Microwave Non‐Destructive Testing of Non‐Dispersive and Dispersive Media Using High‐Resolution Methods

This chapter discusses the principle and application of two model‐based algorithms for processing non‐dispersive and dispersive ground penetrating radar (GPR) data over layered medium under monostatic antenna configuration. Both algorithms have been selected for their super‐time resolution capability and reduced computational burden; they allow GPR to measure a layer thickness smaller than the fraction of the dominant wavelength. For non‐dispersive data, the ESPRIT algorithm is generalized to handle different kinds of data models encountered in experiments and in the literature. For dispersive data, the proposed adaptation of the MPM algorithm allows recovering the full‐time resolution and jointly estimating the time delays and quality factors of a layered medium with reduced bias. Both processing techniques are applied to probe‐layered roadways for NDT&E purposes

In-situ assessment of concrete bridge decks and pavements using stress-wave based methods

Concrete infrastructure of United States is aging and deteriorating. Accurate assessment the condition of concrete infrastructure is critical for its maintenance and rehabilitation. Stress-wave based methods, including ultrasonic surface wave (USW) and impact echo (IE), are becoming popular for characterizing defects and mechanical properties of concrete infrastructures. In this dissertation, a comprehensive literature review of seismic wave theory and common types of defects identified in concrete infrastructures, as well as stress-wave based methods used for concrete infrastructure monitoring and characterizing on a selected concrete bridge deck and two concrete pavement segments are present. The utility and reliability of both methods were carefully evaluated and validated based on the comparison analysis with other destructive or non-destructive testing (NDT) methods carried out in the field or laboratory for the same bridge decks and pavement segments, such as the concrete hydro-demolition, drilling, static modulus of elasticity of concrete specimens in compression and ground penetrating radar (GPR). Detailed investigation of the sensitivity and limitation of stress-wave based methods for different types of defects identified in concrete bridge decks and pavements has been performed and presented. The outcome of this study is to expand the knowledge of stress-wave based methods, to better understand their strengths and limitations, to evaluate the reliability and utility of both the USW and IE test results in characterizing and monitoring defects and mechanical properties of concrete infrastructures. The result of this study is most beneficial for transportation agencies and researchers to use stress-wave based methods properly and effectively for further feasibility studies or monitoring of concrete infrastructures --Abstract, page iv

Non‐destructive assessment of hot mix asphalt compaction/density with a step‐frequency radar: case study on a newly paved road

International audienc

Non-invasive imaging and assessment of pavements

Eight electrical resistivity tomography (ERT) and multi-channel analysis of surface wave (MASW) case studies are presented. The objective is to assess the condition of pavement, base, native soil, and rock all the way down to the top of the bedrock. Each segment of road way is approximately 1000 ft. long. The cases include US 63 north of Rolla, US 54 in Camden County, Rte. 179 in Jefferson City, HWY AT in Franklin County, I-55 in Pemiscot County, I-55 in Perry County, HWY U in Dent County, I-35 in Daviess County. In addition, there are only three types of pavement in these sites portland cement concrete (PCC), asphalt concrete overlaying portland cement concrete (AC/PCC), and full-depth asphalt concrete (AC) pavements. Accordingly, the geophysical tools examined different types of pavements with different distress conditions. Based on the analyses of the acquired ERT and MASW data, the data of both tools correlate reasonably well and generate reliable and comprehensive information about variations in soil and rock rigidity, variations in rock lithology, pattern, placement and density of solution-widened joints and offset of faults, locations of air-filled voids, distribution of dry and moist soil, distribution of clayey soil, and mapping variable depth to top of bedrock. Therefore these technologies can be routinely used by not only the Missouri Department of Transportation but also worldwide agencies in support of its pavement management process. The research demonstrated that the ERT and MASW methods were effective tools for assessing the condition of pavement. This is the first comprehensive assessment of paved sections of roadway to the best of the author knowledge --Abstract, page iii

Assessment of air void content of asphalt using dielectric constant measurements by GPR and with VNA

For several years, Ground Penetrating Radar (GPR) has been used in Finland to evaluate the air void content of asphalt pavements. Air void content is an important quality measure of pavement condition for both old and new asphalt pavements. The objective is to investigate if the existing GPR technique and application employed in Finland is sufficiently accurate to be used as a quality control tool in assessing the compaction of newly laid asphalt pavements. The work comprised field and laboratory experiments and a review of the existing PANK calibration method for the GPR measurements. Field experiments were conducted in the summer of 2013 on highways Vt3 and Vt12, near the City of Tampere. The test roads were paved with SMA16 using an approx. 40 mm thick layer of new asphalt. Roads were measured with GPR several times during the fall of 2013. A total of 36 cores and 2 slabs were obtained from the roads and tested in the laboratory with a Vector Network Analyzer. Measurements were done with a 7 to 17 GHz transmission configuration to measure the reference dielectric constant of the asphalt mixture. A major finding is that the PANK calibration method for the GPR inadvertently reduces observed density variations and may introduce a systematic bias. This makes pavements appear to be more homogenous and dense than they actually are according to conventional measurements.Maatutkaa (Ground Penetrating Radar, GPR) on käytetty Suomessa pitkään asfalttipäällysteiden tyhjätilan määrittämiseen. Tyhjätila on tärkeä kriteeri sekä uusien että vanhojen asfalttipäällysteiden laadun selvittämisessä. Tavoitteena on tutkia, onko Suomessa tällä hetkellä käytössä oleva GPR-tekniikka ja sen soveltaminen tarpeeksi tarkkaa uusien asfalttipäällysteiden tiiveyden mittaamiseen. Työ koostui kenttä- ja laboratoriotutkimuksista sekä GPR-mittausten kalibrointiin käytetyn PANK-kalibraatiomallin arvioinnista. Kenttäkokeet suoritettiin kesällä 2013 Tampereen lähellä valtateillä 3 ja 12. Teiden päällyste oli tyyppiä SMA16, ja uuden asfalttikerroksen paksuus oli 40 mm. Tiet mitattiin 1 GHz maatutkalla useita kertoja syksyn 2013 aikana. Teiltä otettiin 36 poranäytettä ja 2 laattanäytettä, jotka testattiin laboratoriossa vektoripiirianalysaattorilla. Asfalttiseoksen dielektrisyysvakio mitattiin 7-17 GHz läpimittauskonfiguraatiolla vertailuarvojen saamiseksi. Tärkein havainto oli se, että PANK-kalibraatiomallin käyttö maatutkamittauksissa vähentää havaittuja tiheyden vaihteluita ja saattaa lisätä systemaattisen virheen mittauksiin. Tämä saa päällysteet näyttämään tasalaatuisemmilta ja tiiviimmiltä kuin mitä ne oikeasti ovat

