Ground Penetrating Radar Test Research Articles

Applications of geophysical methods in agriculture and their potential in Vietnam

Geophysical methods are very popular in Vietnam and have been applied for several decades in deep-earth investigations such as geological mapping, mineral resource searching, and especially oil and gas exploration. In the world, they have proven to be great tools in agriculture as well for soil characterization and monitoring thanks to their notable advantages including rapid data acquisition, large data coverage, high data density, non-destructive and inexpensive survey implementation. However, in Vietnam, the applications of geophysical methods in agriculture have received little attention probably due to the lack of suitable equipment and data processing techniques. This article gives an overview of popular geophysical methods being applied in agriculture in several countries to characterize and monitor soil properties such as moisture, salinity, density, texture, structure, porosity, etc. The main uses of each method are summarized, and relevant publications are given for reading recommendations with the aim of suggesting similar applications in Vietnam. Accordingly, Ground Penetrating Radar (GPR) and Electromagnetic Induction (EMI) are the most versatile with minimum field crew for data acquisition. They should be prioritized to try in Vietnamese agriculture. Since EMI equipment is not currently available in Vietnam, only a GPR test survey was implemented in the Agricultural Academy experimental field by the authors of Hanoi University of Mining and Geology. The preliminary result shows that the biggest challenge is to find reliable techniques to accurately infer soil properties from measured geophysical parameters, which have no explicit relationship with soil properties. Noise suppression is another problem that needs to be addressed to ensure sufficient data quality.

Numerical modelling of bridge deck reinforcement corrosion based on analysis of GPR data

AbstractThis study explores the impact of corrosion on Ground Penetrating Radar (GPR) responses through practical experiments and numerical modelling, focusing on rebar diameter reduction, corrosion product layer thickness, crack formation and corrosion product filling in vertical and transverse crack. Practical experiments involved GPR testing of reinforced concrete slab. By analyzing B-scans we identify areas with moderate and severe corrosion. Numerical modelling using the Finite Difference Time Domain (FDTD) Method to model GPR signal propagation in a concrete bridge deck with corrosion is applied. Key finding includes a significant 26.70% increase in reflected wave amplitude when corrosion product filling in vertical crack increased by 400%, highlighting its extensive effect on signal GPR propagation. Reduced rebar diameter led to a 9.79% amplitude decrease and a 0.06 ns arrival time delay. Increased corrosion product layer thickness primarily affected arrival time with a 0.06 ns extension but significantly amplified GPR signal amplitude. These findings offer insights for improving GPR based corrosion detection and assessment methods, leading to more robust systems for concrete bridge deck inspection and maintenance. This paper contributes to understanding how corrosion affects the signal that is detected by GPR. This information can be used to improve the way that we manage and assess corrosion in concrete bridge deck.

Geological detection of hard rocks by GPR and signal time-frequency characteristics analysis in urban underground trenchless construction

Abstract The hard rocks in the stratum can pose safety risks and hinder the progress of urban underground tunnel construction using shield and jacking methods, thereby reducing construction efficiency and increasing construction costs. This paper utilizes wavelet scale energy spectrum, wavelet packet theory and statistical methods to conduct research on the detection of special geological formations such as hard rocks and voids, as well as the analysis of their signal time-frequency characteristics based on the ground-penetrating radar (GPR) technique. On the basis of calibrating the permittivity of different types of rock blocks, we established a forward model for detecting hard rocks and voids, and the simulated signals were analyzed in the time and frequency domains. Subsequently, laboratory experiments were conducted to perform GPR tests on different types of hard rocks in natural and water-saturated states and voids, to explore the time-frequency characteristics, frequency band energy variations, and statistical patterns of typical single-trace signals. The results show that the granite detection signal contains more low-frequency components, the sandstone detection signal contains more medium-low frequency components, while the limestone detection signal contains more medium-high frequency components in their natural state; the signal from the karst cave has relatively more low-frequency components than the signal from the empty cavity. The geometric shape of the rock has no influence on the dominant frequency and time-frequency distribution of its reflection signal. Generally, rocks with higher rebound values (hardness) also exhibit larger variance and standard deviation in frequency band energy. The research has important theoretical significance and practical value for the measurement and assessment of special geological features such as hard rocks and voids in urban underground trenchless construction.

