Low-viscosity high-bonding ultra-high performance concrete and preparation method thereof

Abstract

The application discloses a kind of low viscosity high adhesive super high performance concrete, including the following weight parts of raw materials: cement 515~625 parts, fly ash 200~260 parts, silica ash 120~170 parts, limestone powder 185~215 parts, graphene oxide 1.0~1.3 parts, fine aggregate 900~1100 parts, composite water reducing agent 23.4~30.1 parts, air entraining agent 0.035~0.061 parts, steel fiber 140~180 parts, water 172~185 parts.The super high performance concrete of the application considers low viscosity, high adhesive, and high mechanical properties and other characteristics, can effectively improve the construction performance of super high performance concrete and its bonding performance with old bridge concrete and steel structure under complex working conditions, etc., multidirectional guarantee the structural bearing capacity of bridge structure after reinforcement, prolong the service life of bridge engineering.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a low-viscosity, high-adhesion, ultra-high-performance concrete and its preparation method. Background Technology

[0002] With the continuous advancement of socio-economic development and urbanization, population growth and increased transportation demands mean that existing bridges may no longer be able to meet the growing traffic flow and load. At the same time, as bridge structures age, they may be affected by various factors such as natural disasters and material fatigue, leading to structural aging. These problems threaten the safe operation of bridge structures and cause significant socio-economic losses.

[0003] Demolishing old bridges and building new ones involves a high economic burden, while reinforcing existing old bridges is relatively cheaper. Given limited social resources, reinforcing existing old bridges becomes an economical and efficient solution. Using concrete encasing for bridge reinforcement is a common method, effectively improving the bridge's load-bearing capacity, extending its service life, and enhancing its seismic performance. Concrete is a widely available and inexpensive raw material, making it a highly cost-effective bridge reinforcement material. However, ordinary concrete currently suffers from poor workability, poor bond durability, and large structural dimensions. Therefore, improving the pourability and pumpability of concrete encasing materials, the long-term durability of reinforced structures, and lightweight, low-carbon reinforcement structures have become hot research topics.

[0004] Ultra-high performance concrete (UHVPC) is one of the most innovative cement-based composite materials of the 21st century, possessing extremely high mechanical properties and excellent durability, making it a hot topic in concrete materials research. However, traditional UHVPCs typically have high cementitious material content, low water-cement ratios, and high mixture viscosity, which is unfavorable for bridge reinforcement construction under complex and narrow construction conditions, easily leading to potential quality defects. In addition, the mix design of traditional UHVPCs usually does not consider improving the bond strength with the old concrete, and cannot effectively improve the load-bearing capacity and extend the service life of bridges through reinforcement processes such as external wrapping. Summary of the Invention

[0005] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a low-viscosity, high-adhesion, ultra-high-performance concrete for bridge reinforcement. This concrete combines low viscosity, high adhesion, and high mechanical properties, effectively improving the pouring and pumping performance of ultra-high-performance concrete under complex working conditions, as well as its bonding performance with the concrete and steel structure of old bridges. This comprehensively ensures the structural bearing capacity of the reinforced bridge structure and extends the service life of the bridge project.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A low-viscosity, high-adhesion, ultra-high-performance concrete comprises the following raw materials in parts by weight: 515-625 parts cement, 200-260 parts fly ash, 120-170 parts silica fume, 185-215 parts limestone powder, 1.0-1.3 parts graphene oxide, 900-1100 parts fine aggregate, 23.4-30.1 parts composite water-reducing agent, 0.035-0.061 parts air-entraining agent, 140-180 parts steel fiber, and 172-185 parts water; wherein the composite water-reducing agent is composed of ether-based water-reducing masterbatch and ether-based slump-retaining masterbatch.

[0008] In the above scheme, the water-reducing agent is a self-made high water-reducing standard polycarboxylate water-reducing agent with a water reduction rate of ≥40%. Since ether-based water-reducing masterbatch and ether-based slump-retaining masterbatch have good compatibility with powder materials such as fly ash microspheres, silica fume, and ultrafine limestone powder, they can be effectively adsorbed on the surface of powder materials, increasing free water and reducing viscosity.