The non-invasive assessment of the condition of paved areas using electrical resistivity techniques

This work to detect wet areas below a paved surface is part of a 10-year research programme “ATU” (Assessing the Underworld), sponsored by EPSRC to assess the condition of the underworld by various techniques [1]. A low-frequency (5 kHz to 15 kHz) non invasive electrical resistivity technique was applied to a paved surface to assess the condition of upper layers of the asphalt. Generally, the paved surface (e.g. an asphalt pavement) is constructed using a base layer, a sub-base layer and a sub-grade layer or the natural soil foundation. The thickness of the upper typically ranges from 18 mm to 40 mm according to the standards for highway construction in the UK [2]. The electrical resistivity technique applied in this research has been implemented using a capacitive-coupled resistivity (CCR) system. Four square-plate electrodes C1, P1, P2 and C2, of large dimensions compared to the electrode spacing, are operated as inline capacitive sensors: electrodes C1 and C2 act as current sources coupling electrical current into the pavement; while electrodes P1 and P2 operate as receiver sensors to measure the voltage in the media. By this method, the quantity of electrical impedance could be estimated. It is assumed that as the moisture content of the wearing layer increases, its resistivity decreases and its dielectric constant increases. It is believed that this is the first time that this capacitive-coupled resistivity technique has been researched and applied to the condition assessment of asphalt pavement. The separation between the electrode plate and the ground surface affects the capacitance value, and hence, the coupling of the electrical signal into the ground. Thus, the surface roughness of the wearing layer could reasonably be expected to influence the capacitance. Surface roughness effects on capacitors have been studied in the nanoscale integrated circuit (IC) application area. However, no research has been published about the impact of the pavement surface roughness on the impedance measurements, obtained by the capacitive-coupled resistivity technique. In this research a laser profiling instrument with an along-track resolution of 0.125 mm and a typical height resolution of 50 μm has been utilised to measure the asphalt pavement surface roughness height distribution of the areas surveyed using the capacitive coupled resistivity technique. These surface roughness height distribution data will be incorporated into the measurement data processing as correction factors, to achieve more accurate survey results. The moisture content of the wearing layer of asphalt pavements will be estimated using the Cole-Cole model for these corrected results. According to the experiments conducted within the laboratory and field surveys on asphalt pavements in different locations, it is concluded that the measured reactance is an indication of surface roughness (with a typical maximum peak-peak roughness of 1.2 cm for the results presented within this thesis); while the real part of the measured impedance indicates the moisture content of the wearing layer of the asphalt pavement. A larger measured reactance indicates a rougher pavement surface. A smaller real part of the measured impedance indicates a higher moisture content within the sub-surface layer

Development of ground penetrating radar image library for setup parameters.

A significant amount of effort has been put in developing tools to interpret Ground Penetrating Radar signals obtained during surveys. Currently, skilled and experienced users do most of GPR image interpretation. They use experience in deciphering what the GPR signals represent. A successful survey will not only depend on the choice of antenna used, but also on the operating parameters used for the survey. This study aims at providing a library of GPR images taken from known targets with known parameters. The targets include a set of different sizes of steel rebars. The library of GPR images is developed using known targets set in a sand box. Sand has proven to have the same properties as Portland cement concrete in response to GPR signals. The sand box simulates a concrete slab; it is used for ease of placement of different targets with various configurations. The developed library of GPR images will be used for training of GPR users and comparison studies of GPR operating parameters. In the future these images can be used for a pattern recognition algorithm development, or any other theoretical study pertaining to GPR image interpretation

Development of ground penetrating radar image library for setup parameters.

A significant amount of effort has been put in developing tools to interpret Ground Penetrating Radar signals obtained during surveys. Currently, skilled and experienced users do most of GPR image interpretation. They use experience in deciphering what the GPR signals represent. A successful survey will not only depend on the choice of antenna used, but also on the operating parameters used for the survey. This study aims at providing a library of GPR images taken from known targets with known parameters. The targets include a set of different sizes of steel rebars. The library of GPR images is developed using known targets set in a sand box. Sand has proven to have the same properties as Portland cement concrete in response to GPR signals. The sand box simulates a concrete slab; it is used for ease of placement of different targets with various configurations. The developed library of GPR images will be used for training of GPR users and comparison studies of GPR operating parameters. In the future these images can be used for a pattern recognition algorithm development, or any other theoretical study pertaining to GPR image interpretation