Maintenance-free light-weight type jetting ultra-high performance concrete, preparation method and application thereof

Abstract

The application belongs to the technical field of building materials, and particularly discloses a maintenance-free light-weight type jetted ultra-high performance concrete, a preparation method and application thereof. The application comprises 700-900 parts of Portland cement, 120-200 parts of silica ash, 100-200 parts of layered mineral admixture, 30-70 parts of gradient active expansive agent, 600-800 parts of modified lightweight aggregate, 0.5-3 parts of rheological modifier, 40-80 parts of composite fiber, 7-10 parts of water reducing agent and 170-200 parts of water. Based on the synergistic effect among the components, the application further improves the jetting performance, shrinkage performance and interfacial bonding performance of the light-weight ultra-high performance concrete on the basis of realizing continuous jetting, and strengthens the crack resistance, mechanical properties and durability of the light-weight ultra-high performance concrete. The application has the advantages of small apparent density, strong interfacial bonding, single jetting thickness, high crack resistance, low shrinkage, ultra-high strength and high durability, and the like, and does not need formwork, film curing and post-maintenance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of building materials, and more particularly relates to a maintenance-free lightweight type jetted ultra-high performance concrete, a preparation method and applications thereof. BACKGROUND

[0002] With the rapid development of bridge technology, the demand for maintenance and reinforcement of existing bridges is increasing, which puts higher challenges on the performance of reinforcing 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. The replacement concrete reinforcement method and the method of increasing the section thickness have weak interfacial adhesion, insufficient mechanical properties and durability, and require formwork construction, complicated process, low reinforcement efficiency, and high performance, lightweight and efficient construction of reinforcing materials are the urgent needs of existing bridge reinforcement.

[0003] Jetted concrete has high early strength, does not require formwork, and has fast construction efficiency, and is commonly used for structural reinforcement and tunnel lining. However, the existing jetted concrete generally has low late strength, poor durability, and insufficient crack resistance, which restricts 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 attempted to combine ultra-high performance concrete with jetted concrete. Chinese patent CN117105609A discloses a method for preparing ultra-high performance jetted concrete without the aid of a setting accelerator, which uses cement, river sand, coarse aggregate, expanding agent, microsilica, modified quartz sand, nano-alumina, nano-calcium carbonate, polypropylene fiber, composite modified diatomite, stabilizing thickener, and water. In addition, Chinese patent CN113716915A discloses a corrosion-resistant jetted ultra-high performance concrete, which has a synergistic effect between the components, resulting in high early and late strength, low shrinkage, suitable viscosity, good workability, and durability. It can solidify and cure in a short time to form high strength. The above-mentioned patents use conventional jetted UHPC (Ultra-High Performance Concrete) to improve the strength and durability of jetted concrete, but the conventional UHPC has high apparent density, large shrinkage, and strong water-cement ratio sensitivity, which leads to problems such as large self-weight load of the reinforcement layer, shrinkage cracking, and insufficient interfacial adhesion strength.

[0004] Lightweight Ultra-High Performance Concrete (LUHPC) is a new type of cement-based material prepared by using lightweight aggregate to replace fine aggregate in conventional Ultra-High Performance Concrete (UHPC) and based on the close packing theory. It has the characteristics of lightweight, low shrinkage, high strength and high durability. If LUHPC is applied to sprayed concrete, it can not only meet the excellent mechanical properties and durability of sprayed concrete, but also reduce the thickness of the reinforced layer and the self-weight of the reinforcing material, thereby reducing the influence of the self-weight load of the reinforced layer on the bearing capacity of the original structure. At the same time, it can greatly reduce the shrinkage of UHPC and solve the problems of large self-weight and large shrinkage of conventional UHPC, which is an ideal material for bridge structure reinforcement. However, the lightweight aggregate used in LUHPC is quite different from the fine aggregate used in conventional UHPC in terms of material properties. There are many difficulties in incorporating LUHPC into sprayed concrete, which are as follows:

[0005] 1) The water-cement ratio of LUHPC is low, and it is very sensitive to water. When using spray construction, the water absorption characteristics of lightweight aggregate during pumping will cause the water in the slurry to be dispersed, and the pumping performance will be greatly reduced. In addition, the viscosity of LUHPC itself is large, and there is a high risk of pipe blockage.

[0006] 2) Compared with 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. There are problems of aggregate layering and separation from the slurry when using spray construction.

[0007] 3) The high binder and low water-cement ratio of LUHPC result in large shrinkage. The use of spray construction will cause water loss in the lightweight aggregate and slurry during high-pressure spraying, not only intensifying the risk of shrinkage and cracking, but also weakening the interfacial bonding performance between the reinforced layer and the original structure. Moreover, excessive water loss has a negative effect on the hydration process and microstructure formation of the slurry.

