A composite precast concrete segment and its preparation method

Abstract

This invention belongs to the field of precast concrete tunnel segment technology, specifically relating to a composite precast concrete tunnel segment and its preparation method. The composite precast concrete tunnel segment provided by this invention includes a tunnel segment body and a reinforcing cage disposed within the tunnel segment body. The tunnel segment body is made of concrete material, which includes cement, mineral admixtures, coarse aggregate, fine aggregate, early-strength polycarboxylate superplasticizer, functional admixtures, and water. This invention uses isopentenyl alcohol polyoxyethylene ether, triallyl phosphate, L-ethylene glycine, and acrylic acid as monomers to derive an early-strength polycarboxylate superplasticizer, improving the early strength of the concrete. It uses modified polypropylene fiber, lithium silicate, and methylcellulose to form a functional admixture, grafting hydroxyethyl methacrylate onto the surface of the polypropylene fiber to improve the concrete's crack resistance, impermeability, and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of precast concrete segment technology, specifically relating to a composite precast concrete segment and its preparation method. Background Technology

[0002] With the acceleration of urbanization and the continuous advancement of infrastructure construction, precast concrete segments are playing an increasingly important role in various engineering fields. In urban rail transit construction, shield tunneling has become the mainstream method, and precast concrete segments undertake important structural support and protection functions. As a key component of the shield tunnel lining structure, their quality is directly related to the safety and durability of the tunnel structure, and thus affects the stable operation of the entire urban rail transit system.

[0003] In the current production process of precast concrete tunnel segments, quality defects such as air bubbles and cracks often occur. When applied to highway tunnels, subways, and other applications, their ability to block water vapor decreases. Water vapor penetrates into the concrete segments, causing corrosion of the reinforcing steel, affecting the mechanical properties of the segments, and consequently impacting their load-bearing capacity and service life. A common improvement method is the use of new admixtures. For example, crack-resistant agents can effectively reduce shrinkage cracks in concrete during hardening, improving its crack resistance; corrosion inhibitors can delay the corrosion of the reinforcing steel, protecting it from external erosion and extending the segment's service life. However, the use of new admixtures also presents some problems. Some admixtures have poor compatibility with concrete, potentially leading to poor workability, such as rapid slump loss and segregation. The dosage of admixtures also needs precise control. Insufficient dosage may not achieve the desired effect, while excessive dosage may cause other problems, such as reduced strength.

[0004] Chinese patent application CN112608105A discloses a precast segment concrete, comprising 110-140 parts cement, 30-45 parts mineral admixtures, 130-180 parts sand, 250-330 parts gravel, 4-5 parts water-reducing agent, 35-45 parts water, and 15-20 parts modified hydrotalcite powder. The modified hydrotalcite powder is prepared by dissolving calcium nitrate tetrahydrate, aluminum nitrate nonahydrate, and calcium nitrite in deionized water, adding sodium hydroxide solution dropwise at 35-40℃ to adjust the pH to 11-12, stirring, heating to 70-80℃, maintaining the temperature for reaction, vacuum filtering, washing, and drying to obtain modified hydrotalcite powder. However, the amount of cement and mineral admixtures in this formula is relatively small, resulting in insufficient cement density, which cannot meet the strength requirements for early demolding after oxygenation, thus affecting production efficiency. At the same time, the modified hydrotalcite powder uses sodium hydroxide to adjust the pH value and calcium nitrite as a raw material, resulting in a high alkali content in the modified hydrotalcite. When applied to tunnel segment concrete, it will trigger alkali-aggregate reaction, leading to segment cracking and reduced durability. Summary of the Invention

[0005] To address the technical problems of poor mechanical properties and impermeability of concrete in the prior art, the present invention provides a composite precast concrete segment and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A composite precast concrete segment includes a segment body and a reinforcing cage disposed within the segment body. The segment body is made of concrete material, which comprises the following components in parts by weight:

[0008] 100-150 parts cement, 40-50 parts mineral admixtures, 220-260 parts coarse aggregate, 140-150 parts fine aggregate, 3-8 parts early-strength polycarboxylate superplasticizer, 20-30 parts functional admixtures, and 80-100 parts water.

[0009] The preparation method of the early-strength polycarboxylate superplasticizer is as follows: isopentenyl alcohol polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine and sodium bisulfite are added to an ethanol aqueous solution, stirred and dissolved, heated to 50-60℃, and acrylic acid, mercaptopropionic acid and hydrogen peroxide are added dropwise while stirring. After the addition is completed, the reaction is kept at the temperature for 2-3 hours, and then distilled under reduced pressure at 80-85℃ and cooled to obtain the early-strength polycarboxylate superplasticizer.

