Non-autoclaved prestressed concrete pipe pile and pipe pile preparation method

Abstract

The invention discloses a non-autoclaved prestressed concrete pipe pile and a preparation method thereof, and relates to the field of fish culture. According to the autoclave-free prestressed concrete pipe pile and the pipe pile preparation method, through collaborative innovation of a material system and process design, comprehensive breakthrough is achieved in the aspects of mechanical properties, environmental protection benefits and environmental adaptability; in the aspect of technical performance, the hydration activity in a low-temperature environment is remarkably improved due to introduction of the phosphorus slag and the composite exciting agent in the cementing material, so that the compressive strength of the pipe pile in 28 days in the environment of-20 DEG C reaches 95% or above of a standard value (embodiment 3: 98.0 MPa), and meanwhile, the compactness of concrete is improved by 20% or above due to optimal grading of the nickel ore slag sand and the two-graded broken stone; after 300 times of freezing and thawing cycles, the mass loss is only 2.8% (embodiment 1), the chloride ion permeability coefficient is as low as 1.4 * 10 <-12 > m < 2 > / s, and the anti-permeability and durability are obviously superior to those of a traditional autoclaved pipe pile (contrast experiment: freezing and thawing loss rate reaches 46%).

Description

Technical Field

[0001] The invention relates to the technical field of fish farming, in particular to a pressure-free prestressed concrete pipe pile and a pipe pile preparation method. Background Art

[0002] The production of traditional prestressed concrete pipe piles (PHC pipe piles) has long relied on high-pressure steam curing technology, and its core defect is excessive dependence on energy and equipment. High-pressure steam curing needs to be carried out under conditions of 0.9-1.0MPa and 170-180℃, resulting in the consumption of more than 3kg of standard coal per meter of pipe piles and the generation of 8.5kg of CO2 emissions, which seriously conflicts with the goal of green and low-carbon industrial transformation. In addition, the investment cost of autoclave equipment is high, the operation is complicated, and there are safety hazards (such as frequent autoclave explosion accidents), which further restricts the sustainable development of this technology. Although the industry has tried to reduce the steam curing pressure by adding active materials such as mineral powder and silica fume, the existing autoclave-free technology (such as CN103030342B) still faces the problem of insufficient synergy of the material system. Especially in low-temperature environments, the reaction activity of cementitious materials drops sharply, resulting in slow growth of the early strength of the pipe piles, which is difficult to meet the construction progress requirements in cold areas.

[0003] Another shortcoming of the existing autoclave-free technology is the neglect of aggregate grading and durability design. For example, CN111003988A uses nano-silica to improve strength, but does not optimize the aggregate system. The high mud content (≥2.5%) and single gradation of natural sand lead to insufficient concrete density. After 200 freeze-thaw cycles, the mass loss is more than 5%, and the residual slurry volume is as high as 15%-20%, resulting in a waste of resources. At the same time, the traditional curing process directly uses the high-temperature rapid heating mode in cold areas, which leads to the concentration of temperature difference stress inside the pipe pile, which is prone to microcracks and further deteriorates the impermeability and frost resistance. These problems have seriously restricted the application of existing autoclave-free pipe piles in complex environments.

[0004] The contradictions in current technological development are concentrated on the balance between environmental protection needs and performance requirements. On the one hand, the high-pressure steam curing process is gradually being eliminated due to high energy consumption and high emissions; on the other hand, although the existing autoclave-free technology reduces energy consumption, it cannot take into account both strength and durability due to defects in the material system and extensive process, especially in harsh environments such as low temperature and saline soil. It performs poorly. For example, the simple compounding of mineral powder and silica fume (such as CN103030342B) does not solve the problem of stimulating the activity of cementitious materials at low temperatures, while relying solely on high-efficiency water reducers (such as CN112125540A) improves fluidity, but leads to an increase in concrete shrinkage. Therefore, there is an urgent need for a systematic solution to achieve a comprehensive breakthrough in the strength, durability and environmental adaptability of autoclave-free pipe piles through material innovation and refined process control. Summary of the Invention

[0005] (1) Technical problems solved

[0006] Traditional prestressed concrete piles rely on high-pressure steam curing, which results in high energy consumption (coal consumption per ton of pile ≥ 3kg), high carbon emissions (CO2 ≥ 8.5kg / m), and significant equipment safety risks. While existing autoclave-free technology reduces energy consumption, it also suffers from the following drawbacks:

[0007] Insufficient low-temperature activity: In cold regions (temperature ≤ 20°C), the hydration rate of cementitious materials is low, and the 28-day strength is only 70-80% of the standard value;

[0008] Durability defects: mass loss ≥5% after 200 freeze-thaw cycles, chloride ion permeability coefficient ≥3×10 -12 m 2 / s;

[0009] Extensive process: The steam curing system is not adapted to low-temperature environments. Rapid heating causes an internal temperature difference of ≥25°C, which causes microcracks.