[0009] In the above scheme, the solid content of the ether-based water-reducing masterbatch is 40-50%, and the solid content of the ether-based slump-retaining masterbatch is 40-50%.

[0010] In the above scheme, the mass ratio of the ether-based water-reducing masterbatch to the ether-based slump-retaining masterbatch is 1:0.5 to 1.0.

[0011] Furthermore, the ether-based water-reducing masterbatch is obtained by polymerization of acrylic acid, allyl polyoxyethylene ether, and mercaptopropionic acid as the main raw materials; wherein the mass ratio of mercaptopropionic acid, acrylic acid, and allyl polyoxyethylene ether is 1:15-25:75-85.

[0012] Furthermore, the polymerization reaction adopts an oxidation-reduction system, which includes an oxidant and a reducing agent. The oxidant can be ammonium persulfate, etc., and the reducing agent can be vitamin C, etc. The mass ratio of oxidant, reducing agent and mercaptopropionic acid is 0.55-0.65:0.35-0.45:1.

[0013] In the above scheme, the polymerization reaction is carried out at a temperature of 30-35°C for 7-8 hours.

[0014] In the above scheme, the molecular weight of the allyl polyoxyethylene ether is 300-400.

[0015] In the above scheme, the ether-based slump-preserving masterbatch is obtained by polymerization reaction of acrylic acid, hydroxyethyl acrylate, allyl polyoxyethylene ether, and mercaptopropionic acid as the main raw materials; wherein, the mass ratio of mercaptopropionic acid, acrylic acid, hydroxyethyl acrylate, and allyl polyoxyethylene ether is 1:10~20:15~25:55~65.

[0016] In the above scheme, the polymerization reaction adopts an oxidation-reduction system, which includes an oxidant and a reducing agent. The oxidant can be ammonium persulfate, etc., and the reducing agent can be vitamin C, etc. The mass ratio of oxidant, reducing agent and mercaptopropionic acid is 0.55-65:0.35-0.45:1.

[0017] In the above scheme, the polymerization reaction is carried out at a temperature of 40-45°C for 6-8 hours.

[0018] In the above scheme, the molecular weight of the allyl polyoxyethylene ether is 300-400.

[0019] In the above scheme, the cement is silicate or ordinary silicate cement, and its specific surface area is not higher than 380m². 2 / kg, with a strength grade of 52.5 or higher.

[0020] In the above scheme, the fly ash is ultrafine fly ash with a fineness (D50) ≤ 3 μm, a water requirement ratio ≤ 90%, and a 28-day strength activity index ≥ 110%.

[0021] In the above scheme, the silica fume is semi-densified silica fume with a specific surface area of ​​15m³. 2 The content of silica is above 90.0 wt%, the 28-day strength activity index is ≥105%, and the silica content is above 90.0 wt%.

[0022] In the above scheme, the limestone powder is ultrafine limestone powder with a fineness of ≤5% residue on a 0.045mm sieve and a specific surface area of ​​600-800m². 2 / kg, MB value ≤1.2, water requirement ratio ≤95%.

[0023] In the above scheme, the graphene oxide is reduced graphene oxide powder; specifically, it is prepared by chemical oxidation-reduction method using natural flake graphite as raw material (reduced graphene oxide powder prepared by other methods has a significant impact on the workability of the ultra-high performance concrete of this invention); its specific surface area is 350-450 m² / g. 2 / kg, fineness (D50) ≤ 5μm, number of layers is 1 to 5.

[0024] In the above scheme, the graphene oxide is reduced graphene oxide powder, and the fine aggregate is composed of multi-graded quartz sand powder with a gradation of 20-40 mesh, 40-80 mesh, 80-120 mesh, and 325 mesh. The composite ratio is determined to be 20-40 mesh: 40-80 mesh: 80-120 mesh: 325 mesh = 1.3-2.7: 2.4-3.6: 3.6-4.4: 0.7-1.3.

