Search

Resumen La tecnica no destructiva del georradar se basa en la propagacion de las ondas electromagneticas en el rango de las microondas. Actualmente esta tecnica se aplica en un gran numero de estudios en el ambito de la ingenieria civil, tales como el analisis del estado de pavimentos, puentes, tuneles, edificios, en la deteccion y localizacion de instalaciones, asi como en la caracterizacion y diagnostico de materiales de construccion. En este articulo se describe, a modo de ejemplo, un estudio completo en el que se demuestra la gran sensibilidad de la tecnica no destructiva del georradar para evaluar la variacion del contenido de agua en el hormigon endurecido. La evaluacion se realiza mediante el analisis de los parametros de onda electromagnetica que fueron registrados con un equipo comercial de georradar.

The moisture content variations in wood have a significant influence in wood’s physicochemical properties, as well as in its electromagnetic properties and to specific effects upon waves’ characteristics. In particular, this paper focuses on the analysis of the Ground-penetrating Radar’s (GPR) using an antenna of 1.6GHz central frequency capacity to register the velocity and the amplitude of the electromagnetic waves’ variation during the drying process of Pinus pinaster Ait timber joists. The results showed that when timber MC descends, the propagation velocity and amplitude of both the direct and the reflected wave increased. The high correlation found between the variables studied demonstrates GPR efficiency and the innovative application of this technique as a non-destructive evaluation tool for timber structures, particularly when studying its moisture content.

This work presents the results of a ground-penetrating radar (GPR) survey of the Sagrado Corazon de Jesus Church (seventeenth century AD). The church belongs to the artistic heritage of the Society of Jesus and is located in the old part of the city of Valencia (Spain). The GPR survey had two main objectives: discovering subfloor features and determining the causes of structural failure, particularly cracks and fractures detected in the building. For the fieldwork, 200 MHz and 400 MHz centre frequency antennae were used and a total of 53 profiles were acquired. The analysis of the reflection profiles and amplitude time-slices showed the presence of a sloping substrate below part of the church. The slope of this substrate and the fact that the church had been built near the old Arab wall of the city (eleventh century AD) suggests that the church was built on top of a moat (ditch). The variable thickness and differential compaction of the subfloor layers probably caused differential settlings in the building and therefore be the origin of some of the structural failures observed in the church. There was also a reflection hyperbola in the profiles of the east transept of the church that was hypothesized to be the reflection from the ceiling of an undocumented crypt due to its shape, size and location. That reflection feature was tested using a boroscope and found to be a brick barrel-vault crypt. Copyright © 2008 John Wiley & Sons, Ltd.

Ground-penetrating radar (GPR) is a non-destructive geophysical technique that is used to analyse soils and structures by providing continuous images of the interior of the media being analysed. In this paper, we present the methodology and results of a study of the reinforced concrete base of a large block of flats, where flow water and flooding are common in the wet and dry seasons. There are also a large number of cracks and fissures in the soil under the base. The damaged building is located in Valencia (Spain). The measurements were taken during two different seasons to include a period when flooding occurred and a period without flooding. The aim of the study was to determine whether the base would remain watertight in future and to analyse the depth of the damage observed on the surface. The results provided us with a detailed map of the damage and the zones that require more detailed analysis. Such damage affects the whole concrete slab. In addition to this analysis, several measurements were carried out to determine the possible causes of the inundations by locating potential wet areas and zones with high water content. A water table and a well were detected, which could be the cause of the humidity damage.

Durability of concrete structures depends mainly on the ease whereby water and any aggressive chemical agents dissolved therein can penetrate. Therefore, measuring water penetrability in concrete structures is crucial mostly when structures are in service. In this context, nondestructive techniques play an important role. In particular, the electromagnetic waves emitted by ground-penetrating radar (GPR) are very sensitive to the water content of the medium through which they propagate. This fact provides an interesting opportunity to analyze if the GPR technique allows the assessment of water penetrability in concrete with enough accuracy. In line with this, this paper describes the laboratory experiments and relevant analysis carried out to study the capability of GPR to assess water penetrability in hardened concrete. For this purpose, concrete specimens were fabricated and dried in an oven after 90 days of curing. They were then dipped into water and GPR measurements were taken at different intervals, based on coupling a 2.0 GHz antenna. The results showed that the agreement between velocity increments and the waterfront advance was excellent. In addition, a specific processing of the data acquired was developed. This process included the isolation of the reflection due to the waterfront, produced just before the reflection of the bottom of the samples. As a result of this processing, the in-depth waterfront location at different times was determined with high reliability., This work was supported by the Universitat Politecnica de Valencia (Spain) under the PAID-06-12 research plan through a project entitled: "Analisis de la durabilidad del hormigon por medio de la tecnica no destructiva del georradar."

