Rheologically balanced bridge reinforcing self-compacting concrete and preparation method thereof

Abstract

The application relates to the technical field of building materials, and discloses a rheological balance type bridge reinforcing self-compacting concrete and a preparation method thereof. The concrete is made of Portland cement, fly ash, silica fume, aggregate, water, and as key components, a molecular tailored poly carboxylic acid high-performance water reducing agent, a cationic rust inhibitor and a micron-sized piezoelectric ceramic powder. The preparation method pre-mixes the micron-sized piezoelectric ceramic powder with the silica fume, step-by-step dry material mixing is carried out on the powdery material and the aggregate, and the water and various admixtures are made into a composite functional mother liquor. The water reducing agent with a specific long-short side chain molecular structure is adopted, the rheological balance between high fluidity and high segregation resistance of the concrete mixture is realized, meanwhile, the cationic rust inhibitor is chemically passivated and the piezoelectric effect of the micron-sized piezoelectric ceramic powder is synergized, the hardened concrete is endowed with a self-repairing capability, and the long-term durability of the reinforcing structure is improved.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method. Background Technology

[0002] During their service life, bridge structures experience a decline in load-bearing capacity and durability due to factors such as material aging, increased traffic load, and environmental erosion. Therefore, reinforcement and maintenance are necessary to extend their service life. In bridge reinforcement projects, self-compacting concrete is used in scenarios such as structural cross-section enlargement or component repair because it can fill to a dense state under its own weight without vibration.

[0003] However, existing self-compacting concrete presents technical contradictions in practical applications. On the one hand, to ensure the concrete mixture can flow through the dense reinforcement within the structure and completely fill the formwork, it needs high fluidity. However, excessive fluidity reduces the cohesiveness of the paste, causing denser coarse aggregates to settle under gravity, resulting in segregation. Simultaneously, water in the mixture is prone to rise and seep out. This inhomogeneity directly affects the mechanical properties and durability of the hardened concrete. On the other hand, to suppress segregation and bleeding, the viscosity of the mixture is usually increased, but this reduces its fluidity and filling capacity, leaving voids or defects in the structure. Therefore, existing self-compacting concrete struggles to achieve a balance between macroscopic fluidity and microscopic homogeneity, making its final performance highly sensitive to fluctuations in raw materials and on-site construction conditions.

[0004] Furthermore, the long-term durability of concrete used for bridge reinforcement is another key technical indicator. Bridge structures are constantly exposed to the natural environment and subjected to repeated vehicle loads, making them prone to developing microcracks within the concrete. These microcracks provide entry points for corrosive media such as chloride ions and carbon dioxide. When these media reach the surface of the internal reinforcing steel, they damage the passivation film on the steel, causing corrosion, which in turn leads to cracking and spalling of the concrete cover. This severely affects the reinforcement effect and structural safety. Existing concrete materials have limited ability to inhibit steel corrosion and repair microcracks that develop during use. Summary of the Invention

[0005] The purpose of this invention is to provide a rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method, which solves the problems of rheological imbalance and insufficient long-term durability of concrete in the prior art.

[0006] To address the aforementioned technical problems, this invention provides a rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method.

[0007] The first aspect of the present invention provides a rheologically balanced bridge reinforcement self-compacting concrete, made from the following raw materials in parts by weight:

[0008] Silicate cement: 100 parts;

[0009] Fly ash: 25.0-35.0 parts;

[0010] Silica fume: 8.0-12.0 parts;

[0011] Medium sand: 200.0-260.0 parts;

[0012] Coarse aggregate A with a particle size of 5-10mm: 140.0-180.0 parts;

[0013] Coarse aggregate B with a particle size of 10-16mm: 140.0-180.0 parts;

[0014] Water: 35.0-42.0 parts;

[0015] Molecularly tailored customized polycarboxylate high-performance water-reducing agent: 1.5-2.5 parts;

[0016] Cationic rust inhibitor: 0.8-1.5 parts;

[0017] Micron-sized piezoelectric ceramic powder: 0.5-1.2 parts;

[0018] UEA expanding agent: 8.0-12.0 parts;

[0019] Viscosity modifier: 0.02-0.05 parts;

[0020] Sensitivity modifier: 0.1-0.3 parts.

