Anti-freezing agent for concrete in ultralow-temperature high-altitude environment, anti-freezing concrete and preparation method of anti-freezing concrete

Abstract

The invention provides an anti-freezing agent for concrete in an ultralow-temperature high-altitude environment, anti-freezing concrete and a preparation method of the anti-freezing concrete, and belongs to the technical field of concrete. The anti-freezing agent for the concrete in the ultralow-temperature high-altitude environment comprises a first component and a second component, the first component comprises nano crystal nucleus powder and inorganic salt anti-freezing powder, and the second component comprises a nano composite air entraining agent and a foam stabilizer; the mass ratio of the nano crystal nucleus powder to the inorganic salt anti-freezing powder to the nano composite air entraining agent to the foam stabilizer is (20-60): (20-60): (20-60): (0.1-10). The ultralow-temperature anti-freezing early-strength concrete is prepared from the nano-crystal nucleus super-early-strength component, the inorganic salt anti-freezing component, the nano air entraining component and the foam stabilizing component, the construction performance and anti-freezing and early-strength requirements of the concrete in an ultralow-temperature high-altitude environment are met, the applicable temperature can reach-30 DEG C, meanwhile, the long-term durability of the concrete in a freezing and thawing cycle environment is improved, and the concrete has good anti-freezing and early-strength properties. The problems of fast air content loss, large slump loss, poor bubble stability and the like caused by high altitude and low air pressure are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of concrete, in particular to a freezing inhibitor for concrete used in an ultralow-temperature high-altitude environment, a freezing-resistant concrete and a preparation method thereof. BACKGROUND

[0002] In the infrastructure construction landscape of China, the northern region and the high-altitude cold region occupy an important position. The northern region covers Northeast China, North China and most of Northwest China, and the duration of winter is as long as 3-5 months. The extreme low temperature is generally below -20 ℃, among which the extreme low temperature in Mohe, Northeast China, and Hailaer, Inner Mongolia, can reach -35 ℃, and the diurnal temperature difference often maintains at 10-15 ℃. At the same time, the high-altitude region in the west of China (such as the Qinghai-Tibet Plateau, the Pamir Plateau and the Hengduan Mountains) has an altitude of more than 3000 meters, and the altitude of some engineering road sections (such as the Queer Mountain Tunnel of the Sichuan-Tibet Railway and the Tanggula Mountain Pass section of the Qinghai-Tibet Highway) is more than 4500 meters. This region not only has the characteristics of ultralow temperature below -30 ℃, but also has a low-pressure environment with atmospheric pressure only 60%-70% of that in plain areas and oxygen partial pressure less than 70% of that in plain areas.

[0003] With the new urbanization construction in China, major projects such as winter municipal engineering (such as road renovation and bridge construction) in the northern region, energy engineering (such as wind power foundation and oil pipeline), and transportation hubs (such as highland airports and cross-river bridges) and water conservancy projects (such as highland reservoirs and water diversion tunnels) in the high-altitude region of the west of China continue to be implemented, which puts forward strict requirements for the construction adaptability and long-term durability of concrete in extreme environments.

[0004] As the core structural material for engineering construction, the performance of concrete is highly related to environmental conditions. In the conventional low-temperature environment in the northern region in winter, the performance of concrete construction needs to be guaranteed by a freezing inhibitor. If no freezing inhibitor is added, the free water in the mixing water will freeze to form ice crystals below 0 ℃, and the volume of ice crystals will expand by about 9% compared with that of liquid water, which will cause physical extrusion to the unhardened cement stone structure inside the concrete, resulting in the generation of microcracks. After the temperature rises, the ice crystals melt to form pores, which will become the channel for water penetration and freeze-thaw damage, eventually leading to a large loss of the later-stage compressive strength and flexural strength of the concrete, and seriously affecting the structural bearing capacity. Therefore, in the construction of concrete in the northern region in winter, a freezing inhibitor has become an indispensable functional admixture, and its performance directly determines the engineering quality and construction efficiency.

