Quick-hardening early-strength sprayed concrete and preparation method thereof

Abstract

The invention relates to quick-hardening early-strength shotcrete and a preparation method thereof, and belongs to the technical field of concrete materials. The quick-hardening early-strength shotcrete comprises the following components in percentage by mass: 30-40% of cement; 35%-45% of fine aggregate; 25 to 35 percent of coarse aggregate; 0.05 to 0.15% of polyester fiber; 3-6% of an expanding agent; 1-3% of a nano component; the early strength component accounts for 2-5% of the mass of the cement; the water reducing agent accounts for 0.5-1.5% of the mass of the cement; an alkali-free liquid accelerator accounting for 2-8% of the mass of the cement; and the ratio of water to binder is controlled to be 0.38-0.45. The preparation method comprises the six steps of raw material preparation, dry mixing pretreatment, polyester fiber doping, water reducer solution preparation, wet mixing and spraying and curing. Through the synergistic effect of the functional materials, the early strength, the crack resistance and the volume stability of the concrete are effectively improved, and the concrete can be widely applied to construction scenes needing rapid hardening and high-strength early support, such as tunnel lining, slope support, basement support and mine support.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of concrete materials, and relates to a fast-hardening and early-strength type shotcrete and a preparation method thereof, in particular to a fast-hardening and early-strength type shotcrete based on polyester fibers and a composite expansion component and a preparation method thereof. BACKGROUND

[0002] As a special construction technology that high-speed sprays premixed concrete to the construction surface by high-pressure airflow and rapidly hardens, shotcrete has become an indispensable key technology in the fields of tunnel lining, slope support, underground cavern and mine reinforcement, etc. due to its unique advantages of no need for formwork, high construction efficiency and adaptability to complex structural surfaces. However, with the continuous expansion of underground engineering construction scale and the increasing complexity of construction environment, the traditional shotcrete gradually exposes many technical bottlenecks in material performance and construction adaptability, which is difficult to meet the dual requirements of rapid support and long-term durability in modern engineering. The traditional shotcrete uses ordinary Portland cement as the main cementitious material, and has the outstanding problems of insufficient early strength, large construction loss and serious shrinkage cracking. Specifically, the 1-day compressive strength is usually lower than 12 MPa, which cannot meet the requirement of rapid support; the increase of water content for improving pumpability leads to excessive slump, and the rebound rate of shotcrete is as high as 15%-25%; the volume shrinkage rate during the hardening stage is more than 0.05%, which easily causes penetrating cracks and seriously affects the impermeability and bearing capacity of the structure.

[0003] Although the prior art attempts to improve the performance by adding a single component such as a quick-setting agent, a fiber or an expansive agent, there are still obvious technical defects. These improvement measures often lack systematic design and have insufficient synergistic effect among the components, resulting in limited improvement of material performance. For example, relying only on a quick-setting agent to improve early strength can easily cause late strength to decrease; uneven dispersion of nanomaterials or fiber clumping can aggravate the risk of pipe blockage; and the traditional alkaline quick-setting agent can also cause the pH value of the working surface to exceed the standard, which is harmful to the health of construction personnel and the environment. More importantly, the prior art cannot improve the early strength while taking into account the crack resistance, shotcrete adaptability and construction stability, resulting in obvious short boards in the overall performance of the material and failing to meet the engineering requirements under complex geological conditions.

[0004] Therefore, in order to solve these problems, the present application provides a fast-hardening and early-strength type shotcrete and a preparation method thereof. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the present application aims to provide a fast-hardening and early-strength type shotcrete and a preparation method thereof, which can solve the problems of insufficient early strength, poor crack resistance, poor volume stability and limited construction adaptability of the shotcrete material in the prior art.

[0006] To achieve the above-mentioned objects and other related objects, In a first aspect, the present application provides a fast-hardening and early-strength shotcrete, which comprises a base material and an auxiliary material, wherein the base material comprises the following components by mass percentage: Cement: 30-40%; Fine aggregate: 35-45%; Coarse aggregate: 25-35%; Polyester fiber: 0.05-0.15%; Expanding agent: 3-6%; Nano component: 1-3%; The auxiliary material comprises the following components by mass percentage: Early-strength component: 2-5% of the mass of cement; Water reducing agent: 0.5-1.5% of the mass of cement; Alkali-free liquid accelerator: 2-8% of the mass of cement; Water: to control the water-binder ratio to be between 0.38 and 0.45; The length of the polyester fiber is 6-12 mm.

