Experimental Research On Electrical Conductivity And Electrothermal Performance Of Cement-based Composites

With the progress of science and technology,people’s understanding of material composite technology is constantly improving,so more functional requirements for cement-based composites are put forward.The conductive property of cement-based composite material and its conductive property derived from the pressure-sensitive property,temperature-sensitive property and electro-thermal property,etc.Its electro-thermal property is applied to the snow melting and deicing of roads and bridges,which has the advantages of high efficiency,fast,no pollution to the environment and so on.In this paper,the mechanical property,electrical conductivity,electrothermal property and microstructure of cement-based composites with single and compound conductive materials were studied and the mechanism was discussed.The main research contents of this paper are as follows:(1)Experimental research on mechanical properties of conductive cement-based composites.Suitable fibrous and granular conductive materials were selected,the content of carbon fiber was 0.05 Vol.% ～ 0.50 Vol.%,carbon nanotube was 0.025 Vol.% ～ 0.300 Vol.%,steel fiber was 0.2Vol.% ～ 1.0Vol.%,graphite was 2Vol.% ～ 10 Vol.%,the optimal content was selected for compounding.The single and compound conductive materials cement-based composites were prepared,tested their flexural strength and compressive strength to explore the influence of different conductive material contents and combinations on the mechanical properties of cement-based composites.The results show that:1)Carbon fiber can improve the flexural strength of cement-based composites,the content of 0.20 Vol.% ～ 0.35 Vol.% can obviously improve the flexural strength of cement-based composites.With the increase of carbon fiber content,the increase of flexural strength decreases.Carbon fiber can increase the compressive strength of cement-based composites,and it decreases slightly when the content of carbon fiber is 0.45 Vol.% ～ 0.50 Vol.%.2)Carbon nanotubes can slightly improve the strength of cement-based composites at lower content,the appropriate content of carbon nanotubes can significantly improve the strength,when the content of carbon nanotubes is high,the flexural strength of cement-based composites is slightly improved,while the compressive strength is decreased.3)Steel fiber can greatly improve the flexural strength and compressive strength of cement-based composites.4)Graphite can slightly improve the flexural strength of cement-based composites at 2Vol.% ～ 4Vol.%,increasing the graphite content can reduce the flexural strength of cement-based composites.The compressive strength of cement-based composites decreases with the increase of graphite content.5)Compared with the single conductive material,the flexural strength of cement-based composites can be further improved by the mixed conductive material,while the compressive strength is slightly reduced by the mixed conductive material.The effect of conductive materials on mechanical properties of cement-based composites is as follows: steel fiber >carbon fiber > carbon nanotube > graphite.(2)Experimental research on electrical conductivity of conductive cement-based composites.Suitable fibrous and granular conductive materials were selected,with the same content of conductive materials as the research(1).The cement-based composites with single and compound conductive materials were prepared,used electrochemical impedance tester to test the AC impedance of conductive cement-based composites,the frequency-impedance relationship and its equivalent circuit were analyzed,the effects of different contents and combinations of conductive materials on conductive properties and conductive mechanisms of cement-based composites are explored.The results show that:1)The addition of conductive materials has little effect on the ability of the electrode and specimen interface to reserve charge,but can significantly reduce the interfacial resistance.With the increase of the content of conductive materials and the optimization of complex doping,the interfacial capacitance changes to a lesser extent,the resistance has different degrees of reduction.2)The addition of conductive materials has a greater impact on conductive path of the cement matrix.With the increase of the content of conductive materials and the optimization of compound mixing,the overall capacitance of cement matrix increases and the resistance decreases,and the conductive path of cement matrix is significantly improved.3)With the increase of the content of conductive material,the capacitance of the conductive path formed by the conductive material increases or fluctuates slightly,the resistance decreases to varying degrees,and the conductive network formed by the conductive material gradually tends to be perfect.The conductive properties of cement-based composites are greatly improved due to the combined action of the above conductive paths.Comprehensive analysis of the price of conductive materials,the content and combination corresponding of conductive materials to the sudden changes in the value of each circuit element,show that the optimum content of carbon fiber,carbon nanotube,steel fiber and graphite is 0.35 Vol.%,0.175 Vol.%,0.6Vol.%,4Vol.%;B00175D04,A0035D04,C006D04,A0035C006D04,B00175C006D04 have excellent conductivity in cement-based composites mixed with conductive materials.(3)Experimental research on microstructure of conductive cement-based composites.Based on the single and compound conductive material cement-based composites,the preferred ratio was selected,the SEM specimens were prepared,through microstructure morphology analysis,the morphology,distribution and overlap of conductive materials in the cement-based composites were studied.The results show that:1)Carbon fibers present monofilament and uniform dispersion state inside cement-based composites,appearing to lap each other or closer to each other is conducive to the formation of tunneling effect,which is conducive to improving its conductive path;carbon fiber can also improve the flexural strength of cement-based composites.2)Carbon nanotubes present chaotic distribution and good dispersion in cement-based composites,which is conductive to improve the electrical conductivity,and carbon nanotubes can improve flexural strength just like carbon fibers.3)The fracture surface is smoother and the internal structure is more dense,when graphite is added compared with the plain cement-based composites.4)Compared with the single doping,the conductive network of conductive cement-based composites can be further optimized.(4)Experimental research on electro-thermal property of conductive cement-based composites.Based on the single and compound conductive material cement-based composite materials,the cement-based composites plates were prepared,and the conductive cement-based composites were tested by indoor heating and cooling tests,to simulate the electro-thermal properties in engineering applications.The results show that:The surface and internal temperature of the conductive cement-based composites increased greatly after applying voltage.The heating rate of cement-based composites at the early stage of electrification is obviously higher than that at the later stage,and the heating effect is obviously better than that of plain cement-based composites.After turning off the power supply,the temperature of the conductive cement-based composite material drops obviously,and the cooling rate in the initial stage is obviously higher than that in the later stage.After turning off the power supply for 500 min,the temperature values of each point on the surface and inside tend to be consistent and close to room temperature.Comprehensive analysis the mechanical properties,electrical conductivity and microstructure of conductive cement-based composites,choose compound carbon nanotubes,steel fibers,graphite cement-based composite,the content of each conductive material is0.175 Vol.%,0.6Vol.%,4Vol.%,cement-based composite materials compounded conductive materials have good electrical heating performance and can be used to melt ice and snow on roads and bridges in winter.