Search

This paper attempts to evaluate the change in the behavior of the acoustic waves associated with flexure cracks developed in rubberized concretes in a subfreezing environment. Seven normal and rubberized concrete mixtures were developed with different compositions. Prism samples from each mixture were tested at two temperatures (25°C and −20°C) under a four-point monotonic flexure test while being monitored via two attached acoustic emission (AE) sensors to collect the emitted AEs till failure. The AE signal characteristics such as signal amplitudes, number of hits, and cumulative signal strength (CSS) were collected and used for three AE parameter-based analyses: b-value, intensity, and rise time–amplitude (RA) analysis. Analyzing the acoustic activity revealed micro- and macrocracks nucleation, which were found to be associated with a noticeable spike in CSS, historic index [H(t)], severity (Sr) values, and a significant dip in the b-values. In addition, cold temperature was found to increase the micro- and macrocracking onset load and time regardless of mixture composition. Besides, mixtures with a lower C/F, less crumb rubber (CR) content, and/or smaller rubber particle size witnessed higher micro- and macrocrack load and time thresholds. Noticeably, the AE signal attenuation effect caused by the high CR content (up to 30%) at 25°C was significantly relieved when samples were tested at −20°C. Three charts were developed to classify the cracking level based on the values of the intensity analysis parameters [H(t) and S] and RA analysis. Practical Applications: Infrastructure failures can cause severe economic losses and fatalities, but luckily they can be avoided through regular inspections with the aid of nondestructive testing and subsequent repairs. Aging structures need more inspections to detect potential deficiencies, whereas newly constructed ones can safely undergo fewer inspections and preserve resources. Data from nondestructive testing programs can optimize inspection schedules. When it comes to hard-to-reach structures in extreme weather, acoustic emission (AE) has the potential to be a more suitable nondestructive testing technique over other conventional methods. Some concerns were raised regarding the effectiveness of the AE technique for applications involving novel construction materials such as rubberized concrete, because rubber particles have noticeable acoustic absorption capacities that may affect the parameters of the AE waves and impact the posttesting analysis. Another concern was the influence of cold temperature on the AE wave characteristics due to the change in concrete microstructure at low temperatures. This study aimed at addressing these concerns by utilizing AE analysis to highlight the onset of micro- or macrocracks in rubberized concrete mixtures exposed to cold temperatures. Three user-friendly charts are presented that can advise on inspection decisions based on whether deterioration has reached a certain level. [ABSTRACT FROM AUTHOR]

The freeze–thaw (F-T) cycle is one of the weathering factors that can cause rapid deterioration of the mechanical properties of rocks and threaten the stability and durability of rock engineering in cold regions. To study the influence of F-T action on the mechanical and deformation characteristics of sandstone, triaxial compression tests were performed under four confining pressures (0, 1, 3, and 5 MPa) and five F-T cycles (0, 40, 80, 120, and 160). The experimental results show that the stress–strain curves of the sandstone after F-T cycles can be divided into four phases: compaction, elasticity, strain-hardening, and postpeak failure. According to the deformation behaviors of the sandstone with various F-T cycles, an elastoplastic damage constitutive equation was established considering the compaction effect and F-T action. The model parameters were determined, and the theoretical curves were calculated. The comparisons with theoretical and experimental stress–strain curves demonstrate that the formulated constitutive equation can reflect the key deformation stages and mechanical behaviors of sandstone with different F-T cycles. Because the damage variable is introduced in establishing the model, the proposed model can also provide a quantitative description of the macrodamage, which agrees well with the microdamage of the sandstone after many F-T cycles measured by acoustic emission (AE) technology. The formulated constitutive equation in this paper can well describe the experimental deformation curves of sandstone with various F-T cycles and is easy to embed into numerical analysis software. The results can provide a certain theoretical reference for the evaluation of the durability and stability of rock engineering structures impacted by F-T-induced damage in cold regions. [ABSTRACT FROM AUTHOR]

Liquid nitrogen (LN2) fracturing is beneficial to the development and utilization of geothermal energy. In this paper, red sandstone was heated from room temperature to different temperatures (25°C–800°C) and then cooled with LN2. After attaining room temperature, nuclear magnetic resonance (NMR), uniaxial compression, and acoustic emission (AE) tests were conducted, and results were compared for different samples. The results showed that with an increase in quenching temperature difference, the volume of micropores decreased gradually, while the volume of fine pores, mesopores, macropores, and total porosity increased, resulting in the reduction of the compressive strength. A higher quenching temperature difference also reduced the sample's total time to fail, and the failure mode was transformed from single inclined shear failure to conical failure. This is because the thermal stress (caused by the rapid cooling of LN2) expanded the original cracks of the sandstone, leading to high porosity and low compressive strength of the heat-treated and quenched samples. [ABSTRACT FROM AUTHOR]

Microbial induced calcium carbonate precipitation (MICCP) has applications in improving the quality of cementitious constructions by enhancing its compressive strength, reducing porosity, and increasing durability against environmental degradation. In this study, an attempt has been made to develop an in situ, online, and nondestructive ultrasonic monitoring tool to capture bacterial self-healing in cementitious materials using cheaper source of bacterial nutrition medium. Samples casted and cured in corn steep liquor (CSL) and nutrient broth (NB) demonstrated higher ultrasonic pulse transmitted signals at successive days of curing relative to water cured control (C) specimens. The rise in ultrasonic signal due to bacterial admixing and curing is due to calcite precipitation in bacterial admixed and cured specimens. The compressive strength of CSL specimens was 8.8%, 11.4%, and 11.1% higher, while in NB specimens was 13.5%, 14.6%, and 12.7% higher as compared to water casted and cured specimens at 7, 14, and 28 days, respectively. The water absorption in bacterial treated specimens was significantly reduced due to the filling of pores in the mortar matrix and a reduced sorptivity coefficient of 0.0027 and 0.0022 was observed in CSL and NB specimens respectively as compared to 0.0197 of water casted and cured C specimens. This suggests successful calcite precipitation in bacterial treated mortar specimens and ultrasonic pulse transmission monitoring technique can successfully pick up bacterial intrinsic healing and can serve as in situ and nondestructive monitoring technique in civil engineering applications. Bacterial intrinsic self-healing in cementitious materials is an inherent process and this paper highlights the successful implementation of nondestructive and in situ ultrasonic wave monitoring tool to pick the same. Commonly used nondestructive testing (NDT) techniques like ultrasonic pulse velocity (UPV), acoustic emission monitoring can capture crack initiation in cementitious structures but not its intrinsic healing. In present research, ultrasonic wave monitoring has been used to capture bacterial microstructural development in the initial curing period in MICCP. This innovative NDT technology would go a long way in developing an in situ ultrasonic monitoring technique to pick up efficacy of MICCP in concrete structures for on-site applications. [ABSTRACT FROM AUTHOR]

