Abstract:Treatment of peat soil foundation in Yunnan surrounding Dianchi and Erhai Lakes poses complex problems for engineering projects. It is insufficient to rely on ordinary cement to reinforce peat soil. In order to make the reinforcement reliable, this experiment mixed (ultrafine cement) UFC into ordinary cement to form a composite solidify agent. This study aimed to analyze the influence of UFC proportion on the strength of cement-soil in the peat soil environment. Unconfined compressive strength (UCS) and scanning electron microscope (SEM) tests were conducted on samples soaked for 28 and 90 days, respectively. The test results show that without considering the effects of Humic Acid (HA) and Fulvic Acid (FA), incorporating UFC can significantly improve the UCS of cement-soil. The rapid hydration of the fine particles generates a large number of cementitious products, improves the cohesion of the soil skeleton, and fills the pores. However, when the proportion of UFC increases, the aggregate structure formed by a larger quantity of fine particles reduces the hydration rate and degree of cement hydration, making the UCS growth rate of cement-soil insignificant. In the peat soil environment, HA significantly weakened the UCS of cement-soil in both physical and chemical aspects. However, UFC can mitigate the adverse effect of HA on cement-soil by its small particle size, high surface energy, and solid binding ability. In addition, FA has a positive effect on the UCS of cement-soil soaked for 28 days and 90 days. The UFC addition could promote the enhancement effect of FA on cement-soil UCS. SEM test results showed that cement hydration products increased significantly with the increase of UFC proportion, and cementation between hydration products and soil particles was enhanced. The size and connectivity of cement-soil pores were significantly reduced, thereby improving cement-soil structural integrity.

Abstract:The use of in-situ lunar resources to prepare structural materials is an important method in reducing the construction cost of lunar bases. On the basis of preparing simulated lunar regolith, the physical and mechanical properties of radiation sintering hardened simulated lunar regolith were studied. The results indicate that using volcanic slag as raw material, the preparation of simulated lunar regolith can be achieved through processes such as drying, impurity removal, crushing, and screening. The prepared simulated lunar regolith shows good similarity with the real lunar regolith and existing simulated lunar regolith in terms of microstructure, particle size distribution, chemical composition, mineral composition, etc. Simulated lunar regolith hardening was realized through radiation sintering, and the effects of sintering temperature and particle size distribution on the apparent density, sintering shrinkage, and mass loss rate of hardened lunar regolith were studied. The mechanical properties of hardened simulated lunar regolith were determined through monotonic compression tests, and the sintering temperature and particle size distribution of simulated lunar regolith had a significant impact on mechanical properties. Before the monotonic compression failure, the specimen did not undergo significant plastic deformation. The elastic modulus did not change significantly, demonstrating the perfect linear elasticity.

Abstract:With the continuous advancement of the lunar exploration project, lunar construction has become a crucial technological aspect in establishing human base on the Moon. In order to explore the potential of lunar regolith as a construction material, this study investigated the reinforcement of simulated regolith simulant CQU-L1 and CQU-L2 with microbially induced calcium carbonate precipitation (MICP). Tests on unconfined compressive strength (UCS), shear wave velocity, and scanning electron microscope (SEM) were conducted on the MICP treated lunar regolith simulant with different reinforcement times and concentrations of cementing solution (CS). Results indicate that with an increase in MICP reinforcement times and CS concentration, strength of the cured lunar regolith simulant significantly improves. Under the same reinforcement frequency, the strength of the cured lunar regolith simulant increases with the increase in CS concentration. The peak strength of samples reinforced 12 times with 2.0 mol/L CS can reach 1.303 MPa. The trend of soil shear wave velocity is similar with UCS, with a maximum shear wave velocity of 508 m/s. SEM test results demonstrate that with an increase in reinforcement frequency and CS concentration, a denser structure forms in the pores of the cured lunar regolith simulant, and calcium carbonate shows vaterite type. This study provides a new approach to lunar construction using lunar resources and is expected to provide important technical support for future lunar base construction.

