Investigations On The Composite Dielectric Model Of Cement Mixtures Considering The Effect Of Temperature

The dielectric properties of cement mixtures are a critical precondition for the application of ground-penetrating radar(GPR)to the nondestructive testing of cement concrete pavement,the accuracy of nondestructive testing and evaluation of concrete pavement based on GPR technology highly depends on the composite dielectric model of cement mixtures.Cement mixtures,as a kind of temperaturesensitive material,its dielectric properties will change with the change of temperature of pavement during its service time.The estalished composite dielectric models of cement mixtures pay less attention to temperature,therefore,investigations on the influence of temperature on the dielectric properties attaches great importance to promoting the nondestructive testing accuracy of GPR.Based on the problems above,the composite dielectric model of cement mixtures considering the effect of temperature have been researched and studied by the mothod of combining experiments and theoretical analysis.The main contents and conclusions can be drawn as follows:(1)The experimental investigations on the dielectric constant of cement mixtures and its single-phase medium were carried out,and the influence of frequency and tempearture on the dielectric characteristics of cement mixtures and its single-phase medium was analysed in this paper.The results show that the dielectric constants of limestone,cement mortar and cement mixtures will change with the change of frequency and their dielectric constants fluctuate smoothly within the testing frequency;temperature during experiments is reported to be a minor or negligible factor on the dielectric constant of air,which is taken as 1;The dielectric constants of limestone,cement mortar and cement mixtures increase with the increase of temperature in strong linear correlations(all the correlation coefficients are close to 1);(2)On the basis of the conception of structural abstraction and ciucuit theory in this paper,a new dielectric model suitable for cement mixtures is deduced.Compared with the classical models(Rayleigh model,Brown model,CRIM model and Looyenga model),the theoretical prediction values of this model are closer to the experimental testing values,which means the proposed model has higher accuracy and is more suitable to describe and characterise the dielectric properties of cement mixtues;(3)The concept of temperature influence coefficients α of cement mixtures is proposed,as per the changing law of the dielectric constants of cement mixtures,temperature influence coefficients are calculated,in the same time,based on the established dielectric model,a composite dielectric model considering the effect of temperature is established,compared with classical models,the resluts show that: the established dielectric model of cement mixtures considering the effect of temperature has higher accuracy,which can represent and predict the dielectric characteristics of cement mixtures at different temperature conditions more accurately.