Acoustic Emission Hits Research Articles

Two-Step AE Source location for Detecting Tendon Rupture inside PC Box-Girder in-Service

In order to identify tendon rupture inside a prestressed concrete (PC) girder, new acoustic emission (AE) location system is necessary to be practically applied. In PC girder of an in-service highway, PZT sensors are installed at a web and a deck of the PC girder, and elastic waves generated by tendon rupture is simulated by steel ball impact. AE source location assuming the homogeneous velocity distribution is applied in a development view of the box-girder. Then to verify the accuracy of the location results, the effect of elastic-wave propagation at a joined corner between the web and the deck is simulated by FDM. As a result, the attenuation of first-arrival P waves was observed at the joined corner. It implies that wave energy is so attenuated that apparent velocity decreases. Finally, AE locations lead to erroneous solutions in the development view solved with a constant velocity. To solve the problem, a twostep location system is developed. In the first step, two-dimensional plane, where the tendon rupture is to be identified, is selected from the 1st and 2nd arrivals of AE Hits. Then, in the 2nd step, AE locations are determined from remaining AE sensors located on this plane. By applying this system, the location errors are within 5 % at the both web and deck in a 15 m long PC box-girder.

Excavation-induced cracking of clastic rock: A true triaxial instantaneous unloading study with varied levels of initial damage

The cracking and squeezing problem in deep engineering significantly constrains project construction. To reveal the cracking mechanism of rock under instantaneous unloading, a self-designed rigid true triaxial experimental apparatus, equipped with groundbreaking electromagnetic unloading and high-speed camera functions, was utilized to conduct instantaneous unloading tests on clastic rock with varied levels of initial damage. The results indicate that samples undergo severe and irreversible lateral dilation during instantaneous unloading, with dilational strain rapidly increasing at higher initial damage levels. Instantaneous unloading induces the generation of numerous tensile microcracks, which propagate and coalesce rapidly. The crack propagation speed, as well as the length and width of the cracks at failure, increase with the rise of the initial damage level. The samples eventually exhibit two distinct macroscopic fracture zones: a tensile fracture zone and a tensile-shear mixed fracture zone. Analysis of acoustic emission hits and energy indicates that higher initial damage levels correspond to greater unloading damage, with a higher overall proportion of tensile cracks throughout the experiment. Under the induction of blasting excavation, radial stress is rapidly unloaded, and dense tensile cracks emerge in the immediate surrounding rock, leading to cracking and squeezing towards the free face. Importantly, higher initial damage levels intensify the squeezing effect. The self-developed equipment serves as a crucial technical tool for researching excavation unloading, and the insights derived from this study provide valuable guidance for understanding cracking mechanisms and informing the construction of deep engineering projects.

Experimental investigations on the failure characteristics of the slit-contained circular opening under biaxial compression: Insights into the rockburst prevention

The slit-cut method for the rockburst prevention and control is believed effective with its easiness in operation, adjustment and compatibility. However, there is limited advance knowledge of the physics of the slit-cut method, which is vital for the engineering designs. In this study, the biaxial compression tests with a synchronous AE (acoustic emission)-DIC (digital image correlation) monitoring are creatively carried out on the slit-contained circular opening specimens with different slit configurations to demonstrate the academic thoughts and mechanisms of the slit-cut method. The experiments document the two typical failure types namely the internal crack propagation and the dynamic rockburst, which occupy different AE hit rate characteristics and different entropy properties. With the occurrence of rockburst, the AE hit rate presents a bouncing ascend-descend trend, and a higher disorder and chaos is faithfully exhibited. Depending on the slit parameters, the slit-cut method can efficiently mitigate rockburst in terms of the occurrence frequency and magnitude. The underlying mechanism lies in the enhancement of the shear mechanism and the development of the internal cracks through which the stored energy can be greatly dissipated. However, due to the unrestricted shear failure in the slit-contained opening specimens, the opening-scale inward instability can be triggered by the internal crack coalescence, thus posing a threat to the safety of the opening. Implementing the slit-cut method with a consideration of the in-situ stress conditions is evidently essential for the safe excavation.