[0007] Preferably in any of the above solutions, the fine aggregate is medium sand with a particle size not greater than 5 mm.

[0008] Preferably in any of the above solutions, the coarse aggregate is gravel or pebble with a particle size of 5-10 mm.

[0009] Preferably in any of the above solutions, the expanding agent is compounded from UEA type expanding agent and light burned magnesia at a mass ratio of 2-4:1.

[0010] Preferably in any of the above solutions, the nano component is compounded from nano silicon dioxide and nano aluminum oxide at a mass ratio of 1-2:1.

[0011] Preferably in any of the above solutions, the early-strength component consists of high-activity tricalcium aluminate.

[0012] Preferably in any of the above solutions, the water reducing agent is a polycarboxylic acid type water reducing agent.

[0013] In a second aspect, the present application provides a preparation method of a fast-hardening and early-strength shotcrete, which comprises the following steps: S1. Raw material preparation: weigh each raw material according to the predetermined ratio; S2. Dry mixing pretreatment: mix the cement, fine aggregate, coarse aggregate, expanding agent, nano component and early-strength component uniformly, and stir for 2-3 min; S3. Add polyester fiber: add polyester fiber to the dry mixture obtained in S2, and continue stirring for 1-2 min; S4. Configuring water-reducing agent solution: mixing water-reducing agent with water to form water-reducing agent solution; S5. Wet mixing: adding dry mixture obtained in S3 and water-reducing agent solution obtained in S4 into a mixer, wet mixing for 4-5 minutes to form shotcrete mixture; S6. Spraying and curing: adding non-alkali liquid accelerator at the nozzle, and using wet spraying construction, after spraying, timely wet curing or spraying curing agent.

[0014] Preferably in any of the above solutions, the specific operation of the dry mixing pretreatment in S2 is that cement, fine aggregate, coarse aggregate and expanding agent are first added into the mixer, dry mixing at a speed of 13-17 r / min for 1-2 minutes, then adding nano components and early strength components for further dry mixing for 1 minute.

[0015] Preferably in any of the above solutions, the speed of the mixer in S3 is 8-12 r / min, and the speed of the mixer in S4 is 18-22 r / min.

[0016] As described above, the fast-hardening and early-strength shotcrete and the preparation method thereof have the following beneficial effects: 1. In the present application, the synergistic effect of various functional materials effectively improves the early strength, crack resistance and volume stability of the concrete; 2. In the present application, the concrete has good fluidity, adhesion and shotcrete forming efficiency, which can effectively ensure the efficient and stable construction process; 3. In the present application, the concrete can meet the dual requirements of rapid support and long-term durability for complex underground engineering, and is suitable for tunnel lining, slope support, basement support and mine support, and other construction scenes requiring rapid hardening and high-strength early support. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A schematic diagram showing the material composition of the shotcrete; Figure 2 A schematic diagram showing the spraying structure of the shotcrete; Figure 3 A process flow diagram showing the spraying process of the shotcrete. DETAILED DESCRIPTION

[0018] The embodiments of the present application are described below by specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the specification.

[0019] Example 1

[0020] The embodiment provides a fast-hardening and early-strength type shotcrete, which comprises a base material and an auxiliary material, and the base material comprises the following components in percentage by mass: Cement: 30-40%; Fine aggregate: 35-45%; Coarse aggregate: 25-35%; Polyester fiber: 0.05-0.15%; Expanding agent: 3-6%; Nano component: 1-3%; The auxiliary material comprises the following components in percentage by mass: Early-strength component: 2-5% of the mass of cement; Water reducing agent: 0.5-1.5% of the mass of cement; Alkali-free liquid accelerator: 2-8% of the mass of cement; Water: control the water-binder ratio to be between 0.38 and 0.45; Wherein, the length of the polyester fiber is 6-12 mm.

[0021] The mass ratio and proportion of each component are optimized and designed, so that the concrete has excellent fast-hardening and early-strength performance and good construction adaptability.

[0022] In the embodiment, the cement is 42.5-grade Portland cement or composite Portland cement, which provides the base strength and bonding performance of the mixture. The specific surface area is 350 m 2 / kg, the initial setting time is 120 min, and the final setting time is 360 min.

