CN115417631A - Low-shrinkage low-creep concrete serving in plateau complex environment and preparation method thereof - Google Patents

Abstract

The invention discloses a low-shrinkage and low-creep concrete serving in the plateau complex environment and a preparation method thereof, which comprises 300-400kg/ ^m3 of cement, 150-200kg/ ^m3 of mineral admixtures, 10-20kg/m3 of ^m3 dense modified material, 600-700kg/ ^m3 fine aggregate, 1000-1200kg/ ^m3 coarse aggregate, 0.5-5wt% admixture and water accounting for the total amount of cement and mineral admixture; The dense modified material includes CaSO ₄ whiskers and nano-SiO ₂ , wherein the mass ratio of CaSO ₄ whiskers to nano-SiO ₂ is 1.5-2.5:1. The low-shrinkage and low-creep concrete of the present invention not only ensures good volume stability, but also has good mechanical properties and durability, meets the shrinkage and creep requirements of concrete in the complex environment of the plateau, and can be used for long-term service in the complex environment of the plateau. In life engineering.

Description

A low-shrinkage and low-creep concrete serving in the plateau complex environment and its preparation method

technical field

The invention belongs to the technical field of building materials, and in particular relates to a low-shrinkage and low-creep concrete serving in a plateau complex environment and a preparation method thereof.

Background technique

The Sichuan-Tibet Railway starts from Chengdu in the east and ends in Lhasa in the west. It has a total length of 1,838 kilometers and passes through 7 rivers and 8 snow-capped mountains along the way. There are many super-long-span bridges. The on-site environment is harsh, the temperature difference between day and night exceeds 10°C, the total annual solar radiation is 5000-8000MJ/m ² , and the number of days in most areas is as high as 150 days with eight-level strong winds (above 17m/s), with large temperature differences, strong radiation, and strong winds. environmental characteristics. Harsh natural conditions can easily lead to problems such as shrinkage and creep of beam concrete, which will reduce the quality of concrete, reduce the service life of bridge concrete, and increase the risk of running trains.

The shrinkage and creep requirements of high-performance concrete for bridge ^girders under the complex environment of Sichuan-Tibet Railway are relatively high. The cementitious materials of traditional low-shrinkage and low-creep concrete include coarse-grained cement, fly ash, and mineral powder, which are suitable for general environmental conditions, but the temperature effect increases in the harsh environmental conditions of large temperature differences and extreme dryness on the plateau , the water loss is accelerated, and the traditional low shrinkage and low creep concrete cannot effectively improve the different pore structures in the concrete system, and cannot meet the requirements of engineering construction. Patent No. 201811323941.3 discloses a low-shrinkage, low-creep, crack-resistant, high-performance mass concrete, which is prepared with cement and fly ash as cementitious materials, but has high requirements on the mineral composition of cement, and is only suitable for reactor buildings and raft foundations Simple construction of concrete. Patent No. 202210370864.7 discloses a low-shrinkage high-strength concrete and its preparation method, but the large-scale application of vacuum nitriding and microwave radiation treatment processes in plateau environments is difficult, and the transportation of nitrogen increases the cost of concrete preparation. Therefore, it is urgent to develop low-shrinkage and low-creep concrete materials that can serve in the plateau complex environment for a long time.

Contents of the invention

In view of this, the present invention discloses a low-shrinkage and low-creep concrete serving in a plateau complex environment and a preparation method thereof. The low-shrinkage and low-creep concrete not only ensures good volume stability, but also has good mechanical properties and Durability, meeting the shrinkage and creep requirements of concrete in the complex environment of the plateau, and can be used in long-life projects in the complex environment of the plateau.

In order to realize above-mentioned technical purpose, the present invention adopts following technical scheme:

A low-shrinkage and low-creep concrete serving in the complex environment of the plateau, including the following components:

The dense modified material includes CaSO ₄ whiskers and nano-SiO ₂ , wherein the mass ratio of CaSO ₄ whiskers to nano-SiO ₂ is 1.5-2.5:1.

