Concrete for a highly insulating precast component, its preparation method and application

Abstract

The present invention provides a highly insulating concrete, a preparation method thereof and an application. Per cubic meter of this concrete, it includes 300 - 400 kg / m 3 cement, 100 - 200 kg / m 3 mineral admixture, 10 - 15 kg / m 3 paraffin particles, 600 - 800 kg / m 3 fine aggregate, 1000 - 1200 kg / m 3 coarse aggregate, as well as water reducing agent and water; the preparation method is to mix the cement, mineral admixture, paraffin, fine aggregate, coarse aggregate, water reducing agent and water, pour and form, and then carry out steam curing with the mold. The steam curing regime is that the static curing time is 2 - 4 h, the heating time is 2 - 3 h, keep constant temperature at 57 - 65 °C for 8 - 10 h, and cool down for 1 - 2 h. This concrete has good mechanical properties and durability, and has a high resistance. When applied to subway components, it can effectively inhibit the propagation of stray current and improve the operation safety of the subway track system.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete for precast components, and more specifically, to a concrete for high-insulation precast components, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the advancement of the urbanization process in China, the urban scale has been continuously expanding, and various problems faced by big cities have gradually become prominent. Among them, traffic congestion is one of the biggest challenges faced by major cities. Urban rail transit can alleviate the problem of difficult travel for citizens to a certain extent. Therefore, the construction of urban rail transit has developed rapidly in recent years.

[0003] Due to the rapid development of subway projects, precast components with characteristics such as high early strength and fast formwork turnover are widely used in subway project construction, such as shield segments, precast track slabs, precast sleepers, etc. Most precast components are cured and formed by steam curing. Under the steam curing environment, the hydration speed of cement is accelerated, and the components have high early strength. However, the faster reaction speed also makes the internal pores of the concrete coarser than those of the standard-cured concrete, and the impermeability is worse, creating favorable conditions for the propagation of stray current, which is common in subway projects, in precast components. The stray current transmitted to the ground through precast components will cause electrochemical corrosion of the internal steel bars of the components and underground metal pipe networks. According to statistical calculations, when the metal pipelines or tracks continuously pass through 1 ampere of stray current for about one year, the stray current can corrode up to about 10 kg of metal pipelines. In the long run, it will not only cause serious economic and environmental problems, but also affect the operation safety of the subway track system and threaten the lives of passengers.

[0004] Therefore, it is urgent to develop high-resistance precast component concrete to inhibit the propagation of stray current and improve the operation safety of the subway track system. Summary of the Invention

[0005] Based on the above technical problems existing in the prior art, one of the purposes of the present invention is to provide a preparation method of a concrete for high-insulation precast components. Through this method, the resistance of the precast component concrete can be greatly improved, and it has good mechanical properties and durability. It can inhibit the propagation of stray current from precast components to the ground, meet the use requirements of subway precast components, and help solve the economic and environmental problems brought by the propagation of stray current.

[0006] In order to achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A preparation method of a concrete for high-insulation precast components, each cubic meter of the concrete comprises the following components:

[0008] And,

[0009] Water reducing agent, accounting for 0.5 - 2% of the total mass of the gel material; water, accounting for 0.25 - 0.4 of the total mass of the gel material; the gel material is a mixture of cement and mineral admixture;

[0010] The preparation of the concrete includes the following steps:

[0011] Mix the cement, mineral admixture, paraffin, fine aggregate, coarse aggregate, water reducing agent and water evenly, pour and mold, and then carry out steam curing with the mold. The steam curing system is as follows:

[0012] The static curing time is 2 - 4h, the heating time is 2 - 3h, keep the temperature constant at 57 - 65°C for 8 - 10h, and cool down for 1 - 2h.

[0013] In some embodiments, the mineral admixture includes fly ash, slag and metakaolin. The fly ash accounts for 5 - 10% of the total mass of the gel material, the slag accounts for 5 - 10% of the total mass of the gel material, and the metakaolin accounts for 10 - 20% of the total mass of the gel material.