[0008] 4) LUHPC does not need to be formwork when using spray construction, which is efficient and fast. However, LUHPC requires high maintenance, and the surface needs to be covered and moisturized in time after construction to prevent plastic cracks caused by surface water loss. However, the construction method without formwork is difficult to cover and maintain the surface, especially for special-shaped structures such as beam bottoms and pier tops. Not only does it increase the new process, which is contrary to the efficiency of spray construction, but it also puts higher requirements on the open time of the sprayed slurry surface.

[0009] 5) The conventional shotcrete usually uses a setting accelerator to improve the viscosity and sag resistance of the concrete, which essentially promotes the rapid generation of ettringite in the paste to achieve the purpose of rapid thickening, but at the cost of the later strength and durability of the concrete, especially for the UHPC system, in addition to the degradation of strength and durability, the severe hydration reaction during the plastic stage will exacerbate the shrinkage of the UHPC, thereby adversely affecting the structural bearing capacity and interfacial bonding performance.

[0010] Based on the above defects and deficiencies, there is an urgent need in the art to propose a maintenance-free lightweight shotcrete ultra-high performance concrete to realize the maintenance-free shotcrete construction of lightweight ultra-high performance concrete and the overall improvement of the shotcrete performance, shrinkage performance, crack resistance, mechanical properties, durability and interfacial bonding performance. SUMMARY

[0011] In view of the above defects or improvement needs of the prior art, the present application provides a maintenance-free lightweight shotcrete ultra-high performance concrete, a preparation method and applications thereof, wherein a maintenance-free lightweight shotcrete ultra-high performance concrete is designed in combination with the characteristics of lightweight ultra-high performance concrete and the characteristics of shotcrete construction, and the overall performance is improved based on the synergistic effect between the components. On the basis of continuous shotcreting, the shotcrete performance, shrinkage performance, interfacial bonding performance are further improved, the crack resistance, mechanical properties and durability are strengthened, not only the construction does not need to set up forms, the construction efficiency is high, the maintenance-free coating maintenance and post-maintenance are realized, but also the lightweight shotcrete ultra-high performance concrete has the excellent properties of small apparent density, strong interfacial bonding, single shotcreting thickness, high crack resistance, low shrinkage, ultra-high strength and high durability, and has a broad application prospect in the fields of bridge special-shaped structure reinforcement, tunnel and culvert reinforcement and support.

[0012] To achieve the above-mentioned purpose, according to one aspect of the present application, a maintenance-free lightweight shotcrete ultra-high performance concrete is provided, which comprises the following components in mass fraction:

[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 expansive agent, 600-800 parts of modified lightweight aggregate, 0.5-3 parts of rheological modifier, 40-80 parts of composite fiber, 7-10 parts of water reducing agent, and 170-200 parts of water.

[0014] The modified lightweight aggregate comprises a pre-wet moisture lightweight aggregate, a grout layer wrapped on the surface of the lightweight aggregate, and an activation layer provided on the surface of the grout layer and used for activating the grout layer, wherein the activation layer is doped with three-dimensional porous graphene.

[0015] As a further preferred, the coating layer is prepared by a slurry, the slurry includes the following mass fraction of components: cement 40-60 parts, alkali-activated cementitious material 40-60 parts, water glass 10-20 parts, water 20-40 parts;

[0016] Preferably, the alkali-activated cementitious material is one or more of metakaolin, ultra-fine mineral powder.

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

[0018] As a further preferred, the activation layer includes:

[0019] The polyacrylamide forms hydrogen bonds with the organic components in the coating layer in water, and multiple hydrogen bonds are crosslinked into a three-dimensional network structure.

[0020] As a further preferred, the gradient activity expanding agent includes, by mass fraction: 50-60 parts of calcium oxide expanding agent, 25-35 parts of high-activity natural anhydrite, 15-25 parts of medium-activity natural anhydrite;

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

[0022] As a further preferred, the layered mineral admixture is one or more of metakaolin, diatomite, bentonite;

[0023] Preferably, the rheological modifier includes the following mass fraction of components:

[0024] 8-10 parts of rheological adjustment component, 20-40 parts of interfacial bonding component;

[0025] Preferably, the rheological adjustment component includes, by mass fraction: 6-10 parts of wood fiber, 1-3 parts of polyacrylamide;

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

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

[0028] Preferably, the composite fiber comprises 5-15 parts by mass of medium-length steel fiber and 0.1-1 part by mass of short plant fiber;

[0029] Preferably, the steel fiber is 10-15 mm long, and the plant fiber is 1-3 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-type polycarboxylic acid powder water reducing agent with a water reducing rate of ≥30%.

[0032] According to another aspect of the present application, a preparation method of the maintenance-free lightweight jetting ultra-high performance concrete is also provided, comprising:

[0033] Step one, prepare Portland cement, silica fume, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate, rheological modifier, composite fiber, water reducing agent, and water according to the component ratio of the maintenance-free lightweight jetting ultra-high performance concrete;

[0034] Step two, add Portland cement, silica fume, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate, and water reducing agent into a stirring pot;

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

[0036] Step four, add rheological modifier to the mixture prepared in step three, stir until uniform, and obtain the well-mixed lightweight jetting ultra-high performance concrete.