[0005] However, the current building material industry standard for regulating the application of freezing inhibitors, “Concrete Freezing Inhibitor” (JC 475-2004), has been difficult to adapt to the current extreme environment construction requirements. The standard was issued in 2004, and at that time there were few high-altitude extreme low-temperature engineering cases in China. The core technical indicators were designed based on the low-temperature environment below -15 ℃ in the northern plain region, and the particularity of ultralow temperature below -15 ℃ and high-altitude low-pressure environment was not considered.

[0006] With the extension of engineering construction to extreme areas, the limitations of this standard have become increasingly prominent: on the one hand, in the extremely cold northern regions (such as the Greater Khingan Mountains in Heilongjiang and Altai in Xinjiang) and the western high-altitude regions, the winter construction temperature often breaks -20 ℃, and even drops to -30 ℃. If the antifreeze agent still meets the standard of "Concrete Antifreeze" (JC 475-2004), the freezing point of the concrete mixing water can only be reduced to about -15 ℃, and it will freeze within 4-6 hours after pouring. The cement hydration reaction almost stops, which leads to the failure of concrete to form critical frost resistance strength (usually ≥3 MPa), and further causes structural frost damage. On the other hand, the standard only regulates the basic indicators of the freezing point reduction effect, early strength, and steel corrosion of the antifreeze agent, and does not involve the key performance indicators such as air content loss over time, slump retention, and bubble stability in high-altitude low-pressure environments. These indicators are the core factors that affect the workability and durability of concrete in high-altitude construction, and the lag of the standard has become an important bottleneck restricting extreme environment engineering construction.

[0007] More seriously, the high-altitude low-pressure environment will exacerbate the technical problems of concrete construction, forming a double challenge of ultra-low temperature and low pressure. In high-altitude environments, low air pressure can significantly change the physical state of freshly mixed concrete: on the one hand, the internal air of freshly mixed concrete will form tiny bubbles due to the air entrainment during mixing. In a low-pressure environment, the pressure difference inside and outside the bubble increases, leading to a significant acceleration of bubble escape rate. The rapid loss of air content directly leads to the deterioration of concrete workability, and the slump loss rate accelerates, resulting in the inability of concrete to be transported to the work surface through pumping equipment, and the problems of aggregate segregation and surface bleeding during vibration. Remedies such as increasing the amount of cement and adjusting the mixing process are necessary, which not only prolongs the construction period but also increases the cost of single concrete by 15%-20%.

[0008] On the other hand, the poor bubble stability of concrete under the ordinary antifreeze agent system further exacerbates the problem of insufficient frost resistance. The air entraining agent commonly used in ordinary antifreeze agents (such as sodium dodecyl benzene sulfonate) is difficult to precisely control the bubble size and distribution due to the limitation of molecular structure, forming bubbles with a diameter of 0.1-1 mm and uneven bubble wall thickness. In a high-altitude low-pressure environment, these bubbles are easily merged to form large-sized bubbles or broken and escaped due to the pressure difference, resulting in the internal pores of hardened concrete showing uneven size and disordered distribution. During the winter freeze-thaw cycle, water will seep into the pores, and the ice expansion under low temperature will generate internal stress. After repeated action, the cement stone structure around the pores will crack. With the increase of freeze-thaw cycle times, the cracks will continuously expand and eventually lead to the peeling of the concrete surface and the attenuation of strength.

[0009] In addition, the performance defects of traditional antifreeze agents are also magnified in extreme environments. Currently, the antifreeze agents commonly used in winter construction in northern regions are still mainly single types: although chlorate antifreeze agents (such as calcium chloride) have low cost and obvious ice point reduction effect, they can accelerate the corrosion of steel bars, and in high-altitude environments with large humidity fluctuations, the corrosion rate of steel bars is 2-3 times higher than that in plain areas; although nitrate antifreeze agents (such as sodium nitrate) have no corrosion risk, they react with aluminate tricalcium in cement to generate ettringite, which can cause concrete volume expansion in low-temperature environments, and in high-altitude areas with frequent temperature drops, the expansion stress and frost heaving stress are superimposed, which can more easily lead to concrete cracking; alcohol antifreeze agents (such as ethylene glycol) have high volatility, and in high-altitude low-pressure environments, the evaporation rate increases, which not only leads to a decrease in the effective concentration of the antifreeze agent, but also increases the porosity of the concrete, resulting in a decrease in 28-day compressive strength. Even if some projects use composite antifreeze agents, they are mostly simple compounding and are not designed for high-altitude ultra-low temperature environments, and cannot simultaneously solve the four core problems of ice point reduction, strength development, air content maintenance, and bubble stability, making it difficult to meet the construction and durability requirements of current extreme environment projects.