Applicability of available NDT methods for damage detection in concrete elements reinforced or strengthened with FRP

The application of Fiber Reinforced Polymer (FRP) materials in concrete structures has been rising due to their several advantages, including lightweight, high tensile strength, ease of installation, and corrosion resistance. They have been mostly implemented for strengthening and repairing existing structures in the form of an externally bonded system, i.e., sheet, jacket, near surface mounted. Furthermore, they have been recently utilized as internal reinforcement of concrete elements in the form of strands, bars, tendons, etc. Although higher durability and performance are associated with the FRP material in some aspects compared to steel, concerns remain regarding damages and defects in this material, many of which are related to their unique features. Importantly, debonding of FRP materials from a concrete surface or within a concrete element has always been an issue resulting in the premature failure of the structure. To this end, concrete elements strengthened or reinforced with FRP materials has to be inspected periodically to detect potential issues and hence prevent any premature failures. This study first determines all possible or potential damages and anomalies attributed to FRP reinforced/strengthened concrete (FRP-RSC) elements. It then investigates Non-Destructive Testing (NDT) methods that can be applicable to the inspection of FRP-RSC elements from a literature survey of past studies, applications, and research projects. Furthermore, this study evaluates the ability of two of the most commonly used NDT methods, Ground Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU), in detecting FRP bars/strands embedded in concrete elements. GPR and PAU tests were performed on two slab specimens reinforced with GFRP (Glass-FRP) bars, the most commonly used FRP bar, with variations in their depth, size and configuration, and a slab specimen with different types of available FRP reinforcements. The results of this study propose the most applicable methods for detecting FRP and their damage/defects in FRP-RSC elements. This study further investigates the feasibility of two new methods for improving the detectability of embedded FRP bars. By providing the inspection community with more clarity in the application of NDT to FRP, this study offers means for verifying the performance and, therefore, help the proliferation of FRP materials in concrete structures.

Comparative analysis of ultrasonic testing and ground penetrating radar (GPR) for concrete structure evaluation

Nondestructive testing of concrete structures plays a vital role in ensuring its safety and service life. In this paper, two common nondestructive testing techniques for concrete structures, ultrasonic testing and ground penetrating radar testing, are compared and analyzed. The purpose of this study was to evaluate and compare the effectiveness, limitations, and applicability of these two methods for detecting common defects in concrete, such as cracks and corrosion of rebar. But both ultrasonic detection and ground-based radar have their own advantages and limitations. In some cases, the two methods can be combined to provide complementary advantages and improve the accuracy of the assessment.

Feasibility of Conventional Non-Destructive Testing Methods in Detecting Embedded FRP Reinforcements

Fiber-Reinforced Polymer (FRP) bars/strands are the most promising alternative to their steel counterparts for reinforcing concrete elements due to their resistance to corrosion, lighter weight, higher strength and better durability. However, very limited research has been conducted in relation to non-destructive testing (NDT) methods that are applicable to damage detection in FRP bars or the detection of FRP reinforcements embedded in concrete. The ability to assess the condition of the relatively new and unique FRP reinforcements will increase the confidence of the construction industry in their use as a reliable substitute for steel reinforcements. This paper investigates the ability of two of the most commonly used NDT methods, Ground Penetrating Radar (GPR) and Phased Array Ultrasonic (PAU), in detecting FRP bars/strands embedded in concrete elements. GPR and PAU tests were performed on two slab specimens reinforced with GFRP (Glass-FRP) bars, the most commonly used FRP bar, with variations in their depth, size and configuration, and a slab specimen with different types of available FRP reinforcements. The results show that GPR devices can detect GFRP bars/strands and CFRP (Carbon-FRP) strands to some extent, and their detectability increases with the increase in their antenna center frequency. On the contrary, PAU is only capable of detecting GFRP and CFRP strands. The results of this paper also emphasize the need for further research and developments related to NDT applications to embedded FRP bars.