[0023] Of course, the cement is not limited to 42.5-grade Portland cement or composite Portland cement, and other cement meeting the requirements can also be used. For example, 52.5-grade Portland cement or composite Portland cement.

[0024] The fine aggregate is mainly used to fill the voids of the concrete framework and improve the compactness and workability of the concrete.

[0025] In the embodiment, the fine aggregate is river sand with a particle size of 0.15-4.75 mm, an apparent density of 2650 kg / m³, a clay content less than 1%, and a fineness modulus of 2.6.

[0026] The coarse aggregate mainly forms the framework structure of the concrete and provides the basic strength and stability of the concrete.

[0027] In the embodiment, the coarse aggregate is gravel with a particle size of 5-20 mm, an apparent density of 2700 kg / m³, a clay content less than 0.5%, and a needle flake particle content less than 8%.

[0028] Polyester fiber is mainly used to enhance the crack resistance of concrete, reduce plastic shrinkage cracks, and improve the toughness and impact resistance of concrete.

[0029] In this embodiment, polyester fibers with a length of 6-12 mm and a diameter of 18 μm are selected, with a tensile strength greater than 550 MPa and an elastic modulus of 10 GPa.

[0030] Polyester fibers with a length of 6-12 mm can form a good size match with coarse aggregate, ensuring uniform dispersion in concrete without clumping, while effectively bridging micro-cracks and significantly improving toughness and crack resistance. Overly long fibers can cause pipe blockage and increase the rebound rate, while overly short fibers may not fully exert their crack resistance.

[0031] Specifically, the length of polyester fibers is the key to their effectiveness: When the length is within the optimal range of 6-12 mm, the fibers can be uniformly dispersed, keeping the concrete slump at around 180 mm, and significantly reducing the early plastic crack area by 75-85%, with optimal toughness effect. Conversely, if the length deviates from this range, the performance will decrease significantly.

[0032] 3 mm of overly short fibers have insufficient bridging capacity, with an anti-cracking efficiency of only about 40%.

[0033] And 20 mm of overly long fibers cause a sharp drop in slump to 145 mm due to severe clumping, with a pump pressure surge of more than 30%, and a construction rebound rate of up to 15%, which weakens the anti-cracking and toughness effect due to uneven dispersion.

[0034] Therefore, strictly controlling the fiber length within 6-12 mm is the core of achieving the best balance between construction performance and crack resistance and toughness effect. Exceeding this range (such as 3 mm or 20 mm) will result in a significant decrease in construction performance, crack resistance, and workability.

[0035] At the same time, the synergistic effect of polyester fibers and composite expansion agent can significantly enhance the crack resistance and volume stability of concrete, reducing early cracking.

[0036] Expansive agent is mainly used to compensate for the shrinkage of concrete, reduce shrinkage cracks, and improve the volume stability of concrete.

[0037] In this embodiment, the expansive agent is compounded by UEA-type expansive agent and light-burned magnesium oxide at a mass ratio of 3:1. Its main components are calcium oxide, calcium sulfoaluminate, calcium sulfate, and magnesium oxide, with an expansion rate of 0.02-0.05%, an initial expansion time of 2 h, and an expansion duration of 72 h.

[0038] Of course, the mass ratio of the UEA-type expanding agent to the light-burned magnesium oxide in the expanding agent is not limited to 3:1, and can be adjusted according to actual needs, for example, the expanding agent is compounded by the UEA-type expanding agent and the light-burned magnesium oxide at a mass ratio of 2-4:1.

[0039] The UEA-type expanding agent and the light-burned magnesium oxide are combined to have the characteristics of early expansion of the UEA-type expanding agent and late micro-expansion of the light-burned magnesium oxide, can realize the synergistic shrinkage compensation in the whole cycle, effectively overcome the defect that the late shrinkage of the single UEA-type expanding agent may rebound, and thus significantly improve the long-term anti-cracking performance and volume stability of the concrete.

[0040] The nano component is mainly used to fill the micro-pores between the cement hydration products, promote the hydration reaction of the cement, improve the early strength and compactness of the concrete, and enhance the impermeability and corrosion resistance, thereby improving the durability of the material.

[0041] In the embodiment, the nano component is compounded by nano silicon dioxide and nano aluminum oxide at a mass ratio of 1.5:1. The average particle size is 15 nm, and the specific surface area is 200 m² / g.