Cracking is a typical defect of cement concrete pavements. This paper investigates the fracture behavior of cement mortar and concrete materials based on experimental observations using acoustic emission (AE) and embedded SmartRock sensor techniques. Examining the AE signals (e.g., AE counts, events, and energy), the bulk displacement responses using LVDT sensors, and the localized responses using the embedded SmartRock sensor during three-point bending (TPB) tests, the correlation between different types of intelligent sensing parameters and the evolution of macroscopic mechanical properties of cement mixtures was analyzed. In addition, a four-stage development process is proposed to describe the fracturing behaviors of the mortar and concrete, as well as the underlying mechanisms. The results show that the four-stage model proposed in this paper can describe the entire fracture process of concrete or mortar materials, especially the transition from Stage 3 to Stage 4. In addition, the SmartRock sensor can effectively monitor the mechanical degradation of the host matrix during the fracture process, and the AE energy and AE events can be used to predict efficiently the degree of material damage: the material stiffness decreases slowly in the early stages of loading and suddenly in the later stages of loading, which can be characterized by the change in AE energy. The rise time/AE amplitude values are an effective way to characterize the crack propagation of cement mixtures in different stages of fracture and help to conduct a comprehensive evaluation of the health of the material. [ABSTRACT FROM AUTHOR]

The main purpose of this study was to understand the failure mechanism of fly ash fiber–reinforced asphalt specimens under uniaxial compression loading and splitting loading, respectively. The variation of acoustic emission (AE) parameters in the acoustic emission tests during this fracture process was analyzed. The results showed that under uniaxial compression, the failure process of the fiber asphalt specimens could be divided into four stages: the formation of internal microcracks, microcrack propagation, rapid crack propagation, and finally, failure. Shear failure is the main failure form of asphalt specimens, and with the gradual increase of fiber content, the failure mode of specimens gradually changes from shear failure to shear-tensile failure. The correlation analysis between peak value and frequency of acoustic emission parameters shows that there are three frequency bands of fly ash fiber asphalt specimen, namely, 0–30, 30–60, and 150–200 kHz, which correspond to the initial dislocation failure of the interface between aggregate and asphalt mortar, the fracture failure of the interface between fly ash fiber and asphalt mortar, and the complete dislocation failure of the interface between aggregate and asphalt mortar. In recent years, acoustic emission technology has been widely used in the field of nondestructive testing of cement concrete and bridge structures. Nevertheless, the damage identification methods commonly used in asphalt pavement, such as the computational simulation method and image processing method, have low working efficiency, large error, and lack of dynamic perception of the whole damage process, which limits their applicability in practical engineering applications. In this paper, acoustic emission technology has been employed to characterize the damage and crack propagation law of fiber asphalt specimens under various stress states. Through the analysis of the evolution characteristics of acoustic emission signal parameters, the fracture damage characteristics of fiber asphalt samples under different stresses are invested. The research results are of great significance for the popularization and application of acoustic emission technology in the field of nondestructive testing of asphalt pavement. [ABSTRACT FROM AUTHOR]

Coal mine shaft excavation with the freezing method causes surrounding rock deformation under lateral unloading. In this paper, the failure process of frozen sandstone under lateral unloading was studied based on the acoustic emission (AE) response. The point where the deformation of rock samples under lateral unloading accelerates was taken as the plastic yield critical point (PYCP). The PYCP was defined as a fracture warning point. The mechanical properties of frozen rock samples under lateral unloading were also studied according to the AE response, and a damage model was established based on the number of cracks. The research showed that the number of cracks under lateral loading and cumulative acoustic emission energy in frozen sandstone increased slowly with time before the PYCP was reached and rose exponentially after the PYCP was reached. Following the sandstone (20°C) freezing, the peak stress under lateral unloading increased by 2.3–3 times and accounted for 52%–68% of the triaxial compressive strength. The peak stress increased with the initial confining pressure of the frozen rock sample, with a larger value indicating more severe damage. The model results were close to the experimental results before peak stress was reached, and the number of cracks could represent the damage degree and fracture level of the frozen sandstone. [ABSTRACT FROM AUTHOR]

The present study investigates the efficacy of sinusoidal trailing-edge (TE) serrations as a passive means for the reductions of airfoil broadband noise, theoretically and experimentally. Comprehensive parametric studies were conducted to determine the effect of serration amplitudes and wavelengths on the noise reduction performance of a National Advisory Committee for Aeronautics (NACA) airfoil. Initially, the present paper shows the use of the trailing-edge noise (TNO) model for the accurate predictions of the surface pressure spectrum near the TE and hence the far-field noise using the Wiener-Hopf method. The predicted spectra and the noise reduction levels showed good agreement with the measurements for a wide range of frequencies. The present study reveals that the local maximums of the overall noise reductions occur when the transverse turbulence integral length scale is either 1.2 or 0.2 times the serration wavelength, which corresponds to λ/Λt=0.833 or 5, where λ and Λt are the serration wavelength and integral length scale. One of the key findings of the paper is that the serration wavelength at which the highest noise reductions occur when the acoustic emissions vary inversely with the modified Strouhal number Sthm [i.e., wsste(ω)/wbl(ω)∝1/Sthm ] for narrow (i.e., small wavelengths) and wider serrations (i.e., large wavelengths), where wsste and wbl are the acoustic emissions radiated from the serrated and baseline airfoils. Further, the TE serrations are also observed to reduce leading-edge (LE) noise along with the self-noise, which indicates the efficacy of TE serrations in reducing the total far-field noise. [ABSTRACT FROM AUTHOR]

This paper aims to study the strength and damage characteristics of basalt fiber-reinforced concrete (BFRC) under dynamic splitting tensile loads. Brazilian disk splitting tests and acoustic emission (AE) tests were carried out on BFRC herein. The improvement effects of loading rate and fiber content on the dynamic splitting tensile strength of BFRC were studied. Then, AE wavelet analysis methods (wavelet energy spectrum coefficient and maximum wavelet energy value) were employed to analyze the AE signals generated by BFRC. Additionally, a back-propagation (BP) artificial neural network was established to identify the damage stage of BFRC under dynamic splitting tensile loads. The test results showed that the improvement effect of the loading rate on the dynamic splitting tensile strength was enhanced with an increasing loading rate, and the enhancing effect of basalt fiber in the cases of 0.1% or 0.15% fiber dosages was better than that of the others. Most of the AE signals generated by BFRC were low frequency. Furthermore, the loading rate and the addition of fibers had a considerable impact on the wavelet energy spectrum coefficients corresponding to different bands and the distribution of maximum wavelet energy values of BFRC. Finally, the recognition rate of this BP neural network increased with the increment of the number of AE samples with the progress of loading. [ABSTRACT FROM AUTHOR]

The Acoustic Emission (AE) technique is applied to study the failure mode, damage evolution process, and cracking mechanism of reinforced concrete (RC) columns under the coupling effect of exterior compression load and interior reinforcement corrosion. AE signals are collected from different loading stages for corroded and uncorroded RC column specimens. Parameter analyses are conducted to analyze the peak frequency, energy distribution, and phase parameters used to achieve the general changing conditions of AE signals. Fast Fourier Transform is applied to reveal the time-variant rules of signal frequency and energy in different damage stages. Discrete Wavelet Transform is used for a better understanding of the local time-frequency properties of the non-stationary AE signals and optimally interprets the damage evolution process of the RC structure. Results show that the peak frequency has a 3-layered distribution; an obvious "double-peak" trend of the energy distribution indicates two cracking mechanisms: steel/concrete interface damage and aggregate/cement damage. The damage process consists of four stages: micro-crack formation, micro-crack development, crack expansion, and cracking failure. The corrosion behavior remarkably influences the energy distributions of the two cracking mechanisms, the characteristics of the spectra in different stages, and the damage evolution process inside the RC columns. This paper studies the failure mode, damage evolution process, and cracking mechanism of reinforced concrete (RC) columns under the coupling effect of exterior compression load and interior reinforcement corrosion via AE signal analysis. The energy distribution and spectral characteristics show significant differences among different cracking stages. Moreover, those important properties and the damage evolution process are also remarkably affected by the corrosion behavior of the steel reinforcement. The practical meaning of those research outcomes are to provide theoretical supports for the application of AE techniques in the health monitoring of RC structures. The changes in the key properties of AE signals measured and analyzed can be used to capture the state changes and locate the cracking stage, which provides important evidence for the safety evaluation of RC structures. [ABSTRACT FROM AUTHOR]

