Immersion Conditions Research Articles

Fractal Characteristics and Acoustic Emission during the Failure Process of Argillaceous Siltstone with Different Moisture Contents

Compressive strength and tensile strength are the critical parameters to determine rock performance, which can reflect the rock’s resistance to deformation and damage. Brazilian indirect tensile and uniaxial compression tests were carried out on rocks under different water immersion conditions to study acoustic emission (AE) characteristics and crack propagation during rock fracture. The test results show that water has a deteriorating effect on the argillaceous siltstone, with significant attenuation of both compressive and tensile strengths. With the increase in moisture content, the number of AE events decreased, the cumulative AE ringing count showed a gradual rise in steps, and the proportion of AE peak frequencies in the range of 0-200 kHz gradually increased. Natural rock samples are more brittle than water-saturated rock samples. The higher frequency of AE events and the higher energy released during the destruction of natural rock samples reflect in the clustering of high-energy AE source locus near the main rupture surface. The AE source locus is 1-2 energy levels higher in the vicinity of the fracture surface than in the water-saturated rock samples. The rock samples exhibited random packing of mineral particles and contained many clay minerals by SEM analysis of fracture microstructure. Water dissolves mineral particles and cementitious materials, producing microcracks with propagation potential. Analysis of the AE time sequence based on fractal theory reveals that fractal dimension value varies with the increase of moisture content. The variation of the fractal dimension D values for the water-saturated rock samples ranges from 0.4 to 0.65. This indicates that the number of microcracks is higher and their propagation more complex when the moisture content of the specimen is higher. The failure characteristics of the rock samples in the above research can provide a reference for monitoring rock mass stability under tunnel water inflow.

Influence of Filler Type and Rheological Properties of Asphalt Mastic on the Asphalt Mastic-Aggregate Interaction.

The asphalt mastic-aggregate interaction plays an important role in the overall properties of asphalt mixtures and their durability in service in flexible pavements. This paper aims to study the influence of the physico-chemical features of fillers and the rheological properties of asphalt mastics on the bonding behavior between asphalt and aggregate, and the interfacial deterioration mechanism when subjected to static water immersion and pressured water immersion. It was found that the filler type (limestone powder, basalt powder, and granite powder) had a certain influence on the complex modulus of asphalt mastics, and its pore volume and specific surface area had significant effects on the phase angles and permeability of asphalt mastics. The effect of water pressure can accelerate the deterioration of bond strength of the asphalt mastic-aggregate interface in the short term, indicating that the dynamic water pressure generated by the driving load promotes the water damage process in asphalt pavements. In comparison, the residual bond strength ratio of the granite-asphalt mastic aggregate was the highest, while its bond strength was lower than that of the interface between limestone-asphalt mastics and limestone aggregate. This demonstrated that a low asphalt mastic complex modulus and a high phase angle are helpful in improving the durability of asphalt mixtures subjected to static and pressured water immersion conditions.

Comparative experiment of steel bar corrosion at concrete construction joints

Introduction: Construction joint is common and even inevitable in most of the reinforcement concrete structures. This study was to assess the effect of construction joints on chloride-induced corrosion of reinforcing steel in concrete.Methods: Test parameters included two environmental conditions (salt solution immersion condition and cyclic wet-dry condition), two forms of construction joint (direct wet joint and roughened wet joint) and four types of steel bar (mild steel bar, ferritic stainless-steel bar, austenitic-ferritic stainless-steel bar and epoxy-coated steel bar). The corrosion test of 90 specimens was carried out by electrochemical accelerated corrosion method. The weight loss of each steel bar and steel bar section in specimens was measured. An influence coefficient (k_j) of construction joint on local weigh loss of steel bars was defined.Results: Except for epoxy-coated steel bars, the most severe corrosion of experimental steel bars in concrete specimens all occurred at the joints, while the corrosion in non-joint sections of steel bars was relatively uniform and less. The weight loss rate of specimens has the range of 1.18% to 15.73% with an average value of 6.22%. The average k_j of mild steel bars, S11203 stainless steel bars, and S23043 stainless steel bars are 1.38, 1.92, and 1.97, respectively. The average k_j of specimens in immersion condition and cyclic wet-dry condition are 1.44 and 2.07. The corrosion of epoxy-coated steel bars mainly occurred at the damage locations of epoxy coating, not mainly at the joints.Conclusion: Chloride-induced corrosion of steel bars at construction joints was always more severe than at non-joints, especially in cyclic wet-dry environments, even for stainless-steel bar, but epoxy-coated steel bars were excluded.