New evaluation method for defects propagation in toroidal roller bearings using dominant frequency of acoustic emission

ABSTRACT The increased use of roller bearings in recent years has made it vital to develop techniques for Condition Monitoring (CM) of these valuable assets. Toroidal Roller Bearings (TRB) are one of the recent inventions that has revolutionised some industries because of its unique design. In this study, newly produced TRBs were tested using Acoustic Emission (AE), vibration and temperature, on a specially designed test rig. The AE signal was recorded, processed, and analysed using FFT-based methods to transform from the time domain to the frequency domain, and to specify the Dominant Frequency (DF) of each hit in the signal. The result of the analysis was a layout on the time domain of the DFs of all AE hits along with RMSAE and other parameters, this layout was called DF map. The test was divided into three phases, and the DF bands were divided horizontally into three band groups. The aim is to establish a correlation between the phases and DF bands. Knowing the type of defects that are typical for each phase in the test provided insights to what are the DFs of that type. Promising results can be achieved using this measuring method on other types of bearings.

Adaptive stepsize forward–backward pursuit and acoustic emission-based health state assessment of high-speed train bearings

Compressed sensing (CS) is a promising tool for data compression reconstruction. However, fault diagnosis methods for high-speed train bearings based on CS and acoustic emission (AE) technologies have not been reported yet. Notably, the accuracy and speed of CS two-stage reconstruction methods are affected and restricted by prior initial conditions. Therefore, this article proposes adaptive dynamic thresholds applicable to adaptive stepsize forward–backward pursuit (ASFBP), and bearing health state assessment method. First, the adaptive dynamic thresholds for atom selection and deletion are constructed based on the residual feedback mechanism and the atom quality distribution law, which enables ASFBP to realize high-precision rapid reconstruction of signal without any atom priori initial conditions. Second, the initial dictionary length is improved based on the AE hit characteristics. Furthermore, a damage state comprehensive evaluation index (DSCEI) is established using principal component analysis based on AE time-domain hit parameters and compression-domain energy parameter. Compared with the kurtosis index and permutation entropy index, the DSCEI demonstrates better monotonicity and stability in the quantitative evaluation of high-speed train bearing condition. Finally, the validity and stability of the method are verified by testing under complex test conditions resembling actual high-speed train lines, providing valuable insights for the CS-based data-driven bearing fault diagnosis.

Micro- and macro-scale fracture behaviour of brittle rocks: Comparison between the conventional Brazilian test and the advanced universal snap-back indirect tensile test (AUSBIT)

Post-peak behaviour is crucial for the estimation of rock mass fracturing in cave mining operations where hard rocks can exhibit class-II or snap-back response when subjected to loading. Despite the rapid development of research into class-II rocks under compression, the corresponding behaviour in tensile tests has rarely been investigated, which is critical considering the complexity of rock mass fracturing under various stress states. The post-peak response of brittle rocks involves abrupt micro-fracturing, leading to brittle macro-scale behaviour. Controlling the fracture process using the Advanced Universal Snap-Back Indirect Tensile test (AUSBIT) allowed the acquisition of the complete macro-scale class-II behaviour in the post-peak regime, facilitating the use of advanced techniques for insights into both micro and macro-scale fracture. In this study, the AUSBIT tests with digital image correlation (DIC) and acoustic emission (AE) instrumentation were conducted to analyse the progressive failure in Calca granite and Gosford sandstone specimens. Post-test observations of the fracture surfaces were performed using a scanning electron microscope (SEM). From a macroscale viewpoint, the lateral strain control in AUSBIT enabled controlled cracking with significant lateral strain extension prior to failure accompanied by gradual energy dissipation and higher rates of AE activity as smaller magnitudes of energy are being released by each AE hit or microcrack compared to conventional Brazilian tests. The stable microcrack propagation was also identified from SEM observations with more uniform profiles of microcracks and less debris observed in AUSBIT specimens. These findings were more significant in Calca granite, which verified its extreme class-II behaviour while also demonstrating the efficiency of AUSBIT in controlling the violent failure of high-strength brittle rocks commonly encountered in deep mining projects, leading to the acquisition of more accurate material behaviour in terms of micro and macro-scale post-peak features which was unattainable from conventional indirect tensile tests.