[0025] In the above scheme, the air-entraining agent is a cetyldimethylethylammonium bromide anionic surfactant, which is a pale yellow liquid with a pH value of 6 to 9. The air-entraining agent can introduce tiny, stable air bubbles into the concrete. The presence of air bubbles can reduce the friction between the phases of the mixture, making the mixture easier to flow and pump, and improving the castability of ultra-high performance concrete.

[0026] In the above scheme, the steel fiber is copper-plated microfiber steel fiber, which is straight, with an average diameter of 0.18 to 0.22 mm, a length of 12 to 14 mm, and a tensile strength ≥2450 MPa.

[0027] The above-mentioned method for preparing low-viscosity, high-adhesion, ultra-high-performance concrete includes the following steps:

[0028] S1. Weigh out the cement, fly ash, silica fume, limestone powder, fine aggregate and graphene oxide powder according to the proportions, put them into the mixer and mix evenly;

[0029] S2. After mixing the weighed water and air-entraining agent with the composite water-reducing agent, prepare a composite admixture solution, and add it to the mixture obtained in S1 and stir until the powder material is completely fluidized into a plastic state;

[0030] S3. Add steel fibers in proportion and stir evenly (4-6 minutes) to obtain ultra-high performance concrete mixture, which can then be poured and cured according to standard until the specified age.

[0031] The low-viscosity, high-adhesion ultra-high performance concrete prepared according to the above scheme has a spread of 760–850 mm, a T500 time of 4.7–6.6 s, a V-leakage time of 5.9–8.3 s, a viscosity of 7.1–9.7 Pa·s, an air content of ≤4.0%, a 28-day compressive strength of 138–157 MPa, a flexural strength of 23.2–26.6 MPa, and a splitting bond strength of 5.78–6.45 MPa.

[0032] The principle of this invention is as follows:

[0033] In the composite water-reducing agent (viscosity-reducing polycarboxylate superdispersible water-reducing agent) designed and optimized in this invention, both the ether-based water-reducing masterbatch and the ether-based slump-retaining masterbatch are prepared using low molecular weight allyl polyoxyethylene ether. After incorporation into the composite water-reducing agent, on the one hand, the thickness of the hydration film of the cementitious material is increased, leading to an increase in free water, thus improving fluidity and reducing the viscosity of the slurry; on the other hand, the zeta potential between cementitious material particles is increased, resulting in greater repulsion and larger interparticle spacing with smaller interaction forces, thus improving fluidity and effectively preventing the water-reducing agent molecules from entangled, thereby reducing the viscosity of the ultra-high performance concrete mixture. Under the same fluidity conditions, the composite water-reducing agent designed and optimized in this invention results in a lower water-cement ratio and higher matrix strength in the ultra-high performance concrete mixture, macroscopically improving the bonding strength of the ultra-high performance concrete. Simultaneously, the introduction of low molecular weight allyl polyoxyethylene ether in this invention effectively promotes the release of free water between cementitious material particles, participating in the hydration and secondary hydration of cement and mineral admixtures, further synergistically enhancing the interlayer molecular forces of the hydration products, and microscopically improving the bonding strength of the ultra-high performance concrete.

