Study On Electrical Properties Of Cement-based Smart Materials With CCCW

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.