Maintenance-free lightweight spraying ultra-high performance concrete, preparation method and application thereof

Abstract

The invention belongs to the technical field of building materials, and particularly discloses maintenance-free lightweight spraying ultra-high performance concrete as well as a preparation method and application of the maintenance-free lightweight spraying ultra-high performance concrete. Comprising 700 to 900 parts of Portland cement, 120 to 200 parts of silica fume, 100 to 200 parts of a layered mineral admixture, 30 to 70 parts of a gradient active expanding agent, 600 to 800 parts of modified lightweight aggregate, 0.5 to 3 parts of a rheology regulating agent, 40 to 80 parts of composite fiber, 7 to 10 parts of a water reducing agent and 170 to 200 parts of water. Based on the synergistic effect of all the components, on the basis that the light ultra-high performance concrete can be continuously sprayed, the spraying performance, the shrinkage performance and the interface bonding performance are further improved, the anti-cracking performance, the mechanical performance and the durability of the light ultra-high performance concrete are enhanced, formwork erecting, film covering maintenance and later maintenance are not needed in construction, and the construction period is shortened. And moreover, the coating has the advantages of small apparent density, strong interface adhesion, thick single-time spraying, high crack resistance, low shrinkage, ultrahigh strength, high durability and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of building materials, and more specifically, relates to a maintenance-free lightweight sprayed ultra-high performance concrete, a preparation method and an application thereof. Background Art

[0002] With the rapid development of bridge technology, new bridges are gradually becoming saturated, and the demand for maintenance and reinforcement of existing bridges is increasing, which poses higher challenges to the performance of reinforcement materials and construction technology. Traditional reinforcement methods such as carbon fiber cloth / plate bonding and steel bonding are only suitable for small-area reinforcement, and have disadvantages such as aging of the adhesive layer. Replacement concrete reinforcement method, increased cross-section method and other reinforcement methods have thick reinforcement layers, weak interface bonding, insufficient mechanical properties and durability, and require formwork construction, cumbersome procedures, and low reinforcement efficiency. High performance, lightweight and efficient construction of reinforcement materials have become urgent needs for the reinforcement of existing bridges.

[0003] Shotcrete has high early strength, no need for formwork, and high construction efficiency. It is often used for structural reinforcement and tunnel lining. However, the common problems of low late strength, poor durability, and insufficient crack resistance of existing shotcrete restrict its application. Ultra-high performance concrete has been favored by the engineering community in recent years due to its ultra-high mechanical properties and durability. Some scholars have tried to combine ultra-high performance concrete with shotcrete. Chinese patent CN117105609A discloses a method for preparing ultra-high performance shotcrete without accelerator-assisted construction, which is prepared by mixing cement, river sand, coarse aggregate, expansion agent, microsilica powder, modified quartz sand, nano-alumina, nano-calcium carbonate, polypropylene fiber, composite modified diatomaceous earth, stable thickener, and water. In addition, Chinese patent CN113716915A discloses a shotcrete ultra-high performance concrete for anti-corrosion reinforcement. The synergistic effect between the components of the shotcrete ultra-high performance concrete makes it have high early and late strength, low shrinkage, suitable viscosity, good working performance and durability, and can solidify in a short time to form a high strength. The above patent uses conventional sprayed UHPC (Ultra-High Performance Concrete) to improve the strength and durability of sprayed concrete. However, conventional UHPC has a high apparent density, large shrinkage, and strong sensitivity to water-cement ratio, which leads to problems such as large self-weight load of the reinforcement layer, shrinkage cracking, and insufficient interface bonding strength.

[0004] Lightweight Ultra-High Performance Concrete (LUHPC) is a new type of cement-based material that uses lightweight aggregate to replace the fine aggregate in conventional ultra-high performance concrete and is designed and prepared based on the theory of tight packing. It has the characteristics of light weight, low shrinkage, high strength and high durability. If LUHPC is applied to shotcrete, while meeting the excellent mechanical properties and durability of shotcrete, it can reduce the thickness of the reinforcement layer and the deadweight of the reinforcement material, thereby reducing the impact of the deadweight load of the reinforcement layer on the bearing capacity of the original structure. At the same time, it can greatly reduce the shrinkage of UHPC, solve the problems of conventional UHPC's large deadweight and large shrinkage, and is an ideal material for bridge structure reinforcement. However, the lightweight aggregate used in LUHPC has very different material properties from the fine aggregate used in conventional UHPC. There are many difficulties in incorporating LUHPC into shotcrete, which are specifically manifested as follows:

[0005] 1) LUHPC has a low water-cement ratio and is extremely sensitive to water. When using spraying construction, the water absorption characteristics of lightweight aggregate during pumping will cause the slurry to lose water, and the pumping performance will be greatly reduced. In addition, LUHPC itself has a high viscosity, so there is a greater risk of slurry pipe clogging.

[0006] 2) Compared with the quartz sand and river sand used in conventional UHPC, the lightweight aggregate used in LUHPC has low density, large particle size, and low compatibility with the slurry. The use of spraying construction has the problem of aggregate stratification and separation from the slurry.

[0007] 3) LUHPC has high binder and low water-binder ratio, which leads to large shrinkage. The use of spraying construction will cause the lightweight aggregate and paste to lose water during the high-pressure spraying process, which will not only increase the risk of shrinkage cracking, but also weaken the interfacial bonding performance between the reinforcement layer and the original structure. In addition, excessive water loss has a negative effect on the cement hydration process and microstructure formation of the paste.

