Pore structure and thermal conductivity of basalt fiber reinforced foam concrete under freeze-thaw cycles
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摘要: 为研究冻融循环作用下的玄武岩纤维泡沫混凝土(BFRFC)的孔结构及热传导特性。选取四种不同纤维掺量的BFRFC试样，采用X-CT技术和Avizo软件进行三维重构，分析其孔隙结构和纤维分布特征。通过热力学性能测试和COMSOL数值仿真，研究不同冻融循环次数下BFRFC的导热性能变化规律，并基于多孔介质Bruggeman模型以及纤维的串并联导热机理，提出BFRFC的理论导热模型。结果表明，BFRFC的孔径尺寸和形状因子近似对数正态分布，纤维极角和方位角分别在15°~90°和0°~360°范围内均匀分布；BFRFC导热系数处于0.2~0.4W/(m·K)之间，受孔隙率和冻融循环次数的影响，纤维掺量的影响较小；通过建立BFRFC的数值仿真模型，采用COMSOL模拟导热性能，与实验结果基本一致；基于多相介质Bruggeman模型，结合纤维的串并联模型建立的理论导热模型可以有效地预测不同纤维掺量和孔隙率下BFRFC的导热系数，为寒区工程中BFRFC的应用提供了理论依据。Abstract: To study the pore structure and thermal conductivity characteristics of basalt fiber reinforced foam concrete (BFRFC) under freeze-thaw cycles, four BFRFC samples with different fiber contents were selected. X-CT technology and Avizo software were employed for three-dimensional reconstruction to analyze the pore structure and fiber distribution characteristics. Thermodynamic performance tests and COMSOL numerical simulations were conducted to investigate the changes in thermal conductivity of BFRFC under different freeze-thaw cycles. Based on the Bruggeman model for porous media and the parallel and series conduction mechanisms of fibers, a theoretical thermal conductivity model for BFRFC was proposed. The results show that the pore size and shape factor of BFRFC approximately follow a log-normal distribution, with fiber polar and azimuthal angles uniformly distributed in the ranges of 15° to 90° and 0° to 360°, respectively. BFRFC's thermal conductivity ranges from 0.2 to 0.4 W/(m·K), primarily influenced by porosity and freeze-thaw cycles, with fiber content having a smaller impact. By establishing a numerical simulation model of BFRFC and using COMSOL to simulate thermal conductivity, the results were found to be consistent with experimental data. The theoretical thermal conductivity model, based on the Bruggeman model and the parallel-series fiber model, effectively predicts the thermal conductivity of BFRFC under different fiber contents and porosity conditions, providing a theoretical basis for the application of BFRFC in cold region engineering.
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图 3 冻融循环下各BFRFC试样的孔径分布和表面粗糙度
Figure 3. Pore size distributions and surface roughness of different BFRFC samples under freeze-thaw cycles
图 4 冻融循环下各密度等级BFRFC的孔隙形状特征统计
Figure 4. Statistical characteristics of pore shapes for BFRFC of different density grades under freeze-thaw cycles
图 5 玄武岩纤维空间坐标位置示意
Figure 5. Schematic diagram of the spatial coordinates of basalt fibers
图 8 冻融循环下BFRFC的导热性能
Figure 8. Thermal conductivity of each BFRFC under freeze-thaw cycles
图 11 BFRFC传热特征温度分布平面图(t=600 s)
Figure 11. BFRFC heat transfer temperature profile (t=600 s)
图 13 导热并联串联模型结构示意图
Figure 13. Schematic diagram of thermal conductivity parallel and series models
图 15 BFRFC导热系数预测值与实测值和模拟值比较
Figure 15. Comparison of predicted, measured, and simulated thermal conductivity values for BFRFC
表 1 BFRFC的配合比(kg/m3)
Table 1. Mix ratio and of BFRFC (kg/m3)
Sample Cement Water BF Foams 0%BF/FC08* 416.67 208.33 0 35.49 0.15%BF/FC08 416.67 208.33 4.2 35.49 0.30%BF/FC08 416.67 208.33 8.4 35.49 0.45%BF/FC08 416.67 208.33 12.6 35.49 0%BF/FC10 743.05 371.53 0 21.83 0.15%BF/FC10 743.05 371.53 4.2 21.83 0.30%BF/FC10 743.05 371.53 8.4 21.83 0.45%BF/FC10 743.05 371.53 12.6 21.83 *Notes: 0.15% BF represents the basalt fiber content; FC08 represents the foam concrete matrix, where 08 and 10 denote densities of 800 kg/m³ and 1000 kg/m³, respectively.
