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Abstract Integrated vertical flow constructed wetland (IVCW) is a new type of ecological wastewater treatment, and its internal hydrodynamic characteristics are crucial for the efficiency of pollutant removal. To enhance the hydrodynamic characteristics and pollutant removal efficiency of IVCWs, this study systematically investigated the influence mechanisms of substrate arrangement, layer thickness ratio, and hydraulic load on the internal flow field and hydrodynamic characteristics of the IVCW system using CFD technology. Based on these findings, an optimized IVCW system was proposed, and its pollutant removal performance was examined through field measurements. The results showed that the highest hydraulic efficiency within the system (λ = 0.835) was achieved when the substrate was arranged in descending order of resistance coefficient from top to bottom (medium, high, low), with a layer thickness ratio of 1:4:1 and a hydraulic load of 0.7 m/d. Compared to the control group, the optimized IVCW exhibited significantly higher average removal rates for COD (Chemical Oxygen Demand), TP (Total Phosphorus), and TN (Total Nitrogen).This study provides technical support for the improvement and application of the IVCW system and holds significant implications for ecological wastewater treatment.

Abstract In view of the urgent concerns pertaining to the proliferation of rural wastewater discharges and the imperative for decentralized treatment, this article examines the phenomenon of physical clogging in a small-scale horizontal submerged flow artificial wetland system. Through a combination of experimental analysis and CFD-EDM numerical simulations, the impact of clogging on the hydraulic efficiency of the system was subjected to rigorous examination. Based on these findings, an innovative design strategy was proposed, namely the addition of vertical baffles. The experimental results demonstrate that this strategy can markedly prolong the duration of complete clogging of the system by up to 15% and enhance the hydraulic efficiency by 21%. Based on this, a small-scale horizontal submerged artificial wetland wastewater treatment system was designed for rural areas and successfully implemented in Fanrong Village, Rui’an City. This resulted in an enhanced wastewater treatment effect and an improved rural landscape. The findings of this study contribute to the development of a more rational and effective sewage treatment solution for rural areas.

Drying shrinkage of alkali-activated slag (AAS) has gained significant attention since the volumetric instability of this material can generate premature cracking and degrade the long-term durability of concrete structures. The unique shrinkage behavior of AAS originates mainly from the particular characteristics of its main hydrated products. However, few studies have even at-tempted to investigate the shrinkage behavior of hydrated products in AAS materials. This paper presented a new method of investigating drying shrinkage behavior of AAS using focused ion beam (FIB) combined with environmental scanning electron microscopy (ESEM). This innovative experimental method allowed the in-situ measurement of phase-specific shrinkage. The results showed FIB/ESEM technique can be successfully implemented to cementitious material to prepare phase-specific samples. Furthermore, object-oriented finite element method (OOF2) has been utilized to compute the shrinkage behavior of AAS concrete using a proposed multi-scale scheme. The computations can be made at multi-scales which highlight the effect of hydration products on shrinkage behaviors. OOF2 calculation at the micro-length scale predicted an increase in the shrinkage due to the well-dispersed hydration products inside the matrix. At larger scale, the decrease in the overall shrinkage is related to the extremely low shrinkage value by aggregates. The findings reveal OOF2 offers the capability to accurately measure local stress and strain distribution within heterogeneous materials, a feature notably absent in conventional numerical homogenization approaches. The importance of this benefit is highlighted particularly in the context of free-restrained shrinkage prediction, as conventional homogenization methods fail to account for stress.

In order to improve the level of the urban living environment and improve the comfort level of the microclimate, this paper investigates and simulates numerically the influence on the wind environment of different tree species in various tree array layouts, aiming to enhance wind comfort in tree landscapes and reduce the risk of high wind speeds. Initially, the study analyzes the commonly used tree species in Hangzhou’s urban tree arrays (beech, soapberry, and camphor trees), summarizing three types of tree array layouts: retention, through, and enclosure. Subsequently, standard tree models are established to define their crown porosity, trunk elastic modulus, and other physical characteristics. Using fluid–structure interaction methods, the impact of different tree species on the wind environment within various tree array layouts is numerically simulated at a wind speed of 14 m/s. In conclusion, the retention layout is most effective in controlling wind speed. Camphor trees perform excellently in reducing wind speed within both retention and enclosure tree array layouts, with wind reduction efficiencies of 16.06% and 14.09%, respectively. Soapberry trees show optimal wind speed reduction in the through layout, achieving 12.31%.