[0008] 4) When LUHPC is constructed by spraying, there is no need for formwork, and the construction efficiency is high and the construction is fast. However, LUHPC has high requirements for maintenance. After construction, it is necessary to cover the surface with a film to keep it moisturized to prevent plastic cracks caused by surface water loss. However, the formwork-free construction method is more difficult for beam bottoms, pier tops, and other special-shaped structures. It not only adds new processes, which is contrary to the high efficiency of spraying construction, but also puts higher requirements on the surface open time of the sprayed slurry.

[0009] 5) Conventional shotcrete usually uses accelerators to improve the viscosity and anti-sagging properties of concrete. Its essence is to promote the rapid formation of calcium aluminate in the paste to achieve the purpose of rapid viscosity increase and thickening, but it will sacrifice the later strength and durability of the concrete, especially for the UHPC system. In addition to the deterioration of strength and durability, the violent hydration reaction in the plastic period will aggravate the shrinkage of UHPC, which will have a relatively adverse effect on the structural bearing capacity and interface bonding performance.

[0010] Based on the above defects and shortcomings, there is an urgent need in this field to propose a maintenance-free lightweight sprayed ultra-high performance concrete to achieve maintenance-free spraying construction of lightweight ultra-high performance concrete and comprehensively improve the spraying performance, shrinkage performance, crack resistance, mechanical properties, durability, and interface bonding performance. Summary of the invention

[0011] In view of the above defects or improvement needs of the prior art, the present invention provides a maintenance-free lightweight sprayed ultra-high performance concrete, a preparation method and an application thereof, wherein a maintenance-free lightweight sprayed ultra-high performance concrete is designed in combination with the characteristics of the lightweight ultra-high performance concrete itself and the characteristics of sprayable construction, and the overall performance improvement is achieved based on the synergistic effect between the components. On the basis of continuous spraying, its spraying performance, shrinkage performance, and interface bonding performance are further improved, and its crack resistance, mechanical properties and durability are enhanced. Not only does it not require formwork for construction, has high construction efficiency, does not require film maintenance, and does not require later maintenance, but it also has excellent properties such as low apparent density, strong interface bonding, single-shot thickness, high crack resistance, low shrinkage, ultra-high strength and high durability, and has broad application prospects in the fields of reinforcement of special-shaped structures of bridges, and reinforcement and support of tunnels and culverts.

[0012] To achieve the above object, according to one aspect of the present invention, a maintenance-free lightweight sprayed ultra-high performance concrete is provided, comprising the following components in parts by mass:

[0013] 700-900 parts of Portland cement, 120-200 parts of silica fume, 100-200 parts of layered mineral admixture, 30-70 parts of gradient active expansion agent, 600-800 parts of modified lightweight aggregate, 0.5-3 parts of rheology control agent, 40-80 parts of composite fiber, 7-10 parts of water reducer, 170-200 parts of water;

[0014] The modified lightweight aggregate comprises lightweight aggregate pre-moistened with water, a coating layer wrapped on the surface of the lightweight aggregate, and an activation layer arranged on the surface of the coating layer and used to activate the coating layer, wherein the activation layer is doped with three-dimensional porous graphene.

[0015] As a further preferred embodiment, the coating layer is prepared by slurry, and the slurry comprises the following components in parts by weight: 40-60 parts of cement, 40-60 parts of alkali-activated adhesive, 10-20 parts of water glass, and 20-40 parts of water;

[0016] Preferably, the alkali-activated adhesive material is one or more of metakaolin and ultrafine mineral powder.

[0017] As further preferred, the initial aggregate of the lightweight aggregate is one or more of pottery sand, pumice, and expanded perlite; the particle size of the initial aggregate is not greater than 4 mm, and the bulk density of the initial aggregate is ≤700 kg / m 3 Preferably, the cylinder compressive strength of the initial aggregate is ≥7MPa.

[0018] As further preferred, the activation layer comprises:

[0019] Polyacrylamide forms hydrogen bonds with organic components in the batter layer in water, and multiple hydrogen bonds are cross-linked to form a three-dimensional network structure.

[0020] As further preferred, the gradient active expansion agent comprises, by weight: 50 to 60 parts of calcium oxide expansion agent, 25 to 35 parts of high-activity natural anhydrite, and 15 to 25 parts of medium-activity natural anhydrite;

[0021] Preferably, the 7d limited expansion rate of the calcium oxide expansion agent in water is ≥0.55%, the average particle size of the high-activity natural anhydrite is 10 μm to 20 μm, and the average particle size of the medium-activity natural anhydrite is 30 μm to 40 μm.

[0022] As further preferred, the layered mineral admixture is one or more of metakaolin, diatomaceous earth, and bentonite;

[0023] Preferably, the rheology control agent comprises the following components in parts by weight:

[0024] 8-10 parts of rheology adjustment component, 20-40 parts of interface bonding component;

[0025] Preferably, the rheology regulating component comprises, by weight: 6-10 parts of wood fiber and 1-3 parts of polyacrylamide;

[0026] Preferably, the interface bonding component is a redispersible latex powder;

[0027] Preferably, the length of the wood fiber is 800-1000 μm; the polyacrylamide is anionic, with a molecular weight of 800-1200; the redispersible latex powder is ethylene-vinyl acetate polymer;

[0028] Preferably, the composite fiber comprises, by weight: 5-15 parts of medium and long steel fibers and 0.1-1 parts of short-cut plant fibers;

[0029] Preferably, the steel fiber is 10 mm to 15 mm long, and the plant fiber is 1 mm to 3 mm long;

[0030] Preferably, the plant fiber is one or more of sisal, flax, ramie, jute, coconut shell, and bamboo fiber;

[0031] Preferably, the water reducing agent is a shrinkage-reducing polycarboxylic acid powder water reducing agent with a water reduction rate of ≥30%.

