Biochar-loaded phase change material temperature regulating engineered cementitious composites (ECC) and a preparation method thereof

Abstract

The application discloses a kind of biochar load phase change material temperature regulating type engineering cement-based composite material (ECC) and preparation method thereof.The material includes cement, mineral admixture, fine aggregate, water, fiber, biochar load phase change material and water reducing agent.By limiting the specific surface area (300-700 m² / g) of biochar, pore size (5-30 nm), porosity (≥40%), pyrolysis temperature (450-650℃) and particle size (5-200 μm), and the loading rate (40%-60%) of phase change material, using vacuum-normal pressure alternating cycle loading process, the synergistic enhancement of temperature regulating function and bending resistance function is realized.The material under temperature cycle conditions, peak temperature increases by 3-6℃, heat transfer efficiency is improved, while maintaining the high ductility characteristics of ECC.The application has wide application prospect in the fields of building energy saving, underground engineering, infrastructure in cold regions and the like.

Description

Technical Field

[0001] This invention belongs to the field of building materials technology, specifically relating to a biochar-supported phase change material temperature-regulating engineering cement-based composite material (ECC) and its preparation method. Background Technology

[0002] Engineered cementitious composites (ECCs) are cement-based composite materials with high ductility and strain hardening properties. Under tensile loads, they can form multiple microcracks, significantly improving the material's toughness and durability. Due to their excellent mechanical properties and crack resistance, ECCs are widely used in infrastructure projects such as bridges, tunnels, and protective structures. However, in engineering applications, diurnal temperature variations and seasonal temperature changes can generate thermal stress within ECCs, leading to the accumulation and propagation of microcracks, ultimately affecting the long-term durability of the structure.

[0003] Phase change materials (PCMs) technology offers a new approach to solving these problems. PCMs are functional materials capable of undergoing a phase transition within a specific temperature range and absorbing or releasing a large amount of latent heat. By incorporating PCMs into building materials, a large amount of latent heat can be absorbed or released near the phase transition temperature, achieving temperature regulation and energy storage. However, directly applying PCMs to cement-based materials presents challenges related to encapsulation, interface, and long-term stability.

[0004] Porous carrier encapsulation technology is an effective way to solve the application problems of phase change materials. Biochar is a typical porous carbonaceous material with a large specific surface area, tunable pore structure, and good chemical stability, which can effectively encapsulate phase change materials. Moreover, the surface functional groups of biochar can improve the interfacial bonding with cement matrix, and biochar is prepared using agricultural and forestry waste, which is in line with the concept of green and sustainable development.

[0005] Currently, biochar-supported phase change materials are not used in ECC. Therefore, it is urgent to develop a technical solution that utilizes biochar-supported phase change materials to comprehensively optimize the temperature control, heat storage, and durability of ECC, while maintaining its mechanical properties. Summary of the Invention

[0006] The purpose of this invention is to provide a temperature-regulating ECC based on biochar-supported phase change material and its preparation method, which reduces the peak temperature of the ECC, relieves thermal stress and delays crack initiation, while maintaining the mechanical properties of the ECC.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a temperature-regulating ECC supported on biochar, the raw materials of which include cement, mineral admixtures, fine aggregates, mixing water, water-reducing agent, fiber, and biochar supported on phase change material.

[0008] The mixing ratio of the biochar-supported phase change material (ECC) for temperature regulation is as follows (fiber by volume, other raw materials by mass): 100 parts cement; 100-150 parts mineral admixture, preferably 120-140 parts; 90-150 parts fine aggregate, preferably 110-130 parts; 50-130 parts mixing water, preferably 80-100 parts; 0.3-3 parts water-reducing agent, preferably 1-2 parts; fiber volume fraction is 1.5%-2.5% of the ECC slurry volume, preferably 2%; 5-35 parts biochar-supported phase change material, preferably 15-25 parts.

[0009] Furthermore, the cement is general-purpose cement with a strength grade of 42.5 or 52.5.

[0010] Furthermore, the mineral admixture is selected from one or more of fly ash, slag, silica fume, and metakaolin; preferably, it is a composite of fly ash and silica fume, with a mass ratio of (3-5):1.

[0011] Furthermore, the fine aggregate is quartz sand with a particle size range of 100-500μm and a median particle size of 280-360μm.

[0012] Furthermore, the fiber is selected from polyvinyl alcohol (PVA) fiber and polypropylene (PE) fiber; preferably PVA fiber, with a diameter of 30-50 μm and a length of 10-15 mm.

