Composite phase change temperature control aggregate as well as preparation method and application thereof

Abstract

The invention discloses a composite phase change temperature control aggregate, which comprises: a porous support shell with pores on the surface; the porous supporting shell is filled with the phase change material; and the phase change material is frozen to form a solid-phase energy storage body. According to the invention, three targets can be realized at the same time: the phase change temperature control capability of a cement hydration heat release curve is accurately matched; a continuous and stable internal curing moisture supply mechanism; the interface structure and a concrete matrix form high-strength combination.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of concrete materials, in particular to a composite phase change temperature control aggregate and a preparation method and application thereof. BACKGROUND

[0002] The accumulation of hydration heat generated during the hardening process of mass concrete structures has always been a core problem that plagues engineering quality. When the thickness of the structure section exceeds 1.5 m, the heat released by the cement hydration reaction is difficult to effectively diffuse, resulting in a sharp rise in internal temperature to 60-80℃. At the same time, the surface of the concrete rapidly dissipates heat due to contact with air, and the internal and external temperature difference can reach more than 40℃. The tensile stress generated by this steep temperature gradient often exceeds the early tensile strength of concrete, eventually forming penetrating cracks. A flood discharge pier project had to spend a lot of money to reinforce and repair due to such temperature cracks, causing serious economic losses.

[0003] To control temperature cracks, the engineering community usually adopts two types of technical means: external cooling and material modification. Pre-buried cooling water pipes are the most widely used external cooling method, but they have obvious defects in actual construction: the cooling pipe network needs to occupy more than 30% of the space between the steel bars, forcing the construction party to adjust the reinforcement scheme; the leakage risk at the water pipe joint is as high as 15%, and fault maintenance is almost impossible; more importantly, for concrete core areas with a thickness of more than 3 meters, the cooling efficiency decreases exponentially with depth, for example, the detection data of a cross-sea bridge pile cap showed that the cooling effect 50 cm away from the water pipe surface of the concrete decreased by 60% compared with the water pipe surface of the concrete. Material modification technology mainly relies on functional additives, such as microencapsulated phase change materials mixed into concrete. Although this type of material can absorb some heat through phase change, it has two fundamental limitations: the capsule shell of organic phase change materials such as paraffin has weak adhesion to cement paste, resulting in a 18%-22% decrease in 28d compressive strength of concrete; the phase change temperature is mostly concentrated in the range of 45-55℃, which is significantly offset from the cement hydration heat release peak interval (60-70℃).

[0004] Comprehensive analysis shows that the development of new composite materials with synergistic functions has become the key path to break through the industry bottleneck of large temperature difference in mass concrete structures. SUMMARY

[0005] To solve one of the above technical problems, the present patent provides a composite phase change temperature control aggregate and a preparation method and application thereof.

[0006] According to a first aspect of the present application, a composite phase change temperature control aggregate is provided, comprising: a porous support shell with apertures on the surface; a phase change material filled in the interior of the porous support shell; the phase change material is treated by freezing to form a solid phase energy storage body. The phase change material is water-absorbed resin, and the support shell is a cubic steel structure or a spherical steel structure.

[0007] Preferably, the support shell is a cubic steel structure with a wall thickness of 1 mm and a single side size of 20 mm; each outer surface of the support shell is provided with a through hole with a diameter of 1 mm at the center.

[0008] Preferably, the surface of the support shell is provided with an epoxy resin bonding layer, the thickness of the epoxy resin bonding layer is greater than 200 μm, and the epoxy resin bonding layer is roughened to form a concave-convex structure.

[0009] According to a second aspect of the present application, a preparation method of the above-mentioned aggregate is provided, comprising the steps of: (a) preparing a porous support shell with through apertures on the surface; (b) forming a composite phase change material by any of the following ways: (i) filling superabsorbent resin into the shell, and immersing in an aqueous solution until saturated with water, (ii) mixing superabsorbent resin with graphene oxide solution, and vacuum injection into the shell; (c) freezing treatment to freeze and compact the water-absorbed resin.

[0010] Preferably, the pressure of the vacuum injection is ≤0.1 MPa; and the aggregate is subjected to dispersion and anti-sticking treatment before freezing treatment.

[0011] According to a third aspect of the present application, a preparation method of low temperature rise concrete is provided, comprising: (1) based on the cement hydration heat value, the thermophysical parameters of the phase change aggregate, and the structure size, calculating the aggregate volume replacement rate by finite element thermodynamic simulation; (2) replacing natural coarse aggregate with the same volume according to the replacement rate; (3) pre-mixing the components of the concrete except the composite phase change temperature control aggregate to form a semi-finished product; (4) adding the composite phase change temperature control aggregate to the semi-finished product before pouring, and secondary mixing uniformly.