[0010] In summary, with the deep expansion of engineering construction in northern extremely cold regions and western high-altitude regions in China, the problems of lagging standards, insufficient performance of traditional antifreeze agents, and the combined effects of extreme environments have become intertwined, leading to the difficulties of difficult construction, poor quality, and low durability of concrete construction in ultra-low temperature high-altitude environments. How to break through the -30 ℃ ultra-low temperature limit and solve the problems of rapid loss of air content, large loss of slump, and poor bubble stability caused by low air pressure in high-altitude areas has become an urgent need to ensure the quality of major projects in northern winter and western high-altitude regions and to promote the upgrading of concrete admixture technology in China, and also provides a practical background and application scenario for the research and development of new ultra-low temperature high-altitude special antifreeze agents. SUMMARY

[0011] The main purpose of the present application is to provide an antifreeze agent for concrete in an ultra-low temperature high-altitude environment, a freeze-resistant concrete, and a preparation method thereof. The ultra-low temperature freeze-resistant early-strength concrete is prepared by using a nanocrystalline core ultra-early-strength component, an inorganic salt antifreeze component, a nano-air entraining component, and a foam stabilizing component, which meets the requirements of construction performance and freeze-resistant early-strength of concrete in an ultra-low temperature high-altitude environment, and improves the long-term durability of concrete in a freeze-thaw cycle environment, solving the problems of rapid loss of air content, large loss of slump, and poor bubble stability caused by low air pressure in high-altitude areas.

[0012] To solve the above technical problems, the technical scheme adopted by the present application is: a freezing point depressant for concrete under super-low temperature and high altitude environment, comprising a first component and a second component, the first component comprises nano-crystal core powder and inorganic salt freezing point depressant powder, the second component comprises nano-composite air entraining agent and foam stabilizer; the mass ratio of the nano-crystal core powder, inorganic salt freezing point depressant powder, nano-composite air entraining agent and foam stabilizer is 20-60:20-60:20-60:0.1-10.

[0013] The freezing point depressant for concrete under super-low temperature and high altitude environment provided by the present application greatly improves the strength of concrete before freezing by using nano-crystal core powder, reduces the freezing point of free water in concrete by using inorganic salt freezing point depressant powder, and continuously hydrates to generate strength before cooling to the negative temperature freezing point after concrete pouring construction; in addition, to maintain the working performance of concrete during construction and improve the frost resistance of concrete, nano-scale air bubbles are uniformly introduced into the concrete by adding nano-composite air entraining agent, and the stability of the introduced air bubbles under high sea environment is improved under the action of the foam stabilizer; the working performance of concrete is improved through the ball bearing effect of nano-bubbles, and after the concrete hardens to generate strength, uniformly distributed nano-scale closed pores are formed to buffer the impact caused by freezing and thawing, thereby improving the frost resistance of the concrete structure. The freezing point depressant for concrete under super-low temperature and high altitude environment can realize smooth construction of concrete in a low temperature environment of-30 DEG C or below, effectively solving the problems of large loss of slump of fresh concrete, easy freezing and poor frost resistance of hardened concrete under super-low temperature and high altitude environment.

[0014] In the preferred scheme, the nano-crystal core powder in the first component is prepared by ultrasonic spray drying of a nano-calcium silicate aqueous solution.

[0015] In the further preferred scheme, the preparation method of the nano-crystal core powder in the first component specifically comprises the following steps: a water glass and calcium nitrate are subjected to a crystal nucleus generation reaction in an aqueous solution with a pH of 10-14, and a polycarboxylic acid water reducing agent is added for homogenization and dispersion during the reaction, and then ultrasonic spray drying is performed after cooling to obtain the nano-crystal core powder.

[0016] In the still further preferred scheme, the molar ratio of silicate in the water glass to calcium nitrate is 0.5-1:1; the addition amount of the polycarboxylic acid water reducing agent is 5%-15% of the total solution mass; and the ultrasonic frequency of the ultrasonic spray drying is 80-100 KHz.

