Effect Of Freeze-thaw Cycles On Properties Of Steel Fiber Graphite Electrothermal Concrete

Electrothermal concrete is a new type of intelligent concrete,which has been applied in road snow melting and deicing.As both pavement material and heating functional material,the durability of electrothermal concrete not only includes mechanical properties,but also electrical and thermal properties.In this paper,based on freeze-thaw experiments,the mechanism of freeze-thaw damage and the effects of freeze-thaw on mechanical,electrical and thermal properties of steel fiber graphite electrothermal concrete are studied.The main research contents and achievements of this paper are as follows:(1)It is found that the freeze-thaw fatigue damage of steel fiber graphite electrothermal concrete conforms to the low cycle fatigue damage theory.Based on the freeze-thaw damage mechanism of concrete,the freeze-thaw damage mechanism of steel fiber graphite electrothermal concrete is put forward,including the damage hypothesis of conductive phase material caused by the structural damage of graphite and a series of chemical changes of steel fiber,the damage hypothesis of thermal stress caused by the stiffness change of composite material and the mismatch of thermal expansion coefficient.The micro-morphology of steel fiber graphite electrothermal concrete was characterized by means of scanning electron microscopy,and the damage of conductive phase materials by freeze-thaw cycles was studied from the micro-point of view.(2)The change of mass loss rate,dynamic elastic modulus loss and compressive strength of steel fiber graphite electrothermal concrete after different freeze-thaw cycles is studied.The results show that they are negatively correlated with freeze-thaw cycles,and the freeze-thaw cycles resistance of steel fiber graphite electrothermal concrete is better than that of plain concrete under this mix ratio.(3)The electrical properties of steel fiber graphite electrothermal concrete show that its resistivity decreases with the increase of voltage,but with the increase of freeze-thaw cycles,the change rate of resistivity decreases gradually.Under the same voltage,the resistivity is negatively correlated with the number of freeze-thaw cycles in 0-100 cycles,and positively correlated with the number of freeze-thaw cycles in 100-300 cycles.(4)According to the analysis of Engineering examples,steel fiber graphite electrothermal concrete undergoes different freeze-thaw cycles,and its current presents three stages: slow growth stage,rapid growth stage and stable stage.With the increase of freeze-thaw cycles,the current of steel fiber graphite electrothermal concrete decreases at the same voltage.(5)According to ANSYS finite element simulation analysis,under the same input power,the surface temperature and internal temperature of steel fiber graphite electrothermal concrete decrease with the increase of freeze-thaw cycles,and the change of surface temperature and internal temperature decreases,and gradually eases.(6)Under the same power,the number of freeze-thaw cycles is negatively correlated with the total heat production,positively correlated with the heat absorbed by the concrete itself,and negatively linearly correlated with the effective utilization rate of heat.