The progressive damage monitoring and fracture evaluation of plain concrete beam specimens subjected to three-point bending (TPB) are reported in this paper. The objective of the present research is to systematically correlate the fracture behavior of a concrete beam with acoustic emission (AE) data recorded during the present set of experiments. The damage growth and failure mechanisms of the beam specimens are investigated with AE parametric analysis, b-value analysis, and digital image correlation method. Eventually, a reasonable correlation between AE energy and the released fracture energy is established at various stages of loading, which is confirmed with the set of TPB beam experiments and further validated with nonlinear numerical finite-element analysis. The energy released during the cracking processes at different loading stages in the experiment is quantified and systematically analyzed. Acoustic and fracture energies are dependent on active concrete cracking, and their correlation is helpful in determining the extent of damage in the concrete structures. Such a relationship can be used as an operational tool for structural health monitoring of structures as an early warning system supplemented with numerical analysis, a well-calibrated laboratory, and in situ AE experiments. [ABSTRACT FROM AUTHOR]

Identification of noise signals is one of the most challenging problems in health monitoring of a bridge structure using acoustic emission (AE) monitoring and identification technology. Hardware filtering technology and spatial identification technologies are the most common methods used in identifying signals from the defects of the bridge, which have great limitations due to the presence of environmental noise. Therefore, this paper focuses on the AE noise signal from a bridge in an operation state and other specific loading states, which is diagnosed in the hardware filtering technology, spatial identification, and self-organizing map (SOM) neural network, to obtain the new noise recognition methods. It is found that the first two methods can indeed filter the noise signal, but the filtering rate can only reach about 50%, and can barely filter strong noise signals. The SOM neural network had strong self-recognition ability. The classification accuracy of simulated AE signals is 90% and 100%, respectively. The trained network was used to test 183 sample signals, and the defect signal detection accuracy reached 76% and 78.8%; therefore, the noise signal filtering effect is significantly improved. [ABSTRACT FROM AUTHOR]

To study the splitting tensile damage characteristics of concrete, this paper conducted Brazilian disc split tensile tests on concrete and mortar with three water-cement ratios and four loading rates, respectively. Acoustic emission (AE) technology was used for real-time. The test results indicate that in the early loading stage of Brazilian disc specimens, a small number of microcracks are primarily generated at the interface between aggregate and mortar, and microcracks and macrocracks are generated simultaneously at the peak stress. The peak frequency characteristics of AE explain the strength enhancement principle and strain rate effect of concrete damage. The curves of AE cumulative ringing and AE energy counting reflect the internal damage activity of concrete and mortar specimens at different stress stages. Finally, a model that conforms to the macroscopic performance of the concrete dynamic splitting tensile test was established based on the discrete element method (DEM) and Hertz–Mindlin bond model. The simulation was compared with the actual analysis to verify the effectiveness of the parameters. The evolution of concrete damage space was studied through the discrete element simulation results, and the three evolution stages of damage space were summarized, which confirmed that the DEM plays an essential role in the field of micromechanics. [ABSTRACT FROM AUTHOR]

This study investigates the efficacy of differing information entropy calculation approaches for concrete structures undergoing alkali-silica reaction (ASR)-induced cracking. In prior work, information entropy has only been utilized for a better understanding of the damage in metallic structures under external loading. To our knowledge, no research has been published regarding information entropy for concrete structures affected by ASR. This scientific gap is addressed in this paper. Furthermore, the innovation lies in using coefficients of determination instead of b -values for cracking identification. The entropy results show that the randomness of events increases at the earlier stage of ASR, which is expected due to the microcrack formation, and decreases at the later stage due to the formation of macrocracks. Moreover, a correlation is observed between the coefficients of determination and the evolution of the cumulative signal strength. [ABSTRACT FROM AUTHOR]

Uncontrolled pipe breaks are a challenge for water utilities all over the world. This paper describes a technique that enables pipe cracks to be identified at an early stage before they become uncontrolled breaks by utilizing a permanent acoustic monitoring system as part of a smart water network. Multiple acoustic features are selected and extracted from recorded wave files that are associated with proactive repair and uncontrolled pipe break events. The extracted acoustic features and the associated wave file labels (as either crack/leak noise or no crack/leak noise) are used to train a support vector machine model. The trained model has been operationalized in the South Australia Water Corporation's smart water network analytics platform to process incoming new acoustic wave files in a near-real-time manner. If the acoustic wave file is classified as a pipe crack/leak, an alarm is sent to an investigation crew such that leak localization can be conducted and repairs started. The successful detection of multiple pipe cracks/leaks by the developed model after its implementation proves that it is an effective tool to enable proactive management of pipe breaks in water distribution systems. [ABSTRACT FROM AUTHOR]

As an important part of a bridge, bearings easily suffer damage when exposed to various loading and environmental changes during their lifetime. Bearing replacement should be performed in a timely manner if damage occurs to high-speed railway (HSR) bridges. The unique structural form and strict operation requirements mean that bearing replacements of HSR bridges are much more difficult than those of highway bridges. However, compared with bearing replacements of highway bridges, far fewer scientific and engineering studies have been conducted to guide the bearing replacement of HSR bridges. In this paper, based on a three-span continuous concrete box girder HSR bridge, an innovative bearing replacement method using reverse disassembly and assembly techniques is proposed and was implemented at a location under operating HSRs. In addition, safety monitoring measures were undertaken to guarantee the safety of the bridge during bearing replacement. In contrast to the usual monitoring practice focusing on the displacement and the external strain of the structure, this monitoring work adopted the acoustic emission (AE) detection technique to explore the internal structural damage formed in the process of construction. The results suggest that the proposed bearing replacement method, which requires the girder to be jacked up by no more than 9 mm, is a promising practice for this complicated construction, and the start time and evolution of damage in the concrete of a bridge during construction can be captured accurately by AE detection with a parameter-based analysis method. All practices presented in this case study can guide future bearing replacements in similar projects. [ABSTRACT FROM AUTHOR]