Preferably, the mineral admixture consists of a coarse-scale mineral admixture, a meso-scale mineral admixture and a fine-scale mineral admixture;

The coarse-scale mineral admixture is at least one of fly ash and mineral powder, and the dosage is 50-70wt% of the total amount of the mineral admixture;

The mesoscale mineral admixture is at least one of metakaolin, ground zeolite powder and highland barley straw ash, and the dosage is 20-40wt% of the total amount of the mineral admixture;

The fine-scale mineral admixture is silica fume, and the dosage is 5-15wt% of the total amount of the mineral admixture.

Further preferably, in the coarse-scale mineral admixture, the fly ash is the fly ash obtained from coal-fired cooling in a thermal power plant, with a sphericity ≥ 80%, an average particle size of 17 μm, and a specific surface area of 1.1-1.2 m ² /g; ore powder is obtained by dry grinding of blast furnace slag, with an average particle size of 15μm and a specific surface area of 1.7-2.0m ² /g;

Among the mesoscale mineral admixtures, metakaolin is obtained by thermal dehydration of kaolin, with an average particle size of 5 μm and a specific surface area of 14-20 m ² /g; finely ground zeolite powder is made from natural zeolite rocks, with an average particle size of The particle size is 9μm, and the specific surface area is 500-1100m ² /g; the highland barley stalk ash is obtained from the highland barley straw through incineration, impurity removal and grinding, with an average particle size of 10μm and a specific surface area of 15-20m ² /g;

In the fine-scale mineral admixture, silica fume is ferroalloy. When ferrosilicon or industrial silicon (metal silicon) is smelted, SiO ₂ and Si gas volatilized by submerged electric furnace are rapidly oxidized and condensed and precipitated in the air, and its sphericity is ≥ 90%, the particle size is 0.5-1 μm, and the specific surface area is 22-30 m ² /g.

Preferably, the dense modified material also includes graphene oxide, and its addition amount is 0.5-0.8wt% of the total amount of CaSO ₄ whiskers and nano-SiO ₂ , and accounts for 0.01-0.03% of the total amount of cement and mineral admixtures. wt%.

Preferably, the microscopic morphology of CaSO ₄ whiskers is columnar fibers with a length of 10-100 μm, a diameter of 1-10 μm, and an aspect ratio of 5-40. CaSO ₄ whiskers have high strength, high modulus, and high toughness. Features: It can reduce the stress concentration phenomenon at the tip of the crack of the cement test block, improve the elastic modulus of the CSH gel, and consume energy through bridging, deflection, and pulling out to reduce deformation. At the same time, the wetting effect of the whiskers can absorb part of the water, reduce the bleeding pores, and hinder the migration of internal water, thereby reducing the drying shrinkage of the concrete system.

The microscopic morphology of graphene oxide is lamellar, the diameter of the sheet is 300-500nm, the thickness is 0.3-1nm, and the specific surface area is 2600m ² /g. Graphene oxide has the characteristics of high activity and excellent mechanical properties. It can be combined with CSH The gel forms hydrogen bonds, enhances the cohesive force, and promotes the orderly growth of CSH gels.

The microscopic morphology of nano-SiO ₂ is spherical particles, the average particle size is 40nm, and the specific surface area is 150m ² /g. Nano-SiO ₂ has the characteristics of high strength, high toughness, high surface energy and strong stability. It can be combined with Ca(OH) ₂ The secondary hydration reaction occurs to generate more high-density CSH gels, and at the same time exerts the micro-aggregate filling effect and reduces the porosity.

