Bridge concrete for extremely cold areas

Abstract

The invention provides bridge concrete for extremely cold areas. The bridge concrete is prepared from the following raw materials in parts by weight: 320 to 400 parts of P.O 42.5-grade Portland cement, 9 to 16 parts of a composite anti-freezing agent, 12 to 22 parts of surface modified nano silicon dioxide, 85 to 130 parts of a mineral composite admixture, 950 to 1250 parts of aggregate, 0.7 to 1.6 parts of a polycarboxylic acid type air entraining agent and 1.8 to 5.5 parts of polypropylene fiber, wherein the composite anti-freezing agent is formed by compounding calcium nitrate, calcium formate and triethanolamine according to the ratio of (3.2-5.1): (1.9-4.2): 1, and the effective content of Ca (NO3) 2.4 H2O in the calcium nitrate is greater than or equal to 96%. Compared with the prior art, the composite anti-freezing agent has the following beneficial effects that the calcium nitrate provides early-stage anti-freezing, the calcium formate accelerates low-temperature hydration, and the triethanolamine serves as a dispersing agent to improve the synergistic efficiency of all the components.

Description

Technical Field

[0001] The invention belongs to the field of concrete formulation, and in particular relates to bridge concrete for extremely cold regions. Background Art

[0002] Traditional bridge concrete faces three major technical challenges in extremely cold environments: 1. Surface spalling caused by freeze-thaw cycles (tests show that ordinary C50 concrete loses 5.2% mass after 100 freeze-thaw cycles at -30°C); 2. Inadequate 28-day strength due to inadequate low-temperature hydration (conventional antifreeze exhibits less than 60% strength development at -15°C); and 3. Structural cracking caused by thermal stress (approximately 2.3 MPa tensile stress is generated for every 10°C drop in temperature). Some existing technologies utilize ethylene glycol antifreeze, but these suffer from late-stage strength loss. Some proposed aggregate preheating processes consume energy exceeding 120 kWh / m³, making them difficult to implement in engineering applications. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a bridge concrete for extremely cold regions to solve the problems raised in the above background technology.

[0004] The synergistic effect of precise proportion of composite antifreeze and nanomaterial modification is achieved: 1) The molar ratio of calcium nitrate to calcium formate is 1.05-1.25, which reduces the freezing point to -28.1°C (compared to the freezing point of single-component antifreeze, which is >-26.5°C); 2) Modified nano-silica increases the pore fractal dimension to 2.83 (conventional concrete ≤ 2.65), and the relative dynamic elastic modulus retention rate after 300 freeze-thaw cycles is >95%; 3) The three-dimensional buffer network reduces the thermal stress concentration factor to 0.32 (conventionally ≥0.65).

[0005] The present invention is achieved through the following technical solution: A bridge concrete for extremely cold regions, comprising the following raw materials in parts by weight: 320-400 parts of P·O 42.5 grade Portland cement, 9-16 parts of composite antifreeze, 12-22 parts of surface-modified nano-silica, 85-130 parts of mineral composite admixture, 950-1250 parts of aggregate, 0.7-1.6 parts of polycarboxylic acid air-entraining agent, and 1.8-5.5 parts of polypropylene fiber; The composite antifreeze is prepared by mixing calcium nitrate, calcium formate and triethanolamine in the ratio of (3.2-5.1):(1.9-4.2):1, and the effective content of Ca(NO3)2·4H2O in the calcium nitrate is ≥96%.

[0006] As a preferred embodiment, the composite mineral admixture is composed of fly ash / slag powder / silica fume in a mass ratio of (40-60): (30-50): (10-15), and the specific surface area is ≥450m 2 / kg.

[0007] As a preferred embodiment, the particle size distribution of the mineral composite admixture satisfies: Fly ash: 45-55μm D50, water requirement ratio ≤95%; Slag powder: specific surface area 430-480m² / kg, 7d activity index ≥85%; Silica fume: SiO2 content ≥92%, loss on ignition ≤3%; The coefficient of variation of the mixing uniformity of the three is ≤3.5%.

[0008] As a preferred embodiment, the water-binder ratio of the concrete raw materials is between 0.27 and 0.36.

[0009] As a preferred embodiment, the aggregate is a composite aggregate of basalt machine-made sand and regenerated ceramsite, which are mixed in a mass ratio of (7-8): (2-3).

[0010] As a preferred embodiment, the surface-modified nano-silica is grafted with γ-aminopropyltriethoxysilane.