[0014] In some embodiments, the sphericity of the fly ash ≥75%, the average particle size is 14 - 18μm, and the specific surface area is 1.2 - 1.3m 2 / g; the average particle size of the slag is 13 - 17μm, and the specific surface area is 1.8 - 2.1m 2 / g; the average particle size of the metakaolin is 3 - 7μm, and the specific surface area is 14 - 20m 2 / g. Among them, the fly ash is the fly ash obtained by cooling the coal in the thermal power plant; the slag is obtained by drying and grinding the blast furnace slag; the metakaolin is prepared by heating and dehydrating kaolin.

[0015] In some embodiments, the cement is ordinary Portland cement with a strength ≥42.5MPa.

[0016] In some embodiments, the fine aggregate is river sand and / or manufactured sand, and the fineness modulus is 2.5 - 4.0.

[0017] In some embodiments, the particle size of the coarse aggregate ≤16mm, and the part with a particle size of 10 - 16mm is not less than 20%.

[0018] In some embodiments, the coarse aggregate includes limestone and / or basalt.

[0019] In some embodiments, the melting point of the paraffin is 50 - 55°C, and the fineness is 200 - 600 mesh.

[0020] In some embodiments, the water reducing agent includes polycarboxylate water reducing agent, the water reducing rate ≥30%, and the solid content ≥20%.

[0021] The second object of the present invention is to provide concrete for high-insulation prefabricated components obtained by the preparation method of any of the above embodiments.

[0022] The third object of the present invention is to provide a prefabricated component, and the prefabricated component includes the above-mentioned concrete for high-insulation prefabricated components.

[0023] The fourth object of the present invention is to provide the application of the above-mentioned concrete for high-insulation prefabricated components in the preparation of subway components.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] In the technical solution of the present invention, the mineral mixture technology is adopted, and the micro-aggregate effect, activity effect and morphological effect of the mineral mixture are utilized to effectively improve the late strength of the concrete, so that the late strength of the concrete is increased by 10-15% compared with the reference group, and the durability of the concrete is effectively improved; by adding paraffin, paraffin melts during the heating process. On the one hand, as a phase change material, it absorbs the internal heat during the hydration process, reduces the internal and external temperature difference, and reduces the influence of the thermal damage effect during the steam curing process, making the structure more dense. On the other hand, paraffin melts into a molten state during the hydration process and is distributed inside the structure. After the steam curing ends, it solidifies in the internal pores, fills the internal pore passages, strengthens the internal pore structure, and as a high-insulation material, it also increases the resistance of the concrete; the addition of water reducing agent can achieve the purpose of reducing shrinkage, preventing cracking and improving impermeability.

[0026] Through the method of the present invention, the resistance of the precast concrete components can be greatly increased, and it has good mechanical properties and durability, can inhibit the stray current from spreading to the ground through the precast components, meets the use requirements of subway precast components, and helps to solve the economic and environmental problems brought by the spread of stray current.

[0027] The present invention combines specific raw material ratios with steam curing systems to make the obtained concrete have excellent late mechanical properties and insulation properties. The 28-day strength of the concrete obtained by the method of the present invention is >60 MPa, the dry resistance is >1000 kΩ, and the saturated water resistance is ≥6.68 kΩ. Detailed implementation manners

[0028] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific implementations disclosed below.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this invention belongs. The terms used in the description of the present invention herein are for the purpose of describing specific embodiments only and are not intended to limit the present invention.