Crack location and type identification of reinforced concrete columns in service is of great interest to researchers, since it influences the decision-making of maintenance and retrofit. Due to the existing of load and corrosion, the complex stress state leads to complicated crack development which has been a challenge for researchers to determine the crack type. Acoustic emission (AE) method gives a promising solution to non-destructively locate and identify the crack position and type. In this work, corroded reinforced concrete columns were subjected to compression test with different eccentric degree. AE signals during the loading process were recorded. The traditional RA-AF method and a newly proposed Gaussian mixture model (GMM) method were applied to process the data for crack type identification. It was found that due to the large data set, RA-AF cannot identify the crack type in between the shear crack and the tensile crack types. The probability density distribution of GMM result gives an attractive offer to determine the crack type. A simple 4-step method based on GMM plot is proposed to identify the crack type which can calculate the ratio of shear crack and tensile crack in collected signals.

In recent years, cities have experienced frequent climate changes and deteriorating wind environments. Urban vegetation has become an important measure to improve local microclimates with its flexible configuration. Leaves and branches also reorient with the direction of wind, affecting the airflow through the tree. However, trees are usually considered as stationary porous media areas and are not influenced by wind speed in existing numerical simulation studies. Therefore, by considering the response of a tree under natural wind, this study established a fitted relationship between porosity and wind speed by measuring the porosity of trees at different wind speeds in the field. A numerical model of the wind response of the tree was developed, and the tree drag coefficient was changed using the additional source term method to verify the feasibility of the model by measuring the wind environment behind the tree. To understand the effect of the wind-induced response on the surrounding flow field and its variation pattern, the surrounding flow fields of stationary tree (T-S) and wind-induced tree (T-D) at different wind speeds were compared and analyzed. The effect of porosity and height-to-width ratio under the wind-induced response of trees on the wind environment were quantified. It was found that at different wind speeds, as the wind speed increases, the tree porosity gradually increases and the drag coefficient decreases accordingly. The effective shading distance after wind response was 2.4H, which was 0.3H less compared to vertically fixed trees. The minimum wind speed increased linearly with plant porosity, and the minimum wind speed occurrence location and wind speed recovery distance were linearly and negatively correlated with tree height-to-width ratio. Therefore, the flow field around the tree was simulated to provide references for guiding tree planting and mitigating urban wind environments.

This study was conducted to examine the effect on airflow of the shape of an urban road green belt in an asymmetrical street canyon. In this paper, the airflow field at pedestrian height in an asymmetrical street with different building height ratios (ASF) on both sides of the street is modeled and simulated using computational fluid dynamics (CFD) software, ANSYS FLUENT, and the flow rate characteristic distribution index and the average airflow intensity index are used to evaluate and analyze the airflow at the pedestrian level. The study shows that: (1) in an empty street scheme with different building ratios, the static wind area is located on the roof of the downstream building; the closer to the ground in a street with an ASF = 1/3, the lower the airflow rate. However, the situation is the opposite of that in other streets (2/3, 3/1, and 3/2). (2) The position of the green belt makes the windward side flow rate in the step-up street higher than that of the leeward side, and the flow rate of the leeward side in the step-down street is higher than that of the windward side. (3) Compared with other green belt forms, the use of two plates and three belts in the incremental street can increase the circumferential sinking at the roofs of the windward side of the street, thereby improving the wind environment in the entire street. The use of one plate, two-belt and three-plate, four-belt scenarios in the step-down street allows the two ends of the corner vortex to carry more airflow into the interior of the street and reduces both the “wind shadow effect” area in the middle of the street and the “air outlet effect” at both ends.

The study on the influence of early age damage of concrete on its long-term strength development is of great importance. In this work, 102 concrete cubes with and without supplementary cementitious materials (SCMs) were prepared. The pre-loading with loading degrees of 20%, 50%, and 80% of the corresponding compressive strength at 3-, 7-, 14-, and 28 d age was applied to the concrete samples. Then, concrete samples were further cured to 270 d, and the compressive strength was tested by the uniaxial compression test. The acoustic emission signals during the compressive strength test were collected. It is found that the pozzolanic reaction healed the damage caused by the early age damage, and the compressive strength of concrete with the incorporation of SCMs at 270 d age after pre-loading was higher than that of ordinary concrete without SCMs. The peak frequency of the uniaxial compression acoustic emission of concrete can be divided into four frequency intervals to correspond to different damage mechanisms of concrete, namely: interval I (12 ± 5 kHz), interval II (38 ± 5 kHz), interval III (171 ± 5 kHz), interval IV (259 ± 5 kHz).