A low-shrinkage low-hydraulic heat super high performance concrete for ring reinforcement and a preparation method thereof
By using ultra-high performance concrete with low shrinkage and low heat of hydration through dual synergistic optimization of multi-component particle size and activity, the problems of high heat of hydration, large shrinkage and easy cracking in bridge reinforcement have been solved, achieving efficient, economical and durable results in circumferential reinforcement of bridge piers.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUAXIN CEMENT CO LTD
- Filing Date
- 2024-01-26
- Publication Date
- 2026-05-15
AI Technical Summary
Existing bridge reinforcement methods suffer from problems such as high cost, long construction period, easy cracking, and uneven distribution of steel fibers. Traditional ultra-high performance concrete has high heat of hydration and large shrinkage when poured outside the bridge pier, resulting in poor reinforcement effect.
The low-shrinkage, low-heat-of-hydration ultra-high performance concrete is adopted. Through the dual synergistic optimization of multi-component particle size and activity, it uses components such as medium and low heat cement, internal curing aggregate, hydration shrinkage regulator and thickener, combined with basalt fiber and steel fiber to form a network structure, which reduces heat of hydration and shrinkage and improves tensile strength.
It achieves low heat of hydration and low shrinkage of ultra-high performance concrete without cracking in the circumferential reinforcement of bridge piers, improves bearing capacity, saves construction time and cost, and has early strength, high strength and high durability.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of building materials technology, specifically relating to a low-shrinkage, low-heat hydration ultra-high performance concrete for circumferential reinforcement and its preparation method. Background Technology
[0002] The rapid development of bridge engineering is inseparable from society's demand for travel. However, many early bridges can no longer meet current transportation volume and requirements, and have developed various problems due to years of operation. If early bridges are not reinforced and maintained, their defects will worsen, leading to a decrease in their load-bearing capacity or even destruction. Therefore, the reinforcement of existing bridges is urgently needed.
[0003] Common reinforcement methods for bridge piers include demolition and reconstruction, increasing the cross-section, bonding steel plates, and applying external prestressing. Demolition and reconstruction is costly and time-consuming. Increasing the cross-section offers advantages such as high reliability and improved load-bearing capacity, but its disadvantages include larger component volume, increased structural weight, increased foundation load, reduced space under the bridge, long construction period, and poor corrosion resistance and durability. Bonding steel plates can significantly improve the stiffness of the bridge structure, but steel plates are prone to corrosion and the welding process is complex. External prestressing also requires consideration of material durability and fire and rust prevention measures.
[0004] Ultra-high performance concrete (UHPC) refers to fiber-reinforced cementitious composite materials that possess ultra-high mechanical properties, durability, and toughness. However, UHPC uses a much higher amount of binder than ordinary concrete, and to reduce the interfacial transition zone and improve toughness, coarse aggregates are usually removed. This results in high heat of hydration and significant shrinkage in UHPC, leading to a higher risk of cracking. Therefore, in the process of reinforcing bridge piers, if ordinary UHPC is directly poured onto the outside of the pier for reinforcement, the high temperature and large shrinkage often cause large-area cracking of the UHPC layer, leading to reinforcement failure and affecting aesthetics.
[0005] Furthermore, when reinforcing existing bridge piers with externally cast UHPC, the distribution of steel fibers is often disordered due to the high fluidity of UHPC, resulting in a low proportion of fibers distributed along the circumferential direction. This is detrimental to ensuring the tensile strength of the UHPC layer in the circumferential direction of the pier, leading to an increased risk of cracking. Further exploration of low-shrinkage ultra-high performance concrete suitable for circumferential reinforcement has significant research and application value. Summary of the Invention
[0006] The main objective of this invention is to address the problems and shortcomings of existing technologies by providing a high-performance concrete with low heat of hydration, low shrinkage, and suitability for circumferential reinforcement of bridges. This aims to improve the bearing capacity of bridge piers while reducing the space occupied under the bridge and saving reinforcement time and costs.
[0007] To achieve the above objectives, the present invention adopts the following technical solution:
[0008] A low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement comprises the following components and their respective weight percentages: 500-700 parts cement, 120-200 parts silica-alumina mineral admixture, 120-240 parts silica fume, 50-100 parts ultrafine powder, 150-250 parts internal curing aggregate, 8.4-11.8 parts water-reducing agent, 2-10 parts thickener, 8-15 parts hydration shrinkage regulator, 183-275 parts steel fiber, 6-10 parts basalt fiber, 175-238 parts water, and 1000 parts fine aggregate.