[0030] In the following examples, the cement used is ordinary Portland cement P.O42.5, with an average particle size of 20 - 25 μm and a specific surface area of 1.5 - 2.0 m 2 / g; metakaolin is obtained by heating kaolin for dehydration, with an average particle size of 5 - 7 μm and a specific surface area of 15 - 18 m 2 / g; fly ash is fly ash obtained by cooling the coal burned in a thermal power plant, with a sphericity of 80% and an average particle size of 15 - 18 m 2 / g; slag is obtained by drying and grinding blast furnace slag, with an average particle size of 15 - 17 μm and a specific surface area of 17 - 19 m 2 / g;

[0031] Paraffin wax is paraffin wax particles with 200 meshes and a melting point of 51.5 °C;

[0032] Fine aggregate is river sand or manufactured sand, with a fineness modulus of 2.5 - 4.0;

[0033] Coarse aggregate is limestone and basalt with a particle size ≤ 16 mm, and the part with a particle size of 10 - 16 mm is not less than 20%;

[0034] The water - reducing agent is a polycarboxylate water - reducing agent, with a water - reducing rate ≥ 30% and a solid content ≥ 20%;

[0035] In the present invention, kg / m 3 represents the mass of materials added per cubic meter of concrete.

[0036] Example 1

[0037] The concrete for high - insulation precast components in this example is composed of cement, mineral admixtures, paraffin wax particles, fine aggregate, coarse aggregate, water - reducing agent, etc. The composition and dosage of each component are as follows:

[0038]

[0039] Its preparation method includes the following steps:

[0040] Step 1: Mix dry materials

[0041] According to the above - mentioned component composition, put cement, fly ash, slag, metakaolin, and paraffin wax particles into a dry - powder mixer and mix for 4 h, stir evenly to obtain a dry - powder mixture;

[0042] Step 2: Mold the concrete

[0043] Pour the dry powder mixture, fine aggregate, and coarse aggregate obtained in Step 1 into a concrete mixer in sequence, and dry mix for 2 minutes. During this period, add water and water reducer in sequence. Control the mixing time within 5 minutes according to the state of the slurry. Then, perform model casting. After casting, insert embedded electrode plates at equally spaced positions on the forming surface of the specimen according to the four-electrode method (the electrode is a stainless steel screen with a pore diameter of 8 mm, with dimensions of 100×120 mm, and 20 mm is exposed at the upper part for easy measurement; the four electrode plates need to be inserted vertically at equal intervals, with a spacing of 60 mm, and the distance between the two end electrodes from the ends of the specimen is 60 mm each). Then, vibrate and compact. Immediately cover all the specimens with plastic wrap after casting to prevent moisture loss;

[0044] Step 3: Cure the concrete

[0045] Put the specimens obtained in Step 2 into a steam curing box with the molds, and perform steam curing according to the systems in Table 1 respectively. After the curing is completed, put the specimens into saturated lime water at a constant temperature of 20°C and cure until the specified age for testing;

[0046] Step 4: Test the resistance

[0047] Take out the specimens cured for 28 days from the lime water, dry the moisture on the surface of the specimens with dust-free paper, and perform saturated water resistance testing according to the four-electrode method, with a test voltage of 24 V. After the testing is completed, take out the specimens after drying in a vacuum drying oven at 105°C for 48 hours, cool them to room temperature in an environment of 20±2°C, and perform resistance testing in the dry state, with a test voltage of 24 V. The results are as follows:

[0048] Table 1 Saturated water and dry resistances of high-resistance specimens at 28 days under different steam curing parameters

[0049]

[0050]

[0051] Reference group: C60 concrete: Cement 315 kg / m 3 , Fly ash 90 kg / m 3 , Slag 45 kg / m 3 , Fine aggregate 660 kg / m 3 Coarse aggregate 1210 kg / m 3 , Water 135 kg / m 3 , The water reducer is 1% of the mass of the cementitious materials. 3+2+8+2 steam curing system, temperature 60°C, 28-day saturated water resistance 0.483 KΩ, dry resistance 19.54 KΩ, 28-day compressive strength 58.5 MPa. The high-resistance concrete obtained according to the high-resistance mix ratio and the optimal steam curing system has a saturated water resistance increased by more than 20 times and a dry resistance increased by 110 times compared with the above reference group.

[0052] It has been measured that, under the condition that the present invention can ensure that the late strength of the component is not lower than that of the concrete of ordinary precast components, the saturated water resistance of the precast component is increased by 20 times, and the dry resistance of the precast component is increased by 110 times, playing a good role in inhibiting the current propagation.