[0012] Preferably, the replacement rate ranges from 5% to 15%; and for C30-C50 concrete, the replacement rate is negatively correlated with the concrete strength grade.

[0013] Preferably, the replacement rate of C35 concrete is 9.5%-10%; and 5000-5500 cubic phase change aggregates with a side length of 20 mm are added per cubic meter of concrete.

[0014] According to a fourth aspect of the present application, a low temperature rise concrete is provided, comprising the above-mentioned composite phase change temperature control aggregate; the aggregate replaces 5%-15% of the natural coarse aggregate by volume; and according to the semi-adiabatic temperature rise test method, the hydration peak temperature of the concrete is reduced by ≥14.5% compared with that of the ordinary concrete with the same proportion.

[0015] Preferably, when the aggregate of the graphene oxide mixed gel is used, the peak temperature drop is ≥ 18.1%.

[0016] Compared with the prior art, the present application can simultaneously achieve three goals: the phase change temperature control capability of accurately matching the cement hydration heat release curve; the continuous and stable internal curing moisture supply mechanism; and the interface structure of high-strength combination with the concrete matrix. This constitutes the core technical problem that the present application strives to overcome. Compared with ordinary mass concrete, the present application further strengthens the temperature control capability of concrete. The conventional technologies of temperature control of concrete, such as using low-heat cement, adding mineral admixtures, using pre-cooled materials, and setting cooling pipes, cannot effectively solve the problem of temperature cracks caused by hydration heat of concrete. When using low-heat cement, the hydration heat cannot be infinitely reduced due to the composition of the cement material itself and the strength requirement of concrete, and a large amount of heat is inevitably released during the hydration process of low-heat cement, which cannot be used for secondary cooling of concrete during the hydration process. Adding mineral admixtures can only further reduce the cement content due to the limitation of the proportion of parameters, thereby reducing the hydration heat, and also cannot be used for secondary cooling of concrete during the hydration process. Using pre-cooled materials is a commonly used temperature control measure for mass concrete at present. By arranging pipes inside the mass concrete, the heat inside the concrete is absorbed and carried away by the liquid circulating in the pipes during the hydration process of the concrete. However, the pipe arrangement is limited by the space for arranging steel bars inside the concrete and the spacing requirement of the pipe arrangement, and cannot uniformly absorb the heat inside the concrete, and cannot realize the function of internal curing of concrete. Compared with the existing methods, the present application can uniformly perform secondary cooling inside the concrete during the hydration process, and can realize the function of internal curing of concrete through the pores of the aggregate shell, which has significant advantages. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application. In the drawings:

[0018] Figure 1 is a schematic diagram of a composite phase change temperature control aggregate provided according to an embodiment of the present application.

[0019] Figure 2 is a schematic diagram of low-temperature rise concrete prepared by the composite phase change temperature control aggregate according to an embodiment of the present application.

[0020] Figure 3 is a comparison diagram of the semi-adiabatic temperature rise and fall curves of the concrete of the composite phase change aggregate A according to an embodiment of the present application.

[0021] Figure 4 is a comparison diagram of the semi-adiabatic temperature rise and fall curves of the concrete of the composite phase change aggregate B according to an embodiment of the present application.

[0022] Figure 5 It is a composite phase change aggregate C concrete semi-adiabatic heating and cooling curve comparison chart provided according to the embodiment of the present application. DETAILED DESCRIPTION

[0023] The following examples are provided to enable those skilled in the art to more clearly understand the present application. It is to be understood that the following examples do not limit the scope of the present application, but are merely illustrative. The raw materials, reagents or devices mentioned in the following examples, unless otherwise specified, can be obtained commercially or by known methods.

[0024] The application discloses a composite phase change temperature control aggregate, which comprises a porous supporting shell with pores on the surface, a phase change material filled in the inside of the porous supporting shell and a solid phase energy storage body formed by freezing treatment of the phase change material. The phase change material is resin after water absorption, and the supporting shell is a cubic steel structure or a spherical steel structure. The composite phase change temperature control aggregate has a porous high-strength supporting shell, and the inside is filled with a high-water-absorption gel material with heat absorption and internal curing functions. The innovative composite phase change temperature control aggregate is used to replace part of natural coarse aggregate to prepare low-temperature-rise concrete. The composite phase change material can effectively control the temperature inside the mass concrete by phase change heat absorption, so as to form low-temperature-rise concrete, reduce or eliminate the adverse effects of great temperature change caused by hydration heat on the mass concrete structure. In addition, with the hydration of the concrete, the aggregate slowly releases water to the surrounding cement-based material, realizes good internal curing function, further improves the long-term strength development of the concrete, reduces shrinkage and creep, and thus reduces the occurrence and expansion of cracks. The low-temperature-rise concrete prepared by using the composite phase change temperature control aggregate is suitable for mass concrete construction, and can improve the safety and durability of the mass concrete structure.