[0010] In this invention, isopentenyl alcohol polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine, and acrylic acid are used as reactants to initiate a free radical polymerization reaction under a redox initiator system, generating side chain structures with different lengths. The shorter side chains can play a rapid role in the early stage of cement hydration, enhancing the adsorption of water-reducing agent molecules and cement particles, improving the dispersibility of cement particles, and thus promoting the early hydration reaction. The longer side chains provide a continuous steric hindrance effect in the later stage, maintaining the dispersed state of cement particles, which is beneficial to the development of concrete strength in the later stage. Furthermore, isopentenyl alcohol polyoxyethylene ether introduces polyoxyethylene ether groups into the side chain of the water-reducing agent molecule, effectively dispersing cement particles through steric hindrance and promoting their hydration reaction; triallyl phosphate introduces phosphate ester groups into the side chain of the water-reducing agent molecule. These phosphate ester groups can undergo a complexation reaction with calcium ions in cement to form stable complexes, thereby accelerating the cement hydration process. The phosphate ester groups can also form a dense protective film on the surface of cement particles, preventing particle agglomeration, improving particle dispersibility, and promoting cement hydration; L-ethyleneglycine can introduce amino and carboxyl groups into the side chain of the water-reducing agent molecule, and acrylic acid can introduce carboxyl and amino groups into the side chain of the water-reducing agent molecule. It has strong alkalinity and can react chemically with the acidic groups on the surface of cement particles to form chemical bonds, thereby enhancing the adsorption force between the water-reducing agent molecules and cement particles. This strong adsorption effect allows the water-reducing agent to disperse cement particles more effectively and promote the early hydration reaction of cement. The amino group can also react with calcium hydroxide produced during cement hydration to generate mineral phases such as ettringite with early strength, further improving the early strength of concrete. The carboxyl group can form a complex with calcium ions in cement hydration products, breaking the coating layer of petrochemical products on the particle surface, promoting the continuous dissolution and hydration of cement particles, shortening the hydration induction period, and improving the early strength of concrete.

[0011] Furthermore, in the preparation method of the early-strength polycarboxylate superplasticizer, the molar ratio of isopentenyl alcohol polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine and acrylic acid is 1:(0.35-0.52):(0.62-0.75):(4-6).

[0012] This invention regulates the molecular structure of an early-strength polycarboxylate superplasticizer by controlling the molar ratio of isopentenyl polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine, and acrylic acid. The molar ratio of isopentenyl polyoxyethylene ether to acrylic acid determines the dispersibility and dispersion retention of the superplasticizer. A lower acid-ether ratio allows the long side chains of the polyether to provide better steric hindrance, effectively preventing cement particle agglomeration, but slows down the production rate of early hydration products in the cement. Conversely, an increased acid-ether ratio weakens the density of the side chains, resulting in poorer cement particle dispersibility. The amounts of triallyl phosphate and L-ethyleneglycine determine the density of early-strength functional groups in the superplasticizer molecule. Higher amounts increase the early strength of concrete, but worsen cement dispersibility; lower amounts result in a less effective improvement in early concrete strength.

[0013] Furthermore, in the preparation method of the early-strength polycarboxylate superplasticizer, the molar ratio of sodium bisulfite to hydrogen peroxide is (0.5-0.8):1, the amount of hydrogen peroxide used is 0.9%-1.2% of the sum of the amounts of isopentenyl polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine, and acrylic acid; and the amount of mercaptopropionic acid used is 0.1%-0.2% of the sum of the amounts of isopentenyl polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine, and acrylic acid.

[0014] Furthermore, the mass percentage of the ethanol aqueous solution in the preparation method of the early-strength polycarboxylate superplasticizer is 70%-85%.

[0015] Furthermore, the functional admixture is composed of modified polypropylene fiber, lithium silicate and methylcellulose in a mass ratio of (10-15):(3-7):(1-2).