[0009] In the above scheme, the cement can be one of medium-heat silicate cement, low-heat silicate cement, etc., with a strength grade of 42.5 or above.
[0010] In the above scheme, the silica-alumina mineral admixture can be one or more of fly ash, metakaolin, fly ash microspheres, etc.; its water requirement ratio is not greater than 105%, and its activity index after 28 days is not less than 70%.
[0011] In the above scheme, the water requirement ratio of the silica fume is not greater than 125%, and the 28-day activity index is not less than 105%.
[0012] In the above scheme, the ultrafine powder is one or more of quartz powder and heavy calcium carbonate powder; its specific surface area is not less than 750 kg / m². 2 .
[0013] In the above scheme, the hydration shrinkage regulator can be one or more of sodium isooctanol sulfate, lauryl sulfate, etc.
[0014] In the above scheme, the internal curing aggregate is one or more of high-alumina bauxite aggregate and ceramsite.
[0015] Furthermore, the high-alumina bauxite aggregate has a particle size of 1-3 mm or 3-5 mm, or one or more of these sizes; the alumina content in the high-alumina aggregate is not less than 80%. The ceramsite has a water absorption rate of 18-25% and a density of 700-900 kg / m³. 3 .
[0016] In the above scheme, the water-reducing agent is a powdered polycarboxylate water-reducing agent with a water reduction rate of ≥25%.
[0017] In the above scheme, the thickener is alkali-swellable thickener TT-935.
[0018] In the above scheme, the steel fiber is a straight steel fiber with a diameter of 0.15-0.21 mm, a length of 12-13 mm, and an aspect ratio of 60-70; the basalt fiber has a diameter of 0.01-0.015 mm and a length of 8-10 mm.
[0019] In the above scheme, the fine aggregate is one or more of quartz sand, manufactured sand, etc.; its maximum particle size is not greater than 4.25 mm, and the content of stone powder smaller than 0.075 mm is 5-15%.
[0020] Furthermore, the fineness of the quartz sand is 40-70 mesh; the manufactured sand is limestone manufactured sand with a fineness modulus of 2.5-2.7.
[0021] A method for preparing the aforementioned low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement includes the following steps:
[0022] 1) Raw material weighing; each raw material and its weight percentage include: cement 500-700 parts, silica-alumina mineral admixture 120-200 parts, silica fume 120-240 parts, ultrafine powder 50-100 parts, internal curing aggregate 150-250 parts, water-reducing agent 8.4-11.8 parts, thickener 2-10 parts, hydration shrinkage regulator 8-15 parts, steel fiber 183-275 parts, basalt fiber 6-10 parts, water 175-238 parts, and fine aggregate 1000 parts;
[0023] 2) Weigh out the cement, aluminosilicate mineral admixture, silica fume, ultrafine powder, water-reducing agent and fine aggregate, mix and stir to fully premix the powder to obtain mixture A;
[0024] 3) Mix the weighed water and hydration shrinkage regulator, and stir to obtain liquid B;
[0025] 4) Add the weighed internal curing aggregate into liquid B, pre-wet for 2-4 hours, and obtain mixture C;
[0026] 5) Mix mixture A with mixture C and stir until slurry is produced. Add thickener and stir evenly. Then add basalt fiber and steel fiber and stir evenly to obtain the circumferential reinforcement low-shrinkage low-hydration heat ultra-high performance concrete.
[0027] Furthermore, to ensure reinforcement performance, the concrete is poured to the specified elevation, then covered and insulated. After the UHPC hardens, it is kept in the formwork until the temperature difference between the inside and outside is no more than 20°C before demolding. After demolding, it is kept moist for 28 days.
[0028] The working principle of this invention is as follows:
[0029] This invention employs the principle of synergistic optimization of particle size and activity in multiple components. It uses cement, aluminosilicate mineral admixtures, and silica fume as the main active cementitious materials, compounded with micro / nano-scale ultrafine powders that provide physical filling to fill the gaps between particles throughout the system. This ensures that, under the action of appropriate admixtures, the entire system exhibits excellent workability while also maintaining good mechanical and durability properties.