[0021] In a preferred embodiment, the molecularly tailored polycarboxylate superplasticizer is a copolymer having a polymethacrylic acid backbone with two polyoxyethylene side chains of different degrees of polymerization: one is a side chain formed by methoxy polyethylene glycol methacrylate monomers with a degree of polymerization of 40-50, and the other is a side chain formed by methoxy polyethylene glycol methacrylate monomers with a degree of polymerization of 8-10.

[0022] Long side chains with a degree of polymerization of 40-50 form steric hindrance on the surface of cement particles, generating electrostatic repulsion, thereby giving the concrete mixture high fluidity. Short side chains with a degree of polymerization of 8-10 form a hydration layer on the surface of cement particles. In a static state, this hydration layer provides slurry cohesion through intermolecular forces, inhibiting aggregate settling and bleeding.

[0023] Under shear conditions, the hydration layer acts as a lubricant. The synergistic effect of the two side chains gives the concrete mixture high stability when it is at rest, and low viscosity and high fluidity when it is pumped or poured.

[0024] In a preferred embodiment, the cationic corrosion inhibitor is sodium nitrite, and the micron-sized piezoelectric ceramic powder is barium titanate with an average particle size of 1.0-5.0 μm. Sodium nitrite molecules can adsorb onto the surface of the steel reinforcement inside the concrete to form a dense passivation film, inhibiting the electrochemical corrosion of the steel reinforcement by corrosive media such as chloride ions. When the concrete structure is subjected to external loads and stress, the barium titanate particles dispersed in the concrete matrix generate charges on the particle surface due to the piezoelectric effect, forming a local electric field. This local electric field drives the charged calcium ions and silicate ions in the concrete pore solution to migrate and accumulate towards the stress concentration area or the tip of the microcrack, promoting the generation of hydration products, thereby filling and repairing the microcracks.

[0025] In a preferred embodiment, the sensitivity modifier is a physical blend of potato starch ether and ethylene-vinyl acetate redispersible latex powder in a mass ratio of 1:1.

[0026] In a preferred embodiment, the silicate cement is P·II52.5R type silicate cement, and the fly ash is Grade I low-calcium fly ash.

[0027] A second aspect of the present invention provides a method for preparing rheologically balanced bridge reinforcement self-compacting concrete, comprising the following steps:

[0028] S1: The micron-sized piezoelectric ceramic powder and the silica fume are premixed in a preset ratio to prepare a piezoelectric functional premix;

[0029] S2: Put the silicate cement, fly ash, UEA expansion agent and the piezoelectric premix into the mixer and dry mix for 100-150 seconds. Then add the medium sand, coarse aggregate A and coarse aggregate B and continue to dry mix for 50-70 seconds.

[0030] S3: The water, molecularly customized polycarboxylate high-performance water-reducing agent, cationic rust inhibitor, viscosity modifier and sensitivity modifier are premixed into a composite functional mother liquor. Then the composite functional mother liquor is added to a mixer and wet-mixed for 150-210 seconds before being discharged.

[0031] In a preferred embodiment, in step S1, the micron-sized piezoelectric ceramic powder is premixed with 10 times its mass of silica fume in a high-speed shear mixer at a rotation speed of 1200-1800 r / min to break up the agglomeration of the piezoelectric ceramic powder and ensure its uniform dispersion in the cementitious material system.

[0032] In a preferred embodiment, the stirring speed in step S2 is 28-32 r / min, and the stirring speed in step S3 is 38-42 r / min.