The effect of time dependent native oxide surface conditions on the electrochemical corrosion resistance of Mg and Mg-Al-Ca alloys

The time dependent native oxide surface conditions of Mg and Mg-Al-Ca alloys under moderate atmospheric conditions were continuously analysed via in situ SKPFM, in situ XRR and ex situ XPS measurements. The progressive hydration of the MgO layer appears to be the dominant surface reaction for all investigated alloys during the investigated time period up to 24 h. Subsequent electrochemical measurements revealed a reduced corrosion resistance of all Mg alloys under short-term immersion conditions with a higher hydration degree of the native oxide.

Biomimetic, Mechanically Strong Supramolecular Nanosystem Enabling Solvent Resistance, Reliable Fire Protection and Ultralong Fire Warning.

A graphene oxide (GO)-based smart fire alarm sensor (FAS) has gained rapidly increasing research interest in fire safety fields recently. However, it still remains a huge challenge to obtain desirable GO-based FAS materials with integrated performances of mechanical flexibility/robustness, harsh environment-tolerance, high-temperature resistance, and reliable fire warning and protection. In this work, based on bionic design, the supermolecule melamine diborate (M·2B) was combined with GO nanosheets to form supramolecular cross-linking nanosystems, and the corresponding GO-M·2B (GO/MB) hybrid papers with a nacre-like micro/nano structure were successfully fabricated via a gel-dry method. The optimized GO/MB paper exhibits enhanced mechanical properties, e.g., tensile strength and toughness up to ∼122 MPa and ∼1.72 MJ/m3, respectively, which is ∼3.5 and ∼6.6 times higher than those of the GO paper. Besides, it also shows excellent structural stability even under acid/alkaline solution immersion and water bath ultrasonication conditions. Furthermore, due to the presence of promoting reduction effect and atom doping reactions in GO network, the resulting GO/MB network displays exceptional high-temperature resistance, sensitive fire alarm response (∼0.72 s), and ultralong alarming time (>1200 s), showing promising fire safety and protection application prospects as desirable FAS and fire shielding material with excellent comprehensive performances. Therefore, this work provides inspiration for the design and fabrication of high-performance GO-based smart materials that combine fire shielding and alarm functions.

Investigation the effect of freeze–thaw cycle on fracture mode classification in concrete based on acoustic emission parameter analysis

This study experimentally investigates the influence of freeze–thaw (F-T) cycles on the mechanical properties and cracking features of concrete. The specimens, which are previously subjected to various numbers of freezing (-20 °C) and thawing (20 °C) cycles, are tested under unixial compression condition. Integrated acoustic emission (AE) and digital image correlation (DIC) techniques are adopted to study the mechanical characteristics of the concrete specimen subject to different F-T cycles under different immersion condition. The micro-structure of the concrete specimen after F-T cycle treatment is observed with T2 distribution by the nuclear magnetic resonance (NMR) technology. The changes in the amount of uniaxial compressive strength (UCS), elastic modulus, and peak strain of the specimens before and after various F-T cycles are comprehensively analyzed. The results show that the brittleness of the specimen decreases and the ductility increases as the number of F-T cycle increases. The peak load and elastic modulus decreased gradually with the increase of F-T cycle times, and the peak strain presented an upward trend. The concrete specimens without F-T cycle action or subjected to less F-T cycles action suddenly lose their bearing capacity and the failure mode is shear slipping. For the specimens undergoing more F-T cycles action, the stress–strain curve exhibits lower slopes during the strain softening stage. Kernel density estimation (KDE) results show that under the lower F-T cycle, the tensile crack has a higher AF (acoustic emission count/duration) value and a lower RA (rise time/amplitude) value, and the obvious shear/mixed cracking phenomenon occurs after the higher F-T treatment. The K-means clustering method has its advantages in the classification of AE cracking events. The b value increased with the increase of F-T cycles, indicating that F-T cycles can caused internal damage of the specimens, and the degree and scale of internal damage increased with the increase of F-T treatment times. Furthermore, the damage degree of the specimens under semi-immersion in water solution is greater than that under complete immersion in water solution.