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

[0038] First, prepare a slurry layer: pre-wet the lightweight aggregate, place it in the slurry after the saturated surface is dry, the slurry thickness is not more than 1 mm, and the slurry is placed after the slurry is hardened to obtain the standby material;

[0039] Second, prepare an activation layer: soak the standby material in a three-dimensional porous graphene modified polyacrylamide solution for surface activation, and dry after taking out to obtain the modified lightweight aggregate.

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

[0041] First, dissolve polyacrylamide powder in water to form a 0.5‰ polyacrylamide solution, and adjust the PH value of the solution to above 12 using calcium hydroxide.

[0042] Then, 2% of the three-dimensional porous graphene prepared in step one is added to form a mixed solution;

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

[0044] According to another aspect of the present application, there is also provided an application of the maintenance-free lightweight jetting ultra-high performance concrete according to any one of the above embodiments or combinations of multiple embodiments in bridge, tunnel, culvert reinforcement and support.

[0045] As a further preferred, in the application process, when the water in the slurry layer is continuously consumed to a certain extent along with the hydration of cement, the pre-wetting water will be released from the lightweight aggregate into the slurry layer in time;

[0046] In addition, the polyacrylamide in the activation layer forms hydrogen bonds with the organic components in the slurry layer in water, and multiple hydrogen bonds are crosslinked into a three-dimensional network structure to increase the adhesion of the lightweight aggregate surface and the slurry layer.

[0047] Overall, compared with the prior art, the above technical solutions conceived by the present application mainly have the following technical advantages:

[0048] 1. The maintenance-free lightweight jetting ultra-high performance concrete of the present application realizes comprehensive performance improvement based on the synergistic effect of the components, further improves the jetting performance, shrinkage performance and interface adhesion performance on the basis of continuous jetting, and strengthens the anti-cracking performance, mechanical performance and durability performance. The concrete not only has high construction efficiency, is free of formwork, film curing and post-maintenance, but also has small apparent density, strong interface adhesion, single jetting thickness, high anti-cracking performance, low shrinkage, ultra-high strength and high durability, and has a broad application prospect in the fields of bridge special-shaped structure reinforcement, tunnel, culvert reinforcement and support.

[0049] 2. The present application modifies the lightweight aggregate, i.e. first wraps the slurry with cement composite alkali-activated glue material, and then performs surface treatment with three-dimensional porous graphene modified polyacrylamide. The lightweight aggregate is not only highly strengthened, heavy and surface-activated, but also avoids the problems of floating, collapse, pipe blockage and lightweight stratification in the operation process. In addition, the low-dosage three-dimensional porous graphene can construct a high-thermal-conductivity system to timely conduct the hydration heat energy and reduce the temperature difference between the inside and outside of the slurry.

[0050] 3. The present application adopts a plurality of different aging expansion components to be compounded into a gradient active expansion agent, and uses pre-saturation modified lightweight aggregate, plant fiber, wood fiber, layered mineral admixture and other internal curing materials with water absorption-water storage-water release function to provide water for the expansion reaction of the expansion agent, forming a plastic period crack self-healing, early-mid-late gradient shrinkage compensation technology, which can reach a plastic period crack repair rate of 95%, and does not require film curing after construction, and is free of maintenance in the later period, and greatly improves the interface bonding performance of the reinforced layer and the original structure through the reduction of shrinkage.

[0051] 4. The present application adopts a rheological regulator prepared by wood fiber, supplemented by polyacrylamide, and composite redispersible latex powder, 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 in the spraying process, improve the fiber crack resistance of UHPC, and in addition, the redispersible latex powder can penetrate into the interface between the reinforced layer and the original structure to solidify into a film, further strengthening the interface bonding performance.

[0052] 5. The lightweight type sprayed UHPC prepared by the present application has high crack resistance. First, the medium-long steel fiber, chopped plant fiber and micron-sized wood fiber are used to inhibit visible macroscopic cracks, small cracks and micro cracks respectively, forming a fiber gradient crack resistance technology; second, the gradient shrinkage compensation technology of internal curing materials and expansion agent greatly reduces the risk of UHPC shrinkage and cracking, and enhances the UHPC self-repairing ability of the later cracks.

[0053] 6. The present application realizes the comprehensive improvement of the performance of lightweight type sprayed UHPC through the synergy between the components, and the apparent density of the lightweight type sprayed UHPC is ≤2000kg / m 3 , and the continuous operation amount can reach 50m 3 , the single forming thickness is 5cm-25cm, the rebound rate is ≤10%, the 28d compressive strength is 100MPa-200MPa, the 28d bending strength is 20MPa-40MPa, the 7d shrinkage rate is 0με-100με, the 28d bonding strength is 1MPa-3MPa, and the 28d chloride ion rapid migration coefficient is ≤0.8×10 -12 m 2 / s, and has the advantages of film-free, maintenance-free, high crack resistance, etc. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 is a preparation flowchart of a maintenance-free lightweight type sprayed ultra-high performance concrete according to an embodiment of the present application;

[0055] Figure 2 is a schematic diagram of crack self-healing evolution behavior in embodiment 1 of the present application. DETAILED DESCRIPTION

[0056] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application. In addition, the technical features involved in the various embodiments of the present application 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 jetting ultra-high performance concrete, which comprises, by mass fraction: 700-900 parts of Portland cement, 120-200 parts of silica ash, 100-200 parts of layered mineral admixture, 30-70 parts of gradient active expansive agent, 600-800 parts of modified lightweight aggregate, 0.5-3 parts of rheological modifier, 40-80 parts of composite fiber, 7-10 parts of water reducing agent, and 170-200 parts of water.

