Salt Freeze-Thaw Damage Characteristics of Concrete based on Computed Tomography

Freeze–thaw damage and salt erosion are important factors that influence the durability of concrete. In this study, degradation laws of concrete in salt freeze–thaw environment were discussed from the microscopic perspective based on the 3D reconstruction of computed tomography images. A damage model based on concrete aggregate volume and porosity was constructed. Furthermore, the main causes of concrete degradation in the salt freeze–thaw environment were analyzed. Results reveal that, with the increase in salt freeze–thaw cycles, the damage of concrete intensifies gradually, and the uniaxial compressive strength declines steadily. Concrete damages have two causes, namely, changes in concrete porosity and variations in concrete aggregate volume. Damages caused by aggregate volume changes are divided into frost heaving and peeling. In accordance with the constructed damage model, the porosity of concrete materials changes slightly, whereas concrete aggregate volume varies significantly. Aggregate volume changes are the main causes of intensified concrete damages and decreased compressive strength. Research conclusions provide theoretical references to disclosing microscopic damage mechanism of concrete in the salt freeze–thaw environment

1,2,4,3-Triazaborole-based neutral oxoborane stabilized by a Lewis acid

The first example of 1,2,4,3-triazaborole-based oxoborane has been synthesized via hydrogen migration upon the coordination of AlCl3 to the corresponding borinic acid. X-ray diffraction analysis and computational study disclosed the partial B[double bond, length as m-dash]O double-bond property.ASTAR (Agency for Sci., Tech. and Research, S’pore

Bis(N-heterocyclic olefin) Derivative: An Efficient Precursor for Isophosphindolylium Species

We have developed bis­(N-heterocyclic olefin) derivatives <b>2</b> and demonstrated that <b>2</b> can be utilized as precursors for the synthesis of isophosphindolylium species <b>3</b>. X-ray diffraction and density functional theory studies indicate the aromatic property of the PC₄ five-membered ring in <b>3</b>. Despite its cationic nature, the P center in <b>3b</b> exhibits nucleophilic character and thus readily forms a bond with CuCl to afford a copper phosphenium complex <b>4</b>, demonstrating the potential utility of <b>3</b> as a σ-donor ligand

Laser Shock Peening of SiCp/2009Al Composites: Microstructural Evolution, Residual Stress and Fatigue Behavior

SiC particle reinforced aluminum alloy has a wide application in the aerospace industries. In this study, laser shock peening (LSP), an advanced surface modification technique, was employed for SiCp/2009Al composite to reveal its microstructure, microhardness and residual stress evolution. After peening, high densities of dislocations were induced in the aluminum substrate, and stacking faults were introduced into the SiC particle. The microhardness was increased from 155–170 HV to 170–185 HV, with an affected depth of more than 1.5 mm. Compressive residual stresses of more than 200 MPa were introduced. The three-point bending fatigue of the base material, laser peened and milled after laser peened specimens with artificial crack notch fabricated by a femtosecond laser was investigated. The average fatigue lives of laser peened and milled after laser peened specimens were increased by up to 10.60 and 2.66 times, compared with the base material. This combined fundamental and application-based research seeks to comprehensively explore the applicability of LSP on metal matrix composite

Numerical Study of Co-firing Biomass with Lean Coal under Air–Fuel and Oxy-fuel Conditions in a Wall-Fired Utility Boiler

Co-firing biomass under oxy-fuel condition is one of the most attractive methods which is conducive to mitigating CO₂ emissions by combining the advantages of these two respective technologies. The combustion characteristics of a wall-fired utility boiler operating in this mode have been seldom investigated. The burnout behavior of the blended fuel is still controversial. By using the newly proposed combustion mechanisms, a numerical study was carried out in a 600 MW wall-fired boiler to evaluate the influences of oxy-fuel working condition and biomass share on flow, temperature, O₂ distributions, and burnout behavior in this combustion mode. Besides, the effect of biomass injection position was also explored, which has yet to be fully understood. The simulation results show that oxy-fuel working condition affected the combustion characteristics to some extent. The introduction of biomass led to a lower temperature but a better burnout within the furnace. O₂ distribution was also correlated to the biomass share due to the difference in fuel properties. The injection position of biomass presented crucial impacts on particle trajectories, temperature distribution, and O₂ distribution. In addition, due to the increase in residence time and the reduction in trapped particles, an enhanced burnout could be achieved as the biomass inlet was moved down

Determination of Epicenters before Earthquakes Utilizing Far Seismic and GNSS Data: Insights from Ground Vibrations

Broadband seismometers, ground-based Global Navigation Satellite Systems (GNSS), and magnetometers that were located within an epicentral distance of approximately 150 km consistently observed the novel anomalous behaviors of the common-mode ground vibrations approximately 5&ndash;10 days before the M6.6 Meinong earthquake in Taiwan. The common-mode ground vibrations with amplitudes near 0.1 m at frequencies ranging from 8 &times; 10&minus;5 to 2 &times; 10&minus;4 Hz were generated near the region close to the epicenter of the impending earthquake. The common-mode vibrations were consistently observed in seismic and GNSS data associated with five other earthquakes in four distinct areas. The results reveal that the common-mode vibrations could be a typical behavior before earthquakes. The causal mechanism of common-mode vibrations can be attributed to crustal resonance excitations before fault dislocations occur. Potential relationships with other pre-earthquake anomalies suggest that the common-mode vibrations could be ground motion before earthquakes, which was investigated for a significant length of time