Investigation of the mechanical behavior and continuum damage model of sandstone after freezing–thawing cycle action under different immersion conditions

Investigation of the mechanical behavior and continuum damage model of sandstone after freezing–thawing cycle action under different immersion conditions

Effects of salinity, temperature, and immersion conditions on seed germination of invasive Spartina alterniflora Loisel (smooth cordgrass) in Japan

Spartina alterniflora is a halophytic perennial grass species that has invaded coastal wetlands worldwide, including tidal flats in Japan. Rapid removal or eradication of invasive plants is desirable because of their severe ecological impact on local ecosystems. Seed germination is the main cause of its distribution and invasion. Understanding germination characteristics of S. alterniflora is critical for the prediction and early detection of its populations in new environments. Therefore, we aimed to investigate the effects of salinity (0, 10 20, 30, and 40 g/L artificial seawater), temperature (15, 20, 25 °C for constant, and 15/25 °C for alternating), and seed immersion (5 ml and 40 ml medium) based on laboratory experiments to evaluate the physicochemical environmental factors that facilitate the germination of S. alterniflora seeds. The cumulative germination rate and mean germination time were significantly affected by temperature and salinity but not by immersion. Increased salinity gradually reduced the cumulative germination rate in all temperature and immersion conditions. The mean germination time tended to be prolonged with the salinity level. A constant temperature of 25 °C promoted higher seed germination compared to constant temperatures of 15 and 20 °C. Notably, alternating temperature between 15 and 25 °C induced a higher seed germination compared to other constant temperatures. In addition, alternating temperatures varied the mean germination time to facilitate sensitivity to salinity, indicating that temperature fluctuation is a key factor that stimulates seed germination of S. alterniflora. These results suggest that S. alterniflora seeds prefer gaps in vegetation canopies and a low depth of burial in soil. Further studies are needed to analyze prevention strategies for the eradication of this invasive species in Japan.

Durability of BFRP bars embedded in seawater sea sand coral aggregate concrete in simulated seawater environment: Effects of coral coarse aggregate and cement contents

This study evaluates the influences of coral coarse aggregate (CCA) and cement contents on the durability performance of basalt fiber-reinforced polymer (BFRP) bars embedded in seawater sea sand coral aggregate concrete (SSCC). The evaluation is conducted by characterizing the changes in interlaminar shear strength after accelerated exposure in a simulated seawater environment. Accelerated aging tests were conducted under varying exposure durations (60, 120, and 180 days) and temperatures (25, 40, and 55 °C). The 1H low-field nuclear magnetic resonance, Fourier transform infrared spectroscopy, and scanning electron microscopy analyses were conducted to investigate the deterioration mechanisms of embedded BFRP bars. It was found that SSCC-embedded BFRP bars typically have a lower interlaminar shear strength than that of seawater sea sand concrete (SSC)-embedded BFRP bars subjected to the same immersion conditions. This is mainly attributed to the high porosity of CCA, resulting in higher permeability of SSCC than that of SSC. In addition, increasing cement content enhances the initial amount of OH– in SSCC, expands the pitting area of BFRP bars, and maintains OH– concentration better in the exposure tests, accelerating the interlaminar shear strength deterioration of BFRP bars. Microstructure analysis clearly reveals that the deterioration of embedded BFRP bars is mainly caused by resin hydrolysis, fiber-resin interface debonding, and fiber damage after corrosion. Based on the Arrhenius relationship, accelerated aging test results were utilized to predict the service life of SSCC-embedded BFRP bars under the real service condition. The findings of this study are valuable for the application of BFRP bars reinforced SSCC structures under marine environments and provide some insights into improving the long-term performance of SSCC-embedded BFRP bars, i.e., modifying the CCA to minimize the permeability of SSCC and producing low-alkalinity SSCC.