Optimizing Building Rehabilitation through Nondestructive Evaluation of Fire-Damaged Steel-Fiber-Reinforced Concrete.

Fire incidents pose significant threats to the structural integrity of reinforced concrete buildings, often necessitating comprehensive rehabilitation to restore safety and functionality. Effective rehabilitation of fire-damaged structures relies heavily on accurate damage assessment, which can be challenging with traditional invasive methods. This paper explores the impact of severe damage due to fire exposure on the mechanical behavior of steel-fiber-reinforced concrete (SFRC) using nondestructive evaluation (NDE) techniques. After being exposed to direct fire, the SFRC specimens are subjected to fracture testing to assess their mechanical properties. NDE techniques, specifically acoustic emission (AE) and ultrasonic pulse velocity (UPV), are employed to assess fire-induced damage. The primary aim of this study is to reveal that AE parameters-such as amplitude, cumulative hits, and energy-are strongly correlated with mechanical properties and damage of SFRC due to fire. Additionally, AE monitoring is employed to assess structural integrity throughout the loading application. The distribution of AE hits and the changes in specific AE parameters throughout the loading can serve as valuable indicators for differentiating between healthy and thermally damaged concrete. Compared to the well-established relationship between UPV and strength in bending and compression, the sensitivity of AE to fracture events shows its potential for in situ application, providing new characterization capabilities for evaluating the post-fire mechanical performance of SFRC. The test results of this study reveal the ability of the examined NDE methods to establish the optimum rehabilitation procedure to restore the capacity of the fire-damaged SFRC structural members.

Characterization and differences of acoustic signals response of semi-circular red sandstone under combined monotonous and cyclic loadings

After underground coal mining, rocks are often subjected to tensile damage by the interaction of dynamic and static loadings. The process of rock fracture development under dynamic and static loadings will be released in the form of acoustic energy to form an acoustic signal. In addition, the acoustic signals in dynamic loading differ from that in static loading. Therefore, this study conducted three-point bending experiments with continuous dynamic loading and dynamic–static coupling loading on semi-circular red sandstone specimens. The acoustic signals during red sandstone specimens’ tensile damage were monitored in real-time. The results show that red sandstone’s tensile strength and deformation are enhanced under dynamic–static coupling loading. The red sandstone has a more effective acoustic emission hit rate, energy rate, and r during tensile damage under continuous dynamic loading. In dynamic loading, macroscopic fractures are developed in red sandstone, which has few acoustic emission events but releases strong acoustic signals. In static loading, the pores inside the red sandstone are compacted, the rock particles are rearranged, and the tiny fractures are closed, and its acoustic emission events are many but low in energy. In addition, the rock particles in the front area of the static loading fracture are tightly cemented, which increases the difficulty of separating the rock particles in the front area of the fracture under dynamic loading. Then weakening the red sandstone fracture development process and suppressing its acoustic signals. The research results provide more insight into the differences in tensile damage processes in red sandstone under the interaction of dynamic and static loadings.

