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Electrochemical corrosion of AZ31 magnesium alloy in the NH4+-SO42−-Cl− environment is studied. Effect of NH4+ overshadows that of Cl− as the (NH4)2SO4 concentration is 0.005 M or higher, yielding an evolution from localized corrosion to uniform corrosion. Acceleration effect of NH4+ can be attributed to that (i) NH4+ dissolves the inner MgO and hinders the precipitation of Mg(OH)2 and (ii) the buffering ability of NH4+ provides H+, enhances the hydrogen evolution, and expedites the corrosion process. The latter is demonstrated as the dominant factor with the results in unbuffered and buffered environments. The severe corrosion and hydrogen process in NH4+-containing solution results in a high Hads coverage and yields an inductive loop within the low frequency. Meanwhile, SO42− is helpful in generating cracked but partially protective corrosion products, while Cl− could broaden the corrosion area beneath the corrosion product.

Abstract The development of magnetocaloric materials with a significantly enhanced volumetric cooling capability is highly desirable for the application of adiabatic demagnetization refrigerators in confined spatial environments. Here, the thermodynamic characteristics of a magnetically frustrated spin‐7/2 Gd9.33[SiO4]6O2 is presented, which exhibits strongly correlated spin disorder below ≈1.5 K. A quantitative model is proposed to describe the magnetization results by incorporating nearest‐neighbor Heisenberg antiferromagnetic and dipolar interactions. Remarkably, the recorded magnetocaloric responses are unprecedentedly large and applicable below 1.0 K. It is proposed that the S = 7/2 spin liquids serve as versatile platforms for investigating high‐performance magnetocaloric materials in the sub‐kelvin regime, particularly those exhibiting a superior cooling power per unit volume.

The interactions between {10 1‾ 2} twins and basal precipitates in the Mg–8Al-0.5Zn alloys have been investigated using high-resolution transmission electron microscopy. The underlying interaction mechanisms at different twinning processes were analyzed in detail. In the process of twin propagation, the twin tip can traverse across multiple basal precipitates in the form of nucleation of new twins on the opposite side of the precipitates and continuously expand in the grain. Such re-nucleation events are suggested to be driven by the local stress concentration arising from the twin impinging upon the precipitate. During twin thickening, the precipitates undergo a small elastic deflection rather than plastic shearing when the twin engulf them. Furthermore, a large number of I1 stacking faults are activated at the twin-precipitate interface to accommodate the twinning shear. The orientation relationship (OR) of the precipitates inside the twin is changed from Burgers to [2 1‾1‾ 0]α//[11 1‾]β, (0 1‾ 10)α//(011)β, (0001)α//(2‾ 11‾)β when they are engulfed by twin.

Due to the increasingly tight energy supply situation, thermal insulation mortar is more and more widely used in the exterior wall insulation layer of buildings in various countries. However, the existing academic papers have less research on the key properties of thermal insulation mortar such as fire resistance and economic feasibility. Based on the previous research results, this study selected silica fume as an admixture to improve the comprehensive performance of insulation mortar. The goal is to develop a high-performance fireproof insulation mortar. This paper focuses on the fire resistance of the improved insulation mortar. The results show that silica fume mixed into the mortar will play a fine particle filling and hydration gelation cooperation, and the amount of silica fume mixed from 0 to 10% can significantly improve the bond strength and compressive strength of the mortar. For the thermal conductivity and dry density of mortar, there is a certain increase in the range of silica fume dosing from 0 to 4%, while the range of silica fume dosing from 4% to 10% decreases again. Silica fume has a favorable effect on improving the fire resistance of insulating mortar, and the mortar with 10% admixture of silica fume has about 28.30% lower mass loss rate after high temperature and about 14.73% higher relative compressive strength after high temperature after 28 days of maintenance. The final selected optimum admixture of silica fume is 10%, and the best ratio of raw materials is cement: aggregate: water: dispersible emulsion powder: fly ash: diabase rock powder: AOS foaming agent: gelatin: silica fume = 1: 1.67: 2: 0.045: 0.15: 0.225: 0.035: 0.02: 0.138.

2D-layered graphitic carbon nitride (g-C3N4) is regarded as a great prospect as a photocatalyst for H2 generation. However, g-C3N4's photocatalytic hydrogen evolution (HER) activity is significantly restricted by the recombination of photocarriers. We find that cobalt sulfide (CoS2) as a cocatalyst can promote g-C3N4 nanosheets (NSs) to realize very efficient photocatalytic H2 generation. The prepared CoS2/g-C3N4 hybrids display highly boosted photocatalytic H2 generation performance and outstanding cycle stability. The optimized 7%-CoS2/g-C3N4 hybrids show a much improved photocatalytic H2 generation rate of 36.2 ​μmol−1 ​h−1, which is about 180 times as much as bare g-C3N4 (0.2 ​μmol−1 ​h−1). In addition, the apparent quantum efficiency (AQE) of all the samples was computed under light at λ=370 ​nm, in which the AQE of 7%-CoS2/g-C3N4 hybrids is up to 5.72%. The experimental data and the DFT calculation suggest that the CoS2/g-C3N4 hybrid's excellent HER activity is attributable to the lower overpotential and the smaller Co-H bond activation energy for HER. Accordingly, the CoS2 cocatalyst loading effectively boosts the photocatalytic performance of g-C3N4 for H2 evolution. The project promotes fast development of high-efficiency photocatalysts and low-cost for photocatalytic H2 generation.

Measurement(s) motion of construction workers Technology Type(s) wearable motion sensing system Factor Type(s) skeleton joints position Sample Characteristic - Organism construction workers Sample Characteristic - Environment construction site

With the growing economy and technology, disease prevention and individual health are becoming more and more important. It is highly urgent to develop a non-toxic, self-powered, and safe high-voltage power source to prevent diseases spread by mosquitoes, especially in isolated or remote areas. Herein, we reported a high-performance rotary triboelectric nanogenerator (R-TENG) based on customized theoretical simulations and a ferroelectric nanocomposite intermediate layer. The customized theoretical simulations based on gradient electrode gaps were established to optimize gap angles and segment numbers of the electrodes, which could prevent air breakdown and enhance the R-TENG output energy by at least 1.5 times. Meanwhile, the electrical output performance of the TENG was further enhanced with a highly oriented BaTiO3 (BTO) nanoparticles intermediate layer by about 2.5 times. The open-circuit voltage of R-TENG reached more than 6 kV and could continuously light 3420 light-emitting devices (LEDs) or 4 serially connected 36 W household fluorescent lamps. Therefore, a self-powered high-voltage disease prevention system is developed based on the high-performance R-TENG to reduce the risk of disease transmission. This work provides a prospective strategy for the further development of TENGs and expands practical applications of self-powered and high-voltage systems.