Insights from electrochemical crack tip modeling of atmospheric stress corrosion cracking

Crack tip electrochemical conditions are explored utilizing a reactive transport Finite Element Method model for stainless steel 304 exposed to 3 M NaCl. Under simulated full immersion conditions, a steady state pH of 3 and metal chloride concentration of 1.4 M were calculated. It was determined that an increase in cathode length and a decrease in water layer thickness increases total cathodic current per unit thickness, metal chloride concentrations, and decreases crack tip pH. The presented results and discussion call into question whether electrochemical similitude is achieved between different specimens, crack lengths, and between laboratory specimen and field relevant samples.

Microstructure, Deformation Characteristics and Energy Analysis of Mudstone under Water Absorption Process

In geological engineering, a series of safety problems caused by expansive mudstone are common, such as slope instability and roadbed up-arch. In this paper, the mineral composition of mudstones in the Xining area was analyzed by X-ray diffraction (XRD), and the microstructural and morphological changes of mudstones after water absorption were observed by scanning electron microscopy (SEM) test to analyze the internal factors and microstructural evolution patterns of water absorption and swelling of mudstones. Based on the microstructural units, the mudstones were defined into two categories, one is N-type mudstone with flat sheet-like stromatolite units, and the other is SN-type mudstone with more clastic particle units. Water absorption experiments were conducted on the rock samples to study the microstructure of these two types of mudstones under different water absorption conditions. The pore characteristics of the mudstones were analyzed by using Image-Pro Plus to reveal the water absorption mechanism. The results show that the pore area of N-type mudstone is smaller, as well as the distribution of pore diameter. The pore area of N-type mudstone develops rapidly, in the early stage of water absorption, lots of pores are produced, and the pore area of SN-type mudstone shows an overall decreasing trend. The pore area and the number of SN-type mudstones are at a low level after full water absorption. Under the condition of full immersion, water enters the pores rapidly and soluble salts are dissolved in large quantities. The change of water absorption rate of mudstone with time can be divided into the stage of sudden increase, decrease and stability of water absorption rate. Then, based on the stress theory, the relationship between the macroscopic expansion process and the microstructure of mudstone was analyzed. Finally, the energy basis of mudstone water absorption is discussed. In the swelling of mudstone, the energy gradually turns into swelling strain energy.

Respirometric Techniques for Real-Time Monitoring of Corrosion Reactions

Recently, we have introduced novel respirometric methods for real-time monitoring of corrosion, both for atmospheric corrosion [1,2] and immersion conditions [3]. The approach is based on monitoring the rate of the cathodic reactions with help of different types of sensors; this enables to track the O2 reduction reaction and the H2 evolution reaction simultaneously. Different experimental setups have been developed, from static to flow cell scenarios. Moreover, combining respirometry with time-lapse microscopy reveals interesting details on initiation and propagation of corrosion. Most recently, the respirometric setups were coupled with electrochemistry [4], enlarging the corrosion cases to be studied from open-circuit conditions to potential-controlled systems. With this, it is possible for instance to follow and quantify the amount of oxygen evolving during transpassive dissolution of stainless steels at potentials above the water stability region (i.e., the net electrical current/charge can be assigned into partial currents for oxygen evolution and for metal dissolution). Examples will be presented, to illustrate the potential of these techniques to reveal new insights into corrosion mechanisms of active and passive metals and alloys.References M. Strebl, S. Virtanen, Real-Time Monitoring of Atmospheric Magnesium Alloy Corrosion, Journal of The Electrochemical Society 166 (2019) C3001-C3009M. Strebl, M. Bruns, S. Virtanen, Editors’ Choice—Respirometric in Situ Methods for Real-Time Monitoring of Corrosion Rates: Part I. Atmospheric Corrosion, J. Electrochem. Soc. 167 (2020) 21510M.G. Strebl, M.P. Bruns, G. Schulze, S. Virtanen, Respirometric In Situ Methods for Real-Time Monitoring of Corrosion Rates: Part II. Immersion, J. Electrochem. Soc. 168 (2021) 11502M.G. Strebl, M.P. Bruns, S. Virtanen, Coupling Respirometric HER and ORR Monitoring with Electrochemical Measurements, Electrochimica Acta 412 (2022) 140152

