Prestressed concrete beam and method of manufacturing the same

Abstract

This invention relates to a method for preparing prestressed concrete beams, comprising the following steps: S1: mixing and stirring cement, fly ash, fine aggregate, and coarse aggregate to obtain dry material; S2: mixing nano-silica, natural zeolite, and water, and ultrasonically dispersing to obtain a dispersion; mixing and stirring the dry material and the dispersion to obtain wet material; S3: adding a water-reducing agent to the wet material and stirring to obtain concrete slurry; S4: pouring the concrete slurry into a mold for post-tensioned prestressed concrete beams, and then performing a first curing to obtain a concrete beam blank at a curing temperature of 35-55℃; applying prestress to the concrete beam blank to obtain a prestressed concrete beam blank; S5: performing a second curing on the prestressed concrete beam blank at a curing temperature of 40-65℃ to obtain a prestressed concrete beam. This method solves the problems of excessive deformation and cracking of concrete beams after long-term use, slow early strength development of concrete beams, and excessively high cost of concrete beams in existing technologies.

Description

Technical Field

[0001] This invention relates to the field of building materials technology, and in particular to a prestressed concrete beam and its preparation method. Background Technology

[0002] Concrete beams are a widely used building material, combining the compressive strength of concrete with the tensile strength of steel reinforcement, exhibiting excellent compressive strength and durability. However, existing concrete beam technologies also possess some inherent defects, such as shrinkage and creep. Shrinkage refers to the natural reduction in volume of concrete during the hardening process, leading to tensile stress within the concrete and subsequently causing cracks. Creep refers to the inelastic deformation of concrete under sustained loads, i.e., the continuous deformation of concrete under constant loads over time. Shrinkage and creep cause deformation, cracking, and prestress loss in concrete structures, affecting their safety and durability. Existing technologies address shrinkage and creep in concrete beams by employing anti-shrinkage and creep design schemes or using materials of higher standards.

[0003] Existing technologies for treating shrinkage and creep in concrete beams have the following problems:

[0004] (1) Adopting structural solutions that resist shrinkage and creep, such as reserving a margin in the structural dimensions during the design and construction of concrete beams to compensate for shrinkage deformation, but this method does not solve the problem in a substantial way and will still cause quality problems due to shrinkage and creep.

[0005] (2) Use higher standard materials, such as a large amount of high-performance cement, mineral admixtures or other materials that can only be used after complex processing. However, the use of a large amount of high standard materials will also bring high concrete costs. Furthermore, the early strength growth of concrete beams using high-performance cement and mineral admixtures is slower, the curing time is longer, and a complex and stable material supply chain is often required, which has a significant impact on construction progress and cost. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a prestressed concrete beam and its preparation method, which solves the problems of excessive deformation and cracking of concrete beams after long-term use, slow early strength growth of concrete beams, and excessive cost in the prior art.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0010] In a first aspect, the present invention provides a method for preparing a prestressed concrete beam, comprising the following steps:

[0011] S1: Mix cement, fly ash, fine aggregate and coarse aggregate to obtain dry material;

[0012] S2: Mix nano-silica, natural zeolite and water, and disperse by ultrasonication to obtain a dispersion; mix the dry material with the dispersion and stir to obtain a wet material;

[0013] S3: Add water-reducing agent to wet materials and stir to obtain concrete slurry;

[0014] S4: Pour the concrete slurry into the mold of the post-tensioned prestressed concrete beam, and then perform the first curing to obtain the concrete beam blank. The curing temperature is 35-55℃. After applying prestress to the concrete beam blank, the prestressed concrete beam blank is obtained.

[0015] S5: The prestressed concrete beam blank is cured for the second time at a temperature of 40-65℃. After curing, a prestressed concrete beam is obtained.

[0016] By weight, the cement content is 400-600 parts, fly ash content is 10-50 parts, fine aggregate content is 400-1000 parts, coarse aggregate content is 800-1200 parts, natural zeolite content is 5-25 parts, nano silica content is 1-10 parts, water content is 100-200 parts, and water-reducing agent content is 1-10 parts; the cement-to-water ratio of the concrete slurry is 1:0.28-0.4.

[0017] According to a preferred embodiment of the present invention, in step S1, the fine aggregate is at least one of natural sand and manufactured sand; the coarse aggregate is at least one of crushed stone, slag, granite, basalt and construction waste; the mass of fine aggregate with a particle size in the range of 0.315 mm to 2.36 mm should account for 30-50% of the total mass of fine aggregate, and the mass of coarse aggregate with a particle size in the range of 4.75 mm to 19.5 mm should account for 30-50% of the total mass of coarse aggregate.

