Abstract
The formula describing the relationship between the dielectric constant of a composite and the dielectric constants or volume rates of its components is called a dielectric model. The establishment of a cement concrete dielectric model is the basic and key technique for applying electromagnetic wave technology to concrete structure quality testing and internal damage detection. To construct the dielectric model of carbon nanofiber reinforced concrete, the carbon nanofiber reinforced concrete was measured by the transmission and reflection method for dielectric constant ε, and ε,, in the frequency range of 1.7~2.6 GHz as the fiber content was 0, 0.1%, 0.2%, 0.3% and 0.5%. Meanwhile, concrete was considered as a composite material composed of three phases, matrix (mortar), coarse aggregate (limestone gravel) and air, and the dielectric constants and volume rates of each component phase were tested. The Brown model, CRIM (Complex Refractive Index Model) model and Looyenga model commonly used in composite materials were modified based on the experimental data, suitable dielectric models of carbon nanofiber reinforced concrete were constructed, and a reliability check and error analysis of the modified models were carried out. The results showed that the goodness of fit between the calculated curves based on the three modified models and the measured curves was very high, the accuracy and applicability were very strong and the variation rule for the dielectric constant of carbon nanofiber concrete with the frequency of electromagnetic wave could be described accurately. For ε, and ε,,, the error between the dielectric constant calculated by the three modified models and the corresponding measured values was very small. For the dielectric constant ε,, the average error was maintained below 1.2%, and the minimum error was only 0.35%; for the dielectric constant ε,,, the average error was maintained below 3.55%.
Highlights
The formula describing the relationship between the dielectric constant of a composite and the dielectric constants or volume rates of its components is called a dielectric model [1,2]
The mix proportion of carbon nanofiber reinforced concrete was as shown in Table 1, where PC
The transmission and reflection method was used to measure the dielectric constants of carbon nanofiber reinforced concrete as the fiber content was 0, 0.1%, 0.2%, 0.3% and 0.5%
Summary
The formula describing the relationship between the dielectric constant of a composite and the dielectric constants or volume rates of its components is called a dielectric model [1,2]. The dielectric properties and main influence factors of composites can be understood in detail, so as to support relevant theoretical analysis [3,4,5]. There have been many studies on concrete mix proportion, relevant mechanical properties, durability, constitutive relation and dielectric models [12,13]. Scholars all over the world have conducted many studies on the dielectric model of cement concrete based on temperature and frequency, with the chloride effect considered, but there are few reports on the dielectric model of carbon nanofiber reinforced concrete [32,33,34,35]. This study utilized the transmission and reflection method to test the dielectric constant of carbon nanofiber reinforced concrete under different fiber content in the frequency range of 1.7 to. 2.6 GHz and established a modified dielectric model for the Brown model, CRIM model and Looyenga model based on the experimental data
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