[0058] Specifically, the modified lightweight aggregate comprises a pre-wet moisture lightweight aggregate, a slurry layer wrapped on the surface of the lightweight aggregate, and an activation layer provided on the surface of the slurry layer and used for activating the slurry layer, wherein the activation layer is doped with three-dimensional porous graphene. That is, in the present embodiment, the lightweight aggregate is first wrapped with a cement composite alkali-activated glue material, and then surface treated with three-dimensional porous graphene modified polyacrylamide, which not only realizes high strengthening, heavy weighting and surface activation of the lightweight aggregate, avoids problems such as floating, collapse, pipe blockage and lightweight stratification of the lightweight aggregate during operation, but also constructs a high-thermal-conductivity system with low-dosage three-dimensional porous graphene to timely conduct hydration heat energy and reduce the temperature difference between the inside and outside of the slurry.

[0059] Based on the above embodiment, in the present embodiment, the modified lightweight aggregate is prepared by the following method: pre-wetting the lightweight aggregate, wrapping it with slurry after the surface is saturated and dry, the thickness of the slurry is not more than 1 mm, and the slurry is left to stand for 24 hours after wrapping, and the standby material is obtained after the slurry hardens; the standby material is soaked in a three-dimensional porous graphene modified polyacrylamide solution for 2 hours for surface activation, and the modified lightweight aggregate is obtained after drying; the slurry is composed of 40-60 parts of cement, 40-60 parts of alkali-activated glue material, 10-20 parts of water glass, and 20-40 parts of water by mass fraction; the alkali-activated glue material is one or more of metakaolin and ultra-fine mineral powder; the preparation steps of the three-dimensional porous graphene modified polyacrylamide solution include: dissolving polyacrylamide powder in water to form a 0.5‰ polyacrylamide solution, adjusting the pH value of the solution to above 12 with calcium hydroxide, then adding three-dimensional porous graphene with a mass ratio of 2% to the solution to form a mixed solution, and ultrasonic dispersing the mixed solution in an environment of 50-60℃ for 2 hours to obtain the three-dimensional porous graphene modified polyacrylamide solution.

[0060] Based on the scheme of any of the above embodiments or combinations of multiple embodiments, in the embodiment, the lightweight aggregate is first subjected to saturated pre-wetting treatment, when the water in the paste is continuously consumed to a certain extent with cement hydration, the pre-wetting water will be released from the lightweight aggregate into the paste in time, thereby increasing the relative humidity of the paste and reducing the shrinkage of UHPC; secondly, a cement composite alkali-activated glue material is used to coat the surface of the lightweight aggregate to form a high-strength cement stone-polymer shell, which not only avoids the performance loss caused by the low strength of the lightweight aggregate, but also effectively alleviates the problems of lightweight aggregate floating, lightweight stratification and pipe collapse caused by water absorption effect during pumping due to the increase of the average density of the lightweight aggregate and the blocking effect of the water absorption channel of the high-strength shell; finally, the surface of the lightweight aggregate is activated by a three-dimensional porous graphene modified polyacrylamide solution, the polyacrylamide on the surface of the lightweight aggregate forms hydrogen bonds with the organic components in the paste in water, and is crosslinked into a three-dimensional network structure, effectively increasing the adhesion between the surface of the lightweight aggregate and the paste, and avoiding the stratification of the aggregate during the spraying process; and the three-dimensional porous graphene can construct a high-thermal-conductivity system at a low dosage, which can timely conduct the large amount of heat generated by cement hydration to reduce the temperature difference between the inside and outside of the paste and reduce temperature cracks.

[0061] Based on the scheme of any of the above embodiments or combinations of multiple embodiments, in the embodiment, the layered mineral admixture uses one or more of metakaolin, diatomite and bentonite. The metakaolin, diatomite and bentonite and other admixtures have fine particles and high activity, and their filling effect and pozzolanic effect can increase the density of UHPC, improve the microstructure of the paste and increase the late strength of UHPC; the layered structure has the characteristics of large specific surface area and strong water absorption, and 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 curing period to play the internal curing effect.