[0034] The introduced ultrafine fly ash microspheres are a novel sub-nano powder material. Microscopically, they are spherical with small particle sizes, exhibiting good ball-bearing properties and requiring less water. Through their morphology and filling effect, they can effectively reduce the viscosity of ultra-high performance concrete mixtures. The mineral admixtures used in this invention—fly ash microspheres, silica fume, and ultrafine limestone powder—have small particle sizes, effectively filling the gaps between cement and aggregate, resulting in the densest packing of the ultra-high performance concrete material system. This allows for the release of free water from cement-cement, cement-aggregate, cement-mineral admixtures of different particle sizes, and between different mineral admixtures. With the same water consumption, the available free water in ultra-high performance concrete increases, further reducing the viscosity of the ultra-high performance concrete mixture. Furthermore, the mineral admixtures used—fly ash microspheres, silica fume, and ultrafine limestone powder—all possess extremely strong pozzolanic activity. They can undergo a secondary hydration reaction with the cement hydration product Ca(OH)2 to generate a high-quality, insoluble product, hydrated silicate (CSH) gel. This gel is deposited within the voids at the aggregate-cement interface, optimizing the pore structure and enhancing the basic mechanical properties of ultra-high performance concrete. High-quality CSH exhibits significant rigidity and specific surface area, and the van der Waals forces and chemical bonds between high-quality CSH particles are stronger. This can improve the interlaminar shear force of hardened ultra-high performance concrete at the microscopic and submicroscopic levels, thereby enhancing its adhesion. Simultaneously, the incorporation of multilayer graphene oxide powder utilizes graphene's excellent strength and strain hardening characteristics to disperse among the cement hydration products, strengthening the structure of the nanoscale CSH and hindering the initiation and formation of microcracks in ultra-high performance concrete, further improving its interlaminar shear strength and bond strength. This invention utilizes the volcanic activity, micro-aggregate effect, and enhanced interlayer shear force of silica fume and reduced graphene oxide powder to further optimize the pore structure and interface transition zone of ultra-high performance concrete, improve the bonding performance of ultra-high performance concrete, enhance the structural bearing capacity of bridge structures after reinforcement, and extend the service life of bridge projects.

[0035] Secondly, the viscosity-reducing polycarboxylate superplasticizer designed and optimized in this invention exhibits excellent dispersibility for cement, fly ash microspheres, silica fume, ultrafine limestone powder, and quartz powder. By adsorbing onto the surface of powder materials, the ratio of adsorbent groups to steric hindrance groups in the superplasticizer is optimized, improving the dispersing ability of the dispersant and increasing the proportion of colloidal particle dispersions. This reduces the particle size of colloidal particles, increases free water content, and further reduces the viscosity of ultra-high performance concrete mixtures. Finally, the air-entraining agent used in this invention is a hexadecyl dimethyl ethyl ammonium bromide-based anionic surfactant, which is incorporated into the ultra-high performance concrete mixture to form a large number of tiny, stable, closed spherical bubbles. These microbubbles, like ball bearings, reduce the frictional resistance between aggregate particles, thereby using chemical means to further reduce the viscosity of ultra-high performance concrete. This invention utilizes physical methods of mineral admixtures and chemical methods of functional additives to release free water between cement and cement particles from multiple directions, reducing the friction between powder particles. This synergistically improves the problems of high viscosity and difficulty in construction of traditional ultra-high performance concrete mixtures, effectively enhancing the pouring and pumping performance of ultra-high performance concrete under complex bridge reinforcement conditions, and reducing the potential quality defects in the construction of high-viscosity ultra-high performance concrete.

[0036] This invention combines physical methods using mineral admixtures with chemical methods using functional additives to release free water between cement and cement particles from multiple directions, synergistically reducing the viscosity of traditional ultra-high performance concrete and improving the problem of high viscosity and difficulty in construction of ultra-high performance concrete in the narrow working environment of bridge reinforcement. By utilizing the volcanic activity, micro-aggregate effect, and enhanced interlayer shear force of silica fume and reduced graphene oxide powder, the pore structure and interface transition zone of ultra-high performance concrete are further optimized, improving the bonding performance of ultra-high performance concrete, enhancing the structural bearing capacity of the reinforced bridge structure, and effectively extending the service life of bridge engineering.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1) This invention adopts a multi-component cementitious system based on cement, ultrafine fly ash, silica fume, and ultrafine limestone powder, combined with graphene oxide and optimized water-reducing agents, which can ensure mechanical properties while taking into account low viscosity and high adhesion. This improves the problem of high viscosity and difficulty in construction of ultra-high performance concrete in the narrow working environment of bridge reinforcement, effectively improves its bonding effect with old bridge concrete and steel structure, and ensures the structural bearing capacity of bridges and other structures after reinforcement from multiple aspects, effectively extending the service life of bridge projects.