[0042] Of course, the mass ratio of the nano silicon dioxide to the nano aluminum oxide in the nano component is not limited to 1.5:1, and can be adjusted according to actual needs, for example, the nano component is compounded by the nano silicon dioxide and the nano aluminum oxide at a mass ratio of 1-2:1. The specific compounding utilizes the early strength accelerating and early strength enhancing properties of the nano aluminum oxide and the toughening and enhancing properties of the nano silicon dioxide, the two components have a synergistic effect in function, solve the dual requirements of the early strength and the long-term performance of the shotcrete, and the technical effect is much better than that of the single component or other combinations simply listed in the comparative document.

[0043] The water reducing agent is mainly used to reduce the water consumption of the concrete, improve the fluidity and workability of the concrete, and improve the strength and durability of the concrete.

[0044] In the embodiment, the water reducing agent is a polycarboxylic acid high-performance water reducing agent, the water reduction rate is greater than 25%, and the air content is less than 3%.

[0045] The early strength component is mainly used to promote the early hydration reaction of the cement, control the crystal morphology and distribution of the cement hydration products, reduce the porosity and refine the pore size, provide early structural support for the concrete, and thus improve the early strength of the shotcrete.

[0046] In the embodiment, the early strength component is composed of high-activity tricalcium aluminate, the tricalcium aluminate content is not less than 50%, and the tricalcium aluminate is prepared by a high-temperature calcination process, has a dense crystal structure and rich active sites.

[0047] Alkali-free liquid accelerator is mainly used to accelerate the setting and hardening of concrete, improve the early strength of concrete, reduce the rebound amount, and improve the spraying efficiency. At the same time, the risk of alkali-aggregate reaction is reduced, and the long-term performance and environmental protection are improved.

[0048] In this embodiment, the alkali-free liquid accelerator is an alkali-free accelerator with aluminate as the main component, the pH value is 3-4, the solid content is 40%, and the setting time is less than 60s.

[0049] In summary, in this embodiment, through the synergistic cooperation of polyester fibers, nano components, early strength components, UEA-MgO composite expansion agents and other functional components, the integration of "strength-toughness-stability" is realized. Among them, the polyester fiber significantly enhances the crack resistance of the concrete; the nano component accelerates the hydration reaction through the pozzolanic effect, improves the material density and early strength; the composite expansion agent effectively compensates for the shrinkage deformation and improves the volume stability. At the same time, the optimized compounding of alkali-free liquid accelerator and polycarboxylic acid water reducing agent still maintains good spraying beam continuity under the condition of ensuring low slump, providing a reliable solution for efficient support under complex geological conditions.