Dielectric permittivity governs the propagation of electromagnetic waves in materials with low electrical conductivity, as it is the case of wood. This fact makes ground-penetrating radar (GPR) a potential technique for the nondestructive testing of timber. In addition, working with the direct wave has great advantages to physically characterize building materials. In particular, this study analyses the capability of the direct wave to study timber. In order to study the sensitivity of this wave, laboratory experiments were conducted on timber samples of different species and densities, with a GPR system using two different frequencies antennas (2 GHz and 1,6 GHz). Results showed that direct waves had a differential behavior regarding the grain direction analyzed and frequency of radiation. Therefore, the direct wave observation can provide accurate information regarding the physical parameters of timber and making possible to identify probable pathological areas.

The durability of concrete structures depends mainly on the ease with which the water and aggressive chemical agents dissolved therein penetrate it. Moreover, the electromagnetic waves emitted by Ground-penetrating radar (GPR) are very sensitive to the water content of the medium through which they propagate. For all this, the present experimental study analyzed the sensitivity of GPR to assess the location of the waterfront in concrete by means of the comparison of the energy level increments with the absorption coefficient. For this purpose samples of concrete were fabricated and after curing were introduced into water for different time intervals. The results showed that depending on the placement of the antenna regarding the location of the waterfront the agreement varied considerably. Best agreements were found when the antenna was placed in the same surface that was immersed into water and the reflected waves were analyzed.

This work was focused on the establishment of the best criterion to perform the readings of the amplitudes of the waves emitted by ground-penetrating radar, when timber specimens were inspected with an antenna of 1.6 GHz. This is a critical parameter when we are dealing with near-field readings, since no unique definition of this point has reached an agreement in the literature.

In the realm of architecture ground-penetrating radar has been used as nondestructive technique to assess physical properties of wood structures in situ. However, a better understanding of the dielectric anisotropy of timber is needed to develop this application. An experiment was conducted on samples of sawn timber of different species (densities) to study their dielectric responses according to the grain directions using a GPR with a 1.6 GHz antenna. Interesting differences were found: the propagation velocities, as well as the amplitudes of the direct and reflected waves always presented lesser when the electric field was longitudinal to the grain than when transverse. But when the field was propagated in whatever transverse direction some of those parameters not differ greatly., On the other hand, this work is supported partly by the "Programa de Apoyo a la Investigacion y Desarrollo (PAID-00-11)" of the Universitat Politecnica de Valencia. The authors would like to acknowledge the contribution of Dr Briggs of the School of Forest Resources at the University of Washington, Seattle (USA).

The dielectric response of timber to electrical fields is influenced by many factors, one of the most important being the internal structure of the wood. Thus the anisotropy of the wood should be taken into account when the ground-penetrating radar (GPR) technique is used to explore the properties of timber. The work carried out analyzes, by means of a GPR with a 1.6 GHz antenna, the dielectric behavior of Maritime Pine timber according to the direction of the electrical field with respect to the grain. After the acquisition process, the propagation velocities, amplitudes, and spectra variations were compared for all the studied grain directions. Significant differences were found between these parameters when the field was propagated in a parallel direction compared with perpendicular to the grain. However, when the field was propagated in various perpendicular directions to the grain (radial & tangential) the studied parameters were not found to differ greatly.

The dielectric behaviour of timber in an electrical field depends on many factors, and one of the most important is the direction of the fiber. This work analyses the wave parameter variations of the dielectric response of timber according to the direction of an electrical field applied by ground penetrating radar (GPR) with a 1.6 GHz antenna. Two types of tests were performed on samples of maritime pine timber (Pinus pinaster Ait.). After the acquisition process the propagation velocities, amplitudes, and spectra variations were compared for the studied fiber directions. Interesting differences were found between these parameters when the field was propagated in a parallel direction or perpendicularly to the fiber.