[0011] As a preferred embodiment, the method is prepared by the following steps: 1) Aggregate pretreatment: Pre-curing basalt machine-made sand and recycled ceramsite in an environment of 5-10℃ for 48 hours, controlling the moisture content to ≤0.5%; 2) Nanoslurry preparation: Surface-modified nano-silica and dispersant were added to 30% mixing water at a ratio of 100:1.2 and ultrasonically treated to form a uniform suspension; 3) Step-by-step mixing process: Stage 1: Add pre-treated aggregate and 1 / 2 of cementitious materials and dry mix for 45±5s; The second stage: add the remaining cementitious materials, mineral composite admixtures and polypropylene fibers and mix for 70±10s; The third stage: inject the suspension, composite antifreeze agent, polycarboxylic acid air entraining agent and the remaining mixing water, and stir for 120±15s until the slump reaches 200-230mm; 4) Gradient maintenance: After initial setting, the template is heated by electromagnetic induction and maintained at a constant temperature of 8±2℃ for 60h; After removing the formwork, spray the organic silicon curing agent and naturally cure it in an environment of -15 to -25℃ until the age of 28 days.

[0012] After adopting the above technical solution, the beneficial effects of the present invention are: 1. Calcium nitrate provides early antifreeze (the liquid freezing point drops to -28°C), calcium formate accelerates low-temperature hydration (the 3d strength at -20°C can reach 45% of the design value), and triethanolamine acts as a dispersant to improve the synergistic efficiency of each component.

[0013] 2. Surface-modified nano-silica can fill pores of 10-100 nm, reducing the critical pore size from 52 nm to 28 nm and increasing the freeze-thaw durability index by 40%.

[0014] 3. Polypropylene fiber and air-entraining agent form a three-dimensional stress buffer network, which reduces the temperature stress concentration coefficient by 0.3-0.5. DETAILED DESCRIPTION

[0015] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0016] The present invention provides a technical solution: A bridge concrete for extremely cold regions, comprising the following raw materials in parts by weight: 320-400 parts of P·O 42.5 grade Portland cement, 9-16 parts of composite antifreeze, 12-22 parts of surface-modified nano-silica, 85-130 parts of mineral composite admixture, 950-1250 parts of aggregate, 0.7-1.6 parts of polycarboxylic acid air-entraining agent, and 1.8-5.5 parts of polypropylene fiber; The composite antifreeze is prepared by mixing calcium nitrate, calcium formate and triethanolamine in the ratio of (3.2-5.1):(1.9-4.2):1, and the effective content of Ca(NO3)2·4H2O in the calcium nitrate is ≥96%.

[0017] The composite mineral admixture is composed of fly ash / slag powder / silica fume in a mass ratio of (40-60): (30-50): (10-15), and has a specific surface area of ​​≥450m 2 / kg.

[0018] The particle size distribution of the mineral composite admixture satisfies: Fly ash: 45-55μm D50, water requirement ratio ≤95%; Slag powder: specific surface area 430-480m² / kg, 7d activity index ≥85%; Silica fume: SiO2 content ≥92%, loss on ignition ≤3%; The coefficient of variation of the mixing uniformity of the three is ≤3.5%.

[0019] In the concrete raw materials, the water-cement ratio is between 0.27-0.36, wherein water refers to mixing water, excluding aggregate water.

[0020] Binder: Contains Portland cement + composite mineral admixtures This design transcends the limitations of a single water-cement ratio by incorporating mineral admixtures into the cementitious system. Admixtures account for 17%-24% of the total cementitious material. The low water-cement ratio (≤0.35) reduces free water content, lowering the capillary freezing point from -1°C to -5°C. Nano-silica fills pores <50nm, creating a tortuous seepage path and reducing the risk of frost heave damage.

[0021] The aggregate is a composite aggregate of basalt machine-made sand and recycled ceramsite, which is mixed in a mass ratio of (7-8):(2-3).

[0022] The surface-modified nano-silica is grafted with gamma-aminopropyltriethoxysilane; after modification, the absolute value of the Zeta potential is increased to 35-42 mV, and the dispersion stability index in cement paste is greater than or equal to 0.88.

[0023] As an embodiment of the present invention, it is prepared by the following steps: 1) Aggregate pretreatment: Pre-curing basalt machine-made sand and recycled ceramsite in an environment of 5-10℃ for 48 hours, controlling the moisture content to ≤0.5%; 2) Nanoslurry preparation: Surface-modified nano-silica and a dispersant (sodium lignin sulfonate can be used) are added to 30% mixing water at a ratio of 100:1.2 and ultrasonically treated (40kHz, 800W) to form a uniform suspension; 3) Step-by-step mixing process: Stage 1: Add pre-treated aggregate and 1 / 2 of cementitious materials and dry mix for 45±5s; The second stage: add the remaining cementitious materials, mineral composite admixtures and polypropylene fibers and mix for 70±10s; The third stage: inject the suspension, composite antifreeze agent, polycarboxylic acid air entraining agent and the remaining mixing water, and stir for 120±15s until the slump reaches 200-230mm; 4) Step-by-step gradient stirring design principle: In the first stage, dry mixing forms a pre-wrapped layer at the aggregate-binder interface; In the second stage, medium-speed stirring is used to avoid fiber agglomeration (fiber dispersion qualification rate ≥ 98%); In the third stage, high-speed stirring is used to achieve uniform dispersion of nanoparticles (coefficient of variation of slurry uniformity ≤ 2.1%).