[0018] According to a preferred embodiment of the present invention, in step S1, the cement is silicate cement with a particle size of 10-25 μm; the fly ash has a particle size of no more than 20 μm, and the fly ash contains 15-55 wt% SiO2 and 5-30 wt% Al2O3.

[0019] According to a preferred embodiment of the present invention, in step S2, the particle size of the nano-silica is 1-100nm and the purity is ≥95%; the mass of nano-silica with a particle size not exceeding 40nm should account for 30-50% of the total mass of the coarse aggregate.

[0020] According to a preferred embodiment of the present invention, in step S2, the natural zeolite is at least one of analcime, zeolite, calcium cross-shaped zeolite, sodium zeolite, mordenite, flaky zeolite, clinoptilolite, chalcogenite, and octahedral zeolite; the particle size of the natural zeolite is 10 μm-1 mm, and the porosity is 20-50%.

[0021] According to a preferred embodiment of the present invention, in step S2, the ultrasonic frequency of the ultrasonic dispersion is 60kHz-90kHz, and the dispersion time is 10-100min.

[0022] According to a preferred embodiment of the present invention, in step S3, the water-reducing agent is at least one of naphthalene-based, melamine-based, aminosulfonate-based, and aliphatic-based agents.

[0023] According to a preferred embodiment of the present invention, in step S4, the concrete is poured in layers; during the pouring process, the concrete is vibrated and dispersed simultaneously; during the first curing, the curing time is 3-7 days, and the air humidity is 90-100%; in step S4, after curing for A days, the temperature conditions for the first curing are determined according to the following formula:

[0024] f c(T) =f0(1+α·(T-T0))·e ^(-β·(Ttop-T))

[0025] T0: Reference curing temperature, selected according to the standard curing temperature for ordinary concrete;

[0026] f0: Reference curing strength, which is the concrete strength after curing for A days at the reference curing temperature T0, in MPa;

[0027] T: Actual curing temperature;

[0028] f c(T) Actual strength refers to the concrete strength after curing for A days at the actual curing temperature T, expressed in MPa.

[0029] T top : Hydration active temperature, the temperature at which the hydration reaction of concrete is most active, determined experimentally;

[0030] α: Early intensity growth coefficient, 0 < α ≤ 0.1, unitless;

[0031] β: Active change coefficient, 0 < β ≤ 0.1, unitless;

[0032] T0, T and T top Only numerical values ​​are considered, not units; 3 ≤ A ≤ 7.

[0033] According to a preferred embodiment of the present invention, in step S5, during the second curing, the curing time is 1-10 days and the air humidity is 90-100%.

[0034] In a second aspect, the present invention provides a prestressed concrete beam prepared by the preparation method provided in the first aspect.

[0035] (III) Beneficial Effects

[0036] This invention discloses a prestressed concrete beam, which is formed by curing a concrete slurry containing nano-silica, natural zeolite, fly ash, ordinary cement, fine aggregate, and coarse aggregate. This slurry results in a low degree of shrinkage and creep in the cured concrete. Combined with post-tensioning, the prestressed concrete beam exhibits significantly increased shrinkage and creep resistance after curing, compared to existing technologies, through optimized design of the concrete slurry components. Furthermore, the application of prestress increases the load-bearing capacity of the concrete beam, reducing the impact of external loads on the stress structure and thus minimizing the long-term stress on the concrete beam. The technical effect of preventing deformation and cracking after use; the combination of nano-silica + natural zeolite + fine aggregate + coarse aggregate + ordinary cement also enables concrete to have good shrinkage resistance and creep resistance, while having advantages such as low cost, fast curing speed, rapid early strength growth of concrete beams and strong corrosion resistance. Furthermore, since this invention does not involve high-performance or high-grade cement, modified materials or other materials that require complex physical and chemical treatment, it does not require the establishment of a complex supply chain, further reducing the raw material cost and construction cost of the concrete beams of this invention, achieving the technical effect of accelerating the curing time of concrete beams and reducing the cost of concrete raw materials.

[0037] Secondly, because the concrete in the concrete beam of this invention uses a combination of nano-silica, natural zeolite, and ordinary cement, the concrete has good compressive strength, tensile strength, density, corrosion resistance, durability, and self-healing properties. It can also be stably fixed for a long time after strong prestress is applied, which can reduce the loss of prestress and prevent prestress failure.

