Preparation and characterization of carbon nanotubes reinforced volcanic ash-based geopolymer
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摘要: 为研究多壁碳纳米管对火山灰基地聚合物的增强效果与机理，通过显微观察和图像识别对比了不同超声时间多壁碳纳米管分散液中团聚体的数量和面积，确定了适宜的超声分散时长；以不同顺序混合分散液、碱激发剂溶液和火山灰制备地聚合物，通过所得浆体的稠度试验、硬化试件的三点弯曲试验、单轴压缩试验研究了不同掺量、不同种类的多壁碳纳米管对地聚合物工作性能与力学性能的影响，并利用扫描电子显微镜-能谱仪、压汞试验对地聚合产物的微观形貌和孔隙结构进行表征。分析结果表明：随着超声时间的增加，多壁碳纳米管的分散效果改善明显，45 min超声后超过85%的团聚体面积减小至0~100 μm2，总团聚体面积占比小于1%，且平均面积小于50 μm2；先添加多壁碳纳米管分散液再添加碱激发剂溶液的材料混合顺序更有利于纤维的均匀分散和地聚合物工作性能的保持；多壁碳纳米管在0.10%质量掺量时，对火山灰基地聚合物流动度影响不大，且能够有效提升其力学性能；功能化的多壁碳纳米管由于具有更强的亲水性和润湿性，对浆体工作性能的影响更轻微，对硬化试件力学性能的提升更显著，28 d时抗折、抗压强度较参照组最高可分别提升31.0%、15.9%；微观检测结果显示，多壁碳纳米管在地聚合物中发挥了桥接、填充、成核作用，因而实现性能的改善。Abstract: To investigate the reinforcing effect and mechanism of multi-walled carbon nanotubes on volcanic ash-based geopolymer, the numbers and areas of aggregates of multi-walled carbon nanotubes dispersions at different ultrasonic times were compared by using microscopy and image recognition, and an appropriate ultrasonic dispersion time was determined. Geopolymers were prepared by mixing the dispersion, alkaline activator solution, and volcanic ash in different orders. The effects of different types and concentrations of multi-walled carbon nanotubes on the workability and mechanical properties of the geopolymer were investigated by the consistency test of the slurry and the three-point bending test and the uniaxial compression test of hardened specimens. The micro-morphologies and pore structures of the geopolymer products were characterized by scanning electron microscope-energy dispersive spectrometer and mercury intrusion porosimetry. Analysis results show that the dispersion effect of multi-walled carbon nanotubes improves with the increase of ultrasonic time. After 45 min ultrasonication, the areas of more than 85% aggregates decrease to 0-100 μm2, the total ratio of the aggregate areas is less than 1%, and the average area is less than 50 μm2. The order of adding multi-walled carbon nanotube dispersion before adding NaOH solution is more favorable for the uniform dispersion of fibers and the preservation of the geopolymer workability. At a mass content of 0.10%, the multi-walled carbon nanotubes have little effect on the flowability of volcanic ash-based geopolymer and can effectively enhance the mechanical properties. The functionalized multi-walled carbon nanotubes have stronger hydrophilicity and wettability, leading to a slighter impact on the workability of the slurry and a more significant improvement in the mechanical properties of the hardened specimens. The 28 d flexural and compressive strengths can increase by up to 31.0% and 15.9%, respectively, compared with the reference group. The microscopic test results show that multi-walled carbon nanotubes play bridging, filling, and nucleation roles in the geopolymer, thus achieving the improvement of the performance.
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Key words:
- road engineering /
- geopolymer /
- consistency test /
- strength test /
- carbon nanotube /
- micromechanism
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图 1 火山灰原料的X射线粉末衍射测试谱
Figure 1. X-ray powder diffraction test spectrum of volcanic ash material
图 2 火山灰原料的粒径累积分布与频度分布
Figure 2. Cumulative particle size distribution and frequency distribution of volcanic ash material
图 3 不同超声处理时长后MWCNTs的分散效果显微图与团聚体面积分布
Figure 3. Microscopies of MWCNTs dispersion effect in different ultrasonic time and area distribution of agglomerates
图 8 MWCNTs在裂缝发展阶段中的作用机理
Figure 8. Action mechanism of MWCNTs in fracture development stages
图 9 MWCNTs与地聚合物凝胶EDS检测结果
Figure 9. EDS measurement results of MWCNTs and geopolymer gel
表 1 火山灰原料主要化学组成
Table 1. Main chemical compositions of volcanic ash material
种类 SiO2 FeO Al2O3 CaO Na2O K2O MgO TiO2 P2O5 MnO 含量/% 43.3 16.7 16.5 8.8 3.8 3.3 3.0 2.9 0.7 0.3 
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表 2 试验方案
Table 2. Experimental schemes
试验组 MWCNTs种类 质量掺量/% 混合顺序 P0 原始 0.00 先加MWCNTs分散液，再加NaOH溶液 P05 原始 0.05 先加MWCNTs分散液，再加NaOH溶液 P1 原始 0.10 先加MWCNTs分散液，再加NaOH溶液 P15 原始 0.15 先加MWCNTs分散液，再加NaOH溶液 C1 羧基化 0.10 先加MWCNTs分散液，再加NaOH溶液 H1 羟基化 0.10 先加MWCNTs分散液，再加NaOH溶液 P1-2 原始 0.10 加MWCNTs与NaOH的混合溶液
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表 3 团聚体面积相关计算结果
Table 3. Calculation result related to areas of agglomerates
超声处理时长/min 团聚体面积占比/% 平均团聚体面积/μm2 最大团聚体面积/μm2 0 7.61 650 24 727 15 2.31 153 3 227 30 1.87 79 2 365 45 0.86 46 2 242 60 0.53 31 2 231
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表 4 稠度试验结果
Table 4. Consistency test result
试验组 塌落度/mm 塌落扩展度/mm P0 113 201 P05 110 198 P1 106 195 P15 88 183 C1 107 196 H1 111 199 P1-2 35
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表 5 MIP试验孔隙分布统计
Table 5. Pore size distribution statistics in MIP test
试验组 累计进汞量/ (mL·g-1) 平均孔径/ nm 2~50 nm孔隙占比/% 大于50 nm孔隙占比/% 孔隙率/ % P0 0.1230 48.67 5.12 15.57 20.87 P1 0.1152 47.76 5.02 15.05 20.07 C1 0.1089 30.60 6.87 11.58 18.45 H1 0.0949 27.71 6.28 12.12 18.40
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