[0024] 5) Gradient maintenance: After initial setting, the template is heated by electromagnetic induction and maintained at a constant temperature of 8±2℃ for 60h; After removing the formwork, spray the organic silicon curing agent and naturally cure in an environment of -15 to -25℃ until the age of 28 days. Example 1: Prepared from the following raw materials Cement: 380kg (Conch P·O 42.5); Composite antifreeze: 14kg (calcium nitrate: calcium formate: triethanolamine = 4.5:3.2:1); Nano silicon dioxide: 18kg; Mineral composite admixture: fly ash 68kg + slag powder 45kg + silica fume 15kg; Aggregate: basalt sand (5-25mm continuous grading) 890kg + ceramsite (bulk density 1200kg / m³) 310kg; Air entraining agent: 1.1kg; Polypropylene fiber: 4.2kg; Water-cement ratio: 0.31.

[0025] Prepared by the following steps: 1) Aggregate pretreatment: Use a jaw crusher to crush basalt machine-made sand into a continuous gradation of 5-25mm, store it in a constant temperature environment of 10℃ for 72 hours, and control the moisture content to ≤0.5%. After the recycled ceramsite is magnetically separated to remove metal impurities, it is graded by a vibrating screen (5-20mm) to meet the requirements of Class II aggregate in "Pebbles and Crushed Stones for Construction" (GB / T 14685-2022). Then, pre-curing the basalt machine-made sand and recycled ceramsite in an environment of 5-10℃ for 48 hours, and controlling the moisture content to ≤0.5%; 2) Nanoslurry preparation: Surface-modified nano-silica and a dispersant (sodium lignin sulfonate can be used) are added to 30% mixing water at a ratio of 100:1 and ultrasonically treated (40kHz, 800W) to form a uniform suspension; 3) Step-by-step mixing process: Stage 1 (dry mix): Add pre-treated aggregate (basalt sand + cementite) and 50% cementitious materials (cement + mineral admixtures), and stir at low speed (15-20 rpm) for 45 seconds until uniform; Stage 2 (fiber dispersion): Add polypropylene fibers and the remaining gelling material, stir at medium speed (25-30 rpm) for 70 seconds, and visually check for fiber agglomeration. Stage 3 (liquid phase mixing): inject nano suspension, composite antifreeze agent, air entraining agent and remaining mixing water in sequence, and stir at high speed (35-40rpm) for 120 seconds until the slump reaches 200±20mm; 4) Gradient maintenance: After initial setting, the template is heated by electromagnetic induction and maintained at a constant temperature of 8±2℃ for 60h; After removing the formwork, spray the organic silicon curing agent and naturally cure it in an environment of -15 to -25℃ until the age of 28 days.

[0026] The performance test of the concrete is carried out as follows: 1. Mechanical properties test Compressive strength: according to the "Standard for Test Methods of Physical and Mechanical Properties of Concrete" (GB / T 50081-2019); Specimen size: 150mm cube, 3 pieces per group; Loading rate: 0.5 MPa / s, record the strength values ​​at 28 days and 56 days; Flexural strength: measured by three-point bending method (span 450mm) according to JTG E30-2005; 2. Durability test Rapid freeze-thaw cycle: in accordance with the "Standard for Test Methods of Long-term Performance and Durability of Ordinary Concrete" (GB / T50082-2009); Specimen size: 100×100×400mm prism; Cycling system: 4 hours per cycle between -18℃ and 5℃, for a total of 300 cycles; Evaluation indicators: mass loss rate, relative dynamic elastic modulus (measured by ultrasonic method); Chloride ion diffusion coefficient: RCM method (Determination of chloride ion diffusion coefficient of concrete JGJ / T 193-2009); Applied voltage: 30V, test duration 24h; Data collection: Cl⁻ penetration depth was measured by AgNO3 colorimetry; 3. Microstructure Analysis Scanning electron microscopy (SEM): Sample preparation: core sample was gold-sprayed, accelerating voltage 15 kV; Observation focus: interfacial transition zone (ITZ) structure and nanoparticle distribution; Mercury Intrusion Porosimetry (MIP): Testing instrument: pore size analysis range 3nm-360μm; Key parameters: critical pore size, porosity, and pore structure fractal dimension; 4. Project site inspection Coring verification: Use a core drill to take cores (Φ100mm) at the mid-span / support of the beam to test the deviation between the actual strength and the laboratory data (required to be ≤±15%); Infrared thermal imaging: Use a non-contact thermal imager to scan the surface of the structure and identify areas with abnormal temperature gradients (temperature differences ≥10°C indicate potential defects); The performance indicators of this concrete were compared with those of conventional C50 concrete, and the specific results are shown in Table 1. Table 1, performance comparison table