[0010] Waste of resources: residual slurry volume ≥15%, low industrial solid waste utilization rate (≤30%).

[0011] (2) Technical solution

[0012] To achieve the above object, the present invention provides the following technical solutions: a prestressed concrete pipe pile without autoclaving and a method for preparing the pipe pile,

[0013] 1. Cementitious material system design

[0014] Core component synergy mechanism:

[0015] Cement-mineral powder-phosphorus slag ternary system: PO52.5R cement provides early strength, S95 mineral powder optimizes hydration products (CSH gel ratio increased to 65%), and CaO in the phosphorus slag reacts with the activator to form ettringite (AFt), which can continue to hydrate even at low temperatures (-20°C);

[0016] Silica fume-microbead fly ash composite filling: nano silica fume (15,000m 2 / kg) fills the gaps between cement particles, and the ball effect of micro-fly ash (D90≤10μm) reduces the slurry viscosity. The two work together to reduce the porosity from 15% to 8%;

[0017] Exciter-directed activation: sodium sulfate provides SO4 2- Promote the formation of AFt, calcium hydroxide maintains high alkalinity (pH ≥ 12.5), and the reaction activation energy is reduced by 30% at low temperatures.

[0018] 2. Aggregate gradation optimization

[0019] Enhanced frost resistance of nickel ore slag sand:

[0020] Nickel slag with Fe2O3 content ≥8% forms a dense iron phase hydration product (FT gel) at the interface with cement paste, which inhibits ice crystal expansion stress during freeze-thaw cycles;

[0021] The gradation design (fineness modulus 2.8-3.2) matches the Fuller curve, and the bulk density is increased to 1850kg / m 3 .

[0022] Double-graded crushed stone densification design:

[0023] 5-16mm crushed stones fill the gaps between 16-31.5mm crushed stones, reducing the void ratio from 22% to 16%;

[0024] The high hardness of basalt crushed stone (Mohs hardness 7-8) ensures compressive strength ≥105MPa.

[0025] 3. Preparation process innovation

[0026] Refinement of centrifugal process parameters:

[0027] Low speed stage (70-80r / min): uniform distribution, aggregate segregation rate ≤1.2%;

[0028] High-speed stage (450-500r / min): centrifugal force ≥12G, slurry density ≥98%.

[0029] Four-stage maintenance system:

[0030] Static stage (35-40℃): promote initial hydration and form a preliminary strength skeleton;

[0031] Gradient heating (≤30℃ / h): verified by finite element simulation, the internal temperature difference is ≤15℃, avoiding temperature cracks;

[0032] Constant temperature stage (90-95°C): The activator accelerates the reaction and more than 70% CSH gel is generated within 4 hours;

[0033] Natural curing adaptation: dual modes of wet curing (temperate zone) and thermal insulation film + perlite (cold zone) to ensure the later strength development.

[0034] Breakthrough in mechanical properties:

[0035] The 28-day compressive strength reaches 108 MPa (Example 1), which is 25% higher than that of traditional autoclaved piles.

[0036] The 28-day strength retention rate under -20°C environment is ≥95% (Example 3).

[0037] Excellent durability:

[0038] The mass loss after 300 freeze-thaw cycles is only 2.8% (ASTM C666), which is better than the 5.2% of the traditional process;

[0039] Chloride ion permeability coefficient is as low as 1.3×10 -12 m 2 / s (Example 2), the carbonization resistance is improved by 40%.

[0040] Significant green benefits:

[0041] CO2 emissions per ton of pile are reduced to 85kg, a 53% reduction compared to the autoclaving process;

[0042] The comprehensive utilization rate of industrial solid waste (phosphorus slag, nickel slag, fly ash) is ≥45%, and the slurry recovery rate is 100%.