Rock heterogeneity is one of the most important factors when numerically simulating the rock failure process and crack propagation. This paper presents an approach for capturing rock heterogeneity that combines peridynamic theory, digital image processing (DIP), and low-field nuclear magnetic resonance (NMR) imaging. By processing the magnetic resonance images (MRIs) of the rock material, the microstructure distribution is obtained, and the attenuation coefficient is defined and calculated by the number and value of pixels of the rock MRI. Based on bond-based peridynamic theory, the density, bond constant, and critical stretch associated with the material point and bond are revised by the attenuation coefficient and have the same distribution with real rock microstructure. Then, this new approach is used to simulate the crack bifurcation of red sandstone under tension and the failure process of mudstone in an unconfined compression test. The influence of the element's pixel number on the calculation result is discussed. Numerical results show that the crack propagation and the failure process based on the new approach are both distributed nonsymmetrically. In addition, the acoustic emission rule in the peridynamic simulation, which is defined by the number of broken bonds in each loading step, is consistent with the experimental results. The comparison of the numerical and experimental results reveals that the present approach can be used as a supplementary method for analyzing rock damage and failure. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) has been widely used for damage detection and characterization in reinforced concrete (RC) structures. However, there is little work focusing on correlation of AE signatures and physical phenomena involved within the failure process of RC beams. In this paper, AE monitoring was performed on five small-scale RC beams that were subjected to an incremental cyclic loading regimen. Correlation of AE activity with in situ crack progression was performed by comparing AE signatures with a series of real-time images of crack development. Based on the combination of AE response and development of flexural and shear crack patterns, four phases named microcrack formation, macrocrack initiation, crack opening/closing, and near failure were recognizable. Meanwhile, AE cumulative energy (CE) analysis during loading and unloading demonstrated its potential for damage detection and qualification. The test results show crack initiation and propagation are accompanied with significantly greater AE activity in comparison to existing crack reopening or closing; and during the unloading step when the RC beams are near failure, the calculated CE is greater than that for initial crack appearance. In addition, AE event localization method and waveform analysis were performed to aid in identifying the source mechanisms of meaningful events. Crack propagation events were associated with burst type signals. During unloading step near failure, signals of high amplitude and long rise time are located along the reinforcement indicating a potential loss of bond as the reinforcement interacts with its surrounding concrete. The results showed that the combination of each analysis type aided in determining whether AE generated during loading/unloading of RC can be a meaningful parameter in monitoring damage of RC structures. [ABSTRACT FROM AUTHOR]

To predict the fractured rock failure under deep triaxial stress, true triaxial tests were carried out using thermal infrared monitoring and acoustic emissions (AE). Based on the thermal infrared imagery, which may hold potential information for predicting rock failure, this paper proposes the infrared temperature jumping rate (ITJR) to reflect the jumpiness of the temperature field matrix and establishes an infrared advance prediction method. The results show that the high-temperature area will converge and expand gradually, and cracks propagate along a certain direction. In the sudden-temperature-reduction area, rock stripping is easy to occur. At the boundary between high- and low-temperature areas, it is easy to produce breakage cracks and form rock spalling. In the short quiet period, the rock gradually gathers strain energy, which will be released in the fracture period. By comparing the time of AE sudden increase with the time of ITJR mutation, it shows that the method has a good advance prediction effect for rock fracture. [ABSTRACT FROM AUTHOR]

Gently inclined and inclined coal pillars are both subjected to the combined action of compression and shear load. Due to the existence of inclination angle, the fracture and instability behaviors of inclined pillars are different from those of near-horizontal pillars, and the difference is closely related to the load level of the pillar. Therefore, it is of great significance to study the influence of different inclination angles and loading rates on mechanical property and fracture behavior of the coal pillar for its strength design. In this paper, a new rock mechanical properties testing system was used with the combination of acoustic emission (AE) technology, and the changes of mechanical properties of coal specimens under different inclination angles and loading rates were obtained. The main conclusions are as follows: (1) the large of inclination angle, the greater of the peak shear stress. When the inclination angle is small (0°, 5°, 10°, and 15°), the peak stress increases first and then decreases with the increase of loading rate, when the inclination angle is large (20° and 25°), the peak stress gradually decreases. When the inclination angle is greater than 15°, the peak stress decreases with the increase of loading rate, and the decreasing amplitude gradually decreases. (3) The failure mode of the coal specimen is changed from tensile-splitting failure (0°–5°) and tension–shear composite failure (10°) to single shear failure (15°–25°). The loading rate has little effect on the failure mode of the specimen, but a significant effect on its failure degree. The crack initiation (CI) threshold and the crack damage (CD) threshold of coal specimens increase first and then decrease with the increase of inclination angle, and the ratios of CI and CD to peak strength are almost constant. With the increase of loading rate, the ratio of CI and CD to peak strength increases first and then decreases in the inclination angle range of 10°. The ratio of CI and CD to peak strength is basically independent of the loading rate. To comprehensively consider the influence of inclination angle and load level on pillar strength, a new parameter of rock strength under the influence of inclination angle and load level is suggested to be introduced into the empirical formula of pillar strength. [ABSTRACT FROM AUTHOR]

A permanent "leak-before-break" type acoustic monitoring system has been deployed by the South Australian Water Corporation across the Adelaide City Central Business District (CBD) since early 2017. Several analytic approaches applied to the collected acoustic data and results, in terms of reducing the number of uncontrolled pipe main breaks, have been reported. New statistical approaches to the analysis of the data are being continually developed with a statistical method based on the rate of change of the acoustic data within measured spectrums reported in this paper. The method involves the determination of short and long-term noise power level benchmarks, using noise power levels in an empirically determined number of windows with different frequency bin widths, to determine the rate of change of power levels across the frequency spectrum. The rate of change is quantified via the determination of normalized power level changes over weekly and monthly periods and the calculation of noise ratios relative to earlier weekly and monthly periods. Thresholds are applied to determine whether a weekly or monthly change alert should be raised for the investigation of potential cracks. [ABSTRACT FROM AUTHOR]

In this and in the companion paper, the mechanical response of adhesive anchor systems is theoretically and numerically predicted and experimentally observed. The theoretical prediction is on the basis of an elastoplastic damaging model formulated to predict the structural response associated with the development of a fracture in adhesive anchor systems. This part describes the analytical model developed in the framework of a thermodynamically consistent theory, which assumes adhesion where the structure is sound, and friction in correspondence with the fracture. Isotropic damage is considered. The model can predict the structural behavior at the interface between two surfaces of ductile, brittle, or quasi-brittle materials. The Helmholtz free energy is written to model the materials' hardening or softening. Isotropic damage is considered, and the possible effects of dilatancy are taken into account, including nonassociative flow rules. The formulation is implemented into the finite-element code FEAP. In the companion paper, the new model is adopted to predict the mechanical response to the pullout force of postinstalled rebar chemically bonded in concrete. The analytical model and the numerical implementation are experimentally validated by several pullout tests, which are monitored by using an acoustic-emission technique. [ABSTRACT FROM AUTHOR]

The accurate identification and quantification of rock damage are important for the reliable safety assessment of rock engineering. In this paper, stress-strain behavior, passive acoustic emission (AE), and active ultrasonic transmission were measured simultaneously under uniaxial compression to characterize the fracture damage of granites. The deformation and acoustic behaviors with respect to crack initiation and crack damage thresholds were analyzed. Meanwhile, irreversible damage was quantified using different methods. The results show that the marked increase in the AE rate and the average hit energy coincide with the crack initiation stress, ranging from 0.41σc–0.45σc (uniaxial compressive strength), which occurs earlier than the decrease of the P -wave velocity and onset of the rock dilation. The moment in which the average hit energy and ratio of low-frequency AEs start to increase rapidly corresponds to the crack damage stress of 0.71σc–0.74σc. In addition, the fracture damage was quantified by the crack volumetric strain, dissipated energy, modulus loss, AE characteristics, b value (defined as the log-linear slope of the frequency-magnitude distribution of AEs), and ultrasonic properties. It is revealed that the majority of rock damage accumulates after the crack damage stress, corresponding to the appearance of most high-magnitude hypocenters. Rock damage quantified by dissipated energy and AE energy with clear physical meaning is more reasonable and less subjective. Moreover, the precipitous reduction of the b value, a sharp increase in AE energy, and the ratio of low-frequency AEs prior to peak failure is a perfect precursor of potentially brittle failure. [ABSTRACT FROM AUTHOR]