Abstract:The cement has important influence on the mechanical properties of granite residual soil. Kaolinite powder, montmorillonite powder, illite powder and red clay powder are used to replace the fine particles of granite residual soil to remold soil samples. Compression, shear, tensile and disintegration tests are carried out respectively to study the effects of different cements on the mechanical strength of soil. Results show that the soil particle aggregates after kaolin treatment are increased, and a skeleton structure with high strength is formed between the aggregates. However, the existence of large number of pores between the skeletons provides a channel for water intrusion, resulting in enhanced water absorption of the soil. Benefiting from the swelling property of montmorillonite in water, the treated soil surface has fewer pores and dense structure, and the expansive body provides high strength cementation capacity, making the mechanical characteristics of soil significantly improved. The mechanical strength of the soil sample treated with illite is low, but the soil surface appears relatively dense. From perspective of particles dispersed on the soil surface, illite powder is more used as fine material to fill the pores between large particles than as a cement with high strength between soil particles. After physical compaction, the occlusion between particles is enhanced due to compression; At the same time, after a long time of hydration reaction, the cement formed bridge cementation on the particle surface. Under the combined actions above, the mechanical strength of soil has been greatly improved. The type of cement would have a great impact on the mechanical properties. On the one hand, it depends on the characteristics of the cement itself, such as the water swelling characteristics of montmorillonite. On the other hand, it depends on the binding effect of the cement on the soil. The compressive, shear, tensile and collapse resistance of the soil samples are controlled by the binding mode of the cement and the soil sample.

Abstract:The rock mass of the grotto temple has been affected by cooling and heating for a long time, which would lead to the change of the mechanical properties of the rock mass and therefore endangers the grotto temple. In this paper, the Dazu Rock Carving sandstone in Chongqing was taken as the research object, and the mechanical properties of the sandstone were studied through triaxial compression tests. Temperature change process includes high temperature (60 ℃), normal temperature (25 ℃), and low temperature (0 ℃). And the experimental process involves multiple conditions such as different heating-cooling cycle times (5 and 10 times), different durations of high and low temperatures (2 h and 4 h), and different cooling methods (natural cooling and water cooling). These test conditions were designed to analyze the influence of temperature changes on the peak stress and strain, elastic modulus, internal friction angle, cohesion, and failure mode. Results indicate that: The mechanical properties of sandstone weakened after multiple heating-cooling cycles. The values of strength, elastic modulus, cohesion, and internal friction angle decreased at different degrees. The peak strain of sandstone increased after multiple heating-cooling cycles. The failure mode of sandstone under triaxial compression was mainly shear failure with a single shear plane, while the failure mode became complex after multiple heating-cooling cycles, which resulted in the conjugated shear failure of “Y” type. Confining pressure could improve the mechanical properties, which increased the strength and elastic modulus of the sandstone samples.

Abstract:During the operation of deep geological repository, the bentonite as a buffer material would be in a high temperature-strong alkaline environment for a long time, and its physical properties would deteriorate with time. Aging effect on physical property of MX-80 bentonite powder at high temperature and strong alkali conditions was investigated in this paper. MX-80 bentonite was subjected to alkali-heat conditions, i.e.,T=90 ℃ and C_NaOH=0.5 mol/L for duration of 0, 15, 30, 45, 60, 90 days, respectively. The variation of physical properties such as the specific gravity, specific surface area and swell index of MX-80 bentonite was studied through laboratory experiments. Some representative specimens were selected for X-ray diffraction (XRD) tests and thermogravimetric analysis (TGA) tests to provide a reasonable explanation from microscopic perspective. The results showed that the specific gravity, specific surface area and swell index of bentonite decreased sharply from 0 to 45 days, gradually levelling off after then, finally, the reduction amplitudes were 13.6%, 18.5% and 58.1% after 90 days, respectively. Montmorillonite content decreased and albite content increased. The changes of montmorillonite and albite were -23.3% and +3.7% after 90 days. The content of free water, weakly bound water and strongly bound water decreased, and the content of the three decreased by 2.84%, 0.13% and 0.24% respectively after 90 days. The fundamental reason for the deterioration of bentonite physical properties over time under high temperature and strong alkali conditions was the dissolution of montmorillonite.