[0043] (3) Beneficial effects

[0044] Compared with the prior art, the present invention provides a non-autoclaved prestressed concrete pipe pile and a method for preparing the pipe pile, which has the following beneficial effects:

[0045] The present invention achieves comprehensive breakthroughs in mechanical properties, environmental benefits, and environmental adaptability through the collaborative innovation of material systems and process design. In terms of technical performance, the introduction of phosphorus slag and composite activators in the cementitious material significantly improves the hydration activity in a low-temperature environment, so that the compressive strength of the pipe pile in a -20°C environment reaches more than 95% of the standard value after 28 days (Example 3: 98.0 MPa). At the same time, the optimized gradation of nickel ore slag sand and double-graded crushed stone increases the density of the concrete by more than 20%, and the mass loss after 300 freeze-thaw cycles is only 2.8% (Example 1). The chloride ion permeability coefficient is as low as 1.4×10 -12 m 2 / s, the impermeability and durability are significantly better than those of traditional autoclaved pipe piles (comparative experiment: freeze-thaw loss rate ↓46%).

[0046] From the perspective of environmental protection and economy, the present invention completely abandons the high-pressure steam curing process and combines gradient temperature curing with residual slurry control technology to achieve a 53% reduction in CO2 emissions per ton of pipe piles (Example 1: 85kg vs. 180kg in traditional process), a 60% reduction in comprehensive energy consumption, and the residual slurry is controlled within 5% (Example 1: 4.5%), which is recycled and used to prepare cushion concrete, achieving zero resource waste; in addition, the comprehensive utilization rate of industrial solid waste (phosphorus slag, nickel slag, fly ash) in cementitious materials reaches 47% (Example 2), and the production cost is reduced by 20% compared with the traditional process, which is in line with the needs of the circular economy.

[0047] In terms of environmental adaptability, the innovative four-stage maintenance process solves the problem of internal microcracks caused by temperature difference stress in cold areas through precise temperature control (gradient heating rate ≤30℃ / h) and humidity management (≥95%) (SEM observation of crack density reduced by 50%), and is compatible with extreme climatic conditions: in high-altitude cold areas (-30℃), double-layer insulation film and electric heating assistance are used to maintain constant temperature, and coastal saline environments rely on high impermeability to resist chloride ion corrosion; this technology expands the application range of pipe piles from traditional temperate zones to complex geological environments such as high-altitude cold, coastal, and saline-alkali environments, providing green infrastructure with a new type of pile foundation material with high strength, durability and low carbon characteristics (Example 3: -20℃ strength compliance rate is 94.2%). DETAILED DESCRIPTION

[0048] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0049] Example 1 (standard ratio, normal temperature environment application)

[0050] 1. Formulation and raw materials

[0051] Cementitious materials (mass fractions):

[0052] PO52.5R Portland cement: 400 parts (Conch brand, in line with GB 175-2007, 3-day strength 26.5 MPa, 28-day strength 55.2 MPa);

[0053] S95 grade mineral powder: 90 parts (produced by Shougang, with a specific surface area of 425m 2 / kg, 7-day activity index 78%, 28-day activity index 97%);

[0054] Silica fume: 60 parts (produced by Erken, with a specific surface area of 18,000m 2 / kg, SiO2 content 93.5%, amorphous content 91%);

[0055] Microbead fly ash: 60 parts (produced by Huaneng Power Plant, D90 = 8 μm, glass microbead content 88%, surface pretreated with 0.8% silane coupling agent);

[0056] Phosphorus slag: 25 parts (produced in Guizhou, D90 = 42 μm, CaO content 42%, P2O5 content 2.3%);

[0057] Sodium sulfate-calcium hydroxide activator: 6 parts (mass ratio 2.5:1, ground to D50 = 20 μm).

[0058] Aggregate system:

[0059] Nickel ore slag sand: 28% (fineness modulus 3.0, Fe2O3 content 8.5%, crushing value 10%);

[0060] Double-graded crushed stone:

[0061] 5-16mm basalt crushed stone: 32% (crushed value 7%, needle-like particles 3%);

[0062] 16-31.5mm basalt gravel: 22% (porosity 15.8%).

[0063] Admixtures:

[0064] Polycarboxylate water reducer (Subot PCA-I): dosage 1.8% (water reduction rate 32%);

[0065] Plasticizer (zeolite powder: PVC paste resin = 1:0.4): dosage 0.8% (PVC paste resin polymerization degree 1400, paste viscosity 4200 mPa·s).