There has recently been considerable research published on the applicability of monitoring systems for improving civil infrastructure management decisions. Less research has been published on the challenges in interpreting the collected data to provide useful information for engineering decision makers. This paper describes some installed monitoring systems on the Hammersmith Flyover, a major bridge located in central London (United Kingdom). The original goals of the deployments were to evaluate the performance of systems for monitoring prestressing tendon wire breaks and to assess the performance of the bearings supporting the bridge piers because visual inspections had indicated evidence of deterioration in both. This paper aims to show that value can be derived from detailed analysis of measurements from a number of different sensors, including acoustic emission monitors, strain, temperature and displacement gauges. Two structural monitoring systems are described, a wired system installed by a commercial contractor on behalf of the client and a research wireless deployment installed by the University of Cambridge. Careful interpretation of the displacement and temperature gauge data enabled bearings that were not functioning as designed to be identified. The acoustic emission monitoring indicated locations at which rapid deterioration was likely to be occurring; however, it was not possible to verify these results using any of the other sensors installed and hence the only method for confirming these results was by visual inspection. Recommendations for future bridge monitoring projects are made in light of the lessons learned from this monitoring case study. [ABSTRACT FROM AUTHOR]

The available models for estimating the creep strains of concrete generally assume concrete as a homogeneous material. Since concrete is a composite, such models cannot take into account incompatible strains between cement paste and aggregates during creep loading. The main objective of this paper is to demonstrate that initial defects could increase the creep strain level and justify the application of a coupling between creep and damage at the macroscopic scale. To do so, different contents of air-entraining agent were used to simulate the internal defects of concrete and high-stress continuous load was applied to concrete samples with different initial defects. By analyzing the stress-strain curves of concretes containing different initial defects after compression, it was concluded that the existence of internal defects had a significant effect on the basic mechanical properties of concrete samples. Acoustic emission technology was used to obtain the internal acoustic emission response of concrete samples under high stress. Creep development rate is nonlinear to load holding level based on the analysis of experimental data and internal structure of concrete samples. [ABSTRACT FROM AUTHOR]

This paper investigates damage and healing of cementitious materials based on fly ash (FA) with a special focus on the effect of repeated loading on the self-healing performance. In total, 90 prism specimens and 33 cylinder specimens were prepared and tested. Variables including the FA replacement ratio and preloading level were considered. Different methods were adopted to evaluate the self-healing performance, i.e., mechanical tests, acoustic emission (AE) analysis, water absorption measurement, and scanning electron microscope (SEM) observation. Test results revealed that an appropriate amount of cement replaced by FA was beneficial to the self-healing performance of the specimens subjected to a high level of repeated preloading, where the strength increased by 11% and the water absorption rate decreased by 12%, in comparison with that of the undamaged specimens. This was attributed to the active hydration of FA, which was confirmed by an energy dispersive X-ray spectroscopy (EDS) analysis. This study extends understanding of the self-healing performance when subjected to repeated loading and provides some useful suggestions for the self-healing technique based on mineral additives. [ABSTRACT FROM AUTHOR]

The effective strain in composites, along with their potential rupture and debonding, plays a crucial role in predicting the strength of retrofitted reinforced concrete (RC) beams. However, only limited experimental data on these phenomena are available, mainly because of the inadequacy of traditional deformation and strain measurement techniques. This paper presents a comparative analysis of instrumentation for monitoring retrofitted RC elements. In particular, the paper addresses beams retrofitted with composite materials, FRPs (fiber-reinforced polymers), and FRCMs (fiber-reinforced cementitious mortars). It also considers strain gauges, fiber Bragg grating (FBG) sensors, LVDTs, digital image correlation (DIC), and acoustic emission (AE) sensors for monitoring strain, displacement, cracking, and debonding. Experiments on six beams are carried out, and the measured data from the monitoring devices are compared. The accuracy of DIC for strain and displacement monitoring is shown to match the performance of traditional methods, with the added benefit of providing full-field monitoring. The use of AE for detecting cracks and debonding, which is not readily possible using traditional methods, is also demonstrated. This is of particular interest for composite-strengthened RC elements, where accurate measurements of effective strain and debonding of the composite material can lead to the development of more precise design formulas. [ABSTRACT FROM AUTHOR]

This paper presents the numerical and experimental validation of the analytical elastoplastic damaging model proposed in the companion paper (Part I). The validation was carried out by describing the pullout failure of epoxy adhesive anchors. Pullout tests were simulated numerically and performed experimentally. Several specimens made of a rebar embedded in a hardened concrete cylinder by means of polyester resin were tested. Conventional strain gauges and acoustic emission (AE) sensors were used to evaluate the structural response of the system and to monitor the onset and progression of structural damage, respectively. The parametric analysis and the moment tensor analysis of the AE data were used to discriminate among different sources of damage. The results show the ability of the model to predict the response of the anchors and the suitability of the AE method to monitor damage onset and propagation and to discriminate among different source of damage. [ABSTRACT FROM AUTHOR]

This paper presents piezoelectric-based passive/active methods to reliably detect and quantify defects in mass concrete or grout structures. A dual-mode sensing methodology that makes use of both passive acoustic emission detection and active ultrasonic wave evaluation methods utilizing piezoelectric sensors is investigated. Two types of piezoelectric sensors (PES) transducers are used for acquiring the passive and active signals, respectively. A novel imaging method is developed to map and locate the acoustic emission source caused by the damage growth in the subject structure. Active sensing is further used to evaluate the growth of the damage. A proof-of-concept test using simulated damage, a pencil lead break for acoustic emission, and a drill hole of various diameters for crack growth has been conducted to show the effectiveness of the present passive/active methods. The methods have also been applied to detect and evaluate crack growth caused by stepwise loading. The work presented in this paper lays the foundation for further development of a dual-mode sensing mechanism for in situ crack growth detection and evaluation in massive grout or similar material structures. [ABSTRACT FROM AUTHOR]

Rock slope landslides and underground construction destabilization are frequently attributed to shear impairment by intermittent joints, and the support by bolts represents an indispensable technique for reinforcing jointed rocks. Therefore, we conducted laboratory experiments on intermittently jointed rock-like materials that were anchored, employing various anchoring inclination angles and methods, to investigate the influence of bolt anchoring on the shear properties and acoustic emission characteristics of intermittently jointed rock-like materials. Experimental results revealed that the peak shear strength of the anchored intermittently jointed rock-like materials is proportional to the bolt inclination angle. The strain on the joint is inversely related to the peak shear strength and the bolt inclination angle. The full-length anchorage and end anchorage can drastically enhance the mechanical traits of intermittently jointed rock-like materials, effectively impeding the proliferation of shear cracks after reaching the peak shear strength. The anchorage inclination exhibits a positive correlation with the accumulative acoustic emission (AE) energy and, conversely, a negative correlation with the peak AE count. In geotechnical engineering, the anchoring effect of anchor bolts can enhance the integrity of fractured rock masses and improve overall stability. [ABSTRACT FROM AUTHOR]

This research was devoted to the development of a structural health monitoring (SHM) system for helicopter structures using the acoustic emission (AE) method. Experiments were carried out on a test bench to test helicopter fuselage and tail boom joints under dynamic loads. During the experiments, several bolted joints fractured. The process of crack development in the bolt material was controlled by the AE method. The results presented in the paper link AE parameters to the process of crack development. Fractographic analysis was used to validate the experimental results. The dependence of fatigue crack growth in a bolt material taking into account bolt retightening in the joint between the tail boom and fuselage was revealed. [ABSTRACT FROM AUTHOR]