Abstract:Prefabricated vertical drainage plate (PVD)-vacuum preloading method is effective in improving the dredged slurries. However, during the operating process, a dense area (soil column) with a gradually decreasing radius from top to bottom would be generated around the PVD, delaying the soil consolidation rate. Aimed at it, this paper assumed that the soil column radius attenuates linearly with depth, and based on the assumption of equal strain, and the Hansbo,s consolidation theory, the consolidation equation considering the change of soil column radius with depth is deduced. At the same time, by calculating the equation above, the influences of the permeability coefficient, the radius of the soil column and the variation of the radius of the soil column along the depth on the soil consolidation rate were explored, and compared with the existing laboratory test data. The result shows that the smaller the permeability coefficient of the soil column, the slower the dissipation of pore water pressure, and the slower the consolidation rate. As the soil column radius gradually increases, the soil consolidation rate gradually decreases. The smaller the residual coefficient after the attenuation of the soil column radius, the greater the attenuation degree of the soil column radius along the depth, the smaller the influence on the soil consolidation in the weak area, and the faster the soil consolidation rate. In the case of considering the soil column radius attenuation with depth, the presented results are in good agreement with the experimental findings.

Abstract:This study is carried out to investigate the resource utilization of mud water shield residue. Industrial waste residues such as alkali slag and desulfurization gypsum are reasonably used to be combined with the traditional lime, in order to convert waste mud into qualified roadbed filling materials. Through the laboratory compaction tests, CBR tests, unconfined compressive strength tests, wetting-drying cycle tests and microscopic tests, the mechanical properties, immersion stability and durability of shield tunnel residue improved by lime-alkali slag and lime-desulfurization gypsum were studied, and the improvement mechanism was analyzed. The test results show that the mechanical properties of the soil were improved significantly after compound improvement. The water stability and durability were also greatly improved, with better mechanical properties for road use. Among them, the overall water stability performance and durability of the lime-desulfurization gypsum groups were better than the lime-alkali slag groups. During the wetting-drying cycles, the durability of the specimens mixed with 3% desulfurization gypsum was better, with only small cracks not penetrating the specimens during the cycles. The study shows that the shield tunnel residue has good mechanical properties after compound improvement of lime and desulfurization gypsum, and can be used as roadbed filling materials.

Abstract:As one of the most common support structural systems against seismic landslide, pile-anchor structures have become a hot topic of research in the current engineering field for their enhanced seismic resilience under strong earthquake. This study optimizes the seismic performance of pile-anchor structures by introducing viscous dampers and ECC (Engineered Cementitious Composite) ductile components. Based on shake table tests, the characteristics of dynamic behavlors of the new pile-anchor structures are analyzed from aspects of macroscopic failure, model dynamic properties, acceleration response, pile displacement response, dynamic bending moment response, and dynamic axial force response. The experimental results indicate that installation of dampers effectively reduces the dynamic axial force of the anchor cables and prevents its accumulation, with a maximum reduction of up to 47%. The reduction magnitude increases and then decreases with the increase of the seismic intensity, and it can be adjusted by optimizing the design of the dampers. The use of ECC materials improves the deformation capacity of the pile body, enhances the energy dissipation capacity of the anti-sliding pile under seismic action, and overcomes the problem of increased displacement due to the installation of dampers. The combined effect of both significantly improves the seismic performance of pile-anchor structures. The spectral characteristics of seismic waves possesses significant impact on the seismic response pattern of the new structure. The more frequency components close to the fundamental frequency of the slope contained in the seismic waves, the more prominent the dynamic amplification effect. Compared to the action of Sine_5Hz, under the effect of the Wenchuan wave, the amplification factor of the PGA (Peak Ground Acceleration) at the top of the slope could increase by up to 100%.