[0062] According to the scheme of any or multiple combinations of the above embodiments, in the embodiment, the expansive agent comprises, by mass fraction, 50-60 parts of calcium oxide expansive agent, 25-35 parts of high-activity natural anhydrite, and 15-25 parts of medium-activity natural anhydrite, wherein the calcium oxide expansive agent has a 7d limited expansion rate in water of greater than or equal to 0.55%, the high-activity natural anhydrite has an average particle size of 10-20 microns, and the medium-activity natural anhydrite has an average particle size of 30-40 microns. The calcium oxide expansive agent has high early activity and large expansion efficiency, and the expansion product has high filling property for plastic cracks, with a plastic crack repair rate of 95%, which can greatly compensate for the early shrinkage of UHPC and achieve film-free curing of lightweight sprayed UHPC. The high-activity natural anhydrite mainly compensates for the medium-term shrinkage of UHPC, and the medium-activity natural anhydrite mainly compensates for the late-term shrinkage of UHPC, thereby enhancing the late-term crack self-repairing performance of UHPC. In addition, the water release window of the internal curing material matches the expansion window, provides sufficient water for the expansive agent, strengthens the expansion efficiency of the expansive agent, and forms a plastic crack self-healing, early-term to medium-term to late-term gradient shrinkage compensation, and late-term crack self-repairing technology. Furthermore, the use of natural anhydrite as the expansive agent can promote the generation and stable existence of ettringite (high-sulfur type hydrated calcium sulphoaluminate), effectively avoiding problems such as expansion and shrinkage, strength decay, and durability degradation caused by the conversion of ettringite to monosulfur type hydrated calcium sulphoaluminate due to the reduction of sulfate ions.

[0063] According to the scheme of any or multiple combinations of the above embodiments, in the embodiment, the initial aggregate of the modified lightweight aggregate is one or more of ceramic sand, pumice, and expanded perlite; the particle size of the initial aggregate is not greater than 4 mm, and the bulk density is less than or equal to 800 kg / m 3 , and the cylinder compressive strength is greater than or equal to 7 MPa.

[0064] According to the scheme of any or multiple combinations of the above embodiments, in the embodiment, the rheological modifier is composed of 8-10 parts of a rheological adjusting component and 20-40 parts of an interface bonding component; the rheological adjusting component comprises, by mass fraction, 6-10 parts of wood fiber and 1-3 parts of polyacrylamide; and the interface bonding component is a redispersible latex powder. Compared with the traditional rheological modifier that only regulates the rheological property, the wood fiber used in the present application can not only improve the viscosity, thixotropy, and anti-sagging property of UHPC, but also improve the pumping performance of UHPC due to its air entraining property, improve the shrinkage of UHPC due to its hydrophilicity, and inhibit the microcracks of UHPC and improve the crack resistance of UHPC due to its fiber crack resistance; and the redispersible latex powder used in the present application can penetrate into the interface between the reinforced layer and the original structure and solidify into a film, thereby strengthening the interface bonding property.

[0065] In the embodiment based on the scheme of any of the above embodiments or a combination of multiple embodiments, the wood fibers have a length of 800-1000 μm; the polyacrylamide is anionic and has a molecular weight of 800-1200; and the redispersible latex powder is an ethylene-vinyl acetate polymer.

[0066] In the embodiment based on the scheme of any of the above embodiments or a combination of multiple embodiments, the composite fibers are composed of 5-15 parts of medium-length steel fibers and 0.1-1 parts of chopped plant fibers by mass fraction; the steel fibers have a length of 10 mm-15 mm, and the plant fibers have a length of 1-3 mm; and the plant fibers are one or more of sisal, flax, ramie, jute, coconut shell, and bamboo fibers. The use of medium-length steel fibers, chopped plant fibers, and micron-level wood fibers can respectively inhibit visible macro cracks, small cracks, and micro cracks, form a gradient crack resistance technology, and enhance the crack resistance of the UHPC. In addition, the plant fibers, as hydrophilic fibers, can play an internal curing effect to reduce shrinkage and improve the microstructure of the UHPC matrix.

[0067] In the embodiment based on the scheme of any of the above embodiments or a combination of multiple embodiments, the water reducing agent is a shrinkage-reducing polycarboxylic powder water reducing agent with a water reducing rate of ≥30%.

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

[0069] S1, adding Portland cement, silica fume, layered mineral admixture, expanding agent, modified lightweight aggregate, and water reducing agent into a stirring pot.

[0070] S2, slowly adding water into the stirring pot and stirring to a fluidized state, and then adding composite fibers and stirring until uniform.

[0071] S3, adding a rheological composite agent and stirring until uniform, to obtain the well-mixed lightweight jetting ultra-high performance concrete.

[0072] In the embodiment, the optimization of the stirring sequence and other processes can effectively ensure the uniform dispersion of the components of the UHPC and prevent phenomena such as aggregate floating and fiber agglomeration.

[0073] In the embodiment based on the scheme of any of the above embodiments or a combination of multiple embodiments, the maintenance-free lightweight jetting ultra-high performance concrete is used in the field of bridge reinforcement to accelerate the construction speed, improve the construction efficiency, greatly improve the performance of the reinforcement layer, eliminate the need for coating and maintenance, and realize the high performance, lightweight, and high efficiency of the bridge reinforcement material.