Prefabricated and prestressed beams are integral to accelerated bridge construction (ABC) and other construction projects, but concerns exist regarding the development of cracks during curing, form removal, detensioning, transport, installation, and operation. Acoustic emission (AE) sensing techniques have the potential for detecting and locating cracking in prefabricated, prestressed concrete girders used as prefabricated bridge elements and systems (PBES) in ABC as part of a quality assurance/quality control (QA/QC) program. AE measures the elastic waves produced by crack nucleation and growth with an array of point sensors. The AE instrument system is relatively portable, which can allow for it to be an option for off-site fabrication QA/QC and on-site field QA/QC. This paper presents AE measurements and analysis on relatively small laboratory reinforced concrete beam specimens under pullout and three-point bending to demonstrate the efficacy of AE in detecting cracks. It then presents application of AE during detensioning and lifting of full-scale Northeast Extreme Tee (NEXT) beams and Bulb Tee. The results indicate that AE sensing is a practical QA/QC process for PBES elements. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) have become the primary methods for enhancing sustainability in the asphalt industry in recent years. To further enhance sustainability benefits, asphalt producers have begun using RAP and WMA in combination. Research to date has focused on evaluating WMA-RAP mixtures in terms of moisture sensitivity and permanent deformation characteristics as measured in laboratory performance tests. In the present paper, the authors investigate a set of WMA mixtures that encompass a variety of variables, including four WMA additives (Evotherm 3G, Rediset LQ, Sasobit, and Advera) and three RAP contents (0, 15, and 45%). A common belief among practitioners is that the reduced aging in the asphalt binder associated with lower production temperatures in WMA mixtures leaves additional headroom for the incorporation of higher amounts of RAP, which is generally a stiffer, more brittle material. To fully characterize the performance of WMA-RAP mixtures, the authors evaluated the low-temperature, cracking behavior of these mixtures in conjunction with moisture and rutting resistance characterization. They achieved the low temperature testing of WMA-RAP mixtures through the disk-shaped compact tension [DC(T)], indirect tension (IDT) creep compliance, and acoustic emission (AE) tests. Test results showed that chemical additives improved moisture susceptibility according to the AASHTO T 283 standard test and fracture and bulk stress relaxation characteristics using the DC(T) and IDT tests, respectively. The organic Fischer-Tropsch wax-modified WMA mixtures performed the best among the WMA mixtures in terms of rutting resistance. The introduction of RAP led to the increased resistance to permanent deformation and moisture damage. Conversely, RAP reduced thermal cracking resistance according to the low-temperature performance tests in both HMA and WMA. The authors observed the same trend in AE test results as WMA-RAP mixtures exhibited warmer embrittlement temperatures as compared with control mixtures and are therefore expected to be more prone to thermal cracking. On the basis of these findings, thermal cracking resistance remains an issue to be considered in WMA mixtures containing RAP. Additionally, performance testing has shown to be a valuable tool for the evaluation of RAP and WMA mix designs to avoid performance issues in the field. [ABSTRACT FROM AUTHOR]

The excavation of rock masses in deep engineering can induce stress concentration or unloading, which can significantly affect the long-term stability of engineering. To describe the creep mechanical behavior of deep hard rocks after stress adjustment, true triaxial creep tests were conducted through multistage loading and unloading. The effects of σ1 loading, σ2 unloading, and σ3 unloading on creep deformation of granite were investigated. Meanwhile, the changes in creep, acoustic emission (AE) counting, and energy release rates during creep stages were evaluated. The creep failure mode and mechanism of granite were revealed. The results of the true triaxial test showed that both σ1 loading and σ2 unloading accelerate the creep of granite, while σ3 unloading promotes the creep in the σ3 direction, but the creep in σ1 and σ2 directions is not promoted to any significant extent. In the first three creep stages of σ2 unloading, the strain rate of granite changes significantly. Upon approaching the stage of instability fracture, the changes in the AE count rate and energy release rate are more pronounced compared to the strain rate. By analyzing creep curves, a comprehensive three-dimensional nonlinear viscoelastic–plastic damage creep model specifically for granite was established. The consistency between the experimental data and the predicted result obtained from the model shows that the three-dimensional nonlinear viscoelastic–plastic damage creep model can demonstrate the creep behavior of granite under true triaxial σ1 loading and σ2 and σ3 unloading conditions, thereby serving as a valuable reference for assessing the long-term stability of deep rock masses. [ABSTRACT FROM AUTHOR]

In-depth investigations into the effect of water saturation on the damage and failure mechanisms of rock have significance for analyzing the stability of the surrounding rock in water-rich rock masses. Uniaxial compression tests were carried out on two types of sandstone to explore the influence and mechanism of water saturation on their strength and deformation, stress thresholds, energy evolution, and acoustic emission (AE) characteristics. The deduced the following after water saturation: (1) water saturation had an obvious softening effect on both types of sandstone, manifested by a reduction in uniaxial compressive strength and elastic modulus, and an increase in the Poisson's ratio; (2) the normalized crack initiation stress (σci/σf) increased and the normalized crack damage stress (σcd/σf) decreased; (3) the total energy (U), elastic energy (Ue), and dissipated energy (Ud) at the peak strength decreased and the ratio of elastic energy to total energy (Ue/U) decreased; and (4) the peak values of AE count and AE cumulative count decreased in both types of sandstone. Based on our analysis of the AE b-values, the proportion of small-scale ruptures increased. An analysis based on the AE ratio of the rise time to amplitude (RA) value and average frequency (AF) value showed that the proportion of shear fracture increased after water saturation. Our findings provide an indication of the significance of determining the failure mechanism of water-saturated rocks. [ABSTRACT FROM AUTHOR]

This work discussed the results from tests conducted to study the desorption and outburst characteristics of soft and hard coal under different gas conditions. The research found that gas type has a greater influence on the outburst and desorption characteristics of soft coal. Triaxial compression failure can improve the desorption rate of coal specimens, and the gas desorption rate of hard coal is more affected by triaxial compression failure. In the outburst experiments, the greater the test gas pressure, the greater the crush degree of the coal specimen, and the proportion of small-sized coal powder (<0.1 mm) increases but gradually stabilizes. Moreover, the acoustic emission (AE) signals during the outburst process were recorded, and the evolution law of gas pressure in the outburst carven was also analyzed. Finally, the changes in AE signals and gas pressure could be used to predict the damage and destruction characteristics of coal specimens well. [ABSTRACT FROM AUTHOR]

This paper presents a structural health monitoring methodology that uses acoustic emission (AE) features to predict crack growth in structural elements subjected to fatigue. This allows for the prediction of the failure of the structural element at the current load level. The methodology uses Bayesian inference to account for different sources of uncertainty such as uncertainty in the data (AE signal), unknown fracture mechanics parameters, and model inadequacy. The methodology is divided into two main components: a model updating component that uses available data to build a joint probability distribution of the different unknown fracture mechanics parameters, and a prognosis component in which this multivariable probability distribution is sampled to predict the stress intensity factor range at a future number of cycles. The application of the methodology does not require knowledge of the load amplitude nor the initial crack length. The methodology is validated using experimental data from a compact test specimen under cyclic loading. [ABSTRACT FROM AUTHOR]