Nanozymes possess major advantages in catalysis and biosensing compared with natural nanozymes. In this study, the AuPt@BaTiO3 bimetallic alloy Schottky junction is prepared to act as oxidase mimetics, and its photo−piezoelectric effect is investigated. The synergy between the photo−piezoelectric effect and the local surface plasmon resonance enhances the directional migration and separation of photogenerated electrons, as well as hot electrons induced by the AuPt bimetallic alloy. This synergy significantly improves the oxidase−like activity. A GSH colorimetric detection platform is developed based on this fading principle. Leveraging the photo−piezoelectric effect allows for highly sensitive detection with a low detection limit (0.225 μM) and reduces the detection time from 10 min to 3 min. The high recovery rate (ranging from 99.91% to 101.8%) in actual serum detection suggests promising potential for practical applications. The development of bimetallic alloy heterojunctions presents new opportunities for creating efficient nanozymes.

The bonding of cement mortar to the concrete substrate is crucial in buildings. In this study, cement mortar was prepared using manufactured sand (MS) instead of river sand (RS). The bonding strength between manufactured sand mortar (MSM) and concrete substrate was evaluated and the effects of curing age, water-to-cement ratio (w/c) and thermal cycling on the bonding strength were discussed and compared with those of the river sand mortar (RSM). The compressive strength of the MSM was consistently higher than that of the RSM, while the bonding strength of RSM was consistently higher than that of MSM, indicating that the bonding strength does not depend on the compressive strength of the mortar. As the number of thermal cycles increased, the pull-off strengths at the interface between the concrete and MSM or RSM at different w/c ratios all decreased, and the RSM experienced a larger reduction. After 400 cycles, the percentage decrease in bonding strength of MSM sample ranged from 18.62% to 30.86%.

To promote the large-scale recycling of solid waste, the hydration characteristics of blended cement with different amounts of GGBS (ground granulated blast-furnace slag) and SS (steel slag) were investigated. The optimum blending amounts of GGBS and SS in cement were 40% and 10% by mass, and the optimum dosage of Na2SO4 in the C50-S40-SS10 (50 wt.% cement–40 wt.% slag–10 wt.% steel slag) system was 2 wt.%. The flexural and compressive strengths of the C50-S40-SS10 system after adding 2 wt.% Na2SO4 are 57.95% and 9.28% higher than that of pure cement at 28 d. XRD, FT-IR and Ca(OH)2 content analysis were chosen to investigate the hydration products of pure cement and blended cement. The results show that GGBS enhanced the hydration of both cement and SS. And GGBS contributed to the generation of calcium silicoaluminate hydrate (C–A–S–H) in the blended cement system. The addition of Na2SO4 promoted the hydration reaction and contributed to the generation of ettringite (AFt) in the ternary system. The hydration heat evolution results showed that GGBS and SS can reduce the hydration heat of cement. Na2SO4 had similar effects and delayed the time of AFt conversion to monosulfide calcium sulphoaluminate (AFm). A mutual activation mechanism of cement–GGBS–SS ternary system mixed with Na2SO4 was proposed in this study.

Glass curtain walls (GCWs) have become prevalent in office buildings, owing to their lightweight and modular characteristics. However, their lower thermal resistance, compared to opaque walls, results in increased energy consumption. Incorporating phase-change materials (PCMs) provides a viable solution through which to address the susceptibility of GCWs to external conditions, thus enhancing thermal performance and mitigating energy concerns. This study delves into the influences of the glazing solar heat gain coefficient (SHGC), the glazing heat transfer coefficient (U-value), and PCM thickness on the energy performance of buildings. Using Design Builder (DB) software version 6.1.0.006, a multi-story office building was simulated in different climatic zones in China, covering the climatic characteristics of severe cold, cold, hot summer and warm winter, cold summer and winter, and mild regions. The simulation results quantitatively elucidated the effects of the glazing parameters and the number of PCMs on thermal regulation and energy consumption. A sensitivity analysis identified the glazing SHGC as the most influential factor in energy consumption. Additionally, by employing Response Surface Methodology (RSM), the researchers aimed to achieve a balance between minimal building energy consumption and economic cost, ultimately determining an optimal design solution. The results demonstrated significant energy savings, ranging from 20.16% to 81.18%, accompanied by economic savings, ranging from 15.78% to 79.54%, across distinct climate zones in China.

The formation mechanism of MnS inclusions during heat treatment and its effect on the pitting behavior of laser powder bed fusion (L-PBF)-fabricated 316L stainless steel (SS) were investigated. MnS inclusions precipitated at the grain boundaries of the samples, and the spherical oxide particles can become nucleation sites. The quantity and size of the MnS inclusions increased with prolonged heating. Compared with the as-received sample, the pitting of heat-treated L-PBF-fabricated 316L SS samples was mainly induced by the newly generated MnS inclusions rather than the fabricated gas pores and extended along the grain boundaries; this caused the dramatic pitting resistance deterioration.

Ni/Co/SiO2 hydrophobic coatings were fabricated by embedding SiO2 nanoparticles into Ni/Co coatings using pulsed electrodeposition, followed by a liquid-phase hydrophobic treatment. Microstructure and morphology analysis of the composite coatings revealed that the SiO2 nanoparticles were homogenously distributed in the Ni/Co coating, and the surfaces of the samples were close-grained without crack. Furthermore, the SiO2 nanoparticles in the coating formed micro-nano structures on its surface, such that the contact angle reached 125° following the hydrophobic modification. The surface of the hydrophobic coating was found to be abrasion resistant and exhibited long-term stability in water. The corrosion inhibition efficiency of the Ni/Co/SiO2 hydrophobic coatings on a Q235 carbon steel substrate in simulated seawater solution reached 98.6%, indicating optimal anti-corrosion performance.