[0066] 2. Preparation process

[0067] Preprocessing:

[0068] The phosphorus slag was dried to a moisture content of 0.4% and ball-milled to a D90 of 42 μm;

[0069] The nickel ore slag sand is washed with water to a mud content of 0.7% and then dried to a moisture content of 0.2%.

[0070] Stirring:

[0071] Cementitious material and activator are dry-mixed for 2.5 minutes → aggregate is added and dry-mixed for 1 minute → water-reducing agent, plasticizer and water (water-cement ratio 0.28) are injected → forced stirring is performed for 200 seconds → slump is 195 mm.

[0072] Tensioning and forming:

[0073] The prestressed steel bars (Φ9.0mm, strength 1420MPa) were pre-tensioned to 0.72fptk (1022MPa), with an anchoring efficiency coefficient of 0.96;

[0074] Centrifugal parameters: low speed 75r / min×3min→medium speed 230r / min×5min→high speed 480r / min×8min→residual slurry volume 4.5%.

[0075] Maintenance:

[0076] Standing: 38°C constant temperature for 1.5h (humidity 92%);

[0077] Gradient heating: heating in stages within 2 hours (35→60℃: 15℃ / h; 60→90℃: 25℃ / h; 90→95℃: 5℃ / h);

[0078] Constant temperature: 93℃ for 5h (humidity 96%);

[0079] Natural maintenance: wet 3 times a day (water temperature 20℃) at an air temperature of 25℃ for 7 days.

[0080] 3. Performance Testing

[0081]

[0082]

[0083]

[0084]

[0085] Example 2 (Low Cement Energy-Saving Ratio)

[0086] 1. Recipe Adjustment

[0087] Cementitious materials:

[0088] Cement: 380 parts (other components are the same as in Example 1); mineral powder: 100 parts (to compensate for the activity gap).

[0089] 2. Process adjustment:

[0090] The mixing time is extended to 220s (slump 190mm); the constant temperature curing is shortened to 4h (air temperature 28℃).

[0091] 3. Performance Testing

[0092]

[0093]

[0094] Example 3 (Application in cold regions at -20°C)

[0095] 1. Strengthen formula and process

[0096] Cementitious material adjustment:

[0097] Increase the activator to 8 parts (sodium sulfate: calcium hydroxide = 3:1);

[0098] Add 2 parts of calcium nitrite antifreeze (no significant change in chloride ion permeability coefficient). Curing process adjustment:

[0099] Constant temperature maintenance is extended to 7h (ambient temperature -5℃);

[0100] Natural curing: Covered with double-layer thermal insulation film (0.2mm PE + 0.5mm PVC), with 8mm perlite layer filled between the films;

[0101] Electric heating assistance: start the electric heating film at -10℃ (power density 0.4W / cm 2 ), maintain the surface temperature ≥5℃.

[0102] 2. Performance Testing

[0103]

[0104] Comparative experiment (vs traditional autoclaved pipe pile CN103030342B)

[0105]

[0106]

[0107]

[0108] Detailed description of experimental methods

[0109] Compressive strength test:

[0110] Specimen: 100mm×100mm×100mm cube, standard curing to age;

[0111] Equipment: YES-2000 pressure testing machine, loading rate 1.2 MPa / s.

[0112] Freeze-thaw cycle test:

[0113] Conditions: -18°C freezing (4 h) → 20°C water bath thawing (4 h), 300 cycles; mass loss rate = (initial mass - final mass) / initial mass × 100%;

[0114] Dynamic elastic modulus: Resonance frequency method (ASTM C215).

[0115] Chloride ion permeability:

[0116] Method: RCM method (rapid chloride migration test), specimen Φ100×50mm; condition: 30V DC, continuous 24h, measure the chloride ion penetration depth.

[0117] Microstructure analysis:

[0118] Instrument: Hitachi SU8010 field emission electron microscope (SEM);

[0119] Sample processing: gold spraying, accelerating voltage 15kV, observation of interface transition zone and crack distribution.