[0025] The shell is made of a porous high-strength supporting material, such as alloy steel, iron, high-strength ceramic, high-strength polymer material and the like, to ensure that the aggregate provides sufficient structural support for the concrete. The shell part can be a single-layer spherical shell structure or a cubic structure. To ensure the supporting strength of the aggregate, the thickness of the aggregate shell is usually greater than or equal to 1 mm.

[0026] The composite phase change temperature control aggregate is used to replace the gravel aggregate in the concrete, and the volume weight of the composite phase change temperature control aggregate needs to be approximately equal to that of the gravel aggregate, so that the two can be more fully mixed. The composite phase change temperature control aggregate is composed of a shell and a core phase change material filled in the inside, and the volume weight of the composite phase change temperature control aggregate is adjusted by adjusting the thickness and size of the shell. The adjustment and control method is as follows: shell material volume x shell material density + shell internal volume x core material density = concrete gravel material density x composite phase change temperature control aggregate volume.

[0027] The aggregate shell surface distribution hole needs to meet the mechanical properties as a support aggregate in shape and size, and requires the material of the aggregate core part and the external paste to effectively absorb heat and water exosmosis, which not only meets the low hydration heat demand in the production, transportation, pouring construction process of mass concrete, but also realizes the internal curing effect of concrete. The shell is prepared by using a melting and casting dispersion method, mechanical bending, laser cutting, welding and other processes.

[0028] The porosity, pore size and pore distribution need to balance the aggregate support strength, aggregate cost and processing technology, which are mainly determined by the comparison test of the concrete strength of the aggregate and the non-participating aggregate, and the control deviation value of the concrete strength is less than 5%. The porosity and pore distribution are arranged as uniformly as possible under the allowable processing technology. The pore size of the shell is usually less than or equal to 2mm. Under the condition of a certain porosity, the larger the pore size of the shell, the smaller the aggregate support strength, and the smaller the pore size, the more difficult the processing, but the internal curing performance of the composite phase change aggregate is better.

[0029] The filling material is a single or composite material with high heat absorption capacity and internal curing function. In addition to water-absorbing resin, the filling material can also include phase change materials, composite phase change materials, concrete internal curing materials, graphene composite materials, paraffin, liquid metals, organic polymer materials or mixed materials of multiple materials, etc. According to the phase change temperature of the core material and the temperature range of the hydration heat release of the concrete, the selection and proportioning of the filling material are determined, the heat absorption amount of the concrete at the hydration heat peak period is calculated, and the water release rate in the later period is calculated, so as to realize temperature control and internal curing.

[0030] The preparation method of the low-temperature rise concrete of the present application includes the following steps:

[0031] Step 1: Determine the aggregate replacement rate of mass concrete. According to the initial mix proportion of mass concrete, the cement hydration heat value of mass concrete, the heat absorption parameters of composite phase change temperature control aggregate, the temperature control target of the engineering project and other control conditions, the thermodynamic analysis method is used to calculate the required aggregate replacement rate (the proportion value of the composite phase change temperature control aggregate to the coarse aggregate of the concrete), the coarse aggregate with a particle size greater than 15mm is replaced, and the aggregate replacement rate is usually 5%-15%.

[0032] Step 2: Determine the pre-processed concrete mix proportion. According to the initial mix proportion of mass concrete and the determined aggregate replacement rate, the amount of coarse aggregate in mass concrete is adjusted to the initial mix proportion minus the initial mix proportion multiplied by the aggregate replacement rate, and the other material parameters in the initial mix proportion remain unchanged, and the new concrete mix proportion is the pre-processed concrete mix proportion.

[0033] Step 3: Process the low-temperature rise concrete semi-finished product. According to the pre-processed concrete mix proportion, the concrete is pre-mixed to form a low-temperature rise concrete semi-finished product.

[0034] Step 4: Preparation of low-temperature concrete. Before pouring, the prepared composite phase change temperature control aggregate is added to the low-temperature concrete semi-finished material, and secondary stirring is uniformly completed to prepare the low-temperature concrete.