The structural performance of shield tunnel structures is highly susceptible to degradation under complex environmental loads, with the most common manifestation being bolt preload loss. In this study, a shield tunnel numerical simulation model was established to analyze the seismic response of shield tunnels with varying degrees of bolt preload loss. Firstly, the deformation patterns of shield tunnel structures under seismic loads were analyzed. Subsequently, ellipticity and joint opening were selected as seismic resilience assessment indicators based on the mechanical response. A seismic resilience assessment model was then established, including three states: normal state, affected state, and recovered state. The results show a direct relationship between the recovery capacity of tunnel structures and the initial performance of the lining structure, as well as the magnitude of the load. The lower the degree of structure degradation, the greater the structural recovery capacity. Additionally, there is a positive correlation between residual deformation and the initial performance loss of shield tunnel structures, as well as the intensity of seismic loads. This study contributes to enriching the theoretical framework for the seismic resilience assessment of shield tunnels, which have significant implications and provide valuable references for engineering safety.

Shield tunnels can experience preload loss in their connecting bolts during the operational phase, leading to changes in tunnel structure stiffness, which, in turn, affect the seismic performance of shield tunnels. A refined three-dimensional model of shield tunnel was established using the finite element method to study the impact of preload loss in connecting bolts on the seismic dynamic response of shield tunnels. An artificial viscoelastic boundary was used to simulate the propagation of seismic waves from an infinitely distant field. This study investigated the effects of different levels of preload loss on the seismic response of shield tunnels. In addition, the Arias intensity, which can reflect the degree of seismic impact on structures, was used to analyse the extent of damage to the tunnel. The conclusions drawn from the study are as follows: As the level of preload loss increases, the tightness of the segments during the static phase gradually deteriorates, and the maximum joint opening during the seismic loading phase continues to increase. Post-earthquake non-recoverable ellipticity and radial deformation progressively increase with an increase to preload loss level. Overall tunnel damage becomes more significant with the degree of preload loss increases depending on the Arias intensity. Preload loss leads to a decrease in the overall structural stiffness and an increase in longitudinal relative displacement. In conclusion, preload loss also affects structural failure mode and seismic performance. These research findings are of reference value for enhancing the seismic performance of shield tunnel structures and ensuring engineering safety.

The critical problem restricting the development and application of phase change energy piles is that adding phase change materials to concrete generally reduces its thermal conductivity. Therefore, exploring a scheme to improve the heat transfer performance of phase change energy piles is necessary. In this study, steel fibers were added to energy piles to enhance the heat exchange capacity between the pile and the surrounding soil. The model tests were conducted on two types of energy piles: a fiber-reinforced pile and a fiber-reinforced phase change pile. Based on laboratory tests, a three-dimensional thermo–hydro–mechanical coupled finite-element model was established to characterize the phase transformation process of FRPC piles accurately. Then, the thermal parameters of the phase change concrete pile were optimized and analyzed to explore the feasibility of improving the application of the phase change pile. The results reveal that the cooling condition where the initial ground temperature was higher than the phase change temperature was more suitable for the FRPC pile. When the flow rate was increased by 50%, the peak heat power of the FRPC pile increased by 25.7%. There is an optimal economic flow rate to balance the system’s energy consumption and heat power in different conditions. Increasing thermal conductivity and specific heat capacity are effective solutions to improve the heat transfer capacity of concrete piles. The energy pile that was enhanced with the high-thermal-conductivity PCM is a good choice to improve long-term operation performance.

Abstract Copper ions (Cu2+) pollution poses a serious threat to Marine ecology and fisheries, but the online detection is difficult due to seawater interference. Herein, photo‐assisted barrier effect is introduced into electrochemical detection as a driver to generate electrochemical response. The n–n junction barrier exhibits excellent adjusting effect on electrochemical response under photoexcitation and could effectively drive electrochemical response by Cu2+ adsorption. The prepared Ti/TiO2/In2O3/Chitosan wire is used for direct Cu2+ detection, and the trace detection with the low detection limit (59.08 nm) is achieved. The strong interference of seawater is resisted effectively by using photo‐assisted barrier effect, and the good recovery rate (94.9–107.1%) in the actual seawater detection make it promising for practical applications. It is a new approach to develop electrochemical sensors by using photo‐assisted barrier effect to resist interference.

The arrangement of multiple culverts has gradually increased in road engineering. However, the arrangement will face a series of risks in both the construction and operation stages. A numerical model was established to analyze the construction and operation safety of multiple steel corrugated pipe arch culverts by using a fully fluid–solid coupling two-dimensional (2D) model of a highway project. The sensitivity of factors affecting the settlement of the composite foundation such as modulus and depth of ground reinforcement was discussed. Based on the results of the 2D model, a fully fluid–solid coupling three-dimensional (3D) model was established to study the influence of dynamic cyclic vehicle load on the mechanical properties of multiple steel corrugated pipe arch culverts. The ground deformation, soil stress and pore pressure, structure stress, and deformation were analyzed. The results show that the maximum settlement of the soil in the arch culvert area is at the junction of the two different arch culverts after construction. The maximum vertical deformation of the structure appears at the vault, and the arch waist is prone to stress concentration. Under cyclic vehicle dynamic load, the ground deformation, structural stress, and arch culvert subgrade deformation showed a rapid growth stage, and then tended to be stable. The weak points in the structure during the construction and operation stages were revealed, which can provide a useful reference for the design and construction of multiple steel corrugated pipe arch culverts.

Herein, ceramic-reinforced CoCrNiMoxCB high-entropy alloy coatings were prepared by laser cladding, and the synergistic improvement of wear and corrosion resistance was realized. The effects of molybdenum on the phases, microstructures, and chemical compositions of the coatings were also studied. Wear mechanisms changed from adhesive wear to abrasive plough with the increase of Mo content, leading to excellent improvement in wear resistance. The corrosion resistance was remarkably improved with excellent passive ability and pitting resistance. Coherent interfaces and composition transition at the interfaces provide a nano-scale explanation for the excellent wear and corrosion trade-off of the Mo-8 coating. The results show that the wear and corrosion resistance of the coatings can be improved with the addition of molybdenum.

