Analysis on pore characteristics of hybrid basalt-polypropylene fiber-reinforced concrete based on nuclear magnetic resonance technology
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摘要:
采用核磁共振(Nuclear magnetic resonance，NMR)测试了玄武岩-聚丙烯混杂纤维混凝土(HBPRC)的孔隙特征，对比分析了玄武岩纤维(BF)和聚丙烯纤维(PF)及二者混杂对HBPRC的抗压强度、孔隙率、孔径分布和曲折度的影响，并基于核磁共振T2谱和孔隙结构分形理论对4个孔径区域的孔隙结构分形维数进行了量化。结果表明：随着BF的添加，T2谱反映出适量的BF可以减小混凝土的孔隙率，而且有利于减小大孔体积占比；而随着PF含量增加，T2谱面积增加，且混凝土内部孔隙有变大的趋势。掺入BF-PF混杂纤维对混凝土的孔隙特征会产生正协同作用，当BF和PF掺量均为0.05vol%时，协同作用最佳，与普通混凝土相比，抗压强度提高了3.52%、孔隙率降低了1.47%、曲折度提高了8.20%。凝胶孔体积占比增大了8.76%，大孔体积占比降低了5.30%，孔径分布得到优化。HBPRC的孔隙结构具有明显的分形特征，孔隙结构分形维数在过渡孔、毛细孔和大孔区域依次增加，此外，分形维数越大，抗压强度越大。通过微观分析认为，纤维在混凝土基体中的粘结状态和分布是影响HBPRC孔隙分形特征的主要原因。
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关键词:
- 玄武岩-聚丙烯混杂纤维混凝土 /
- 核磁共振 /
- 孔隙特征 /
- 抗压强度 /
- 孔隙结构分形维数
Abstract:The pore characteristics of hybrid basalt-polypropylene fiber-reinforced concrete (HBPRC) was tested by nuclear magnetic resonance (NMR). The effects of basalt fiber (BF) and polypropylene fiber (PF) as well as their blends on the compressive strength, porosity, pore size distribution and tortuosity of HBPRC were analyzed comparatively. The fractal dimensions of the pore structure in four pore-size regions were quantified based on the T2 spectra of NMR and pore structure fractal theory. The results show that with the addition of BF, the T2 spectrum reflects that the appropriate amount of BF can reduce the porosity of concrete, and it is beneficial to reduce the percentage of large pore volume. But as the PF content increases, the T2 spectral area increases and there is a tendency for the pores of the concrete to become larger. Incorporation of BF-PF hybrid fibers produces a positive synergistic effect on the pore characteristics of concrete. The synergistic effect is optimal when the dosage of both BF and PF is 0.05vol%, which improves the compressive strength by 3.52%, reduces the porosity by 1.47%, increases the volume percentage of gel pores by 8.76%, increases the tortuosity by 8.20%, and reduces the volume percentage of large pores by 5.30%, and optimizes the distribution of pore size, as compared with ordinary concrete. There are obvious fractal characteristics in the pore structure of HBPRC, and the fractal dimensions of the pore structure of HBPRC increases sequentially in the region of transition pores, capillary pores, and large pores. In addition, the larger the fractal dimension, the greater the compressive strength. It is concluded from the microscopic analysis that the bonding state and distribution of fibers in the concrete matrix are the main reasons affecting the pore fractal characteristics of HBPRC.
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图 2 MesoMR12-060H-I 岩石微观孔隙结构分析与成像系统
Figure 2. MesoMR12-060H-I rock microscopic pore structure analysis and imaging system
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图 6 (a) PF断裂形貌；(b) 纤维搭接；(c) BF-PF三维纤维网
Figure 6. (a) PF fracture morphology; (b) Fibers overlap; (c) Three-dimensional bearing fiber mesh of BF-PF
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图 7 单掺BF试件横向弛豫时间分布
Figure 7. Transverse relaxation-time distribution of single doped BF specimen
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图 8 单掺PF试件弛豫时间分布
Figure 8. Transverse relaxation-time distribution of single doped PF specimen
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图 13 HBPRC横向弛豫时间与分形特征的关系
Sv—Cumulative pore volume fraction; T2—Transverse relaxation time
Figure 13. Relationship between transverse relaxation time and fractal characteristics of HBPRC
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图 14 不同孔隙的HBPRC的孔隙结构分形维数
Figure 14. Fractal dimension of pore structure of HBPRC with different pores
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图 15 纤维与混凝土基体粘结
ITZ—Interfacial transition zone; CH—Ca(OH)2
Figure 15. Bonding between fibers and concrete matrix
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图 17 HBPRC抗压强度与孔隙结构分形维数的关系
R2—Goodness of fit
Figure 17. Relationship between compressive strength and fractal dimension of pore structure of HBPRC
表 1 胶凝材料和玄武岩纤维(BF)的化学组成(wt%)
Table 1 Chemical composition of cementitious materials and basalt fiber (BF) (wt%)
Composition SiO2 Al2O3 Fe2O3 CaO MgO Cement 34.67 7.90 2.93 35.50 1.77 Fly ash 50.77 22.68 5.64 5.98 1.74 BF 51.40 15.40 9.80 9.00 5.70 
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表 2 BF和聚丙烯纤维(PF)的物理力学性能
Table 2 Physical and mechanical of BF and polypropylene fiber (PF)
Type Density/(kg·m−3) Tensile strength/MPa Elastic modulus/GPa Diameter/μm Length/mm BF 2.65 ≥ 2400 ≥40 15 18 PF 0.91 270 0.3 30 19
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表 3 玄武岩-聚丙烯混杂纤维混凝土(HBPRC)配合比
Table 3 Mix proportions of hybrid basalt-polypropylene fiber-reinforced concrete (HBPRC)
Mixture Mixture composition/(kg·m−3) C W CA S FA PBS BF PF BF0PF0 320 160 1068 712 100 6.3 0 0 BF0.05PF0 320 160 1068 712 100 6.3 1.3 0 BF0.1PF0 320 160 1068 712 100 6.3 2.6 0 BF0PF0.05 320 160 1068 712 100 6.3 0 0.5 BF0PF0.1 320 160 1068 712 100 6.3 0 0.9 BF0.05PF0.05 320 160 1068 712 100 6.3 1.3 0.5 BF0.1PF0.05 320 160 1068 712 100 6.3 2.6 0.5 BF0.05PF0.1 320 160 1068 712 100 6.3 1.3 0.9 BF0.1PF0.1 320 160 1068 712 100 6.3 2.6 0.9 Notes: "C" refers to cement; "W" refers to water; "CA" refers to coarse aggregate; "S" refers to river sand; "FA" refers to fly ash; "PBS" refers to performance water reducer; "0", "0.05", "0.1" represent the fiber volume content of 0vol%, 0.05vol%, 0.1vol%, respectively.
