High-strength frost-resistant concrete precast product and method for producing the same

Abstract

This invention provides a high-strength, freeze-thaw resistant precast concrete component and its preparation method. The high-strength, freeze-thaw resistant precast concrete component includes a concrete matrix and an antifreeze admixture. The concrete matrix comprises the following raw materials in parts by weight: 320-420 parts cement, 1200-1400 parts coarse aggregate, 700-850 parts fine aggregate, 180-250 parts mineral admixture, 18-25 parts steel fiber, 180-200 parts water, and 8-12 parts polycarboxylate superplasticizer. The antifreeze admixture accounts for 1.2-1.8 wt% of the concrete matrix and contains 70-80 wt% hydrophobic temperature-sensitive aerogel. The hydrophobic temperature-sensitive aerogel is composed of an aryl borate-poly(N-acryloylmorpholine) polymer shell coated with a nano-calcium carbonate-alumina core. The high-strength, freeze-thaw resistant precast concrete components provided by this invention are prepared through concrete mixing, molding, and gradient curing. They exhibit freeze-thaw resistance with a mass loss rate of ≤0.90% after 600 freeze-thaw cycles at -20℃ and a residual strength ratio of ≥78% at -20℃. They are suitable for the construction of cast-in-place concrete and large-area road projects in cold regions and harsh environments.

Description

Technical Field

[0001] This invention relates to the field of precast concrete technology, specifically to a high-strength, freeze-thaw resistant precast concrete component and its preparation method. Background Technology

[0002] Precast concrete components are widely used in construction, transportation, and water conservancy projects due to their advantages such as high construction efficiency and controllable quality. However, in cold regions or extreme climates, precast concrete components are susceptible to internal structural damage due to freeze-thaw cycles, resulting in decreased strength and durability. Current technologies for improving the freeze-thaw resistance of concrete mainly include incorporating air-entraining agents, antifreeze agents, or fiber reinforcement, but these methods struggle to simultaneously meet the requirements of high strength and high freeze-thaw resistance. Furthermore, traditional curing processes for precast concrete components often rely on water curing or ordinary curing agents, which are ineffective in low-temperature environments, further impacting their mechanical properties and durability.

[0003] Therefore, developing a precast concrete component that combines high strength and excellent frost resistance is of great significance for expanding the application of precast components. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a high-strength, freeze-resistant precast concrete component and its preparation method to meet the engineering needs of cold regions or low-temperature environments.

[0005] To achieve the above objectives, the first aspect of the present invention provides a high-strength, freeze-thaw resistant precast concrete component, comprising the following raw materials by weight:

[0006] 320-420 parts cement, 1200-1400 parts coarse aggregate, 700-850 parts fine aggregate, 180-250 parts mineral admixture, 18-25 parts steel fiber, 180-200 parts water, 8-12 parts polycarboxylate superplasticizer;

[0007] The mineral admixture is composed of silica fume, fly ash, mineral powder and metakaolin in a mass ratio of 3-4:3-4:1-2:1-2;

[0008] The antifreeze admixture accounts for 1.2 to 1.8 wt% of the concrete matrix and contains 70 to 80 wt% hydrophobic temperature-sensitive aerogel. The hydrophobic temperature-sensitive aerogel is composed of an aryl borate ester-poly(N-acryloylmorpholine) polymer shell encapsulating a nano-calcium carbonate-alumina core. Its porosity is 90 to 95%, Tg ≤ -40℃, and the mass loss rate after 10 freeze-thaw cycles at -30℃ is ≤1.25%.

[0009] This invention achieves high-strength, frost-resistant concrete by incorporating an antifreeze admixture into the concrete matrix. The hydrophobic, temperature-sensitive aerogel in the antifreeze admixture exhibits a synergistic effect of "physical barrier, chemical inhibition, temperature-sensitive stress buffer, and structural support."

[0010] 1) Physical barrier against moisture intrusion: The highly hydrophobic aryl borate ester surface of the aerogel, combined with its porous adsorption structure, prevents external moisture from entering the concrete at the source and adsorbs and fixes free water, avoiding the formation of large ice crystals and reducing volume expansion damage. This is the basic line of defense against freezing.

[0011] 2) Chemical inhibition of ice crystal formation and growth: The polyglycerol added to the core can form hydrogen bonds with water molecules, reduce the ice crystal formation energy barrier, and delay the formation and growth of ice crystals; the polar groups such as -COOH contained in the shell regulate the ice crystal morphology, destroy the regular growth structure of ice crystals, and avoid local stress concentration.

[0012] 3) Temperature-sensitive stress buffer to offset frost heave stress: Poly(N-acryloylmorpholine) segments are temperature-sensitive: they can shrink at low temperatures, leaving space for ice crystal expansion; they can rebound when heated and restore water-blocking function, adaptively offsetting frost heave stress and avoiding pore cracking.

[0013] 4) Rigid support resists cracking: The rigid nano-calcium carbonate-alumina core supports the outer shell, maintaining structural stability; and resists physical damage from concrete molding vibration, pressure and freeze-thaw cycles, avoiding the breakage and failure of hydrophobic temperature-sensitive aerogel.

[0014] Furthermore, the cement is sulfoaluminate cement with a strength grade of 42.5 or higher;

[0015] The silica fume has an SiO2 content ≥ 92 wt% and a specific surface area ≥ 15 m². 2 / g; fly ash is Class F, Grade I; mineral powder is Grade S95;

[0016] The metakaolin is obtained by calcining kaolin at 700–750℃, and its specific surface area is ≥20m². 2 / g, the sum of active SiO2 and Al2O3 content ≥85wt%.