To study mechanism of microstructure evolution in TiAl based alloys during heat treatment, Ti44Al alloy was heat treated at 1240 °C for 0.5/1.0/2.0/2.5/3.0/5.0/7.0 h before being quenched in water. Chemical composition, phase component and microstructure are characterized by XRF, XRD, OM, SEM and EDS. In addition, microstructure evolution of Ti44Al alloy was in-situ observed through laser scanning confocal microscopy (LSCM) coupled with digital image correlation techniques during heat treatment at 1240 °C. Results show that both as-cast and heat-treated Ti44Al alloys contain two phases. As-cast alloy is fully lamellar microstructure. γ phases will dissolve, re-precipitate and grow up in turns with extension of heat treatment time. Microstructure evolution of Ti44Al alloy obtained through water quenching is consistent with the results through in-situ observation during heat treatment. Lamellar microstructure becomes more uniform, due to sufficient precipitation of γ phases during heat treatment in (α + γ) phase domain. Micro-hardness reaches the highest value about 440 HV after heat treatment for 2.0 h. Besides, a model of “diffusion and thickening” is proposed in this study, namely that morphology evolution of γ phases in gains is achieved through directional diffusion of Al and Ti atoms during heat treatment. In this process, lamellar γ phases grow up and thicken due to some adjacent γ phases dissolving. Based on the model, diffusion coefficient (Dv = 2.94 × 10−3 μm2/s) of Ti atoms at 1240 °C is calculated in this study, which provides basic data for controlling morphology of lamellar phases during subsequent heat treatment.

In order to investigate the plastic workability of TiB reinforced near-α high-temperature titanium matrix composite, 3 vol.% TiB/Ti-6Al-4Sn-10Zr-1Mo-1Nb-1W-0.3Si composite were hot compressed over a temperature range of 850–1100 °C and a strain rate range of 0.01–0.5 s−1. Microstructures of the composite after hot compression were observed by scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The constitutive equations of this composite were calculated and the processing map was established. The results show that the activation energy of (α + β) phase and β phase region were 758550 J · mol−1 and 220510 J · mol−1, respectively. In the stable regions, equiaxed α phase accounting for a high proportion was formed in the matrix at low temperature and strain rate, and became more obvious with increasing of temperature and stain rate. Whereas, in the unstable region the microstructure is mainly characterized by the debonding of TiB closely associated with strain hardening in the matrix, and incomplete recrystallization of β phase in the β phase region at high strain rate. More specially, softening mechanisms in stable during deformation were different under different parameters. The softening mechanism is dominated by the dynamic recrystallization when the process is about 900 °C/0.1–0.01 s−1, but gradually becoming by periodic competition of dynamic recrystallization and dynamic recovery when the processes is 950–1100 °C/0.1 s−1. This difference is mainly attributed to the decreasing of activation energy of at elevated temperature. Finally, the hot deformation processing parameters are optimized as temperature range of 900–950 °C and strain rate of 0.01–0.1 s−1.

Ti44Al alloys were conducted cyclic directional heat treatment (DHT) for 1, 4 and 6 cycles at 1750 K to obtain directional microstructure and research their microstructure evolution. Microstructure was observed and mechanical properties was tested. Results show that grains of all treated Ti44Al alloys grow up obviously, the width of grains increases and the number of grains decreases with increasing of cycles. More columnar grains are obtained and spacing of lamellar γ and α2 phases decreases to 0.60 μm approximately after cyclic DHT for 4 cycles. Refinement of lamellar phases is caused by increasing of nucleation sites for γ phases. And it is noted that the spacing of lamellar phases is homogenized after DHT, compared with that of as-cast Ti44Al alloy. In addition, there are about 80% columnar grains with small angles (less 60°) between their growth directions and orientation of lamellar phases after DHT. Micro-hardness of Ti44Al alloys increases firstly and then decreases with increasing of cycles. Micro-hardness value is the highest about 312.9 HV for Ti44Al alloy after 4 cycles of DHT, which increases by 28% compared with that of as-cast alloy (244.8 HV), due to thin and uniform lamellar phases. Compression strength of Ti44Al alloy also increases from 900 MPa to 1200 MPa after DHT, due to directional microstructure and jagged grain boundary.

Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation, which optimize a ground source heat pump system for the utilization of shallow geothermal energy. In this study, based on the principle of similarity, the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated. The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m × 2.5 m × 2.0 m (length × width × height). The pile was heated using water in the polyethylene (PE) pipe, which was connected to a water cycle temperature controller. At a constant inlet water temperature of 55 °C, three thermal cycles were carried out with the same heating and cooling periods and different water flow rates. The temperature distributions in the pile and soil, in addition to the pore pressure, soil pressure, and displacement of the pile, were monitored to clarify the thermo-mechanical behavior of the pile and soil. The heat transfer efficiency was analyzed based on the temperature difference and water flow rates. The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application. Furthermore, focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.

The porous few-layer g-C3N4 (PFL-g-C3N4) is prepared by a simple molecular self-assembly method. Compared with pure g-C3N4, the as-prepared PFL-g-C3N4 is ultrathin, the surface is rich in pores, and the photocatalytic nitrogen fixation activity is greatly increased to 8.20 mM h−1 gCat−1. Few-layer and ultrathin nature of PFL-g-C3N4 can provide a larger specific surface area, expose more active sites, and reduce the diffusion path of charges and protons from the inside to the surface. In addition, the porous structure can narrow the band gap, thereby increasing the light absorption range and enhancing the light absorption capability. Meanwhile, the presence of nitrogen vacancies causes PFL-g-C3N4 to move to a more negative conductive band value. More importantly, the isotopic experiments using 15N2 as nitrogen source confirm the ammonia production originating from N2 rather than the decomposition of g-C3N4. Therefore, PFL-g-C3N4 can greatly improve the efficiency of visible light photocatalytic nitrogen fixation. Keywords: Molecular self-assembly, g-C3N4, Porous structure, Nitrogen vacancies, Photocatalytic nitrogen fixation

A new stiffened composite pipe pile was developed for improving the foundation of reclaimed ground in ocean engineering. To study the bearing capacity of the stiffened composite pipe pile group, a combination of field test and finite element method was used. Firstly, field tests were performed on the proposed single stiffened composite pipe pile. The single stiffened composite pipe pile model was verified by comparing the numerical simulation results with the field test results. The load transfer mechanism from the stiffened core to the cemented soil and the surrounding soil was clarified. Further, a 3D finite element model of the stiffened composite pipe pile group was established based on the single stiffened composite pipe pile model. Finally, the bearing capacity of the pile group and the stress distribution of each pile were analysed and the influence of the pile spacing on the pile bearing capacity was discussed. The results showed that the axial stress of both the side and corner piles decreased rapidly with an increase in the pile spacing, and the stress-bearing ratio decreased. The stress-bearing ratio of the central pile increases with an increase in pile spacing. The smaller the pile spacing, the larger the load proportion of the composite pile group and the larger the foundation settlement. The optimal design scheme was a composite pile with a 500 mm stiffened core diameter, 700 mm outer cemented soil diameter, and a spacing between piles of four times the cemented soil diameter (2.8 m) considering the group pile bearing capacity and the economic benefits of the project. These results provide a reference for the design and construction of stiffened composite piles for ground improvement projects.