Experimental study on dynamic response of hard rock blasting under in-situ stress

Deep mine rock mass is in high static stress and dynamic disturbance coupling conditions, its mechanical properties and failure mode is different from the shallow rock mass, which leads to low rock blasting efficiency and engineering geology hazards. In-depth research on the dynamic response of rock blasting under in-situ stress will help to optimize the blasting design, improve the blasting efficiency and safety of blasting operations, and provide theoretical support for rock blasting in deep mines. In this study, the blasting experiment was conducted on granite specimens under different biaxial static stress conditions. Meanwhile, the dynamic response of rock blasting was monitored, collected, and analyzed using a high-speed digital image correlation (DIC) measurement system, a strain wave acquisition system, and an acoustic emission (AE) system. The results show that small and medium pre-static loads inhibit blast crack propagation, at which time the cumulative AE hits from dynamic loads (CAECd) are more than those from pre-static loads (CAECs), but large pre-static loads promote crack propagation, at which time CAECs are more than CAECd. Secondly, as pre-static load increases, the specimen's maximum strain (εmax) decreases first and then increases, but as lateral pressure coefficient (K) increases, the εmax in the direction of lower static stress decreases gradually and the εmax in the direction of higher static stress remains constant. In addition, the confining pressure magnitude and K affect the area and shape of the failure zone of the specimen, as well as the size and propagation direction of the radial crack. Especially when the confining pressure is high, the specimen will undergo shear failure, and the smaller K is the more serious the shear failure. Finally, the failure criterion of rock under dynamic-static coupling conditions is proposed based on the energy index, and different failure types of rock are discussed.

An Experimental Study of the Acoustic Signal Characteristics of Locked-Segment Damage Evolution in a Landslide Model.

Three-section landslides are renowned for their immense size, concealed development process, and devastating impact. This study conducted physical model tests to simulate one special geological structure called a three-section-within landslide. The failure process and precursory characteristics of the tested samples were meticulously analyzed using video imagery, micro-seismic (MS) signals, and acoustic emission (AE) signals, with a focus on event activity, intensity, and frequency. A novel classification method based on AE waveform characteristics was proposed, categorizing AE signals into burst signals and continuous signals. The findings reveal distinct differences in the evolution of these signals. Burst signals appeared exclusively during the crack propagation and failure stages. During these stages, the cumulative AE hits of burst signals increased gradually, with amplitude rising and then declining. High-amplitude burst signals were predominantly distributed in the middle- and high-frequency bands. In contrast, cumulative AE hits of continuous signals escalated rapidly, with amplitude monotonously increasing, and high-amplitude continuous signals were primarily distributed in the low-frequency band. The emergence of burst signals and high-frequency AE signals indicated the generation of microcracks, serving as early-warning indicators. Notably, the early-warning points of AE signals were detected earlier than those of video imagery and MS signals. Furthermore, the early-warning point of burst signals occurred earlier than those of continuous signals, and the early-warning point of the classification method preceded that of overall AE signals.

Combined Passive and Active Ultrasonic Stress Wave Monitoring of Concrete Structures: An Overview of Data Analysis Techniques and Their Applications and Limitations

Combined passive [or acoustic emission (AE)] and active ultrasonic stress (US) wave monitoring has been shown to provide a more holistic picture of ongoing fracture processes, damage progression, as well as slowly occurring aging and degradation mechanisms in concrete structures. Traditionally, different data analysis techniques have been used to analyze the data generated from these two monitoring approaches. For AE data analysis, for instance, signal amplitudes, hit rates, source localization, and b-value analysis have been used to detect and locate cracking. On the other hand, amplitude tracking, magnitude squared coherence (MSC), and coda wave interferometry (CWI) are examples that have been employed for US data analysis. In this presentation, we explore these data analysis techniques and show where their respective applications and limitations might be. After providing an overview of the monitoring approach and the different data analysis techniques, results and observations from select laboratory experiments, as well as an in-service structure are discussed. Finally, suggestions for further work are proposed.