In the present paper the mechanical and acoustic emission (AE) behaviors of full-scale reinforced concrete beams are evaluated. One of the beams was constructed in two parts, which were assembled later in order to evaluate the effect of the joints in the structural behavior. The load was applied by means of a four-point-bending configuration. It is revealed that at initial stages of loading, the conventional measurements of strain and deflection, as well as pulse velocity, do not show any discrepancy, although the structural performance of the two beams is eventually proven to be quite different. On the contrary, AE parameters, even from early load steps, indicate that the damage accumulation is much faster in the assembled beam. This is confirmed by the calculated sources of AE events which are close to the construction joints. The results show that the AE technique is suitable to monitor the deterioration process of full-scale structures and yields valuable information that cannot be obtained at the early stages of damage by any other way. [ABSTRACT FROM AUTHOR]

This paper describes an experimental investigation to assess the development of the localized damage zone in concrete tested in compression. Cylindrical specimens were loaded and unloaded at different maximum strain levels. The mechanical response was measured and compared with acoustic emission activity. As expected, the acoustic emission activity increased with an increase in load. To establish a correlation between mechanical damage and acoustic emission activity, the acoustic emission events were categorized on the basis of their amplitude and duration. Higher amplitude and longer duration events occurred in the specimens at higher damage levels. A linear correlation was observed between the mechanical fracture energy and the measured acoustic emission energy. Triangulation was used to locate the position of the acoustic emission events and to assess the development of the damage zone during testing. The compression damage zone (CDZ) was found to develop at the time of peak stress with a length of approximately 1.2 times the diameter of the specimen. The size of the CDZ was observed to increase to double the diameter of the specimen at 1.6 times the strain at peak. While preliminary, these results indicate how the damage develops to form a zone that influences the stiffness degradation and the postpeak response of the concrete. [ABSTRACT FROM AUTHOR]

Concrete bridges in the United Kingdom represent a major legacy that is starting to show signs of distress. Therefore, the need for monitoring them is an urgent task. The acoustic emission (AE) technique was proposed as a valid method for monitoring these bridges but more study is needed to develop methods of analyzing the data recorded during the monitoring. The writers would like to propose a b-value analysis as a possible way to process AE data obtained during a local monitoring. The b-value is defined as the log-linear slope of the frequency-magnitude distribution of acoustic emissions. This paper presents the results of a b-value analysis carried out on data recorded during a laboratory test on a reinforced concrete beam designed as representative of a bridge beam. During the experiment, the specimen was loaded cyclically and it was continuously monitored with an AE system. The data obtained were processed and a b-value analysis was carried out. The b-value was compared with the applied load, with a damage parameter, and with the cracks appearing on the beam. The damage parameter represents the cumulative damage in terms of total sum of acoustic emissions. The results showed a good agreement with the development of the fracture process of the concrete. From a study of the b-value calculated for a whole loading cycle and for each channel, some quantitative conclusions were also drawn. Further development work is needed to make the b-value technique suitable for practical use on a real bridge. [ABSTRACT FROM AUTHOR]

A stepped cyclic loading test was designed to investigate the stress memory and acoustic emission characteristics of siltstone under different previous stress levels. This study aims to improve the applicability of the acoustic emission in situ stress measurement method in porous weak cementation strata. The stress memory failure range for siltstone and the memory stress correction formula were determined based on characteristic stress value. The analysis of acoustic emission characteristics revealed the failure mechanism of the Kaiser effect of siltstone, and the following conclusions were obtained. Crack initiation stress can serve as the failure criterion for the stress memory effect in siltstone. Therefore, the failure range for the stress memory effect in siltstone can be defined as a previous stress of less than 15.3 MPa and a memory stress of less than 13.7 MPa. The pore compaction process in siltstone and the friction-generated acoustic emission signal during this process negatively affect stress memory. The primary cause of the stress memory effect in rocks is the irreversible development of new internal cracks. The compression rebound effect of primary soft pores in siltstone mainly causes the Kaiser effect to fail. The compression rebound effect of primary soft pores in siltstone is the main reason for the failure of the Kaiser effect. [ABSTRACT FROM AUTHOR]

Due to the differences of physical and mechanical properties of asphalt pavement materials, asphalt pavement (asphalt mixture) presents complex characteristics. To explore the acoustic emission (AE) wave characteristics of asphalt pavement materials, the automatic sensor test (AST) method was used on coarse aggregate, asphalt, and asphalt mixture at different temperatures. The results show that the peak amplitude and frequency of AE waves in coarse aggregate is the largest, followed by asphalt, and asphalt mixture is the smallest. For asphalt mixture, the larger the nominal maximum size of aggregate, the more serious the waveform distortion, the more complex the frequency distribution, and the smaller the amplitude range of AE waves. AE waves in coarse aggregate is not sensitive to temperature, while the peak amplitude of AE waves in asphalt is linearly related to temperature. The peak amplitude and temperature of AE waves in three gradations of asphalt mixtures can be fitted to obtain the corresponding second-order polynomial. AE wave attenuation is mainly reflected in asphalt mixture, while low-temperature sensitivity is mainly reflected in asphalt and asphalt mixture. [ABSTRACT FROM AUTHOR]

Stud connectors are widely used as shear keys in steel–concrete composite girder bridges, owing to their advantages of easy processing, quick construction, and excellent connection performance. Stud connectors are buried in concrete; therefore, conventional detection methods cannot effectively and reliably detect damage to them. In this study, an acoustic emission (AE)-based methodology was developed to monitor long-term damage to bridge structures and their key components. Damage to stud connectors during the shear failure process was dynamically monitored using the AE technique. AE signals from the entire stud damage process were collected. Subsequently, the characteristic parameters of AE were extracted. According to the process diagram, association graph, and cumulative chart of each characteristic parameter, we first investigated the distributive regularity for the five characteristic AE parameters (energy, ringing count, amplitude, rise time, and duration) of the stud in the elastic, elastic–plastic, plastic, and fracture failure stages. The correlation diagram of amplitude and frequency was also studied. Subsequently, based on the damage factor theory, a damage model of the stud was established by considering the cumulative values of energy and ringing count as the main parameters. The model was further verified using experimental data. More importantly, this proves the feasibility of the model in the quantitative description of the damage process in studs. This study also provides experimental data and a theoretical basis for the detection and evaluation of stud damage in steel–concrete composite girder bridges. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the steel-to-concrete bond phenomenon in two kinds of deformed bars: black steel and hot-dip galvanized steel. The differences in the steel-to-concrete bond behavior are identified in terms of the load-slip curves and the acoustic emission (AE) patterns measured during pull-out tests. Test results show that the bond capacity and the initial stiffness of the bond stress-slip curve of black steel are approximately 20 and 50% greater, respectively, than those of galvanized steel, and the slip corresponding to the maximum bond stress is approximately 20% times larger in the latter. By measuring the AE activity, it is possible to identify the transitional points between the four stages characterizing interaction between the concrete and the bar subjected to pull-out force. Each transition coincides with a sudden drop in the AE activity. [ABSTRACT FROM AUTHOR]