[0016] This invention employs modified polypropylene fibers, lithium silicate, and methylcellulose as a functional admixture. Through the synergistic effects of crack resistance, densification, and thickening, it enhances the crack resistance, impermeability, and mechanical properties of concrete. The modified polypropylene fibers in concrete constrain the plastic shrinkage and drying shrinkage of the cement paste through a bridging effect, forming a three-dimensional network structure that prevents the propagation of microcracks during concrete hardening. Lithium silicate reacts with cement hydration products to form a dense hydrated calcium silicate gel, filling defects in the interfacial transition zone between the cement paste and aggregate, thus improving interfacial bond strength. Methylcellulose slows down the rate of moisture evaporation within the concrete, preventing surface shrinkage cracks caused by rapid water loss, and improves the workability of the concrete, preventing the formation of interconnected pores due to bleeding.

[0017] Furthermore, the preparation method of the modified polypropylene fiber is as follows: Polypropylene fiber is placed in anhydrous ethanol, ultrasonically cleaned, filtered, and dried. Then, it is placed in a potassium permanganate solution and ultrasonically stirred at 60-65℃ for 30-40 minutes. After filtration, it is soaked in hydrochloric acid solution for 10-20 minutes, filtered again, washed with deionized water until neutral, dried, and then added together with toluene into a reaction vessel. Nitrogen is purged to remove oxygen, and the temperature is raised to 70-80℃. After stirring for 30 minutes, a toluene solution of benzoyl peroxide is added dropwise, and the reaction is stirred for 1-1.5 hours. Hydroxyethyl methacrylate is added dropwise, and after the addition is complete, the temperature is raised to 90-95℃ and the reaction is maintained for 4-6 hours. 30-45 mL of an ethanol solution of hydroquinone is added, and the mixture is stirred for 30-40 minutes. After cooling, the fiber is filtered, washed, and dried to obtain the modified polypropylene fiber.

[0018] This invention involves etching polypropylene fibers in potassium permanganate under ultrasonic assistance to increase the number of active sites on the polypropylene fiber surface. Then, hydroxyethyl methacrylate is grafted onto the polypropylene fiber surface under the initiation of benzoyl peroxide, introducing polar groups such as hydroxyl and ester groups. The increased surface roughness and polar groups of the polypropylene fibers enhance the adhesion between the polypropylene fibers and concrete, enabling the polypropylene to more effectively transfer stress and form a strong three-dimensional network inside the concrete. When microcracks occur, this network provides greater bridging resistance, effectively inhibiting crack initiation and propagation, and effectively improving the crack resistance and mechanical properties of concrete.

[0019] Furthermore, in the preparation method of modified polypropylene fiber, the mass percentage of potassium permanganate solution is 5%-8%, the mass percentage of hydrochloric acid solution is 10%-15%, the mass percentage of benzoyl peroxide in toluene solution is 3%-5%, and the mass percentage of hydroquinone in ethanol solution is 0.1%-0.3%; the mass ratio of polypropylene fiber, hydroxyethyl methacrylate and benzoyl peroxide is 10:(3-5):(0.2-0.3).

[0020] Furthermore, the mineral admixture is composed of silica fume, slag powder, fly ash and zeolite powder in a mass ratio of (4-8):(27-31):(22-25):(8-13).

[0021] This invention employs a mineral admixture composed of silica fume, slag powder, fly ash, and zeolite powder, which is added to concrete segments. Silica fume reacts with calcium hydroxide generated during cement hydration to produce a large amount of dense hydrated calcium silicate gel, filling the capillary pores within the concrete and significantly reducing the diffusion coefficient of aluminum ions. Slag powder exhibits a microcrystalline nucleation effect, accelerating cement hydration and balancing early and later strength development in concrete. It also reduces internal porosity through a filling effect, improving interface defects and enhancing impermeability. The spherical particles of fly ash improve the workability of concrete, and the pozzolanic effect promotes secondary hydration to generate gel substances, optimizing the internal structure and interface transition zone of the concrete and enhancing its mechanical properties. Zeolite powder contains active silica and alumina, combining the activity and adsorption characteristics of pozzolanic ash. When added to concrete, it reacts with calcium hydroxide to generate cementitious substances, increasing compressive strength, and its porous structure adsorbs moisture and harmful ions, reducing seepage channels and improving the concrete's impermeability.

[0022] Furthermore, the coarse aggregate is 12-20mm continuously graded crushed stone with an apparent density of 2700 kg / m³. 3 The fine aggregate is coarse sand with a fineness modulus of 3.0-3.5.