[0030] 1) This invention employs a low heat of hydration, hydration regulation, and shrinkage regulation system. On one hand, it uses medium- and low-heat cement as the main cementitious material. Since its dominant mineral is dicalcium silicate, the content of tricalcium aluminate and tricalcium silicate, which have high heat of hydration, is low, significantly reducing the total heat release of UHPC. However, this leads to problems such as slow hydration process, slow strength development (especially slow tensile strength development in the UHPC reinforcement layer), and low resistance to shrinkage deformation, thus impacting the construction period. To address these technical problems, this invention further introduces hydration shrinkage regulation components such as sodium isooctanol sulfate and lauryl sulfate. On one hand, these two components can significantly reduce the surface tension of capillary water in UHPC, thereby reducing the self-shrinkage of UHPC and achieving a shrinkage reduction effect. On the other hand, sodium isooctanol sulfate can play an early strength role in UHPC, compensating for the slow hydration development of the system.
[0031] 2) This invention employs an internal curing aggregate-slow-release shrinkage regulation system. On one hand, high-alumina aggregate and ceramsite with a certain water absorption rate are used as internal curing aggregates to ensure that UHPC provides strength growth in the later stages. On the other hand, if the shrinkage-reducing agent acts directly on the UHPC matrix, there is a problem of mismatch between the shrinkage-reducing effect and the hydration development, resulting in good early shrinkage-reducing effect but poor inhibition of later shrinkage. Therefore, internal curing aggregate is used as a carrier for part of the shrinkage-reducing component. As the cement hydration process progresses, its pore water solution is gradually released into the capillaries, reducing the surface tension of the capillary water, thereby reducing the auto-shrinkage of UHPC in the middle and later stages, achieving an improved effect of simultaneously reducing the auto-shrinkage of UHPC in the early, middle, and late stages.
[0032] 3) This invention uses TT-935 as a thickening component. Its associative monomer structure contains both hydrophilic and hydrophobic chains, which can generate large micelle structures similar to surfactants within or between its molecules. After micelle formation, it helps to fix the emulsion particles, water molecules, or other particles in the system relatively statically, thereby reducing the mobility of these molecules (or particles). While ensuring the workability and pouring density of UHPC, it also ensures the consistency of the slurry, improves the bonding between steel fibers and the slurry, and promotes the distribution of steel fibers along the direction of slurry flow, thereby improving the overall tensile strength of the UHPC ring. On the other hand, TT-935 is a copolymer of sodium polyacrylate and butyl methacrylate. The acrylic groups in it can react with calcium ions in UHPC to generate stable compounds, reducing free calcium ions in concrete, lowering the alkalinity of UHPC, thereby reducing alkali-aggregate reaction and chloride ion penetration. At the same time, the generated polymer compounds can further fill the voids and capillaries in UHPC, improving the compactness of concrete while reducing the autogenous shrinkage of UHPC.
[0033] 4) Introducing a basalt fiber-steel fiber synergistic composite toughening system, in which the basalt fiber has a fine diameter and is dispersed in the slurry to form a network structure, which can reduce the generation of early microcracks in UHPC, especially cracks during the plastic period, and indirectly reduce the risk of later cracks; while the steel fiber can provide sufficient tensile strength for UHPC, further reducing the risk of cracking.
[0034] The low-shrinkage ultra-high performance concrete prepared according to the above scheme exhibits excellent mechanical properties. Its 1-day compressive strength reaches a maximum of 68.1 MPa, 1-day tensile strength reaches a maximum of 8.2 MPa, 3-day compressive strength reaches a maximum of 128.3 MPa, 3-day tensile strength reaches a maximum of 10.5 MPa, 28-day compressive strength reaches a maximum of 155.3 MPa, and 28-day tensile strength reaches a maximum of 13.8 MPa. It also has low heat of hydration, with a maximum adiabatic temperature rise of 48.5℃, far lower than the 70–80℃ of ordinary UHPC. Furthermore, it exhibits low shrinkage, with 3-day autogenous shrinkage less than 50 μm / m, 7-day autogenous shrinkage less than 80 μm / m, and 28-day autogenous shrinkage less than 200 μm / m, far lower than the 500–900 μm / m of traditional UHPC at 28 days. Finally, it demonstrates excellent durability, with a chloride ion permeability coefficient less than 2 × 10⁻⁶. -14 m 2 ·s -1 After 500 freeze-thaw cycles, the mass loss was 0, and the relative dynamic elastic modulus was 99.8%.