[0017] Furthermore, the coarse aggregate is 5-16mm continuously graded diabase crushed stone; the fine aggregate is medium sand with a fineness modulus of 2.6-3.0 and a moisture content of ≤0.5wt%.

[0018] The steel fiber is a hooked or sheared steel fiber with a length of 15-20 mm, an aspect ratio of 65-75, and a tensile strength ≥1000 MPa.

[0019] The water reduction rate of the polycarboxylate superplasticizer is 25-35%.

[0020] Furthermore, the hydrophobic temperature-sensitive aerogel is prepared by the following steps:

[0021] S1. Preparation of core dispersion: Nano-calcium carbonate and nano-alumina with a mass ratio of 7:3 to 8:2 are ultrasonically dispersed in a solution containing 0.5 to 1.0 wt% silane coupling agent-ethanol. 1 to 3 wt% polyglycerol and 0.5 to 2 wt% sorbitan monooleate are added to promote dispersion, thus obtaining the core dispersion.

[0022] S2. Preparation of polymer solution: Under nitrogen protection, N-acryloylmorpholine aqueous solution and arylboronic acid ester-ethanol solution with a molar ratio of 7-8:1 are polymerized at 60-70°C in the presence of an auxiliary agent until the viscosity reaches 1800-2000 cP, thus obtaining a polymer solution.

[0023] S3, Core-shell assembly: The polymer solution of S2 is dropped into the core dispersion of S1 at a dropping rate of 1-2 mL / min, and 0.05-0.2 wt% ammonium persulfate is added. Crosslinking and curing are continued at 60-70℃ for 3-4 h. Under vacuum ≤10 Pa, the temperature is gradually reduced to -55℃ at a gradient of -5 to -10℃ / h and freeze-dried for 30-36 h. After washing with water, a hydrophobic thermosensitive aerogel with a core-shell structure is obtained. The thickness of the outer shell is 7-16 nm.

[0024] Further, in step S1, the average particle size of the nano-calcium carbonate is 25-40 nm, the average particle size of the nano-alumina is 80-150 nm, and the degree of polymerization of the polyglycerol is 5-8.

[0025] Further, in step S2, the auxiliary agent includes crosslinking agent N,N'-methylenebisacrylamide, catalyst ammonium persulfate and pore-forming agent ammonium bicarbonate, with amounts of 0.3-1 wt%, 1-5 wt% and 1.5-3 wt% respectively, all based on the total mass ratio of N-acryloylmorpholine and arylboronic acid ester;

[0026] The arylboronic ester is a borate ester formed by an aromatic hydrocarbon group (such as phenyl) and an aromatic heterocyclic group (such as pyridyl or pyrazolyl) with pinacol, and is selected from at least one of 4-carboxyphenylboronic acid pinacol ester, 4-pyridineboronic acid pinacol ester, diboronic acid pinacol ester, and 1-Boc-pyrazole-4-boronic acid pinacol ester.

[0027] Furthermore, the antifreeze admixture also includes 20-30 wt% auxiliary additives, comprising N-oleoyl-D-sphingosine and caprylic / capric triglyceride in a mass ratio of 1:(0.3-0.6). Specifically, N-oleoyl-D-sphingosine is a long-chain hydrophobic molecule that can embed itself into the surface of the aerogel pores to form a double hydrophobic layer, enhancing the water-blocking effect; caprylic / capric triglyceride is a low-freezing-point humectant that can further lower the freezing point of free water inside the concrete and inhibit ice crystal formation. N-oleoyl-D-sphingosine can also bind to the poly(N-acryloylmorpholine) segments of the aerogel shell through hydrogen bonds, enhancing the elasticity of the hydrophobic temperature-sensitive aerogel.

[0028] The second aspect of this invention provides a method for preparing the high-strength, frost-resistant precast concrete component described in the first aspect, specifically comprising the following steps:

[0029] (1) Concrete mixing: Preheat coarse aggregate at 60-80℃ for 2-3 hours until the moisture content is ≤0.5wt%, and dry mix it with cement, mineral admixtures and fine aggregate in a mixer for 2-3 minutes; add steel fiber and 70wt% water and mix for 1-2 minutes; then add polycarboxylate superplasticizer, antifreeze admixture and remaining water and mix for 3-4 minutes to obtain concrete mixture;

[0030] (2) Molding: Pour the concrete mixture into a mold coated with release agent, vibrate, let stand for 2-3 minutes, then press and mold, and hold the pressure for 30-60 seconds;

[0031] (3) Curing: The formed concrete is subjected to high humidity curing for 60 hours, steam curing for 60 hours and mold covering curing for 14 days to obtain precast concrete components.

[0032] Further, in step (2): the vibration frequency is: high frequency 50-60Hz, low frequency 15-20Hz, and the pressure for pressing is 3-5MPa.

[0033] Further, in step (3): the high humidity curing is: humidity ≥90%, first pre-curing at 5~10℃ for 12h, curing at 20℃ for 24h, and then sealing for 12h;

[0034] Pre-curing at 5–10℃ can inhibit flash setting of sulfoaluminate cement, smoothly initiate hydration, and avoid early defects. High-humidity curing at 20℃ can promote the initial formation of ettringite, forming the early skeleton of concrete, and activate the activity of mineral admixtures. Sealed curing for 12 hours locks in water and reserves moisture for the continuous formation of ettringite and the secondary hydration of mineral admixtures, ensuring the continuity of the reaction.