Abstract:In order to study the bearing characteristics of single loaded rock-socketed pile under horizontal load, pseudo-static model tests considering the vertical and horizontal loadings were adopted in view of the challenge of dynamic test, in which rock and pile are simulated with similar material. The elastic bending moment, rock pressure around the pile and the hysteresis curve of the pile top are analyzed under different slopes and elastic modulus of rock. The results show that the horizontal bearing capacity of pile foundation of rock slope is mainly related to shallow slope within the range of buried depth above 3D (D is pile diameter) . The failure pattern of the downslope rock mass is similar with that of the soil slope, which goes through three stages: the emergence of cracks, the development of failure surface and the failure of the shallow slope body, even though the upslope rock mass has not formed a complete failure surface. Finally, the shear failure of pile foundation leads to the failure of horizontal bearing capacity, indicating that when the slope is of rock, the slope mainly affects the positive bearing capacity. When the slope angle ranges from 15° to 30°, the positive bearing capacity increases by 41.3%, while the negative bearing capacity only increases by 0.15%. The slope material strength has an impact on both positive and negative bearing capacity. The pile-rock elastic modulus ratio changes from 2.8 to 0.9, while the positive and negative bearing capacity increase by 80.7% and 73.5%, respectively.

Abstract:An analytical solution based on non-tension Pasternak foundation composite beam with considering soil shear and interlayer disengaging for the double-block ballastless track, is derived to study the influence of uneven settlement of the subgrade on its deformation. Heaviside step function is introduced to describe the disengaging behavior between the track and the subgrade, and the differential governing equation is solved by finite difference method. A three-dimensional beam-body space FE model is also established to cross-check the applicability of the FEM analytical model and determine its scope of application. The results show that when the settlement deformation of the subgrade is relatively gentle, the calculation results of the analytical model and the FE model are almost indistinguishable, the deviation of the two models is getting larger as settlement of the subgrade exacerbated; For a given subgrade settlement wavelength of 20 m, when the settlement amplitude reaches greater than 21 mm, the analytical model is not applicable; Under the given condition that settlement amplitude of the subgrade is 20 mm, the analytical model is applicable to the subgrade settlement condition with a settlement wavelength greater than 19.8 m.

Abstract:Underground power pipelines are generally buried in the soil in the form of box culverts. When such existing pipelines are involved in underground construction, the in-situ support protection method is generally used to ensure the stability of the box culvert during the construction process. The determination of the distance between the support points mainly depends on the engineering experience. In this paper, considering the cross-sectional properties of the box culvert and the settlement effect in the soil, the mechanical models of the middle-span and the side-span of the box culvert are respectively established, the vertical displacement of the box culvert is calculated, and the allowable support points are deduced. Based on the maximum spacing value, a calculation method for the spacing between the support points of buried box culverts under in-situ support protection is proposed, and the accuracy and engineering suitability of the calculation method are verified by a case of the in-situ protection project of large-diameter pipe culverts at Yunnan Road Station of Nanjing Metro Line No. 5. The full-span longitudinal deformation pattern and parameter sensitivity of the buried box culvert are further analyzed through numerical simulation. The research shows that: the spacing between the supporting points of the box culvert side span is 8 m, the spacing of the middle span is 8.73 m, and at least 12 supporting points need to be set for the whole span. Within the range of three times of parameter magnification, with increase of reinforcement depth, width and soil compressive modulus, the displacement of the box culvert gradually decreases.