[0033] In a preferred embodiment, the specific steps for preparing the composite functional mother liquor in step S3 are as follows: first, the molecularly tailored polycarboxylate high-performance water-reducing agent, viscosity modifier, and sensitivity modifier are added to the water and stirred at a stirring rate of 300-500 r / min for 180-300 seconds; then, the cationic rust inhibitor is added and stirred at a stirring rate of 300-500 r / min for 30-60 seconds.

[0034] In summary, the present invention has at least one of the following beneficial technical effects:

[0035] 1. The molecularly tailored polycarboxylate high-performance water-reducing agent used in this invention has a molecular structure that simultaneously contains two types of polyoxyethylene side chains with specific degrees of polymerization: long and short. The long side chains impart high fluidity and extensibility to the mixture through steric hindrance, while the short side chains provide moderate cohesion, effectively inhibiting aggregate segregation and bleeding. This combined effect enables the concrete mixture to achieve high filling permeability while maintaining excellent homogeneity, thus resolving the technical contradiction between high fluidity and anti-segregation properties.

[0036] 2. This invention constructs a dual protection system for internal steel reinforcement by combining a cationic corrosion inhibitor with micron-sized piezoelectric ceramic powder. The cationic corrosion inhibitor forms a chemical passivation film on the surface of the steel reinforcement, directly inhibiting the corrosion of media such as chloride ions. At the same time, when micron-sized piezoelectric ceramic powder generates microcracks in the concrete matrix, it can promote the self-repair of the cracks by utilizing the piezoelectric effect. This synergistic effect effectively delays the corrosion process of the steel reinforcement and improves the long-term durability of the reinforced structure.

[0037] 3. In the preparation method of the present invention, by pre-mixing the micron-sized piezoelectric ceramic powder, using step-by-step dry mixing, and uniformly adding the composite functional mother liquor made from multiple liquid phase components, the uniform dispersion of each functional component in the concrete system is ensured. Combined with the optimized mass ratio of each component, the stable realization of various properties of the concrete of the present invention is guaranteed, and the reliability and construction adaptability of the product are improved. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to comparative examples and examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Silicate cement, CAS: 65997-15-1;

[0040] Fly ash, CAS: 68131-74-8;

[0041] Silica fume, CAS: 69012-64-2;

[0042] Methacrylic acid, CAS: 79-41-4;

[0043] Methoxylated polyethylene glycol methacrylate, CAS: 26915-72-0;

[0044] Ammonium persulfate, CAS: 7727-54-0;

[0045] 3-Mercaptopropionic acid, CAS: 107-96-0;

[0046] Sodium hydroxide, CAS: 1310-73-2;

[0047] Cationic rust inhibitor (sodium nitrite), CAS: 7632-00-0;

[0048] Piezoelectric ceramic powder (barium titanate), CAS: 12047-27-7;

[0049] Potato starch ether, CAS: 9005-25-8;

[0050] Ethylene-vinyl acetate redispersible latex powder, CAS: 24937-78-8.

[0051] Examples 1-3:

[0052] Example 1:

[0053] This embodiment provides a rheologically balanced bridge reinforcement self-compacting concrete and its preparation method.

[0054] The raw materials for preparing this rheologically balanced bridge reinforcement self-compacting concrete include, by mass parts:

[0055] 100 parts of silicate cement;

[0056] 25.0 parts fly ash;

[0057] 8.0 parts silica fume;

[0058] 200.0 portions of medium-grade sand;

[0059] Coarse aggregate A140.0 parts with a particle size of 5-10mm;

[0060] Coarse aggregate B140.0 parts with a particle size of 10-16mm;

[0061] 35.0 parts water;

[0062] 1.5 parts of molecularly customized polycarboxylate high-performance water-reducing agent;

[0063] 0.8 parts of cationic rust inhibitor;

[0064] 0.5 parts of micron-sized piezoelectric ceramic powder;

[0065] 8.0 parts of UEA expanding agent;

[0066] 0.02 parts viscosity modifier;

[0067] 0.1 parts of sensitivity modifier.

