Electrical Conductivity And Smart Properties Of Fe_1-δO Waste Mortar

Smart concrete has self-diagnosis, adaptive function, and damage self-repairing, so it can be used to monitor structure health and detect injury. Carbon fiber, graphite, carbon black, and steel fiber can be used to make smart concrete. But carbon fiber is high in price, low in dispersion and complicate in surface treatment. With the increasing of graphite and carbon black content, the compressive strength of conductive concrete decreases markedly. Steel fibers are easy to be oxidized, so the electrical resistivity of steel fiber reinforced concrete increase with age. The above problems hamper the application of conductive concrete. So it is very important to study the conductive smart concrete which has electrical conductivity, compressive sensitivity, and good mechanical properties.Fe_1-δO includes FeO, Fe₂O₃ and Fe₃O₄, all of which are nonstoichiometric compounds and have structure defect, so Fe_1-δO have the properties of semiconductor. The electrical resistivity of FeO and Fe₃O₄ are 5×10^-2Ω·cm and 4×10^-3Ω·cm respectively, which are basically the same as that of pitch-based carbon fiber. The content of Fe_1-δO is over 30% in the magnetic fly ash and steel slag, so the above-mentioned two kinds of waste may be used as conductive materials to make electrical conductive mortar. Using the magnetic fly ash and steel slag as the conductive materials, the price of the waste mortar, which is made by the technique in making normal mortar, is very low. When the waste content is beyond the percolation threshold, they have good conductivity, compression sensitivity and excellent mechanical properties. With the increasing of waste content, its electrical resistivity is close to that of CFRC and graphite concrete to which the coarse aggregate is added; while its compression sensitivity is better than the above two types of concrete.Fe_1-δO waste conductive mortar is a smart material. The author analyzes the mechanism of conductive and compression sensitivity. On the basis of the study of electrical conductivity and smart properties, the author first studies its conductive properties and smart properties under different loading conditions, and then studies some factors that influence the electrical conductivity and smart properties, including the water content, temperature, content of waste, curing regime. Main results are as follows:â‘ The electrical conductivity and compressive sensitivity of conductive mortar increase with the increasing of waste content. With the age increasing, the electrical conductivity decreases and the compressive sensitivity increases.â‘¡With the increasing of electrical conductivity and age, the influences of water content, temperature, curing regime and specimen size are weakening gradually.â‘¢The loading modes have great influence on the compression sensitivity of conductive mortar. Under the pressure, conductive mortars have good compression sensitivity.â‘£Under the uniaxial loading, with the increasing of loading rate, the compression sensitivity increases.⑤Under the triaxial loading, with the increasing of confining pressure, when under relatively low stress, the compression sensitivity weakensâ‘¥Under the recycling loading, when the maximum stress is within the elastic limit, the resistivity of mortar changes periodically with the stress changing, but the change of resistivity lags behind that of the stress.On the basis of the above examination, the author studies the erosion environment condition which influences the electrical conductivity and smart properties of mortar, including freeze-thaw cycle, dry-wet cycle, acid, alkali, salt and carbonation. At the same time, the author studies the relationship of electrical conductivity and smart properties changing with the mechanical properties.Freeze-thaw, acid and sulfate have remarkable adverse influences on the electrical conductivity, compressive sensitivity, and mechanical properties. After dry-wet cycles, the electrical conductivity and compressive sensitivity decrease slowly. After long-term immersion into alkali solution and salt solution, the electrical conductivity and compressive sensitivity increase remarkably. Carbonation has no effect on the electrical conductivity or compressive sensitivity. The change in electrical conductivity is remarkably related to the mechanical properties. Therefore by monitoring the resistivity change of waste mortar can reflect the change of mechanical properties. That indicates monitoring the resistivity change of cement-based materials can provide reference for evaluating the durability and injury of cement-based materials.