[0038] Furthermore, because a higher curing temperature is used during the curing stage in the concrete beam preparation of this invention, the higher curing temperature intensifies the reaction between cement and other materials in the concrete, increasing the cement hydration rate and causing early pre-creep in the concrete beam. Compared with the prior art, early pre-creep in concrete beams can significantly reduce the curing time during the preparation process, allowing the concrete beam to reach the predetermined strength earlier, shortening the construction time, and accelerating the construction progress. At the same time, early pre-creep in concrete beams can also further reduce the shrinkage and creep of prestressed concrete beams in the later stages, improving the overall performance of the concrete beam. Attached Figure Description

[0039] Figure 1 The graph shows the elastic modulus test data for Examples 1-2 and Comparative Examples 1-4;

[0040] Figure 2 The graph shows the compressive strength test data for Examples 1-2 and Comparative Examples 1-4;

[0041] Figure 3 The figures show strain test data for Examples 1-2 and Comparative Examples 3-4. Detailed Implementation

[0042] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0043] This invention provides a method for preparing a prestressed concrete beam, comprising the following steps:

[0044] S1: Mix cement, fine aggregate and coarse aggregate together to obtain dry material.

[0045] S2: Mix nano-silica, natural zeolite and water, then ultrasonically disperse to obtain a dispersion; mix the dry material with the dispersion and stir to obtain a wet material.

[0046] S3: Add water-reducing agent to wet materials, mix, and then obtain concrete.

[0047] S4: Pour concrete into the mold for post-tensioned prestressed concrete beams. After pouring, perform the first curing to obtain concrete beam blanks. The curing temperature can be 35-55℃. Insert prestressing tendons into the pre-reserved ducts inside the concrete beam blanks (tendon insertion treatment). Then, tension the prestressing tendons to the design stress level and fix them with anchors (tensioning treatment). After fixing, fill the pre-reserved ducts with grouting agent and seal them to obtain prestressed concrete beam blanks.

[0048] S5: The prestressed concrete beam blank is cured for the second time. The curing temperature can be 40-65℃. After curing, a prestressed concrete beam is obtained.

[0049] By weight, cement can be 400-600 parts, fly ash can be 10-50 parts, fine aggregate can be 400-1000 parts, coarse aggregate can be 800-1200 parts, natural zeolite can be 5-25 parts, nano silica can be 1-10 parts, water can be 100-200 parts, and water-reducing agent can be 1-10 parts; the ratio of the total weight of cement, fly ash, natural zeolite, and nano silica to the weight of water can be 1:0.28-0.4.

[0050] Preferably, by weight, the cement can be 450-550 parts, fly ash can be 20-40 parts, fine aggregate can be 500-700 parts, coarse aggregate can be 1000-1200 parts, natural zeolite can be 10-20 parts, nano silica can be 5-10 parts, water can be 150-200 parts, and water-reducing agent can be 2-8 parts; the glue-to-water ratio, that is, the ratio of the total weight of cement, fly ash, natural zeolite and nano silica to the weight of water, can be 1:0.32-0.36.

[0051] Preferably, in step S1, the stirring time can be 60-300s, and the stirring speed can be 60-120r / min.

[0052] Preferably, in step S1, the fine aggregate may include at least one of natural sand and manufactured sand; the coarse aggregate may include at least one of crushed stone, slag, granite, basalt and coarse aggregate made from construction waste.

[0053] More preferably, the fine aggregate may include natural sand and manufactured sand; the coarse aggregate may include at least two of the following: crushed stone, slag, granite, basalt and coarse aggregate made from construction waste.

[0054] Preferably, the mass of coarse aggregate in the range of 4.75mm to 19.5mm should account for 30-50% of the total mass of coarse aggregate, and the mass of fine aggregate in the range of 0.315mm to 2.36mm should account for 30-50% of the total mass of fine aggregate.

[0055] The use of a large amount of coarse aggregate further reduces the cost of concrete raw materials without affecting the overall performance.

[0056] Preferably, in step S1, the cement is ordinary Portland cement with a grade of 52.5R, and the particle size of the cement can be 10-25μm.

[0057] Preferably, in step S1, the particle size of the fly ash does not exceed 20 μm, and the SiO2 content in the fly ash can be 15-55 wt%, and the Al2O3 content can be 5-30 wt%.

[0058] More preferably, in step S1, the SiO2 content in the coal ash can be 30-55 wt%, and the Al2O3 content can be 20-30 wt%.

[0059] The addition of fly ash can enrich the particle size gradient of silica. Through the synergistic effect of silica and alumina with nano-silica and natural zeolite, the strength, wear resistance, durability and fluidity of concrete beams can be further improved.

[0060] Preferably, in step S2, the particle size of the nano-silica can be 1-100 nm, and the purity is ≥95%; the content of nano-silica with a particle size not exceeding 40 nm is ≥50 wt%.

[0061] The role of nano-silica is as follows:

[0062] (1) It fills the micropores inside the concrete, increases the density of the concrete, reduces the shrinkage caused by water evaporation, and improves the strength and stiffness of the concrete.