Assessing Electrolyte Transport through an Aircraft Coating System Using EIS

Electrochemical impedance spectroscopy (EIS) is frequently employed to nondestructively evaluate coating systems. However, there are several challenges associated with this approach. One of these challenges is associated with isolating the physical processes that are contributing to the measured impedance. We attempted to address this concern by measuring several of the coating system components before starting the exposures and attempted in-situ measurements of some properties during the course of the exposures.In this work, we analyze impedance data obtained from a two-layer coating system that was applied to AA 2024 substrates that were subjected to either immersion and simulated outdoor exposure conditions. The impedance data from the full coating system is compared with data obtained from coating systems in which gold electrodes were inserted between the layers of the coating system that could be used to monitor changes in each coating layer. Several equivalent circuit models were evaluated before settling on a modified coatings equivalent model. Using this approach, we were able to estimate several coating system parameters, including electrolyte penetration depth as a function of temperature, and solution concentration from the values obtained from the equivalent circuit model. Acknowledgments The Department of Defense Strategic Environmental Research and Development Program (SERDP) sponsored this project under work unit 5399. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of the Office of Naval Research, the U.S. Navy, the Department of Defense, or the U.S. government.

Evaluating Localized Corrosion Susceptibility of Austenitic Stainless Steels Exposed to Varying Nitrate to Chloride Ratio Droplets

Austenitic stainless steels (SS), utilized extensively in coastal environments due to their enhanced corrosion resistance, are susceptible to localized corrosion and stress corrosion cracking (SCC) when exposed to chloride environments. One potential scenario under which SCC may pose a concern is the interim storage and the eventual transport of spent nuclear fuels (SNF) in SS canisters. The SS canisters may be subjected to marine sea-salts and elevated temperatures; however, assessing the current damage state on the surface of these canisters is difficult due to high radiation levels dictating confinement within a limited-access overpack. Hence, accelerated tests are needed in order to help predict potential materials degradation on the surface of these canisters. Another important factor related to SNF storage is the fact that the canisters are located in a variety of climates across the United States. Salt compositions and daily fluctuations of relative humidity (RH) and temperature differ widely by location. Of particular interest, inland sites have a higher nitrate concentration in comparison to coastal locations. One governing brine property for corrosion is the amount of nitrate present in the brine as this can serve to passivate a corroding alloy. Herein, we evaluate the influence of nitrate to chloride ratios on the pitting susceptibility of SS304L under full immersion and cyclic RH conditions. The results of this study are discussed in terms of potential canister degradation. Acknowledgements SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2022-3796 C.

Combination of Galvanic Interaction and Acoustic Emission Measurements on Damaged Painted Al Alloys: Towards Instrumented Witness Coupons for Outdoor Corrosion Testing