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

[0075] 1) The lightweight aggregate is subjected to saturated pre-wetting treatment, and after the surface is dry, it is left for standby.

[0076] 2) Select cement 50 parts, alkali-activated adhesive material 40 parts, water glass 15 parts, and water 25 parts by mass fraction, and add them into a mortar mixer in turn to stir until fluidization, to prepare a slurry.

[0077] 3) The saturated pre-wetting lightweight aggregate with a dry surface is wrapped in the slurry, the wrapping thickness is not greater than 1 mm, and after wrapping, it is left to stand for 24 h, and after the slurry body hardens, the standby material is obtained.

[0078] 4) Polyacrylamide powder is dissolved in water to form a polyacrylamide solution with a concentration of 0.5 ‰, and calcium hydroxide is used to adjust the PH value of the solution to above 12; 2% of the solution by mass is added to form a mixed solution; the mixed solution is placed in a 55℃ environment for ultrasonic dispersion for 2 h to prepare a three-dimensional porous graphene modified polyacrylamide solution.

[0079] 5) The standby material is soaked in the three-dimensional porous graphene modified polyacrylamide solution for 2 h for surface activation, and after being taken out, it is dried to obtain the modified lightweight aggregate.

[0080] In addition, the maintenance-free lightweight type jetting ultra-high performance concrete prepared by any embodiment or combination of multiple embodiments of the present application can be applied to bridge, tunnel, culvert reinforcement and support, and during application, when the water in the wrapping layer is continuously consumed to a certain extent with cement hydration, the pre-wetting water will be released from the lightweight aggregate into the wrapping layer in time;

[0081] In addition, the polyacrylamide in the activation layer and the organic components in the wrapping layer form hydrogen bonds in water, and multiple hydrogen bonds are crosslinked into a three-dimensional network structure to increase the adhesion between the surface of the lightweight aggregate and the wrapping layer.

[0082] The specific implementation of the present application will be described below in combination with a specific engineering embodiment.

[0083] Example 1

[0084] Example 1 provides a maintenance-free lightweight type jetting ultra-high performance concrete, and the preparation method is as follows:

[0085] (1) Based on the modified Andre-Anderson model, the benchmark mix ratio of the lightweight type jetting UHPC is designed to determine the volume ratio of cement, silica fume, admixture and modified lightweight aggregate; based on the closest wet packing theory, the parameters of water reducing agent and water are determined; according to the performance design, the proportion of expansive agent and steel fiber is determined, and the obtained lightweight type jetting UHPC mix ratio is shown in Table 1.

[0086] (2) First, the Portland cement, silica fume, layered mineral admixture, expansion agent, modified lightweight aggregate, water reducing agent are added into the stirring pot and mixed evenly; then slowly add water and stir until fluidization, after fluidization, add composite fiber, stir until uniform; finally add rheological modifier, stir evenly to get the mixed lightweight type sprayed UHPC.

[0087] (3) The mixed UHPC is sprayed on the structure to be reinforced, and the lightweight type sprayed UHPC reinforcement construction is completed.

[0088] Table 1 lightweight type sprayed UHPC mix proportion (kg / m 3 )

[0089]

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

[0093] In this embodiment, the rheological modifier is composed of 8 parts of wood fiber, 2 parts of polyacrylamide and 35 parts of redispersible latex powder by mass fraction.

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

[0095] Example 2

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

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

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

[0099] In this embodiment, the composite fiber is composed of 10 parts of steel fiber and 0.2 parts of plant fiber by mass.

[0100] Comparative Example 1

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

[0102] Comparative Example 2

[0103] Comparative Example 2 is basically the same as Example 1, except that the lightweight aggregate of Comparative Example 2 is only wrapped with slurry and is not soaked in the three-dimensional porous graphene modified polyacrylamide solution.

[0104] Comparative Example 3

[0105] Comparative Example 3 is basically the same as Example 1, except that the fine aggregate of Comparative Example 3 is all equal-volume quartz sand without lightweight aggregate.

[0106] Comparative Example 4

[0107] Comparative Example 4 is basically the same as Example 1, except that the expansive agent of Comparative Example 4 is all calcium oxide.

[0108] Comparative Example 5

[0109] Comparative Example 5 is basically the same as Example 1, except that the expansive agent of Comparative Example 5 is composed of 55 parts of calcium oxide and 50 parts of magnesium oxide expansive agent.

[0110] Comparative Example 6

[0111] Comparative Example 6 is basically the same as Example 1, except that the expansive agent of Comparative Example 6 is composed 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 basically the same as Example 1, except that Comparative Example 7 does not use a rheological modifier.

[0114] Comparative Example 8

[0115] Comparative Example 8 is basically the same as Example 1, except that the rheological modifier used in Comparative Example 8 is composed of 8 parts of wood fiber and 2 parts of polyacrylamide without an interfacial bonding component.