The development and utilization of underground space is an effective way to make intensive use of resources, solve "big city disease" and achieve high-quality development. The expansion and renovation of underground space in a central urban area is likely to cause serious damage to surrounding structures. In this study, a deep foundation excavation for the reconstruction of an urban subway station in the Greater Bay Area was chosen for analysis using the finite element method. Different from common excavation engineering, the interaction between the three coupling factors of train dynamic load, foundation excavation, and viaduct pile foundation were analyzed. Six different cases were calculated considering different working conditions of excavation depth and train dynamic load. Soil was evaluated using modified Cam-Clay model. The physical parameters of the soil were determined through on-site and laboratory tests. The results were compared with monitoring data, and the accuracy of the finite element model was verified. The settlement and influence range of the soil, and displacement and internal forces of viaduct piles were analyzed. The maximum settlement of the soil occurred in the direction of the short side of the foundation pit. The maximum value was approximately 0.53 times the excavation depth. The settlement increased by approximately 49% when applying the train load. The dynamic load had an aggravating influence on the horizontal displacement of the top of the pile, with a maximum increase of 51%. Moreover, the dynamic load increased the negative bending moment of the viaduct piles. This study provides a reference for the design and construction of geotechnical engineering projects.

In this study, a coherent ceramic strengthening wear-corrosion resistant CoCrNiMo high entropy alloy coating was successfully fabricated on 304 stainless steel (304ss) by laser cladding. Constituent phases, microstructure, and chemical composition were thoroughly investigated. The hardness and wear resistance were evaluated. Electrochemical tests were performed to measure the corrosion resistance of the passive film. The parameters of the passive films were calculated using the Mott-Schottky and the point defect model. TEM analysis was used to explain the high hardness and superior corrosion resistance on the base of the composition and boundary characteristics between different phases. Combining the results of wear and corrosion assessment, we deduce that a critical content of 2–3 at.% exists for B4C at which the best wear-corrosion tradeoff of the coating can be achieved. This strategy can be valuable in the development of both wear- and corrosion-resistant equipment in the marine environment.

A proper treatment of granite residual soil (GRS) in geotechnical practices requires both macro and microscopic evaluations. In this study, uniaxial and oedometric compression tests were conducted to investigate the mechanical properties of the saturated untreated and cement-treated GRS. Meanwhile, XRD, SEM, and MIP tests were conducted to identify the presence and types of C–S–H and the changes in the pore structure after cement treatment. The effects of cement treatment on the uniaxial compressive strength, secant modulus, compressibility, and vertical yielding pressure were revealed and the mechanisms of the soil structure to be modified through cement treatment were clarified based on the test results. A threshold volumetric cement content of 2–3% was determined based on the mechanical properties and microstructural characteristics of the saturated cement-treated GRS. Cement contents below this threshold would produce inadequate cementation between the soil particles. In contrast, cement contents above this threshold are considered inefficient because the transformation of the soil structure from single-porosity to dual-porosity increases the total porosity and retards the strength and stiffness gains.

Voids, a common defect in tunnel construction, lead to the deterioration of the lining structure and reduce the safety of tunnels. In this study, ground-penetrating radar (GPR) was used in tunnel lining void detection. Based on the finite difference time domain (FDTD) method, a forward model was established to simulate the process of tunnel lining void detection. The area of the forward image and the actual void area was analyzed based on the binarization method. Both the plain concrete and reinforced concrete lining with various sizes of air-filled and water-filled voids were considered. The rationality of the model was verified by measured data. It was observed that the response mode of voids can be hyperbolic, bowl-shaped, and strip-shaped, and this depends on the void’s width. Compared with the air-filled voids, water filling increases the response range of the voids and produces a virtual image. Although the diffracted wave caused by a steel bar will bring about significant interference to the void response, the center position of the voids can be accurately located using 3D GPR.

Abstract Herein, we constructed urchin‐like TiO2 hollow nanospheres (HNSs) by hydrothermal targeted etching, and used it as a substrate to load semi‐metal 1T′‐MoS2 nanosheets as effective nitrogen reduction reaction (NRR) electrocatalysts. 1T′‐MoS2/TiO2 HNSs composites display outstanding NRR activity with the highest NH3 yield of 29.62 μg h−1 mg−1cat. at −0.75 V versus RHE. Besides, the highest FE of 24.9% is obtained at −0.65 V. The remarkable NRR performance is attributed to the high conductivity of 1T′‐MoS2 and the urchin‐like structure of TiO2 hollow nanospheres. DFT calculations display that the 1T′‐MoS2 in 1T′‐MoS2/TiO2 makes the activation and further reduction of *N2 more thermodynamically favorable than pristine TiO2, contributing to better NRR catalytic activities. 15N isotopic labeling experiment reveals that N in produced NH3 comes from N2 of electrolyte.

Abstract The biggest challenging issue in photocatalysis is efficient separation of the photoinduced carriers and the aggregation of photoexcited electrons on photocatalyst’s surface. In this paper, we report that double metallic co-catalysts Ti3C2 MXene and metallic octahedral (1T) phase tungsten disulfide (WS2) act pathways transferring photoexcited electrons in assisting the photocatalytic H2 evolution. TiO2 nanosheets were in situ grown on highly conductive Ti3C2 MXenes and 1T-WS2 nanoparticles were then uniformly distributed on TiO2@Ti3C2 composite. Thus, a distinctive 1T-WS2@TiO2@Ti3C2 composite with double metallic co-catalysts was achieved, and the content of 1T phase reaches 73%. The photocatalytic H2 evolution performance of 1T-WS2@TiO2@Ti3C2 composite with an optimized 15 wt% WS2 ratio is nearly 50 times higher than that of TiO2 nanosheets because of conductive Ti3C2 MXene and 1T-WS2 resulting in the increase of electron transfer efficiency. Besides, the 1T-WS2 on the surface of TiO2@Ti3C2 composite enhances the Brunauer–Emmett–Teller surface area and boosts the density of active site.