[0032] According to another aspect of the present invention, there is also provided a method for preparing a maintenance-free lightweight sprayed ultra-high performance concrete, comprising:

[0033] Step 1: prepare silicate cement, silica fume, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate, rheology control agent, composite fiber, water reducing agent and water according to the component proportion of maintenance-free lightweight sprayed ultra-high performance concrete;

[0034] Step 2: Add silicate cement, silica fume, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate and water reducing agent into a mixing pot;

[0035] Step 3, slowly add water to the stirring pot and stir until fluidized, add the composite fiber after fluidization, and stir until uniform;

[0036] Step 4: add the rheological composite agent to the mixture prepared in step 3, and stir evenly to obtain the mixed lightweight sprayed ultra-high performance concrete.

[0037] As further preferred, the preparation method of the modified lightweight aggregate comprises:

[0038] First, prepare the coating layer: pre-wet the lightweight aggregate, and after the saturated surface is dry, place it in the slurry to coat it with slurry, the coating thickness is not more than 1mm, and let it stand after coating, and obtain the spare material after the slurry hardens;

[0039] Secondly, prepare the activation layer: soak the prepared material in a three-dimensional porous graphene-modified polyacrylamide solution to activate the surface, take it out and dry it to obtain the modified lightweight aggregate;

[0040] Preferably, the preparation steps of the three-dimensional porous graphene-modified polyacrylamide solution include:

[0041] First, polyacrylamide powder is dissolved in water to form a polyacrylamide solution with a concentration of 0.5‰, and the pH value of the solution is adjusted to above 12 using calcium hydroxide;

[0042] Next, adding 2% of the three-dimensional porous graphene by mass ratio to the solution prepared in step 1 to form a mixed solution;

[0043] Finally, the mixed solution is placed in an environment of 50-60° C. for ultrasonic dispersion to obtain a three-dimensional porous graphene-modified polyacrylamide solution.

[0044] According to another aspect of the present invention, there is also provided an application of maintenance-free lightweight sprayed ultra-high performance concrete according to any one of the above embodiments or a combination of multiple embodiments in the reinforcement and support of bridges, tunnels and culverts.

[0045] As a further preferred embodiment, during the application process, when the water in the coating layer is continuously consumed to a certain extent as the cement is hydrated, the pre-wetted water will be released from the lightweight aggregate into the coating layer in a timely manner;

[0046] In addition, the polyacrylamide in the activation layer forms hydrogen bonds with the organic components in the coating layer in water, and multiple hydrogen bonds are cross-linked to form a three-dimensional network structure to increase the adhesion between the lightweight aggregate surface and the coating layer.

[0047] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0048] 1. The maintenance-free lightweight sprayed ultra-high performance concrete of the present invention achieves comprehensive performance improvement based on the synergistic effect between the various components. On the basis of continuous spraying, its spraying performance, shrinkage performance, and interface bonding performance are further improved, and its crack resistance, mechanical properties and durability are enhanced. It not only does not require formwork during construction, has high construction efficiency, does not require film maintenance, and does not require later maintenance, but also has excellent properties such as low apparent density, strong interface bonding, single-shot thickness, high crack resistance, low shrinkage, ultra-high strength and high durability. It has broad application prospects in the fields of reinforcement of special-shaped structures of bridges, and reinforcement and support of tunnels and culverts.

[0049] 2. The present invention modifies the lightweight aggregate, namely, firstly coats it with cement composite alkali activated adhesive, and then uses three-dimensional porous graphene modified polyacrylamide for surface treatment, which not only realizes high strengthening, heavy quality and surface activation of lightweight aggregate, avoids the problems of floating, collapse, pipe blockage and lightweight stratification of lightweight aggregate during operation, but also can construct a high thermal conductivity system with a low dosage of three-dimensional porous graphene, timely conducts hydration heat energy and reduces the temperature difference between the inside and outside of the slurry.

[0050] 3. The present invention adopts a variety of different time-dependent expansion components to form a gradient active expansion agent, and utilizes pre-saturated modified lightweight aggregate, plant fiber, wood fiber, layered mineral admixture and other internal curing materials with water absorption-water storage-water release functions to supply water for the expansion reaction of the expansion agent, thereby forming a plastic period crack self-healing and early-middle-late gradient compensation shrinkage technology. The plastic period crack repair rate can reach 95%, and no film curing is required after construction, and no maintenance is required in the later stage. The interface bonding performance between the reinforcement layer and the original structure is greatly improved by reducing shrinkage.

[0051] 4. The present invention adopts wood fiber, supplemented with polyacrylamide, and composite redispersible latex powder to prepare a rheology control agent, which can not only ensure the good pumping performance, spraying performance, and mechanical properties of UHPC, but also effectively reduce the water loss of slurry during the spraying process and improve the crack resistance of UHPC fiber. In addition, the redispersible latex powder can penetrate into the interface between the reinforcement layer and the original structure to solidify into a film, further strengthening its interfacial bonding performance.

[0052] 5. The lightweight sprayed UHPC prepared by the present invention has high crack resistance. First, medium and long steel fibers, short-cut plant fibers, and micron-sized wood fibers are used to suppress visible macro cracks, fine cracks, and micro cracks, respectively, forming a fiber gradient crack resistance technology; secondly, the gradient compensation shrinkage technology of the internal curing material and the expansion agent greatly reduces the risk of UHPC shrinkage cracking, while enhancing the UHPC's later crack self-repairing ability.

