Characterization, Applications and New Technologies of Civil Engineering Materials and Structures.

With the continuous development of large-scale maintenance of infrastructure, accurate, reasonable, and efficient mechanical behavior evaluation and performance prediction of civil materials and structures have become the keys to improving service durability and intelligent maintenance management for infrastructure [...].

Metagenomic and metaproteomic insights into the microbiome and the key geobiochemical potentials on the sandstone of rock-hewn Beishiku Temple in Northwest China.

Metagenomics and metaproteomics analyses were used to determine the microbial diversity and taxon composition, as well as the biochemical potentials of the microbiome on the sandstone of Beishiku Temple located in Northwest China. Taxonomic annotation of the metagenomic dataset revealed the predominant taxa of the stone microbiome on this cave temple with characteristics of resistance to harsh environmental conditions. Meanwhile, there were also taxa in the microbiome that showed sensitivity to environmental factors. The taxa distribution and the metabolic functional distribution patterns by the metagenome and metaproteome, respectively, showed clear differences. The high abundance of energy metabolism represented in the metaproteome suggested that there were active geomicrobiological cycles of elements within the microbiome. The taxa responsible for reactions in the nitrogen cycle from both metagenome and metaproteome supported a metabolically active nitrogen cycle, and the high activity of Comammox bacteria indicated the strong metabolic activity of ammonia oxidation to nitrate in the outdoor site. The SOX-related taxa involved in the sulfur cycle showed higher activity outdoors than indoors, and on the outdoor ground than at the outdoor cliff, as detected through metaproteomic analysis. The development of petrochemical industry in the vicinity resulting in the deposition of sulfur/oxidized sulfur via atmosphere may stimulate the physiological activity of SOX. Our findings provide metagenomic and metaproteomic evidence for microbially driven geobiochemical cycles that result in the biodeterioration of stone monuments.

Effects of Aging and Immersion on the Healing Property of Asphalt-Aggregate Interface and Relationship to the Healing Potential of Asphalt Mixture.

The self-healing ability of asphalt-aggregate bonding interfaces can maintain the mechanical properties of asphalt mixtures. However, the interface's healing ability will also be affected by moisture and aging. In order to clarify the influence of moisture and aging on the healing ability of a bonding interface, the effects of healing period and temperature on the self-healing level of interfacial strength were measured. The healing master curve of the strength was established. Thereafter, the effects of soaking time, salt solution concentration, and thermal aging on the healing degree of interfacial strength were measured. Based on digital image processing technology and the meso-finite element method, the influence of the interface on the healing performance of the mixture was simulated and analyzed, which was then verified by the beam bend healing test. The results show that the healing index of bonding strength increases with the ascent of healing temperature and period. Healing index gradually decreases with the extension of soaking period, and the higher the concentration of salt in the solution, the worse the healing performance of interfacial strength. After asphalt aging, the healing potential of the interface is weakened. There is a good linear relationship between the healing level of an asphalt-aggregate interface and the level of strength and fracture energy of the mixture. However, the actual healing level of an asphalt mixture is obviously lower than that of the interface, due to the addition of mineral filler. This paper provides a method for predicting the recovery performance of asphalt pavement.

Diversity and Composition of Culturable Microorganisms and Their Biodeterioration Potentials in the Sandstone of Beishiku Temple, China.

Microbial colonization on stone monuments leads to subsequent biodeterioration; determining the microbe diversity, compositions, and metabolic capacities is essential for understanding biodeterioration mechanisms and undertaking heritage management. Here, samples of epilithic biofilm and naturally weathered and exfoliated sandstone particles from different locations at the Beishiku Temple were collected to investigate bacterial and fungal community diversity and structure using a culture-based method. The biodeterioration potential of isolated fungal strains was analyzed in terms of pigmentation, calcite dissolution, organic acids, biomineralization ability, and biocide susceptibility. The results showed that the diversities and communities of bacteria and fungi differed for the different sample types from different locations. The population of culturable microorganisms in biofilm samples was more abundant than that present in the samples exposed to natural weathering. The environmental temperature, relative humidity, and pH were closely related to the variation in and distribution of microbial communities. Fungal biodeterioration tests showed that isolated strains four and five were pigment producers and capable of dissolving carbonates, respectively. Their biomineralization through the precipitation of calcium oxalate and calcite carbonate could be potentially applied as a biotechnology for stone heritage consolidation and the mitigation of weathering for monuments. This study adds to our understanding of culturable microbial communities and the bioprotection potential of fungal biomineralization.