[0068] Preparation method of molecularly customized polycarboxylate high-performance water-reducing agent:

[0069] In a four-necked flask equipped with a mechanical stirrer, a reflux condenser, a constant pressure dropping funnel, and a nitrogen delivery tube, add 150g of deionized water and all of the methoxy polyethylene glycol methacrylate monomer with a degree of polymerization of 40-50 on the polyoxyethylene side chain.

[0070] Start stirring and purge with nitrogen for 30 minutes. Place the reaction flask in a constant temperature water bath and heat to 68-72℃. Dissolve all the methacrylic acid monomer, methoxy polyethylene glycol methacrylate monomer with a degree of polymerization of 8-10 on the polyoxyethylene side chain, and 3-mercaptopropionic acid in 50g of deionized water to prepare the first mixed solution; dissolve ammonium persulfate in 30g of deionized water to prepare the second solution.

[0071] Simultaneously, the first mixed solution and the second solution were added dropwise, with the first mixed solution added completely over 3.0 hours and the second solution added completely over 3.5 hours. After the addition was complete, the reaction temperature was raised to 73-77℃ and the reaction was maintained at this temperature for 1.5 hours. After cooling to room temperature, the pH value was adjusted to 6.0-7.0 using a 30% sodium hydroxide aqueous solution, yielding a molecularly tailored polycarboxylate high-performance water-reducing agent with a solid content of 40%.

[0072] Methods for preparing concrete:

[0073] S1: Premix micron-sized piezoelectric ceramic powder and silica fume in a high-speed shear mixer at a speed of 1200-1800 r / min for 10 minutes to prepare a piezoelectric functional premix.

[0074] S2: Add silicate cement, fly ash, UEA expansion agent and piezoelectric premix to the mixer and dry mix at a speed of 28-32 r / min for 100-150 seconds; then add medium sand, coarse aggregate A and coarse aggregate B, and continue to dry mix at a speed of 28-32 r / min for 50-70 seconds.

[0075] S3: Water, molecularly customized polycarboxylate high-performance water-reducing agent, cationic rust inhibitor, viscosity modifier and sensitivity modifier are premixed into a composite functional mother liquor. Then, the mother liquor is uniformly added to the mixer within 30 seconds and wet-mixed at a speed of 38-42r / min for 150-210 seconds before being discharged.

[0076] Example 2:

[0077] This embodiment provides a rheologically balanced bridge reinforcement self-compacting concrete and its preparation method.

[0078] The raw materials for preparing this rheologically balanced bridge reinforcement self-compacting concrete include, by mass parts:

[0079] 100 parts silicate cement; 30.0 parts fly ash; 10.0 parts silica fume; 230.0 parts medium sand; 160.0 parts coarse aggregate A with a particle size of 5-10mm;

[0080] Coarse aggregate B160.0 parts with a particle size of 10-16mm;

[0081] 38.5 parts water;

[0082] 2.0 parts of molecularly customized polycarboxylate high-performance water-reducing agent;

[0083] 1.15 parts of cationic rust inhibitor;

[0084] 0.85 parts of micron-sized piezoelectric ceramic powder;

[0085] 10.0 parts of UEA expanding agent;

[0086] 0.035 parts of viscosity modifier;

[0087] 0.2 parts of sensitivity modifier.

[0088] Preparation process:

[0089] Except for the different formulation components and dosages, the other raw material preparation steps and sealing component preparation steps are exactly the same as in Example 1.

[0090] Example 3:

[0091] This embodiment provides a rheologically balanced type of self-compacting concrete for bridge reinforcement and its preparation method.