In the present invention, CaSO ₄ whiskers and nano-SiO ₂ with a certain proportion are added to the concrete as dense modified materials. First, nano-SiO ₂ is a nano-scale granular zero-dimensional material, and CaSO ₄ whiskers are micron-scale columnar ones. Dimensional materials, the synergy of the two can fill the pores of different sizes and shapes in the cement system, greatly reduce the number of gel pores and capillary pores, and hinder the shrinkage and creep caused by the evaporation of water inside the concrete caused by the extreme dry environment on the plateau; secondly , the addition of CaSO ₄ whiskers provides more nucleation sites for the CSH gel generated by the hydration reaction of nano-SiO ₂ , promotes the aggregation of CSH gel along the whiskers instead of dispersion, and forms columnar hydration groups. The degree of hydration and the increase of hydration products will make the concrete system denser. At the same time, the hydration reaction of CaSO ₄ whiskers produces ettringite, which can crystallize rapidly, has expansibility, increases the solid phase volume, and forms a hard skeleton structure, which can inhibit the deformation of concrete under shrinkage and creep; again, the invention People found that when the amount of nano-SiO ₂ is too much, agglomeration will occur and affect its effect, and when the amount of CaSO ₄ whiskers is too much, it will cause excessive volume expansion and surface cracking. Therefore, it is necessary to strictly control the mixing of the two materials. amount, in order to achieve the synergistic effect of reducing shrinkage creep.

The inventors also found that on the basis of CaSO ₄ whiskers and nano-SiO ₂ at a ratio of 1.5-2.5:1, further adding graphene oxide to the compact modified material can further reduce the shrinkage and creep of concrete. First of all, graphene oxide is a two-dimensional nano-scale sheet honeycomb material. Graphene oxide with high surface energy can form a good covalent connection with nano-SiO ₂ , and effectively inhibit the interaction between nano-SiO ₂ particles and graphene oxide through electrostatic repulsion. Agglomeration phenomenon, and provide nucleation sites for the pozzolanic reaction of nano-SiO ₂ , as the pozzolanic reaction of nano-SiO ₂ proceeds on the graphene oxide sheet, a denser graphene oxide nanosheet network structure will be formed, Forming columnar or flower-like hydration groups, the synergistic effect of nano-SiO ₂ -CaSO ₄ whisker columnar hydration groups and nano-SiO ₂ -graphene oxide columnar hydration groups forms multi-scale reinforcement for filling pores, bridging cracks, and inhibiting deformation Effect. Secondly, the active functional groups on the surface of graphene oxide combine with CaSO ₄ whiskers to form negative charges, which can improve the compatibility and interfacial adhesion between CaSO ₄ whiskers and cement matrix _. Aspect ratio, reduce the diameter of CaSO ₄ whiskers, enhance the role of CaSO ₄ whiskers in strengthening and toughening, absorbing and dissipating energy in the deformation process; again, graphene oxide is expensive and prone to agglomeration at high dosages, so this paper The main part of the invented dense modified material is nano-SiO ₂ and CaSO ₄ whiskers, and graphene oxide can be used as an auxiliary material to further improve the performance of concrete.

Preferably, the fine aggregate is river sand or machine-made sand, and the fineness modulus is 2.8-4.0.

Preferably, the coarse aggregate is limestone or basalt crushed stone with a particle size of ≤15mm, wherein the part with a particle size of 10-15mm is not less than 20%.

Preferably, the additive is at least one of water reducer, defoamer and shrinkage reducer;

The superplasticizer is at least one of polycarboxylate superplasticizers, naphthalene superplasticizers, melamine superplasticizers, and amino acid salt superplasticizers. By adsorbing on the surface of cement particles, the unit water consumption can be reduced , disperse cement particles, improve the fluidity of concrete mixture;

The defoamer is at least one of silicone defoamers, polyether defoamers, polyether modified silicon defoamers, high carbon alcohol defoamers, silicon-free defoamers and mineral oil defoamers One, by reducing the surface tension of the bubbles, destroying the elastic membrane of the bubbles, inhibiting the generation and development of the bubbles, and reducing the porosity;

The shrinkage reducer is polyhydroxy compound NA-SP series concrete shrinkage reducer, alkyl polyoxyethylene ether JM-SRA series concrete shrinkage reducer, polyether and aliphatic organic compound JSJ type shrinkage reducer, methyl ether-based polymer and ethylene glycol series At least one of the polymer ZZD-A concrete shrinkage reducers can reduce shrinkage by reducing the surface tension of the liquid phase in the concrete capillary.