[0039] 2) The preparation method involved in this invention is relatively simple and convenient to implement, and is suitable for widespread application. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the mixing state of the low-viscosity, high-adhesion, ultra-high-performance concrete prepared in Example 1 of the present invention;

[0041] Figure 2 This is a schematic diagram of the bonding performance test of the low-viscosity, high-adhesion ultra-high-performance concrete prepared in Example 2 of the present invention;

[0042] Figure 3 This is a SEM image of the low-viscosity, high-adhesion, ultra-high-performance concrete graphene oxide prepared in Example 1 of the present invention. Detailed Implementation

[0043] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

[0044] In the following embodiments, the cement is type II Portland cement with a strength grade of 52.5 and a specific surface area not exceeding 370 m². 2 / kg; the fly ash is ultrafine fly ash with a water requirement ratio of 88% and a 28-day strength activity index of 116%; the silica fume is semi-dense silica fume with a specific surface area of ​​15.6 m². 2 / g, 28d strength activity index 118%, silica content 94wt%; limestone powder is ultrafine limestone powder with a specific surface area of ​​640m². 2 / kg, MB value 0.7; the fine aggregate is composed of multi-graded quartz sand powder, and the determined composite ratio (mass ratio) is 20-40 mesh: 40-80 mesh: 80-120 mesh: 325 mesh = 1.8: 3.2: 4.0: 1.0.

[0045] The water-reducing agent used is a self-made high-water-reducing standard polycarboxylate water-reducing agent with a water reduction rate of 40%. The specific preparation method includes the following steps:

[0046] 1) Ether-based water-reducing masterbatch: Acrylic acid, allyl polyoxyethylene ether 300, and mercaptopropionic acid were polymerized in an aqueous solution at 30°C under ammonium persulfate-vitamin C redox catalysis for 7 hours to obtain an ether-based water-reducing masterbatch. The mass ratio of acrylic acid, allyl polyoxyethylene ether 300, mercaptopropionic acid, ammonium persulfate, vitamin C, and water was 15:85:1:0.6:0.4:102. The solid content of the obtained ether-based water-reducing masterbatch was 50%.

[0047] 2) Ether-based slump-preserving masterbatch: Acrylic acid, hydroxyethyl acrylate, allyl polyoxyethylene ether 300, and mercaptopropionic acid were polymerized in an aqueous solution at 30°C under ammonium persulfate-vitamin C redox catalysis for 7 hours to obtain an ether-based slump-preserving masterbatch. The mass ratio of acrylic acid, hydroxyethyl acrylate, allyl polyoxyethylene ether 300, mercaptopropionic acid, ammonium persulfate, vitamin C, and water was 10:15:65:1:0.6:0.4:153. The solid content of the obtained ether-based slump-preserving masterbatch was 40%.

[0048] 3) The composite water-reducing agent is obtained by compounding ether-based water-reducing masterbatch and ether-based slump-retaining masterbatch at a mass ratio of 1:1 at room temperature.

[0049] The surfactant is a hexadecyl dimethyl ethyl ammonium bromide-based anionic surfactant; the steel fiber is a commercially available copper-plated microfiber steel fiber with a straight structure, an average diameter of 0.20–0.22 mm, a length of 12–14 mm, and a tensile strength ≥2450 MPa; the graphene oxide is reduced graphene oxide powder, prepared from natural flake graphite through a chemical oxidation-reduction method, with a specific surface area of ​​350–450 m² / g. 2 / kg, fineness (D50) ≤ 5μm, number of layers is 1 to 5.

[0050] In the following examples and comparative examples, the low-viscosity, high-adhesion ultra-high performance concrete was prepared using the following steps unless otherwise specified:

[0051] S1. Weigh out the cement, fly ash, silica fume, limestone powder, fine aggregate and graphene oxide powder according to the proportions, put them into the mixer and mix evenly;

[0052] S2. Add water and the composite additives, which are a mixture of air-entraining agent and water-reducing agent, in proportion and stir until the powder material is completely fluidized into a plastic state;

[0053] S3. Add steel fibers in proportion and stir for 4-6 minutes to obtain ultra-high performance concrete mixture, which can then be poured and cured according to standard for 28 days.