[0092] The raw materials for preparing this rheologically balanced bridge reinforcement self-compacting concrete include, by mass parts:

[0093] 100 parts of silicate cement;

[0094] 35.0 parts of fly ash;

[0095] 12.0 parts silica fume;

[0096] 260.0 parts of medium sand;

[0097] Coarse aggregate A180.0 parts with a particle size of 5-10mm;

[0098] Coarse aggregate B180.0 parts with a particle size of 10-16mm;

[0099] 42.0 parts water;

[0100] 2.5 parts of molecularly customized polycarboxylate high-performance water-reducing agent;

[0101] 1.5 parts of cationic rust inhibitor;

[0102] 1.2 parts of micron-sized piezoelectric ceramic powder;

[0103] 12.0 parts of UEA expanding agent;

[0104] 0.05 parts viscosity modifier;

[0105] 0.3 parts of sensitivity modifier.

[0106] Preparation process:

[0107] Except for the different formulation components and dosages, the other raw material preparation steps and sealing component preparation steps are exactly the same as in Example 1.

[0108] Comparative Examples 1-3:

[0109] Comparative Example 1:

[0110] Compared with Example 2, the difference is that instead of using a molecularly tailored polycarboxylate superplasticizer, an equal mass fraction of conventional polycarboxylate superplasticizer is used; otherwise, they are the same.

[0111] Comparative Example 2:

[0112] The difference from Example 2 is that no cationic rust inhibitor and micron-sized piezoelectric ceramic powder are added; all other aspects are the same.

[0113] Comparative Example 3:

[0114] Compared with Example 2, the difference is that instead of using a molecularly tailored polycarboxylate superplasticizer, an equal mass fraction of conventional polycarboxylate superplasticizer is used, and no cationic rust inhibitor or micron-sized piezoelectric ceramic powder is added; all other aspects are the same.

[0115] Test Examples 1 and 2:

[0116] Test Example 1:

[0117] The concrete mixtures prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to fresh mix performance tests immediately after being discharged from the mixer.

[0118] Test method:

[0119] 1. Collapse expansion and T500 time test

[0120] This test was conducted in accordance with GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", and the specific steps are as follows:

[0121] After wetting the slump cone, place it in the center of a wet steel plate. One person steps on the foot pedal and uses a scoop to fill the cone with concrete in two batches, each time filling to about half the height of the cone. No vibration or tamping is performed during the filling process. After filling, scrape off the excess mixture at the top and lift the slump cone vertically and steadily upwards. This process should be completed within 5-10 seconds. Start timing from the moment the slump cone is lifted and record the time required for the concrete mixture to expand to its maximum diameter. Measure the diameter of the final expanded paving in two mutually perpendicular directions and take the average as the slump expansion. At the same time, record the time required for the edge of the expanded paving to reach a circle with a diameter of 500 mm, which is the T500 time.

[0122] 2. V-funnel outflow time test

[0123] This test was conducted in accordance with GB / T50080-2016, and the specific steps are as follows:

[0124] After wetting the inner wall of the V-shaped funnel, close the discharge port at the bottom. Fill the V-shaped funnel with concrete mixture at once, smooth the top surface with a scraper, let it stand for 1 minute, then open the discharge port and start timing. Record the time from when the discharge port is opened until all the mixture in the funnel has flowed out and the light can be seen from the discharge port at the intersection of the diagonals inside the funnel. This time is the V-funnel outflow time.

[0125] 3. U-shaped box test

[0126] This test was conducted in accordance with GB / T50080-2016, and the specific steps are as follows:

[0127] Wet the inner wall of the U-shaped box and close the middle partition. Fill the box with concrete mix from one side until it is full. After standing for 1 minute, lift the middle partition. The concrete mix will flow to the other side of the box under gravity. After the mix stops flowing, measure the height of the concrete mix surface on both sides of the box and calculate the height difference (Δh).