[0035] Compared with the prior art, the present application has the following effects. Compared with mass concrete, the temperature control capability of the concrete is further enhanced. The conventional techniques for temperature control of concrete, such as using low-heat cement, adding mineral admixtures, using pre-cooled materials, and setting cooling pipes, cannot effectively solve the problem of temperature cracks caused by hydration heat of concrete. When using low-heat cement, the hydration heat cannot be infinitely reduced due to the composition of the cement material itself and the strength requirement of the concrete, and a large amount of heat is inevitably released during the hydration process of the low-heat cement, which cannot be further reduced. The mineral admixtures can only further reduce the cement content and thus reduce the hydration heat, and cannot be further reduced. The use of pre-cooled materials is a common temperature control measure for mass concrete. Pipes are arranged inside the mass concrete, and the heat inside the concrete is absorbed and removed by the liquid circulation in the pipes during the hydration process of the concrete. However, the pipe arrangement is limited by the space for arranging steel bars inside the concrete and the spacing requirement of the pipe arrangement, and cannot uniformly absorb the heat inside the concrete, and cannot realize the curing function inside the concrete. Compared with the existing methods, the present application can uniformly reduce the temperature inside the concrete during the hydration process, and can realize the curing function inside the concrete through the pores of the aggregate shell, which has obvious advantages.

[0036] Example 1: Preparation of low-temperature concrete using composite phase change aggregate A.

[0037] 1. Preparation of phase change aggregate A:

[0038] (1) Select 1mm thick galvanized steel plate (steel type Q345) as the raw material for making the aggregate shell;

[0039] (2) Laser cutting and spot welding method is used to make a 20mm cube steel shell, and a small hole with a diameter of 1mm is drilled on each face of the steel shell, and the small hole is located at the center of each face of the cube; the main process parameters of the laser cutting method are as follows. Laser type: fiber laser, power ≥1000W. Auxiliary gas oxygen purity ≥99%, pressure 0.8-1.5MPa, used for steel cube edge splicing. The welding process selects gas shielded welding. Adjust the welding speed, if there are pores, slow down the welding speed, if burn through, appropriately increase the welding speed. The welding wire diameter is selected to be 2mm. The phase change aggregate shell is completed, and the shape is as shown in the cube. Figure 1

[0040] ​(3) Put 3.5 mg of solid SAP resin particles into a cubic steel shell, and then put the cubic steel shell containing the SAP resin particles into water, and wait until the SAP resin particles inside the cubic steel shell absorb water and swell to fill the cubic steel shell.

[0041] (4) Put the prepared aggregate into a -18°C environment and freeze for more than 24 hours, so that the temperature inside and outside the aggregate is basically the same, the water-absorbing resin inside the aggregate is frozen and dense, and the aggregate is frozen to a target temperature (usually ≤-10°C) inside the aggregate. The temperature inside and outside the aggregate is basically the same, which completes the preparation of the composite phase change temperature control aggregate, and the aggregate is taken out and dispersed for use.

[0042] 2. Preparation of low-temperature-rise concrete Figure 2

[0043] Step 1: The mixing ratio of the reference C35 ordinary mass concrete is cement 260 kg / m 3 , fly ash 90 kg / m 3 , slag 100 kg / m 3 , expansive agent 30 kg / m 3 , sand 735 kg / m 3 , coarse aggregate 1080 kg / m 3 , water reducing agent 7 kg / m 3 , and water 170 kg / m 3 . The cement hydration heat value is 215 kJ / kg (3d), the latent heat of fusion of the composite phase change temperature control aggregate is 238 kJ / kg, and the specific heat capacity is 3.9 kJ / (kg·℃). The internal temperature of the mass concrete during construction is required to be controlled within 52°C. According to the above control conditions, the required aggregate volume replacement rate of the project is calculated to be 9.5% through finite element thermodynamic analysis algorithm.

[0044] Step 2: Adjust the coarse aggregate 1080 kg / m 3 in the mixing ratio of the reference C35 ordinary mass concrete to 977.4 kg / m 3 , and the phase change aggregate is 5130 (0.04104 cubic meters of phase change aggregate are matched per cubic meter of concrete: 0.02 3 ×5130=0.04104), and the other materials are unchanged, to determine the initial mixing ratio of the low-temperature-rise concrete.

[0045] Step 3: According to the initial mixing ratio of the low-temperature-rise concrete, the initial mixing ratio of the low-temperature-rise concrete is fine-tuned according to the concrete mixing ratio test regulation to determine the production mixing ratio of the low-temperature-rise concrete of the project.

[0046] ​Step 4: According to the mix proportion of low temperature rise concrete of the project, the concrete is pre-mixed without adding phase change aggregate to form a low temperature rise concrete semi-finished product.

[0047] Step 5: Before pouring the concrete, the prepared composite phase change temperature control aggregate is added to the low temperature rise concrete semi-finished product, and secondary mixing is uniform to complete the preparation of the low temperature rise concrete. Then the mass concrete is poured.