[0054] Example 1

[0055] A type of low-viscosity, high-adhesion, ultra-high-performance concrete for bridge reinforcement comprises the following raw materials and their respective weight proportions: 585 parts cement, 245 parts fly ash, 130 parts silica fume, 190 parts limestone powder, 1.17 parts self-made 3-layer graphene oxide, 1000 parts fine aggregate, 23.4 parts composite water-reducing agent, 0.046 parts air-entraining agent, 160 parts steel fiber, and 180 parts water.

[0056] from Figure 1 As can be seen from the above, the low-viscosity, high-adhesion ultra-high performance concrete for bridge reinforcement prepared in this embodiment has excellent workability and good fluidity.

[0057] Example 2

[0058] A type of low-viscosity, high-adhesion, ultra-high-performance concrete for bridge reinforcement comprises the following raw materials and their respective weight proportions: 540 parts cement, 250 parts fly ash, 170 parts silica fume, 210 parts limestone powder, 1.30 parts self-made 5-layer graphene oxide, 980 parts fine aggregate, 27.5 parts composite water-reducing agent, 0.035 parts air-entraining agent, 140 parts steel fiber, and 174 parts water.

[0059] from Figure 2 As can be seen from the above, the low-viscosity, high-adhesion ultra-high performance concrete for bridge reinforcement prepared in this embodiment has good adhesion to old concrete, and the splitting and breaking is old concrete.

[0060] Example 3

[0061] A type of low-viscosity, high-adhesion, ultra-high-performance concrete for bridge reinforcement comprises the following raw materials and their respective weight proportions: 620 parts cement, 220 parts fly ash, 150 parts silica fume, 200 parts limestone powder, 1.23 parts self-made single-layer graphene oxide, 1060 parts fine aggregate, 29.6 parts composite water-reducing agent, 0.055 parts air-entraining agent, 180 parts steel fiber, and 184 parts water.

[0062] from Figure 3 As can be seen from the data, the graphene oxide in the microstructure of the low-viscosity, high-adhesion, ultra-high-performance concrete for bridge reinforcement prepared in this embodiment is uniformly distributed, which effectively increases the strength of the concrete matrix.

[0063] Comparative Example 1

[0064] A common ultra-high performance concrete material is prepared in the same way as in Example 1, except that the ultra-high performance concrete used is a commercially available ultra-high performance dry mix. The dry mix is ​​a premixed mixture of powder materials, steel fibers, powder composite admixtures, etc., with a strength grade of C120 and a water-to-material ratio of 9.0%.

[0065] Comparative Example 2

[0066] A common ultra-high performance concrete material is prepared in the same way as in Example 1, except that the ultra-high performance concrete used is a commercially available ultra-high performance dry mix. The dry mix is ​​a premixed mixture of powder materials, steel fibers, liquid composite admixtures, etc., with a strength grade of C150 and a water-to-material ratio of 8.5%.

[0067] Comparative Example 3

[0068] A common ultra-high performance concrete was prepared using the same method as in Example 1. The raw materials and their respective weight proportions were as follows: 585 parts cement, 245 parts fly ash, 130 parts silica fume, 190 parts limestone powder, 1000 parts fine aggregate, 34.6 parts commercially available ultra-high performance concrete water-reducing agent, 0.055 parts air-entraining agent, 160 parts steel fiber, and 180 parts water. The commercially available viscosity-reducing ultra-high performance concrete water-reducing agent used had a water reduction rate of 46% and a solid content of 35.6%.

[0069] Comparative Example 4

[0070] A common ultra-high performance concrete was prepared using the same method as in Example 2. The raw materials and their respective weight proportions were as follows: 540 parts cement, 250 parts fly ash, 170 parts silica fume, 210 parts limestone powder, 42.5 parts commercially available ultra-high performance concrete water-reducing agent, 0.035 parts air-entraining agent, 140 parts steel fiber, and 174 parts water. The commercially available viscosity-reducing ultra-high performance concrete water-reducing agent used had a water reduction rate of 46% and a solid content of 35.6%.