[0063] (2) It reacts with cement hydration products (Ca(OH)2) (volcanic ash reaction) to generate more hydrated calcium silicate (CSH) gel, which enhances the compressive and tensile strength of concrete, accelerates the strength growth of concrete, and shortens the curing time of concrete.

[0064] (3) Improve the interfacial transition zone (ITZ) between aggregate and cement paste. Nano-silica can fill the ITZ and promote the hydration reaction, improve the bonding strength of the interface, and reduce cracks in the interfacial area.

[0065] Preferably, in step S2, the particle size of the nano-silica can be 1-40 nm.

[0066] Preferably, in step S2, the natural zeolite may include at least one of analcime, zeolite, calcium cross-shaped zeolite, sodium zeolite, mordenite, flaky zeolite, clinoptilolite, chalcogenite, and octahedral zeolite; the particle size of the natural zeolite may be 10 μm-1 mm, and the porosity of the natural zeolite may be ≥20%.

[0067] More preferably, in step S2, the particle size of the natural zeolite can be 0.1 mm to 1 mm, and the particle size of the natural zeolite is larger than that of the cement.

[0068] Preferably, in step S2, the porosity of the natural zeolite can be 20-50%.

[0069] The function of natural zeolite is as follows:

[0070] (1) Cement can react fully with other cementitious materials. High curing temperature will cause the water in the concrete to be lost quickly, which may prevent the cement clinker and other cementitious materials from fully hydrating. By utilizing the high water absorption properties of natural zeolite, the water is released after the natural zeolite loses water quickly, which promotes the secondary hydration of unhydrated cement clinker and other cementitious materials and improves the performance of prestressed concrete beams. At the same time, natural zeolite also has a certain pozzolanic reaction, which can react with Ca(OH)2 in the cement hydration products to generate more CSH gel, further improving the high strength and durability of concrete beams.

[0071] (2) Improve the durability of concrete. Natural zeolite has excellent adsorption capacity and can adsorb harmful substances such as chloride ions and sulfate ions in concrete, thereby improving its corrosion resistance.

[0072] (3) Accelerate cement hydration. Natural zeolite utilizes its porous structure and the nano-silica and water adsorbed in its pores to promote the rapid generation of hydrated calcium silicate (CSH) gel in the cement paste near the natural zeolite with the natural zeolite as the center. The CSH gel generated near different natural zeolites are interconnected, which further improves the early strength of the concrete beam and makes the concrete beam solidify faster.

[0073] Preferably, in step S2, the ultrasonic frequency for ultrasonic dispersion can be 60kHz-90kHz, and the dispersion time can be 10-100min; the stirring time for mixing the dry material and the dispersion liquid can be 60-120s, and the stirring speed can be 40-80r / min. Ultrasonic dispersion uniformly disperses nano-silica into the pores of water and natural zeolite, allowing the nano-silica and natural zeolite to mix better with other materials. Ultrasonic dispersion also removes any residual air in the pores of natural zeolite, enabling the natural zeolite to absorb more water. Residual air in the pores of natural zeolite may cause more air bubbles to form in the concrete beam and needs to be removed.

[0074] Preferably, in step S3, the stirring time can be 60-120s, and the stirring speed can be 100-150 / min.

[0075] Preferably, in step S3, the water-reducing agent may include at least one of naphthalene-based, melamine-based, aminosulfonate-based, and aliphatic-based agents.

[0076] Preferably, in step S4, the concrete is poured in layers; during pouring, the concrete is vibrated and dispersed.

[0077] More preferably, in step S4, during pouring, the concrete is dispersed by vibration. The vibration time can be 10-30 seconds, the vibration frequency can be 4000-12000 vpm, and the spacing between vibration points can be 25-50 cm. Vibration removes air bubbles from the concrete, promotes the compact arrangement of aggregates, thereby improving the density and strength of the concrete. At the same time, it allows nano-silica to be better dispersed into the micropores and capillaries in the concrete.

[0078] More preferably, in step S4, during pouring, the concrete is dispersed by ultrasonic oscillation. The ultrasonic frequency can be 20kHz-50kHz, the dispersion time can be 5s-40s, and the spacing between the dispersion points can be 50-200cm. Through ultrasonic oscillation dispersion, utilizing the ultrasonic cavitation effect, the materials in the concrete are dispersed and blended more uniformly, reducing porosity and air bubbles in the concrete. In particular, it allows nano-silica to disperse more uniformly, effectively filling the micropores and capillaries in the concrete. Ultrasonic oscillation dispersion also allows more nano-silica to intervene in the ITZ between the aggregate and cement paste, improving the microstructure of the interface transition zone, increasing the interfacial bond strength, thereby reducing microcracks in the interface area and reducing the overall shrinkage and creep of the concrete. However, attention must be paid to the dispersion time and the spacing between dispersion points to prevent aggregate sedimentation. Furthermore, ultrasonic oscillation dispersion requires the use of an ultrasonic vibrator, which increases construction costs.