[0048] 3. C35 low temperature rise concrete temperature control performance test (semi-adiabatic temperature rise test):

[0049] (1) Compare the temperature rise curves of C35 low temperature rise concrete and C35 ordinary concrete to analyze the control effect of C35 low temperature rise concrete on hydration heat. The mix proportion of C35 ordinary mass concrete is cement 260 kg / m 3 , fly ash 90 kg / m 3 , slag 100 kg / m 3 , expansive agent 30 kg / m 3 , sand 735 kg / m 3 , coarse aggregate 1080 kg / m 3 , water reducing agent 7 kg / m 3 , and water 170 kg / m 3 .

[0050] (2) Test step 1: Prepare a group of ordinary concrete according to the mix proportion of C35 ordinary concrete; replace the coarse aggregate of C35 ordinary concrete with composite phase change temperature control aggregate, and the replacement rate is 10% during the test, and the remaining material proportion is unchanged to prepare another group of low temperature rise concrete. Step 2: Put the two groups of concrete into ABS material cylindrical containers with a bottom diameter of 250 mm and a height of 300 mm. Step 3: Set temperature sensors in the center of the cylindrical container, and link the sensors to the temperature acquisition instrument. Step 4: Wrap the cylindrical container with air retaining gel felt temperature material, and place the concrete test piece in the insulation barrel with good but imperfect thermal insulation performance. Step 5: Place the insulation barrel in a test environment of 25±1℃. Step 6: Collect data for 168 hours continuously after pouring the concrete, and the collection frequency is 12 times per minute. The test proves that the peak temperature of the test piece with composite phase change aggregate 1 is reduced by 5.7℃ compared with the reference concrete test piece during the hydration process, the temperature rise amplitude is reduced by 14.5%, and the peak appearance time is delayed by 6h. It shows that the low temperature rise concrete prepared by using composite phase change aggregate A has significant temperature control and cooling effect. The test data comparison effect is shown in Figure 3 .

[0051] 4. C35 low temperature rise concrete compressive strength test:

[0052] (1) Compare the compressive strength of C35 low temperature rise concrete and C35 ordinary concrete, and analyze the influence of C35 low temperature rise concrete on the compressive strength performance of concrete. The mixing proportion of C35 ordinary mass concrete is cement 260 kg / m 3 , fly ash 90 kg / m 3 , slag 100 kg / m 3 , expansive agent 30 kg / m 3 , sand 735 kg / m 3 , coarse aggregate 1080 kg / m 3 , water reducing agent 7 kg / m 3 , water 170 kg / m 3 .

[0053] (2) Test step 1: Prepare a batch of ordinary concrete test blocks according to the mixing proportion of C35 ordinary concrete; replace part of the coarse aggregate gravel in C35 ordinary concrete with composite phase change temperature control aggregate A, the replacement rate is 9.5% during the test, and the remaining material proportion is unchanged to prepare another batch of low temperature rise concrete test blocks. Step 2: Prepare 3 groups of each of the two kinds of concrete, each group has 3 150x150x150mm cubic concrete standard test blocks, and perform standard curing. Step 3: Test the compressive strength of one group of test blocks at 3d, 7d and 28d according to GB / T 50081 "Standard Test Methods for Mechanical Properties of Ordinary Concrete", and record the compressive strength.

[0054] The test data analysis shows that the compressive strength of the concrete with composite phase change aggregate A is reduced to a certain extent compared with the reference group, and the comparison test shows that the 28d compressive strength is reduced by about 8.1%, the influence of adding composite phase change aggregate A on the strength of concrete is limited, and the cubic shape of the phase change aggregate shell is a feasible aggregate shell shape. The comparison of the compressive strength test data of concrete is shown in Table 1.

[0055] Example two: Prepare low temperature rise concrete by using composite phase change aggregate B.

[0056] 1. Prepare phase change aggregate B:

[0057] (1) Select 1mm thick galvanized steel sheet (steel type Q345) as the raw material for making aggregate shell;

[0058] (2) Laser cutting and spot welding method is used to make a cube steel shell with a side length of 20 mm. Each face of the steel shell has a small hole with a diameter of 1 mm, and the small hole is located at the center of each face of the cube. The main process parameters of laser cutting method are as follows: laser type: fiber laser, power ≥ 1000 W. Auxiliary gas: oxygen purity ≥ 99%, pressure 0.8-1.5 MPa, used for steel cube edge splicing. The welding process selects gas shielded welding. Adjust the welding speed, if there are pores, slow down the welding speed, if it is burned through, appropriately speed up the welding speed. The welding wire diameter is selected to be 2 mm. Complete the preparation of the phase change aggregate shell, and the shape is shown in Figure 1 .

[0059] (3) Surface treatment is carried out on the phase change aggregate shell, and the surface of the aggregate shell is coated with epoxy resin glue for multiple times, and the coating thickness is greater than 200 μm. The surface of the epoxy resin glue is treated to make it rough.