[0053] 6. The present invention achieves a comprehensive improvement in the performance of lightweight spray UHPC through the synergy between the various components, and its apparent density is ≤2000kg / m 3 , continuous operation volume can reach 50m 3 The thickness of a single molding is 5cm to 25cm, the rebound rate is ≤10%, the compressive strength at 28d is 100MPa to 200MPa, the bending strength at 28d is 20MPa to 40MPa, the shrinkage rate at 7d is 0με to 100με, the bonding strength at 28d is 1MPa to 3MPa, and the rapid migration coefficient of chloride ions at 28d is ≤0.8×10 -12 m 2 / s, and has the advantages of no coating, no maintenance, and high crack resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a preparation flow chart of a maintenance-free lightweight sprayed ultra-high performance concrete according to an embodiment of the present invention;

[0055] Figure 2 It is a schematic diagram of the self-healing evolution behavior of cracks in Example 1 of the present invention. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0057] The present embodiment provides a maintenance-free lightweight sprayed ultra-high performance concrete, which includes, by mass: 700-900 parts of silicate cement, 120-200 parts of silica fume, 100-200 parts of layered mineral admixture, 30-70 parts of gradient active expansion agent, 600-800 parts of modified lightweight aggregate, 0.5-3 parts of rheology control agent, 40-80 parts of composite fiber, 7-10 parts of water reducer, and 170-200 parts of water.

[0058] Specifically, the modified lightweight aggregate includes pre-moistened lightweight aggregate, a coating layer wrapped on the surface of the lightweight aggregate, and an activation layer disposed on the surface of the coating layer and used to activate the coating layer, wherein the activation layer is doped with three-dimensional porous graphene. That is, in this embodiment, the lightweight aggregate is firstly coated with cement composite alkali-activated adhesive, and then surface treated with three-dimensional porous graphene-modified polyacrylamide, which not only achieves high strengthening, heavy quality and surface activation of lightweight aggregate, avoids the problems of floating, collapse, pipe blockage and lightweight stratification of lightweight aggregate during operation, but also a low amount of three-dimensional porous graphene can construct a high thermal conductivity system, timely conduct hydration heat energy, and reduce the temperature difference between the inside and outside of the slurry.

[0059] Based on the above embodiment scheme, in this embodiment, the modified lightweight aggregate is prepared by the following method: pre-wetting the lightweight aggregate, and after the saturated surface is dry, the lightweight aggregate is placed in a slurry for coating, the coating thickness is not more than 1mm, and the coating is allowed to stand for 24 hours, and the slurry is hardened to obtain the reserve material; the reserve material is placed in a three-dimensional porous graphene modified polyacrylamide solution and immersed for 2 hours for surface activation, and the modified lightweight aggregate is obtained after being taken out and dried; the slurry is composed of 40-60 parts of cement, 40-60 parts of alkali-activated adhesive, and 10-20 parts of water glass by mass. , 20-40 parts of water; the alkali-activated colloid is one or more of kaolin and ultrafine mineral powder; the preparation steps of the three-dimensional porous graphene modified polyacrylamide solution include: dissolving polyacrylamide powder in water to form a polyacrylamide solution with a concentration of 0.5‰, adjusting the pH value of the solution to above 12 with calcium hydroxide, and then adding 2% of the three-dimensional porous graphene in a mass ratio to the solution to form a mixed solution, placing the mixed solution in an environment of 50-60°C for ultrasonic dispersion for 2 hours to obtain a three-dimensional porous graphene modified polyacrylamide solution.

[0060] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the lightweight aggregate is first subjected to saturated pre-wetting treatment. When the water in the slurry is continuously consumed to a certain extent as the cement is hydrated, the pre-wetting water will be released from the lightweight aggregate into the slurry in time, thereby increasing the relative humidity of the slurry and reducing the shrinkage of UHPC; secondly, cement composite alkali-activated adhesive is used on the surface of the lightweight aggregate for slurry coating and strengthening to form a layer of high-strength cement stone-geopolymer shell, which can not only avoid the performance loss caused by the low strength of the lightweight aggregate, but also the high-strength shell can increase the average density of the lightweight aggregate and block the water absorption pores. It can effectively alleviate the problems of lightweight aggregate floating, lightweight stratification and pipe collapse and blockage caused by water absorption effect during pumping. Finally, the surface of lightweight aggregate is activated by three-dimensional porous graphene modified polyacrylamide solution. The polyacrylamide on the surface of lightweight aggregate forms hydrogen bonds with the organic components in the slurry in water and cross-links into a three-dimensional network structure, which effectively increases the adhesion between the surface of lightweight aggregate and the slurry and avoids aggregate stratification during spraying. The high thermal conductivity system that can be constructed with three-dimensional porous graphene at a low dosage can timely conduct a large amount of heat energy generated by cement hydration to reduce the temperature difference between the inside and outside of the slurry and reduce temperature difference cracks.

[0061] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the layered mineral admixtures are one or more of metakaolin, diatomaceous earth, and bentonite. Admixtures such as metakaolin, diatomaceous earth, and bentonite have fine particles and high activity. Their filling effect and volcanic ash effect can increase the density of UHPC, improve the slurry microstructure, and improve the later strength of UHPC; their layered structure has the characteristics of large specific surface area and strong water absorption. The early water absorption and storage effect can effectively improve the viscosity and thixotropic properties of UHPC, and the stored water is released in the later stage of maintenance to exert the internal maintenance efficiency.