Optical characteristics of bilayer decoupling MoS2 grown by the CVD method.

Study of exciton recombination process is of great significance for the optoelectronic device applications of two-dimensional transition metal chalcogenides (TMDCs). This research investigated the decoupling MoS2 structures by photoluminescence (PL) measurements. First, PL intensity of the bilayer MoS2 (BLM) is about twice of that of the single layer MoS2 (SLM) at low temperature, indicating no transition from direct bandgap to indirect bandgap for BLM due to the decrease of interlayer coupling which can be shown by Raman spectra. Then, the localized exciton emission appears for SLM at 7 K but none for BLM, showing different exciton localization characteristics. The PL evolution with respect to the excitation intensity and the temperature further reveal the filling, interaction, and the redistribution among free exciton states and localized exciton states. These results provide very useful information for understanding the localized states and carrier dynamics in BLM and SLM.

Community assembly, potential functions and interactions between fungi and microalgae associated with biodeterioration of sandstone at the Beishiku Temple in Northwest China.

Fungi, cyanobacteria and algae are specific microbial groups associated with the deterioration and safety of stone monuments. In this study, high-throughput sequencing analysis was used to investigate the diversity, distributions, ecological functions, and interaction patterns of both the fungal and microalgal (including cyanobacteria and algae) communities on sandstone in the Beishiku Temple, located on the ancient Silk Road. The results showed that the core phyla of fungi were affiliated with unclassified Lecanoromycetes, Engyodontium, Knufia, Epicoccum, Endocarpon, and Cladosporium of Ascomycota whereas the phyla of microalgae were dominated by prokaryotic Cyanobacteria and eukaryotic Chlorophyta. The environmental factors of temperature, relative humidity, and light intensity were monitored simultaneously. The structure of the microbial communities was much more strongly shaped by soluble Cl-, Na+, NO3- ions than by the light intensity, moisture content or temperature, especially for the weathered sandstone located outside the caves. The co-occurrence network analysis suggested that a more stable community structure was evident outside the caves than inside. The stronger positive connections and coexistence patterns that were detected indicate a strong adaptability of fungi and microalgae to the distinct oligotrophic microhabitats on sandstone. The metacommunity co-occurrence network exhibited the ecological predominance of fungi, and most of the functional fungi in the biofilms outside the caves belonged to the Lichenized group, based on the FUNGuild prediction. These findings highlight the ecology and functions of stone-inhabiting microorganisms to further advance the current understanding and knowledge of sandstone biodeterioration for protection and management.

Moisture content and material density affects severity of frost damage in earthen heritage.

Successful conservation of earthen heritage requires an understanding of interactions between environmental and climatic conditions, soil-based materials and human interventions. Frost cycling is likely to be an important contributor to the deterioration of earthen heritage, with frost damage known to cause deterioration features such as flaking and granular disintegration. However, it is not clear how important a contribution frost cycling makes in comparison with other agents. Previous earthen heritage studies have focused on other agents of deterioration, such as wind and rain, or investigated the role of freeze-thaw cycles under conditions unrepresentative of many earthen sites. We investigate how density and moisture content affect the severity of frost damage on earthen heritage using materials and conditions informed by those found at earthen sites in NW China. We prepared rammed earth cubes (5 × 5 × 5 cm) at two densities (1.65 and 1.75 g cm-3) and with five moisture content levels between 0.46 and 8%. Samples were subjected to 80 freeze-thaw temperature cycles (+7 to -15 °C) in an environmental cabinet. Deterioration was recorded using visual assessment, measurements of surface roughness, ultrasonic pulse velocities, a Vicat needle test and mass loss. Results showed frost damage was dependent on moisture content and density of rammed earth samples. Samples with <2% moisture content showed no visible frost damage. Samples with higher moisture contents (>6%) and higher densities exhibited the greatest deterioration with surface granulation, salt efflorescence and flakes detaching from the parent cubes. This suggests that frost damage to rammed earth is likely to be focused in periods when rainfall or snowmelt is followed by freeze-thaw temperature cycling. In addition, results suggest that if higher density earthen materials are used for repairs or restoration for sites in dryland environments, these could be more vulnerable to frost damage than lower density materials.

Abnormal temperature-dependent photoluminescence characteristics of ReS2nanowalls.