[0023] The present invention also provides a method for preparing composite precast concrete segments, comprising the following steps:

[0024] S1: Fix the steel cage and complete the installation of the embedded parts;

[0025] S2 mixes cement, mineral admixtures, coarse aggregates, fine aggregates and functional admixtures, adds a mixed solution of early-strength polycarboxylate superplasticizer and water, and stirs evenly to obtain concrete material;

[0026] S3: Generate a 3D digital model based on the shape and size of the segment, import the 3D digital model into the 3D printing software, use the concrete material obtained in step S2 for 3D printing, demold after curing for 24 hours, steam curing for 7-14 days, and natural curing for 28 days to obtain the concrete segment.

[0027] This invention uses 3D printing technology. During the printing process, the entire pipe segment is printed continuously, avoiding the gaps and weak interfaces caused by traditional mold splicing, and improving the pipe segment's impermeability, corrosion resistance and mechanical properties.

[0028] Compared with the prior art, the composite precast concrete segment and its preparation method provided by the present invention have the following technical advantages:

[0029] (1) The present invention uses isopentenyl alcohol polyoxyethylene ether, triallyl phosphate, L-ethylene glycine and acrylic acid as monomers to prepare an early-strength polycarboxylate superplasticizer under the action of an initiator in a redox system, which effectively improves the early strength of concrete, shortens the demolding time of concrete segments and improves production efficiency.

[0030] (2) The present invention uses modified polypropylene fiber, lithium silicate and methylcellulose to form a functional admixture, which improves the crack resistance, impermeability and mechanical properties of concrete through the synergistic effect of crack resistance, compaction and thickening.

[0031] (3) In this invention, hydroxyethyl methacrylate is grafted onto the surface of polypropylene fiber, which improves the interfacial bonding strength between polypropylene fiber and concrete, and effectively improves the crack resistance and mechanical properties of concrete. Attached Figure Description

[0032] Figure 1 This is a molecular structure diagram of an early-strength polycarboxylate superplasticizer;

[0033] Figure 2 The NMR spectrum of the early-strength polycarboxylate superplasticizer prepared in Example 3;

[0034] Figure 3 Infrared spectrum of the modified polypropylene fiber prepared in Example 6. Detailed Implementation

[0035] The following description, in conjunction with specific embodiments, provides further details, but the present invention is not limited to these embodiments. Those skilled in the art can make various modifications based on the fundamental principles of the present invention, but all modifications that do not depart from the fundamental principles of the present invention are within its scope.

[0036] Unless otherwise specified, all raw materials described in this specific embodiment are commercially available. The molecular structure of the early-strength polycarboxylate superplasticizer described in this specific embodiment is as follows: Figure 1 As shown; the cement is P·O 42.5 silicate cement.

[0037] In this specific embodiment, the composite precast concrete segment includes a segment body and a reinforcing cage disposed within the segment body. The segment body is made of concrete. The preparation method of the composite precast concrete segment includes the following steps:

[0038] S1: Fix the steel cage and complete the installation of the embedded parts;

[0039] S2 mixes cement, mineral admixtures, coarse aggregates, fine aggregates and functional admixtures, adds a mixed solution of early-strength polycarboxylate superplasticizer and water, and stirs evenly to obtain concrete material;

[0040] S3: Generate a 3D digital model based on the shape and size of the segment, import the 3D digital model into the 3D printing software, use the concrete material obtained in step S2 for 3D printing, demold after curing for 24 hours, steam curing for 7-14 days, and natural curing for 28 days to obtain the concrete segment.

[0041] Preparation Example 1

[0042] The preparation method of early-strength polycarboxylate superplasticizer is as follows: 10 mol of isopentenyl alcohol polyoxyethylene ether, 3.5 mol of triallyl phosphate, 6.2 mol of L-ethyleneglycine and 0.27 mol of sodium bisulfite are added to 1 L of 70% (w / w) ethanol aqueous solution, stirred and dissolved, heated to 50℃, and simultaneously added dropwise with stirring, 40 mol of acrylic acid, 0.06 mol of mercaptopropionic acid and 0.54 mol of hydrogen peroxide. After the addition is completed, the reaction is kept at the temperature for 2 h, distilled under reduced pressure at 80℃, and cooled to obtain early-strength polycarboxylate superplasticizer.