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表 4 HBPRC的横向弛豫T2谱峰面积比例
Table 4 Transverse relaxation-time T2 spectral peak area percentage of HBPRC
Mixture Peak 1/% Peak 2/% Peak 3/% Peak 4/% BF0PF0 62.60 13.91 10.18 13.28 BF0.05PF0 72.54 11.55 8.70 7.19 BF0.1PF0 61.79 13.66 10.07 14.46 BF0PF0.05 51.43 13.69 12.42 22.44 BF0PF0.1 56.05 13.77 10.25 19.92 BF0.05PF0.05 69.48 12.72 10.97 6.81 BF0.1PF0.05 64.08 13.52 9.44 12.94 BF0.05PF0.1 55.91 15.72 10.96 17.39 BF0.1PF0.1 65.80 14.44 12.14 7.60
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其他相关附件
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目的
研究不同掺量的玄武岩-聚丙烯混杂纤维增强混凝土(HBPRC)的谱分布、孔隙率、孔径分布、曲折度等孔隙特征以及孔隙结构分形维数与抗压强度的关系。
方法采用核磁共振技术、SEM微观形貌分析及分形理论共同揭示了BF、PF及BF-PF混杂对混凝土孔隙特征和抗压强度的影响。结果表明：适量的BF可以减小混凝土的孔隙率，随着PF含量增加，混凝土内部孔隙有扩大的趋势。BF和PF分别为0.05%混杂时可在混凝土内部形成均匀分布的三维纤维网，在混凝土中发挥出正协同作用。BF0.05PF0.05较普通混凝土孔隙率降低了1.47%，凝胶孔占比增大了8.76%，大孔占比降低了5.30%，混凝土的孔径分布得到优化，同时抗压强度和曲折度得到提高；通过分形理论表明HBPRC的孔隙结构具有明显的分形特征，孔隙结构分形维数随着孔径增大而减小，且与抗压强度有相关关系；通过微观分析认为，纤维在混凝土基体中的粘结状态和分布是影响HBPRC孔隙分形特征的主要原因。
结论综上，BF-PF混杂可以减小混凝土的孔隙率、优化孔径分布、提高孔隙的曲折度，使混凝土具有更好的孔隙特征，同时得出HBPRC的孔隙结构具有明显的分形特征，而且孔隙结构分形维数既可以作为其孔隙分形特征的定量表达，也可以客观反应其抗压强度。
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混杂纤维可以在混凝土发挥各自的纤维优势，相互激发、相互补充，达到取长补短的效果，有利于减少混凝土的固有缺陷，提升混凝土的性能，在纤维混凝土领域吸引了越来越多的研究。玄武岩-聚丙烯混杂纤维增强混凝土(HBPRC)作为一种新型的建筑材料尚处于一个初期的探索阶段，明晰两种纤维及其混杂对混凝土孔隙结构的影响可助力HBPRC的推广及应用。
采用核磁共振(Nuclear Magnetic Resonance，NMR)测试了HBPRC的孔隙特征，对比分析了玄武岩纤维(BF)和聚丙烯纤维(PF)以及二者混杂对HBPRC的抗压强度、孔隙率、孔径分布和曲折度的影响，并基于核磁共振T2谱和孔隙结构分形理论对4个孔径区域的孔隙结构分形维数进行了量化。结果表明：随着BF的添加，T2谱反映出适量的BF可以减小混凝土的孔隙率，而且有利于减小大孔体积占比；而随着PF含量增加，T2谱面积增加，且混凝土内部孔隙有变大的趋势。掺入BF-PF混杂纤维对混凝土的孔隙特征会产生正协同作用，当BF和PF掺量均为0.05%时，协同作用最佳，与普通混凝土相比，抗压强度提高了3.52%、孔隙率降低了1.47%、曲折度提高了8.20%。凝胶孔体积占比增大了8.76%，大孔体积占比降低了5.30%，孔径分布得到优化。HBPRC的孔隙结构具有明显的分形特征，孔隙结构分形维数在过渡孔、毛细孔和大孔区域依次增加，此外，分形维数越大，抗压强度越大。通过微观分析认为，纤维在混凝土基体中的粘结状态和分布是影响HBPRC孔隙分形特征的主要原因。
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