[0062] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the expansion agent includes, by mass, 50-60 parts of calcium oxide expansion agent, 25-35 parts of high-activity natural anhydrite, and 15-25 parts of medium-activity natural anhydrite. The calcium oxide expansion agent has a 7d limited expansion rate in water of ≥0.55%, the high-activity natural anhydrite has an average particle size of 10μm-20μm, and the medium-activity natural anhydrite has an average particle size of 30μm-40μm. The calcium oxide expansion agent has high early activity and large expansion efficiency. The expansion product has high filling capacity for plastic cracks, and the plastic crack repair rate can reach 95%. It can greatly compensate for the early shrinkage of UHPC and realize the non-filming maintenance of lightweight sprayed UHPC; the high-activity natural anhydrite mainly compensates for the mid-term shrinkage of UHPC, and the medium-activity natural anhydrite mainly compensates for the late shrinkage of UHPC, enhancing the late crack self-repairing performance of UHPC. Secondly, the water release window of the internal curing material matches the expansion window, providing sufficient water for the expansion agent, strengthening the expansion efficiency of the expansion agent, and forming plastic period crack self-healing, early-mid-late gradient compensation shrinkage, and late crack self-repair technology. In addition, natural anhydrite is used as an expansion agent, and its sulfate ions can promote the formation and stable existence of calcium sulfoaluminate (high-sulfur calcium sulfoaluminate hydrate), effectively avoiding the expansion and shrinkage, strength attenuation, and durability degradation caused by the conversion of calcium sulfoaluminate to monosulfur calcium sulfoaluminate hydrate due to the reduction of sulfate ions in the later stage.

[0063] Based on any one of the above embodiments or a combination of multiple embodiments, in this embodiment, the initial aggregate of the modified lightweight aggregate is one or more of pottery sand, pumice, and expanded perlite; the particle size of the initial aggregate is not greater than 4 mm, and the bulk density is ≤800 kg / m 3 , cylinder pressure strength ≥7MPa.

[0064] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the rheology control agent is composed of 8-10 parts of rheology control components and 20-40 parts of interface bonding components; the rheology control components include, by mass, 6-10 parts of wood fiber and 1-3 parts of polyacrylamide; the interface bonding component is a redispersible latex powder. Compared with the traditional rheology control agent that only controls rheological properties, the wood fiber used in the present invention can not only improve the viscosity, thixotropic properties and anti-sagging properties of UHPC, but also its air entraining properties can improve the pumping performance of UHPC, its hydrophilicity can be used as an internal curing material to improve the shrinkage of UHPC, and its fiber crack resistance can inhibit UHPC microcracks and improve the crack resistance of UHPC; the redispersible latex powder used in the present invention can penetrate into the interface between the reinforcement layer and the original structure to solidify into a film, thereby strengthening its interface bonding properties.

[0065] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the length of the wood fiber is 800-1000 μm; the polyacrylamide is anionic with a molecular weight of 800-1200; and the redispersible latex powder is ethylene-vinyl acetate polymer.

[0066] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the composite fiber is composed of 5-15 parts of medium-long steel fibers and 0.1-1 parts of short-cut plant fibers by mass; the steel fiber is 10mm to 15mm long, and the plant fiber is 1 to 3mm long; the plant fiber is one or more of sisal, flax, ramie, jute, coconut shell, and bamboo fiber. The medium-long steel fiber and short-cut plant fiber used, supplemented by micron-level wood fiber, can respectively inhibit visible macro cracks, fine cracks, and micro cracks, forming a gradient anti-crack technology, which enhances the anti-crack performance of UHPC. In addition, as a hydrophilic fiber, plant fiber can exert an internal curing effect to reduce shrinkage and improve the microstructure of the UHPC matrix.

[0067] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the water reducer is a shrinkage-reducing polycarboxylic acid powder water reducer with a water reduction rate of ≥30%.

[0068] like Figure 1 As shown, based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the preparation method of maintenance-free lightweight sprayed ultra-high performance concrete includes the following steps:

[0069] S1, add silicate cement, silica fume, layered mineral admixture, expansion agent, modified lightweight aggregate and water reducing agent into the mixing pot.

[0070] S2, slowly add water into the stirring pot and stir until fluidized, then add the composite fiber after fluidization and stir until uniform.

[0071] S3, add the rheological compound and stir evenly to obtain the mixed lightweight sprayed ultra-high performance concrete.

[0072] In this embodiment, by optimizing the processes such as the stirring sequence, the uniform dispersion of the UHPC components can be effectively ensured, and the phenomena such as aggregate floating and fiber agglomeration can be prevented.

[0073] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the maintenance-free lightweight sprayed ultra-high performance concrete is used in the field of bridge reinforcement to speed up construction, improve construction efficiency, greatly improve the performance of the reinforcement layer, and eliminate the need for coating and maintenance, thereby achieving high performance, lightweight and efficient construction of bridge reinforcement materials.

[0074] Based on any of the above embodiments or a combination of multiple embodiments, in this embodiment, the preparation method of the modified lightweight aggregate used in the following embodiments is as follows:

[0075] 1) Carry out saturated pre-wetting treatment on lightweight aggregate and keep it for use after its surface is dry.

[0076] 2) Select 50 parts of cement, 40 parts of alkali-activated adhesive, 15 parts of water glass and 25 parts of water by weight, add them into a mortar mixer in sequence and stir until fluidized to prepare a slurry.

[0077] 3) Place the saturated surface-pre-wetted lightweight aggregate in the slurry and coat it with the slurry. The coating thickness should not exceed 1mm. Let it stand for 24 hours after coating. After the slurry hardens, the spare material is obtained.

[0078] 4) dissolving polyacrylamide powder in water to form a polyacrylamide solution with a concentration of 0.5‰, and adjusting the pH value of the solution to above 12 using calcium hydroxide; adding 2% of three-dimensional porous graphene in a mass ratio to the solution to form a mixed solution; placing the mixed solution in an environment of 55°C and ultrasonically dispersing for 2 hours to prepare a three-dimensional porous graphene-modified polyacrylamide solution.

[0079] 5) The prepared material is placed in a three-dimensional porous graphene-modified polyacrylamide solution and immersed for 2 hours for surface activation, and then taken out and dried to obtain the modified lightweight aggregate.