[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0036] 1) The low-shrinkage, low-heat-of-hydration ultra-high performance concrete of the present invention, while ensuring the construction performance of UHPC without affecting the construction period, also takes into account extremely low shrinkage rate, low heat of hydration, high tensile strength, good workability and durability.
[0037] 2) The low-shrinkage, low-heat-of-hydration ultra-high performance concrete described in this invention can be used for external casting reinforcement of ring-shaped structures such as bridge piers of existing bridges. Due to its low heat of hydration, low shrinkage, and high tensile strength, it can still ensure the integrity of the UHPC layer without cracking under such a high-constraint environment and give full play to its excellent mechanical properties. In addition, the low-shrinkage ultra-high performance concrete has properties such as early strength, high strength, and high durability, which can quickly and with high quality complete the reinforcement work of existing bridge piers. It has high economic and social value and is suitable for widespread application. Attached Figure Description
[0038] Figure 1 This document details a UHPC reinforcement project for a bridge pier and the cracking that occurred.
[0039] Figure 2 Photographs of a simulated circular ring reinforcement experiment (left) and a core drilling experiment (right) conducted on the ultra-high performance concrete described in Example 2;
[0040] Figure 3 A photograph of the cross-section of the core sample after it was cut and polished along the direction perpendicular to the ground following the simulated circular reinforcement experiment of the ultra-high performance concrete described in Example 2.
[0041] Figure 4 The image shows a cross-sectional photograph of the core sample after it was cut and polished along the direction perpendicular to the ground following a simulated circular reinforcement experiment of the ultra-high performance concrete described in Comparative Example 3. Detailed Implementation
[0042] The present invention will be further described in detail below through specific implementation examples. These implementation examples are based on the technology of the present invention, and detailed implementation methods and specific operating procedures are given. However, the scope of protection of the present invention is not limited to the implementation examples given below.
[0043] Example 1
[0044] A low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement comprises, by weight, the following components: 700 parts cement, 160 parts fly ash microspheres, 220 parts silica fume, 80 parts ultrafine powder, 200 parts internal curing aggregate, 9.3 parts water-reducing agent, 4 parts thickener, 12 parts hydration shrinkage regulator, 173 parts steel fiber, 6.2 parts basalt fiber, 189 parts water, and 1000 parts fine aggregate.
[0045] The cement used is low-heat silicate cement (P.LH 42.5); the fly ash microspheres have a water requirement ratio of 95% and a 28-day activity index of 110%; the silica fume has a water requirement ratio of 115% and a 28-day activity index of 118%; the ultrafine powder is quartz powder with a specific surface area of 850 kg / m². 2 The internal curing aggregate is high-alumina bauxite aggregate with an aluminum content of 80% and a particle size of 1-3 mm; the water-reducing agent is powdered polycarboxylate water-reducing agent with a water reduction rate of 30%; the thickener is TT-935 (Rohm and Haas TT-935); the hydration shrinkage regulator is sodium isooctanol sulfate; the steel fiber (straight type) has a diameter of 0.19-0.21 mm and a length of 12-13 mm; the basalt fiber has a diameter of 0.01-0.016 mm and a length of 8-10 mm; the fine aggregate is quartz sand with a fineness of 40-70 mesh.
[0046] The preparation method of the low-shrinkage, low-heat-of-hydration ultra-high performance concrete includes the following steps:
[0047] 1) According to the above raw material formula, mix cement, silica-alumina mineral admixture, silica fume, ultrafine powder, water-reducing agent and fine aggregate, stir, and after the powder is fully premixed, obtain mixture A;
[0048] 2) Mix the weighed water and hydration shrinkage regulator, and stir to obtain liquid B;
[0049] 3) Add the weighed internal curing aggregate into liquid B, pre-wet for 2-4 hours, and obtain mixture C;
[0050] 4) Mix mixture A with mixture C and stir until slurry is produced. Add thickener and stir evenly. Then add basalt fiber and steel fiber and stir evenly to obtain the circumferential reinforcement low-shrinkage low-hydration heat ultra-high performance concrete.