[0116] Comparative Example 9

[0117] Comparative Example 9 is substantially identical to Example 1, except that the rheology control agent used in Comparative Example 9 is composed 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 substantially identical to 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 control agent used is composed of 8 parts of hydroxypropyl methylcellulose, 2 parts of polyacrylamide, and 35 parts of redispersible latex powder; and 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 substantially identical to Example 1, except that the rheology control agent used in Comparative Example 11 is composed 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 flow and apparent density of the ultra-high performance concrete prepared in each example were tested according to the test method of the Standard Test Methods for Properties of Ordinary Concrete Mixtures GB / T 50080-2016, the viscosity and yield stress were tested using a rotational rheometer, the shrinkage performance of the test piece was tested according to the Standard Test Methods for Long-term Properties and Durability of Ordinary Concrete GB / T 50082-2009, the shrinkage test piece was directly cast into shape, the final setting was taken as the test zero point, the non-contact method was used to test the shrinkage within 3d after the final setting, and the contact method was used to test the shrinkage after 3d of molding; the mechanical properties, horizontal and vertical rebound rates, bonding strength, and resistance to chloride ion penetration performance were tested according to the Technical Specification for Shotcrete JGJ / T 372-2016, the test pieces for mechanical properties and resistance to chloride ion penetration performance were cut from a shotcrete large plate with a size of not less than 450mm x 450mm x 120mm, the bonding strength was measured by directly axially pulling the rock-UHPC layer binary core test piece; a shotcrete large plate was also made by a one-time shot forming method for testing the maximum single shot thickness, after the shot was completed, it was placed outdoors for static protection without any curing measures such as coating and watering, a crack observation instrument was used to observe and record the length and width of the cracks on the shot surface within 24h after the shot was completed, the total cracking area per unit area was calculated according to the Standard Test Methods for Long-term Properties and Durability of Ordinary Concrete GB / T 50082-2009, and the test results are shown in Tables 1 and 2.

[0123] Table 1 Working performance, rheological performance, and shot performance of lightweight shot UHPC prepared in Examples 1-2 and Comparative Examples 1-11

[0124]

[0125]

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

[0127]

[0128]

[0129] The crack resistance and self-repairing performance of the examples were tested according to the Standard Test Methods for Long-term Performance and Durability of Ordinary Concrete GB / T 50082-2009. After the UHPC was poured into the mold, the surface center of the test piece was subjected to a wind speed of not less than 5 m / s using a fan to induce surface cracking. After blowing for 1 h (1 h after molding), the fan was turned off and the surface crack changes were observed and the cracking area was counted after 23 h of standing. The crack statistics are shown in Table 3, and the crack evolution of Example 1 is shown in Figure 2 .

[0130] Table 3 Self-repairing performance of lightweight type jetting UHPC prepared in Examples 1-2 and Comparative Examples 1-11

[0131]

[0132]

[0133] The results in Tables 1-3 show that the lightweight type jetting ultra-high performance concrete prepared in Examples 1-2 not only meets the requirements of lightweight, high performance, high interfacial adhesion of reinforcing materials, but also has excellent workability, rheological properties and jetting performance, which can realize efficient jetting construction. The low shrinkage / micro-expansion technology of physical and chemical synergy of internal curing and the fiber grading crack resistance technology make it have the characteristics of low shrinkage, high crack resistance and efficient self-repairing, which can realize the non-coating and non-maintenance of special-shaped structure reinforcement. The jetting construction method of the non-maintenance lightweight type jetting ultra-high performance concrete prepared by the present application significantly improves the construction efficiency, and the lightweight high-strength characteristics not only greatly improve the bearing capacity of the damaged structure, but also reduce the negative effects of its own load on the original structure. In addition, the high durability, low shrinkage, high crack resistance and self-healing performance greatly reduce the maintenance cost in the later period and prolong the service life of the structure.

[0134] Compared with Example 1, the original aggregate used in Comparative Example 1 was not treated at all, and the light aggregate was seriously layered during the jetting process. Comparative Example 2 used a slurry treatment on the original light aggregate, but did not perform surface activation in the three-dimensional porous graphene modified polyacrylamide solution, and the light aggregate still showed slight layering during the jetting process.

[0135] Compared with Example 1, the apparent density of the UHPC prepared by using quartz sand in Comparative Example 3 is high, the shrinkage is significantly increased, and the crack resistance and self-repairing ability are both significantly decreased.

[0136] Compared with Example 1, the shrinkage of the UHPC prepared by using calcium oxide expansive agent in Comparative Example 4 is significantly increased, especially the late shrinkage, and the mechanical properties are all decreased. The calcium oxide expansive agent has high activity and large early expansion amount, and starts to react in the plastic period, which produces large invalid expansion amount. Not only does it lead to insufficient expansion compensation shrinkage in the later period, but also the reverse use of water affects the cement hydration process in the plastic period, thereby affecting the mechanical properties of the UHPC.