[0017] In the preferred scheme, the inorganic salt freezing point depressant powder in the first component is obtained by mixing sodium sulfate, sodium nitrate and sodium metaaluminate in a mass ratio of 5-30:5-30:5-20.

[0018] In the preferred scheme, the nano-composite air entraining agent in the second component is prepared by modifying silica ash with a mixed solution of acrylic acid and air entraining agent.

[0019] The modified silica ash in the present application is to uniformly attach air entraining agent molecular materials in the microporous structure, so that the bubbles can be continuously and stably introduced during the later concrete mixing process, and the air content is ensured to be stable.

[0020] In a further preferred embodiment, the air entraining agent comprises an anionic air entraining agent or a cationic air entraining agent.

[0021] In a further preferred embodiment, the anionic air entraining agent is selected from alkyl benzene sulfonate, alkyl sulfonate, rosin soap or sodium laurate.

[0022] In a further preferred embodiment, the cationic air entraining agent is selected from cetyl trimethyl ammonium bromide.

[0023] In a further preferred embodiment, the preparation method of the nanocomposite air entraining agent in the second component specifically comprises the following steps: S1, preparing a mixed solution of 10-15 L of propionic acid with a concentration of 5 wt% and air entraining agent with a concentration of 2 wt%; S2, adding 1 kg of silica ash into the mixed solution of step S1, and adding concentrated sulfuric acid with a mass of 1% of the total mass of the mixed solution at 90-110 ℃, and stirring for 1 h; S3, washing and filtering the reaction product in step S2, and drying to obtain.

[0024] In a further preferred embodiment, the D50 of the silica ash is 5-10 μm. 50 =5~10 μm.

[0025] In a further preferred embodiment, the stirring rate in step S2 is 100-120 revolutions per minute.

[0026] In a further preferred embodiment, the drying temperature in step S3 is 110-130 ℃, and the duration is 10-15 h.

[0027] In a preferred embodiment, the foam stabilizer in the second component is a mixture of polyacrylamide, sodium carboxymethyl cellulose and macromolecular fatty alcohol polyoxyethylene ether in a mass ratio of 1-4:1-4:1-2.

[0028] Polyacrylamide and sodium carboxymethyl cellulose physically stabilize the foam by significantly increasing the viscosity of the system, and fatty alcohol polyoxyethylene ether as a non-ionic surfactant can be adsorbed on the bubble liquid film, reduce the interfacial tension, and possibly enhance the liquid film strength through intermolecular forces. The combination of the three can jointly act in both viscosity improvement and interfacial film stabilization to achieve better foam stabilization effect.

[0029] The application further provides the antifreezing concrete under super-low temperature and high altitude environment, which comprises cement 260-400 parts by mass, fly ash 50-150 parts by mass, silica ash 0-50 parts by mass, sand 500-800 parts by mass, stone 800-1200 parts by mass, the antifreezing agent for concrete under super-low temperature and high altitude environment 1-20 parts by mass, water reducing agent 5-10 parts by mass and water 150-200 parts by mass.

[0030] The preparation method of the antifreezing concrete under super-low temperature and high altitude environment comprises the following steps: The cement, fly ash, silica ash, sand, stone and the first component of the antifreezing agent for concrete under super-low temperature and high altitude environment are put into a mixer, and after dry mixing, the second component of the antifreezing agent for concrete under super-low temperature and high altitude environment, water and water reducing agent are added, and the mixture is continuously stirred to obtain the antifreezing concrete under super-low temperature and high altitude environment.

[0031] Compared with the prior art, the application has the following advantages: (1) The antifreezing agent for concrete under super-low temperature and high altitude environment provided by the application can rapidly stimulate the hydration reaction after the concrete is poured, and can improve the early compressive strength of the concrete, and can greatly reduce the damage to the microstructure caused by entering the negative temperature.

[0032] (2) The antifreezing agent for concrete under super-low temperature and high altitude environment provided by the application can reduce the freezing point of free water in the fresh concrete, prolong the hydration reaction time of the concrete, and can also hydrate a small amount of water during the mixing of the concrete, improve the hydration heat release, and prolong the normal temperature time of the concrete after entering the mold; in addition, the inorganic antifreezing salt can react with calcium hydroxide, the hydration product of the concrete, to improve the pore structure of the hydration product and increase the compactness of the concrete structure, and improve the strength and frost resistance of the concrete.