[0120] It can be seen that the present invention has achieved a comprehensive breakthrough in mechanical properties, environmental benefits and environmental adaptability through the collaborative innovation of material system and process design. In terms of technical performance, the introduction of phosphorus slag and composite activator in the cementitious material significantly improves the hydration activity in low temperature environment, so that the compressive strength of the pipe pile in a -20°C environment after 28 days reaches more than 95% of the standard value (Example 3: 98.0MPa). At the same time, the optimized gradation of nickel ore slag sand and double-graded crushed stone increases the density of concrete by more than 20%, and the mass loss after 300 freeze-thaw cycles is only 2.8% (Example 1). The chloride ion permeability coefficient is as low as 1.4×10 - 12 m 2 / s, the impermeability and durability are significantly better than those of traditional autoclaved pipe piles (comparative experiment: freeze-thaw loss rate ↓46%).

Claims

1. A non-pressure steaming prestressed concrete pipe pile, characterized in that: Prepared from the following components in parts by weight: 380-420 parts of PO52.5R Portland cement, having a 3-day compressive strength of ≥25 MPa and a 28-day compressive strength of ≥52.5 MPa (GB 175-2007); 80-100 parts of S95 grade granulated blast furnace slag powder, with a specific surface area of 400-450m 2 / kg, activity index ≥75% in 7 days, ≥95% in 28 days (GB / T 18046-2017); 50-70 parts of silica fume, the specific surface area of the silica fume is ≥15,000m 2 / kg, silicon dioxide content ≥92%, loss on ignition ≤4% (GB / T 27690-2011); 50-70 parts of micro-bead fly ash, wherein the micro-bead fly ash has a particle size distribution D90 ≤ 10 μm, a water requirement ratio ≤ 95%, and a loss on ignition ≤ 5% (GB / T 1596-2017); 20-30 parts of phosphorus slag, wherein the particle size D90 of the phosphorus slag is ≤45 μm, the phosphorus pentoxide content is ≤3%, and the calcium oxide content is ≥40%; 5-8 parts of a composite activator of sodium sulfate and calcium hydroxide, wherein the mass ratio of sodium sulfate to calcium hydroxide is 2:1-3:1; The fine aggregate is nickel ore slag sand, accounting for 25-30% of the total mass of the aggregate, the nickel ore slag sand has a fineness modulus of 2.8-3.2, a mud content of ≤1.0%, and a crushing value of ≤12%; The coarse aggregate is double-graded crushed stone, of which 5-16 mm particle size crushed stone accounts for 30-35%, 16-31.5 mm particle size crushed stone accounts for 20-25%, and the crushed stone is basalt crushed stone with a crushing value of ≤8% and a needle-like particle content of ≤5%.

2. The autoclave-free prestressed concrete pipe pile and the method for preparing the pipe pile according to claim 1, characterized in that: The preparation method of the sodium sulfate and calcium hydroxide composite activator is as follows: sodium sulfate powder and calcium hydroxide powder are mixed in proportion and then ground to a particle size of ≤45 μm and a coefficient of variation of mixing uniformity of ≤5%; The amorphous silicon dioxide content in the silica fume is ≥90%, and the BET specific surface area measured by nitrogen adsorption method is between 15,000-20,000m 2 / kg.

3. The autoclave-free prestressed concrete pipe pile and the method for preparing the pipe pile according to claim 1, characterized in that: The nickel ore slag sand has an Fe2O3 content of ≥8%, and EDX analysis shows that its surface is coated with a calcium silicate hydrate (CSH) gel layer with a thickness of 50-100 nm; The double-graded crushed stone adopts the optimized design of Fuller ideal gradation curve, with a void ratio of ≤16% and a bulk density of ≥1600kg / m 3 .

4. The autoclave-free prestressed concrete pipe pile and the method for preparing the pipe pile according to claim 1, characterized in that: The glass microbead content of the microbead fly ash is ≥85%, and the surface is pretreated with 0.5-1.0% silane coupling agent; The active calcium oxide content in the phosphorus slag is ≥35%, and XRD detection shows that the main mineral components are dicalcium silicate (C2S) and glass phase, wherein the glass phase content is ≥60%.

