sodium silicate is 1:1, and the two account for 2.5% to 4% of the mass of the calcined product.

5. The admixture for shotcrete according to claim 1, characterized in that: The dispersant is at least one of a powder carboxylic acid water reducer and a naphthalene water reducer.

6. The admixture for shotcrete according to claim 1, characterized in that: The shrinkage reducing agent is magnesium oxide waste residue that has been dried at 105° C., cooled, and ground.

7. The admixture for shotcrete according to claim 6, characterized in that: The specific surface area of ​​the magnesium oxide waste slag is 300 m2 / kg to 400 m2 / kg.

8. A method for preparing the admixture for shotcrete according to any one of claims 1 to 7, characterized in that: The method comprises the following steps: Mix silica fume, rapid hardening sulphoaluminate cement, reinforcing agent, dispersant, shrinkage reducing agent and regulating agent evenly.

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