[0050] The embodiment provides a preparation method of a fast-hardening and early-strength type sprayed concrete, which comprises the following steps: S1. Raw material preparation: according to the predetermined proportion, silicate cement or composite silicate cement, natural medium sand (as fine aggregate), gravel (as coarse aggregate), polyester fiber, expansion agent, polycarboxylic acid high-efficiency water reducing agent, nano component powder, early strength component powder and alkali-free liquid accelerator are weighed. Various raw materials should meet the current national or industry standards; S2. Dry mixing pretreatment: first, the weighed cement, fine aggregate, coarse aggregate and expansion agent are added into a horizontal forced mixer, and dry mixing is carried out at a speed of 13-17 r / min for 1-2 min, then the nano component and the early strength component are continuously dry mixed for 1 min, so that the powdery components are uniformly distributed in the aggregate to form a uniform dry mixing system; S3. Adding polyester fiber: slowly add polyester fiber in the dry mixing material obtained in S2, and continue to stir at a speed of 8-12 r / min for 1-2 min, so that the fiber is fully dispersed in the dry mixing system, avoiding the phenomenon of clumping or winding, and ensuring the consistency and stability of the reinforcing effect; In this process, polyester fiber is added during dry mixing, which can utilize the collision and shearing force between aggregates to effectively scatter the fiber bundle, so that it is initially and uniformly dispersed in the dry material, thereby avoiding the phenomenon that the fiber is easily clumped in the water reducing agent solution, laying a more solid foundation for subsequent uniform mixing with water, and finally obtaining concrete with more uniform fiber distribution and more excellent mechanical properties; Meanwhile, the step-by-step dry mixing of various dry materials in S2 and S3 can achieve "targeted dispersion" according to the characteristics of the materials, thereby ensuring the uniformity and performance of the final mixture; First, the basic materials such as cement, fine aggregate, coarse aggregate and expansive agent are mixed to create a "carrier" that is uniformly premixed for subsequent nano components; then, nano materials are added, which can effectively break up the inevitable agglomerates by using the "sand milling" effect generated by the aggregate in the stirring process, achieving uniform distribution at the nano scale. Finally, on the basis of uniform powder, polyester fibers are added, and stirring is carried out at a low speed, which can greatly avoid the breakage and damage of fibers caused by collision with sharp aggregate at the initial stage of mixing, as well as the problem of clumping caused by adhesion with powder, ensuring uniform dispersion of fibers in the form of single filaments, thereby stabilizing the bridging and toughening effect of the fibers; Therefore, the operations of S2 and S3 can effectively avoid uneven dispersion of nano materials, fiber clumping or breakage caused by one-time input of all dry materials, and effectively improve the final performance of the concrete; S4. Configure water reducing agent solution: add polycarboxylate superplasticizer according to the designed dosage into an appropriate amount of water and mix thoroughly to form a water reducing agent solution; the water-cement ratio can be adjusted according to factors such as construction environment temperature and sand ratio, and controlled between 0.40 and 0.45 to ensure that the concrete has good workability and early strength development potential; S5. Wet mixing: add the dry mixture obtained in S3 and the water reducing agent solution obtained in S4 to the mixer together, and wet mix for 4-5 minutes at a speed of 18-22 r / min to make the slurry evenly wrap the aggregate, forming a shot mixture with good flowability, cohesiveness and pumpability; S6. Spraying and curing: during the construction process of the sprayed concrete, a metering device is arranged at the front end of the pipeline or the nozzle of the spraying equipment, and a setting accelerator is added to the metering device. The setting accelerator is uniformly injected before the concrete is sprayed, and wet spraying construction is adopted. After spraying is completed, wet curing or spraying curing agent is carried out in time. This process can realize "spraying and setting simultaneously", improve the construction efficiency and reduce material loss.

[0051] Meanwhile, during the spraying process, wet spraying equipment is used for on-site construction, and the nozzle air pressure, spraying distance, spraying angle and feeding rate are controlled to avoid high rebound rate and aggregate segregation. After spraying and molding, wet curing or spraying curing agent should be carried out in time according to the environmental temperature and humidity to maintain a suitable curing environment, promote the full hydration reaction, ensure the effectiveness of the expansive component, and finally form a dense, crack-resistant and volume-stable sprayed concrete support structure.

[0052] In this embodiment, the fast-hardening and early-strength shotcrete is suitable for the temperature range of-5-40℃, and can adapt to the construction requirements of complex environments such as underground engineering, tunnels and mines; at the same time, since the alkali-free liquid accelerator is used, the health hazard to the operators is small, and the construction safety is high.

[0053] Example 2

[0054] The preparation method of the fast-hardening and early-strength shotcrete in this embodiment includes the following steps: S1. Raw material preparation: 35 kg of cement, 30 kg of gravel, 35 kg of natural medium sand, 4.5 kg of expanding agent, 0.7 kg of nano component, 1.05 kg of early-strength component, 0.1 kg of polyester fiber, 0.35 kg of polycarboxylate high-performance water reducing agent, 2.8 kg of alkali-free liquid accelerator and 15.05 kg of water are weighed according to the predetermined proportion; In this process, the construction site preparation needs to be carried out before the raw material preparation process, and the raw materials need to be inspected and accepted; At the same time, the weighed polyester fiber is treated to make the length of the polyester fiber 6mm; S2. Dry mixing pretreatment: first, the weighed cement, gravel, natural medium sand and expanding agent are added into the JZC350 type horizontal forced mixer, and dry mixing is carried out at a speed of 15r / min for 2min, then the nano component and early-strength component are added and dry mixing is continued for 1min, so that the powdery components are uniformly distributed in the aggregate to form a uniform dry mixing system; S3. Add polyester fiber: slowly add polyester fiber to the dry mixing material obtained in S2, and continue to stir at a speed of 10r / min for 2min, so that the fiber is fully dispersed in the dry mixing system, avoiding the phenomenon of clumping or winding, and ensuring the consistency and stability of the reinforcing effect; S4. Configuration of water reducing agent solution: add polycarboxylate high-efficiency water reducing agent into the weighed clean water and mix thoroughly to form a water reducing agent solution; S5. Wet mixing: slowly add the water reducing agent solution obtained in S4 to the dry mixing material obtained in S3, and wet mix at a speed of 20r / min for 5min, until the mixture is uniform and consistent, with a slump of 88cm, meeting the fluidity requirements of shotcrete construction; S6. Spraying and curing: Spraying: the wet mixed mixture obtained in S5 is loaded into the hopper of the PZ-5 type spraying machine, and the spraying pressure is set to 0.6 MPa; the alkali-free liquid accelerator is delivered to the nozzle through an independent pipeline and mixed with the mixture; The spraying distance is kept at 1.5 m, the spraying angle is kept between 60° and 90°, the spraying thickness is controlled at 5 cm per layer, and when multiple layers are sprayed, the next layer is sprayed after the previous layer is initially set; during the spraying process, the nozzle is kept moving uniformly to ensure that the sprayed layer is dense and uniform, without cavities, cracks, and delamination; Curing: immediately after spraying is completed, the sprayed surface is covered with a plastic film to prevent water evaporation; Curing is carried out at an ambient temperature of 20±2℃ and a relative humidity of greater than 95%; for the first 3 days, water is sprayed 3 times per day, and then 2 times per day thereafter, and the curing period is not less than 14 days to ensure that the concrete is fully hydrated and reaches the design strength.