[0071] Comparative Example 5

[0072] A type of low-viscosity, high-adhesion, ultra-high-performance concrete for bridge reinforcement comprises the following raw materials and their respective weight proportions: 620 parts cement, 220 parts fly ash, 150 parts silica fume, 200 parts limestone powder, 1.23 parts self-made single-layer graphene oxide, 1060 parts fine aggregate, 32.8 parts composite water-reducing agent, 0.055 parts air-entraining agent, 180 parts steel fiber, and 184 parts water. The preparation method of the composite water-reducing agent is roughly the same as that described in the above embodiments, except that the commonly used propylene alcohol polyoxyethylene ether APEG2400 macromonomer is used instead of the allyl polyoxyethylene.

[0073] Performance testing

[0074] The performance of the ultra-high performance concrete prepared in Examples 1-3 and Comparative Examples 1-5 was tested. The spread, T500, V-leakage time, air content, compressive strength, flexural strength, and splitting bond strength were tested according to the relevant provisions of the national standard "Test Procedures for Cement and Cement Concrete in Highway Engineering" (JG / J 3420). The slurry viscosity was measured using a Viskomat XL mortar rheometer manufactured by Schleibinger GmbH, Germany.

[0075] The test results are shown in Table 1 below:

[0076] The low-viscosity, high-adhesion ultra-high performance concrete for bridge reinforcement described in this invention has a spread of 760–850 mm, a T500 time of 4.7–6.6 seconds, a V-leakage time of 5.9–8.3 seconds, and a viscosity of 7.1–9.7 Pa·s.

[0077] With an air content of ≤4.0%, a 28-day compressive strength of 138–159 MPa, a flexural strength of 23.2–28.6 MPa, and a splitting bond strength of 5.78–6.55 MPa, it exhibits excellent castability, bonding performance, and mechanical strength.

[0078] Table 1. Concrete performance test results

[0079]

[0080] As shown in Table 1, the low-viscosity, high-bonding ultra-high performance concrete for bridge reinforcement prepared in Examples 1, 2, and 3 exhibits superior workability performance indicators such as spread, T500, V-leakage time, and viscosity compared to Comparative Examples 1, 2, 3, 4, and 5. With similar air content in the ultra-high performance concrete mixtures, the spread of these examples reaches a maximum of 845 mm, while the T500 time is reduced by more than 35%, the V-leakage time by more than 40%, and the slurry viscosity by nearly 50%. Furthermore, the compressive and flexural strengths are superior, and the bond strength is increased by more than 30%. These examples demonstrate extremely low viscosity and workability, effectively meeting the demands of complex bridge reinforcement construction environments. This is primarily due to the low-viscosity ultra-high performance concrete for bridge reinforcement prepared in this invention, which, through physical means of mineral admixtures and chemical means of self-made functional admixtures, releases free water between cement and other powder material particles in multiple directions, synergistically reducing the viscosity of traditional ultra-high performance concrete. Furthermore, the basic mechanical properties of the low-viscosity ultra-high performance concrete for bridge reinforcement prepared by this invention are no weaker than those of traditional ultra-high performance concrete, and its splitting strength is even better than that of traditional ultra-high performance concrete. It can be seen that this invention uses fly ash, silica fume, and limestone powder to replace part of the cement. The secondary hydration and micro-aggregate effect improve the microstructure of the low-viscosity ultra-high performance concrete, eliminating the reduction in mechanical properties caused by low viscosity. At the same time, by incorporating multilayer graphene oxide powder, the excellent strength and strain hardening characteristics of graphene itself are utilized to disperse between the hydration products of cement, enhance the structure of nanoscale CSH, and hinder the initiation and formation of microcracks in ultra-high performance concrete, further improving the interlayer shear capacity and bond strength of ultra-high performance concrete.

