碳纳米管与PVA纤维复合增强的水泥基材料的制备与性能

发布时间：2018-02-24 10:20

本文关键词： 水泥基材料聚乙烯醇纤维碳纳米管强度变形　出处：《重庆大学》2014年硕士论文　论文类型：学位论文

【摘要】：众所周知，纤维增强技术是提高混凝土韧性，减少开裂风险的重要技术手段。在此基础上，美国学者Victor Li通过微观力学的优化，形成一种水泥石基体对纤维的握裹力承担的纤维拉力略大于尖端扩展力的理想状态，从而研制出具有应变硬化性能特征的水泥基材料-ECC（Engineered Cementitious Composite），这一材料及其制备方法在近年来日益引起了国内学者的研究兴趣。目前，国内研制的ECC的强度和极限变形能力整体较低，还有较大的提升空间。为了获得整体强度较高，极限变形能力较好的纤维增强水泥基材料，本论文在原有ECC配制技术基础上，进一步采用碳纳米管从纳米尺度增强水泥石基体的强度和变形能力，制备碳纳米管与PVA纤维复合增强的水泥基材料。通过改变加料方式、改变减水剂种类、改变水灰比、改变纤维掺量、碳纳米管增强基体等方式，以抗折、抗压与抗弯性能为主要考察指标，研究了水灰比、纤维掺量等对碳纳米管与PVA纤维复合增强水泥基材料性能的影响规律。通过研究碳纳米管的掺量对其增强效果的影响，发现掺量越高，增强效果越显著。与不掺碳纳米管的基准组相比，掺1.5‰碳纳米管的水泥基材料的28天抗折强度增加15%。碳纳米管的增强效果受其分散程度的影响。在通过研究碳纳米管的分散后发现，采用超声波分散对于碳纳米管的分散要好于其他类型的机械分散，外加剂对于碳纳米管在溶液中分散起到稳定作用。通过改变聚乙烯醇纤维掺量和碳纳米管掺量、进行了双因素正交试验，经过实验发现，对于同等纤维掺量下，碳纳米管掺量的增加对于抗折强度具有一定的提高作用，抗压强度变化较小。两种因素相比，聚乙烯醇纤维掺量对于抗折强度与抗压强度的极限增强效果要大于碳纳米管。通过研究加料顺序的影响，发现纤维的加入时间对于拌合物的工作性能参数Γ2影响大，宜采用先掺法，尽管此种方法易产生扬尘。而外加剂的加入时间对于拌合物的工作性能参数Γ2影响较小，建议采用同掺法或后掺法，因为同掺法或后掺法更加方便。通过研究外加剂种类的影响，发现采用不同减水剂其最佳掺量不尽相同，聚羧酸高效减水剂为1%，，萘系高效减水剂为1.5%。聚羧酸高效减水剂比萘系高效减水剂更易产生引气现象，导致试件内部产生较多气孔，因此，萘系高效减水剂达到的最佳性能优于聚羧酸高效减水剂，水泥基材料性能也更稳定。通过研究水灰比的影响发现，水灰比对拌合物工作性能和强度影响显著。水灰比较低时，拌合物过干稠，工作性能不良，成型不密实，强度低；水灰比较高时，拌合物则轻微泌水，成型后孔隙多，强度也低。只有一定范围的水灰比才能获得拌合物工作性能良好，强度较高的水泥基材料。结合水灰比对拌合物工作性能和3d、7d、28d抗折强度与抗压强度的影响的试验结果，确定水灰比宜控制在0.3-0.4之间。通过研究各组成成分掺量的影响，发现聚乙烯醇纤维掺量较低时，随着掺量的增加，水泥基材料的强度不断提高，而工作性能变化不明显。但纤维掺量大于2.5%后，拌合物工作性能和硬化体力学性能明显降低，将硬化体横断面折断后发现此时纤维产生了明显的团聚现象，纤维增强效率明显降低。试验测定，在水灰比为0.4，萘系高效减水剂掺量为2%，聚乙烯醇纤维先掺，掺量为2%，碳纳米管采用超声波分散，掺量为1.5‰时，其28天抗压强度为52MPa，三点抗弯强度（抗折强度）为14MPa，四点抗弯强度为8.2MPa，四点抗弯对应的最大位移为20mm。
[Abstract]:As everyone knows, the fiber reinforced technology is to improve the toughness of concrete, an important technical means to reduce the cracking risk. On this basis, the American scholar Victor Li by optimizing the micro mechanics, the formation of the ideal state of a cement matrix of fiber fiber tensile grip wrapped force for slightly larger than the tip extension force, in order to develop cement based materials -ECC with the characteristics of strain hardening (Engineered Cementitious Composite), this material and its preparation method in recent years has caused the domestic scholar's research interest. At present, the domestic development of ultimate strength and deformation capacity of ECC is low, there is a large room for improvement.
In order to obtain high overall strength, good ability limit deformation of fiber reinforced cementitious composite, this paper based on the original ECC preparation technology, the carbon nanotube reinforced cement matrix strength and deformation ability from the nano scale preparation of carbon nanotubes and PVA composite reinforced fiber cement base material. By changing the feeding mode, change the effect of different water reducers, changing the water cement ratio, change the fiber content, the matrix mode of carbon nanotubes reinforced, flexural, compressive and flexural performance as the main indexes, the effects of water cement ratio, fiber content on carbon nanotubes and PVA composite reinforced influence the properties of cement-based materials.
Enhancement effect to the content of carbon nanotubes, found that the content is higher, the enhancement effect is more significant. Compared with the reference group with carbon nanotubes, cement-based materials doped with 1.5 carbon nanotubes% of the 28 day flexural strength increased 15%. carbon nanotubes by the dispersion degree of influence in through the study on the dispersion of carbon nanotubes found by ultrasonic dispersion in dispersion of carbon nanotubes is better than other types of mechanical dispersion, stable to additive effects on carbon nanotubes dispersed in solution.