[0128] 4. Wet sieve segregation rate test

[0129] This test was conducted in accordance with Appendix D of JG / T472-2015 "Technical Specification for Application of Self-Compacting Concrete", and the specific steps are as follows:

[0130] Take a 10kg ± 0.1kg sample of concrete mixture, let it stand for 15 minutes, and pour it into a 5mm aperture test sieve. Place a known mass collection tray under the sieve and record the mass of mortar that passes through the sieve and falls into the collection tray. The wet sieve segregation rate is calculated as the percentage of the mass of mortar passing through the sieve relative to the total mass of the mixture sample.

[0131] Test results:

[0132] Table 1: Performance test results of freshly mixed concrete in the examples and comparative examples

[0133] Test Project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Collapse spread (mm) 715 762 485 758 502 T500 time (s) 5.8 4.4 - 4.6 - V. Outflow time from the funnel (s) 10.4 8.3 >60 (Congestion) 8.5 >60 (Congestion) U-shaped box filling height difference (mm) 18 11 53 14 49 Wet sieve separation rate (%) 12.6 9.8 6.4 10.3 6.8

[0134] The "-" indicates that the measurement could not be performed effectively due to insufficient liquidity.

[0135] Results analysis:

[0136] The data in Table 1 show that the concrete mixtures of Examples 1-3 all exhibited high slump expansion, moderate T500 and V-funnel outflow times, low U-box filling height difference, and low wet sieve segregation rate. Comparative Examples 1 and 3, due to the use of conventional polycarboxylate superplasticizers, had low slump expansion values ​​and showed insufficient fluidity or passage barriers in the V-funnel and U-box tests. Compared with Example 2, Comparative Example 2 had similar values ​​for various indicators of fresh mix workability.

[0137] The above test results show that the molecularly tailored polycarboxylate high-performance water-reducing agent used in this technical solution can enable concrete mixtures to achieve high fluidity. In the molecular structure of this water-reducing agent, the long polyoxyethylene side chains with a degree of polymerization of 40-50 generate a steric hindrance effect between cement particles, which is the reason for the high extensibility of the mixture. At the same time, the short polyoxyethylene side chains with a degree of polymerization of 8-10 form a hydration layer on the surface of cement particles, which provides the necessary cohesive force in the static state, allowing the paste to coat the aggregate, thereby inhibiting segregation and bleeding. This is confirmed by the low wet sieve segregation rate data of Examples 1-3.

[0138] Comparing the results of Example 2 and Comparative Example 1, with the type of water-reducing agent as the only variable, the slump expansion of the former was 762 mm, while that of the latter was only 485 mm. Furthermore, the former had an effective V-funnel outflow time and a low U-shaped box filling height difference. This comparison demonstrates that the specific molecular structure of this molecularly tailored polycarboxylate high-performance water-reducing agent is the technical basis for simultaneously achieving high fluidity, high filling throughput, and high anti-segregation properties, thereby achieving a rheological equilibrium state of the mixture and resolving the contradiction between high fluidity and slurry homogeneity.

[0139] Test Example 2:

[0140] The hardened physical and mechanical properties and durability of the concrete prepared in Examples 1-3 and Comparative Examples 1-3 were tested.

[0141] Test method:

[0142] 1. Compressive strength and flexural strength tests

[0143] This test was conducted in accordance with GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", and the specific steps are as follows:

[0144] Cube specimens with dimensions of 100mm×100mm×100mm were prepared and cured under standard curing conditions (temperature (20±2)℃, relative humidity ≥95%) for 3 days, 7 days and 28 days. The pressure testing machine was used for testing. For flexural strength testing, beam specimens with dimensions of 100mm×100mm×400mm were prepared and cured under standard curing conditions for 28 days. The four-point bending loading method was used for testing.

[0145] 2. Drying shrinkage rate test

[0146] This test was conducted in accordance with GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", and the specific steps are as follows:

[0147] Prismatic specimens with dimensions of 100mm×100mm×515mm were prepared and demolded after standard curing for 3 days. Their initial length was measured, and then the specimens were transferred to a constant temperature and humidity chamber (temperature (20±2)℃, relative humidity (60±5)%) for drying. The length change of the specimens was measured periodically using a length comparator, and the drying shrinkage rate at 28 days was calculated.