Abstract:In order to reduce the dynamic disturbance of adjacent structures caused by blasting construction of foundation pit by using blasting, field test to study the vibration reduction law of the blasting barrier holes was conducted relying on the blasting construction project of foundation pit of No. 1 comprehensive well of Shenzhen Metro Line 16. Based on monitoring of the ground vibration under different blasting barrier hole parameters, influence of blasting barrier hole on peak velocity and dominant frequency of particle vibration on the ground and the influence of parameters of blasting barrier hole on its vibration barrier effect were analyzed. It is found that when the diameter of the blasting barrier hole increases, the vibration isolation rate of vibration barrier hole (VIR) in horizontal radial and horizontal tangential directions increase first and then decrease, the VIR in vertical direction increases and the VIR based on resultant velocity increases. Furthermore the VIR decreases first and then tends to be stable with increase of the row spacing of the damping vibration barrier holes. In addition, when the proportion of water filling in the blasting barrier hole increases, the VIR in horizontal radial direction decreases, the VIR in horizontal tangential and vertical directions increase first and then decrease, and the VIR based on resultant velocity increases first and then decreases.

Abstract:In urban construction, the safety and economic efficiency of pit excavation projects are crucial. Traditional pit support structure design methods typically rely on conservative strategies and focus primarily on strength control, which leads to inefficiencies in precise deformation control and fails to meet the complex demands of modern urban construction. To address these issues, this paper introduces a new reverse-design multi-objective optimization model that integrates deformation control with economic efficiency, aimed at enhancing the effectiveness and cost-effectiveness of pit support structure designs. The model includes a bilaterally coupled deformation calculation model for pit supports, a multi-objective framework that integrates deformation control and cost optimization, and a solution strategy based on metaheuristic algorithms. Comparative analysis with four types of metaheuristic algorithms, along with in-depth case studies of actual engineering projects, demonstrates that this method not only effectively achieves precise deformation control but also optimizes cost efficiency. Notably, the semi-empirical and semi-random heuristic algorithms demonstrate superior efficiency and versatility in addressing complex optimization challenges.

Abstract:Reasonably designing the active failure limit support force of the tunnel face is the key to maintaining the stability of the shield tunnel. At present, most of the limit support force calculation methods are not suitable for the complex shield tunnel engineering design. Based on the traditional wedge-shaped calculation model and considering the lateral pressure coefficient under the influence of soil arch effect, a calculation model for the active failure limit support force of the tunnel face in layered soil was established by introducing the excavation inclination angle and seepage effect. Combined with a practical engineering case, the soil and design parameters that affect the limit support force were analyzed. The results show that the limit support force of the tunnel face increases significantly with the increase of construction depth, groundwater level height, soil weight and excavation inclination angle, while decreases nonlinearly with the increase of internal friction angle and cohesion; When considering the lateral pressure coefficient under the influence of soil arching effect, the calculated value of the limit support force is reduced; The limit support force significantly increases after considering the effect of seepage; The parameter changes of different soil layers have a significant impact on the limit support force.

Abstract:In order to improve the carrying capacity of the pultruded glass fiber reinforced plastics (GFRP) tube, five specimens were produced with carbon fiber reinforced plastics (CFRP) cloth with different restraint methods and axial compression tests were conducted. The damage mode of this restrained combined column was obtained. Through the analysis of the CFRP restraint effect and the load-bearing performance of this column, the load-bearing capacity calculation model was established. The results show that the squeezed GFRP and the concrete are crushed when the test piece is damaged, some specimens were accompanied by a band tear of CFRP. Disruption morphology increases with the effect of lateral constraint, development from typical cracking fracture to brittle crushing destruction and shear destruction. The bearing capacity of test parts gradually increases with the decrease of CFRP distance, test piece bearing capacity can be greatly improved at a CFRP distance of <100 mm, Maximum increase of 1.5 times, when the CFRP spacing is ≥100 mm, the improvement of the carrying capacity is not obvious. The change of CFRP spacing and layout mode improved the deformation performance of the test parts significantly, the ductility of the components can be significantly improved. Based on the theory of restrained concrete, the calculation model of specimen bearing capacity established by considering different CFRP spacing and the effect of GFRP bearing action has a high accuracy of calculation results.