[0080] In addition, the maintenance-free lightweight sprayed ultra-high performance concrete prepared by any embodiment or a combination of multiple embodiments of the present invention can be applied to the reinforcement and support of bridges, tunnels, and culverts. During the application process, when the moisture in the mortar layer is continuously consumed to a certain extent as the cement is hydrated, the pre-wetted moisture will be released from the lightweight aggregate into the mortar layer in time;

[0081] In addition, the polyacrylamide in the activation layer forms hydrogen bonds with the organic components in the coating layer in water, and multiple hydrogen bonds are cross-linked to form a three-dimensional network structure to increase the adhesion between the lightweight aggregate surface and the coating layer.

[0082] The specific implementation of the present invention is described below in conjunction with specific engineering examples.

[0083] Example 1

[0084] Example 1 provides a maintenance-free lightweight sprayed ultra-high performance concrete, the preparation method of which is as follows:

[0085] (1) The benchmark mix design of lightweight sprayed UHPC was carried out based on the modified Andre-Anderson model to determine the volume ratio of cement, silica fume, admixtures and modified lightweight aggregate; the parameters of water reducer and water were determined based on the closest wet packing theory; the proportion of expansive agent and steel fiber was determined according to performance design. The obtained lightweight sprayed UHPC mix ratio is shown in Table 1.

[0086] (2) First, add silicate cement, silica fume, layered mineral admixture, expansion agent, modified lightweight aggregate, and water reducer into a mixing pot and mix them evenly; then slowly add water and stir until fluidized, add composite fiber after fluidization, and stir until uniform; finally, add rheological composite agent, stir evenly to obtain a mixed lightweight sprayed ultra-high performance concrete.

[0087] (3) The mixed ultra-high performance concrete is sprayed onto the reinforced structure to complete the lightweight sprayed UHPC reinforcement construction.

[0088] Table 1 Lightweight spray UHPC mix ratio (kg / m 3 )

[0089]

[0090] In this embodiment, the initial aggregate used in the modified lightweight aggregate is shale pottery sand, and the bulk density is 746kg / m 3 , the apparent density is 1744kg / m 3 The alkali activated adhesive material used is kaolin, which is modified according to the above steps. The bulk density of the modified lightweight aggregate is 884kg / m 3 , the apparent density is 1756kg / m 3 .

[0091] In this embodiment, the layered mineral admixture is metakaolin.

[0092] In this embodiment, the expansion agent is composed of 55 parts of calcium oxide, 30 parts of high-activity natural anhydrite and 20 parts of medium-activity natural anhydrite by mass.

[0093] In this embodiment, the rheology control agent is composed of 8 parts of wood fiber, 2 parts of polyacrylamide and 35 parts of redispersible latex powder by weight.

[0094] In this embodiment, the composite fiber consists of 10 parts of steel fiber and 0.1 parts of plant fiber by mass.

[0095] Example 2

[0096] The difference between Example 2 and Example 1 is that:

[0097] The initial aggregate used in the modified lightweight aggregate in Example 2 is pumice with a bulk density of 753 kg / m 3 , the apparent density is 1754kg / m 3 The alkali activated adhesive material used is ultra-fine mineral powder, and the modified lightweight aggregate has a bulk density of 912kg / m 3 , the apparent density is 1769kg / m 3 .

[0098] In this embodiment, the layered mineral admixture is diatomaceous earth.

[0099] In this embodiment, the composite fiber consists of 10 parts of steel fiber and 0.2 parts of plant fiber by weight.

[0100] Comparative Example 1

[0101] Comparative Example 1 is substantially the same as Example 1, except that the lightweight aggregate used in Comparative Example 1 is original aggregate without modification.

[0102] Comparative Example 2

[0103] Comparative Example 2 is basically the same as Example 1, except that the lightweight aggregate in Comparative Example 2 is only subjected to slurry coating treatment and is not immersed in the three-dimensional porous graphene-modified polyacrylamide solution.

[0104] Comparative Example 3

[0105] Comparative Example 3 is substantially the same as Example 1, except that the fine aggregate in Comparative Example 3 is entirely quartz sand of equal volume and contains no lightweight aggregate.

[0106] Comparative Example 4

[0107] Comparative Example 4 is substantially the same as Example 1, except that the expansion agent in Comparative Example 4 is entirely calcium oxide.

[0108] Comparative Example 5

[0109] Comparative Example 5 is substantially the same as Example 1, except that the expansion agent of Comparative Example 5 consists of 55 parts of calcium oxide and 50 parts of magnesium oxide expansion agents.

[0110] Comparative Example 6

[0111] Comparative Example 6 is substantially the same as Implementation 1, except that the expansion agent of Comparative Example 6 consists of 60 parts of high-activity natural anhydrite and 40 parts of medium-activity natural anhydrite.

[0112] Comparative Example 7

[0113] Comparative Example 7 is substantially the same as Example 1, except that no rheology control agent is used in Comparative Example 7.

[0114] Comparative Example 8

[0115] Comparative Example 8 is substantially the same as Example 1, except that the rheology control agent used in Comparative Example 8 is composed of 8 parts of wood fiber and 2 parts of polyacrylamide, and does not contain an interface bonding component.

[0116] Comparative Example 9

[0117] Comparative Example 9 is substantially the same as Example 1, except that the rheology control agent used in Comparative Example 9 consists of 8 parts of hydroxypropyl methylcellulose, 2 parts of polyacrylamide and 35 parts of redispersible latex powder.

[0118] Comparative Example 10

[0119] Comparative Example 10 is basically the same as Example 1, except that: the components of Comparative Example 10 do not contain internal curing materials, specifically, the fine aggregate used in Comparative Example 10 is quartz sand; the admixture used is silica fume; the rheology controller used is composed of 8 parts of hydroxypropyl methylcellulose, 2 parts of polyacrylamide and 35 parts of redispersible latex powder; the composite fibers used are all 10 parts of steel fibers and 0.1 parts of polyethylene fibers.