[0043] Preparation Example 2

[0044] The preparation method of early-strength polycarboxylate superplasticizer is as follows: 10 mol of isopentenyl alcohol polyoxyethylene ether, 5.2 mol of triallyl phosphate, 7.5 mol of L-ethyleneglycine and 0.79 mol of sodium bisulfite are added to 1 L of 85% (w / w) ethanol aqueous solution, stirred and dissolved, heated to 60℃, and simultaneously added dropwise with stirring, 60 mol of acrylic acid, 0.17 mol of mercaptopropionic acid and 0.99 mol of hydrogen peroxide. After the addition is completed, the reaction is kept at the temperature for 3 h, distilled under reduced pressure at 85℃, and cooled to obtain early-strength polycarboxylate superplasticizer.

[0045] Preparation Example 3

[0046] The preparation method of early-strength polycarboxylate superplasticizer is as follows: 10 mol of isopentenyl alcohol polyoxyethylene ether, 4.6 mol of triallyl phosphate, 6.9 mol of L-ethyleneglycine and 0.44 mol of sodium bisulfite are added to 1 L of 80% (w / w) ethanol aqueous solution, stirred and dissolved, heated to 55℃, and simultaneously added dropwise with stirring, along with 52 mol of acrylic acid, 0.11 mol of mercaptopropionic acid and 0.74 mol of hydrogen peroxide. After the addition is complete, the reaction is kept at the temperature for 2.5 h, distilled under reduced pressure at 83℃, and cooled to obtain early-strength polycarboxylate superplasticizer.

[0047] Preparation Example 4

[0048] The preparation method of modified polypropylene fiber is as follows: 100g of polypropylene fiber is placed in anhydrous ethanol (solid-liquid ratio of 1:50), ultrasonically cleaned for 30min, filtered, dried, and then placed in a 5% potassium permanganate solution. The fiber is stirred and ultrasonically cleaned at 60℃ for 30min, filtered, and then soaked in a 10% hydrochloric acid solution for 10min. After filtration, the fiber is washed with deionized water until neutral, dried at 80℃ for 2h, and then added together with toluene into a reaction vessel (solid-liquid ratio of 1:15). Nitrogen is purged to remove oxygen. The mixture was stirred and heated to 70°C. After stirring for 30 minutes, a 3% (w / w) toluene solution of benzoyl peroxide (2 g) was added dropwise. The mixture was stirred and reacted for 1 hour. Then, 30 g of hydroxyethyl methacrylate was added dropwise at a uniform rate. After the addition was complete, the temperature was raised to 90°C and the mixture was kept at this temperature for 4 hours. Finally, 30 mL of a 0.1% (w / w) hydroquinone ethanol solution was added, and the mixture was stirred for 30 minutes. The mixture was then cooled, filtered, and washed three times with toluene, anhydrous ethanol, and deionized water, respectively. The mixture was then dried at 60°C for 8 hours to obtain modified polypropylene fibers.

[0049] Preparation Example 5

[0050] The preparation method of modified polypropylene fiber is as follows: 100g of polypropylene fiber is placed in anhydrous ethanol (solid-liquid ratio of 1:50), ultrasonically cleaned for 30min, filtered, dried, and then placed in an 8% potassium permanganate solution. The fiber is stirred and ultrasonically cleaned at 65℃ for 40min, filtered, and then soaked in a 15% hydrochloric acid solution for 20min. After filtration, the fiber is washed with deionized water until neutral, dried at 80℃ for 2h, and then added together with toluene into a reaction vessel (solid-liquid ratio of 1:15). Nitrogen is purged to remove oxygen, and the mixture is stirred. The mixture was heated to 80℃ and stirred for 30 min. Then, a 5% (w / w) toluene solution of benzoyl peroxide (3 g) was added dropwise. The mixture was stirred for 1.5 h. Then, 50 g of hydroxyethyl methacrylate was added dropwise at a uniform rate. After the addition was complete, the temperature was raised to 95℃ and the mixture was kept at that temperature for 6 h. Then, 45 mL of a 0.3% (w / w) hydroquinone ethanol solution was added and stirred for 40 min. The mixture was cooled, filtered, and washed three times with toluene, anhydrous ethanol, and deionized water, respectively. The mixture was then dried at 60℃ for 8 h to obtain modified polypropylene fibers.