[0051] Example 2
[0052] A low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement is prepared in a manner largely similar to that of Example 1, except that, by weight, it comprises the following components: 650 parts cement, 180 parts fly ash microspheres, 200 parts silica fume, 80 parts ultrafine powder, 230 parts internal curing aggregate, 10.8 parts water-reducing agent, 6 parts thickener TT-935, 12 parts hydration shrinkage regulator, 189 parts steel fiber, 6.2 parts basalt fiber, 175 parts water, and 1000 parts fine aggregate.
[0053] Example 3
[0054] A low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement is prepared in a manner largely similar to that of Example 1, except that, by weight, it comprises the following components: 700 parts cement, 160 parts fly ash microspheres, 220 parts silica fume, 80 parts ultrafine powder, 200 parts internal curing aggregate, 9.3 parts water-reducing agent, 4 parts thickener TT-935, 12 parts hydration shrinkage regulator, 262 parts steel fiber, 9.4 parts basalt fiber, 189 parts water, and 1000 parts fine aggregate.
[0055] Example 4
[0056] A low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement is prepared in a manner largely similar to that of Example 1, except that, by weight, it comprises the following components: 700 parts cement, 160 parts metakaolin, 220 parts silica fume, 80 parts ultrafine powder, 200 parts internal curing aggregate, 9.3 parts water-reducing agent, 4 parts thickener TT-935, 10 parts hydration shrinkage regulator, 262 parts steel fiber, 9.4 parts basalt fiber, 195 parts water, and 1000 parts fine aggregate; wherein the cement is medium-heat silicate cement (P.MH 42.5), the water requirement ratio of metakaolin is 116%, the 28-day activity index is 112%, and the hydration shrinkage regulator is lauryl ketone.
[0057] Example 5
[0058] A low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement is prepared in a manner largely similar to that of Example 1, except that, by weight, it comprises the following components: 700 parts cement, 160 parts fly ash microspheres, 220 parts silica fume, 80 parts ultrafine powder, 200 parts internal curing aggregate, 9.3 parts water-reducing agent, 4 parts thickener TT-935, 10 parts hydration shrinkage regulator, 262 parts steel fiber, 9.4 parts basalt fiber, 195 parts water, and 1000 parts fine aggregate; wherein the cement is medium-heat silicate cement (P.MH 42.5); the hydration shrinkage regulator is lauryl ketone; and the fine aggregate is limestone manufactured sand with a fineness modulus of 2.5 and a maximum particle size of no more than 4.75 mm, and a content of stone powder smaller than 0.075 mm of 10 wt%.
[0059] In the preparation process of the low-shrinkage, low-hydration-heat ultra-high performance concrete described in this invention, various powder raw materials are premixed, and a hydration shrinkage regulator and water are mixed to obtain a solution, which is then mixed with the internal curing aggregate for pre-wetting. Finally, all materials are mixed to obtain the low-shrinkage, low-hydration-heat ultra-high performance concrete. On the one hand, the preparation process is simple, and on the other hand, the internal curing effect of porous aggregates is fully utilized. Not only can internal moisture be released during hydration to regulate the internal humidity of the hardened paste and effectively reduce shrinkage, but the hydration shrinkage regulator component inside the aggregate also has a slow-release effect, regulating the strength development of shrinkage in the later stages of UHPC curing, and further improving the mechanical properties and durability of the prepared low-shrinkage, low-hydration-heat ultra-high performance concrete for circumferential reinforcement.
[0060] Comparative Example 1
[0061] An ultra-high performance concrete, by weight, comprises the following components: 700 parts cement, 160 parts fly ash microspheres, 220 parts silica fume, 80 parts ultrafine powder, 200 parts internal curing aggregate, 9.3 parts water-reducing agent, 217 parts steel fiber, 6.2 parts basalt fiber, 189 parts water, and 1000 parts fine aggregate.
[0062] The cement used is low-heat silicate cement (P.LH 42.5); the fly ash microspheres have a water requirement ratio of 95% and a 28-day activity index of 110%; the silica fume has a water requirement ratio of 115% and a 28-day activity index of 118%; the ultrafine powder is quartz powder with a specific surface area of 850 kg / m². 2 The internal curing aggregate is high-alumina bauxite aggregate with an aluminum content of 80% and a particle size of 1-3 mm; the water-reducing agent is powdered polycarboxylate water-reducing agent with a water reduction rate of 30%; the steel fibers are 0.19-0.21 mm in diameter and 12-13 mm in length; the basalt fibers are 0.014-0.016 mm in diameter and 8-10 mm in length; the fine aggregate is quartz sand with a fineness of 40-70 mesh.