In the present invention, additives such as water reducer, defoamer, and shrinkage reducer are used to reduce particle agglomeration through electrostatic repulsion, ensuring uniform dispersion of particles in the concrete system, effective discharge of air bubbles, and reduction of capillary pressure. Auxiliary mineral admixtures and dense modified materials further increase the homogeneity and compactness of the concrete system and maintain the volume stability of the system.

The present invention also provides a method for preparing the above-mentioned low-shrinkage and low-creep concrete serving in the plateau complex environment, comprising the following steps:

Step 1: Mix the dense modified material, admixture and water, stir magnetically at a speed of 500-1500r/min for 5-20 minutes, and then place it in an ultrasonic cell breaker, keep the power at 60-70%, and alarm at 80°C. Ultrasonic dispersion for 10-15 minutes to obtain a dense modified dispersion;

Step 2: After mixing the cement and the mineral admixture, place it in a mixer, and fully mix the ingredients to obtain a dry powder mixture;

Step 3: Pour the dry powder mixture, coarse aggregate, and fine aggregate into the concrete mixer in sequence, mix well, then add the compact modifier dispersion, stir for 2 to 5 minutes, and then maintain the model after pouring.

In the present invention, in combination with on-site construction conditions, standard curing or steam curing can be selected. When carrying out standard curing, it is necessary to place the formed test piece in an environment with a temperature of 20±2°C and a relative humidity above 95% for maintenance until the specified age; when performing steam curing, first place the formed test piece at 20±2°C Stop statically for 1-3 hours in the environment, control the steam curing box to reach the peak temperature of 60-80 °C after a period of time at a heating rate of 20 °C/h, maintain the peak temperature for 8 hours, and then cool down naturally, transfer to a temperature of 20±2 °C, relative humidity 60% of the standard drying shrinkage environment continues to maintain to the specified age.

Based on the closest packing theory, the present invention adds mineral admixtures with different microscopic shapes to carry out reasonable particle gradation design, realizes all-round filling from coarse scale to fine scale, and promotes the separation of Ca(OH) ₂ and mineral admixtures Effective secondary hydration reaction, through the particle gradation of coarse and fine aggregates, the aggregate particles and cementitious materials can cooperate to achieve the maximum dense accumulation and improve the volume stability of concrete. In high-performance concrete with low water-to-binder ratio, the role of mineral admixtures is that, on the one hand, there are a large number of unhydrated mineral admixtures in the system, which help to increase the macroscopic elastic modulus of concrete and reduce the creep value , to speed up the completion of concrete creep. On the other hand, secondary hydration reaction occurs between mineral admixtures and Ca(OH) ₂ crystals. In the early stage, the secondary hydration reaction of medium and fine-scale mineral admixtures such as silica fume and metakaolin is the main one. The secondary hydration of mineral powder and/or fly ash coarse-scale mineral admixture is mainly used, and the combination of front and rear can make the hydration reaction more thorough, the structure compactness is better, and at the same time avoid the orientation of a large number of Ca(OH) ₂ crystal formation Arrangement optimizes the interface structure of cement stone, reduces porosity, fills large pores in concrete (Jawed classification method), increases capillary channel resistance, reduces water evaporation, and inhibits drying shrinkage and creep of concrete. More importantly, through the addition of dense modified materials in the present invention, on the one hand, the dense modified materials have a huge specific surface area, which provides more nucleation sites for CSH gels, nano-SiO ₂ , CaSO ₄ whiskers, oxidation Graphene provides zero-dimensional, one-dimensional, and two-dimensional nucleation sites for the growth of CSH gels, and the random distribution of point-line two-level or point-line-plane three-level structure builds a stronger CSH gel. Glue skeleton, so as to effectively reduce the viscous flow under external disturbance. On the other hand, the particle size of the dense modified material is below 10 μm or even reaches the nanoscale, which can block the pore channels of cement stone, increase the compactness of the concrete system, optimize the interface transition zone, and thus restrict the migration of internal moisture.