[0060] (4) The SAP resin particles and the phase change solution with a graphene oxide solution concentration less than 0.1% are fully mixed to form a gel.

[0061] (5) The mixed solution and the shell are put into a sealed container, the container is vacuumed, and after the water absorbing SAP resin particles absorb the phase change solution and fill the entire shell, the container is opened.

[0062] (6) The prepared aggregate is placed in a-18℃ environment for more than 24 h, and the temperature inside and outside the aggregate is basically the same. The water absorbing resin in the aggregate is frozen and dense. The aggregate is taken out and dispersed for use.

[0063] 2. The scheme for preparing low temperature rise concrete is the same as that in case 1.

[0064] 3. C35 low temperature rise concrete temperature control performance test (semi-adiabatic heating test):

[0065] (1) Compare the temperature rise curves of C35 low temperature rise concrete and C35 ordinary concrete, and analyze the control effect of C35 low temperature rise concrete on hydration heat. The mixing proportion of C35 ordinary mass concrete is as follows: cement 260 kg / m 3 , fly ash 90 kg / m 3 , slag 100 kg / m 3 , expansive agent 30 kg / m 3 , sand 735 kg / m 3 , coarse aggregate gravel 1080 kg / m 3 , water reducing agent 7 kg / m 3 , water 170 kg / m 3 .

[0066] (2) Test Step 1: A group of ordinary concrete is prepared according to the C35 ordinary concrete ratio; the coarse aggregate gravel part in the C35 ordinary concrete is replaced with the composite phase change temperature control aggregate, and the replacement rate is 10% during the test, and the remaining material ratio is unchanged to prepare another group of low temperature rise concrete. Step 2: Put the two groups of concrete into the ABS material cylinder container with a diameter of 250mm and a height of 300mm. Step 3: Set a temperature sensor at the center position of the cylinder container, and link the sensor to the temperature acquisition instrument. Step 4: Wrap the cylinder container with air gel felt temperature material, and place the concrete test piece in the insulation barrel with good but not perfect thermal insulation performance. Step 5: Place the insulation barrel in a test environment of 25±1℃. Step 6: Collect data for 168h continuously after the concrete is poured, and the collection frequency is 12 times / min. The test proves that the test piece with composite phase change aggregate B has a peak temperature reduction of 7.5℃ during the hydration process, and the reduction rate is 18.1%, and the peak appearance time is delayed by 6h. It shows that the low temperature rise concrete prepared by using composite phase change aggregate B has significant temperature control and cooling effect. The test data comparison effect is shown in Table 1. Figure 4 .

[0067] 4, C35 low temperature rise concrete compressive strength test (the scheme is the same as in Example 1):

[0068] Step 1: Replace the coarse aggregate gravel part in the C35 ordinary concrete with the composite phase change temperature control aggregate B, and the replacement rate is 9.5% during the test, and the remaining material ratio is unchanged to prepare a batch of low temperature rise concrete test blocks. Step 2: Prepare 3 groups of low temperature rise concrete with composite phase change temperature control aggregate B, each group has 3 150x150x150mm cubic concrete standard test blocks, and perform standard curing. Step 3: Test the compressive strength of one group of test blocks according to GB / T 50081 "Standard for Testing Methods of Mechanical Properties of Ordinary Concrete" at 3d, 7d and 28d, and record the compressive strength.

[0069] The test data analysis shows that the concrete with composite phase change aggregate B has a certain degree of reduction in compressive strength compared with the reference group concrete. The comparison test shows that the 28d compressive strength is reduced by about 7.6%. The addition of composite phase change aggregate B and composite phase change aggregate A has a similar effect on the strength of the concrete, but the influence is limited. The cubic shape of the phase change aggregate shell is a feasible aggregate shell shape. The comparison of the test data of the compressive strength of the concrete is shown in Table 1.

[0070] Example Three: Prepare low temperature rise concrete by using composite phase change aggregate C.

[0071] 1, Preparation of phase change aggregate C:

[0072] (1) Select a 1.5mm thick steel plate (steel type Q345) as the raw material for making the aggregate shell;

[0073] (2) Using stamping and shearing process to cut the steel plate into a circular steel sheet with a diameter of 32 mm, and then putting the circular steel sheet into a concave hemispherical mold, and using a convex hemispherical mold to stamp the circular steel sheet into a hemispherical body, and then using electric arc welding to weld two hemispherical bodies to form a complete hollow spherical body, and then drilling the hollow spherical body to complete the preparation of the spherical phase change aggregate shell, and the shape is as shown in the spherical body. Figure 1

[0074] (3) Put 5.0 mg of solid SAP resin particles into the porous hollow steel ball shell, and then put the porous hollow steel ball containing SAP resin particles into water, and wait for the internal SAP resin particles to absorb water and swell to fill the porous hollow steel ball.