[0051] Preparation Example 6

[0052] The preparation method of modified polypropylene fiber is as follows: 100g of polypropylene fiber is placed in anhydrous ethanol (solid-liquid ratio of 1:50), ultrasonically cleaned for 30min, filtered, dried, and then placed in a 5%-8% potassium permanganate solution. The fiber is stirred and ultrasonically cleaned at 63℃ for 35min, filtered, and then soaked in a 13% hydrochloric acid solution for 15min. After filtration, the fiber is washed with deionized water until neutral, dried at 80℃ for 2h, and then added together with toluene into a reaction vessel (solid-liquid ratio of 1:15). Nitrogen is purged to remove oxygen, and the mixture is stirred. The mixture was heated to 75°C and stirred for 30 minutes. Then, a 4% (w / w) toluene solution of benzoyl peroxide (2.5 g) was added dropwise. The mixture was stirred for 1.2 hours. Then, 40 g of hydroxyethyl methacrylate was added dropwise at a uniform rate. After the addition was complete, the temperature was raised to 93°C and the mixture was kept at that temperature for 5 hours. Then, 39 mL of a 0.2% (w / w) hydroquinone ethanol solution was added and stirred for 35 minutes. The mixture was cooled, filtered, and washed three times with toluene, anhydrous ethanol, and deionized water, respectively. The mixture was then dried at 60°C for 8 hours to obtain modified polypropylene fibers.

[0053] Example 1

[0054] A composite precast concrete segment includes a segment body and a reinforcing cage disposed within the segment body. The segment body is made of concrete material, which comprises the following components in parts by weight:

[0055] 100g cement, 40g mineral admixture, 220g coarse aggregate, 140g fine aggregate, 3g early-strength polycarboxylate superplasticizer, 20g functional admixture, and 100g water.

[0056] The functional admixture consists of modified polypropylene fiber, lithium silicate, and methylcellulose in a mass ratio of 10:3:1; the mineral admixture consists of silica fume, slag powder, fly ash, and zeolite powder in a mass ratio of 4:27:22:8; the coarse aggregate is 12-20mm continuously graded crushed stone with an apparent density of 2700 kg / m³. 3 The fine aggregate was coarse sand with a fineness modulus of 3.0; the early-strength polycarboxylate superplasticizer was prepared in Preparation Example 1; and the modified polypropylene fiber was prepared in Preparation Example 4.

[0057] Example 2

[0058] A composite precast concrete segment includes a segment body and a reinforcing cage disposed within the segment body. The segment body is made of concrete material, which comprises the following components in parts by weight:

[0059] 150g cement, 50g mineral admixture, 260g coarse aggregate, 150g fine aggregate, 8g early-strength polycarboxylate superplasticizer, 30g functional admixture, and 80g water.

[0060] The functional admixture is composed of modified polypropylene fiber, lithium silicate, and methylcellulose in a mass ratio of 15:7:2; the mineral admixture is composed of silica fume, slag powder, fly ash, and zeolite powder in a mass ratio of 8:31:25:13; the coarse aggregate is 12-20mm continuously graded crushed stone with an apparent density of 2700 kg / m³. 3 The fine aggregate is coarse sand with a fineness modulus of 3.5; the early-strength polycarboxylate superplasticizer was prepared in Preparation Example 2; and the modified polypropylene fiber was prepared in Preparation Example 5.

[0061] Example 3

[0062] A composite precast concrete segment includes a segment body and a reinforcing cage disposed within the segment body. The segment body is made of concrete material, which comprises the following components in parts by weight:

[0063] 135g cement, 48g mineral admixture, 240g coarse aggregate, 145g fine aggregate, 5g early-strength polycarboxylate superplasticizer, 26g functional admixture, and 92g water.

[0064] The functional admixture is composed of modified polypropylene fiber, lithium silicate, and methylcellulose in a mass ratio of 13:5:1; the mineral admixture is composed of silica fume, slag powder, fly ash, and zeolite powder in a mass ratio of 6:29:24:11; the coarse aggregate is 12-20mm continuously graded crushed stone with an apparent density of 2700 kg / m³. 3 The fine aggregate is coarse sand with a fineness modulus of 3.3; the early-strength polycarboxylate superplasticizer was prepared in Preparation Example 3; and the modified polypropylene fiber was prepared in Preparation Example 6.

[0065] Comparative Example 1

[0066] The concrete material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that this comparative example uses a commercially available polycarboxylate superplasticizer instead of an early-strength polycarboxylate superplasticizer.