Three-point bending test and acoustic emission (AE) monitoring of notched beams with different volume fractions of steel fiber ultrahigh-performance concrete (UHPC) were carried out. The results show that the initiation toughness, unstable toughness, and fracture energy of UHPC notched beams increase at first and then decrease with the increase of fiber fraction. Based on the stress intensity factor theory, the simplified formulas for calculating initiation toughness and fracture energy were derived. The acoustic emission signal of the UHPC notched beam fracture process was analyzed, and the characteristics of the UHPC material fracture process were characterized by AE energy and cumulative count. Based on the excellent correlation between AE signal and fracture characteristics, it was found that there is an excellent linear relationship between AE energy and fracture energy, and the relationship between cumulative count and crack mouth opening displacement was established. [ABSTRACT FROM AUTHOR]

This study investigates the change in the acoustic emission (AE) parameters emitted in rubberized concrete under abrasion action at a sub-freezing temperature (−20°C). Seven concrete mixtures were developed with two coarse-to-fine aggregate ratios (C/F) (2.0 and 0.7), various crumb rubber (CR) content (0%, 10%, 20%, and 30%), and different rubber particle sizes [4.5 mm CR and 0.4 mm powder rubber (PR)]. Rotating cutter tests were conducted on three 100 mm cubic samples from each mixture at −20°C and 25°C while monitored via an AE system. AE parameters such as amplitude, number of hits, and signal strength were collected and underwent two parameter-based analyses: b -value and intensity analysis approaches, resulting in three additional parameters: b -value, severity (Sr), and the historic index [ H(t) ]. Results showed that testing concrete samples under abrasion at cold temperature, −20°C , resulted in a decrease in the emitted number of hits, cumulative signal strength (CSS), Sr , H(t) , and an increase in b -values compared to testing at 25°C. Furthermore, incorporating rubber particles was found to decrease the AE signals' amplitudes significantly at 25°C and slightly at −20°C , which manifested the higher wave attenuation occurrence at ambient temperature compared to cold temperature. AE analysis also showed a decrease in the abrasion resistance for mixtures with higher C/F, higher CR content, and larger rubber particle size. These decreases were more noticeable at 25°C compared to −20°C. Finally, the study developed two damage classification charts to estimate the ranges of abrasion mass loss percentage and wear depth in terms of the intensity analysis parameters: Sr and H(t). [ABSTRACT FROM AUTHOR]

In this study, inclined shear tests (ISTs) coupled with acoustic emission (AE) monitoring and discrete element method (DEM) numerical simulations were employed to investigate the influence of the water/binder (w/b) ratio (w/b=0.35 and 0.23) and aggregate shape (rounded and angular) on the macro- and microfracture behavior of cement-based materials subjected to shear stress. The experimental results show that macrofracture parameters such as shear strength and stiffness increase as the w/b ratio decreases; however, they are not affected by aggregate shape, in agreement with simulations. The aggregate shape is related to the microcrack behavior. The microcrack distribution in the cement-angular aggregate mixture is confined to the area of the central shear zone, with much lower scatter than that in the cement-rounded aggregate mixture, in which microcracks are scattered around the central shear zone, in line with the macrocrack behavior. This finding is consistent with the numerical simulation results. The DEM simulation results show that the w/b ratio affects macroparameters, namely, Young's modulus (E) and Poisson's ratio (v). The value of E increases as the w/b ratio is reduced and vice versa. The aggregate shape affects only the microparameters (bond properties), which are higher for angular aggregates than rounded aggregates. A method of determination of the DEM input parameters (both micro- and macroparameters) considering different w/b ratios and aggregate shapes was proposed as well. This work provides insights into both the macro and microfracture behavior of cement mortar from the viewpoint of both tests and the relatively new DEM modeling technique. Verified with the IST data, which is rarely found in existing literature, there is generally good agreement between the simulations and tests. Moreover, a unique way of modeling, especially angular aggregate shape has been demonstrated. Further, some reference bond properties and a way to estimate them have been provided for similar simulations. The application of the model presented in this study may be extended to evaluate the strength of rock and assess its suitability as a potentially effective nuclear waste repository site or even evaluate the strength of confined concrete columns (structures) in future studies. These interesting ideas have been presented, for example, because due to the interlocking nature of angular aggregates, the bond properties of cement-based materials made of angular aggregates were found to be higher than those of their rounded aggregate counterparts. [ABSTRACT FROM AUTHOR]

The main cause of degradation for reinforced concrete (RC) structures is the corrosion of the steel reinforcement. Laboratory tests aimed at studying durability are typically accelerated to provide usable results within a reasonable period of time, and well-established electrochemical techniques are used for the assessment of corrosion. However, because these techniques are not suitable for continuous monitoring and are often intrusive, nondestructive testing (NDT) techniques are also suitable for monitoring. Acoustic emission (AE) is one of the NDT techniques used to detect the onset and progression of corrosion. This paper presents an accelerated corrosion test setup and AE monitoring methodology based on the historic index, , for laboratory experiments on RC specimens. Accelerated corrosion is attained by increasing the capillarity suction of RC exposed to chlorides. The frequency spectrum of the AE signals before and after the initiation of corrosion is investigated to isolate the frequency components associated with corrosion. It is shown that the AE signals generated by early corrosion excite a well-defined narrow band of the frequency spectrum. [ABSTRACT FROM AUTHOR]

This paper presents the development and validation of a cyberinfrastructure architecture for research in nondestructive evaluation (NDE) using acoustic emission (AE) data. Existing cyberinfrastructures for civil engineering focus in the curation and preservation of data. In contrast, the proposed cyberinfrastructure is intended to serve as a tool to enable innovation by providing a platform to prototype analysis techniques and sharing data and analysis methods among a research team while removing the burden of memory and computational cost from the user. This is achieved by streamlining the access of large and complex experimental data sets, facilitating the selection of part of the experimental data depending on data features, distributing data analysis using a distributed computing strategy, and allowing the creation of new data features that can be used for subsequent analysis. The experimental data set potentially include data from AE sensors, strain gages, load cells, clip gages, and accelerometers. The proposed framework uses a relational database to store data, web services for data communication, a Condor pool for high throughput computing, and a graphical interface for interaction with the user. An example using data obtained from a compact tension fatigue test is used to show the capabilities of the developed framework. [ABSTRACT FROM AUTHOR]

This paper focuses on the feasibility of using acoustic emission (AE) techniques to evaluate stability of foams produced from paving-grade asphalt binders. The study compared asphalt foamability index [expansion ratio (ER) and half-life (H-L)] measurements with AE measurements for the same foamed asphalt produced using a Wirtgen Model WLB 10 S Laboratory Asphalt Foaming Device. Both ER and H-L are used to characterize the suitability of asphalt binders to produce good-quality foamed asphalt binders for pavement construction. However, current methods for determining foamability are considered as empirical, operator-dependent, and cannot be used for continuous monitoring of the foaming process. Two performance-graded asphalt binders, four foaming water contents, and two foaming temperatures were used. Spectral analyses using a test for white noise suggest AE signals resulting from asphalt foaming are not white noise () and therefore could be useful for evaluating foamed asphalt stability. The evolution with time of AE amplitude during foamed asphalt decay suggests two distinct stages related to foam stability. A clear amplitude dynamics characterized by shorter-duration lower-amplitude foam decay followed by longer-duration higher-amplitude foam collapse was found for all the asphalt binders tested. AE energy, a measure of elastic energy released by collapsing foam bubbles, was found to be sensitive to H-L. The results demonstrate that AE may be useful for characterizing foaming characteristics in a more fundamental manner than existing manual methods. The techniques and results summarized here provide the basis for further investigation into application of AE measurements to monitor and control foamed asphalt stability. [ABSTRACT FROM AUTHOR]