KEYWORDS: 3D modeling, Thermography, Thermal modeling, 3D scanning, Nondestructive evaluation, Cultural heritage, Scanners, Data modeling, Data fusion, 3D image processing
The authentication and sustainability of cultural heritage monuments are of great importance due to their uniqueness. Recent accidents and natural disasters have taught us that all monuments, even the most protected such as the cathedral Notre-Dame de Paris, can be destroyed by an unexpected event. For these reasons, it is of paramount importance the creation of a monument database containing fusion data not only of the accurate 3D model and precise representation of the artifacts/monuments but also about the condition and procedures of restoration and preservation and the structural health of the antiquities by means of quantitative non-destructive techniques, such as Infrared Thermography. The 3D model of a monument would guarantee the accurate restoration of the monument in case of a catastrophic disaster, while the 3D model of an artifact together with the entire related metadata would provide a digital identity, therefore guaranteeing the sustainability of the item. Also, in case of a movable artifact, it will be a useful tool towards the validation / authentication of the artifact in case it is damaged or missing.
This study aims in developing an advanced 3d digitization and nondestructive evaluation methodology that will serve as a baseline to advanced Augmented Reality (AR) and Virtual Reality (VR) applications of sites with archaeological interest in order to enhance not only the on-site experience for the visitors and the visitors via internet but as well to provide a useful tool for the preservatives, through improved supervision processes during maintenance. To this regard, a consolidated database is being created by the use of the best combination of state-of-the-art techniques of 3D digitization not only of the archaeological site itself but also of archaeological findings that at this time are presented in the museum. All the aforementioned data, created a database of the monument that aims to provide an augmented and virtual experience which is beyond the state of the art not only to the visitors but also to the preservative teams and it will help definitely towards the sustainability of the monument.
In this study, fracture experiments on fiber reinforced concrete beams are conducted. The aim is to examine the level of restoration in the different types of fiber reinforced concrete specimens by means of acoustic emission (AE) technique. The concrete specimens have been reinforced with three different types of metal fibers by means of shape and geometry and were tested in four-point bending. Consequently, they were repaired by means of suitable epoxy agent and mechanically loaded again. The repair has been conducted with epoxy resin injection to the main macrocrack that has been developed during the four-point bending. This work discusses the passive monitoring of fracture in repaired with epoxy resin fiber reinforced concrete specimens and shows that AE parameters provide good insight of the microstructure and characterize the level of restoration which is important especially when other NDE techniques cannot be used because of construction limitations.
Nowadays, the use of adhesives in building materials for enhancing the mechanical properties and the final performance at the maximum level is standard practice. Moreover, the interest of the construction industry for extensively testing the effectiveness of the new modified products is increased. This study aims to examine the fracture behavior of mortar specimens modified with waterproofing adhesives using acoustic emission (AE). For the mortar beams' production, the portion of active mix water has been changed with the use of different kinds of emulsion resins for investigating the waterproofing mechanism at final usage. For this, the slurries that have been examined are commonly used at the construction of swimming pools. The specimens were tested in three-point bending and compression. The ultrasonic velocity of the samples was also determined. The results indicate that the use of adhesives in mortars can be successfully characterized by AE and ultrasonic parameters, making elastic wave nondestructive evaluation a valuable tool in the growing sector of building materials using adhesives.