[0120] Comparative Example 11

[0121] Comparative Example 11 is basically the same as Example 1, except that the rheology control agent used in Comparative Example 11 consists of 8 parts of hydroxypropyl methylcellulose, 2 parts of polyacrylamide and 35 parts of redispersible latex powder, and the fibers used in Comparative Example 11 are all steel fibers.

[0122] The slump expansion and apparent density of the ultra-high performance concrete prepared in each embodiment were tested according to the test method of "Standard for Test Methods of Ordinary Concrete Mixtures" GB / T 50080-2016, and the viscosity and yield stress were tested by a rotational rheometer; according to the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" GB / T 50082-2009 test specimens for shrinkage performance. The shrinkage specimens were directly cast and formed. The final setting was used as the test zero point. The non-contact method was used to test the shrinkage within 3 days from the final setting to the forming, and the contact method was used to test the shrinkage after 3 days of forming. According to the Technical Specification for Application of Shotcrete JGJ / T372-2016, the mechanical properties, horizontal rebound rate, vertical rebound rate, bonding strength and chloride ion penetration resistance were tested. The mechanical properties and chloride ion penetration resistance specimens were cut from a large spraying plate with a size of not less than 450mm×450mm×120mm. The bonding strength was measured by direct axial tension of a rock-UHPC layer binary drill core specimen. Another large spraying plate was made by a one-time spraying molding method for the single maximum spraying thickness test. After the spraying was completed, it was placed outdoors for static protection without any maintenance measures such as covering or sprinkling. A crack observation instrument was used to observe and record the length and width of cracks on the spraying surface within 24 hours after the spraying was completed. According to the Standard for Test Methods for Long-term Performance and Durability of Ordinary Concrete GB / T The total crack area per unit area was calculated and the test results are shown in Tables 1 and 2.

[0123] Table 1 Working performance, rheological properties and injection performance of lightweight sprayed UHPC prepared in Examples 1 to 2 and Comparative Examples 1 to 11

[0124]

[0125]

[0126] Table 2 Mechanical properties, crack resistance, durability and shrinkage properties of lightweight sprayed UHPC prepared in Examples 1 to 2 and Comparative Examples 1 to 11

[0127]

[0128]

[0129] The crack resistance and self-repair performance of the embodiment were tested with reference to the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" GB / T 50082-2009. After UHPC was poured into the mold, a fan was used to make the center of the specimen surface subject to a wind speed of not less than 5m / s to induce surface cracking. After blowing for 1 hour (molding for 1 hour), the fan was turned off and the specimen was left to stand for 23 hours. The changes in surface cracks were observed and the crack area was counted. The crack statistics are shown in Table 3. The crack evolution of Example 1 is shown in Table 3. Figure 2 shown.

[0130] Table 3 Self-repairing properties of lightweight sprayed UHPC prepared in Examples 1 to 2 and Comparative Examples 1 to 11

[0131]

[0132]

[0133] The results in Tables 1 to 3 show that the lightweight sprayed ultra-high performance concrete prepared in Examples 1 to 2 not only meets the requirements of lightweight, high performance, and high interface adhesion of the reinforcement material, but also has excellent working performance, rheological properties, and spraying performance, which can realize efficient spraying construction. The low shrinkage / micro-expansion technology of internal maintenance and the physical and chemical synergy of the expansion agent and the fiber graded anti-cracking technology enable it to have low shrinkage, high crack resistance, and efficient self-repairing characteristics, which can realize the reinforcement of special-shaped structures without film and maintenance. The maintenance-free lightweight sprayed ultra-high performance concrete prepared by the present invention has a spraying construction method that does not require formwork and film maintenance, which significantly improves the construction efficiency. Its lightweight and high-strength characteristics greatly improve the bearing capacity of the damaged structure while reducing the negative effects of its own load on the original structure. In addition, its high durability, low shrinkage, high crack resistance, and self-healing properties greatly reduce the later maintenance costs and extend the service life of the structure.

[0134] Compared with Example 1, the original aggregate used in Comparative Example 1 was not treated in any way, and the light aggregate spraying stratification phenomenon was serious during the spraying process. In Comparative Example 2, the original light aggregate was coated with slurry, but was not placed in a three-dimensional porous graphene-modified polyacrylamide solution for surface activation. The light aggregate still had slight stratification during the spraying process.

[0135] Compared with Example 1, the ultra-high performance concrete prepared in Comparative Example 3 entirely using quartz sand has a high apparent density, significantly increased shrinkage, and significantly decreased crack resistance and self-repairing ability.

[0136] Compared with Example 1, the ultra-high performance concrete prepared by using calcium oxide expansion agent in Comparative Example 4 has significantly increased shrinkage, especially late shrinkage, and all mechanical properties have decreased. Calcium oxide expansion agent has high activity and large early expansion. It starts to react in large quantities in the plastic period, producing a large amount of ineffective expansion, which not only leads to insufficient compensation for shrinkage in the late expansion, but also affects the cement hydration process in the plastic period, thereby affecting the mechanical properties of UHPC.

[0137] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A maintenance-free lightweight sprayed ultra-high performance concrete, characterized in that: The composition includes the following components in parts by weight: 700-900 parts of Portland cement, 120-200 parts of silica fume, 100-200 parts of layered mineral admixture, 30-70 parts of gradient active expansion agent, 600-800 parts of modified lightweight aggregate, 0.5-3 parts of rheology control agent, 40-80 parts of composite fiber, 7-10 parts of water reducer, 170-200 parts of water; The modified lightweight aggregate comprises lightweight aggregate pre-moistened with water, a coating layer wrapped on the surface of the lightweight aggregate, and an activation layer arranged on the surface of the coating layer and used to activate the coating layer, wherein the activation layer is doped with three-dimensional porous graphene.