[0053] Example 2

[0054] The component ratios of the concrete for the precast component in this example are as follows:

[0055]

[0056] Its preparation method is the same as that of Example 1, the difference being that the steam curing system is as follows:

[0057] The static curing time is 4h, the heating time is 2h, it is kept at a constant temperature of 60 ± 2°C for 10h, and the cooling time is 2h; after the curing is completed, the test piece is placed in saturated lime water at a constant temperature of 20°C for curing until the age to be measured; the test piece cured for 28d is taken out and tested by the method of Example 1. After testing, the 28d compressive strength is 62.5MPa, the dry resistance is 1556.457 kΩ, and the saturated water resistance is 7.56 kΩ.

[0058] Example 3

[0059] The component ratios of the concrete for the precast component in this example are as follows:

[0060]

[0061] Its preparation method is the same as that of Example 1, the difference being that the steam curing system is as follows:

[0062] The static curing time is 4h, the heating time is 2h, it is kept at a constant temperature of 60 ± 2°C for 10h, and the cooling time is 2h; after the curing is completed, the test piece is placed in saturated lime water at a constant temperature of 20°C for curing until the age to be measured; the test piece cured for 28d is taken out and tested by the method of Example 1. After testing, the 28d compressive strength is 65.5MPa, the dry resistance is 1756.528 kΩ, and the saturated water resistance is 7.96 kΩ.

[0063] The technical features of the above-described examples can be combined arbitrarily. For the sake of brief description, not all possible combinations of the technical features in the above examples are described. However, as long as the combinations of these technical features do not conflict, they should all be considered as the scope described in this specification.

[0064] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A preparation method of concrete for high-insulation precast components, characterized in that, per cubic meter of the concrete includes the following components: Cement 300~400 kg / m 3 Mineral admixture: 100~200 kg / m 3 Paraffin particles 10~15 kg / m 3 Fine aggregate 600~800 kg / m 3 Coarse aggregate 1000~1300 kg / m 3 ; and, a water reducing agent, accounting for 0.5-2% of the total mass of the gel material; water, accounting for 0.25-0.4 of the total mass of the gel material; the gel material is a mixture of cement and mineral admixture; the mineral admixture includes fly ash, slag and metakaolin, the fly ash accounts for 5-10% of the total mass of the gel material, the slag accounts for 5-10% of the total mass of the gel material, and the metakaolin accounts for 10-20% of the total mass of the gel material; The sphericity of the fly ash is ≥75%, the average particle size is 14 - 18 μm, and the specific surface area is 1.2 - 1.3 m 2 / g; the average particle size of the slag is 13 - 17 μm, and the specific surface area is 1.8 - 2.1 m 2 / g; the average particle size of the metakaolin is 3 - 7 μm, and the specific surface area is 14 - 20 m 2 / g; the fine aggregate is river sand and / or manufactured sand, with a fineness modulus of 2.5-4.0; the particle size of the coarse aggregate ≤ 16 mm, and the part of 10-16 mm is not less than 20%; the preparation of the concrete includes the following steps: mix the cement, mineral admixture, paraffin, fine aggregate, coarse aggregate, water reducing agent and water, pour and form, and then carry out steam curing with the mold, and the steam curing system is: the static curing time is 3-4 or 6 h, the heating time is 2-3 h, keep constant temperature at 57-65 °C for 8-10 h, and cool down for 1-2 h.

2. The preparation method of concrete for high-insulation precast components according to claim 1, characterized in that, the coarse aggregate includes limestone and / or basalt.

3. The preparation method of concrete for high-insulation precast components according to claim 1, characterized in that, the melting point of the paraffin is 50-55 °C, and the fineness is 200-600 mesh.

4. Concrete for high-insulation precast components obtained by the preparation method according to any one of claims 1-3.

5. A precast component, characterized in that, it includes the concrete for high-insulation precast components according to claim 4.

6. Application of the concrete for high-insulation precast components according to claim 4 in the preparation of subway components.

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