[0055] Example 3

[0056] The preparation method of the fast-hardening and early-strength sprayed concrete in this example includes the following steps: S1. Raw material preparation: 30 kg of cement, 35 kg of crushed stone, 35 kg of natural medium sand, 0.9 kg of expanding agent, 0.3 kg of nano component, 0.6 kg of early-strength component, 0.05 kg of polyester fiber, 0.1 kg of polycarboxylate high-performance superplasticizer, 1.2 kg of non-alkali liquid accelerator, and 12.9 kg of water are weighed according to the predetermined proportion; In this process, before the raw material preparation process, the construction site needs to be prepared, and the raw materials need to be inspected and accepted; At the same time, the weighed polyester fiber is treated to make the length of the polyester fiber 9 mm; S2. Dry mixing pretreatment: first, the weighed cement, crushed stone, natural medium sand, and expanding agent are added to a JZC350 type horizontal forced mixer, and dry mixing is carried out at a speed of 13 r / min for 2 min, then the nano component and early-strength component are added and dry mixing is continued for 1 min, so that the powdery components are uniformly distributed in the aggregate to form a uniform dry mixing system; S3. Add polyester fiber: slowly add polyester fiber to the dry mixing material obtained in S2, and continue to stir at a speed of 12 r / min for 2 min to make the fiber fully dispersed in the dry mixing system, avoid clumping or winding, and ensure the consistency and stability of the reinforcement effect; S4. Prepare the superplasticizer solution: add the polycarboxylate high-efficiency superplasticizer to the water and mix thoroughly to form a superplasticizer solution; S5. Wet mixing: slowly add the superplasticizer solution obtained in S4 to the dry mixing material obtained in S3, and wet mix at a speed of 18 r / min for 4 min until the mixture is uniform and consistent, with a slump of 96 m, meeting the fluidity requirements of the spraying construction; S6. Spraying and curing: Spraying: the wet mixed mixture obtained in S5 is loaded into the hopper of a PZ-5 type spraying machine, and the spraying pressure is set to 0.5 MPa; the liquid non-alkali accelerator is delivered through an independent pipeline to the nozzle to be mixed with the mixture; The spraying distance is kept at 1.2 m, the spraying angle is kept between 60° and 90°, the spraying thickness is controlled at 4 cm per layer, and when multiple layers are sprayed, the next layer is sprayed after the previous layer is initially set; the nozzle is kept moving uniformly during spraying to ensure that the sprayed layer is dense and uniform, without voids, cracks and delamination; Curing: immediately after spraying, the sprayed surface is covered with a plastic film to prevent water evaporation; Curing is carried out under the condition of ambient temperature of 20±2℃ and relative humidity greater than 95%; water is sprayed for curing 2 times a day for the first 3 days, and then 1 time a day, and the curing period is not less than 14 days to ensure that the concrete is fully hydrated and reaches the design strength.