[0063] The preparation method of the ultra-high performance concrete includes the following steps:
[0064] 1) According to the above raw material formula, mix cement, silica-alumina mineral admixture, silica fume, ultrafine powder, water-reducing agent and fine aggregate, stir, and after the powder is fully premixed, obtain mixture A;
[0065] 2) Add the weighed mixing water to the internal curing aggregate, pre-wet for 2-4 hours to obtain mixture B;
[0066] 3) Mix mixture A with mixture B and stir until slurry is produced. After stirring evenly, add basalt fiber and steel fiber and stir evenly to obtain the circumferential reinforcement low-shrinkage low-hydration heat ultra-high performance concrete.
[0067] Comparative Example 2
[0068] An ultra-high performance concrete, with the same material proportions as in Example 1, is prepared by the following steps:
[0069] 1) According to the above raw material formula, mix cement, silica-alumina mineral admixture, silica fume, ultrafine powder, water-reducing agent and fine aggregate, stir, and after the powder is fully premixed, obtain mixture A;
[0070] 2) Add 50% of the mixing water to the weighed internal curing aggregate, pre-wet for 2-4 hours, and obtain mixture B;
[0071] 3) Mix the remaining 50% of the stirring water and the hydration shrinkage regulator, and stir to obtain liquid C;
[0072] 4) Mix mixture A, mixture B and liquid C, stir until slurry is produced, add thickener, stir evenly, add basalt fiber and steel fiber, stir evenly to obtain the circumferential reinforcement low shrinkage low hydration heat ultra-high performance concrete.
[0073] Comparative Example 3
[0074] An ultra-high performance concrete is prepared in a manner similar to that of Example 1, except that the thickener used is hydroxypropyl methylcellulose ether produced by Suzhou Xingbang, with a viscosity of 400 mPa·s.
[0075] The mechanical properties, impermeability, and shrinkage properties of the low-shrinkage, low-heat-of-hydration ultra-high performance concrete obtained in Examples 1-5 and Comparative Examples 1-3 of this invention were tested, and the test results are shown in Table 1. Except for the adiabatic temperature rise, all tests were conducted according to T / CBMF 96-2020 "Ultra-High Performance Concrete," and the autogenous shrinkage was tested using the corrugated pipe method; the adiabatic temperature rise was tested according to GB / T50080-2016.
[0076] Table 1. Performance test results of ultra-high performance concrete obtained in Examples 1-5 and Comparative Examples 1-3.
[0077]
[0078] As shown in Table 1, the UHPC of this invention exhibits excellent mechanical properties. Its 1-day compressive strength reaches 68.1 MPa, its 1-day tensile strength reaches 8.2 MPa, its 3-day compressive strength reaches 128.3 MPa, its 3-day tensile strength reaches 10.5 MPa, its 28-day compressive strength reaches 155.3 MPa, and its 28-day tensile strength reaches 13.8 MPa. The UHPC of this invention also has low heat of hydration, with a maximum adiabatic temperature rise of 48.5℃, far lower than the 70–80℃ of ordinary UHPC. Furthermore, the UHPC of this invention exhibits low shrinkage, with a 3-day self-shrinkage of less than 50 μm / m, a 7-day self-shrinkage of less than 80 μm / m, and a 28-day self-shrinkage of less than 200 μm / m, far lower than the 28-day self-shrinkage value of 500–900 μm / m of traditional UHPC.
[0079] like Figure 1 As shown, severe cracking appeared on the surface of the bridge piers after conventional UHPC reinforcement. Based on the severe cracking problem associated with UHPC reinforcement of bridge piers, an experiment simulating UHPC bridge pier reinforcement using ultra-high performance concrete as described in Example 2 of this invention was conducted. Figure 2 (Left) After 28 days, the surface of the UHPC layer remained intact without cracks. Core samples were taken from this UHPC layer. Figure 2 (Right) The core sample was cut and polished along a direction perpendicular to the ground before being photographed. Figure 3 As can be seen, the steel fibers are mostly distributed circumferentially (parallel to the ground) and are relatively uniformly distributed, which is beneficial for achieving good crack resistance. If the performance of UHPC is not adjusted (Comparative Example 3), the steel fiber distribution is as follows: Figure 4 The fiber distribution is disordered, and the steel fibers contribute little to the tensile strength and crack resistance of UHPC.