On the whole, in terms of physical filling, the present invention rationally arranges particle gradation based on the closest packing theory, reduces the number of pores in the system, and improves the transition zone of the concrete interface; in terms of chemical modification, it designs an The dense modified material with high modulus can improve the elastic modulus and compactness of C-S-H gel, and strengthen the water bondage between layers, so as to achieve the effect of comprehensively reducing concrete shrinkage and creep while improving strength. At the same time, the preparation method of the present invention There are no complicated things, and it can be applied to production in the plateau environment. This is of great significance for improving the service ability of concrete in the complex environment of the plateau, improving the dimensional stability and durability of concrete, and accelerating the transportation construction and economic development of the western region.

Description of drawings

Fig. 1 is the prismatic concrete specimen and the physical picture of the performance test that the embodiment 1 of the present invention makes.

detailed description

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with examples, but the implementation of the present invention is not limited thereto.

In the present invention, the average particle size of the cement is 20 μm, and the specific surface area is 1.6-1.8 m ² /g;

Fly ash is the fly ash obtained from coal-fired cooling in thermal power plants, with a sphericity ≥ 80%, an average particle size of 17μm, and a specific surface area of 1.1-1.2m ² /g; ore powder is obtained by dry grinding of blast furnace slag. The average particle size is 15μm, and the specific surface area is 1.7-2.0m ² /g;

Metakaolin is processed by heat dehydration of kaolin, with an average particle size of 5μm and a specific surface area of 14-20m ² /g; ground zeolite powder is made from natural zeolite rock, with an average particle size of 9μm and a specific surface area of 500-200m2/g. 1100m ² /g; highland barley stalk ash is obtained from highland barley stalks through incineration, impurity removal and grinding, with an average particle size of 10μm and a specific surface area of 15-20m ² /g;

Silica fume is ferroalloy when smelting ferrosilicon or industrial silicon (metal silicon), SiO ₂ and Si gas volatilized by submerged electric furnace are rapidly oxidized and condensed and precipitated in the air. Its sphericity is ≥90%, and the particle size is 0.5～ 1μm, the specific surface area is 22-30m ² /g.

The microscopic morphology of CaSO ₄ whiskers is columnar fibers with a length of 10-100 μm, a diameter of 1-10 μm, and an aspect ratio of 5-40.

The microscopic morphology of graphene oxide is sheet-like, with a sheet diameter of 300-500 nm, a thickness of 0.3-1 nm, and a specific surface area of 2600 m ² /g.

The microscopic appearance of nano-SiO ₂ is spherical particles, the average particle diameter is 40nm, and the specific surface area is 150m ² /g.

The fine aggregate is river sand or machine-made sand, and the fineness modulus is 2.8-4.0.

Coarse aggregate is limestone or basalt gravel, particle size ≤ 15mm, of which the particle size is not less than 20% in the range of 10-15mm.

In the present invention, kg/ ^m3 represents the mass of materials added per cubic meter of concrete.

Example 1

A method for preparing low-shrinkage and low-creep concrete serving in a plateau complex environment, comprising the following steps:

Step 1: Prepare dense modified material dispersion

Step 1.1, weighing. The dosage of CaSO ₄ whiskers is 9.6kg/m ³ , the dosage of nano-SiO ₂ is 4.8kg/m ³ , the dosage of polycarboxylate superplasticizer is 8.2kg/m ³ , and the dosage of alkyl polyoxyethylene ether JM-SRA series concrete shrinkage reducer 4kg/m ³ , the amount of polyether modified silicon defoamer is 0.5kg/m ³ , and the amount of water is 126kg/m ³ .

Step 1.2, magnetic stirring. The materials described in step 1.1 were mixed, placed in a magnetic stirrer, and stirred magnetically for 5 min at a rotational speed of 1000 r/min.

In step 1.3, place the solution prepared in step 1.2 in an ultrasonic cell disruptor, and ultrasonically disperse for 10 min under the conditions of 65% power and an alarm temperature of 80° C. to obtain a dense modified material dispersion.