[0057] Example 4

[0058] The preparation method of the fast-hardening and early-strength sprayed concrete in this example includes the following steps: S1. Raw material preparation: 40 kg of cement, 25 kg of crushed stone, 35 kg of natural medium sand, 3.2 kg of expanding agent, 1.2 kg of nano component, 2.0 kg of early-strength component, 0.15 kg of polyester fiber, 0.45 kg of polycarboxylate high-performance superplasticizer, 0.6 kg of non-alkali liquid accelerator and 17.2 kg of water are weighed according to the predetermined proportion; In this process, site preparation is also required before the raw material preparation process, and the raw materials are inspected and accepted upon arrival; At the same time, the weighed polyester fiber is treated to have a length of 12 mm; S2. Dry mixing pretreatment: the weighed cement, crushed stone, natural medium sand and expanding agent are first added to a JZC350 type horizontal forced mixer, and dry mixed at a speed of 17 r / min for 1 min, then the nano component and early-strength component are added and dry mixed for another 2 min, so that the powdery components are uniformly distributed in the aggregate to form a uniform dry mixing system; S3. Adding polyester fiber: slowly add polyester fiber to the dry mixing material obtained in S2, and continue to stir at a speed of 12 r / min for 1 min to ensure that the fiber is fully dispersed in the dry mixing system, avoiding clumping or winding, and ensuring the consistency and stability of the reinforcing effect; S4. Preparation of superplasticizer solution: add polycarboxylate superplasticizer into water and mix well to form a superplasticizer solution; S5. Wet mixing: the water reducing agent solution obtained in S4 is slowly added to the dry mixture obtained in S3, and wet mixing is carried out at a rotation speed of 22 r / min for 4 min until the mixture is uniform and consistent, and the slump reaches 80 cm, meeting the fluidity requirement for spraying construction; S6. Spraying and curing: Spraying: the wet mixed mixture obtained in S5 is loaded into the hopper of a PZ-5 type spraying machine, and the spraying pressure is set to 0.7 MPa; the alkali-free liquid accelerator is delivered through an independent pipeline to the nozzle to mix with the mixture; The spraying distance is kept at 1.8 m, and the spraying angle is kept between 60° and 90°; the spraying thickness is controlled at 6 cm per layer, and when multiple layers are sprayed, the next layer is sprayed after the previous layer is initially cured; the nozzle is kept moving uniformly during spraying to ensure that the sprayed layer is dense and uniform, without voids, cracks, and delamination; Curing: after spraying is completed, the sprayed surface is immediately covered with a plastic film to prevent water evaporation; Curing is carried out under the condition of an ambient temperature of 20±2℃ and a relative humidity of more than 95%; water is sprayed for curing 4 times a day for the first 3 days, and then 2 times a day thereafter, and the curing period is not less than 14 days to ensure that the concrete is fully hydrated and reaches the design strength.

[0059] In Examples 2-4, after the spraying construction is completed, the concrete surface is shaped, the joint is treated, and the like, and curing of the concrete is carried out after the treatment is completed.

[0060] After the concrete curing is completed, the spraying effect is observed, and if the spraying effect meets the performance requirement, the spraying is completed; if the spraying effect does not meet the performance requirement, re-spraying is carried out.

[0061] Comparative Example 2

[0062] The same as Example 2, except that in the comparative example, there is no polyester fiber and expansion agent and the related operation steps.

[0063] Comparative Example 3

[0064] The same as Example 3, except that in the comparative example, there is no polyester fiber and expansion agent and the related operation steps.

[0065] Comparative Example 4

[0066] The same as Example 4, except that in the comparative example, there is no polyester fiber and expansion agent and the related operation steps.

[0067] The concrete obtained in Example 2, Example 3, Example 4, Comparative Example 2, Comparative Example 3, and Comparative Example 4 is respectively subjected to performance testing, and the test results are shown in Table 1: Table 1: Performance test results of concrete in each example

[0068] From table 1, the fast hardening and early strength type shotcrete has the following excellent performances: 1. High early strength: 3h compressive strength can be increased by at least 30.4%, 1d compressive strength can be increased by at least 20.3%, 3d compressive strength can be increased by at least 13.9%, and 28d compressive strength can be increased by at least 9.8%. Therefore, the fast hardening and early strength characteristics enable the shotcrete to form effective support in a short time, improve construction efficiency and safety; 2. Good crack resistance: 28d splitting tensile strength can be increased by at least 11.5%. Due to the addition of polyester fiber and expanding agent, the crack resistance of the concrete is significantly improved, and can effectively resist shrinkage cracks and cracks under external force; 3. Excellent bonding performance: the bonding strength with the base layer can be increased by at least 31.2%, which is much higher than the bonding strength of ordinary shotcrete, ensuring that the shotcrete layer is tightly combined with the base layer and is not easy to fall off; 4. Low rebound rate: due to the use of alkali-free liquid accelerator and optimized mix proportion, the rebound rate in the spraying process is controlled below 12%, which greatly reduces the waste of materials and environmental pollution.