Study on temporal and spatial response of pressure stimulated current induced by coal deformation and rupture

The pressure stimulated current (PSC) signal emitted during the deformation and fracture processes of coal and rock materials holds significant importance for monitoring dynamic disasters in coal mines. However, the spatial response characteristics remain inadequately explored, posing significant challenges to the identification of risk-prone areas for underground dynamic disasters. To study the temporal and spatial response characteristics of PSC signal, the PSC response experiment in the failure process of raw coal under load was carried out, PSC signals from various spatial positions of coal were collected throughout the loading process. The results show that the sudden increase of axial PSC and the sudden decrease of transverse PSC appear with the sudden increase of acoustic emission (AE) hit rates, which is the main characteristic of the aggravation of coal internal fracture degree. The PSCs are closely related to the damage characteristics of the sample in terms of its corresponding position and drop time, which can better reflect the fracture concentration location of the coal sample. Building upon this foundation, the paper explained the internal factors contributing to variations in PSC spatial response characteristics of coal samples during load failure and emphasizes the inhibitory effect of crack development on PSC changes.

Revealing evolution law and failure mechanism of interface damage in concrete-encased CFST columns by acoustic emission technology

Concrete-Encased Concrete-Filled Steel Tubular (CFST) has extensive applications in high-rise buildings and bridge engineering as a high-performance composite structure. The severe bond failure between Concrete-Filled Steel Tubular and the outer concrete poses a significant threat to the integrity and safety of the structure. Considering the concealed and random nature of interface damage, this study proposes a real-time monitoring and evaluation method for Concrete-Encased CFST interface damage based on acoustic emission (AE) technology. Four groups of experiments on Concrete-Encased CFST column interface shear was conducted to investigate the influence of the number of shear connectors on the bond failure mechanism between CFST and the outer concrete. The signal characteristics of three kinds of AE sensors with different operating frequency ranges were analyzed to guide the selection of sensors according to the monitoring targets. The structural damage development trend has been recognized by analyzing the change rule of AE feature parameters. RA-AF correlation analysis has been used to identify the evolution law of cracks and the failure mechanism of the structure. The b-value analysis has been used to evaluate the damage severity of the structure. From the above three aspects, the damage evolution law and failure mechanism of the interface can be revealed. The results indicate that the R3α sensor is suitable for early warning of damage, the R15α sensor can be used for monitoring and warning of structural failure, and the R6α sensor can be used to describe and evaluate the whole process of damage. Based on the features of AE hit rate, cumulative hits, and cumulative energy, the damage process of Concrete-Encased CFST column interface can be accurately divided into the elastic stage, local slip stage, shear connector fracture stage, and slip stage. The RA-AF correlation analysis showed that the shear cracks were detected to develop rapidly before the peak load, and a significant number of tensile cracks caused by cracking of the outer concrete appear around the peak load. The changes of b-value can effectively reflect the magnitude of damage and record the occurrence of major damage.

Comparative study on fracture evolution in steel fibre and bar reinforced concrete beams using acoustic emission and digital image correlation techniques

In recent decades, the demand for sustainable construction practices has increased, but raw materials such as reinforcing steel remain scarce. Therefore, steel fibres have emerged as a popular and sustainable choice in the construction industry, offering a cost-effective alternative to traditional steel bar reinforcement for both flatwork and elevated structures. The purpose of this study is therefore to compare the performance of fracture behaviour between steel fibre-reinforced concrete (SFRC) and steel bar-reinforced concrete (SBRC) beams subjected to three-point bending. The fracture process was monitored by using two non-invasive techniques: acoustic emission (AE) and digital image correlation (DIC). The damage level was identified by characterizing the parameter-based AE data such as hit rate, energy release, count, rise time, amplitude, and signal strength. DIC images were employed to visualise the crack propagation in parallel with the AE data. To further understand the fracture characteristics, the integration of 2D source localization of AE events (based on local AE fracture energies) with DIC results was investigated. The parameter-based AE results showed that SBRC beam experienced a high density of AE hits with large peak amplitude events that were accelerated during the pre-peak loading phase. The Ib-value analysis revealed that SBRC beam exhibited a higher degree of fracture magnitude during the primary crack development process than SFRC beam. Following the main cracking stage, SFRC beam demonstrated an improved post-cracking softening behavior and superior ability to arrest crack propagation compared to SBRC beam. The integration of local AE fracture energy and DIC results provided a novel approach for a better understanding of the fracture behaviour in both SFRC and SBRC beams. This study’s findings contribute to more precise monitoring of fracture evolution in SFRC and SBRC beams, ultimately improving the selection process for primary reinforcement in flatwork and elevated structures.