[0033] (3) The antifreezing agent for concrete under super-low temperature and high altitude environment provided by the application can mix with the nano air entraining agent and the foam stabilizer, the nano air entraining agent can uniformly introduce the nanoscale bubbles in the concrete, and the stability of the introduced bubbles in the high sea environment can be improved under the action of the foam stabilizer, the working performance of the concrete can be improved through the ball bearing effect of the nano bubbles, and after the concrete hardens and generates strength, the uniformly distributed nanoscale closed pores can buffer the impact caused by freezing and thawing to improve the frost resistance of the concrete structure.

[0034] (4) In the high-altitude environment of ultra-low temperature and low pressure, the air content in the fresh concrete loses a lot over time, resulting in too fast loss of concrete slump, affecting normal construction operation, and the bubble stability in ordinary concrete is poor, and the concrete forms air holes of different sizes after hardening, resulting in poor concrete anti-freezing and thawing capacity. In view of the above technical problems, the antifreeze for concrete in the high-altitude environment of ultra-low temperature is provided, which realizes the smooth construction of concrete in the low-temperature and low-pressure environment below-30 DEG C, and effectively solves the problems of large loss of fresh concrete slump over time, easy freezing and poor anti-freezing and thawing cycle capacity of hardened concrete in the high-altitude environment of ultra-low temperature. DETAILED DESCRIPTION

[0035] The technical solutions of the present application are further described and illustrated by examples. The raw materials used in the examples can be purchased or prepared by conventional methods.

[0036] The nanocrystalline core powder is prepared by the following method: the silicate in water glass and calcium nitrate are weighed according to the molar ratio of 1:1, and then the crystal nucleus generation reaction is carried out in the aqueous solution with PH of 11, the total solution mass 10% of polycarboxylic acid water reducing agent (the solid content of water reducing agent is 10%) is added during the reaction process for homogenization and dispersion, and after cooling, the nanometer calcium silicate crystal core powder is prepared by spray drying.

[0037] The inorganic salt antifreeze powder is prepared by the following method: sodium sulfate, sodium nitrate and sodium metaaluminate are weighed according to the molar ratio of 1:1:1, and then mechanical stirring is carried out in the blender for 10 minutes in the environment of 10 DEG C, and the inorganic salt antifreeze powder is prepared.

[0038] The nanometer air entraining agent is prepared by the following method: S1, a mixed solution of 5wt% propionic acid and 2wt% sodium dodecyl benzene sulfonate is prepared with water as solvent, 10 L; S2, 1 kg of silica fume with particle size of 5~10 μm is added into the mixed solution of step S1, and 1% concentrated sulfuric acid with total mass of the mixed solution is added at 110 DEG C, and the reaction is stirred at a speed of 100~120 r / min for 1 h; S3, the reaction product in step S2 is washed and filtered, and is placed in an oven at 130 DEG C for drying for 15 h. 50

[0039] The foam stabilizer is prepared by the following method: polyacrylamide, sodium carboxymethyl cellulose and macromolecular fatty alcohol polyoxyethylene ether are mixed according to the mass ratio of 4:4:2 to prepare.

[0040] Example 1 ​An antifreeze agent for concrete under super-low temperature and high altitude environment, comprising a first component and a second component, wherein the first component comprises nano calcium silicate crystal core powder 7.6 parts and inorganic salt antifreeze powder 3.8 parts by mass fraction, and the second component comprises nano air entraining agent 3.8 parts and foam stabilizer 0.38 parts.

[0041] An antifreeze concrete under super-low temperature and high altitude environment, comprising cement 300 parts, fly ash 80 parts, sand 760 parts, stone 1070 parts, the antifreeze agent for concrete under super-low temperature and high altitude environment 15.58 parts, water reducing agent 5.5 parts and water 190 parts by mass fraction.