[0079] Preferably, in step S4, during the first curing, the curing temperature can be 35-55℃, the curing time can be 3-7 days, and the curing air humidity can be 90-100%. The concrete beam blank is cured to 75-90% of the design strength before the prestressing tendons are inserted (tendon insertion treatment).

[0080] More preferably, in step S4, the curing temperature during the first curing can be 40-50℃.

[0081] More preferably, in step S4, the curing temperature can be 45°C during the first curing.

[0082] Preferably, in step S4, after curing for A days, the temperature conditions for the first curing are determined according to the following formula:

[0083] f c(T) =f0(1+α·(T-T0))·e ^(-β·(Ttop-T))

[0084] T0: Reference curing temperature, selected according to the standard curing temperature of concrete. In this invention, T0 is generally 20℃.

[0085] f0: Reference curing strength, which is the concrete strength after curing for A days at the reference curing temperature T0, in MPa;

[0086] T: Actual curing temperature, curing temperature during the first curing;

[0087] f c(T) Actual strength refers to the concrete strength after curing for A days at the actual curing temperature T, expressed in MPa.

[0088] Ttop The active hydration temperature is the temperature at which the concrete hydration reaction is most active, determined experimentally. In this invention, the active hydration temperature is 43-47℃, preferably 45℃.

[0089] α: Early intensity growth coefficient, 0 < α ≤ 0.1, unitless;

[0090] β: Active change coefficient, 0 < β ≤ 0.1, unitless;

[0091] T0, T and T top Only numerical values ​​are considered, not units; 3 ≤ A ≤ 7.

[0092] This formula is only applicable to concrete beam blanks prepared using the method of this invention, with a fixed concrete formula and preparation method. It is used to estimate the theoretical actual strength of the concrete beam blank at different curing temperatures during a specific curing time. It can also be used to determine the theoretical curing temperature using the target strength. In reality, there are many interfering factors (such as inconsistent porosity of natural zeolite), and the strength of the concrete beam blank will not completely match the theoretical value. After reinforcement treatment, the equation does not hold due to the influence of prestressed tendons.

[0093] In this invention, concrete beam specimens (or concrete block specimens) are prepared using the method described in this invention. During the first curing, the concrete beam specimens are cured at a reference curing temperature (the standard curing temperature of concrete is generally 20±2℃, preferably 20℃). The strength at curing time A days is recorded as the reference curing strength. Then, the strength development of two groups of concrete beam specimens prepared using the method of this invention is tested under different actual curing temperatures. The strength of these two groups of concrete beam specimens at curing time A days is recorded as the actual strength. α and β are calculated; α is the early strength growth coefficient, 0<α≤0.1, unitless; the value of α varies depending on the specific concrete mix proportions (mainly affected by changes in natural zeolite and nano-silica) and the properties of the cement; the larger the α, the faster the concrete beam hardens. β is the activity coefficient, 0 < β ≤ 0.1, and has no unit. The value of β changes according to the activity of the concrete hydration reaction; the larger the β, the greater the impact of temperature changes on the concrete beam. All the concrete beam specimens mentioned above used concrete with the same mix proportions. After obtaining α and β, with the concrete mix proportions unchanged, the strength of the concrete beam blank at different curing temperatures and a curing time of A days can be predicted using this formula, facilitating reinforcement installation and other processes.

[0094] Preferably, in step S4, the prestressing tendon can be steel strand, steel wire bundle, or heat-treated steel bar; the pre-drilled pipe can be corrugated pipe, steel pipe, or plastic pipe; the anchor can be a wedge-type anchor, a support-type anchor, a cone plug-type anchor, a gripping anchor, or a combined anchor; the grouting agent can be one of the following: micro-expansion grouting agent, non-shrinkage grouting agent, high-performance cement-based grouting agent, early-strength grouting agent, ordinary silicate cement grouting agent, corrosion-resistant grouting agent, low-temperature grouting agent, and high-flowability grouting agent.

[0095] Preferably, in step S4, different post-tensioned prestressed concrete beam molds are selected according to the design scheme of the concrete beam.

[0096] Preferably, in step S4, different prestressing tendons, anchorages, pre-reserved duct pipes, and grouting agents are selected according to the design scheme of the concrete beam. Different prestressing application amounts and prestressing tendon tensioning equipment are also selected according to the design scheme of the concrete beam.