After real environmental exposures, the presence of corrosion damages on aircraft structures may be detected by means of non-destructive techniques (NDT). However, corrosion initiation and mechanism behind the defect cannot be distinguished by currently used physical methods. Therefore, aircraft industry needs sensors able to detect both corrosion initiation and its propagation.Few years ago, a new test sample design providing accelerated response during atmospheric corrosion tests was reported by G.S. Frankel research group [[1],[2]]. A painted Al alloy panel, uncoated through-hole noble fasteners and scribes, was specially designed to measure the galvanic current between fasteners and scribes during exposure in a salt fog chamber using a zero-resistance ammeter.But galvanic current measurement remains an electrochemical technique which could be difficult to be implemented in environments expected to be encountered in service, even if some attempts were described in literature [[3]]. More robust NDT methods, like acoustic emission was suggested to evaluate corrosion damage on Al alloys [[4]] but their application has not been yet transferred to instrumented witness coupons.Recently a European program [[5]] was launched to validate the application of ultrasonic corrosion sensors for real time detection of early stages of localized corrosion on Al alloys. Following our previous work on laboratory-scale tests based on mass transport control from inhibitors leaching from primer exposed at scribes [[6]], this talk describes the laboratory validation of acoustic emission combined with galvanic corrosion current measurements to evaluate the role of depletion of available corrosion inhibitors in the paint on scratched plates, mimicking riveted aircraft panels, exposed to chloride environments, in various conditions, i.e. immersion and salt spray conditions. [1] C.A. Matzdorf, W.C. Nickerson,B.C. Rincon Troconis,G.S. Frankel, Longfei Li, R.G. Buchheit, Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 1—Concept, Corrosion, 69 (2013) 1240-1246. [2] Z.Feng and G.S. Frankel, Galvanic Test Panels for Accelerated Corrosion Testing of Coated Al Alloys: Part 2—Measurement of Galvanic Interaction, Corrosion,70 (2014) 95-106. [3] Z. Feng, G.S. Frankel,W.H. Abbott,C.A. Matzdorf, Galvanic attack of coated al alloy panels in laboratory and field exposure, Corrosion, 72 (2016) 342-355. [4] A. Prateepasen, C. Jirarungsatian, Implementation of acoustic emission source recognition for corrosion severity prediction, Corrosion, 67 (2011), 056001/1-056001/11. [5] Early detection and progress monitoring and prediction of corrosion in aeronautic Al alloys through calibrated Ultrasonic-CorROSion Sensor application, EU H2020 Grant agreement ID: 864905, https://cordis.europa.eu/project/id/864905 [6] R. Oltra and F.Peltier, Laboratory-scale testing of the anti-corrosion effectiveness of a primer coating on a bare AA2024 surface, Surface Interface Analysis, 48 (2016) 775–779.

Memristor‐Based Security Primitives Robust to Malicious Attacks for Highly Secure Neuromorphic Systems

Internet‐of‐things (IoT) edge devices with a memristive neuromorphic system can more effectively enhance daily lives. However, cyberattacks remain critical concerns for smart IoT edge devices that process a vast body of information via networks. Herein, a highly secure neuromorphic system is reported, which can be implemented using a physically unclonable function (PUF) that exploits the high entropy achieved via the stochastic switching of a poly(1,3,5‐trivinyl‐1,3,5‐trimethyl cyclotrisiloxane) (pV3D3)‐based memristor. The excellent insulating property of pV3D3 enhances the stochasticity of the tunneling distance for randomly ruptured Cu filaments. The pV3D3 memristor‐based PUF (pV3D3‐PUF) achieves near‐ideal 50% averages for uniformity and uniqueness, excellent reliability under conditions of mechanical stress and water immersion, and reconfigurability‐bolstering security without additional hardware. Using stochastic in‐memory computing, the pV3D3‐PUF shows resilience to machine learning attacks. Furthermore, a cryptography protocol is demonstrated, which enables artificial intelligence service implementation without security issues for PUF‐integrated pV3D3 memristor‐based neuromorphic systems.

Effect of crack width and wet-dry cycles on the chloride penetration resistance of engineered cementitious composite (ECC)

• Influence of crack width and wet-dry cycles on the chloride ingress in cracked ECC was investigated. • Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. • The “maximum phenomenon” is observed for both water-soluble and bound chloride ions profiles under wet-dry cycles. • The change of the mineral phases and porosity is related with the chloride binding behaviour. The resistance of cracked ECC against chloride ingress is mainly governed by the accumulated crack width of all the cracks rather than the maximum width of multiple cracks. However, most studies focus on the influence of a single fine crack (<100 μm), which is far smaller than the accumulated crack width. To this end, this study focuses on a relatively large crack width scale. Cracks with widths of 0.1, 0.2 and 0.3 mm were notched on an ECC specimen. Both NaCl solution immersion and wet-dry cycles conditions were applied. Chloride penetration profile as well as the change of total and water-soluble chloride ion content was measured. Relationship between the bound chloride and water-soluble chloride was studied. X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP) tests were carried out to show the influence of crack width and wet-dry cycles on the changes of the mineral phases, porosity and pore size distribution in the vicinity of the crack.