[0042] The preparation method of the antifreeze concrete under super-low temperature and high altitude environment, comprising the following steps: The cement, fly ash, silica ash, sand, stone and the first component of the antifreeze agent for concrete under super-low temperature and high altitude environment are put into a mixer, and after dry mixing, the second component of the antifreeze agent for concrete under super-low temperature and high altitude environment, water and water reducing agent are added, and the mixture is continuously stirred to obtain the antifreeze concrete under super-low temperature and high altitude environment.

[0043] Example 2 An antifreeze agent for concrete under super-low temperature and high altitude environment, comprising a first component and a second component, wherein the first component comprises nano calcium silicate crystal core powder 3.8 parts and inorganic salt antifreeze powder 7.6 parts by mass fraction, and the second component comprises nano air entraining agent 3.8 parts and foam stabilizer 0.38 parts.

[0044] An antifreeze concrete under super-low temperature and high altitude environment, comprising cement 300 parts, fly ash 80 parts, sand 760 parts, stone 1070 parts, the antifreeze agent for concrete under super-low temperature and high altitude environment 15.58 parts, water reducing agent 5.5 parts and water 190 parts by mass fraction.

[0045] The preparation method of the antifreeze concrete under super-low temperature and high altitude environment, comprising the following steps: The cement, fly ash, silica ash, sand, stone and the first component of the antifreeze agent for concrete under super-low temperature and high altitude environment are put into a mixer, and after dry mixing, the second component of the antifreeze agent for concrete under super-low temperature and high altitude environment, water and water reducing agent are added, and the mixture is continuously stirred to obtain the antifreeze concrete under super-low temperature and high altitude environment.

[0046] Example 3 An antifreeze agent for concrete under super-low temperature and high altitude environment, comprising a first component and a second component, wherein the first component comprises nano calcium silicate crystal core powder 7.6 parts and inorganic salt antifreeze powder 7.6 parts by mass fraction, and the second component comprises nano air entraining agent 3.8 parts and foam stabilizer 0.38 parts.

[0047] An antifreeze concrete under super low temperature and high altitude environment, comprising, by mass fraction, cement 300 parts, fly ash 80 parts, sand 760 parts, stone 1070 parts, the antifreeze agent for concrete under super low temperature and high altitude environment 19.38 parts, water reducing agent 5.5 parts and water 190 parts.

[0048] The preparation method of the antifreeze concrete under super low temperature and high altitude environment, comprising the following steps: The first component of the antifreeze agent for concrete under super low temperature and high altitude environment, the second component of the antifreeze agent for concrete under super low temperature and high altitude environment, water and water reducing agent are added into the mixer after dry mixing, and the antifreeze concrete under super low temperature and high altitude environment is prepared by continuing to mix uniformly.

[0049] Example 4 An antifreeze agent for concrete under super low temperature and high altitude environment, comprising a first component and a second component, wherein the first component comprises nano calcium silicate crystal nucleus powder 3.8 parts and inorganic salt antifreeze powder 3.8 parts, and the second component comprises nano air entraining agent 3.8 parts and foam stabilizer 0.38 parts.

[0050] An antifreeze concrete under super low temperature and high altitude environment, comprising, by mass fraction, cement 300 parts, fly ash 80 parts, sand 760 parts, stone 1070 parts, the antifreeze agent for concrete under super low temperature and high altitude environment 11.78 parts, water reducing agent 5.5 parts and water 190 parts.

[0051] The preparation method of the antifreeze concrete under super low temperature and high altitude environment, comprising the following steps: The first component of the antifreeze agent for concrete under super low temperature and high altitude environment, the second component of the antifreeze agent for concrete under super low temperature and high altitude environment, water and water reducing agent are added into the mixer after dry mixing, and the antifreeze concrete under super low temperature and high altitude environment is prepared by continuing to mix uniformly.

[0052] Comparative Example 1 An antifreeze agent, which is basically consistent with Example 4, and the only difference is that only inorganic salt antifreeze powder is contained.

[0053] An antifreeze concrete, which is basically consistent with Example 4, and the only difference is that the amount of the antifreeze agent is 3.8 parts and the amount of water reducing agent is 6.5 parts.

[0054] Comparative Example 2 An antifreeze agent, which is basically consistent with Example 4, and the only difference is that only nano calcium silicate crystal nucleus powder is contained.