[0148] 3. Reinforcing steel corrosion potential test

[0149] This test was conducted according to the half-cell potential method in GB / T50082-2009, and the specific steps are as follows:

[0150] Prismatic specimens measuring 100mm × 100mm × 300mm were fabricated, with a 10mm diameter HRB400 plain round steel bar embedded in the center of each specimen. The protective layer thickness of the steel bar was 45mm. After standard curing for 28 days, the specimens were placed in a 3.5% (mass fraction) NaCl solution for a wet-dry cycle accelerated corrosion test. Each cycle consisted of 4 days of immersion and 3 days of drying. On day 90, a saturated copper sulfate electrode (CSE) was used as a reference electrode to measure the potential of the steel bar relative to the reference electrode.

[0151] Test results:

[0152] Table 2: Test results of hardened concrete in the examples and comparative examples

[0153] Test item mechanical properties Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 3D compressive strength (MPa) 48.2 51.7 53.1 49.5 50.8 48.7 7-day compressive strength (MPa) 69.4 73.2 75.8 70.3 72.5 69.1 28-day compressive strength (MPa) 85.6 90.1 92.5 87.2 89.4 86.4 28-day flexural strength (MPa) 9.7 10.3 10.8 9.9 10.1 9.6

[0154] Table 3: Durability test results of hardened concrete in the examples and comparative examples

[0155] Test item durability performance Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[28d drying shrinkage rate (×10 -6 )]]> 398 365 341 371 486 495 90-day steel reinforcement corrosion potential (mV vs. CSE) -215 -188 -165 -203 -496 -521

[0156] Results analysis:

[0157] The data in Tables 2 and 3 show that the hardened concrete prepared in Examples 1-3 all exhibit high early and late compressive and flexural strengths. The mechanical property data of Comparative Example 1 showed no significant difference from those of the Example groups. The 28-day drying shrinkage rates of Examples 1-3 were lower than those of Comparative Examples 2 and 3. Regarding the corrosion potential of the reinforcing steel, the potential values ​​of Examples 1-3 at 90 days of age were all within the lower corrosion risk range, while the potential values ​​of Comparative Examples 2 and 3 were within the high corrosion risk range.

[0158] The difference in the corrosion potential of the steel bars between the Example Group and Comparative Examples 2 and 3 in the above test results is due to the introduction of cationic corrosion inhibitors and micron-sized piezoelectric ceramic powders in the Example Group. The cationic corrosion inhibitor, namely sodium nitrite, has nitrite ions that can react with ferrous ions on the steel bar surface to form a dense γ-Fe2O3 passivation film. This passivation film physically blocks the contact between corrosive media such as chloride ions and the steel bar matrix, inhibiting the anodic process of electrochemical corrosion. At the same time, the barium titanate particles dispersed in the matrix cause stress concentration at the crack tip when microcracks are generated in the concrete due to drying shrinkage or external loads, resulting in surface charges due to the piezoelectric effect. The resulting local electric field promotes the migration of ions in the pore fluid to the microcrack area, promotes the generation of hydration products, fills the microcracks, and reduces the transport rate of corrosive media.

[0159] Comparing Example 2 and Comparative Example 2, with other components remaining the same, the 90-day steel corrosion potential of the former was -188mV, while that of the latter was -496mV. This comparison shows that the coexistence of cationic corrosion inhibitor and micron-sized piezoelectric ceramic powder is the key technology for achieving low steel corrosion risk in hardened concrete. These two components, through chemical film formation and physical self-healing, respectively, together constitute a protective system for the internal steel reinforcement, solving the durability problem of concrete during long-term service.