[0027] Example 2: By controlling the molar ratio of calcium nitrate to calcium formate in the range of 1.05-1.25 (see Table 2), the optimal balance between the liquid phase freezing point and the early strength development is achieved.

[0028] Table 2, comparison of ratio schemes

[0029] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A bridge concrete for extremely cold regions, characterized in that: The invention comprises the following raw materials in parts by weight: 320-400 parts of P·O 42.5 grade Portland cement, 9-16 parts of composite antifreeze, 12-22 parts of surface-modified nano-silica, 85-130 parts of mineral composite admixture, 950-1250 parts of aggregate, 0.7-1.6 parts of polycarboxylic acid air-entraining agent, and 1.8-5.5 parts of polypropylene fiber; The composite antifreeze is prepared by mixing calcium nitrate, calcium formate and triethanolamine in the ratio of (3.2-5.1):(1.9-4.2):1, and the effective content of Ca(NO3)2·4H2O in the calcium nitrate is ≥96%; The components are synergistically configured to achieve: a) Liquid freezing point ≤ -28℃, and 3d strength at -20℃ reaches more than 45% of the design strength; b) Nano-silica fills 10-100nm pores, with a critical pore size of ≤28nm; c) Polypropylene fiber and air entraining agent form a three-dimensional buffer network, and the temperature stress concentration coefficient is ≤0.

35.

2. The extremely cold region bridge concrete according to claim 1, characterized in that: The composite mineral admixture is composed of fly ash / slag powder / silica fume in a mass ratio of (40-60):(30-50):(10-15), and has a specific surface area of ​​450m2 / kg or more.

3. The extremely cold region bridge concrete according to claim 2, characterized in that: The particle size distribution of the mineral composite admixture satisfies: Fly ash: 45-55μm D50, water requirement ratio ≤95%; Slag powder: specific surface area 430-480m² / kg, 7d activity index ≥85%; Silica fume: SiO2 content ≥92%, loss on ignition ≤3%; The coefficient of variation of the mixing uniformity of the three is ≤3.5%.

4. The extremely cold region bridge concrete according to claim 3, characterized in that: The water-to-binder ratio of the concrete raw materials is between 0.27 and 0.

36.

5. The extremely cold region bridge concrete according to claim 1, characterized in that: The aggregate is a composite aggregate of basalt machine-made sand and recycled ceramsite, which is mixed in a mass ratio of (7-8):(2-3).

6. The extremely cold region bridge concrete according to claim 1, characterized in that: The surface-modified nano-silica is grafted with γ-aminopropyltriethoxysilane, and the absolute value of the Zeta potential after modification is 35-42 mV, and the dispersion stability index in cement paste is ≥0.

88.

7. The extremely cold region bridge concrete according to claim 1, characterized in that: Prepared by the following steps: 1) Aggregate pretreatment: Pre-curing basalt machine-made sand and recycled ceramsite in an environment of 5-10℃ for 48 hours, controlling the moisture content to ≤0.5%; 2) Nanoslurry preparation: Surface-modified nano-silica and dispersant were added to 30% mixing water at a ratio of 100:1.2 and ultrasonically treated to form a uniform suspension; 3) Step-by-step mixing process: Stage 1: dry mix pretreated aggregate and 1 / 2 cementitious material at 15-20 rpm for 45±5 seconds; The second stage: add the remaining cementitious materials, mineral composite admixtures and polypropylene fibers at a speed of 25-30 rpm and mix for 70 ± 10 seconds; The third stage: inject the suspension, composite antifreeze agent, polycarboxylic acid air entraining agent and remaining mixing water at a speed of 35-40 rpm, and stir for 120±15 seconds until the slump reaches 200-230 mm; 4) Gradient maintenance: After initial setting, the template is heated by electromagnetic induction and maintained at a constant temperature of 8±2℃ for 60h; After removing the formwork, spray the organic silicon curing agent and naturally cure it in an environment of -15 to -25℃ until the age of 28 days.

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