[0035] The steam curing is carried out in a steam curing chamber with a humidity of ≥98%; first, steam curing is carried out at 35℃ for 12 hours, and then steam curing is carried out at 45℃ for 48 hours; wherein, the heating rate is ≤15℃ / h and the cooling rate is ≤10℃ / h.

[0036] Stepwise heating from 35℃ to 45℃: accelerates cement clinker hydration, promotes uniform growth of ettringite, and strengthens the early skeleton; 45℃ steam curing: activates secondary hydration of mineral admixtures, fills pores, and improves density; and avoids temperature stress cracks caused by uneven thermal expansion and contraction through slow heating and cooling.

[0037] The curing temperature for the mold covering is 20–25°C.

[0038] This preparation method employs gradient curing and phased control: high humidity curing to smoothly initiate hydration and avoid early defects; steam curing to accelerate hydration within the stable range of ettringite through a medium-low temperature to medium temperature gradient, while avoiding temperature stress; and mold curing to achieve later strength optimization and shrinkage control, locking in antifreeze properties.

[0039] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0040] The present invention improves the freeze-thaw resistance of precast concrete by adding a composite antifreeze admixture: the hydrophobic temperature-sensitive aerogel has multiple antifreeze mechanisms and works synergistically with N-oleoyl-D-sphingosine and caprylic / capric triglyceride to achieve an antifreeze enhancement effect; enabling the concrete to achieve a freeze-thaw resistance of ≤0.90% mass loss rate after 600 freeze-thaw cycles at -20℃ and ≥78% residual strength ratio at -20℃.

[0041] The method for preparing high-strength, frost-resistant precast concrete components provided by this invention includes concrete mixing, vibration-pressurization molding, and gradient curing steps. It is an economical, effective, and simple new process. By rationally designing the concrete formula and curing system, precast concrete components with both high strength and excellent frost resistance are successfully prepared. They are suitable for engineering construction in cold regions and harsh environments and have broad application prospects. Attached Figure Description

[0042] Figure 1 The full pore size distribution of the hydrophobic thermosensitive aerogels prepared in Examples 1-6 is shown. The x-axis represents pore size / nm, and the y-axis represents distribution frequency / %; Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention; obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods used are conventional methods; the materials and reagents used, unless otherwise specified, can be obtained commercially.

[0044] The sources of the main raw materials and production equipment involved in the following examples and comparative examples are as follows:

[0045] Nano-calcium carbonate, purity >99%, average particle size 30nm, specific surface area 24.20m². 2 / g, moisture content 0.28wt%, Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0046] Nano-alumina, purity >99%, average particle size 100nm, specific surface area 35.19m² 2 / g, Anhui Zhonghang Nanotechnology Development Co., Ltd.

[0047] 4-Carboxyphenylboronic acid pinacol ester, purity 97%; 4-pyridineboronic acid pinacol ester, purity 97%, Sigma-Aldrich.

[0048] N-Acryloylmorpholine, 99% purity, Anhui Youya Chemical Co., Ltd.;

[0049] Polyglycerol-6 (degree of polymerization 6), purity 98%; N-oleoyl-D-sphingosine, purity 98%; caprylic / capric triglyceride, purity 98%, Shanghai Maclean Biochemical Technology Co., Ltd.

[0050] Polar Bear Rapid Hardening Sulfoaluminate Cement, conforming to standard GB20472-2006, with a strength grade of 52.5, was purchased from Tangshan Polar Bear Building Materials Co., Ltd.; its technical specifications are shown in Table 1.

[0051] Table 1

[0052]

[0053] Class F, Grade I power plant fly ash, specific surface area 440 m² 2 / kg, Guangzhou Hengyun Thermal Power Co., Ltd. SF94 silica fume, average particle size 0.12μm, Gansu Sanyuan Silicon Materials Co., Ltd. S95 grade mineral powder, density 3.0g / cm³. 3 Its quality standard is GB / T 18046-2017, Guangdong Xinze Building Materials Co., Ltd.

[0054] The physical and technical properties of the above three mineral admixtures are shown in Table 2.

[0055] Table 2

[0056]

[0057] Kaolin powder, 6000 mesh, whiteness 93.1%, Mohs hardness 7, moisture content 0.5 wt%, purchased from Guangdong Senxin Industry & Trade Co., Ltd.; metakaolin was obtained by calcining the kaolin at 750℃ for 3 hours. The specific surface area after grinding is 398 m². 2 / kg, with an average particle size of 15.32μm.

[0058] The chemical composition of the above four mineral admixtures is shown in Table 3.

[0059] Table 3 (Unit: wt%)

[0060] chemical composition <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO <![CDATA[Fe2O3]]> MgO <![CDATA[SO3]]> <![CDATA[K2O]]> <![CDATA[Na2O]]> other fly ash 49.65 24.41 0.92 13.87 0.83 0.86 0.15 1.83 7.48 silica ash 94.2 0.72 0.44 1.07 0.34 / / / 3.23 Slag powder 32.81 10.55 37.04 3.66 8.95 2.08 0.03 0.02 4.86 metakaolin 53.25 44.56 0.15 0.5 0.13 0.87 0.18 0.03 0.33

[0061] The river sand used is medium sand from Zone II with a fineness modulus of 2.6, which meets the requirements of GB / 14684-2011 standard. It was purchased from Qingyuan River Sand Company.