Tensile characteristics of carbon textile-reinforced mortar incorporating short amorphous metallic and nylon fibers under designed environmental conditions

This study experimentally investigated the mechanical tensile properties of carbon textile-reinforced mortar (TRM) composites utilizing amorphous metallic and nylon short fibers with lengths of 15 and 12 mm, respectively, at 0.4 % and 0.7 % fiber content under the designed conditions. The conditions of the ambient control, water immersion, sulfate immersion, and wet-dry cycle sulfate attack were designed to investigate the tensile characteristics of the TRM composite and the effectiveness of applying short fibers under normal and harsh environments accelerated using a temperature and humidity machine. The experiments included tensile tests for dried carbon textiles, water absorption tests for mortar matrices with and without short fibers, external damage inspection for TRM specimens and compressive tests for mortar matrices after exposure to the designed conditions. Furthermore, based on RILEM TC 232-TDT, tensile tests of 60 TRM specimens were performed after exposure to the designed conditions. The results indicate that the existence of both amorphous metallic and nylon short fibers significantly improves the TRM tensile properties under all conditions, in which the amorphous metallic fiber was found to be more effective at low strain levels, whereas the positive effect generated by nylon fibers only considerably appeared at high strain values. In addition, a positive effect was observed under the prolonged water immersion condition. Besides, the TRM specimens without short fibers were severely damaged under the designed sulfate attack, and utilizing them could prevent the propagation of the damage, in which applying 0.4 % nylon fibers proved to provide the highest resistance capability.

Photosynthesis in Response to Different Salinities and Immersions of Two Native Rhizophoraceae Mangroves.

Mangrove ecosystems are vulnerable to rising sea levels as the plants are exposed to high salinity and tidal submergence. The ways in which these plants respond to varying salinities, immersion depths, and levels of light irradiation are poorly studied. To understand photosynthesis in response to salinity and submergence in mangroves acclimated to different tidal elevations, two-year-old seedlings of two native mangrove species, Kandelia obovata and Rhizophora stylosa, were treated at different salinity concentrations (0, 10, and 30 part per thousand, ppt) with and without immersion conditions under fifteen photosynthetic photon flux densities (PPFD μmol photon·m−2·s−1). The photosynthetic capacity and the chlorophyll fluorescence (ChlF) parameters of both species were measured. We found that under different PPFDs, electron transport rate (ETR) induction was much faster than photosynthetic rate (Pn) induction, and Pn was restricted by stomatal conductance (Gs). The Pn of the immersed K. obovata plants increased, indicating that this species is immersed-tolerant, whereas the Pn level of the R. stylosa plants is salt-tolerant with no immersion. All of the plants treated with 30 ppt salinity exhibited lower Pn but higher non-photochemical quenching (NPQ) and heat quenching (D) values, followed by increases in the excess energy and photoprotective effects. Since NPQ or D can be easily measured in the field, these values provide a useful ecological monitoring index that may provide a reference for mangrove restoration, habitat creation, and ecological monitoring.

Increasing help-seeking among people with depression by self-distancing using mental time-travel

Background Past research indicates that self-distancing through perspective-taking may increase help-seeking intentions among some people with depression. Aims The current pre-registered study tested the effect of self-distancing through mental time-travel on help-seeking attitudes, intentions, outcome expectations, and self-stigma. Methods Participants with elevated depressive symptomatology who had not yet sought help for current feelings of depression (n = 859) were randomly assigned to a self-distancing writing task, a self-immersive writing task, or a control condition. Results Help-seeking attitudes were significantly higher in the distancing condition than in the immersive or control conditions. Additionally, self-distancing through mental time-travel resulted in higher help-seeking intentions compared to the control condition but was not significantly different from the immersive condition. The immersive condition was not significantly different from the control for any outcomes. Interactions show that both self-distancing and the immersive task weakened the negative relationship between depression severity and help-seeking attitudes and intentions. Conclusion Extending scholarship investigating self-distancing and help-seeking intentions, results show that self-distancing through mental time-travel can result in more favorable help-seeking attitudes compared to a control.