Impedance Spectroscopy Of UHPC:Measurement,Interpretation,And Application

Ac impedance spectroscopy（AC-IS） is a significant electrochemical technology which can be mainly used to character the electrochemical property of materials with respect to the electrochemical properties and microstructure of the material. Since 1980 s when the AC-IS was used to Cement-based Materials Testing, it has been widely applied in the engineering for its non-destructive property. This work investigates the stray impedance correction method in the ACIS test, verifies the equivalent circuit of ultra-high performance concrete ACIS and analyzes the change of impedance parameter of ultra-high performance concrete.Based on the placement of wires and fixtures in the correction of stray impedance by AC-IS, a reference correction method of stray impedance is proposed. Results show that, in the test range of 15 MHz, comparing with results without stray impedance correction, the maximum error of fitting parameters of concrete specimens can be 69.61% in 3d and 75.58% in 210 d respectively. Comparing with the traditional impedance correction method, the maximum error of fitting parameters of concrete specimens can be 50% and 10.58%. However, the contact resistance and shorting wire position in reference correction method has slight influence on the results and can thus be neglected to guarantee the analysis of AC impedance dataThe change of fineness and content of bulk component quartz sand of cement-based materials can induce the two circles in the impedance spectroscopy, which indicates that the fineness and content of quartz sand and hydration age can change the bulk microstructure, resulting into the separation of matrix and impedance response of pore structure. The results indicate that the mortar specimens have both the bulk property and pore structure property, however the R（RC） can only reflect an interface which and not be applied in the impedance analysis of cement-based materials. The two circles also occur when soak the cement specimens with 0.15, 0.3 and 0.45 water-cement ratio in the alcohol and tap water. It represents that changing the pore solution to change the pore structure characteristics can also promote the separation of matrix and pore structure. Fitting the impedance spectroscopy of cement paste specimens soaked in the alcohol using（R₁C₁）（R₂C₂） and（R₁C₁（R₂C₂）） circuit, results show that the fitted character bulk resistance R₂ by（R₁C₁）（R₂C₂） is smaller than character pore resistance R₁ by（R₁C₁）（R₂C₂）, which is not consistent with the microscopic structure of concrete. However, the fitted parameter by（R₁C₁（R₂C₂）） circuit agrees well with microscopic structure of concrete indicating it application of Impedance spectroscopy analysis of ultra-high performance concreteIn the research the AS-IC of ultra-high performance concrete is tested and analyzed using（RC（RC））. Results show that with the increase of steel fiber content, bulk resistors R₁ and discontinuous pores R₂ will decrease. Comparing with the non-fiber specimen, the R₁ and R₂ will significantly decrease. With the increase of curing period, no matter how much steel fiber content, concrete matrix resistance R₁ and R₂ will increase and then decrease, reaching to the peak at 56 d. The change of bulk resistor R₁ in the hydration 3-56 d fits well with the positive linear relationship. As the fiber content increase, the slope of the fitted curve decreases exponentially. The change pattern of R₂ and R₁ is similar expect for the concrete with 2% fiber whose R₂ will always increase. With the increase of fiber content, the increase rate of non-communication hole will decrease exponentially. In the hydration 3d, 7d, 14 d and 28 d, compressive strength of concrete specimens with different fiber content will decrease exponentially with the increase of non-communication hole resistor R₂With the increase of fiber content, constant phase element of ultra-high performance concrete CPE₁ and constant phase element of discontinuous pores CPE₂ increase. In the hydration 3-14 d and 14-9d, the change of CPE₁ of different fiber content concrete has the linear negative relation and negative power function relation respectively with the increase of period. The change of CEP2 of discontinuous pores also linearly increase with the period. The increase rate of CPE₂ also has a positive exponentially relationship with fiber contentThe change pattern of impedance parameters of ultra-high performance concrete specimens with different shape and length is similar. When the steel fiber content is more than 1%, the R₁ of concrete with end-hooked steel fiber is larger than that with wave steel fiber. With increase of the fiber content, the increase rate will increases gradually. The R₂ changes slightly with the fiber content for the two fiber types. For the concrete with different length of steel fiber, as the fiber content increases, R₁ decreases, however, R₁ of concrete specimens with shorter fiber is larger than that with longer fiber. R₂ of discontinuous pores resistor is gradually reduced. When the fiber content is between 1% and 3%, the discontinuous pores resistor R₂ is essentially the same. When the fiber content is 2%, the discontinuous pores resistor R₂ of concrete specimens with shorter fiber is larger than that with longer fiber...