[0062] The crushed stone is diabase with a continuous gradation of 5-16mm, with a crushing index of 10%, a needle-like and flaky particle content of 8%, and a mud content of ~0.9%. The origin is Jiangxi Province.

[0063] Hook-shaped steel fiber, 18mm in length, 70 aspect ratio, tensile strength 1200MPa, Anping County Zhihui Engineering Materials Co., Ltd.

[0064] D-JSS1 type polycarboxylate superplasticizer, with a solid content of 35%, was purchased from Guangzhou Dashengshi Building Materials Co., Ltd. Its product specifications are shown in Table 4.

[0065] Table 4 (Unit: %)

[0066]

[0067] LGJ-10E Refrigerated Dryer, Sihuan Furui Instrument Technology Development (Beijing) Co., Ltd. Brookfield DV-III Viscometer (USA), Prisys International Trading (Shanghai) Co., Ltd.

[0068] Preparation Example 1

[0069] Preparation of hydrophobic thermosensitive aerogel:

[0070] S1. Disperse 75g of nano-calcium carbonate and 25g of nano-alumina in anhydrous ethanol containing 0.5wt% silane coupling agent KH-550; add 1.5wt% polyglycerol-6 and 1wt% sorbitan monooleate, and sonicate at 200W for 30min to obtain the core dispersion.

[0071] S2. Under nitrogen protection, an aqueous solution containing 0.75 mol N-acryloylmorpholine and an ethanol solution containing 0.1 mol 4-carboxyphenylboronic acid pinacol ester were mixed separately, and 2 wt% N,N'-methylenebisacrylamide, 1.0 wt% ammonium persulfate and 2 wt% ammonium bicarbonate were added and stirred until homogeneous; the reaction was carried out at 65°C until the viscosity reached 2000 cP to obtain a polymer solution.

[0072] S3. The S2 polymer solution was added dropwise to the S1 core dispersion at a rate of 1.5 mL / min, and stirred for 1 h after the addition was complete. 0.1 wt% ammonium persulfate was added, and the mixture was cured at 65 °C for 3 h. The crosslinked product was pre-frozen at -40 °C for 2 h; then, it was freeze-dried at -7 °C / h under a vacuum of 5 Pa for 30 h; and then desorbed at 5 °C / h under a vacuum of 0.1 kPa for 10 h by heating to 25 °C. The product was ultrasonically cleaned twice with pure water (30 kHz, 5 min / time) to remove residual ammonium bicarbonate, soaked in ethanol / water (v:v = 1:1) solvent for 2 h, and replaced three times with anhydrous ethanol (2 h / time) to obtain a hydrophobic thermosensitive aerogel.

[0073] Preparation Example 2

[0074] The difference from Preparation Example 1 is that in step S2, the molar ratio of N-acrylomorpholine to 4-carboxyphenylboronic acid pinacol ester is adjusted to 8:1, that is, the dosage of 4-carboxyphenylboronic acid pinacol ester and N-acrylomorpholine is 0.094 mol and 0.756 mol, respectively.

[0075] Preparation Example 3

[0076] The difference from Preparation Example 1 is that the total amount of arylboronic acid ester remains unchanged in step S2, and 0.375 mol of 4-pyridineboronic acid pinacol ester, 0.375 mol of 4-carboxyphenylboronic acid pinacol ester, and 1 mol of N-acryloylmorpholine are copolymerized.

[0077] Preparation Example 4

[0078] The difference from Preparation Example 1 is that in step S3, the freeze-drying gradient cooling rate is -5℃ / h, and the endpoint is still -55℃.

[0079] Preparation Example 5

[0080] The difference from Preparation Example 1 is that in step S1, the amounts of nano-calcium carbonate and nano-alumina are adjusted to 60g and 40g, respectively.

[0081] Preparation Example 6

[0082] The difference from Preparation Example 1 is that in step S3, the dropping rate of the polymer solution in S2 is 3 mL / min, and the crosslinking curing time is extended to 5 h.

[0083] BSD-PS type specific surface area and pore size analyzer, Best Instrument Technology (Beijing) Co., Ltd. AutoPore IV9500 mercury porosimeter, Shenzhen Huapu General Technology Co., Ltd. DYE-2000S type constant stress concrete compression testing machine, Cangzhou Huayun Experimental Instrument Co., Ltd. LAUDA Scientific video optical contact angle measuring instrument LSA60, Beijing Dongfang Defei Instrument Co., Ltd. HDK-3 / 5 / 9 concrete freeze-thaw testing machine, Shanghai Meiyu Instrument Equipment Co., Ltd.

[0084] Performance tests were performed on preparation examples 1 to 6, and the results are summarized in Table 5.

[0085] Density is measured using a density balance, and the water contact angle is measured using a contact angle meter (static drop method).

[0086] Pore ​​size distribution: Samples were pretreated to constant weight before testing. The pore size distribution of the hydrophobic temperature-sensitive aerogel was calculated using nitrogen adsorption-desorption isotherms and DFT method for mesopores (2–50 nm) and micropores (<2 nm). The macropore size distribution (>50 nm) was obtained by calculating the macropore size using mercury porosimetry (test pressure 70 MPa) and pressure-volume curves. The overall pore size distribution of the hydrophobic temperature-sensitive aerogel was then obtained. The results are shown in [Figure number missing]. Figure 1 .