To reduce or evaluate the damage of tunnels in seismically active areas when earthquakes happen, it is very important to quickly predict the tunnel damage. This study proposes an anti-entropy–fuzzy analytic hierarchy process (FAHP) combination weighting method for tunnel earthquake damage prediction. The tunnel cross section is a symmetrical structure. The method uses tunnel damage data from the tunnels in a region where earthquake disasters have occurred as sample data to calculate the standard earthquake damage index. The weights of evaluation factors are determined by combining the FAHP and anti-entropy weighting. The correction coefficient of each evaluation factor is obtained by considering the degree of each evaluation factor’s influence on the average damage index. Then, the earthquake damage and the corresponding damage degree of each tunnel are obtained by weighting calculation. In this study, 55 tunnels in the Wenchuan earthquake-affected area are taken as analysis cases. In these cases, 45 cases of damage tunnels are used as sample data, and 10 random tunnels are used as training cases. The calculated results are compared with the observed results. The proposed method is confirmed simple and easy to implement, which can greatly reduce the workload of field investigation, calculation and analysis. The results is of great significance to the rapid earthquake emergency assessment and post earthquake recovery of tunnels.

The three-dimensional (3D) printing technique for cement-based materials has been actively investigated and utilized in civil engineering. However, there is no systematic review of the fabricating devices. This paper reviews the software and hardware for extrusion-based 3D concrete printing. Firstly, a dedicated tool path generating software is urgently needed to meet the cementitious printing applications and to improve printing quality with toolpath optimizations. Secondly, the existing printing equipment was summarized and discussed, concluding the pros and cons of various 3D motion systems, material systems, and nozzle units. Suitable choices for scientific research and engineering applications were recommended. The reinforcing techniques were categorized and concluded with the existing drawbacks and the research trend. A hybrid manufacturing system of 3D printing and the reinforcing technique was then proposed with a system diagram and flowchart.

Engineered cementitious composite (ECC) is a unique material, which can significantly contribute to self-healing based on ongoing hydration. However, it is difficult to model and predict the self-healing performance of ECC. Although different machine learning (ML) algorithms have been utilized to predict several properties of concrete, the application of ML on self-healing prediction is considerably rare. This paper aims to provide a comparative analysis on the performance of various machine learning models in predicting the self-healing capability of ECC. These models include four individual methods, linear regression (LR), back-propagation neural network (BPNN), classification and regression tree (CART), and support vector regression (SVR). To improve prediction accuracy, three ensemble methods, namely bagging, AdaBoost, and stacking, were also studied. A series of experimental works on the self-healing performance of ECC samples was conducted, and the results were used to develop and compare the accuracy among the ML models. The comparison results showed that the Stack_LR model had the best predictive performance, showing the highest coefficient of determination (R2), the lowest root-mean-squared error (RMSE), and the smallest prediction error (MAE). Among all individual models studies, the BPNN model performed the best in terms of the RMSE and R2, while SVR performed the best in terms of the MAE. Furthermore, SVR had the smallest prediction error (MAE) for crack widths less than 60 μm or greater than 100 μm, while CART had the smallest prediction error (MAE) for crack widths between 60 μm and 100 μm. The study concluded that the individual and ensemble methods can be used to predict the self-healing of ECC. Ensemble models were able to improve the accuracy of prediction compared to the individual model used as their base learner, i.e., a 2.3% to 4.9% reduction in MAE. However, selecting an appropriate individual and ensemble method is critical. To improve the performance accuracy, researchers should employ different ensemble methods to compare their effectiveness with different ML models.

Different formulations for 3D printable cementitious composites have been developed for extrusion-based printing. However, there is a lack of configuration guides for actual printing operations, which integrate one printable material and one printing system closely. Three testing methods for configuration determination were proposed and tested with three material proportions, with initial setting times of 2, 8, and 13 min, respectively. The building index (BI) measures the layer stacking stability based on the material, scale, and device. The height reduction test (HRT) quantifies the shortening in the height of the printed filaments. The leaning angle (LA) refers to the maximum slope of the stacked layers. In this study, results showed the critical values were (a) 0.167 for the height reduction ratio (HRR), (b) 40° for LA, and (c) 0~19.1, 0~61.1, and 0~99.4 for BI of the three mixtures. They were the meta parameters used to guide the CAD sketching, material development, and printing configurations, including the printing speed and layer height.

Three-dimensional (3D) printed concrete has recently received considerable research attention. In buildings, phase change materials (PCMs) with excellent thermoregulatory properties and thermal storage capacity can improve the insulation capacity of external walls and reduce energy consumption. In this study, microencapsulated paraffin was added to a 3D printable material and a 3D printed phase-change concrete was developed, resulting in good printability and buildability. The compressive and flexural strengths were declined maximally by 44.6% and 37.5%, respectively, with 20 wt% PCM mixed. Results from 3D printed room models proved the thermo-regulated performance by regulating the room temperature when mixed with 20 wt% PCM. With the addition of PCM, 3D printed facilities can have sufficient thermal comfort.

Lack of reinforcements is an existing drawback of 3D printed cementitious components, which is an urgent concern. A staple-inserting apparatus was developed and installed on a 3D printer and automatically fabricated 3D printed and staple-reinforced components with 98% successful insertion to achieve inner- and inter-reinforcement of the printed strips. The inserted staples inside the printed strips improved the compressive strength by 25% maximum owing to the inner locking effect by the staple pins, while the flexural strength did not increase because the scattered staples functioned separately. The staples over the strip interfaces remarkably increased the flexural stress by 46–120%. The inserted staples demonstrated a significant strip locking effect, but the unavoidable voids decreased the bonding between staples and the composite. The mechanical analysis concluded that the printing parameters considerably affected the reinforcing rate. The staple inserting technique proved the feasibility of automatic fabrication of fiber-reinforced and printed concrete structures.

Various heat-resistant alloys have been used in industry; however, the bridge between the bulk mechanical properties and the underlying micro- and nanoscopic local properties remains an issue [...]