[0055] A kind of antifreeze concrete, it is basically consistent with example 4, the only difference is that the antifreeze agent is 3.8 parts, the water reducing agent is 6.5 parts.

[0056] Comparative example 3 An antifreeze agent, it is basically consistent with example 4, the only difference is that only contains nano calcium silicate crystal nucleus powder and inorganic salt antifreeze powder, and the mass ratio of the two is 1:1.

[0057] A kind of antifreeze concrete, it is basically consistent with example 4, the only difference is that the antifreeze agent is 7.6 parts, the water reducing agent is 6.5 parts.

[0058] Comparative example 4 An antifreeze agent, it is basically consistent with example 4, the only difference is that contains nano calcium silicate crystal nucleus powder, inorganic salt antifreeze powder and nano air entraining agent, and the mass ratio of the three is 1:1:1.

[0059] A kind of antifreeze concrete, it is basically consistent with example 4, the only difference is that the antifreeze agent is 11.4 parts.

[0060] Detection and analysis The components of examples 1-4 and comparative examples 1-4 are shown in Table 1.

[0061] Table 1 Components of examples 1-4 and comparative examples 1-4

[0062] The antifreeze and crack resistant concrete prepared by the above method is demolded after pre-curing at 20±3 ℃ for 4 h, and then negative temperature curing at different negative temperature for 7 d (from the time of adding water to molding), and then placed in an environment at 20±3 ℃ for thawing. After thawing, the compressive strength test, crack observation or standard curing are carried out. At the same time, the same control group concrete is demolded after curing at 20±3 ℃ for 1 d and then transferred to standard curing, and the compressive strength is tested after the specified age, and the slump and air content of each sample are tested. The performance of the concrete is shown in Table 2. In the table, R -7d is the ratio of the compressive strength of the negative temperature curing concrete for 7 d to the compressive strength of the reference concrete cured for 28 d, and the unit is percentage (%); R -7d+28d is the ratio of the compressive strength of the negative temperature curing concrete for 7 d and then standard curing for 28 d to the compressive strength of the reference concrete cured for 28 d, and the unit is percentage (%); R 28d is the ratio of the compressive strength of the reference concrete cured for 28 d to the compressive strength of the reference concrete cured for 28 d. The reference concrete is the concrete without antifreeze and crack resistant agent.

[0063] The compressive strength was tested according to the Standard Test Methods for Mechanical Properties of Concrete GB / T 50081-2019, the slump test method was tested according to the Standard for Quality Control of Concrete (GB50164-2011), the air content test method was tested according to the Standard Test Methods for Properties of Fresh Ordinary Concrete GB / T 50080-2016, and the test was carried out in a low-temperature and low-pressure test box. The results are shown in Table 2.

[0064] Table 2 Performance table of examples 1-4 and comparative examples 1-4

[0065] As can be seen from comparative examples 1-4, under the environment of-30 ℃, the comparative examples 1-4 cannot meet the requirements of slump, air content and strength.

[0066] The 1 h slump of comparative example 1, comparative example 2 and comparative example 3 is only 100 mm, 95 mm and 120 mm respectively, and the air content after 1 h is only 1.3%, 1.2% and 2.2% respectively, which cannot meet the construction performance and strength performance requirements of concrete under the condition of-30 ℃ low temperature in high altitude areas.

[0067] The antifreeze agent in comparative example 4 contains nano calcium silicate crystal nucleus powder, inorganic salt antifreeze powder and nano air entraining agent components, the 1 h slump is 175 mm, and the air content after 1 h is 3.9%, which is improved compared with comparative examples 1, 2 and 3, but it cannot meet the construction performance and strength performance requirements of concrete under the condition of-30 ℃ low temperature in high altitude areas.

[0068] Example 4 adds nano crystal nucleus, inorganic antifreeze salt, nano air entraining agent and foam stabilizer components, the 1 h slump is 220 mm, and the air content after 1 h is 5.8%, which is improved compared with comparative example 4, and the working performance and strength performance meet the construction performance and strength performance requirements of concrete under the condition of-30 ℃ low temperature in high altitude areas.

[0069] Through the performance comparison test of comparative examples 1, 2, 3 and 4, it can be concluded that the composition of the present application is reasonable, and the lack of one of them will adversely affect the performance of the concrete.