Two samples with [001] orientated rhenium disulfide (ReS2) nanowalls (NWs) grown above and in front of precursor (NH4ReO4) by chemical vapor deposition were investigated. The temperature-dependent photoluminescence (PL) indicated that the PL peak exhibited linear blue-shift at a rate of ∼0.24 meV K-1with increasing the temperature from 10 to 300 K, while the linewidth monotonically increased due to the exciton-phonon interaction. This abnormal blue-shift of PL emission energy, which is explained by a competition between the band gap shrinkage and the energy level degeneracy with respect to the increase of temperature and lattice constant, enables ReS2NWs to possess great potential for development of thermal sensors. In addition, exciton localization effect in the ReS2NWs from abundant edges and weak interlayer interaction was also observed to be related to the height and density of ReS2NWs. These results not only enrich the understanding for exciton dynamics in ReS2NWs, but also help to exploit ReS2NWs for device applications.

Localized state effect and exciton dynamics for monolayer WS2.

The two-dimensional transition metal dichalcogenides (TMDCs) have been considered as promising candidates for developing a new generation of optoelectronic devices. Accordingly, investigations of exciton dynamics are of great importance for understanding the physics and the performance of devices based on TMDCs. Herein, after exposure to ambient environment for six months, monolayer tungsten disulfide (WS2) shows formation of localized states. Photoluminescence (PL) and time-resolved PL (TRPL) spectra demonstrate that these localized states have significant impacts on the exciton dynamics, including energy states filling, thermal activation and redistribution, and the decay behavior of excitons. These observations not only enrich the understanding for localized states and correlated exciton dynamics of aged monolayer WS2, but also reveal a possible approach to modulate the optical properties of TMDCs via the aging process.

Deterioration risk of dryland earthen heritage sites facing future climatic uncertainty.

Uncertainties over future climatic conditions pose significant challenges when selecting appropriate conservation strategies for heritage sites. Choosing effective strategies is especially important for earthen heritage sites located in dryland regions, as many are experiencing rapid environmentally-driven deterioration. We use a newly developed cellular automaton model (ViSTA-HD), to evaluate the environmental deterioration risk, over a 100-year period, under a range of potential climate and conservation scenarios. Results show increased wind velocities could substantially increase the overall deterioration risk, implying the need for wind-reducing conservation strategies. In contrast, predicted increases in rainfall are not likely to increase the overall deterioration risk, despite greater risk of rain-driven deterioration features. Of the four conservation strategies tested in our model, deterioration risk under all climatic scenarios was best reduced by increasing the coverage of natural, randomly-distributed vegetation to 80%. We suggest this approach could be an appropriate long-term conservation strategy for other earthen sites in dryland regions.

Field testing study on the rainfall thresholds and prone areas of sandstone slope erosion at Mogao Grottoes, Dunhuang.

The Dunhuang Mogao Grotto is a famous Buddhist monument and was inscribed in the list of world cultural heritage sites by UNESCO in 1987. Water poses a major threat to the preservation of this heritage even though it is located in an arid region. This study was conducted to investigate the effect of rainfall on rock erosion. Specifically, the formation mechanism of slope runoff and the erosion threshold of rainfall were analyzed, and erosion-prone areas of the site were identified. This was carried out using field artificial rainfall simulation testing, and the results inform methods of preventing rainfall-induced cliff erosion. In addition, the rainfall threshold and erosion-prone areas obtained from the experiment were further validated and optimized using monitoring data for natural rainfall and historic documentation. The threshold value of erosive rainfall obtained by empirical statistical analysis method was found to be similar to that obtained by the runoff generation mechanism. The areas identified as prone to erosion using field tests coincided with areas of historic erosion as recorded in site documentation. Furthermore, the forecast grade of cliff slope erosion and its erosion-prone areas are determined after comprehensive analysis of the results obtained by these two methods. The research results are critical for the monitoring, early warning, and prevention of cliff slope erosion. The research methods can also be used as reference in areas for which rainfall data are missing.

Aging Mechanism of a Diatomite-Modified Asphalt Binder Using Fourier-Transform Infrared (FTIR) Spectroscopy Analysis.