[0087] Glass transition temperature (T) g Differential scanning calorimetry (DSC) was used, and the test was performed using a TA DSC Q2000 differential scanning calorimeter. Nitrogen flow rate was 50 mL / min. 5–10 mg of the polymer from step S2 was placed in an aluminum crucible. The temperature was first increased from -100°C to 100°C at a rate of 10°C / min to eliminate thermal history; then cooled back to -100°C at a rate of 20°C / min; subsequently, the temperature was increased from -100°C to 100°C at a rate of 10°C / min. The midpoint of the second heating curve was taken as T. g value.

[0088] Mass loss rate: The sample was first frozen at -30℃ for 24h; then thawed naturally at room temperature for 24h; the freeze-thaw cycle was repeated 10 times, and the mass of the dried sample before and after the freeze-thaw was recorded. The freeze-thaw mass loss rate = (m(before freeze-thaw) - m(after freeze-thaw)) / m(before freeze-thaw) × 100%.

[0089] Table 5

[0090]

[0091]

[0092] Based on Preparation Example 1, when the proportion of arylboronic esters decreased (Preparation Example 2), the reduction in crosslinking sites caused the polymer chains to stretch slightly, resulting in a slight increase in pore space during freeze-drying. When 4-pyridineboronic acid pinacol ester was added to the polymer copolymer (Preparation Example 3), the pyridine ring maintained the hydrophobic pores and prevented excessive collapse of macropores, with mesopores accounting for 73%; however, because the polarity of the pyridine ring was slightly stronger than that of 4-carboxyphenylboronic acid pinacol ester, the water contact angle decreased (142°). In Preparation Example 4, a slower freeze-drying condition was selected, which helped to form a more uniform nanoporous structure with fewer defects, resulting in the highest porosity (95.0%); the porous structure provided better stress buffering and water-blocking effects, with the lowest freeze-drying loss rate (0.60%).

[0093] In the hydrophobic thermosensitive aerogel prepared in Example 5, excessive alumina in the core led to core aggregation and decreased dispersibility, making it difficult for the polymer shell to uniformly coat the agglomerates. During freeze-drying, interstitial macropores formed around the agglomerates, disrupting the mesopore structure and creating pore regions of varying sizes (see...). Figure 1 In Example 6, the mesopore size dropped sharply to 65%, and the antifreeze loss rate increased to 1.27%. Due to the faster dropping rate and longer crosslinking time, the polymer shell was over-crosslinked and uneven, resulting in an increased shell thickness. The pore channels were compressed, and some mesopores were converted into micropores or macropores with a wide pore size distribution, resulting in a porosity of 88.5%.

[0094] Examples 1-4

[0095] A high-strength, freeze-thaw resistant precast concrete component, with a diameter of 1m 3 Based on concrete, the amount of concrete matrix used is shown in Table 6.

[0096] Table 6 (Unit: kg / m³) 3 )

[0097]

[0098] The antifreeze admixture used was 1.5 wt% of the concrete matrix, comprising 75 wt% hydrophobic thermosensitive aerogel, 16 wt% N-oleoyl-D-sphingosine, and 9 wt% caprylic / capric triglyceride. The hydrophobic thermosensitive aerogel component consisted of the products obtained in Preparation Examples 1-4.

[0099] The preparation steps are as follows:

[0100] (1) Concrete mixing: After preheating the crushed stone at 60℃ for 3 hours, transfer it to the HJW-30 / 60 forced single-shaft concrete mixer and mix it with river sand for 2-3 minutes; add cement and mineral admixtures and dry mix for 2-3 minutes; add steel fiber and 70wt% water and mix for 1-2 minutes; finally add polycarboxylate superplasticizer, antifreeze admixture and remaining water and mix for 3-4 minutes to obtain fresh concrete mixture (slump of 62mm).

[0101] (2) Molding: Pour the concrete mixture into a mold coated with a release agent, vibrate at a high frequency of 55Hz for 15s + low frequency of 18Hz for 30s; pressurize at 3.5MPa and hold for 40s.

[0102] (3) Curing: The formed concrete is pre-cured at 5℃ for 12 hours, 20℃ for 24 hours, and sealed for 12 hours at 95% humidity. Then it is transferred to a steam curing box at 98% humidity. The temperature is increased to 35℃ at a rate of 10℃ / h and steamed for 12 hours. The temperature is then increased to 45℃ and kept for 48 hours. The temperature is then decreased to 25℃ at a rate of 8℃ / h and covered for curing for 14 days.

[0103] Examples 5-6

[0104] A high-strength, frost-resistant precast concrete component differs from Example 1 in that the amount of antifreeze admixture used is 1.2 wt% and 1.8 wt% of the concrete matrix, respectively.

[0105] Comparative Example 1

[0106] A precast concrete component differs from Example 1 in that the hydrophobic thermosensitive aerogel in the antifreeze admixture is not encapsulated, i.e., only step S1 is used in Preparation Example 1.

[0107] Comparative Example 2

[0108] A precast concrete component differs from Example 1 in that the hydrophobic thermosensitive aerogel in the antifreeze admixture has no core structure, i.e., step S1 is omitted in preparation Example 1.

[0109] Comparative Example 3

[0110] A precast concrete component differs from Example 1 in that the antifreeze admixture used contains only a single component of hydrophobic temperature-sensitive aerogel, and its dosage is the same as that in Example 1.

[0111] Comparative Examples 4-5

[0112] A precast concrete component differs from Example 1 in that the hydrophobic temperature-sensitive aerogel contained in the antifreeze admixture is obtained from Preparation Examples 5 and 6, respectively.

[0113] Comparative Example 6

[0114] A precast concrete component differs from Example 1 in that, while keeping the total amount of mineral admixtures unchanged, the mass ratio of silica fume, fly ash, mineral powder, and metakaolin is adjusted to 5:1:1:1.