5. The autoclave-free prestressed concrete pipe pile and the method for preparing the pipe pile according to claim 1, characterized in that: The compressive strength of the pipe pile meets the following indicators: 3-day compressive strength ≥60MPa; 28-day compressive strength ≥105MPa; Under standard curing conditions of -20℃, the 28-day compressive strength is ≥95% of the standard value; The durability indicators of pipe piles include: After 300 freeze-thaw cycles, the mass loss is ≤3% and the relative dynamic elastic modulus is ≥90% (ASTM C666 Procedure A); Chloride ion diffusion coefficient ≤1.5×10 -12 m 2 / s(ASTM C1202); Carbonization depth 28 days ≤ 2.0mm (GB / T 50082-2009); The surface of the pipe pile is coated with a nano-silica-based waterproof coating with a coating thickness of 0.2-0.5mm, a contact angle ≥120°, and alkali resistance (immersion in 10% NaOH for 28 days) without falling off.

6. A method for preparing the autoclave-free prestressed concrete pipe pile according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Raw material pretreatment: The phosphorus slag was dried at 105±5℃ to a moisture content of ≤0.5%, and then ball-milled to a D90 of ≤45μm; Wash the nickel ore slag sand with water until the mud content is ≤1.0%, and dry it at 50-60℃ until the moisture content is ≤0.3%; S2. Ingredients and mixing: Dry mix the cementitious materials (cement, mineral powder, silica fume, micro-fly ash, phosphorus slag) and activator according to the proportion for 2-3 minutes; Add aggregate (nickel ore slag sand, double-graded crushed stone) and continue dry mixing for 1 minute; Add polycarboxylic acid high-efficiency water-reducing agent (water-reducing rate ≥ 30%) and plasticizer (mixed by zeolite powder and PVC paste resin at a ratio of 1:0.3-0.5), inject mixing water (water-binder ratio 0.28-0.32), force stirring for 180-240 seconds, and control the slump out of the machine to be 180-200mm; S3, forming and tensioning: Place the prestressed steel bar skeleton into the pile mold and apply prestress using the pre-tensioning method. The tensioning control stress is 0.7-0.75 times the standard value of the steel bar tensile strength, and the anchoring efficiency coefficient is ≥0.95; Pump the concrete mixture into the mold, and control the feeding rate at 0.8-1.2m 3 / min; S4, centrifugal molding: Low speed stage: 70-80r / min centrifugal for 3 minutes, the fabric uniformity deviation is ≤5%; Medium speed stage: centrifuge at 200-250r / min for 5 minutes, initial density ≥90%; High-speed stage: centrifugal at 450-500r / min for 8 minutes, the final pile wall thickness tolerance is ≤±2mm, and the residual slurry volume is ≤5%; S5. Maintenance process: Static stage: maintain at a constant temperature of 35-40℃ for 1.5h in an environment with humidity ≥90%; Gradient heating: increase the temperature to 90-95°C within 2 hours at a rate of ≤30°C / h; Constant temperature curing: curing at 90-95℃ and humidity ≥95% for 4-6 hours (extended to 7 hours when the ambient temperature is ≤20℃); Natural curing: When the temperature is greater than 20℃, wet curing is carried out 3 times a day, and the temperature difference between the water temperature and the pile temperature is ≤15℃; when the temperature is ≤20℃, cover with double-layer insulation film (inner layer is 0.2mm PE film, outer layer is 0.5mm PVC film), and fill 5-10mm perlite insulation layer between the films.

7. The method for preparing a non-autoclaved prestressed concrete pipe pile according to claim 6, characterized in that: The amount of the plasticizer in the batching and stirring steps is 0.5-1.0% of the total mass of the gelling material, and the polymerization degree of the PVC paste resin is 1300-1500, and the paste viscosity is 3000-5000 mPa·s (25° C.).

8. The method for preparing a non-autoclaved prestressed concrete pipe pile according to claim 6, characterized in that: The gradient temperature rise stage in the curing process adopts segmented temperature control: Stage 1: 35°C → 60°C, heating rate 15°C / h; The second stage: 60℃→90℃, heating rate 25℃ / h; The third stage: 90℃→95℃, heating rate 5℃ / h.

9. The method for preparing a non-autoclaved prestressed concrete pipe pile according to claim 6, characterized in that: During the natural curing stage, when the temperature is ≤-10℃, electric heating insulation film is used for auxiliary heating, and the heating power density is ≤0.5W / cm 2 , maintain the surface temperature of the pipe pile ≥5℃.

10. The method for preparing a non-autoclaved prestressed concrete pipe pile according to claim 6, characterized in that: After the residual slurry is recovered, the water-binder ratio is adjusted to 0.35-0.40 and used to prepare a cushion concrete with a compressive strength of ≥30 MPa.

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