By changing the content of PVA fiber and carbon nanotubes content, the double factor orthogonal experiment, it is found that for the same fiber dosage, increase the carbon nanotube content has a certain improving effect on the flexural strength, compressive strength changes little. Two factors than PVA fiber dosage for the ultimate the flexural strength and compressive strength of the reinforcing effect than carbon nanotubes.
By studying the effects of feeding order, found that fiber adding time performance parameters for the gamma mixture of 2 high impact, should adopt the first mixing method, although this method is easy to produce dust. The performance parameters for the gamma mixture adding time while agent 2 has little effect, suggestions by or after mixing with mixing method because, after mixing with mixing method or method is more convenient.
By studying the effects of different types of additives, find the optimal dosage of water reducer is not the same, polycarboxylate superplasticizer is 1%, naphthalene superplasticizer 1.5%. polycarboxylate superplasticizer than naphthalene superplasticizer are more susceptible to air entraining phenomenon, resulting in thespecimens produced more holes, so the best performance is better than naphthalene reducing agent of polycarboxylate superplasticizer and cement base material performance is more stable.
By studying the influence of water cement ratio, affect the performance and strength of mixture working water cement ratio significantly. The water cement ratio is low, the mixture is too dry and thick, bad performance, forming dense, low strength; water cement ratio is high, the mixture is slight bleeding, after forming porous, low strength. Only a certain range of the ratio of water to cement mixture can obtain good work performance, high strength cement-based materials. Combined with the performance and 3D mixture operating water cement ratio of 7D, the effect of test results of 28d flexural strength and compressive strength, determine the water cement ratio should be controlled between 0.3-0.4.
By studying the effects of each component content, found the content of PVA fiber is low, with the increase in volume, the strength of the cement base material continues to improve, and work performance does not change significantly. But the fiber content is greater than 2.5%, the mixture performance and strength of hardening can significantly reduce the broken, hardening after the time found that the body cross section fibers produced obvious agglomeration and fiber reinforced efficiency is significantly reduced.
In the experiment, the water cement ratio is 0.4, naphthalene superplasticizer is 2%, polyvinyl alcohol fiber first doped, doped with 2% carbon nanotubes by ultrasonic dispersion, adding amount of 1.5 per thousand, the 28 days compressive strength of 52MPa, three point bending strength (bending strength) is 14MPa. Four point bending strength is 8.2MPa, the maximum displacement of four point bending corresponding to 20mm.

【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU528

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