In this paper, Fourier-transform infrared (FTIR) spectroscopy was used to evaluate the effects of diatomite on aging properties of an asphalt binder. The modified asphalts included 5%, 10%, and 15% diatomite, and were prepared in the laboratory. The changes in functional groups of asphalt were employed to investigate the aging mechanisms of the modified and control asphalts. Effects of diatomite on the anti-aging properties of asphalt were analyzed via the changes in intensity of the absorption peaks. Results showed that there were no new functional groups generated after diatomite mixing with asphalt. This indicated that the process of diatomite modification was just physical mixing. Furthermore, parts of saturates and aromatics were volatilized in the aging process of modified asphalt. Polar molecules reacted with oxygen in aging. Meanwhile, carbonyl (C=O) and sulfoxide (S=O) were also generated. The aging resistance of modified asphalt was the best when the diatomite content was 10%. The work of this paper may provide a new perspective to evaluate asphalt aging.

Rebar Corrosion Investigation in Rubber Aggregate Concrete via the Chloride Electro-Accelerated Test.

Erosion effect of chloride ions from the marine, deicing salt, saline-alkali land and some industrial environments will cause the corrosion of rebar in concrete, which is one of the most harmful factors affecting the durability of concrete structure. It had been proved that the incorporation of rubber aggregates increase the capillary saturation of cement concrete and reduce the corrosion degree of rebar. This paper investigated the rebar corrosion behavior in rubber aggregate concrete under the chloride electro-accelerated corrosion condition and such an investigation has not been seen in any public literature. Two water-cement ratios (0.45 and 0.55) and four rubber contents (0, 50, 100, and 150 kg/m³) were selected for experiment. Four-point bending tests of concrete beam were conducted before and after chloride ion erosion in order to determine effect of rubber aggregate on the durability of rebar. Results showed that rebar corrosion degree decreased with the increase of rubber aggregate in concrete. Besides, the more the dosage of rubber is, the better the anti-crack performance of cement concrete. This will postpone the crack development and reduce the peak of rebar corrosion.

Dynamic Characteristics and Failure Mechanism of Vegetated Revetment under Cyclic Loading.

This research is focused on the dynamic behavior and failure mechanisms of an ecologically vegetated bituminous mixture applied in a riverbank revetment model. The dynamic bearing capacity of the vegetated riparian slope was evaluated. The dynamic soil pressure distribution and deformation were analyzed, followed by 3D elastic⁻plastic finite element modeling. Experimental results showed that the cumulative vertical settlement increased rapidly with the loading time. Vegetation added into bituminous mixtures was found to be effective in inhibiting the development of the vertical displacement of sand. The research described in this paper provides a theoretical basis and guidelines for the protection of riverbank slopes.

Photoluminescence Study of the Interface Fluctuation Effect for InGaAs/InAlAs/InP Single Quantum Well with Different Thickness.

Photoluminescence (PL) is investigated as a function of the excitation intensity and temperature for lattice-matched InGaAs/InAlAs quantum well (QW) structures with well thicknesses of 7 and 15 nm, respectively. At low temperature, interface fluctuations result in the 7-nm QW PL exhibiting a blueshift of 15 meV, a narrowing of the linewidth (full width at half maximum, FWHM) from 20.3 to 10 meV, and a clear transition of the spectral profile with the laser excitation intensity increasing four orders in magnitude. The 7-nm QW PL also has a larger blueshift and FWHM variation than the 15-nm QW as the temperature increases from 10 to ~50 K. Finally, simulations of this system which correlate with the experimental observations indicate that a thin QW must be more affected by interface fluctuations and their resulting potential fluctuations than a thick QW. This work provides useful information on guiding the growth to achieve optimized InGaAs/InAlAs QWs for applications with different QW thicknesses.

Reuse of Boron Waste as an Additive in Road Base Material.

The amount of boron waste increases year by year. There is an urgent demand to manage it in order to reduce the environmental impact. In this paper, boron waste was reused as an additive in road base material. Lime and cement were employed to stabilize the waste mixture. Mechanical performances of stabilized mixture were evaluated by experimental methods. A compaction test, an unconfined compressive test, an indirect tensile test, a modulus test, a drying shrinkage test, and a frost resistance test were carried out. Results indicated that mechanical strengths of lime-stabilized boron waste mixture (LSB) satisfy the requirements of road base when lime content is greater than 8%. LSB can only be applied in non-frozen regions as a result of its poor frost resistance. The lime-cement-stabilized mixture can be used in frozen regions when lime and cement contents are 8% and 5%, respectively. Aggregate reduces the drying shrinkage coefficient effectively. Thus, aggregate is suggested for mixture stabilization properly. This work provides a proposal for the management of boron waste.