FROM THE EXPERIENCE OF THE GEORADAR SURVEY ON THE SITE LOCATION OF THE CHURCH OF THE NATIVITY OF THE VIRGIN IN THE VILLAGE MALA PETRIKIVKA, DNIPROPETROVSK REGION

Problem statement. Ground-penetrating radar tests as a component of territory geophysical investigations are also used in the historical reconstruction − in our case, on the site of the Church of the Nativity of the Virgin in the village of Mala Petrikyvka (Dnipropetrovsk region). A ground-penetrating radar survey was conducted, preceded by a thorough critical analysis of historical sources. Measurements were done using MALA GPR with operating frequencies of 250 MHz and limited to 800 MHz. The purpose of the article. In order to critically reviewing the historical myth that existed for a long time around this architectural monument of the 18th-19th centuries, it was necessary to uncover underground cavities, as well as to conduct a search for hidden ancient structures both in the areas adjacent to the church building and directly inside the church itself. Conclusions. As a result of the conducted research, the features of surface and buried building structures attributed to the dry and moistened loess soils of this territory on GPR profiles were revealed. In areas of moistened loess soil, any objects at working depths at a frequency of 250 MHz were not displayed by the device − due to a high degree of signal attenuation. GPR profiles of this area did not reveal any significant anomalies, which indicate the presence of fairly voluminous linear underground structures, which is confirmed by the survey of the adjacent territory. The conducted investigations can be considered only primary and involve further, more detailed, studies on selected areas, including inside the building itself. Since it was not possible to find information about the previously performed ground-penetrating radar surveys on the territory of the church and the surrounding area, the surveys carried out by PSACEA can be considered the first of their kind. They are especially valuable in view of the fact that a complete restoration of the temple is planned.

Testing of Structural Integrity of U-Shaped Sheet Pile in Canal Engineering Using Ground Penetrating Radar

Compared with other piles with the same cross-sectional area, “U-shaped” structural section sheet pile can increase the moment of inertia of the structure’s section. Due to the large excavation depth of the open section of the “Yin Jiang Ji Huai” river canal project in Anhui province, China, the unprotected excavated inclined canal slope covers a large land area, which results in the current situation of high housing demolition costs and a shortage of land resources in densely populated areas. In this study, the non-destructive testing of a U-shaped sheet-pile wall to protect the vertical slope of the underwater expansive soil in the canal project is studied, which is of great significance in reducing the construction area and minimizing the cost of construction. It is necessary to test the structural integrity of the U-shaped sheet pile, which is also vital to ensuring the whole project quality. Ground penetrating radar (GPR) is used to detect the structural integrity of the U-shaped sheet pile in expansive soil. On the basis of identification and conversion of the original GPR data format, the processing methods based on the time-varying automatic gain and wavelet analysis are implemented. This case study proves that the GPR testing method is effective to estimate the quality of the U-shaped sheet pile.

Development of a Simulation-Based Approach for Cold In-Place Recycled Pavement Moisture-Content Prediction Using Ground-Penetrating Radar

Ground-penetrating radar (GPR) recently has been used for quality control and quality assurance of the asphalt concrete (AC) pavement-construction process. The objective of this study was to investigate the feasibility of estimating, by using GPR, the moisture content in AC pavement. This application is particularly important for emulsion-stabilized cold in-place recycling (CIR) and cold central-plant recycling (CCPR), where monitoring the moisture content is necessary for deciding the timing of opening the road to traffic, overlay placement, or both. Four field tests were performed using GPR on CIR- or CCPR-treated AC pavement. A numerical simulation model of AC pavement with internal moisture was generated using the information from mix design, and virtual GPR tests were performed using the finite-difference time-domain (FDTD) method. After calibration, a moisture-prediction formula derived from the simulation model was used to correlate the dielectric constant predicted by GPR to the moisture content within cold recycled layers. The GPR signal was “denoised” by improving its stability and mitigating the measured-height mismatch. The in-situ moisture content was predicted using the proposed method and compared with field-collected samples. Results showed that the proposed method is effective in estimating CIR- and CCPR-layer moisture content. The variation of dielectric constants in field tests is also discussed. A testing protocol for predicting moisture content using GPR is suggested for CIR and CCPR pavement.

Factors Contributing to Fatigue Cracking in Flexible Pavements in Oklahoma: A Case Study Using Laboratory and Field Investigation and AASHTOWare Simulation

