【作者】 董旭；

【导师】 范晓明；

【作者基本信息】 武汉理工大学 ， 建筑材料与工程， 2009， 硕士

【摘要】 内掺碳纤维、石墨等导电相的水泥基机敏材料除了具有优越的力学性能外,还具有良好的电学性能,在结构健康监测、交通监测、电磁屏蔽等方面有着广泛的应用前景。本研究采用两电极法和四电极法测试材料的体积电阻,Instron5882万能材料试验机测试材料的力学性能和进行试块的压阻试验加载。采用Keithley 2700数据自动分析系统记录电压,直流电流由Keithley 2400恒流源提供,并用JSM-5610LV扫描电镜分析材料的微观结构。通过掺入含活性化学物质CCCW材料(水泥基渗透结晶防水材料)及使用经过浓硝酸浸泡的短切碳纤维,有效提高了水泥基机敏材料电学性能的稳定性。主要研究内容及结论如下:(1)研究了不同碳纤维掺量水泥净浆试块的渗流现象及其在循环荷载下的压阻特性,分析了碳纤维掺量不同时水泥净浆试块的压阻性能差异产生的原因。结果表明:当适量地掺入碳纤维时,试块的电阻变化率和压应力存在较好的对应关系。碳纤维掺量为水泥质量的1.0%～1.2%时,试块具有较佳的压阻性能。(2)研究了不同碳纤维掺量水泥砂浆试块的渗流现象及其在循环荷载下的压阻特性和材料的力学性能,分析了碳纤维含量对水泥砂浆试块的压阻性能和抗压强度的影响。结果表明:碳纤维掺量为加入水泥质量的3.0%～4.0%时,试块的压阻性能较好;碳纤维掺量为水泥质量的1.4%时,抗压强度达到最大值59.1MPa。(3)研究了碳纤维-石墨水泥砂浆试块在循环荷载下的压阻特性及石墨含量对试块抗压强度的影响。结果表明:试块的电阻变化率和压应力也存在较好的对应关系。在碳纤维含量为所加水泥质量分数的1.0%,石墨掺量为20%～30%时,试块的压阻性能最好;掺与不掺KIM的碳纤维-石墨水泥砂浆试块的抗压强度均随石墨掺量的增加而降低,但是,在石墨掺量相同条件下,掺入KIM后试块的抗压强度有一定提高。(4)掺加CCCW后可在一定程度上减弱试块的极化效应,有效提高测试试块的电阻稳定性;此外,对碳纤维表面进行氧化处理后,大大增强了其在水泥基体中的分散性,也有益于试块电学性能的稳定。(5)对机敏材料渗流现象机理、极化现象机理进行了讨论,提出了渗流现象的有效介质模型,并对机敏材料的压阻机理进行了理论分析。更多还原

【Abstract】 Cement-based smart materials added with conductive phases like carbon fiber, graphite etc.are provided with not only good electrical properties but excellent mechanical properties.Therefore,they can be used widely in many aspects,such as structural health monitoring,traffic monitoring and electromagnetic shielding etc.In this work,the volume resistances of materials were tested by 2-probe method and 4-probe method.Instron5882 universal material testing machine were adopted to measure the mechanical properties of materials and to supply loading for piezoresistivity experiment.DC current was supplied by Keithley 2400 constant current source and the voltage was measured by Keithley 2700 data auto-collection analysis system.The microstructure of the materials was analyzed by Scaning Electron Microscope(SEM).CCCW(Cementitious Capillary Crystalline Waterproofing Materials) was added as an admixture and the short carbon fibers were soaked by concentrated nitric acid.The main researching content and results are as follows:(1) The percolation phenomena of the cement paste with different content of carbon fiber and the pressure sensitivity under the cyclic loading were studied.The reasons for producing the pressure sensitivity differences of the cement paste with different content of carbon fiber were also analyzed.The results indicates that there exists a better corresponding relationship between the fractional variation in resistance of testing blocks and compressive stress.When the content of carbon fiber is 1.0wt.%(by the weight of cement,same as following)～1.2wt.%,the pressure sensitivity of test blocks is the best.(2) The percolation phenomena,pressure sensitivity and mechanical properties of the cement mortar with different content of carbon fiber were studied.The result proves that the test blocks have the better pressure sensitivity when the content of carbon fiber is 3.0 wt.%～4.0 wt.%;The compressive strength of materials reaches the maximum value 59.1 MPa with the adding amount of 1.4wt.%carbon fiber.(3) The pressure sensitivity of the carbon fiber-graphite cement mortar under the cyclic loading and influences of different graphite content to the compressive strength of the test blocks are studied.The results proves that there also exists the better corresponding relationship between the fractional variation in resistance and the compressive stress of the test blocks.The best pressure sensitivity of test blocks can be obtained with 1.0%carbon fiber and 20 wt.%～30 wt.%graphite powder.The compressive strength of the carbon fiber-graphite cement mortar test blocks with CCCW or not decreases with the content of the graphite,and the compressive strength of the test blocks with CCCW is bigger than that of the ones without CCCW at the condition of same amount graphite addition.(4) The polarization effect of the test blocks can be weakened to a certain extent by adding CCCW,thus the stability in resistance of the test blocks will be improved effectively.In addition,the carbon fibers treated by surface oxidation can increase their dispersion in the cement-based bodies,which is also beneficial to the stability of the electrical properties of test blocks.(5) The paper dicusses the mechanism of the smart materials about the percolation phenomena and polarization phenomena,and puts forward to the effective media model of the percolation phenomena and analyzed the pressure-resistivity mechanism of smart materials in theory.更多还原