[0013] Furthermore, the biochar-supported phase change material is a composite particle of biochar-supported phase change material; the biochar is prepared by pyrolysis of plant residues under anaerobic or limited oxygen conditions, and has the following technical parameters: specific surface area 300-700 m² / g, preferably 400-600 m² / g, average pore size 5-30 nm, preferably 10-20 nm, porosity ≥40%, preferably ≥50%, particle size 5-200 μm, preferably 10-100 μm; the phase change material is selected from paraffin waxes, fatty acids, polyethylene glycols, or their compound systems, and has the following technical parameters: phase change temperature 35℃-80℃, preferably 50℃-70℃; latent heat ≥100 J / g, preferably ≥150 J / g; attenuation ≤15% after 100 cycles; the loading rate of the biochar-supported phase change material is 30%-70% (mass ratio), preferably 40%-60%.

[0014] This invention also provides a method for preparing the above-mentioned biochar-supported phase change material temperature-regulating ECC, comprising the following steps: S1: Preparation of biochar-supported phase change materials S11: Dry the biochar at 110-120℃ for 2-4 hours to remove surface moisture and volatile substances, and cool it to room temperature for later use; S12: Heat the phase change material to a molten state, and control the temperature at 10-20℃ above the phase change temperature; S13: With a mass ratio of biochar to phase change material of 1: loading rate, slowly add the pretreated biochar to the molten phase change material and stir at 80℃-90℃ for 30-60 minutes to allow the biochar to fully impregnate the molten phase change material. S14: Promote the infiltration of phase change material into the pores of biochar by alternating vacuum and atmospheric pressure: vacuum degree is -0.08~-0.095MPa, maintain for 20-30 minutes; restore atmospheric pressure, maintain for 10-15 minutes; repeat the vacuum-atmospheric pressure alternation 3-5 times; S15: Cool to room temperature to obtain agglomerates, mechanically crush them, and sieve them to obtain biochar-supported phase change material particles with a particle size of 200-300μm, for later use.

[0015] S2: Preparation of Temperature-Regulated ECC Slurry S21: Add cement, mineral admixtures, and fine aggregates to a mixer according to the proportions, and mix for 1-2 minutes to form dry material; S22: Dissolve the water-reducing agent in the mixing water, then slowly add it to the dry mixture and stir for 3-5 minutes to form a wet mixture; S23: Add the biochar-supported phase change material to the wet mixture in batches, stirring for 1-2 minutes between each batch, with a total stirring time of 5-8 minutes, to form a slurry; S24: Add fiber and stir at low speed for 3-5 minutes to ensure the fiber is evenly dispersed in the slurry.

[0016] S3: Molding and Curing S31: Pour the functionalized cement-based composite material slurry prepared in S2 into a mold and vibrate it on a vibrating table for 30-60 seconds to remove air bubbles; S32: Cover with plastic film and let stand at room temperature for 24 hours before demolding; S33: Place the specimens in a standard curing room (temperature 20±2℃, relative humidity ≥95%) for 28 days.

[0017] The present invention has the following beneficial effects: (1) Relief of thermal stress: The temperature-regulating ECC of the present invention increases the peak temperature by 3-6°C under temperature cycling conditions. Compared with the ECC control group that does not use biochar-supported phase change material, the temperature fluctuation range is reduced by 40%-55%.

[0018] (2) Improved heat storage capacity: Compared with the ECC control group, the heat storage capacity of the temperature-regulating ECC of the present invention is increased from 1 J / g to 1.5 J / g, which is 50% higher.

[0019] (3) Maintaining mechanical properties: The compressive strength, flexural strength and deformation capacity of the temperature-regulating ECC of the present invention are roughly the same as those of the ECC control group.

[0020] (4) Reliable preparation process: The vacuum-atmospheric pressure alternating cyclic loading process is adopted, and the loading rate of phase change material in biochar is controllable; the parameters of the temperature-controlled ECC preparation method are clear and suitable for industrial production.

[0021] (5) Environmental protection and sustainability: This invention utilizes biochar prepared from agricultural and forestry waste, realizing the resource utilization of waste, which is in line with the concept of sustainable development.