[0075] (4) Put the prepared aggregate into a -18°C environment for more than 24 hours, and the temperature inside and outside the aggregate is basically the same, the water absorbing resin inside the aggregate is frozen and dense, and the aggregate is frozen to the target temperature (usually ≤-10°C) inside the aggregate, and the temperature inside and outside the aggregate is basically the same, which completes the preparation of the composite phase change temperature control aggregate, and the aggregate is taken out and dispersed for use.

[0076] 2. The preparation scheme of low temperature rise concrete is the same as that of case 1 (the aggregate volume replacement rate is also 9.5%).

[0077] 3. C35 low temperature rise concrete temperature control performance test (semi-adiabatic temperature rise test):

[0078] (1) Compare the temperature rise curves of C35 low temperature rise concrete and C35 ordinary concrete, and analyze the control effect of C35 low temperature rise concrete on hydration heat. The mixing proportion of C35 ordinary mass concrete is cement 260 kg / m 3 , fly ash 90 kg / m 3 , slag 100 kg / m 3 , expansive agent 30 kg / m 3 , sand 735 kg / m 3 , coarse aggregate gravel 1080 kg / m 3 , water reducing agent 7 kg / m 3 , and water 170 kg / m 3 .

[0079] ​(2) Test Step 1: A group of ordinary concrete is prepared according to the C35 ordinary concrete ratio; the coarse aggregate gravel part in the C35 ordinary concrete is replaced with the composite phase change temperature control aggregate, and the replacement rate is 10% during the test, and the remaining material ratio is unchanged to prepare another group of low temperature rise concrete. Step 2: Put the two groups of concrete into the ABS material cylinder container with a diameter of 250mm and a height of 300mm. Step 3: Set a temperature sensor at the center position of the cylinder container, and link the sensor to the temperature acquisition instrument. Step 4: Wrap the cylinder container with air gel felt temperature material, and place the concrete test piece in the insulation barrel with good but not perfect thermal insulation performance. Step 5: Place the insulation barrel in a test environment of 25±1℃. Step 6: Collect data for 168h continuously after the concrete is poured, and the collection frequency is 12 times / min. The test proves that the test piece with composite phase change aggregate B has a peak temperature reduction of 7.5℃ during the hydration process, and the reduction rate is 18.1%, and the peak appearance time is delayed by 6h. It shows that the low temperature rise concrete prepared by using composite phase change aggregate B has significant temperature control and cooling effect. The test data comparison effect is shown in Table 1. Figure 5 .

[0080] 4, C35 low temperature rise concrete compressive strength test (the scheme is the same as example 1):

[0081] Step 1: Replace the coarse aggregate gravel part in the C35 ordinary concrete with the composite phase change temperature control aggregate C, and the replacement rate is 9.5% during the test, and the remaining material ratio is unchanged to prepare a batch of low temperature rise concrete. Step 2: Prepare 3 groups of low temperature rise concrete with composite phase change temperature control aggregate C, each group has 3 150x150x150mm cubic concrete standard test blocks, and perform standard curing. Step 3: Test the compressive strength of one group of test blocks according to GB / T 50081 "Standard for Testing Methods of Mechanical Properties of Ordinary Concrete" at 3d, 7d and 28d, and record the compressive strength.

[0082] The test data analysis shows that the concrete with composite phase change aggregate C has a certain degree of reduction in compressive strength compared with the reference group concrete. The comparative test shows that the 28d compressive strength is reduced by about 5.0%, and the influence of adding composite phase change aggregate C on the strength is better than that of adding composite phase change aggregate A or B, and the spherical shell of the composite phase change aggregate has less influence on the mechanical properties of the concrete. The comparison of the test data of the compressive strength of the concrete is shown in Table 1.

[0083] Comparative Example 1: Low temperature rise concrete is prepared by using composite phase change aggregate D.

[0084] 1, Preparation of phase change aggregate D:

[0085] (1) Select 1mm thick galvanized steel sheet (steel type Q345) as the raw material for making the aggregate shell;

[0086] (2) Laser cutting and spot welding method is used to make a cube steel shell with a side length of 20 mm. Each face of the steel shell has a small hole with a diameter of 1 mm, and the small hole is located at the center of each face of the cube. The main process parameters of the laser cutting method are as follows: laser type: fiber laser, power ≥ 1000 W. Auxiliary gas oxygen purity ≥ 99%, pressure 0.8-1.5 MPa, used for steel cube edge splicing. The welding process selects gas shielded welding. Adjust the welding speed, if there are pores, slow down the welding speed, if it is burned through, appropriately speed up the welding speed. The welding wire diameter is selected to be 2 mm. The phase change aggregate shell is completed, Figure 1 The cube shape is shown.