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表 2 不同冻融次数下BFRFC的孔隙尺寸特征
Table 2. Pore size characteristics of BFRFC under different freeze-thaw cycles
Sample Freeze-thaw
CyclesPorosity/% Pore
numberPore diameter/ μm Distribution parameters X-CT Saturated water
absorptionError Max Min Average μ σ 0%BF/FC08 0 15.43 15.87 −2.85% 326725 4480.61 44.54 458.14 6.03 0.4 40 35.75 35.67 0.22% 300971 4657.25 44.54 642.03 6.35 0.43 80 43.79 43.87 −0.18% 294860 4721.06 44.54 768.12 6.54 0.45 0.15%BF/FC08 0 14.91 15.29 −2.55% 315854 4503.13 44.54 447.85 6.02 0.39 40 34.54 34.44 0.29% 275417 4678.84 44.54 624.54 6.32 0.42 80 42.54 42.67 −0.31% 288012 4745.87 44.54 723.01 6.48 0.39 0.30%BF/FC08 0 14.44 14.84 −2.77% 305145 4534.57 44.54 434.74 6.01 0.36 40 32.87 32.75 0.37% 289874 4705.89 44.54 594.47 6.23 0.43 80 41.87 41.94 −0.17% 281245 4765.47 44.54 688.17 6.42 0.4 0.45%BF/FC08 0 14.02 13.75 1.93% 294180 4556.17 44.54 425.15 5.99 0.34 40 31.82 31.64 0.57% 283498 4724.53 44.54 576.1 6.19 0.42 80 40.71 40.98 −0.66% 274507 4787.56 44.54 641.58 6.35 0.39 0%BF/FC10 0 10.94 11.51 −5.21% 483346 3000.06 44.54 307.18 5.77 0.22 40 19.92 19.90 0.10% 466913 3407.16 44.54 410.41 6.02 0.24 80 26.04 26.47 −1.65% 404889 3870.43 44.54 565.45 6.24 0.29 0.15%BF/FC10 0 10.69 10.45 2.25% 461487 3035.25 44.54 289.73 5.64 0.23 40 19.54 19.87 −1.69% 446674 3458.12 44.54 384.62 5.92 0.25 80 25.87 25.86 0.04% 398743 3954.78 44.54 501.41 6.15 0.27 0.30%BF/FC10 0 10.54 10.92 −3.61% 439784 3094.54 44.54 271.45 5.58 0.26 40 18.95 18.77 0.95% 425174 3536.89 44.54 358.14 5.83 0.27 80 25.71 25.87 −0.62% 394155 4001.34 44.54 479.54 6.13 0.24 0.45%BF/FC10 0 9.93 10.25 −3.22% 417611 3136.87 44.54 244.18 5.51 0.27 40 18.09 18.54 −2.49% 406178 3597.48 44.54 337.4 5.72 0.23 80 24.65 24.55 0.41% 384755 4068.15 44.54 461.34 6.06 0.28 Notes: Due to the testing accuracy and resolution limitations of the X-CT equipment, the smallest pore diameter recorded for the BFRFC specimens is 44.54 μm. However, it is expected that the actual minimum pore diameters of each specimen are likely to be less than 44.54 μm and vary between samples.
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表 3 BFRFC各相材料属性
Table 3. Properties of Each Phase Material in BFRFC
Material Density/(kg·m−3) Elastic modulus/GPa Poisson's ratio Thermal conductivity/ (W·(m·K)−1) Specific heat capacity/ (J·(kg·K)−1) Cement 3150 34 0.200 0.508 850 BF 2800 65 0.227 0.035 700 Air 1.208 − − 0.023 1000
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表 4 不同纤维掺量的BFRFC导热性能
Table 4. Thermal conductivity of BFRFC in different fiber contents
Materials Fiber fraction /% Thermal conductivity/ (W·(m·K)−1) Error
$E = \left( {\frac{{{\lambda _{\text{t}}} - {\lambda _{\text{s}}}}}{{{\lambda _{\text{t}}}}}} \right)$Test result λt Comsol simulation λs FC08 0 0.372 0.382 −2.69% 0.15 0.382 0.370 3.14% 0.30 0.399 0.379 5.01% 0.45 0.394 0.373 5.33% FC10 0 0.433 0.440 −1.62% 0.15 0.428 0.437 −2.10% 0.30 0.414 0.401 3.14% 0.45 0.415 0.391 5.78%
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表 5 BFRFC各项因素与导热系数的灰关联度
Table 5. Grey correlation of BFRFC influence factors with thermal conductivity
Factors Porosity Freeze-thaw cycle Fiber Grey correlation 0.95 0.72 0.51
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