The demolition waste that is produced by the construction industry is one of the highest generators of solid waste worldwide. Moreover, the construction industry consumes massive amounts of all extracted natural resources. It is thus crucial to encourage more sustainable, environmental and economical construction practices. Nowadays, the proper modification of the recycled aggregates is of high demand because they mitigate the main disadvantages of recycled aggregates, like the increased porosity and water absorption. Although a lot of research has been performed in the modification of coarse recycled aggregates, the modification of fine recycled aggregates has not been adequately investigated. In this study, the outer surface of fine recycled concrete aggregates has been modified by coating them with three different types of modification cement paste, spreadable, elastomeric, water-soluble sealant, and a mixed variety of both modifications. The coated samples were nondestructively examined through the thickness (longitudinal mode), and the ultrasound velocity measurements were processed by a new developing method based on MATLAB that can provide automatically enhanced and high-quality data. The goal is to compare the influence of the cement paste coating of the fine recycled concrete aggregates utilizing ultrasound velocity measurements during the hardening of mortar. Results showed that the coating modification of fine recycled concrete aggregates affects the water absorption, as well as the elastic properties of the mortar. This led to a better understanding of the mechanism of hydration in recycled aggregates mortars, as well as in recycled aggregates concrete.
Different measurement methodologies have been used in bridge monitoring due to seismic, environmental and operating loading. Moreover, bridge monitoring systems have influence in the smooth operation of the traffic load in big cities and thus it’s crucial to encourage monitoring techniques that are flexibly adaptable to various construction building models. Even though a lot of research has been performed in bridge health monitoring in order to identify damages or deterioration of the structural elements there is still a need for a method that could combine multisensor techniques in big data processing for multisource loading. The behavior of the cable-stay bridge model is being monitored via acoustic emission and 2D laser Doppler vibrometry systems. In each case, both static and dynamic loading conditions have been applied. The goal is to correlate the results of these nondestructive evaluation techniques during static and dynamic response of different support situations. The purpose of this work is to improve bridge design and enable the detection of distributed failures during a multifactor loading system.
This study aims in examining the fracture behavior of recycled mortar specimens using the acoustic emission technique. To produce the recycled mortar beams, a portion of fine recycled concrete aggregates has been used, and the specimens were tested in three-point bending. This work led to a comparison between the fracture behavior of recycled mortar specimens with steel fiber-reinforced and baseline mortars fabricated with 100% natural sand. The results indicate that the use of recycled aggregates in mortars can be successfully characterized by acoustic emission parameters. This approach offers a reliable evaluation of the fracture mechanism making acoustic emission a valuable nondestructive evaluation tool in the growing sector of recycled building materials.
The present paper deals with the acoustic emission (AE) monitoring of fracture behavior of repaired marble specimens. Different types of specimens were ultrasonically interrogated. Subsequently, damage was induced to these specimens by three-point bending. The damaged specimens were repaired using a suitable epoxy agent; then they were mechanically loaded again. Apart from the well-known correlation of pulse velocity to strength for building materials, which also holds for the materials used in this study, AE provides a unique insight in the fracture behavior of the specimens. A statistical analysis of the experimental data has been performed to investigate the correlation between AE parameters and the strength of the specimens. This work discusses the passive monitoring of fracture in repaired marble specimens and shows that AE parameters, well-known to successfully characterize cementitious materials, also provide satisfactory results in characterizing monolithic materials such as marble. It is concluded that AE monitoring during a proof loading can provide good insight information of the materials and characterize their restoration.
The mechanical behavior of a fiber-reinforced concrete after extensive thermal damage is studied in this paper. Undulated steel fibers have been used for reinforcement. After being exposed to direct fire action at the temperature of 850°C, specimens were subjected to bending and compression in order to determine the loss of strength and stiffness in comparison to intact specimens and between the two types. The fire damage was assessed using nondestructive evaluation techniques, specifically ultrasonic pulse velocity (UPV) and acoustic emission (AE). Apart from the strong, well known, correlation of UPV to strength (both bending and compressive), AE parameters based mainly on the frequency and duration of the emitted signals after cracking events showed a similar or, in certain cases, better correlation with the mechanical parameters and temperature. This demonstrates the sensitivity of AE to the fracture incidents which eventually lead to failure of the material and it is encouraging for potential in-situ use of the technique, where it could provide indices with additional characterization capability concerning the mechanical performance of concrete after it subjected to fire.