Electronic Coupling in Nanoscale InAs/GaAs Quantum Dot Pairs Separated by a Thin Ga(Al)As Spacer.

The electronic coupling in vertically aligned InAs/GaAs quantum dot (QD) pairs is investigated by photoluminescence (PL) measurements. A thin Al0.5Ga0.5As barrier greatly changes the energy transfer process and the optical performance of the QD pairs. As a result, the QD PL intensity ratio shows different dependence on the intensity and wavelength of the excitation laser. Time-resolved PL measurements give a carrier tunneling time of 380 ps from the seed layer QDs to the top layer QDs while it elongates to 780 ps after inserting the thin Al0.5Ga0.5As barrier. These results provide useful information for fabrication and investigation of artificial QD molecules for implementing quantum computation applications.

Solid-state synthesis and luminescent properties of yellow-emitting phosphor NaY(MoO4)2:Dy3+ for white light-emitting diodes.

A yellow-emitting phosphor NaY(MoO4)2:Dy(3+) was synthesized using a solid-state reaction at 550 °C for 4 h, and its luminescent properties were investigated. Its phase formation was studied using X-ray powder diffraction analysis, and there were no crystalline phases other than NaY(MoO4)2. NaY(MoO4)2:Dy(3+) produced yellow emission under 386 or 453 nm excitation, and the prominent luminescence was yellow (575 nm) due to the (4) F9/2 → (6) H13/2 transition of Dy(3+). For the 575 nm emission, the excitation spectrum had one broad band and some narrow peaks; the peaks were located at 290, 351, 365, 386, 426, 453 and 474 nm. Emission intensities were influenced by the Dy(3+) doping content and a concentration quenching effect was observed; the phenomenon was also proved by the decay curves. Moreover, the Commission International de I'Eclairage chromaticity coordinates of NaY(MoO4)2:Dy(3+) showed similar values at different Dy(3+) concentrations, and were located in the yellow region.

Luminescence and energy transfer of tunable emission phosphor Ca2PO4Cl:Ce(3+), Mn(2+).

A series of Ca2PO4Cl:Ce(3+), Mn(2+) phosphors are synthesized by a high temperature solid state reaction method, and their luminescent properties are investigated. Ca2PO4Cl:Ce(3+), Mn(2+) has an obvious absorption in the region of 300-350 nm, and energy transfer from Ce(3+) to Mn(2+) in Ca2PO4Cl has been validated, and proved to be a resonant type via a dipole-dipole interaction. Orange red emission intensity of Mn(2+) can be obviously enhanced via the efficient energy transfer from Ce(3+) to Mn(2+), and critical distance of energy transfer is also calculated by concentration quenching method, and about 14.1 Å. The results show that Ce(3+) ion may be an available sensitizer for Ca2PO4Cl:Mn(2+), and Ca2PO4Cl:Ce(3+), Mn(2+) may have potential application in white light emitting diodes.

[Spectral characteristics of Ba3SiO4Cl2 : Eu2+ phosphor for white LED].

Ba3SiO4Cl2 : Eu2+ was synthesized by a high temperature solid state method. BaCO3 (A. R.), BaCl2 (A. R.), SiO2 (99.99%) and Eu2O3 (99.99%) were used as the raw materials. The final phase was checked with a conventional X-ray diffraction (XRD) (D/max-rA, CuKalpha, 40 kV, 100 mA, lambda = 0.154 06 nm). The spectral characteristics of the phosphors were performed by using a Hitachi F-4600 fluorescence spectrophotometer equipped with a 450 W Xe lamp. Ba3SiO4Cl2 : Eu2+ showed broad emission bands at 445 and 510 nm under the 365 nm radiation excitation. For the two emission peaks, the excitation spectra have two different spectral distributions, and the excitation peaks locate at 350 and 400 nm, respectively. The results indicate that different Eu2+ emission centres exist in Ba3SiO4Cl2. The emission intensity of the 445 and 510 nm peaks is influenced by Eu2+ doped content. With increasing its content, the emission intensity of 445 nm gradually increases, and that of 510 nm decreases. With washing the phosphor, the 445 nm emission peak disappears, and the emission spectrum has only the 510 nm emission band, and its intensity is lower than that of the original phosphor.