[0115] Comparative Example 7

[0116] A precast concrete component differs from Example 1 in that the curing operation in step (3) is: standard curing for 28 days.

[0117] Performance tests were conducted on the precast concrete components of Examples 1-6 and Comparative Examples 1-7. During the tests, except for Comparative Example 7 which was directly cured naturally for 28 days, the total curing time for the other precast concrete components was 28 days, including 19 days of gradient curing and 9 days of natural curing.

[0118] The testing methods for each indicator are as follows:

[0119] 1. Relevant performance tests at room temperature (20℃)

[0120] A. Compressive strength: Refer to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". For 150mm×150mm×150mm specimens, use a DYE-2000S constant stress compressive testing machine to apply pressure at a constant loading rate of 0.5MPa / s until the specimen fails. Record the maximum load and calculate the 28-day compressive strength.

[0121] B. Chloride ion migration coefficient: Non-steady-state migration tests were conducted according to GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete": [The following text appears to be a separate, unrelated section:] ... The sample was placed in an electrolytic cell: the cathode was a 3 wt% NaCl solution, and the anode was a 0.3 mol / L NaOH solution. A 30 V DC voltage was applied for 24 hours. After the test, the sample was split open, sprayed with 0.1 mg NO3 solution for color development, and the chloride ion penetration depth X was measured using a rapid chloride ion penetration tester. d Calculate D-RCM: D-RCM=[0.0239×(273+T)×X d ] / [(U-2)×t]. Where: T, test temperature (°C), L, sample thickness (m); U, absolute voltage (V); t, test time (s).

[0122] C. Freeze-thaw cycle durability: According to GB / T 50082. Using an HDK-3 / 5 / 9 type concrete freeze-thaw testing machine, standard precast specimens were subjected to 600 freeze-thaw cycles (freezing at -18±2℃ for 4 hours and thawing at 4±2℃ for 4 hours). The mass loss rate before and after freeze-thaw was measured, and the calculation formula is: Mass loss rate = (initial mass - final mass) / initial mass × 100%.

[0123] D. Permeability Resistance Grade: Refer to GB / T 50082-2009. The permeability height method is used, with a water pressure of 1.2 MPa and constant pressure for 8 hours. The permeability resistance grade is determined based on the average permeability height.

[0124] The concrete test results above are the average of 5 parallel experiments and are summarized in Table 7.

[0125] Table 7

[0126]

[0127] 2. Low-temperature related performance testing

[0128] A. Low-temperature chloride ion diffusion coefficient: This directly assesses the resistance of concrete to chloride ion erosion under low-temperature freeze-thaw conditions. The chloride ion migration coefficient at -20℃ is determined using the RCM method.

[0129] Will The cylindrical sample was pre-cooled in a constant temperature chamber (-20±1℃) until the center temperature of the sample stabilized at -20℃. The cathode cell contained 3wt% NaCl (simulated de-icing salt) antifreeze (50% ethylene glycol solution, maintained at -20℃ to prevent freezing), and the anode cell contained 0.3mol / L NaOH antifreeze. A 30V DC voltage was applied, and the test was conducted for 96 hours. The chloride ion migration coefficient D at -20℃ was calculated. low The calculation formula is the same as the D-RCM calculation formula under normal temperature testing.

[0130] B. Low-Temperature Fracture Energy and Residual Strength: This assesses the toughness, crack resistance, and resistance to crack propagation of concrete at low temperatures. Higher fracture energy and residual strength indicate better low-temperature crack resistance. Refer to RILEM TC-187 test.

[0131] Three-point bending beam specimens (100mm × 100mm × 400mm) with pre-existing cracks were prepared. The specimens were pre-cooled in an ambient temperature chamber at -20±1℃ until the center temperature stabilized. Three-point bending tests were performed at -20℃ using a universal testing machine equipped with cryogenic fixtures. Load-displacement (crack opening displacement CMOD) curves were recorded until fracture, and the fracture energy G was calculated. f (N / m): This is the total area under the load-displacement curve divided by the net area of ​​the ligament. Record the residual strength corresponding to the peak load, and calculate the residual strength ratio = maximum load at fracture / peak load × 100%.

[0132] The test results were the average of five parallel experiments and are summarized in Table 8.

[0133] Table 8

[0134] concrete <![CDATA[D low (×10 -12 m 2 / s)]]> <![CDATA[G f (N / m)]]> Residual strength ratio % Example 1 0.95 180 86.5 Example 2 1.05 168 83.7 Example 3 0.88 190 87.2 Example 4 0.65 235 90.5 Example 5 1.05 160 81.5 Example 6 0.70 225 89.2 Comparative Example 1 3.25 80 55 Comparative Example 2 3.85 60 47 Comparative Example 3 2.20 125 75 Comparative Example 4 2.55 105 65 Comparative Example 5 2.30 120 68 Comparative Example 6 2.60 110 70 Comparative Example 7 3.55 90 62

[0135] Tables 7-8 demonstrate that this invention, through the internal incorporation of an antifreeze admixture containing predominantly hydrophobic temperature-sensitive aerogel, enhances low-temperature toughness through a dual mechanism of reducing ice crystal formation by adsorbing capillary water and buffering frost heave stress by mitigating pore deformation. This effectively resists low-temperature freeze-thaw damage, chloride salt corrosion, and brittle fracture. The precast concrete components in Examples 1-6 exhibit a 28-day compressive strength of 76.3-79.5 MPa and a chloride ion diffusion coefficient of 0.95-1.50 × 10⁻⁶ MPa. -12 m 2 / s, impermeability grade ≥P11; excellent freeze-thaw resistance in harsh low-temperature environments, with a mass loss rate ≤0.90% after 600 freeze-thaw cycles. Moreover, Example 4 has the highest low-temperature fracture energy and the greatest resistance to crack propagation at low temperatures; Example 3 has excellent concrete impermeability due to the pyridine ring contained in the antifreeze admixture maintaining hydrophobic pores; however, the polarity of the pyridine ring increases slightly, and the freeze-thaw resistance of the concrete decreases slightly.