[0097] Preferably, in step S5, during the second curing, the curing temperature can be 40-65℃, the curing time can be 1-10 days, the air humidity can be 90-100%, and the curing can be carried out to the design level.

[0098] Preferably, in step S5, during the second curing, the curing period is 1-10 days, the curing temperature can be 40-55℃, and the air humidity can be 90-100%.

[0099] More preferably, after the second curing, a further curing period of 0-90 days is required, with a curing temperature of 15-30℃ and an air humidity of 90-100%, until the design level is achieved. Different curing times and curing plans can be selected as needed.

[0100] Providing a higher ambient temperature during the hydration of concrete beams accelerates the hydration of cement clinker and pozzolanic materials in the concrete, achieving early pre-creep and reducing the shrinkage and creep of prestressed concrete beams in the later stages.

[0101] The present invention also provides a prestressed concrete beam prepared by the prestressed concrete beam preparation method of the present invention, comprising concrete, prestressed tendons, ordinary steel bars, pre-drilled pipes, pipe grouting agent, and anchorages.

[0102] To better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present invention can be understood more clearly and thoroughly, and that the scope of the present invention can be fully conveyed to those skilled in the art.

[0103] Example 1

[0104] This embodiment provides a prestressed concrete beam, comprising concrete, steel strands, ordinary reinforcing bars, corrugated pipes, ordinary silicate cement grouting agent, and wedge-type anchorages. The raw materials of the concrete are, by weight, 485 parts cement, 31 parts fly ash, 15.5 parts clinoptilolite, 7.41 parts nano silica, 301 parts manufactured sand, 301 parts natural sand, 802.9 parts crushed stone, 344.1 parts granite, 5.93 parts aminosulfonate water-reducing agent, and 189 parts water; the water-cement ratio is 0.35; the chemical composition of cement, fly ash, clinoptilolite, and nano silica is shown in Table 1.

[0105] This embodiment also provides a method for preparing a prestressed concrete beam, including:

[0106] S1: Mix cement, natural sand, manufactured sand, quarry gravel and granite to obtain dry material; the mixing time is 120s and the mixing speed is 80r / min.

[0107] S2: Mix nano-silica, clinoptilolite and water, and then disperse them ultrasonically to obtain a dispersion; mix the dry material with the dispersion and stir to obtain a wet material; the ultrasonic frequency of the ultrasonic dispersion is 90kHz and the dispersion time is 60min; the stirring time of the dry material and the dispersion is 80s and the stirring speed is 60r / min.

[0108] S3: Add aminosulfonate water-reducing agent to the wet material and stir. After stirring, concrete is obtained. The stirring time is 80 seconds and the stirring speed is 125 / min.

[0109] S4: Concrete is poured into a post-tensioned prestressed concrete beam mold containing four corrugated pipes, using a layered pouring method. During pouring, a vibratory compactor is used for dispersion. After pouring, the beam undergoes its first curing to obtain the concrete beam blank. The vibration dispersion frequency is 8000 vpm, the dispersion time is 15s, and the spacing between vibration dispersion points is 50cm. During the first curing, the curing temperature is 45℃, the curing time is 7 days, and the air humidity is 95%. Four steel strands are inserted into the corrugated pipes within the concrete beam blank, and then the steel strands are tensioned. The total tension control force is P = 781.2KN (4 × 195.3KN), and the steel strands are fixed with clamp-type anchors. After tensioning, ordinary silicate cement grouting agent is filled into the corrugated pipes and sealed to obtain the prestressed concrete beam blank.

[0110] S5: The prestressed concrete beam blank is cured for the second time and demolded. It is cured at 45℃ for 5 days with a curing air humidity of 95%. After demolding, the prestressed concrete beam is obtained.

[0111] In step S4, before pouring, strain gauges are pre-embedded in the concrete beam mold (this does not affect performance and is only a testing step) for data measurement. After obtaining the prestressed concrete beam, surface-mounted strain gauges are installed on the prestressed concrete beam (this is only a testing step) for data measurement. In step S5, after obtaining the prestressed concrete beam, it is stored and cured for 75 days at a temperature of 20°C and an air humidity of 95% (this is only a testing step) to facilitate subsequent data testing; the elastic modulus and strain tests are performed on the prestressed concrete beam of this embodiment. The elastic modulus test results are shown in […]. Figure 1 The strain test results are shown in Figure 3 .

[0112] Example 2

[0113] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 1 is that the amount of clinoptilolite in the concrete raw materials is 25 parts, and the water-cement ratio is 0.34.

[0114] Elastic modulus and strain tests were performed on the prestressed concrete beam of this embodiment. The results of the elastic modulus test are shown below. Figure 1 The strain test results are shown in Figure 3 .