Current work deals with the non-destructive evaluation (NDE) of the fatigue behavior of metal matrix composites (MMCs) materials using Infrared Thermography (IRT) and Acoustic Emission (AE). AE monitoring was employed to record a wide spectrum of cracking events enabling the characterization of the severity of fracture in relation to the applied load. IR thermography as a non-destructive, real-time and non-contact technique, allows the detection of heat waves generated by the thermo-mechanical coupling during mechanical loading of the sample. In this study an IR methodology, based on the monitoring of the intrinsically dissipated energy, was applied for the determination of the fatigue limit of A359/SiCp composites. The thermographic monitoring is in agreement with the AE results enabling the reliable monitoring of the MMCs’ fatigue behavior.
In construction sector marble and granite are widespread because of their unique properties through the centuries. The issue of repair in these materials is crucial in structural integrity and maintenance of the monuments through the world, as well as in modern buildings. In this study fracture experiments on granite specimens are conducted. The goal is to compare the typical acoustic emission (AE) signals from different modes (namely bending and shear) in plain granite and marble specimens as well as repaired in the crack surface with polyester adhesive. The distinct signature of the cracking modes is reflected on acoustic waveform parameters like the amplitude, rise time and frequency. Conclusions about how the repair affects the mechanical properties as well as the acoustic waveform parameters are drawn. Results show that AE helps to characterize the shift between dominant fracture modes using a simple analysis of AE descriptors as well as the integrity of the specimen (plain or repaired). This offers the potential for in-situ application mainly in the maintenance of the monuments where the need for continuous and nondestructive monitoring is imperative, but always care should be taken for the distortion of the signal, which increases with the propagation distance and can seriously mask the results in an actual case.
The characterization of the dominant fracture mode may assist in the prediction of the remaining life of a concrete structure due to the sequence between successive tensile and shear mechanisms. Acoustic emission sensors record the elastic responses after any fracture event converting them into electric waveforms. The characteristics of the waveforms vary according to the movement of the crack tips, enabling characterization of the original mode. In this study fracture experiments on concrete beams are conducted. The aim is to examine the typical acoustic signals emitted by different fracture modes (namely tension due to bending and shear) in a concrete matrix. This is an advancement of a recent study focusing on smaller scale mortar and marble specimens. The dominant stress field and ultimate fracture mode is controlled by modification of the four-point bending setup while acoustic emission is monitored by six sensors at fixed locations. Conclusions about how to distinguish the sources based on waveform parameters of time domain (duration, rise time) and frequency are drawn. Specifically, emissions during the shear loading exhibit lower frequencies and longer duration than tensile. Results show that, combination of AE features may help to characterize the shift between dominant fracture modes and contribute to the structural health monitoring of concrete. This offers the basis for in-situ application provided that the distortion of the signal due to heterogeneous wave path is accounted for.
The prediction of the remaining life of a structure can be assisted by the characterization of the current cracking mode.
Usually tensile phenomena precede shear fracture. Due to the different movement of the crack sides according to the
dominant mode, the emitted elastic energy possesses waveforms with different characteristics. These are captured by
acoustic emission sensors and analyzed for their frequency content and waveform parameters. In this study fracture
experiments on structural materials are conducted. The goal is to check the typical acoustic signals emitted by different
modes as well as to estimate the effect of microstructure in the emitted wave as it propagates from the source to the
receivers. The dominant fracture mode is controlled by modification of the setup and acoustic emission is monitored by
two sensors at fixed locations. Signals belonging to tensile events acquire higher frequency and shorter duration than
shear ones. The influence of heterogeneity is also obvious since waveforms of the same source event acquired at
different distances exhibit shifted characteristics due to damping and scattering. The materials tested were cement
mortar, as a material with microstructure, and granite as representative of more homogeneous materials. Results show
that in most cases, AE leads to characterization of the dominant fracture mode using a simple analysis of few AE
descriptors. This offers the potential for in-situ application provided that care is taken for the distortion of the signal,
which increases with the propagation distance and can seriously mask the results in an actual case.
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