[0136] The antifreeze admixture in the precast concrete component of Comparative Example 1 is a nano-mixture filler without an outer shell. It mainly fills the pores and acts as a crystal nucleus in the concrete, and has a certain strength (28-day compressive strength of 56.5 MPa). However, it has a high surface energy and is prone to agglomeration during concrete mixing, which can easily generate microcracks. Therefore, its impermeability strength is only P7. Moreover, it lacks the elastic buffering effect provided by the hydrophobic temperature-sensitive aerogel with a three-dimensional network structure. At low temperatures, the concrete cannot adaptively shrink and release stress, resulting in a significant deterioration in its freeze-thaw resistance: its freeze-thaw mass loss rate reaches 7.5%.

[0137] In Comparative Example 2, the antifreeze admixture in the precast concrete was a loose, hydrophobic, temperature-sensitive aerogel polymer porous body without a core. Due to the lack of rigid support from the nano-core, the concrete had low mechanical strength (28-day compressive strength of only 44.3 MPa). The polymer porous body was easily crushed during concrete mixing, failing to form a pore buffer framework and potentially causing defects; therefore, its impermeability grade was only P5. Simultaneously, the lack of chemical inhibition from nano-calcium carbonate-alumina reinforcement and polyglycerol hydroxyl groups to reduce ice crystal surface energy led to an increase in the chloride ion permeability coefficient of the concrete. Repeated stress during freeze-thaw cycles caused microcrack propagation, resulting in a sharp increase in freeze-thaw mass loss rate to 8.2%. In contrast, while the concrete in Comparative Example 6 experienced a decrease in freeze-thaw resistance due to core agglomeration, the hydrophobic temperature-sensitive aerogel did not completely fail, demonstrating the crucial role of the core in structural stability.

[0138] The antifreeze additive used in Comparative Example 3 contained only hydrophobic thermosensitive aerogel, lacking the synergistic antifreeze and buffering effects of N-oleoyl-D-sphingosine and caprylic / capric triglyceride. This resulted in the isolation of the antifreeze function of the hydrophobic thermosensitive aerogel: the aerogel relied solely on its own pores to adsorb water, which could not effectively lower the freezing point, nor could it completely resist the destruction of ice crystals in the freeze-thaw cycle. This led to an increase in the freeze-thaw mass loss rate (2.70%), and a significant decrease in strength and impermeability.

[0139] Comparative Example 4, containing a hydrophobic thermosensitive aerogel, has a dense outer shell with insufficient porosity and a permeability rating of P9. Its Tg = -35.5℃, resulting in a concrete freeze-thaw mass loss rate of 4.20%. During freeze-thaw cycles, ice crystals lacked sufficient buffer space, and the residual strength at -20℃ was only 65%, confirming the stress buffering effect of the thermosensitive shrinkage of the poly(N-acryloylmorpholine) segments. Comparative Example 5, also due to the poor performance of the hydrophobic thermosensitive aerogel, showed a concrete freeze-thaw mass loss rate of 3.80% after 600 cycles, demonstrating the crucial role of porous adsorption in reducing ice crystal damage.

[0140] In Comparative Example 6, the proportion of kaolin in the mineral admixtures of the concrete raw materials was insufficient, resulting in incomplete secondary hydration, increased concrete porosity, and decreased density; therefore, the impermeability grade was only P8, and the chloride ion diffusion coefficient increased to 3.15 × 10⁻⁶. -12 m 2 / s, freeze-thaw mass loss rate 3.3%. Comparative Example 7, using standard curing, showed incomplete conversion of ettringite, leading to the decomposition of ettringite, a hydration product of sulfoaluminate cement. The early-stage concrete skeleton was weak, with a 28-day compressive strength of only 50 MPa, a freeze-thaw mass loss rate of 4.50%, and a chloride ion diffusion coefficient of 4.00 × 10⁻⁶. -12 m 2 / s.

[0141] This invention, through the rational design of concrete formulation and curing system, successfully produces precast concrete components with both high strength and excellent frost resistance. The concrete achieves a mass loss rate of ≤0.90% after 600 freeze-thaw cycles at -20℃ and a residual strength ratio of ≥78% at -20℃. It is suitable for engineering construction in cold regions and harsh environments and has broad application prospects.