Step 2: Mix dry powder

According to the amount of cement 320.4kg/m ³ , the amount of fly ash 90kg/m ³ , the amount of metakaolin 45kg/m ³ , and the amount of silica fume 15kg/m ³ were mixed, placed in a mixer and mixed for 8 hours to obtain a dry powder mixture.

Step Three: Forming the Concrete

Pour the dry powder mixture in step 2, river sand 675kg/m ³ , and limestone crushed stone 1113kg/m ³ into the concrete mixer in sequence, dry mix for 2 minutes, and evenly add the compact modifier dispersion prepared in step 1. state, control the stirring time for 4 minutes, and carry out model pouring.

Step Four: Curing the Concrete

After pouring and molding, the mold is cured for 1 day, and after the mold is removed, it is cured in a standard environment with a temperature of 20±2°C and a relative humidity of 95% or more. 5) The shrinkage test is performed in a constant temperature and humidity environment of %, and the creep test piece is moved into the same constant temperature and humidity environment after 14 days of curing for creep testing.

For the test methods of drying shrinkage and creep, refer to "Standards for Test Methods of Long-term Performance and Durability of Ordinary Concrete" GB/T 50082-2009 and combine with relevant engineering requirements. Among them, the drying shrinkage rate adopts the contact method, and a vertical concrete shrinkage meter and a dial gauge with an accuracy of ±0.001mm are used for detection. The size of the prismatic concrete specimen is 100mm×100mm×400mm, and 3 specimens are set for the same ratio. The creep degree adopts the pressure creep test method, and the spring-type compression creep meter and dial gauge are used for detection. The size of the prismatic concrete specimen is 100mm×100mm×400mm, and three specimens are set in the same ratio.

After testing, in this embodiment, the drying shrinkage rate of the concrete at 28 days is 0.035%, the drying shrinkage rate at 56 days is 0.04%, and the creep degree at 90 days is 12.84×10 ^-6 /MPa.

Example 2

A method for preparing low-shrinkage and low-creep concrete serving in a plateau complex environment, characterized in that it comprises the following steps:

Step 1: Prepare dense modified material dispersion

Step 1.1, weighing. The dosage of CaSO ₄ whiskers is 9.6kg/m ³ , the dosage of nano-SiO ₂ is 4.8kg/m ³ , the dosage of graphene oxide is 0.1kg/m ³ , the dosage of polycarboxylate superplasticizer is 8.2kg/m ³ , and the dosage of alkyl polyoxygen The dosage of vinyl ether JM-SRA series concrete shrinkage reducer is 4kg/m ³ , the dosage of polyether modified silicon defoamer is 0.5kg/m ³ , and the dosage of water is 126kg/m ³ .

Step 1.2, magnetic stirring. The materials described in step 1.1 were mixed, placed in a magnetic stirrer, and stirred magnetically for 5 min at a rotational speed of 1500 r/min.

In step 1.3, place the solution prepared in step 1.2 in an ultrasonic cell disruptor, and ultrasonically disperse for 15 minutes under the conditions of 65% power and an alarm temperature of 80° C. to obtain a dense modified material dispersion.

Step 2: Mix dry powder

According to the amount of cement 320.4kg/m ³ , the amount of mineral powder 90kg/m ³ , the amount of highland barley straw ash 45kg/m ³ , and the amount of silica fume 15kg/m ³ were mixed, placed in a mixer and mixed for 8 hours to obtain a dry powder mixture.

Step Three: Forming the Concrete

Pour the dry powder mixture in step 2, machine-made sand 675kg/m ³ , and limestone crushed stone 1113kg/m ³ into the concrete mixer in sequence, dry-stir for 2 minutes, and evenly add the compact modifier dispersion prepared in step 1, according to the state of the slurry , control the stirring time for 4 minutes, and carry out model pouring.