[0067] Comparative Example 2

[0068] The concrete material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is as follows: The preparation method of the early-strength polycarboxylate superplasticizer in this comparative example is as follows: 20 mol of isopentenyl alcohol polyoxyethylene ether, 4.6 mol of triallyl phosphate, 6.9 mol of L-ethyleneglycine and 0.44 mol of sodium bisulfite are added to 1 L of 80% ethanol aqueous solution, stirred and dissolved, heated to 55°C, and simultaneously added dropwise with stirring, along with 42 mol of acrylic acid, 0.11 mol of mercaptopropionic acid and 0.74 mol of hydrogen peroxide. After the addition is completed, the reaction is kept at the temperature for 2.5 h, distilled under reduced pressure at 83°C, and cooled to obtain the early-strength polycarboxylate superplasticizer.

[0069] Comparative Example 3

[0070] The concrete material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that an equal amount of lithium silicate is used instead of methylcellulose in the functional admixture of this comparative example.

[0071] Comparative Example 4

[0072] The concrete material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that an equal amount of modified polypropylene fiber is used instead of lithium silicate in the functional admixture of this comparative example.

[0073] Comparative Example 5

[0074] The concrete material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that an equal amount of polypropylene fiber is used instead of modified polypropylene fiber in the functional admixture of this comparative example.

[0075] Comparative Example 6

[0076] The concrete material described in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that the mineral admixture in this comparative example is composed of silica fume, slag powder, fly ash and zeolite powder in a mass ratio of 13:5:11:20.

[0077] Test case

[0078] Mechanical properties of the concrete materials prepared in Examples 1-3 and Comparative Examples 1-6 were tested according to GB / T 50081-2019; impermeability and crack resistance of the concrete materials prepared in Examples 1-3 and Comparative Examples 1-6 were tested according to GB / T 50082-2024 "Standard for Test Methods of Long-Term Performance and Durability of Concrete". The test results are shown in Table 1.

[0079] Table 1 Performance Test Results

[0080]

[0081] As shown in Table 1, the concrete material provided by this invention has good mechanical properties, impermeability, and crack resistance. Combined with the test results of Examples 1-3 and Comparative Examples 1-6, it can be seen that the early-strength polycarboxylate superplasticizer prepared by this invention can effectively promote early hydration reaction, improve the early strength and density of concrete; methylcellulose can play a water-retaining role, preventing rapid drying shrinkage and crack formation in concrete, thereby improving the mechanical properties, crack resistance, and impermeability of concrete; lithium silicate can improve the interfacial bonding performance between concrete and aggregates, and increase concrete density; modified polypropylene fiber can improve the crack resistance and mechanical properties of concrete; the dosage ratio of mineral admixtures affects the mechanical properties and impermeability of concrete.

[0082] In addition, the present invention also performed NMR spectroscopy on the early-strength polycarboxylate superplasticizer prepared in Preparation Example 3, and the test results are shown in [Figure 1]. Figure 2 Infrared spectroscopy was performed on the polypropylene fibers and the modified polypropylene fibers prepared in Example 6. The test results are shown in [Figure 1]. Figure 3 .

[0083] Depend on Figure 2 It can be seen that the characteristic peak of -CH3 is at 0.89 ppm, the characteristic peak of -CH2 is at 1.07-1.42 ppm, the characteristic peaks of -CH are at 1.57 ppm and 2.37 ppm, the characteristic peaks of -CH are at 3.35 ppm-3.55 ppm, the characteristic peak of -CH2 in polyoxyethylene ether is at 3.35 ppm, the characteristic peak of -CH2 in phosphate ester group is at 4.55 ppm, the characteristic peak of -NH2 is at 8.93 ppm, the characteristic peak of carboxyl group in L-ethyleneglycine is at 12.39 ppm, and the characteristic peak of carboxyl group in acrylic acid is at 10.63 ppm.

[0084] Depend on Figure 3 It can be seen that the modified polypropylene fiber at 3400cm -1 The characteristic peak of hydroxyl groups appeared at 1730 cm⁻¹. -1 The presence of characteristic peaks for ester groups indicates that hydroxyethyl methacrylate has been successfully grafted onto the surface of polypropylene fibers.

[0085] The above embodiments are merely illustrative of the present invention and are not intended to limit the invention. Those skilled in the art should not modify the above embodiments without departing from the spirit and scope of the present invention. All equivalent modifications or alterations made by those skilled in the art without departing from the technical concept of the present invention are still within the protection scope of the present invention.

