Preparation And Characterization Of Cement-based Electric Modules

Electric concrete, mixed with conductive heating components, is a function cement-based composite material which can not only maintain the performance of structural material, but also having the features of electric heating material. Electric concrete, which has potential application prospect, can be applied to a variety of fields including melting snow on both road and bridge in winter,indoor heating of construction, distortion correction about concrete structure. Besides, it can be also applied to some engineering field including electromagnetic shielding, grounding discharge, cathodic protection on metal. So, research on electric concrete has great significance.Cement-based electric heating modules were made by using black carbon and carbon fiber as conductive phase and the mixture ratio was optimized by analyzing the factors including mixing technology, aggregate, water, conductive phase and so on. Experimental results show that the conductivity of specimens, made by stirring together the carbon fiber, water and dispersant in advance, are the best and stable. The particle size of sand has only little effect on electrical conductivity, when the fiber length is longer than the maximum of its. But cement-sand ratio exceeding by 0.5 has a significant effect on electrical conductivity. Resistance presents linear downward trend when the cement-sand ratio is between 0.3~0.5. Conductivity of specimens is smaller with the increase of dosage of conductive phase, it can reach 0.23 ?·m when the content of carbon black and carbon fiber is 0.5 % and 1.0 % respectively.Heating effect of specimens with different resistivity between 0.27~13.1 ?·m were analyzed under the condition of temperature 20±1 ℃. Platinum resistance temperature sensor(PT100) and data collector(CR1000) with high precision were selected to obtain the surface temperature of the specimens and the experimental data was recorded through the Logger Net test system. Heat effect of specimens was analyzed by the scale and velocity of rise in temperature. Results show that when the resistivity was in the range of 1.08~5.26 ?·m, specimens performed steady with rise in temperature of 6.85 to 26.5 ℃(velocity of rise in temperature is between 0.1~0.34 ℃·min-1) and were suitable for use as electrothermal materials. Temperature rise of surface is less than 5.0 ℃ when the resistivity is 13.10 ?·m and the heating effect is poor. Temperature rise in local scope exceeds 60 ℃ and velocity of rise in temperature reaches 3.22 ℃·min-1 when the resistivity is 0.27 ?·m which is easy to cause temperature stress. Besides, temperature prediction model based on both resistivity and energizing time was established.