[0069] In summary, the synergistic effect of the functional materials in the application effectively improves the early strength, crack resistance and volume stability of the concrete, and can be widely applied to tunnel lining, slope support, basement support and mine support and other construction scenes requiring fast hardening, high early strength support. Therefore, the application effectively overcomes the shortcomings of the prior art and has high industrial utilization value.

[0070] The above examples only exemplarily illustrate the principles and effects of the application, and are not used to limit the application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the application should be covered by the claims of the application.

Claims

1. A fast-setting, early-strength shotcrete, characterized in that, The concrete comprises a base material and auxiliary materials, wherein the base material comprises the following components in parts by weight percentage: Cement: 30-40%; Fine aggregate: 35~45%; Coarse aggregate: 25~35%; Polyester fiber: 0.05%–0.15%; Expanding agent: 3-6%; Nanoparticles: 1-3%; The excipients comprise the following components by weight percentage: Early-strength component: 2-5% of cement mass; Water-reducing agent: 0.5-1.5% of the cement mass; Alkali-free liquid quick-setting agent: 2-8% of cement mass; Water: Control the water-to-binder ratio between 0.38 and 0.45; The polyester fiber has a length of 6 to 12 mm.

2. The rapid-hardening, early-strength shotcrete according to claim 1, characterized in that: The fine aggregate is medium sand with a particle size of no more than 5 mm.

3. The rapid-hardening, early-strength shotcrete according to claim 1, characterized in that: The coarse aggregate is crushed stone or pebbles with a particle size of 5-10 mm.

4. The rapid-hardening, early-strength shotcrete according to claim 1, characterized in that: The expanding agent is a compound of UEA-type expanding agent and lightly calcined magnesium oxide in a mass ratio of 2 to 4:

1.

5. The rapid-hardening, early-strength shotcrete according to claim 1, characterized in that: The nano-component is composed of nano-silica and nano-alumina in a mass ratio of 1 to 2:

1.

6. The rapid-hardening, early-strength shotcrete according to claim 1, characterized in that: The early strength component is composed of highly active tricalcium aluminate.

7. The rapid-hardening, early-strength shotcrete according to claim 1, characterized in that: The water-reducing agent is a polycarboxylate-based water-reducing agent.

8. A method for preparing rapid-hardening, early-strength shotcrete as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Raw material preparation: Weigh each raw material according to the predetermined ratio; S2. Dry mixing pretreatment: Mix cement, fine aggregate, coarse aggregate, expansion agent, nano-components and early strength components evenly and stir for 2-3 minutes; S3. Add polyester fiber: Add polyester fiber to the dry mixture obtained in S2 and continue stirring for 1 to 2 minutes; S4. Prepare water-reducing agent solution: Mix water-reducing agent with water to form water-reducing agent solution; S5. Wet mixing: Add the dry mixture obtained in S3 and the water-reducing agent solution obtained in S4 to the mixer and wet mix for 4-5 minutes to form a spray mixture; S6. Spraying and curing: Add alkali-free liquid quick-setting agent to the nozzle and apply wet spraying. After spraying, perform wet curing or apply curing agent in a timely manner.

9. The method for preparing rapid-hardening, early-strength shotcrete according to claim 8, characterized in that: The specific operation of the dry mixing pretreatment in S2 is as follows: first, cement, fine aggregate, coarse aggregate and expansion agent are added to the mixer and dry mixed at a speed of 13-17 r / min for 1-2 min, and then nano-components and early strength components are added and dry mixed for another 1 min.

10. The method for preparing rapid-hardening, early-strength shotcrete according to claim 8, characterized in that: In step S3, the speed of the mixer is 8-12 r / min, and in step S4, the speed of the mixer is 18-22 r / min.

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