2. The maintenance-free lightweight sprayed ultra-high performance concrete according to claim 1, characterized in that: The coating layer is prepared by slurry, and the slurry includes the following components by weight: 40-60 parts of cement, 40-60 parts of alkali-activated adhesive, 10-20 parts of water glass, and 20-40 parts of water; Preferably, the alkali-activated adhesive material is one or more of metakaolin and ultrafine mineral powder.

3. The maintenance-free lightweight sprayed ultra-high performance concrete according to claim 1, characterized in that: The initial aggregate of the lightweight aggregate is one or more of pottery sand, pumice, and expanded perlite; the particle size of the initial aggregate is not greater than 4 mm, and the bulk density of the initial aggregate is ≤700 kg / m 3 Preferably, the cylinder compressive strength of the initial aggregate is ≥7MPa.

4. The maintenance-free lightweight sprayed ultra-high performance concrete according to claim 1, characterized in that: The activation layer comprises: Polyacrylamide forms hydrogen bonds with organic components in the batter layer in water, and multiple hydrogen bonds are cross-linked to form a three-dimensional network structure.

5. The maintenance-free lightweight sprayed ultra-high performance concrete according to claim 1, characterized in that: The gradient active expansion agent comprises, by weight: 50 to 60 parts of calcium oxide expansion agent, 25 to 35 parts of high-activity natural anhydrite, and 15 to 25 parts of medium-activity natural anhydrite; Preferably, the 7d limited expansion rate of the calcium oxide expansion agent in water is ≥0.55%, the average particle size of the high-activity natural anhydrite is 10 μm to 20 μm, and the average particle size of the medium-activity natural anhydrite is 30 μm to 40 μm.

6. The maintenance-free lightweight sprayed ultra-high performance concrete according to claim 1, characterized in that: The layered mineral admixture is one or more of metakaolin, diatomaceous earth and bentonite; Preferably, the rheology control agent comprises the following components in parts by weight: 8-10 parts of rheology adjustment component, 20-40 parts of interface bonding component; Preferably, the rheology regulating component comprises, by weight: 6-10 parts of wood fiber and 1-3 parts of polyacrylamide; Preferably, the interface bonding component is a redispersible latex powder; Preferably, the length of the wood fiber is 800-1000 μm; the polyacrylamide is anionic, with a molecular weight of 800-1200; the redispersible latex powder is ethylene-vinyl acetate polymer; Preferably, the composite fiber comprises, by weight: 5-15 parts of medium and long steel fibers and 0.1-1 parts of short-cut plant fibers; Preferably, the steel fiber is 10 mm to 15 mm long, and the plant fiber is 1 mm to 3 mm long; Preferably, the plant fiber is one or more of sisal, flax, ramie, jute, coconut shell, and bamboo fiber; Preferably, the water reducing agent is a shrinkage-reducing polycarboxylic acid powder water reducing agent with a water reduction rate of ≥30%.

7. A method for preparing maintenance-free lightweight sprayed ultra-high performance concrete, characterized in that: include: Step 1: prepare silicate cement, silica fume, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate, rheology control agent, composite fiber, water reducing agent and water according to the component proportion of maintenance-free lightweight sprayed ultra-high performance concrete; Step 2: Add silicate cement, silica fume, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate and water reducing agent into a mixing pot; Step 3, slowly add water to the stirring pot and stir until fluidized, add the composite fiber after fluidization, and stir until uniform; Step 4: add the rheological composite agent to the mixture prepared in step 3, and stir evenly to obtain the mixed lightweight sprayed ultra-high performance concrete.

8. The method for preparing a maintenance-free lightweight sprayed ultra-high performance concrete according to claim 7, characterized in that: The preparation method of the modified lightweight aggregate comprises: First, prepare the coating layer: pre-wet the lightweight aggregate, and after the saturated surface is dry, place it in the slurry to coat it with slurry, the coating thickness is not more than 1mm, and let it stand after coating, and obtain the spare material after the slurry hardens; Secondly, prepare the activation layer: soak the prepared material in a three-dimensional porous graphene-modified polyacrylamide solution to activate the surface, take it out and dry it to obtain the modified lightweight aggregate; Preferably, the preparation steps of the three-dimensional porous graphene-modified polyacrylamide solution include: First, polyacrylamide powder is dissolved in water to form a polyacrylamide solution with a concentration of 0.5‰, and the pH value of the solution is adjusted to above 12 using calcium hydroxide; Next, adding 2% of the three-dimensional porous graphene by mass ratio to the solution prepared in step 1 to form a mixed solution; Finally, the mixed solution is placed in an environment of 50-60° C. for ultrasonic dispersion to obtain a three-dimensional porous graphene-modified polyacrylamide solution.

9. Use of the maintenance-free lightweight sprayed ultra-high performance concrete as described in any one of claims 1 to 7 in the reinforcement and support of bridges, tunnels and culverts.

10. The use of a maintenance-free lightweight sprayed ultra-high performance concrete according to claim 9, characterized in that: During the application process, when the moisture in the coating is continuously consumed to a certain extent as the cement is hydrated, the pre-wetted moisture will be released from the lightweight aggregate into the coating in time; In addition, the polyacrylamide in the activation layer forms hydrogen bonds with the organic components in the coating layer in water, and multiple hydrogen bonds are cross-linked to form a three-dimensional network structure to increase the adhesion between the lightweight aggregate surface and the coating layer.

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