[0080] 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-shrinkage, low-heat-of-hydration ultra-high-performance concrete for circumferential reinforcement, characterized in that, The components and their respective weight percentages are as follows: cement 500-700 parts, silica-alumina mineral admixture 120-200 parts, silica fume 120-240 parts, ultrafine powder 50-100 parts, internal curing aggregate 150-250 parts, water-reducing agent 8.4-11.8 parts, thickener 2-10 parts, hydration shrinkage regulator 8-15 parts, steel fiber 183-275 parts, basalt fiber 6-10 parts, water 175-238 parts, and fine aggregate 1000 parts; The hydration shrinkage regulator is one or more of sodium isooctanol sulfate and laurocapram.
2. The low-shrinkage, low-heat-of-hydration ultra-high performance concrete according to claim 1, characterized in that, The cement is one of medium-heat silicate cement or low-heat silicate cement, and its strength grade is 42.5 or above.
3. The low-shrinkage, low-heat-of-hydration ultra-high-performance concrete according to claim 1, characterized in that, The silica-aluminate mineral admixture is one or more of fly ash, metakaolin, and fly ash microspheres; its water requirement ratio is not greater than 105%, and its 28-day activity index is not less than 70%; the silica fume water requirement ratio is not greater than 125%, and its 28-day activity index is not less than 105%; the ultrafine powder is one or more of quartz powder and heavy calcium carbonate powder; its specific surface area is not less than 750 kg / m². 2 .
4. The low-shrinkage, low-heat-of-hydration ultra-high-performance concrete according to claim 1, characterized in that, The internal curing aggregate is one or more of high-alumina bauxite aggregate and ceramsite.
5. The low-shrinkage, low-heat-of-hydration ultra-high-performance concrete according to claim 1, characterized in that, The water-reducing agent is a powdered polycarboxylate water-reducing agent with a water reduction rate of ≥25%.
6. The low-shrinkage, low-heat-of-hydration ultra-high performance concrete according to claim 1, characterized in that, The thickener is thickener TT-935.
7. The low-shrinkage, low-heat-of-hydration ultra-high-performance concrete according to claim 1, characterized in that, The steel fiber is a straight steel fiber with a diameter of 0.15~0.21mm, a length of 12~13mm, and an aspect ratio of 60~70; the basalt fiber has a diameter of 0.01~0.015mm and a length of 8~10mm.
8. The low-shrinkage, low-heat-of-hydration ultra-high performance concrete according to claim 1, characterized in that, The fine aggregate is one or more of quartz sand and manufactured sand; Its maximum particle size is no more than 4.25 mm, and the content of stone powder smaller than 0.075 mm is 5-15%.
9. The method for preparing low-shrinkage, low-heat-of-hydration ultra-high performance concrete for circumferential reinforcement as described in any one of claims 1 to 8, characterized in that, Includes the following steps: 1) Weighing the raw materials; The raw materials and their respective weight percentages include: cement 500-700 parts, silica-alumina mineral admixture 120-200 parts, silica fume 120-240 parts, ultrafine powder 50-100 parts, internal curing aggregate 150-250 parts, water-reducing agent 8.4-11.8 parts, thickener 2-10 parts, hydration shrinkage regulator 8-15 parts, steel fiber 183-275 parts, basalt fiber 6-10 parts, water 175-238 parts, and fine aggregate 1000 parts; 2) Weigh out the cement, aluminosilicate mineral admixture, silica fume, ultrafine powder, water-reducing agent and fine aggregate, mix and stir to fully premix the powder to obtain mixture A; 3) Mix the weighed water and hydration shrinkage regulator, and stir to obtain liquid B; 4) Add the weighed internal curing aggregate into liquid B, pre-wet for 2-4 hours, and obtain mixture C; 5) Mix mixture A with mixture C and stir until slurry is produced. Add thickener and stir evenly. Then add basalt fiber and steel fiber and stir evenly to obtain the circumferential reinforcement low-shrinkage low-hydration heat ultra-high performance concrete.