Phase change material (PCM) is a substance that can absorb or release sufficient latent heat at phase transition. By encapsulating phase change paraffin in hollow steel balls in the concrete, an energy pile with PCM was innovatively produced to improve energy efficiency for the ground heat pumping system. Laboratory tests were carried out on both PCM energy pile and traditional concrete pile to evaluate the thermo mechanical performance. Two piles were heated and cooled through inside tubes at a constant flow rate. The laboratory tests on the two piles were symmetrical for the two horizontal directions in geometry, and heat transfer process follows conservation laws of energy. The temperature response of the pile and soil, internal strain, pile displacement, pore pressure, and soil pressure under heating-cooling cycles were examined. Compared with the traditional concrete pile, the PCM energy pile can effectively reduce the surrounding soil temperature. The use of PCM in the pile can improve the capacity of heat storage and make the pile more effective in heat exchange. Non-uniform thermal strain and accumulations of heat and irrecoverable displacement were observed in the repeated heating-cooling process. The study can provide references for the practical implication of PCM energy piles.

An increasing number of recent studies have indicated that the best balance of mechanical properties of a high-entropy alloy (HEA) needed to meet the requirements of practical structural applications require to produce second precipitates in an HEA matrix. This type of alloy is more appropriately classified as a complex concentrated alloy (CCA) rather than an HEA. Here, we report a simple strategy for the fabrication of CCA coatings with high mechanical properties. In this strategy, the face-centred cubic (FCC)-based Co25Cr25Cu12.5Ni25Al12.5 (at.%) system was chosen, and spark plasma sintering was first used to prepare the Co25Cr25Cu12.5Ni25Al12.5 CCA clad layer directly on a Q235 substrate from simple mixed powders. Our results show that the CCA coating was fabricated successfully on the substrate and that the clad layer exhibited a dense microstructure, a low dilution ratio and good metallurgical bonding with the substrate. A high density of hierarchical intragranular nanoprecipitates was contained in the clad layer. Precipitation strengthening, as one of the main strengthening mechanisms, contributes to a microhardness value of 455 HV for the clad layer, which is much higher than those of most reported FCC-structured HEAs, even some BCC-structured refractory HEAs and several BCC-based HEAs with high Al contents. Keywords: Complex concentrated alloy coating, Spark plasma sintering, Hierarchical nanoprecipitates, Precipitation strengthening, Mechanical properties

Phase change materials (PCMs) have received extensive attention due to their high latent heat storage density and isothermal behavior during heat charging and discharging processes. The application of PCMs in buildings would match energy supply and demand by using solar energy effectively, thereby reducing building energy consumption. In this study, a diatomite/paraffin (DP) composite was prepared through a vacuum-impregnated process. The thermo-physical performance, thermal stability, chemical structure and thermal reliability of the DP composite were evaluated. To develop a structural–functional integrated energy storage building material, carbon fibers (CF) were chosen as the reinforcing material. The mechanical and thermal properties of CF-reinforced DP/gypsum were examined. It is evident that the flexural strength and thermal conductivity of DP/gypsum containing 1 wt. % CF increased by 176.0% and 20.3%, respectively. In addition, the results of room model testing demonstrated that the presence of CF could enhance the overall thermal conductivity and improve the thermo-regulated performance of DP/gypsum. Moreover, the payback period of applying CF-reinforced DP/gypsum in residential buildings is approximately 23.31 years, which is much less than the average life span of buildings. Overall, the CF reinforced DP/gypsum composite is promising for thermal energy storage applications.

Tricalcium aluminate (C3A) is the most reactive component of the Portland cement and its hydration has an important impact on the workability and early strength of concrete. Recently, nanomaterials such as nano-silica (nano-SiO2) have attracted much attention in cement-based materials because of its pozzolanic reactivity and the pore-filling effect. However, its influence on the hydration of C3A needs to be well understood. In this study, the hydration kinetics of C3A mixed with different percentages of nano-SiO2 were studied and compared with pure C3A. The hydration products were examined by different characterization techniques including XRD, XPS, and NMR spectroscopy and isothermal calorimetry analyses. The XRD results showed that the addition of nano-SiO2 promoted the conversion of the intermediate product C4AH13. The isothermal calorimetry results showed that the addition of nano-SiO2 significantly reduced the hydration exotherm rate of C3A from 0.34 to less than 0.1 mW/g. With the presence of nano-SiO2, the peaks for Q1 were observed in 29Si MAS-NMR measurements, and the content of Q1 increased from 6.74% to 30.6% when the nano-SiO2 content increased from 2 wt.% to 8 wt.%, whereas the proportion of Q4 gradually decreased from 89.1% to 63.6%. These results indicated a pozzolanic reaction provoked by the nano-SiO2 combined with aluminate structures generating C-A-S-H gel.

ZnO hollow microspheres with a diameter of approximately 1.4 μm were successfully synthesized by a facile one-step chemical precipitation method using trisodium citrate dihydrate as a morphology control agent. The ZnO hollow microspheres consisted of nanoplates and had good dispersibility. Control experiments revealed that trisodium citrate dihydrate played an important role in regulating the morphologies of ZnO products. The morphology of the ZnO product evolved from nanowires to hollow microspheres with the addition of trisodium citrate dihydrate. The sensor response of ZnO hollow microspheres toward 100 ppm n-butanol reached 86.6 at the optimum operating temperature of 340 °C, which was approximately three times higher than that of ZnO nanowires. In addition, the ZnO hollow microspheres also displayed good selectivity and long-term work stability toward n-butanol. The excellent gas sensing performance of ZnO hollow microspheres may be ascribed to the unique hollow sphere structure with high exposed polar crystal surface.

To reduce the thermal response and improve the heat storage capacity of energy piles, a phase change (PC) energy pile was proposed. This innovative PC pile is made of concrete containing macro-encapsulated PCM hollow steel balls (HSB) as coarse aggregates. A numerical model was developed to simulate the thermo-mechanical behaviors of the PC pile under thermal cycles and sustained loading. The computational model is a three-dimensional model that is symmetrical for the two horizontal directions in geometry. Heat transfer process follows conservation laws of energy. The numerical model was validated by the experiments conducted on the PC pile and the results show that the model can reproduce the major thermo-mechanical effects. Then, the model was used to compare the performance between the ordinary concrete pile and the PC pile in saturated sand under the same experimental conditions, where the piles were considered to be thermo-elastic in nature and the sand was considered as a Mohr–Coulomb elastic-plastic material. The thermo-mechanical response of the PC pile under different thermal loads was analyzed. The results show that at the end of heating, the temperature, strain, and displacement of the PC pile were lower than those of the ordinary pile. As the thermal loading increased, the range of temperature change in the soil around the PC pile increased, as well as the strain and displacement of the pile. The residual strain and plastic displacement after the temperature cycles also increased with the increase of thermal loading. Therefore, when designing phase change energy piles, full consideration should be given to the matching of thermal loads and PC temperature, so as to balance the heat transfer rate of the pile and the thermal response.