Abstract:The structural high-strength (HS) rivet demonstrated advantages including preload stability and excellent resistance to loosening, fatigue and delayed fracture. Thus, the HS rivet has become a promising alternative to the HS bolt currently used in the ring-flange connection of wind turbine towers. However, relevant studies are still lacked and required on the fatigue performance of HS rivets in ring-flange connections. In the work, comparative model fatigue tests and refined numerical analysis were conducted on the ring-flange connection with HS rivets, in order to investigate its fatigue feature and deterioration mechanism. Firstly, based on the load transfer feature of ring flange connections, model fatigue tests of twelve specimens were conducted after the static tensile test. The tested twelve specimens included six with HS rivets and six with HS bolts. Further, multi-scale finite element analysis was performed with refined models, in accordance with the local strain-based SWT fatigue evaluation approach. According to the result, the first engaged thread of rivets/bolts is prone to fatigue failure in both the two types of specimens. Under the 2 million loading cycles, the equivalent fatigue strength of HS rivet specimens shows a mean value of 68.9 MPa, which increases by 32.2% compared with the value (52.1 MPa) of HS bolt specimens. The stress concentration at the root of the threads could be effectively mitigated due to the flattened thread and the increased contact area of inner-outer threads between the sleeve ring and HS rivet. Consequently, the fatigue performance of HS rivets is enhanced. As above, this study suggested that in the fatigue check of ring-flange connections with structural HS rivets, the fatigue strength of HS rivets could be determined as FAT 56, in accordance with the power constant of m = 3.

Abstract:Snow and ice on roads, bridges and reservoir dam panels in cold regions seriously affect the performance of the project, and have a significant impact on the safe operation and maintenance of the project. The extensive use of de-icing materials, e.g., de-icing salt and snow melting agents, lead to serious environmental pollution. Conductive concrete, as an environmentally friendly and efficient snow/ice melting technology, plays an important role in ensuring the safe operation and maintenance of engineering, extending the service life of the project, and improving the service quality of engineering. At the same time, the use of conductive concrete as building materials in cold areas has indoor heating function, which can alleviate the energy shortage to some extent. This paper reviews the preparation process of commonly-used conductive concrete, analyses the mechanical-electrical-thermal properties of some kinds of conductive concrete, e.g., carbonaceous conductive concrete, metallic conductive concrete and complex-phase conductive concrete, and then researches the influence of conductive materials on the mechanical performance of conductive concrete (e.g., conductivity, frost resistance, and durability). Based on the above analysis, the research concepts of conductive concrete in cold regions are proposed considering the goals of high performance and low cost: 1) Recycling materials, such as recycled carbon fiber, should be widely used to develop multiphase conductive concrete; 2) Magnetic separation fly ash, slag, and silica fume are extensively used as admixtures in conductive concrete; 3) Investigating the heating and conductivity performances of conductive concrete under the low charging voltage; 4) Utilizing comprehensive clean energy (e.g., solar energy, wind energy, etc.) to generate electricity for conductive concrete; 5) Exploring the conductive concrete-geotechnical-environment feedback mechanism under complicated engineering environment.

Abstract:To investigate the relationship between concrete and its constituent materials in the acoustic emission characteristics of the damage, uniaxial compression tests of concrete, cement mortar and limestone were carried out, and the acoustic emission signals during the failure process of the three were collected simultaneously. The mechanical properties, acoustic emission energy spectrum, amplitude, frequency, peak frequency and acoustic emission b-value of the three materials were statistically analyzed. The results show that the peak frequency and amplitude of the acoustic emission signals from all three specimens increase at the time of imminent damage. The frequency distribution of all three shows a normal distribution, with the largest proportion in the 90-120 kHz range. The dynamic b-value trends for cement mortar and concrete do not fluctuate much and remain in a relatively high value range, the dynamic b-value of limestone shows a trend of increasing first and then decreasing, and decreases rapidly near the peak stress, indicating the coming of main fracture. The overall b-value and peak frequency distribution of concrete are between limestone and cement mortar, the overall b-value of cement mortar mixed with limestone is close to that of concrete, this reflects the superposition effect of acoustic emission characteristics of the failure of concrete and its constituent materials.