Macro-micro mechanical behavior of saturated cemented sands during drained triaxial shearing

To enhance the understanding of the macro-micro mechanical behavior of cemented sands, a series of drained triaxial shearing tests were conducted on saturated cemented sands with varying cement contents and confining stresses. These tests incorporated high-performance acoustic emission (AE) monitoring and an environmental scanning electron microscope (ESEM) technique. The results yielded quantitative interpretations of macro-mechanical response, microstructural variation, and AE behaviors. Specifically, increasing cement content led to an exponential reduction in porosity (or pore area ratio) and a power increase in pore number, possibly due to the production of hydration products that segment large pores. Relationships were established among peak strength (or AE hits), cement content, and confining stress. However, AE trends diverged from those observed in peak strength due to microstructural modifications under different cement contents and their resulting differences in micromechanical behavior during shearing. General relationships between AE rate and mechanical parameters were established during the initial shearing stage, regardless of cement content and confining stress. Moreover, AE evolution efficiently characterized subtle variations in failure patterns due to its high sensitivity to failure-induced structural modifications. These contributions have the potential to establish a non-destructive field evaluation framework and provide guidelines for the efficient utilization of cemented soils in geological and geotechnical engineering applications.

Insight into the elastoplastic behavior of Beishan granite influenced by temperature and hydraulic pressure

Granite is an ideal host rock for high-level radioactive waste (HLW) repositories. In the deep environment of HLW repositories, granite is subjected to variable temperature and hydraulic pressure. In order to investigate the influence of temperature and hydraulic pressure on the elastoplastic behavior of the Beishan granite, the present paper implemented a set of triaxial compression experiments at various temperatures and hydraulic pressures corresponding to the environment of HLW repositories. The deformation processes, damage evolution, elastic coefficients, and strength of the Beishan granite were analyzed, resulting in a limited change versus temperature and hydraulic pressure. The residual strengths of granite are similar, but a higher temperature surpasses about 70 °C degrades the friction strength of granite. Evidence from the acoustic emission (AE) hits shows the damage rate is accelerated by improved temperature and hydraulic pressure. According to the experiment-based mechanism, a modified elastoplastic model was proposed which considered thermal pressurization and changeable compressibility. The results of computation based on the proposed model match well the experiment data.

Effect of cementation on the mechanical response of sands using acoustic emission technique

This study investigates the impact of cementation on the mechanical behavior of sands with various cement content (CSR) in drained triaxial compression, employing both Acoustic Emission (AE) and Environmental Scanning Electron Microscopy (ESEM) measurements. The experimental findings, encompassing quantitative statistics of stress-strain relations, microstructure variations, and AE characteristics, demonstrate that: the addition of CSR from 1% to 20% leads to an exponential rise in peak strength and stiffness, marking a transition from ductile to brittle mechanical failure, which is pinpointed between CSR levels of 5% to 10%. AE characteristics unveil an upward-opening parabola of normalized AE hits with CSR, a clear transition zone identification, and three distinct types of AE rate evolutions corresponding to failure patterns of ductile bulging, shear banding, and brittle fracturing, respectively. It suggests an intimate correlation with the intrinsic differences in micro-mechanical behaviors and AE propagation properties of cemented sands with varying CSRs. Notably, the bulging and shear banding processes are divided by AE into three stages, whereas fracturing is characterized into five stages. Two precursory AE anomalies associated with incipient failure and complex failure modes are observed, emphasizing the advantage of using AE to reflect the internal micro-mechanical behavior of cemented sands over conventional stress-strain manifestations.