[0022] (6) Broad application prospects: The material of this invention can be applied to fields such as building energy conservation, underground engineering, and infrastructure in cold regions, and has significant economic and social benefits. Attached Figure Description

[0023] Figure 1 Example 1: Schematic diagram of the preparation process of multifunctional ECC based on biochar-supported phase change material; Figure 2 : Morphology of biochar used in Example 1 as observed by scanning electron microscopy; Figure 3 Morphology of the biochar-supported phase change material prepared in Example 1, as observed by scanning electron microscopy; Figure 4 Figure 1 shows the leakage test results of the biochar-supported phase change material in Example 1. Figure 5 : Test curves of top surface and temperature regulation performance in Example 1; Figure 6 Example 1: Stress-deflection curves from a bending test; Figure 7 Figure 2 shows the leakage test results of biochar-supported phase change material in Example 2. Figure 8 : Test curves of top surface and temperature regulation performance in Example 2; Figure 9 Example 2: Stress-deflection curves from the bending test; Figure 10 Figure 3 shows the leakage test results of the biochar-supported phase change material in Example 3. Figure 11 : Test curves of top surface and temperature regulation performance in Example 3; Figure 12 Example 3: Stress-deflection curves from the bending test; Figure 13 Comparative Example 1: Top surface and temperature regulation performance test curves; Figure 14 : Stress-deflection curves from the bending test in Comparative Example 1; Figure 15 Comparative Example 2: Top surface and temperature regulation performance test curves; Figure 16 : Stress-deflection curves from the bending test in Comparative Example 2; Figure 17 Figure 3 shows the leakage test results of the biochar-supported phase change material in Comparative Example 3. Figure 18 Comparative Example 3: Top surface and temperature regulation performance test curves; Figure 19 : Stress-deflection curves from the bending test in Comparative Example 3; Figure 20 Figure 4 shows the leakage test results of the biochar-supported phase change material in Comparative Example 4. Figure 21 Comparative Example 4: Top surface and temperature regulation performance test curves; Figure 22 : Stress-deflection curves from the bending test in Comparative Example 4; Detailed Implementation To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to the accompanying drawings.

[0024] Example 1: The first embodiment of the present invention The raw materials used in this embodiment are as follows: cement is 42.5 grade ordinary Portland cement; mineral admixture is a composite of fly ash and silica fume in a mass ratio of 4:1; fine aggregate is quartz sand with a particle size of 200-250μm; fiber is PVA fiber; mixing water is tap water; water-reducing agent is polycarboxylate-based water-reducing agent; biochar is prepared by pyrolysis of bamboo at 500-600℃, with a specific surface area of ​​520m² / g, an average pore size of 15nm, a porosity of 55%, and a particle size of 10-100μm; phase change material is paraffin wax with a phase change temperature of 61℃ and a latent heat of phase change of 150J / g; the loading rate of biochar on phase change material is 40%, and the particle size of biochar-loaded phase change material is 200-300μm.

[0025] The formulation of this embodiment is as follows (excluding PVA fiber, by mass parts): 100 parts cement, 80 parts fly ash, 20 parts slag powder, 100 parts fine aggregate, 100 parts water, 1.2 parts water-reducing agent, 2% volumetric content of PVA fiber, and 20 parts biochar-supported phase change material.

[0026] The preparation process in this embodiment is as follows ( Figure 1 ): Step 1: Preparation of biochar-supported phase change materials Step 11: Dry the biochar at 110℃ for 3 hours, then cool to room temperature for later use. Figure 2 ); Step 12: Heat the paraffin phase change material to 80°C until it is completely molten; Step 13: Add the pretreated biochar to the molten paraffin phase change material slowly at a mass ratio of 1:0.4, and stir at 80°C for 30 minutes. Step 14: Perform vacuum-atmospheric pressure alternating cycles on the stirred biochar and phase change material mixture: vacuum degree -0.09MPa, maintain for 25 minutes; restore to atmospheric pressure, maintain for 12 minutes; repeat 4 times; Step 15: After cooling to room temperature, mechanically pulverize and pass through an 80-mesh sieve to obtain biochar-supported phase change material particles with a particle size of 200-300 μm. Figure 3 ).

[0027] Step 2: Preparation of Temperature-Regulated ECC Slurry Step 21: Add cement, mineral admixtures, and quartz sand to a planetary mixer according to the specified ratio, and dry mix for 2 minutes; Step 22: Dissolve the water-reducing agent in the mixing water and slowly pour it into the dry material, stir for 4 minutes to form a wet mixture; Step 23: Add the biochar-supported phase change material to the wet mixture in 3 batches, stirring for 1.5 minutes between each batch, for a total stirring time of 7 minutes; Step 24: Add PVA fiber and stir at low speed for 4 minutes.