Abstract Fatigue cracking is one of the major structural distresses in flexible pavements. In this study, probable causes of fatigue cracking were investigated using field and laboratory testing and In this study, probable causes of fatigue cracking were investigated using field ang laboratory testing and AASHTOWare Pavement ME Design (PMED) simulations. Field tests including Ground Penetrating Radar (GPR), Falling Weight Deflectometer (FWD), and Dynamic Cone Penetration (DCP) were performed on a flexible pavement section of US 412 located in Noble County, Oklahoma. Also, asphalt cores and soil samples were collected for laboratory testing. The GPR test results revealed significant delamination in the asphalt layer. Also, the GPR images indicated that the disturbance zone was confined within the asphalt layer and cracks were generated from surface as well as from existing pavement layers below. The DCP and FWD test results indicated that the pavement section was not structurally adequate to support traffic and needed rehabilitation in the near future. The moduli of the asphalt layers were found to be quite low, indicating improper compaction during construction. Also, the densities of the top-lifts of the asphalt cores were found to be low. Moreover, the cracking resistance of the extracted asphalt cores was poor based on the Illinois flexibility index test results. Superpave Performance Grade of the extracted binder indicated excessive aging of the binder because of long exposure to the environment. The brittleness of mix resulting from aging was considered a potential contributor to fatigue cracking of the pavement at this site. A parametric study was conducted to understand the variation of fatigue cracking with the changes in input properties in PMED, namely pavement structural components and material properties. Pavement thickness, roadway densities, and layer moduli of existing underlying pavement were found as the most influential factors. The findings of the parametric study supported the findings of the field and laboratory investigation.

Analytical Models and Laboratory Measurements to Explore the Potential of GPR for Quality Control of Marble Block Repair through Resin Injections

This work aims to analyze theoretically and with laboratory tests the sensitivity of high-frequency GPR (Ground-Penetrating Radar) to resin injections used in the building and ornamental stone industries to repair marble blocks before final slab cutting. We simulate uniform fractures in the laboratory using small regular marble blocks and we compare the results of GPR tests with the analytical model of the thin bed reflections. We performed two series of GPR surveys with a 3 GHz antenna, progressively increasing the fracture thickness from 0.25 mm to 16 mm, to analyze the results on two simulated conditions: open fracture and repaired fracture. The repaired condition was simulated by substituting the resin layer with polyvinyl chloride (PVC) sheets because the permittivity of PVC is quite similar to the permittivity of epoxy resin. According to the analytical models, when a thin air-filled fracture is filled with resin, the received signal amplitude is expected to decrease by 33% (26% if resin is simulated with PVC). The results showed a very good match between the predictions and the real data observations when the fracture is thicker than 4 mm. Although the analytical and laboratory results show some deviations when the fracture is thinner than 4 mm, the qualitative trend of the amplitude variations is still consistent with the predictions and the 3 GHz antenna can resolve the change in the filling material down to the minimum tested thickness (0.25 mm). As a result, our findings validate the GPR method as a proper tool for nondestructive quality control of resin injections in marble fractures.

A Novel Multifrequency GPR Data Fusion Algorithm Based on Time-Varying Weighting Strategy

Ground-Penetrating Radar (GPR) technology plays an important role in near-surface geophysical survey. Usually, the dataset acquired by higher frequency antenna has higher resolution but limited penetration depth; while the dataset collected by lower one has deeper penetration depth but lower resolution. It is necessary to fuse several different frequency datasets into a composite displayed profile to get a trade-off between penetration depth and resolution. In such case, we propose a novel multi-frequency GPR data fusion method and test it on the data acquired from a limestone quarry in the Taihang Mountains of China. In our algorithm, time-varying weighting factors are calculated by virtues of a sliding time window, i.e. designed with segmented signals. According to this approach, we can achieve better local characteristics of the signal as well as the smoothness of the signal waveform. The results show that the spectrum bandwidth of the fused signal is broadened, and the fusion profile significantly improves the imaging of internal structures for limestone on different scales.

Development of Condition Assessment Index of Ballast Track Using Ground-Penetrating Radar (GPR).

The condition of the ballast is a critical factor affecting the riding quality and the performance of a track. Fouled ballast can accelerate track irregularities, which results in frequent ballast maintenance requirements. Severe fouling of the ballast can lead to track instability, an uncomfortable ride and, in the worst case, a derailment. In this regard, maintenance engineers perform routine track inspections to assess current and future ballast conditions. GPR has been used to assess the thickness and fouling levels of ballast. However, there are no potent procedures or specifications with which to determine the level of fouling. This research aims to develop a GPR analysis method capable of evaluating ballast fouling levels. Four ballast boxes were constructed with various levels of fouling. GPR testing was conducted using a GSSI (Geophysical Survey Systems, Inc.) device (400, 900, 1600 MHz), and a KRRI (Korea Railroad Research Institute) GPR device (500 MHz), which was developed for ballast tracks. The dielectric permittivity, scattering of the depth (thickness) values, signal strength at the ballast boundary, and area of the frequency spectrum were compared against the fouling level. The results show that as the fouling level increases, the former two variables increase while the latter two decrease. On the basis of these observations, a new integrated parameter, called a ballast condition scoring index (BCSI), is suggested. The BCSI was verified using field data. The results show that the BCSI has a strong correlation with the fouling level of the ballast and can be used as a fouling-level-indicating parameter.