Damage assessment of precast reinforced concrete beam-column connections using AE technology

The beam-column connection is both the critical area and the weak part for the prefabricated reinforced concrete (PC) frame structure. The ductile connection with a U-shaped shell has been well-developed for the PC cross-shaped connection. In this paper, two optimizing reinforcement methods in the U-shell were proposed to improve the seismic performance of the PC beam-column connection. Three full-scale PC beam-column connections were designed and produced. Then, reversed cyclic loading was applied to the connections with acoustic emission (AE) technology as the measuring method to investigate the failure modes and damage mechanisms under seismic actions. The results show that increasing the connecting reinforcement area can effectively promote the bearing capacity of components while setting stirrups enables improving energy-dissipating capacity. Based on the variation of AE hits, the loading process can be divided into three stages, and the optimization effects of two measures were reflected at the different loading stages. According to the Ib-value analysis, it can be seen that the cyclic development of microcrack propagation and macrocrack penetration was the main failure mode of components. Besides, the k-means algorithm was used to classify the AE signals into four clusters with different crack patterns. In addition, based on AE energy calculation, the damage prediction model was constructed for the three full-scale specimens.

In-line monitoring of cryogenic three-point bending test of fiber-reinforced composites using acoustic emission

Remotely in-line monitored acoustic emission (AE) of interlaminar shear strength tests in a 3-point bending test of fiber-reinforced polymer composites (FRP) conducted under cryogenic conditions in liquid nitrogen (LN2) were studied. The AE sensors were reversibly mounted at the outer components of the testing machine to thermally decouple them from the cryogenic area and use AE signal transmission through the testing machine structure as a waveguide. The damage mechanisms and effect of the cryogenic temperature were studied at 296 K room temperature (RT) and in LN2 at 77 K, considering machine and process noises. The correlation of machine data with acoustics and the AE hit analysis revealed matrix cracking as the most frequent damage mechanism under both conditions but with different failure mechanisms. At RT and applying higher loads, the most damage suddenly occurred, and the specimen failed. In LN2, the damage occurred continuously from the beginning of testing. The amount of fiber failure increased, and the AE feature ranges enlarged. This study presents a method by AE for remote monitoring the mechanical response of FRP in cryogenic fluids such as liquid hydrogen. The method provides a new approach to support the more efficient development of FRP materials for storage vessel structures and structural health monitoring systems.

Rock weathering: The effects of varying rock moisture on controlled weathering cycles in low porosity limestone

Examples of rockwall weathering processes include diurnal heating and cooling, diurnal and seasonal freezing, wetting and drying and thawing/seasonal active-layer thawing. These stress-loading processes often occur synergistically and cause a weakening of the rockwall through the propagation of sub-critical cracks. The Acoustic Emissions (AE) released by these cracking events can be measured in order to quantify the weathering efficacy. While the effects of thermal cycling are well studied, rock moisture content and its control on these weathering processes is rarely considered in detail.To better understand rock moistures effect on weathering processes we subjected Wetterstein limestone samples with different starting moisture contents (0 %, 25 %, 50 %, 75 %, 100 %) to thermal cycling above (5 to 35 °C) and below (5 to −10 °C) freezing and a longer freezing cycle with gradual stepped thawing (10 to −10 °C). In addition to this we simulated wetting and drying cycles at a constant temperature. For all of these weathering cycles, relative efficacy was assessed by amount of AE hits and change in effective porosity.Rock moisture was found to have little effect on the overall AE count and effective porosity increase over shorter thermal cycling. However, freeze-thaw cycling was shown to have similar weathering effect to thermal cycling of 3 K greater thermal gradient above freezing. Meanwhile longer duration freezing cycles see an increase of rock moisture create 4× as many cracking events compared to dry samples. More re-freezing events are seen in lower saturation samples and when considered with the synergistic effects of wetting and drying in natural open systems, the presence and mobility of pore water are considered to be more important than the quantity.