[0115] Example 3

[0116] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 1 is that the natural zeolite in the concrete raw material is chalcogenide. In step S5: during the second curing, the beam is cured at 40°C for 10 days, and then demolded to obtain the prestressed concrete beam.

[0117] The compressive strength of the prestressed concrete beam obtained in Example 3 was tested, and the axial compressive strength was 76.2 MPa.

[0118] Example 4

[0119] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 3 is that in step S4: during pouring, the concrete is ultrasonically dispersed using ultrasound. The ultrasonic frequency is 40kHz, the dispersion time is 7s, and the spacing between the dispersion points of the ultrasonic oscillation dispersion is 80cm.

[0120] The compressive strength of the prestressed concrete beam obtained in Example 4 was tested, and the axial compressive strength was 80.5 MPa.

[0121] Example 5

[0122] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 1 is that in step S4: during the first curing, the beam is cured at 50°C for 3 days; in step S5: during the second curing, the beam is cured at 55°C for 5 days, and then demolded to obtain the prestressed concrete beam.

[0123] Example 6

[0124] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 1 is that in step S4: during the first curing, the beam is cured at 40°C for 7 days; in step S5: during the second curing, the beam is cured at 40°C for 7 days, and then demolded to obtain the prestressed concrete beam.

[0125] Comparative Example 1

[0126] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 1 is that the curing temperature in steps S4 and S5 is 20°C.

[0127] The elastic modulus of the prestressed concrete beam in this comparative example was tested. The results of the elastic modulus test are shown below. Figure 1 .

[0128] Comparative Example 2

[0129] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 2 is that the amount of clinoptilolite in the raw materials of the concrete is 31 parts.

[0130] The elastic modulus of the prestressed concrete beam in this comparative example was tested. The results of the elastic modulus test are shown below. Figure 1 .

[0131] Comparative Example 3

[0132] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 1 is that the concrete raw materials do not include nano-silica.

[0133] Elastic modulus and strain tests were performed on the prestressed concrete beams in this comparative example. The results of the elastic modulus test are shown below. Figure 1 The strain test results are shown in Figure 3 .

[0134] Comparative Example 4

[0135] This embodiment provides a prestressed concrete beam and its preparation method. The difference from Embodiment 1 is that the concrete raw materials do not include clinoptilolite.

[0136] Elastic modulus and strain tests were performed on the prestressed concrete beams in this comparative example. The results of the elastic modulus test are shown below. Figure 1 The strain test results are shown in Figure 3 .

[0137] The compressive strength of the prestressed concrete beams obtained in Examples 1-2, 5-6 and Comparative Examples 1-4 were tested according to GB / T50081-2019. The results of the compressive strength tests are shown in Table 2.

[0138] Table 1. Chemical composition of cement, fly ash, clinoptilolite, and nano-silica in Example 1.

[0139]

[0140] Table 2. Axial compressive strength (MPa) of concrete beams in Examples 1-2, 5-6, and Comparative Examples 1-4 at different total curing times.

[0141] Example 1 57.6 66.5 77.6 78.6 Example 2 58.1 66.9 76.2 77.1 Example 5 60.5 72.8 none none Example 6 53.2 60.6 none none Comparative Example 1 42.8 49.4 69.1 70.8 Comparative Example 2 49.6 56.3 63.2 65.2 Comparative Example 3 50.4 58.2 67.4 68.4 Comparative Example 4 51.6 61.3 65.9 66.4

[0142] Note: The total curing time is the sum of the curing times in steps S4 and S5 of the concrete beam preparation process.

[0143] Using the data from Comparative Example 1 of the present invention as a reference curing temperature T0 and a reference curing intensity f0, calculations show that the concrete beam blank prepared using the preparation method of Example 1 of the present invention has α = 0.0142, β = 0.0052, and equation f c(T) =f0(1+α·(T-T0))·e ^(-β·(Ttop-T)) In the middle, Tt op =45℃, T0=20℃, T=45℃, f0=42.8 after 3 days of curing, f0=49.4 after 7 days of curing. It can be estimated that: the strength of the concrete beam blank of Example 1 is 57.96 after 3 days of curing and 66.86 after 7 days of curing. The actual measured strength of the concrete beam blank of Example 1 is 57.6 after 3 days of curing and 66.5 after 7 days of curing, which meets the expectations.

[0144] The preparation methods and concrete formulations of Examples 5-6 are the same as those of Example 1, and their strengths also meet expectations.

[0145] According to the data in Table 2, we can find that:

[0146] Compared with the prestressed concrete beam of Comparative Example 1, the prestressed concrete beam of Example 1 exhibits significantly faster early compressive strength growth due to the use of higher curing temperatures in the early stages of curing to induce creep. This allows it to reach the expected strength earlier and proceed with subsequent treatments more quickly. The overall curing time to reach the design compressive strength is also shorter, resulting in a faster prestressed concrete beam preparation speed.