Step Four: Curing the Concrete

After pouring the concrete, stop at 20°C for 3 hours, heat up to 60°C at a rate of 20°C/h over 2 hours, maintain 60°C for 8 hours, and then cool down naturally for steam curing. Remove the mold after steam curing, and put it in a standard environment with a temperature of 20±2°C and a relative humidity of 95% or more for curing. The shrinkage test was carried out in a constant temperature and humidity environment, and the creep test piece was moved into the same constant temperature and humidity environment after 14 days of curing for creep testing.

After testing, in this embodiment, the drying shrinkage rate of the concrete at 28 days is 0.025%, the drying shrinkage rate at 56 days is 0.03%, and the creep degree at 90 days is 11.56×10 ^-6 /MPa.

Comparative example 1

Same as Example 1, the only difference is that no compact modifying material is added (that is, no CaSO ₄ whiskers and nano-SiO ₂ are added).

After testing, in this comparative example, the drying shrinkage rate of concrete at 28 days is 0.06%, the drying shrinkage rate at 56 days is 0.068%, and the creep degree at 90 days is 16.35×10 ^-6 /MPa.

Comparative example 2

Same as Example 1, the only difference is that only 14.4kg/m ³ of nano-SiO ₂ is added.

After testing, in this comparative example, the drying shrinkage rate of the concrete at 28 days is 0.052%, the drying shrinkage rate at 56 days is 0.057%, and the creep degree at 90 days is 15.98×10 ^-6 /MPa.

Comparative example 3

With embodiment 1, difference is only to add _{14.4kg/m CaSO 4} ^whiskers .

After testing, in this comparative example, the drying shrinkage rate of the concrete at 28 days is 0.045%, the drying shrinkage rate at 56 days is 0.05%, and the creep degree at 90 days is 14.76×10 ^-6 /MPa.

Comparative example 4

Same as Example 1, the only difference lies in the addition of 4.8kg/m ³ of CaSO ₄ whiskers and 9.6kg/m ³ of nano-SiO ₂ .

After testing, in this comparative example, the drying shrinkage rate of the concrete at 28 days is 0.038%, the drying shrinkage rate at 56 days is 0.043%, and the creep degree at 90 days is 13.23×10 ^-6 /MPa.

Claims (10)

1. The low-shrinkage low-creep concrete serving in the complex environment of the plateau is characterized by comprising the following components:

the dense modified material comprises CaSO ₄ Whisker and nano SiO ₂ In which CaSO ₄ Whisker and nano SiO ₂ The mass ratio of (A) to (B) is 1.5-2.5: 1.

2. the low-shrinkage low-creep concrete serving in a complex environment at plateau as claimed in claim 1, wherein the mineral admixture is composed of a coarse-scale mineral admixture, a medium-scale mineral admixture and a fine-scale mineral admixture;

the coarse mineral admixture is at least one of fly ash and mineral powder, and the using amount of the coarse mineral admixture is 50-70 wt% of the total amount of the mineral admixture;

the medium-scale mineral admixture is at least one of metakaolin, finely ground zeolite powder and highland barley straw ash, and the using amount of the medium-scale mineral admixture is 20-40 wt% of the total amount of the mineral admixture;

the fine-scale mineral admixture is silica fume, and the using amount of the fine-scale mineral admixture is 5-15 wt% of the total amount of the mineral admixture.

3. The low-shrinkage low-creep concrete serving in the complex environment of the plateau as claimed in claim 2, wherein in the coarse mineral admixture, fly ash is fly ash obtained by cooling fire coal of a thermal power plant, the sphericity degree of the fly ash is more than or equal to 80%, the average particle size of the fly ash is 17 μm, and the specific surface area of the fly ash is 1.1-1.2 m ² (ii)/g; the mineral powder is obtained by dry grinding blast furnace slag, the average particle size is 15 mu m, and the specific surface area is 1.7-2.0 m ² /g；

In the medium-scale mineral admixture, metakaolin is prepared by heating and dehydrating kaolin, the average particle size is 5 mu m, and the specific surface area is 14-20 m ² (ii)/g; the finely ground zeolite powder is formed by finely grinding natural zeolite rock, the average grain diameter is 9 mu m, and the specific surface area is 500-1100 m ² (ii)/g; the ash is prepared by burning highland barley straw, removing impurities, and grinding, has average particle diameter of 10 μm and specific surfaceThe product is 15-20 m ² /g；