[0081] This invention is not limited to the embodiments described above. Those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention. Contents not described in detail in this specification are prior art known to those skilled in the art.

Claims

1. A low-viscosity, high-cohesion, ultra-high-performance concrete, characterized in that, The raw materials include the following parts by weight: 515-625 parts cement, 200-260 parts fly ash, 120-170 parts silica fume, 185-215 parts limestone powder, 1.0-1.3 parts graphene oxide, 900-1100 parts fine aggregate, 23.4-30.1 parts composite water-reducing agent, 0.035-0.061 parts air-entraining agent, 140-180 parts steel fiber, and 172-185 parts water; the composite water-reducing agent is composed of ether-based water-reducing masterbatch and ether-based slump-retaining masterbatch. The ether-based water-reducing masterbatch is obtained by polymerization of acrylic acid, allyl polyoxyethylene ether, and mercaptopropionic acid as the main raw materials. The ether-based slump-preserving masterbatch is obtained by polymerization reaction of acrylic acid, hydroxyethyl acrylate, allyl polyoxyethylene ether, and mercaptopropionic acid as the main raw materials. The molecular weight of the allyl polyoxyethylene ether is 300-400. In the ether-based water-reducing masterbatch, the mass ratio of mercaptopropionic acid, acrylic acid, and allyl polyoxyethylene ether is 1:15~25:75~85. In the ether-based slump-preserving masterbatch, the mass ratio of mercaptopropionic acid, acrylic acid, hydroxyethyl acrylate, and allyl polyoxyethylene ether is 1:10~20:15~25:55~65.

2. The low-viscosity, high-cohesion, ultra-high-performance concrete according to claim 1, characterized in that, The specific surface area of ​​the cement is not higher than 380m². 2 / kg, with a strength grade of 52.5 or higher; the fly ash is ultrafine fly ash with a fineness ≤3μm, a water requirement ratio ≤90%, and a 28-day strength activity index ≥110%; the silica fume is semi-dense silica fume with a specific surface area of ​​15m³. 2 The content of silica is above 90.0 wt%, the 28-day strength activity index is ≥105%, and the silica content is above 90.0 wt%.

3. The low-viscosity, high-cohesion, ultra-high-performance concrete according to claim 1, characterized in that, The limestone powder is ultrafine limestone powder, with a fineness of ≤5% residue on a 0.045mm sieve and a specific surface area of ​​600~800m². 2 / kg, MB value ≤1.2, water requirement ratio ≤95%.

4. The low-viscosity, high-cohesion, ultra-high-performance concrete according to claim 1, characterized in that, The graphene oxide mentioned is reduced graphene oxide powder with a specific surface area of ​​350~450m². 2 / kg, fineness ≤5μm, number of layers 1~5.

5. The low-viscosity, high-adhesion ultra-high performance concrete according to claim 1, characterized in that, The fine aggregate is composed of multi-graded quartz sand powder with gradations of 20~40 mesh, 40~80 mesh, 80~120 mesh, and 325 mesh. The determined composite ratio is 1.3~2.7:2.4~3.6:3.6~4.4:0.7~1.

3.

6. The low-viscosity, high-cohesion, ultra-high-performance concrete according to claim 1, characterized in that, The water reduction rate of the composite water-reducing agent is ≥40%.

7. The low-viscosity, high-adhesion ultra-high performance concrete according to claim 1, characterized in that, The air-entraining agent is hexadecyl dimethyl ethyl ammonium bromide with a pH of 6-9.

8. The method for preparing low-viscosity, high-adhesion, ultra-high-performance concrete according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Weigh out the cement, fly ash, silica fume, limestone powder, fine aggregate and graphene oxide powder according to the proportions, put them into the mixer and mix evenly; S2. After mixing the weighed water and air-entraining agent with the composite water-reducing agent, prepare a composite admixture solution, and add it to the mixture obtained in S1 and stir until the powder material is completely fluidized into a plastic state; S3. Add steel fibers in proportion and mix evenly to obtain ultra-high performance concrete mixture, pour into shape, and cure according to standard to the specified age.

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