[0070] It should be understood that the above examples are only used to illustrate the content of the present application and are not used to limit the protection scope of the present application. In addition, it should be understood that after reading the content taught by the present application, those skilled in the art can make various modifications or modifications to the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application.

Claims

1. An antifreeze agent for concrete used in ultra-low temperature and high-altitude environments, characterized in that, It comprises a first component and a second component. The first component comprises nanocrystalline nucleus powder and inorganic salt antifreeze powder, and the second component comprises nanocomposite air-entraining agent and foam stabilizer. The mass ratio of the nanocrystalline nucleus powder, inorganic salt antifreeze powder, nanocomposite air-entraining agent and foam stabilizer is 20~60:20~60:20~60:0.1~10.

2. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 1, characterized in that, The nanocrystalline nucleus powder in the first component is prepared by ultrasonic spray drying of nano-calcium silicate aqueous solution.

3. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 2, characterized in that, The preparation method of the nanocrystalline nucleus powder in the first component specifically includes the following steps: water glass and calcium nitrate undergo a nucleation reaction in an aqueous solution with a pH of 10-14, and a polycarboxylate superplasticizer is added during the reaction to homogenize and disperse the powder. After cooling, the powder is ultrasonically spray-dried to obtain the final product.

4. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 3, characterized in that, The molar ratio of silicate to calcium nitrate in the water glass is 0.5~1:1; the amount of polycarboxylate superplasticizer added is 5%~15% of the total solution mass; and the ultrasonic frequency of the ultrasonic spray drying is 80~100 kHz.

5. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 1, characterized in that, The inorganic salt antifreeze powder in the first component is obtained by mixing sodium sulfate, sodium nitrate and sodium aluminate in a mass ratio of 5~30:5~30:5~20.

6. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 1, characterized in that, The second component, the nanocomposite air-entraining agent, is prepared by modifying silica fume with a mixed solution of acrylic acid and the air-entraining agent.

7. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 6, characterized in that, The preparation method of the nanocomposite air-entraining agent in the second component specifically includes the following steps: S1. Prepare 10-15 L of a mixed solution of propionic acid and air-entraining agent with a concentration of 5 wt% and 2 wt%; S2. Add 1 kg of silica fume to the mixed solution described in step S1, and add concentrated sulfuric acid at 90~110 °C, which is 1% of the total mass of the mixed solution, and stir the reaction for 1 h. S3. Wash and filter the reaction product from step S2, and then dry it to obtain the final product.

8. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 6, characterized in that, The air-entraining agent includes anionic or cationic air-entraining agents.

9. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 1, characterized in that, The anionic air-entraining agent is selected from alkylbenzene sulfonic acid, alkyl sulfonate, rosin soap or sodium laurylate; the cationic air-entraining agent is selected from hexadecyltrimethylammonium bromide.

10. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 1, characterized in that, The D of the silica fume 50 =5~10 μm.

11. The antifreeze agent for concrete in ultra-low temperature and high altitude environments according to claim 1, characterized in that, The foam stabilizer in the second component is obtained by mixing polyacrylamide, sodium carboxymethyl cellulose and macromolecular fatty alcohol polyoxyethylene ether in a mass ratio of 1~4:1~4:1~2.

12. A type of antifreeze concrete for ultra-low temperature and high altitude environments, characterized in that, The composition, by weight, includes 260-400 parts cement, 50-150 parts fly ash, 0-50 parts silica fume, 500-800 parts sand, 800-1200 parts stone, 1-20 parts antifreeze agent for concrete in ultra-low temperature and high altitude environments as described in any one of claims 1-11, 5-10 parts water-reducing agent, and 150-200 parts water.

13. A method for preparing antifreeze concrete for ultra-low temperature and high altitude environments as described in claim 12, characterized in that, The process includes the following steps: cement, fly ash, silica fume, sand, stone, the first component of the antifreeze agent for concrete used in ultra-low temperature and high altitude environments are added to a mixer and dry-mixed evenly. Then, the second component of the antifreeze agent for concrete used in ultra-low temperature and high altitude environments, water, and water-reducing agent are added, and the mixture is stirred evenly to prepare the antifreeze concrete for ultra-low temperature and high altitude environments.

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