In the fine mineral admixture, the siliceous dust is SiO volatilized by an ore-smelting electric furnace when ferroalloy is used for smelting ferrosilicon or industrial silicon ₂ And Si gas is quickly oxidized, condensed and precipitated in the air, the sphericity degree of the Si gas is more than or equal to 90 percent, the particle size is 0.5 to 1 mu m, and the specific surface area is 22 to 30m ² /g。

4. The concrete with low shrinkage and low creep serving in complex environments in plateaus as claimed in any one of claims 1 to 3, wherein the dense modified material further comprises graphene oxide in an amount of CaSO ₄ Whisker and nano SiO ₂ 0.5-0.8 wt% of the total amount and 0.01-0.03 wt% of the total amount of the cement and the mineral admixture.

5. The low-shrinkage low-creep concrete for the complex environment on plateau as claimed in claim 4, wherein CaSO ₄ The microscopic appearance of the whisker is columnar fiber, the length is 10-100 μm, the diameter is 1-10 μm, and the length-diameter ratio is 5-40;

the microscopic morphology of the graphene oxide is lamellar, the diameter of the lamellar is 300-500 nm, the thickness of the lamellar is 0.3-1 nm, and the specific surface area of the graphene oxide is 2600m ² /g；

Nano SiO ₂ The micro-morphology of the nano-particles is spherical particles, the average particle diameter is 40nm, and the specific surface area is 150m ² /g。

6. The low-shrinkage low-creep concrete serving in the complex plateau environment as claimed in claim 4, wherein the fine aggregate is river sand or machine-made sand, and the fineness modulus is 2.8-4.0.

7. The low-shrinkage low-creep concrete serving in the complex environment of the plateau as claimed in claim 4, wherein the coarse aggregate is limestone or basalt broken stone, the grain size is less than or equal to 15mm, and the part with the grain size of 10-15 mm is not less than 20%.

8. The low-shrinkage low-creep concrete serving in the complex environment of the plateau as claimed in claim 4, wherein the additive is at least one of a water reducing agent, a defoaming agent and a shrinkage reducing agent.

9. The low-shrinkage low-creep concrete serving in the complex environment of the plateau as claimed in claim 8, wherein the water reducing agent is at least one of a polycarboxylic acid-based superplasticizer, a naphthalene-based superplasticizer, a melamine-based superplasticizer and an amino acid salt superplasticizer;

the defoaming agent is at least one of an organic silicon defoaming agent, a polyether modified silicon defoaming agent, a high-carbon alcohol defoaming agent, a silicon-free defoaming agent and a mineral oil defoaming agent;

the shrinkage reducing agent is at least one of polyhydroxy compound NA-SP series concrete shrinkage reducing agents, alkyl polyoxyethylene ether JM-SRA series concrete shrinkage reducing agents, polyether and aliphatic organic matter JSJ type shrinkage reducing agents, methyl ether-based polymers and ethylene glycol series polymers ZZD-A type concrete shrinkage reducing agents.

10. The preparation method of the low-shrinkage low-creep concrete serving in the complex environment of the plateau as claimed in any one of claims 1 to 9, which is characterized by comprising the following steps:

the method comprises the following steps: mixing the dense modified material, the additive and water, magnetically stirring at the rotating speed of 500-1500 r/min for 5-20 min, placing in an ultrasonic cell disruption instrument, keeping the power at 60-70%, alarming at 80 ℃, and ultrasonically dispersing for 10-15 min to obtain a dense modified dispersion liquid;

step two: mixing cement and mineral admixture, placing the mixture in a mixer, and fully mixing the mixture to obtain a dry powder mixture;

step three: and pouring the dry powder mixture, the coarse aggregate and the fine aggregate into a concrete mixer in sequence, fully and uniformly stirring, then adding the dense modifier dispersion liquid, stirring for 2-5 min, and curing after casting the model.

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