[0028] Step 3: Shaping and Curing Step 31: Pour the slurry prepared in Step 2 into molds of 40 mm×40 mm×40 mm, 100 mm×100 mm×20 mm and 200 mm×45 mm×15 mm, and vibrate for 45 seconds. Pour 5 specimens into each mold group. Step 32: Cover with film and let stand at room temperature for 24 hours before demolding; Step 33: Place the specimen in a curing room with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days.

[0029] The performance test content and results of this embodiment include: (1) Leakage test of phase change material: The leakage of biochar-supported phase change material particles was observed by the filter paper absorption quantitative method. Figure 4 The leakage rate of the phase change material was measured to evaluate its stability and anti-leakage capability. Test results showed that the leakage rate of the biochar-supported phase change material was <2%, indicating excellent stability.

[0030] (2) Temperature regulation performance test (testing the back temperature): Place the 100 mm × 100 mm × 20 mm specimen, which has been cured for 28 days, in a temperature control chamber. The temperature cycle range is 20-80℃, the cycle is 24 hours, and the cycle is repeated 32 times. A temperature sensor is embedded in the center of the specimen, and the temperature change is recorded. Figure 5 The test results include: an average peak temperature of 55.6℃ and an average temperature fluctuation of 20-55.6℃.

[0031] (3) Mechanical property testing: A compressive strength test was conducted on a 40 mm × 40 mm × 40 mm specimen cured for 28 days, and a four-point bending test was conducted on a 200 mm × 60 mm × 18 mm specimen cured for 28 days. Figure 6 The test results are as follows: average compressive strength 42.3 MPa, average flexural strength 5.9 MPa, and ultimate deflection 4.5 mm.

[0032] Example 2: The second embodiment of the present invention The difference between this embodiment and Example 1 is that the loading rate of the biochar-supported phase change material is 50%, and the amount used is 10 parts; in preparation step 13, the mass ratio of biochar to phase change material is 1:0.5. Everything else is the same as in Example 1.

[0033] The performance test results of this embodiment include: (1) Leakage test of phase change material: (2) Peak temperature test: The peak temperature was 54.8℃, and the temperature fluctuation was 20-54.8℃. (3) Mechanical performance test: compressive strength 38.5 MPa, tensile strength 5.7 MPa, ultimate deflection 4.5 mm.

[0034] Example 3: The third embodiment of the present invention The difference between this embodiment and Example 1 is that the loading rate of the biochar-supported phase change material is 60%, and the amount used is 30 parts; in preparation step 13, the mass ratio of biochar to phase change material is 1:0.6. Everything else is the same as in Example 1.

[0035] The performance test content and results of this embodiment include: (1) Leakage test of phase change material (2) Temperature cycling test: The peak temperature is 54.0℃, and the temperature fluctuation is 20-54℃. (3) Mechanical performance test: compressive strength 35.2 MPa, tensile strength 5.3 MPa, ultimate deflection 3.8 mm.

[0036] Comparative Example 1: ECC control group without added biochar-supported phase change material The difference between this comparative example and Example 1 is that no biochar-supported phase change material is added in the formulation; and steps 1, 21, and 24 are omitted from the preparation steps. All other steps are the same as in the example.

[0037] The performance test content and results of this comparative example include: (1) Temperature cycling test: The peak temperature was 48.9℃, and the temperature fluctuation was 20-48.9℃. (2) Mechanical performance test: compressive strength 42.5 MPa, tensile strength 6.6 MPa, ultimate deflection 4.2 mm.

[0038] Comparative Example 2: Biochar only, without supporting phase change materials The difference between this comparative example and Example 1 is that: in this example, biochar without phase change material is used, and the amount of biochar is 20 parts; steps 12-15 are omitted from the preparation steps, and only biochar is added in step 24. All other steps are the same as in the example.

[0039] The performance test content and results of this comparative example include: (1) Temperature cycling test: The peak temperature was 46.4℃, and the temperature fluctuation was 20-46.4℃. (2) Mechanical performance test: compressive strength 42.3 MPa, tensile strength 5.5 MPa, ultimate deflection 3.8 mm.

[0040] Comparative Example 3: Direct addition of phase change material without biochar encapsulation The difference between this comparative example and Example 1 is that: phase change material is used directly in the formulation, with an amount of 13 parts, and biochar encapsulation is not involved; steps 12-15 are omitted in the preparation steps, and only phase change material is added in step 24. All other steps are the same as in the example.