Abstract:Preparing phosphogypsum for building materials is an effective way to consume phosphogypsum on a large scale. However, direct incorporation of phosphogypsum in powder form poses a risk of non-point source contamination. Therefore, the paper proposed to prepare pressed particles with phosphogypsum as the main raw material. Meanwhile, cement was used as the cementitious material, and the filling samples were prepared by adding these particles, then the tests such as compressive strength, determination of phosphorus (fluorine) pollutants, pore structure analysis, and microscopic morphological analysis were carried out to verify the filling effect of these particles. The results show that the strength performance of particles-filled samples is better than that of powders-filled samples, and their phosphorus (fluorine) fixation effect is also superior, after soaking for 90 days, the fluoride concentration in the leaching solution of particles-filled samples is 0.035 mg/L, and the phosphorus concentration is 0.35 mg/L, both of which meet the first-level emission standards, and the excellent performance of particles-filled samples is explained by pore structure analysis and microscopic morphological analysis. This research has successfully verified that phosphogypsum has a good filling effect when filled with building materials in the form of particles.

Abstract:In order to study the effect of electric curing on the early strength development of mortar mixed with calcium formate early strength agent under a negative temperature environment, calcium formate early strength agent with 2% mass of cementitious material was mixed into the mortar, and electric curing was carried out by passing alternating current in a -10°C environment. During the test, the real-time changes of the internal temperature of the mortar under different energization parameters were monitored by a thermometer, and finally, the strength of the mortar energized for one day and the strength of the subsequent standard curing for 3 days and 7 days under different energization parameters were tested. The test results show that the addition of calcium formate to the mortar can effectively reduce the resistance and thus improve the energizing efficiency, and the initial resistance of the mortar specimens with calcium formate is 1/4 that of the mortar without calcium formate, so that it can achieve a good heating effect at a lower applied voltage. Calcium formate also has an obvious early strength effect after 1 day of electrical curing, which can promote the early strength development of the mortar. The strengths at 3 days and 7 days of the calcium formate-doped mortar increased by 59% and 29%, respectively, compared with the un-doped calcium formate mortar under the same energizing parameters.

Abstract:City trees are an important part of urban landscaping and greening. In recent years, climate change has caused the migration of city trees, which affects the sustainable development of urban living environment. Therefore, it is urgent to understand the suitable distribution areas and habitats of city trees under climate change. Based on the distribution status of 50 species of city trees in 147 cities in China, we used the MaxEnt model to study the changes of suitable distribution zones of city trees under the climate of 2070s, and analyzed the future suitability of city trees through the overlap of distribution zones and urban administrative areas, so as to provide a basis for urban landscape planning in China. The results showed that: There are 50 common city trees in China, belonging to 24 families and 42 genera, among which Styphnolobium japonicum, Cinnamomum camphora and Ginkgo biloba are the most widely used, 65.6% of cities use native species, and 89.5% of cities use broadleaf trees; under climate change, the direction of movement of suitable areas for city trees is complex, and the area tends to contract (68%), with Rhizophora apiculata and Ulmus laevis showing the greatest changes; the future suitability of city trees is related to the source and urban location, and the suitability of native plants is higher to exotic species; the proportion of high suitability municipal trees is higher in northern cities, while low suitability city trees dominate in the south. In the future, comprehensive considerations should be made to guide the high-quality development of urban landscaping according to local conditions.