[0142] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-strength, freeze-thaw resistant precast concrete component, comprising a concrete matrix and an antifreeze admixture, characterized in that: The concrete matrix comprises the following raw materials in parts by weight: 320-420 parts cement, 1200-1400 parts coarse aggregate, 700-850 parts fine aggregate, 180-250 parts mineral admixture, 18-25 parts steel fiber, 180-200 parts water, 8-12 parts polycarboxylate superplasticizer; The mineral admixture is composed of silica fume, fly ash, mineral powder and metakaolin in a mass ratio of 3~4:3~4:1~2:1~2; The antifreeze admixture accounts for 1.2 to 1.8 wt% of the concrete matrix and contains 70 to 80 wt% hydrophobic temperature-sensitive aerogel. The hydrophobic temperature-sensitive aerogel consists of an arylborate-poly(N-acryloylmorpholine) polymer shell encapsulating a nano-calcium carbonate-alumina core. Its porosity is 90~95%, Tg≤-40℃, and the mass loss rate is ≤1.25% after 10 freeze-thaw cycles at -30℃. The hydrophobic temperature-sensitive aerogel is prepared by the following steps: S1. Preparation of core dispersion: Nano-calcium carbonate and nano-alumina with a mass ratio of 7:3 to 8:2 are ultrasonically dispersed in a solution containing 0.5 to 1.0 wt% silane coupling agent-ethanol. 1 to 3 wt% polyglycerol and 0.5 to 2 wt% sorbitan monooleate are added to promote dispersion, thus obtaining the core dispersion. S2. Preparation of polymer solution: Under nitrogen protection, N-acryloylmorpholine aqueous solution and arylboronic acid ester-ethanol solution with a molar ratio of 7~8:1 are polymerized at 60~70℃ in the presence of an auxiliary agent until the viscosity reaches 1800~2000 cP, thus obtaining a polymer solution. S3, Core-shell assembly: The polymer solution of S2 is dropped into the core dispersion of S1 at a dropping rate of 1~2 mL / min, and 0.05~0.2 wt% ammonium persulfate is added. Crosslinking and curing are carried out at 60~70℃ for 3~4 h. Under vacuum ≤10 Pa, the temperature is gradually reduced to -55℃ at a gradient of -5~-10℃ / h and freeze-dried for 30~36 h. After washing with water and drying, a hydrophobic thermosensitive aerogel with a core-shell structure is obtained. The thickness of the outer shell is 7~16 nm. In step S2, the auxiliary agent includes crosslinking agent N,N'-methylenebisacrylamide, catalyst ammonium persulfate and pore-forming agent ammonium bicarbonate, with amounts of 0.3~1wt%, 1~5wt% and 1.5~3wt% respectively, all based on the total mass of N-acryloylmorpholine and arylboronic acid ester; The arylboronic ester is selected from at least one of 4-carboxyphenylboronic acid pinacol ester, 4-pyridineboronic acid pinacol ester, diboronic acid pinacol ester, and 1-Boc-pyrazole-4-boronic acid pinacol ester.

2. The precast concrete component as described in claim 1, characterized in that, The cement is sulfoaluminate cement with a strength grade of 42.5 or higher; The silica fume has an SiO2 content ≥ 92wt% and a specific surface area ≥ 15m². 2 / g; fly ash is Class F, Grade I; mineral powder is Grade S95; The metakaolin is obtained by calcining kaolin at 700~750℃, and its specific surface area is ≥20m². 2 / g, the sum of active SiO2 and Al2O3 content ≥85wt%.

3. The precast concrete component as described in claim 1, characterized in that, The coarse aggregate is 5-16mm continuously graded diabase crushed stone; the fine aggregate is medium sand with a fineness modulus of 2.6-3.0 and a moisture content ≤0.5wt%. The steel fibers are end-hooked or sheared steel fibers with a length of 15~20mm, an aspect ratio of 65~75, and a tensile strength ≥1000MPa; The water reduction rate of the polycarboxylate superplasticizer is 25-35%.

4. The precast concrete component as described in claim 1, characterized in that, In step S1, the average particle size of nano-calcium carbonate is 25-40 nm, the average particle size of nano-alumina is 80-150 nm, and the degree of polymerization of polyglycerol is 5-8.

5. The precast concrete component as described in claim 1, characterized in that, The antifreeze additive also includes 20-30 wt% auxiliary additives, including N-oleoyl-D-sphingosine and caprylic / capric triglyceride in a mass ratio of 1:(0.3-0.6).

6. The method for preparing precast concrete components as described in any one of claims 1 to 5, characterized in that, Specifically, the steps include the following: (1) Concrete mixing: Preheat coarse aggregate at 60~80℃ to a moisture content of ≤0.5wt%, and dry mix it with cement, mineral admixtures and fine aggregate in a mixer for 2~3min; add steel fiber and 70wt% water and mix for 1~2min; then add polycarboxylate superplasticizer, antifreeze admixture and remaining water and mix for 3~4min to obtain concrete mixture; (2) Molding: Pour the concrete mixture into a mold coated with release agent, vibrate, let stand for 2-3 minutes, then press and mold, and hold the pressure for 30-60 seconds; (3) Curing: The formed concrete is subjected to high humidity curing for 60 hours, steam curing for 60 hours and mold covering curing for 14 days to obtain precast concrete components.

7. The preparation method according to claim 6, characterized in that, In step (2): the vibration frequency is: high frequency 50~60Hz, low frequency 15~20Hz, and the pressure for pressing is 3~5MPa.

8. The preparation method according to claim 6, characterized in that, In step (3): the high humidity curing is: humidity ≥90%, first pre-curing at 5~10℃ for 12h, curing at 20℃ for 24h, and then sealing for 12h; The steam curing is carried out in a steam curing chamber with a humidity of ≥98%; first, steam curing is carried out at 35℃ for 12 hours, and then steam curing is carried out at 45℃ for 48 hours; wherein, the heating rate is ≤15℃ / h and the cooling rate is ≤10℃ / h. The curing temperature for the mold covering is 20~25℃.

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