[0087] (3) Put the aggregate shell into water, and put the aggregate shell, water and container into a-18°C environment for more than 24 hours. The temperature inside and outside the aggregate is basically the same, the water inside the aggregate freezes into ice blocks, and the aggregate freezes to the target temperature (usually ≤-10°C). The temperature inside and outside the aggregate is basically the same, which completes the preparation of the composite phase change temperature control aggregate. Take out the frozen aggregate, scatter and disperse, and remove the surface ice blocks for use.

[0088] 2. C35 low temperature rise concrete compressive strength test (the scheme is the same as example 1):

[0089] Step 1: Replace the coarse aggregate gravel part in C35 ordinary concrete with composite phase change temperature control aggregate D, the replacement rate is 9.5% during the test, and the remaining material proportion is unchanged to prepare a batch of low temperature rise concrete. Step 2: Prepare 3 groups of low temperature rise concrete with composite phase change temperature control aggregate D, each group has 3 150x150x150mm cubic concrete standard test blocks, and perform standard curing. Step 3: Test the compressive strength of one group of test blocks according to GB / T 50081 "Standard for Testing Methods of Mechanical Properties of Ordinary Concrete" at 3d, 7d and 28d respectively, and record the compressive strength.

[0090] Test data analysis shows that the compressive strength of the concrete with composite phase change aggregate D is greatly reduced compared with the reference group, and the comparative test shows that the 28d compressive strength is reduced by about 43.6%. The main reason is that the liquid water in the composite phase change aggregate D is released during the preparation of the concrete, which changes the water-cement ratio of the concrete, and thus reduces the strength of the concrete. The composite phase change aggregate D is an unqualified low temperature rise concrete preparation aggregate. The comparison of concrete compressive strength test data is shown in Table 1.

[0091] Table 1 Comparison of concrete strength test with different types of composite phase change aggregate

[0092]

[0093] Those skilled in the art will understand that the above embodiments are only exemplary embodiments, and various changes, substitutions and modifications can be made without departing from the spirit and scope of the present application.

Claims

1. A composite phase change temperature control aggregate, characterized in that: include: A porous support shell with pores on its surface; a phase change material filled in the porous supporting shell; The phase change material is frozen to form a solid phase energy storage body.

2. The aggregate according to claim 1, characterized in that The phase change material is a resin after absorbing water, and the supporting shell is a cubic steel structure or a spherical steel structure.

3. The aggregate according to claim 1, characterized in that An epoxy resin bonding layer is provided on the surface of the supporting shell. The epoxy resin bonding layer has a thickness greater than 200 μm and is roughened to form a concave-convex structure.

4. A method for preparing the aggregate according to any one of claims 1 to 3, comprising the steps of: (a) preparing a porous support shell with through pores on its surface; (b) forming a composite phase change material by any of the following methods: (i) filling the shell with a highly absorbent resin and immersing it in an aqueous solution until it is saturated with water, (ii) mixing a super absorbent resin with a graphene oxide solution and injecting the mixture into the housing under vacuum; (c) The water-absorbing resin is frozen and compacted by freezing treatment.

5. The method according to claim 4, wherein the pressure of the vacuum injection is ≤0.1 MPa; and the aggregate is subjected to dispersion and anti-sticking treatment before freezing treatment.

6. A method for preparing low-temperature-rise concrete, comprising: (1) Based on the calorific value of cement hydration, the thermophysical parameters and structural dimensions of phase-change aggregate, the aggregate volume replacement rate was calculated through finite element thermodynamic simulation; (2) replacing natural coarse aggregate by equal volume at the replacement rate stated; (3) pre-mixing the concrete components except the composite phase change temperature-controlled aggregate to form a semi-finished product; (4) Add the composite phase change temperature-controlled aggregate to the semi-finished product before pouring and stir it evenly for a second time.

7. The method according to claim 6, characterized in that The replacement rate ranges from 5% to 15%. For C30-C50 concrete, the replacement rate is negatively correlated with the concrete strength grade.

8. The method according to claim 7, characterized in that The replacement rate of C35 concrete is 9.5%-10%; 5000-5500 cubic phase change aggregates with a side length of 20mm are added to each cubic meter of concrete.

9. A low temperature rise concrete, characterized in that: Include: The composite phase change temperature-controlled aggregate according to any one of claims 1 to 3; The aggregate replaces 5%-15% of natural coarse aggregate by equal volume; Measured by the semi-adiabatic heating test method, its hydration peak temperature is ≥14.5% lower than that of ordinary concrete with the same mix ratio.

10. The concrete according to claim 9, characterized in that When graphene oxide mixed gel aggregate is used, the peak temperature decreases by ≥18.1%.

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