Abstract:Chemical oxidation technology based on strong oxidants is an effective means to achieve the removal of recalcitrant organic pollutants. Compared with gaseous oxidants such as ozone and liquid oxidants such as hydrogen peroxide, solid oxidants such as permanganate have the advantages of long life, ease of use and low risk of leakage, and have great advantages in removing refractory organic pollutants in water. In recent years, in order to further improve the efficiency of solid oxidants in removing refractory pollutants, it has been widely recognized that the method of adding reducing mediators enhanced the removal of organic pollutants by oxidants, especially in the degradation of emerging pollutants. This paper summarizes the combination systems of several reducing mediators with solid oxidants permanganate, ferrate and periodate involved in the field of water treatment. Then, the application of reducing mediator-enhanced solid oxidant systems in practical water treatment engineering is summarized and discussed. Through the collection and summary works on this topic, it is expected to promote more comprehensive and in-depth basic research and contribute to more practical promotion and application of water treatment engineering.

Abstract:Iron/manganese sulfides exist widely in the anoxic underground environment. The element cycling process of Fe, Mn and S controls the material cycling and energy conversion process in the underground environment. Usually, iron sulfides can produce reactive oxygen species (ROS) with O₂ disturbance by providing electrons to reduce O₂. However, the specific mechanism of ROS production by the reaction between manganese sulfides and O₂ is still unclear. Herein, manganese sulfide (MnS), a prevalent natural form of manganese sulfide minerals, was studied to explore the species, kinetics and reaction mechanisms of ROS generated by the activation of O₂ by MnS. The results showed that MnS could activate O₂ to produce a large number of ROS, including ·OH, H₂O₂ and O₂^·-. The maximum cumulative ·OH reached 389.0 μmol/L using 1 g/L MnS with initial pH 3 at 200 r/min stirring speed, and the yield of ·OH was 4.4 and 149.6 times greater than that of FeS and FeS₂ oxygenation under the same molar concentration, respectively. The reduction of O₂ by MnS resulted in the generation of O₂^·- through the transfer of single electron, followed by the acquisition of an additional electron to form H₂O₂. The dissolved Mn²⁺ catalyzed O₂/H₂O₂ to produce ·OH with low efficiency, but the structural Mn(II) could efficiently catalyze H₂O₂ to produce abundant ·OH, indicating that heterogeneous catalysis of H₂O₂ played an important role in ·OH production. Additionally, the soluble S^2- might facilitate electrons transfer to high-valence Mn(Ⅲ)/Mn(Ⅳ) to promote the regeneration of structural Mn(Ⅱ), which further promoted the production efficiency of ·OH via strengthening the electron cycle of Mn(Ⅱ)/Mn(Ⅲ). Furthermore, the degradation efficiency of phenol (5 mg/L) by MnS/O₂ system was up to 97.4% within 3 h, indicating that the activation of O₂ by MnS showed great potential in the environmental remediation.

Abstract:The catalytic oxidation process combined with micro-nano bubbles is a new method to treat dye wastewater, which solves the problem of difficult biodegradable organic pollutants and reduces the chroma of dye wastewater, and has a good application prospect.Taking simulated cationic dye wastewater as the research object, with manganese nitrate/activated carbon (Mn/GAC) as the catalyst, the cationic dye wastewater was treated by ozone catalytic oxidation process combined with micro-nano bubbles aeration technology. Based on the determination of the initial concentration of cationic dye wastewater and ozone concentration, orthogonal tests of catalyst dosage, initial pH value of wastewater and initial wastewater temperature carried out, and their influence on the treatment effect of cationic gold X-GL dye wastewater was investigated. Experimental results show that catalytic oxidation of micro-nano bubbles can have a good effect on the chroma removal of cationic gold X-GL dye wastewater. When the amount of catalyst is 3.5 g/L, the initial pH is 9.4, and the initial temperature is 23.6 ℃, the verification experiment is carried out under this optimum combination condition, and the experimental results show that the best chroma removal rate is 95.6%. It shows that the treatment of dye wastewater by this process has achieved the expected effect and has a certain guiding significance.