A ground source heat pump system is a highly efficient renewable heating, cooling, and ventilation system that utilizes the ground as a heat source or sink via ground heat exchangers. Energy pile is an energy geotechnical structure that couples a ground heat exchanger with a geotechnical structure, leading to low capital cost. The design of energy piles can be challengeable due to their complicated geometries and the requirement of mechanical load. This study focuses on the heat transfer across the concrete–soil interface of energy piles in urban areas. Case studies from two projects, the Lambeth College and Shell Centre projects, are presented and discussed. The back analysis of two energy pile cases illustrated that the heat transfer coefficient at the pile–soil interface can differ between the cooling mode and the heating mode. It can be concluded that the difference in the heat transfer coefficient is influenced by a number of factors such as soil properties, concrete (grout) properties, and the installation method.

In this study, hydrocalumite-like Ca2Al-NO3− layered double hydroxides (Ca-Al LDHs) with different microstructures were synthesized. The crystalline properties, structure composition, morphology and particle size distribution of the Ca-Al LDH (CAL) samples were illustrated. To obtain the chloride uptake performances of CAL, the influences of contact time, initial concentration of Cl−, pH of reaction solution and coexistence anions on the chloride uptake were examined systematically. Compared to the CAL samples obtained at a higher aging temperature, CAL synthesized at 60 °C demonstrated the minimum average particle size (6.148 μm) and the best Cl− adsorption capacity (211.324 mg/g). Based on the test results, the main adsorption mechanism of chloride ion on CAL was recognized as an interlayer anion exchanging reaction other than the dissolution-precipitate mode. With the increase in the pH value of reaction solution from 7 to 13, it was found that the amount of chloride ion adsorbed by CAL increased slightly, and the solution could remain at relatively high pH value even after the adsorption. The presence of CO32− and SO42− reduced the adsorption capacity of CAL dramatically as compared with OH− due to the destruction of layered structure and the formation of precipitates (CaCO3 or CaSO4). The interference sequence of the investigated anions on the chloride uptake of CAL was SO42−, CO32− and OH−, and the order of interlayer anionic affinity was Cl− > OH− > NO3−. The results illustrated that the synthesized CAL could be used as a promising chloride ion adsorbent for the corrosion inhibition of reinforcement embedded cement-based materials.

Sulfate attack is one of the most important factors that lead to the performance deterioration of concrete materials. The progress of the sulfate diffusion depth in concrete is an important index that quantitatively characterizes the rate of concrete damage, cracking, and spalling due to sulfate attacks. The progress of the diffusion depth of concrete to sulfate attack is systematically investigated in this paper by both theoretical and experimental study. A newly time-varying model of the diffusion depth is developed, which has comprehensively considered a mass of parameter of complex environments for the first time. On this basis, a method is further proposed for effectively predicting the residual life of in-service concrete structures subject to sulfate attack. Integrating the data from the self-designed high-temperature dry-wet accelerated corrosion test and a large amount of experimental data reported in the existing literatures, the effectiveness and accuracy of the time-varying model of the diffusion depth by sulfates are finally verified.

In this study, the effects of graphene oxide (GO) on the microstructure of cement mortars were studied using scanning electron microscopy (SEM), thermogravimetric (TG), and X-ray diffraction (XRD) techniques. Cement mortar samples with different proportions of GO (0.02, 0.04, 0.06, and 0.08 wt % based on the weight of cement) were prepared. The test results showed that GO affected the crystallization of cement hydration products, C–S–H (calcium silicate hydrate is the main hydrate product) and CH (calcium hydroxide). The morphology of hydration products changed with the increase of GO content. Furthermore, the results of XRD analyses showed that the diffraction peak intensity and the crystal grain size of CH (001), (100), (101), and (102) for GO samples increased considerably compared with the control sample. Based on the results, it can be understood that GO can modify the crystal surface of CH, leading to the formation of larger crystals.

Dispersion of carbon nanotubes (CNTs) is a challenge for their application in the resulting matrixes. The present study conducted a comparison investigation of the effect of four surfactants: Alkylphenol polyoxyethylene ether (APEO), Silane modified polycarboxylate (Silane-PCE), I-Cationic polycarboxylate (I-C-PCE), and II-Cationic polycarboxylate (II-C-PCE) on the dispersion of hydroxyl functionalized multi-walled carbon nanotubes (MWCNTs–OH). Among the four surfactants, APEO and II-C-PCE provide the best and the worst dispersion effect of CNTs in water, respectively. Dispersion effect of MWCNTs–OH has been characterized by optical microscope (OM), field emission-scanning electron microscope (FE-SEM), and Ultraviolet–visible spectroscopy (UV–Vis).The OM images are well consistent with the UV–Vis results. Based on the chemical molecular structures of the four surfactants, the mechanism of MWCNTs–OH dispersion in water was investigated. For each kind of surfactant, an optimum surfactant/MWCNTs–OH ratio has been determined. This ratio showed a significant influence on the dispersion of MWCNTs–OH. Surfactant concentration higher or lower than this value can weaken the dispersion quality of MWCNTs–OH.

To analyze the effect of summer ventilation on the thermal performance and energy efficiency of buildings utilizing phase change materials (PCMs), this paper simulated the indoor temperature variation and energy saving performance of buildings constructed with PCM under different ventilation conditions from June to September. With EnergyPlus and degree-day method, 48 ventilation schemes, including eight ventilation periods (3 h per period) and six ventilation quantities (0.5 ac/h to 3 ac/h), were modeled and simulated in five cities located in different climate regions in China. According to the results, it is believed that the simultaneous use of PCM and ventilation can significantly improve the indoor thermal comfort and offer a good energy saving performance in summer. Considering the economic benefits, different optimal ventilation schemes (including ventilation periods and ventilation quantities) were suggested for different climate regions.