Multi-sensor data collection and fusion using autoencoders in condition evaluation of concrete bridge decks

This paper presents a multi-sensor data collection and data fusion procedure for nondestructive evaluation/testing (NDE/NDT) of a concrete bridge deck. Three NDE technologies, vertical electrical impedance (VEI), ground-penetrating radar (GPR), and high-definition imaging (HDI) for surface crack detection, were deployed on the bridge deck. A neural network autoencoder was trained to quantify the relationship between VEI and GPR results using the data collected at common positions. This relationship was then used for fusion of VEI and GPR data to increase the reliability and spatial resolution of the NDE measurements and to generate a data-fused condition map that showed novel characteristics. Threshold values for VEI and GPR tests were obtained and used to determine the color scale in the fused map. Surface cracks identified from HDI show reasonable agreement with the deterioration areas on the data-fused condition map. Chloride concentration measurements on sound and deteriorated areas of the deck were consistent with the NDE results.

Validation of nondestructive methods for assessing stone masonry using artificial neural networks

The aim of this study is to deepen the technical and scientific knowledge related to the characterization of granite masonry based on geophysical tests, mechanical techniques, and neural networks. We used a nondestructive test method to characterize traditional stone masonry and further obtained data on the mechanical parameters of the elements. Historic buildings are typically constructed with stone masonry and make up the urban heritage. The maintenance and rehabilitation of historic buildings are crucial for maintaining interest in history, owing to the historical and cultural values of such buildings. The preservation of buildings classified as historical and cultural heritage is of collective interest, as they mark the history of society. Because the research object is considered a traditional structure, the use of destructive test techniques is discouraged. Thus, a mechanical characterization simulation tool using artificial neural networks (ANNs) was developed and applied to traditional granite walls. This database was developed through ground-penetrating radar (GPR) and sonic tests to characterize wall samples built. The walls were analyzed in a controlled environment, and the elastic modulus was used in response to the ANNs. Two case studies representing traditional granite masonry buildings in Portugal were evaluated through nondestructive characterization tests. For the Mancelos church and Miguel Bombarda Street building, ANNs were applied based on the sonic and GPR test results. The feasibility of using ANN simulation tools for characterizing traditional and historic buildings constructed with granite stone masonry was demonstrated.

A 0.1–4.0-GHz Inductorless Direct-Sequence Spread-Spectrum-Based Ground-Penetrating Radar System-on-Chip

This letter presents a 0.1-4.0-GHz broadband serial direct-sequence spread-spectrum (DS/SS)-based inductor-free ground-penetrating radar (GPR) system-on-chip (SoC). A time-domain digital correlation-based time-of-flight measurement is employed for radar ranging instead of using a frequency chirp or pulse, which allows a higher degree of flexibility. With no conventional RF up/down conversion present, the radar offers complete programmability over frequency and bandwidth (BW) up to 4.0 GHz. In-field GPR test with actual rover prototype is performed to validate the capability and characterize the overall performance of the DS/SS radar system. Implemented in 28-nm CMOS, the demonstrated prototype radar SoC offers a fine resolution of 3.75 cm and consumes 46.2 mW from 1-V supply. This makes it suitable for low-power applications such as planetary exploration.

Application of Ground-Penetrating Radar for Living Trees Detection

In order to evaluate the potential hazards, researchers are working on revealing the inner structural of a living trunk using different diagnostic techniques. Nondestructive techniques (NDTs), such as stress wave method and ultrasonic wave method, have become increasingly convenient and economical in trees detection. To improve forest management and to prevent collapses of trees, it is necessary to investigate the internal part of tree trunks. In order to do it non-invasively, ground-penetrating radar (GPR) appears as a promising inspection device. Each of these NDTs has its pros and cons. Among all, the GPR is capable of multiple measurements with hardly any damage to the body of a tree, perfect for investigations on roots and trunks of living trees. 15 camphor trees are selected and subject to GPR testing for the study. The results of inductive method and GPR wave signals indicate that the GPR image shows “wavy” features when an eccentric void is found inside a tree, meaning that the travel time is the shortest for the return signals when the antenna is closest to the void. However, GPR wave signals appear to be discontinuous and fluctuate when there are irregular cavities. The signal time is defined by using the metal plate to generate strong reflection in the case of on-site monitoring. The internal condition of tree trunk is usually tested based on detecting 2D image of tree trunk by the stress wave method, as to confirm that the application of GPR is feasible to detect the trunk of camphor tree. The method proposed in this paper can realize the accurate localization and imaging distribution of the internal defects of the trees by the radar wave scanning images.