Claims

1. A rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method, comprising the following parts by weight of raw materials: Silicate cement: 100 parts; Fly ash: 25.0-35.0 parts; Silica fume: 8.0-12.0 parts; Medium sand: 200.0-260.0 parts; Coarse aggregate A with a particle size of 5-10mm: 140.0-180.0 parts; Coarse aggregate B with a particle size of 10-16mm: 140.0-180.0 parts; Water: 35.0-42.0 parts; Molecularly tailored customized polycarboxylate high-performance water-reducing agent: 1.5-2.5 parts; Cationic rust inhibitor: 0.8-1.5 parts; Micron-sized piezoelectric ceramic powder: 0.5-1.2 parts; UEA expanding agent: 8.0-12.0 parts; Viscosity modifier: 0.02-0.05 parts; Sensitivity modifier: 0.1-0.3 parts.

2. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 1, characterized in that, The molecularly tailored polycarboxylate high-performance water-reducing agent is a copolymer, which is synthesized through the following steps: Under nitrogen protection, methoxy polyethylene glycol methacrylate monomers with a degree of polymerization of 40-50 in the side chains of polyoxyethylene are dissolved in water and heated to 68-72℃. Over 3.0-3.5 hours, a first mixed solution consisting of methacrylic acid monomer, methoxy polyethylene glycol methacrylate monomer with a degree of polymerization of 8-10 on the side chain of polyoxyethylene and a chain transfer agent are simultaneously added dropwise, along with a second solution formed by dissolving ammonium persulfate in water. After the addition is complete, raise the temperature to 73-77℃ and maintain the temperature for 1.5 hours. After cooling, adjust the pH value to 6.0-7.0 with sodium hydroxide solution.

3. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 1, characterized in that, The cationic rust inhibitor is sodium nitrite, the micron-sized piezoelectric ceramic powder is barium titanate, and the average particle size of the micron-sized piezoelectric ceramic powder is 1.0-5.0 μm.

4. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 1, characterized in that, The sensitivity modifier is composed of potato starch ether and ethylene-vinyl acetate redispersible latex powder in a mass ratio of 1:

1.

5. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 1, characterized in that, The silicate cement is P·II52.5R type silicate cement, and the fly ash is Grade I low-calcium fly ash.

6. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 1, characterized in that, Includes the following steps: S1: The micron-sized piezoelectric ceramic powder is premixed with the silica fume to prepare a piezoelectric functional premix; S2: Put the silicate cement, fly ash, UEA expansion agent and the piezoelectric premix into the mixer and dry mix for 100-150 seconds. Then add the medium sand, coarse aggregate A and coarse aggregate B and continue to dry mix for 50-70 seconds. S3: Water, molecularly customized polycarboxylate high-performance water-reducing agent, cationic rust inhibitor, viscosity modifier and sensitivity modifier are premixed into a composite functional mother liquor. Then, the composite functional mother liquor is added to a mixer and wet-mixed for 150-210 seconds before being discharged.

7. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 6, characterized in that, In step S1, micron-sized piezoelectric ceramic powder and silica fume are premixed in a high-speed shear mixer at a rotation speed of 1200-1800 r / min.

8. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 6, characterized in that, The stirring speed in step S2 is 28-32 r / min, and the stirring speed in step S3 is 38-42 r / min.

9. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 6, characterized in that, In step S3, the specific steps for preparing the composite functional mother liquor are as follows: First, add the molecularly tailored polycarboxylate high-performance water-reducing agent, viscosity modifier, and sensitivity modifier to the water, and stir at a stirring rate of 300-500 r / min for 180-300 seconds to allow the polymer components to completely dissolve. Then add the cationic rust inhibitor and continue stirring at a stirring rate of 300-500 r / min for 30-60 seconds until the mixture is homogeneous.

10. The rheologically balanced self-compacting concrete for bridge reinforcement and its preparation method according to claim 6, characterized in that, In step S3, the composite functional mother liquor is uniformly added to the mixer within 30 seconds.