Claims

1. A composite precast concrete segment, characterized in that, It includes a tunnel segment body and a reinforcing cage disposed within the tunnel segment body. The tunnel segment body is made of concrete, and the concrete material comprises the following components in parts by weight: 100-150 parts cement, 40-50 parts mineral admixtures, 220-260 parts coarse aggregate, 140-150 parts fine aggregate, 3-8 parts early-strength polycarboxylate superplasticizer, 20-30 parts functional admixtures, and 80-100 parts water. The preparation method of the early-strength polycarboxylate superplasticizer is as follows: isopentenyl alcohol polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine and sodium bisulfite are added to an ethanol aqueous solution, stirred and dissolved, heated to 50-60℃, and acrylic acid, mercaptopropionic acid and hydrogen peroxide are added dropwise while stirring. After the addition is completed, the reaction is kept at the temperature for 2-3 hours, and then distilled under reduced pressure at 80-85℃ and cooled to obtain the early-strength polycarboxylate superplasticizer; the molar ratio of isopentenyl alcohol polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine and acrylic acid is 1:(0.35-0.52):(0.62-0.75):(4-6); The functional admixture is composed of modified polypropylene fiber, lithium silicate and methylcellulose in a mass ratio of (10-15):(3-7):(1-2).

2. The composite precast concrete segment according to claim 1, characterized in that, In the preparation method of the early-strength polycarboxylate superplasticizer, the molar ratio of sodium bisulfite to hydrogen peroxide is (0.5-0.8):1, the amount of hydrogen peroxide used is 0.9%-1.2% of the sum of the amounts of isopentenyl polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine, and acrylic acid; and the amount of mercaptopropionic acid used is 0.1%-0.2% of the sum of the amounts of isopentenyl polyoxyethylene ether, triallyl phosphate, L-ethyleneglycine, and acrylic acid.

3. The composite precast concrete segment according to claim 1, characterized in that, The mass percentage of the ethanol aqueous solution in the preparation method of the early-strength polycarboxylate superplasticizer is 70%-85%.

4. The composite precast concrete segment according to claim 1, characterized in that, The modified polypropylene fiber is prepared as follows: Polypropylene fiber is placed in anhydrous ethanol, ultrasonically cleaned, filtered, and dried. Then, it is placed in a potassium permanganate solution and ultrasonically stirred at 60-65℃ for 30-40 minutes. After filtration, it is soaked in hydrochloric acid solution for 10-20 minutes, filtered again, washed with deionized water until neutral, and dried. Then, it is added together with toluene into a reaction vessel, nitrogen is purged to remove oxygen, and the temperature is raised to 70-80℃. After stirring for 30 minutes, a toluene solution of benzoyl peroxide is added dropwise, and the reaction is stirred for 1-1.5 hours. Hydroxyethyl methacrylate is added dropwise, and after the addition is complete, the temperature is raised to 90-95℃ and the reaction is maintained for 4-6 hours. 30-45 mL of hydroquinone ethanol solution is added, and the reaction is stirred for 30-40 minutes. After cooling, the fiber is filtered, washed, and dried to obtain the modified polypropylene fiber.

5. The composite precast concrete segment according to claim 4, characterized in that, In the preparation method of modified polypropylene fiber, the mass percentage of potassium permanganate solution is 5%-8%, the mass percentage of hydrochloric acid solution is 10%-15%, the mass percentage of benzoyl peroxide in toluene solution is 3%-5%, and the mass percentage of hydroquinone in ethanol solution is 0.1%-0.3%; the mass ratio of polypropylene fiber, hydroxyethyl methacrylate and benzoyl peroxide is 10:(3-5):(0.2-0.3).

6. The composite precast concrete segment according to claim 1, characterized in that, The mineral admixture is composed of silica fume, slag powder, fly ash and zeolite powder in a mass ratio of (4-8):(27-31):(22-25):(8-13).

7. The composite precast concrete segment according to claim 1, characterized in that, The coarse aggregate is 12-20mm continuously graded crushed stone with an apparent density of 2700 kg / m³. 3 The fine aggregate is coarse sand with a fineness modulus of 3.0-3.

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8. The method for preparing composite precast concrete segments according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Fix the steel cage and complete the installation of the embedded parts; S2 mixes cement, mineral admixtures, coarse aggregates, fine aggregates and functional admixtures, adds a mixed solution of early-strength polycarboxylate superplasticizer and water, and stirs evenly to obtain concrete material; S3: Generate a 3D digital model based on the shape and size of the segment, import the 3D digital model into the 3D printing software, use the concrete material obtained in step S2 for 3D printing, demold after curing for 24 hours, steam curing for 7-14 days, and natural curing for 28 days to obtain the concrete segment.

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