[0147] Compared to the prestressed concrete beam of Example 2, the prestressed concrete beam of Comparative Example 2 had a lower final strength due to the excessive use of natural zeolite and the excessively high water content in the inner layer.

[0148] Compared with the prestressed concrete beam of Example 1, the prestressed concrete beam of Comparative Example 3 has lower strength because it does not use nano-silica and lacks the synergistic effect between nano-silica and natural zeolite.

[0149] Compared to the prestressed concrete beam in Example 1, the prestressed concrete beam in Comparative Example 4 did not use natural zeolite, resulting in a significant loss of moisture after high-temperature curing, which could not be replenished. This led to a smaller increase in strength and a lower upper limit of strength.

[0150] according to Figure 1 Elastic modulus test results and Figure 3 The strain test results show that the prestressed concrete beams of Examples 1 and 2 have higher elastic modulus and stronger resistance to deformation; they also have slower strain rates and higher ultimate tensile strength.

[0151] In summary, the prestressed concrete beam and its preparation method of the present invention can solve the problems of excessive deformation and cracking of concrete beams after long-term use, slow early strength growth of concrete beams, and excessive cost.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a prestressed concrete beam, characterized in that, Includes the following steps: S1: Mix cement, fly ash, fine aggregate and coarse aggregate to obtain dry material; S2: Nano-silica, natural zeolite and water are mixed and ultrasonically dispersed to obtain a dispersion; the dry material is mixed and stirred with the dispersion to obtain a wet material; the ultrasonic frequency of the ultrasonic dispersion is 60kHz-90kHz and the dispersion time is 10-100min. S3: Add water-reducing agent to wet materials and stir to obtain concrete slurry; S4: Pour the concrete slurry into the mold of the post-tensioned prestressed concrete beam, and then carry out the first curing to obtain the concrete beam blank. The curing temperature is 35-55℃, the curing time is 3-7 days, and the air humidity is 90-100%. After applying prestress to the concrete beam blank, the prestressed concrete beam blank is obtained. S5: The prestressed concrete beam blank is cured for the second time. The curing temperature is 40-65℃, the curing time is 1-10 days, and the air humidity is 90-100%. After curing, the prestressed concrete beam is obtained. By weight, the cement comprises 400-600 parts, fly ash 10-50 parts, fine aggregate 400-1000 parts, coarse aggregate 800-1200 parts, natural zeolite 5-25 parts, nano silica 1-10 parts, water 100-200 parts, and water-reducing agent 1-10 parts; the cement-to-water ratio of the concrete slurry, i.e., the ratio of the total weight of cement, fly ash, natural zeolite, and nano silica to the weight of water, is 1:0.28-0.

4.

2. The preparation method according to claim 1, characterized in that, In step S1, the fine aggregate is at least one of natural sand and manufactured sand; the coarse aggregate is at least one of crushed stone, slag, granite, basalt and construction waste; the mass of fine aggregate with a particle size in the range of 0.315mm to 2.36mm should account for 30-50% of the total mass of fine aggregate, and the mass of coarse aggregate with a particle size in the range of 4.75mm to 19.5mm should account for 30-50% of the total mass of coarse aggregate.

3. The preparation method according to claim 1, characterized in that, In step S1, the cement is silicate cement with a particle size of 10-25 μm; the fly ash has a particle size of no more than 20 μm, and the SiO2 content in the fly ash is 15-55 wt%, and the Al2O3 content is 5-30 wt%.

4. The preparation method according to claim 1, characterized in that, In step S2, the nano-silica has a particle size of 1-100nm and a purity of ≥95%; the content of nano-silica with a particle size of no more than 40nm is ≥50wt%.

5. The preparation method according to claim 1, characterized in that, In step S2, the natural zeolite is at least one of analcime, zeolite, calcium cross-shaped zeolite, sodium zeolite, mordenite, flaky zeolite, clinoptilolite, chalcogenite, and octahedral zeolite; the particle size of the natural zeolite is 10μm-1mm and the porosity is 20-50%.

6. The preparation method according to claim 1, characterized in that, In step S3, the water-reducing agent is at least one of naphthalene-based, melamine-based, aminosulfonate-based, and aliphatic-based agents.

7. The preparation method according to claim 1, characterized in that, In step S4, the concrete is poured in layers; during the pouring process, the concrete is vibrated and dispersed while being poured.

8. A prestressed concrete beam, characterized in that, The prestressed concrete beam is prepared by the preparation method described in any one of claims 1-7.

Images