The moisture content (MC) is a critical parameter for most physical and chemical pathologies of timber and, in the case of structural wood, a MC > 20% can be dangerous for any load-bearing construction. The complexity of evaluating MC while timber is in use by means of the current methods (oven-drying and resistance wood meter) led us to test non-destructive techniques to evaluate this parameter on site. With this in mind, measurements with two non-destructive techniques, ground-penetrating radar (GPR) and ultrasound, were carried out on joists of Pinus pinaster Ait. from their initial green state until the point of hygroscopic equilibrium moisture content. In particular, the analysis presented in this paper focuses on the capacity of each technique to register the velocity variations of their waves during the timber drying process. Prior to the GPR analysis, it was necessary to distinguish between differences in the propagation velocity of electromagnetic waves (vEM) attributable to the wood anisotropy and those due to variations in MC. The propagation velocity of the electromagnetic waves was always found to be lower when the electrical field was parallel to the grain of the wood than when it was perpendicular to it. However, when the field was perpendicular, its direction whether radial or tangential, did not significantly affect the vEM. The direct measurements illustrate the ability of the GPR technique to characterize the MC of timber as a clear decrease in the MC resulted in an increase in the vEM. A strong correlation was obtained between the two parameters with coefficients of determination, R2 > 90%. Longitudinal elastic wave velocities (vP) were assessed by means of a ultrasound technique during the timber drying process. Despite the fact that the vP increased with the decreasing MC of each joist, the determination coefficient between these two variables was very low. The analysis presented in this paper is a successful application of the GPR technique to the study of wood s physical properties and has a promising future for the non-destructive, on-site analysis of timber MC., Financial support for this research was provided by the Spanish Ministry of Science and Innovation under the 2009-2012 national research and development plan through a project entitled: 'Integration of advanced and non-destructive evaluation techniques for structural timber and the restoration and conservation of heritage buildings (BIA2008-00342)'. We would like to thank our colleagues at the materials laboratory of the Escuela Tecnica Superior de Gestion de la Edificacion at the Universidad Politecnica de Valencia, Spain. The translation of this paper was funded by the Universidad Politecnica de Valencia.

The moisture content (MC) has a significant influence in wood’s physicochemical properties and therefore in most types of wood pathologies. The MC variation leads to modifications of its electromagnetic properties and to specific effects upon waves’ characteristics. Given the advantages of the direct electromagnetic wave (DW) observation, the aim of this work is to asses the ability of this wave to provide access to timber MC characterization. For this purpose, GPR measurements were carried out on timber joists (1.6 GHz central frequency). The dielectric behaviour of wood varies according to the direction of the fiber. Therefore, it is necessary to distinguish between differences attributable to the wood anisotropy and those due to variations in MC. With this aim, prior to the MC analysis, assays were carried out in different directions regarding the fiber. The results of this study show very satisfactory correlations between DW amplitudes and MC in all fiber directions. These results showed, in agreement with theory, that a decrease of MC results in an increase of the DW amplitude. These results demonstrates the GPR efficiency and the innovative application of this technique as a non-destructive evaluation tool for the rapid sounding of timber structures.

This work analyzes the efficiency of the ground penetrating radar (GPR) technique for the evaluation of strength grading of structural sawn timber. For this end, tests were performed on pinus radiata timber samples using GPR and other common evaluation techniques: visual grading and ultrasound-based evaluation. In order to determine the level of reliability of the different grading methods for timber structures, the results obtained with each method are compared to the results obtained from experimental bending-strength tests undertaken in accordance with standard EN408. Finally, the level of reliability of the GPR technique is compared to that of the other methods analyzed in this paper. The results obtained in this work show that GPR can be a valuable tool for the evaluation of structural timber, since it is a non-destructive technique, fast and easy to use, and what is more important, more reliable than other current evaluation methods used for timber grading.

Developing a nondestructive system is crucial to inspect water contents in timber structures because the amount of water, beyond a certain point, can compromise the structure strength. With this in mind, the present work is aimed at analyzing the capability of ground penetrating radar technique (GPR), with a 2 GHz antenna, to detect water content variations in timber. To do that, GPR measurements were conducted on timber samples at two water content states: at hygroscopic equilibrium (HE) and after 72 hours of complete immersion in water. Given the anisotropic nature of timber, the data acquisition was performed in two directions respect to the grain, parallel and perpendicular. The obtained results highlighted that GPR can be a very suitable technique to monitor water content in timber structures that are in service, since it was confirmed that propagation velocities decreased as the water content increased for all samples and acquisition displays (parallel or perpendicular to the grain). Moreover, the dielectric anisotropy is more evident when the samples had been immersed in water than when they were at their HE.

This work shows the geophysical study carried out at La Lonja de los Mercaderes of Valencia (15th c. Spain), which was declared a World Heritage site in 1996 by UNESCO. The main objective has been to determine the exact outline of the Moorish moat and map it by using two geophysical techniques: Gravimetry and GPR. The study has been carried out as part of the Project for the Restoration and Cleaning of the building. Gravimetric and GPR studies were conducted in two and three areas, respectively. The correlation and modelling of the results of these techniques has lead us to conclude that the moat is in fact beneath La Lonja, showing its outline and dimensions. Moreover, this study also allows us to assume that in some areas the moat is partially filled in. The results obtained in this survey are a good example of combining high resolution methods, i.e. GPR and microgravimetry, as an efficient and respectful tool in cultural Heritage. This combination of techniques could help to avoid destructive actions both in excavations works and in restoration projects as well as in the rehabilitation and cleaning of historical buildings, specially in World Heritage Sites.