Study Of Dielectric Properties And Dielectric Modeling Of Non-Water Reactive Polyurethane Injection Materials

The polymer grouting technology utilizes a non-water-reactive polyurethane twocomponent grouting material that finds extensive application in various infrastructure projects like roads,dams,high-speed rail ballastless tracks,tunnels,and underground pipelines.To assess the effectiveness of the grouting process,nondestructive testing through a ground penetrating radar system proves advantageous due to its efficiency,speed,and ability to preserve the original structure without causing any damage.The construction of dielectric models and the utilization of electromagnetic waves for nondestructive testing can aid in comprehending the dielectric properties of polyurethane grouting materials.This understanding can then be applied to enhance the safety of construction projects such as dams and embankments.Polyurethane materials are foam-like materials created by a reaction of a two-component material mixture.Their macrostructure is dependent on the microstructure and morphology,making it necessary to analyze the microstructure of polyurethane materials to provide a reference for subsequent analysis of their dielectric properties.This paper aims to the dielectric properties of polyurethane grouting materials.To achieve this,a vector network analyzer with a coaxial probe was utilized to measure the dielectric constant and dielectric loss values of polyurethane specimens under various density and frequency conditions.The conductivity was then calculated from the dielectric loss values.Based on the conventional effective dielectric model,the dielectric model of polyurethane injection materials was constructed.The main research contents and conclusions of this paper are as follows:(1)This paper presents an analysis of electron microscope test results which reveal that polyurethane material exhibits a pore-bubble structure on a microscopic scale.This structure comprises of multiple pore bubbles in close contact,each of which exists independently and is dispersed.When the material density is low,the pore bubble shape is somewhere between round and polygonal,and the contact surface between each pore bubble is significant.As density increases,the shape of pore bubbles gradually transitions from polygonal to elliptical and circular,resulting in a decrease in the contact surface between them.Additionally,the diameter of pore bubbles decreases while the free space increases.The wall thickness of pore bubbles between adjacent pores also increases,contributing to a decrease in material porosity with increasing density.(2)In this study,we measured the dielectric constant of polyurethane specimens with varying densities using an automatic frequency sweep.The sweep was conducted at 50 Hz intervals within the frequency range of 500 MHz to 6000 MHz.Upon analyzing the frequency and dielectric test results,we discovered that: As the frequency increases,so does the conductivity.However,the dielectric constant and dielectric loss values decrease slightly.This pattern remains consistent across specimens of varying density.Furthermore,the higher the frequency and density,the lower the value of dielectric loss.Furthermore,it is worth noting that even the specimens with the highest density exhibited a conductivity of no more than 0.1.This suggests that the non-water reactive polyurethane grouting material,possesses extremely low electrical conductivity.An analysis of the density and dielectric test data revealed that the dielectric constant tends to increase as the specimen density decreases.This relationship can be accurately modeled by a quadratic polynomial.Using the fitting formula,we can determine that the dielectric constant of the gas phase approaches a value of 1 as the density tends towards 0.This value is consistent with the dielectric constant of most gases.(3)To further investigate the dielectric properties of non-water reactive polyurethane grouting materials,this paper presents a dielectric model based on four conventional effective dielectric models for hole-type materials.Through comparison with improved model calculations,it is discovered that the dielectric constants of the materials are strongly correlated with their porosity.After comparing the results of dielectric constant calculations using the parallel model,Lichtenecker-Rother model,Clausius-Mosotti model,and Maxwell-Garnett model,it can be concluded that the Maxwell-Garnett model exhibits superior accuracy in predicting the dielectric constants of non-water-reactive polyurethane materials.This model produced the lowest average relative error of 0.39%.Therefore,the improved Maxwell-Garnett model is better suited as a predictive dielectric model for non-water-reactive polyurethane grouting materials in high frequency and low density states.