Application of Ground Penetrating Radar in Detecting Deeply Embedded Reinforcing Bars in Pile Foundation

Ground penetrating radar (GPR) has been widely used for nondestructive testings in civil engineering. However, the GPR has not been adequately applied in detecting deeply embedded reinforcing bars, which is usually difficult to be revealed in radar image due to the wave interference and attenuation in large depth penetration. This study presents a new approach for the GPR detection of deeply embedded reinforcing bars in the reinforced concrete pile foundation. The aim of the GPR survey is to determine the existence and the depth of internal reinforcing bars in the pile foundation for solving engineering dispute. Low centre frequency antenna was used in GPR field testing to obtain the reflected raw data. Optimized procedures of digital filtering techniques were applied to process the GPR raw data. The deeply embedded reinforcing bars are revealed in the radar image after the field testing and postprocessing procedures. The depth of the reinforcing bars was estimated based on the hyperbola match method. The GPR test results were validated by the excavation of the pile foundation. The low centre frequency antenna has been found to be essential to obtain the reflected wave signals of deeply embedded reinforcing bars. The optimized processing procedures is useful to identify and display the reinforcing bars in radar image. The combination of low centre frequency antenna and the postprocessing procedures make the detection of deeply embedded reinforcing bars feasible. The proposed GPR testing method has been found to be effective to estimate the depth of deeply embedded reinforcing bars, which provides the key information for solving engineering dispute.

Estimation of flexible pavement structural capacity using machine learning techniques

The most common index for representing structural condition of the pavement is the structural number. The current procedure for determining structural numbers involves utilizing falling weight deflectometer and ground-penetrating radar tests, recording pavement surface deflections, and analyzing recorded deflections by back-calculation manners. This procedure has two drawbacks: falling weight deflectometer and ground-penetrating radar are expensive tests; back-calculation ways has some inherent shortcomings compared to exact methods as they adopt a trial and error approach. In this study, three machine learning methods entitled Gaussian process regression, M5P model tree, and random forest used for the prediction of structural numbers in flexible pavements. Dataset of this paper is related to 759 flexible pavement sections at Semnan and Khuzestan provinces in Iran and includes “structural number” as output and “surface deflections and surface temperature” as inputs. The accuracy of results was examined based on three criteria of R, MAE, and RMSE. Among the methods employed in this paper, random forest is the most accurate as it yields the best values for above criteria (R = 0.841, MAE = 0.592, and RMSE = 0.760). The proposed method does not require to use ground penetrating radar test, which in turn reduce costs and work difficulty. Using machine learning methods instead of back-calculation improves the calculation process quality and accuracy.

Asphalt Layer Density and Air Voids Content: GPR and Laboratory Testing Data Reliance

The assurance of asphalt pavement layer compaction, expressed by ratio between field and laboratory bulk density and air voids content, is one of the main criteria of the durability of asphalt road pavement. Destructive measures should be applied and cores should be taken from the asphalt pavement seeking to determine the representative compaction level of the constructed asphalt layers. New methods are constantly being sought for fast, non-destructive and accurate asphalt layer density and air void determination on road. Ground Penetrating Radar (GPR) can allow determining the qualitative characteristics of asphalt pavement across the entire length of the road without causing damage to the road structure. Relative dielectric permittivity, usually called dielectric value or constant, is the leading property used in GPR applications on road pavement surveys. This article presents GPR measurement results from asphalt base and binder layers of four test sections. GPR measurements were conducted immediately after the end of asphalt layer compaction process. Test points on each layer were selected and density, air void content were determined by drilling cores and testing them in the laboratory. To estimate asphalt layer density and air void content, GPR data were analysed using different existing mathematical models. To justify the reliability of the data measured by GPR, results were checked by comparing them with the results measured directly on cores taken from the asphalt pavement layers.