[0137] Those skilled in the art will easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A maintenance-free lightweight type jetted ultra-high performance concrete, characterized by, Components comprising the following mass parts: 700~900 parts of Portland cement, 120~200 parts of silica ash, 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 rheological modifier, 40~80 parts of composite fiber, 7~10 parts of water reducing agent, 170 parts~200 parts of water; the layered mineral admixture is one or more of metakaolin and bentonite; The modified lightweight aggregate includes a pre-wet moisture lightweight aggregate, a slurry layer wrapped on the surface of the lightweight aggregate, and an activation layer provided on the surface of the slurry layer and used for activating the slurry layer, the activation layer includes three-dimensional porous graphene and polyacrylamide, the slurry layer is prepared from a slurry, and the slurry includes 40-60 parts of cement, 10-20 parts of water glass, 20-40 parts of water, and 40-60 parts of alkali-activated adhesive material.

2. A maintenance-free lightweight type jetted ultra high performance concrete according to claim 1, characterized in that, The alkali-activated adhesive material is one or more of metakaolin and ultra-fine mineral powder.

3. A maintenance-free lightweight type jetted ultra high performance concrete according to claim 1, characterized by, The initial aggregate of the lightweight aggregate is one or more of ceramic sand, pumice, and expanded perlite, the particle size of the initial aggregate is not greater than 4 mm, the bulk density of the initial aggregate is ≤700 kg / m3, and the cylinder compressive strength of the initial aggregate is ≥7 MPa.

4. A maintenance-free lightweight sprayed ultra-high-performance concrete according to claim 1, characterized in that, The gradient active expansion agent includes, in mass parts, 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 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 10μm~20μm, and the average particle size of the medium-activity natural anhydrite is 30μm~40μm.

5. A maintenance-free lightweight type jetted ultra high performance concrete according to claim 1, characterized in that, The rheological modifier includes 8-10 parts of a rheological adjusting component and 20-40 parts of an interfacial bonding component, the rheological adjusting component includes, in mass parts, 6-10 parts of wood fiber and 1-3 parts of polyacrylamide; The interfacial bonding component is a redispersible latex powder, the wood fiber has a length of 800-1000μm; The polyacrylamide is anionic and has a molecular weight of 800-1200, and the redispersible latex powder is an ethylene-vinyl acetate polymer; The composite fiber includes, in mass parts, 5-15 parts of medium-length steel fiber and 0.1-1 part of short-cut plant fiber; The steel fiber has a length of 10mm~15mm, the plant fiber has a length of 1~3mm, the plant fiber is one or more of sisal, flax, ramie, jute, coconut shell, and bamboo fiber, and the water reducing agent is a shrinkage-type polycarboxylic acid powder water reducing agent with a water reducing rate of ≥30%.

6. A method for preparing a maintenance-free lightweight type of sprayed ultra-high performance concrete, characterized by, The application of the maintenance-free lightweight jet ultra-high performance concrete as claimed in any one of claims 1-5 comprises: Step one, preparing Portland cement, silica ash, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate, rheological modifier, composite fiber, water reducing agent, and water according to the component ratio of the maintenance-free lightweight jet ultra-high performance concrete; Step two, adding Portland cement, silica ash, layered mineral admixture, gradient active expansion agent, modified lightweight aggregate, and water reducing agent into a stirring pot; Step three, slowly add water to the stirring pot and stir to fluidization, after fluidization, add composite fibers, stir until uniform; Step four, add rheological modifier to the mixture prepared in step three, stir until uniform, to obtain the mixed lightweight jet super high performance concrete.

7. A method of preparing a maintenance-free lightweight type jetted ultra-high performance concrete according to claim 6, characterized in that, The preparation method of the modified lightweight aggregate comprises: First, prepare the slurry layer: pre-wet the lightweight aggregate, and after the saturated surface is dry, wrap it in the slurry with a thickness of not more than 1mm, then stand still after wrapping, and obtain the standby material after the slurry hardens; Second, prepare the activation layer: soak the standby material in the three-dimensional porous graphene modified polyacrylamide solution for surface activation, and dry it after taking out to obtain the modified lightweight aggregate; The preparation steps of the three-dimensional porous graphene modified polyacrylamide solution comprise: First, dissolve the polyacrylamide powder in water to form a polyacrylamide solution with a concentration of 0.5‰, and adjust the PH value of the solution to above 12 by using calcium hydroxide; Next, add three-dimensional porous graphene with a solution mass ratio of 2% to form a mixed solution; Finally, place the mixed solution in an environment of 50-60℃ for ultrasonic dispersion, to obtain the three-dimensional porous graphene modified polyacrylamide solution.

8. The application of the maintenance-free lightweight jet super high performance concrete according to any one of claims 1-5 in bridge, tunnel, culvert reinforcement and support.

9. The application of maintenance-free light-weight jetted ultra-high performance concrete according to claim 8 in the bridge, tunnel, culvert reinforcement and support, characterized in that, During application, when the water in the slurry layer is continuously consumed to a certain extent with cement hydration, the pre-wet water will be released from the lightweight aggregate into the slurry layer in time.

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