[0041] The performance test content and results of this comparative example include: (1) Leakage test of phase change material (2) Temperature cycling test: The peak temperature was 62.7℃, and the temperature fluctuation was 20-62.7℃. (3) Mechanical performance test: compressive strength 32.2 MPa, tensile strength 4.7 MPa, ultimate deflection 1.2 mm.

[0042] Comparative Example 4: Biochar loading on phase change materials is too high The difference between this comparative example and Example 1 is that the loading rate of the biochar-supported phase change material is 75%, while the rest is the same as in Example 1.

[0043] The performance test content and results of this embodiment include: (1) Leakage test of phase change material (2) Temperature cycling test: peak temperature is 60℃, temperature fluctuation is 20-60℃.

[0044] (3) Mechanical performance test: compressive strength 33.8 MPa, tensile strength 5.3 MPa, ultimate deflection 3.8 mm.

[0045] The performance comparison of each embodiment and comparative example is shown in the table below. As can be seen from the comparison table, the present invention, by adding biochar to support the phase change material, controlling the phase change material loading rate, and employing a vacuum-atmospheric pressure alternating cyclic loading process, achieves a good balance between the temperature regulation performance, mechanical properties, and energy storage capacity of the engineering cement-based material, significantly outperforming the comparative example. Compared to Comparative Example 1, Embodiments 1-3 show an improvement of over 50% in temperature regulation performance; over 15% improvement in deformation capacity compared to Comparative Example 2; over 10% improvement in flexural strength compared to Comparative Example 3; and over 10% improvement in compressive strength compared to Comparative Example 4.

[0046]

Claims

1. A biochar-supported phase change material reinforced engineering cement-based composite material, characterized in that, The following components are included by mass parts: Cement: 100 parts; Mineral admixtures: 20-80 parts; Fine aggregate: 30-80 parts; Water: 25-45 parts; Fiber: 1-3 parts; Biochar-supported phase change material: 5-30 parts; Water-reducing agent: 0.5-2 parts.

2. The material according to claim 1, characterized in that, The biochar has a specific surface area of ​​300-700 m² / g (preferably 400-600 m² / g), an average pore size of 5-30 nm (preferably 10-20 nm), a porosity of ≥40% (preferably ≥50%), a pyrolysis temperature of 450-650℃ (preferably 500-600℃), and a particle size of 5-200 μm (preferably 10-100 μm).

3. The material according to claim 1, characterized in that, The phase change material is selected from one or more of paraffins, fatty acids, and polyethylene glycols, with a phase change temperature of 50–70℃ (preferably 55–65℃), a latent heat of phase change ≥120 J / g (preferably ≥150 J / g), and a decay of ≤15% after 100 cycles.

4. The material according to claim 1, characterized in that, The loading rate of the biochar-supported phase change material is 30%-70% (by mass) (preferably 40%-60%).

5. A method for preparing the material according to any one of claims 1-4, characterized in that... Includes the following steps: Step 1: Dry the biochar at 110-120℃ for 2-4 hours, then cool to room temperature; Step 2: Heat the phase change material to 10-20°C above the phase change temperature to melt it. Add the pretreated biochar according to the set loading rate and stir at 80-90°C for 30-60 minutes. Use a vacuum-atmospheric pressure alternating cycle to promote the infiltration of the phase change material into the pores of the biochar. The vacuum degree is -0.08 to -0.095 MPa. Maintain the vacuum for 20-30 minutes and the atmospheric pressure for 10-15 minutes. Repeat this process 3-5 times. Cool to room temperature to obtain biochar-supported phase change material composite particles. Step 3: Crush and sieve the composite particles to obtain particles with a diameter of 200-300μm; Step 4: Dry mix cement, mineral admixtures, and fine aggregates for 1-2 minutes; dissolve water-reducing agent in water and add it, stirring for 3-5 minutes; add biochar-supported phase change material in 3-5 batches, stirring for 1-2 minutes between each batch, for a total stirring time of 5-8 minutes; add fiber and stir at low speed for 3-5 minutes. Step 5: Pour and vibrate for 30-60 seconds, cover with film and let stand for 24 hours before demolding, and cure for 28 days according to standard.

6. The material according to claim 1, characterized in that, The prepared biochar-supported phase change material-reinforced engineering cement-based composite material exhibits a peak temperature increase of 3-6℃, a temperature fluctuation range reduction of 40%-55%, and a heat storage capacity increase of 50% under temperature cycling conditions.

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