Wind-driven device for cooling permafrost.

Preserving permafrost subgrade is a challenge due to global warming, but passive cooling techniques have limited success. Here, we present a novel wind-driven device that can cool permafrost subgrade by circulating coolant between the ambient air and the subgrade. It consists of a wind mill, a mechanical clutch with phase change material, and a fluid-circulation heat exchanger. The clutch engages and disengages through freezing and melting phase change material, while the device turns off when the outside air temperature exceeds a certain threshold, preventing heat from penetrating the subgrade. Two-year observations demonstrate that the device effectively cooled permafrost measuring 8.0 m in height and 1.5 m in radius by 0.6-1.0 °C, with an average power of 68.03 W. The device can be adapted for cooling embankments, airstrip bases, pipe foundations, and other structures. Further experimentation is required to evaluate its cooling capacity and long-term durability under various conditions.

Enhancing road performance of lead-contaminated soil through biochar-cement solidification: An experimental study.

The effectiveness of cement-based solidification for remediating heavy metal-contaminated soil diminishes at high levels of contamination. To overcome this limitation, the potential of a biochar-cement composite curing agent to enhance the properties of Pb 2+ contaminated soil was investigated in this study. The permeability, unconfined compressive strength (UCS), and leaching characteristics of the biochar-cement composite material were assessed under varying biochar contents. The results revealed that the addition of 1-5 wt% biochar in cement significantly improved the UCS of the solidified soil. However, excessive biochar contents had a detrimental effect on the strength of samples. Additionally, the incorporation of 3.0% biochar reduced the hydraulic conductivity and porosity to 7.75 × 10-9 cm/s and 43.12%, respectively. Moreover, the biochar-cement composite material exhibited remarkable efficiency in treating highly concentrated Pb2+ contaminated soil, with leaching concentration decreasing significantly with increasing biochar content, falling below the Chinese hazardous waste identification standard. Overall, the utilization of a biochar-cement composite curing agent in the solidification of heavy metal-contaminated soil could be considered a promising subgrade filler technique.

A review on the influencing factors of pavement surface temperature.

Pavement surface temperature is of great significance to pavement performance and pavement design, as well as the development of cool pavements. The variation of a pavement surface temperature is complicated as it is jointly affected by various factors, including air temperature, solar irradiance, wind speed, and pavement texture. This study overviews the internal and external factors that affect the pavement surface temperature in the field. It is found that air temperature is the main external climatic factor affecting the pavement surface temperature during the course of a day. Although solar radiation dictates the thermal partition at the pavement surface, it mainly influences daytime pavement temperature but vanishes at night. Pavements in calm weather can be 3-10 °C hotter than those in windy weather, depending on the time of the day and the season. Other external factors such as passing vehicles also influence the pavement surface temperature at a degree 1-3 °C. Also, the shading effect of urban trees can affect pavement surface temperature and urban microclimate. Internal factors that vary pavement surface temperature include albedo, thermal conductivity, heat capacity, and emissivity. Among them, albedo controls the pavement surface temperature while other factors play a secondary role. The results of this review provide a scope of research for developing sustainable and advanced solutions for future municipal pavement construction and urban heat island (UHI) mitigation.

Experimental study on the thermal characteristics of urban mockups with different paved streets.

Pavements in urban area absorb more sunlight due to the canyon-like geomorphology of the urban geometry and store more heat due to the great thermal bulk properties of concrete. Heat released from pavements warms up the urban air, contributing to the urban heat island. Recently, the uses of cool pavements to reduce the pavement temperature as an urban heat island mitigation have gained momentum. Understanding the temperature and solar insolation of a pavement in an urban area is important to adopt the right cool pavement option for the right place. This study measured the temperature of paved streets in an urban mockup for 4 days in summer. It is found that east-west (EW) streets are the hottest place in an urban area, followed by the intersection, and finally the south-north (SN) street and that increasing the pavement's albedo reduces the pavement temperature effectively. The dark gray pavement in an open space is hotter than that in an urban canyon. The heat storage in the building blocks keeps the pavement warmer more than 2 °C at nighttime. The EW street is exposed to solar insolation for long hours, so it is suitable for preferentially developing reflective cool pavements.

A case in subtropical climate city: Assessing the bioretention hydraulic performance on storm in response to poor permeability soil.

Bioretention has been widely used in China for the purpose of sponge city construction. In subtropical climate areas, the performance of bioretention cell under condition of low infiltration underlying soil and heavy storms is still poorly understood. This study aimed to assess the effects of low infiltration underlying soil and precipitation characteristics on the hydraulic performance of a bioretention cell using the Storm Water Management Model (SWMM). The hydraulic performance of a bioretention cell were investigated under a Typical year rainfall event (P(total) (total precipitation) = 1299.2 mm) and seven heavy storms (i.e., Ptotal range from 53.1 mm to 287.3 mm), at different SF(i) (seepage rates of the underlying soil) (i.e., range from 2.5 mm/h to 15 mm/h). Then, sensitivity of the optimal design to the different design parameters, including the hydraulic conductivity of soil medium layer and the berm height of surface layer, was examined. The results show that the increase in SF(i) was effective in increasing the ARVR(i) (annual runoff volume reduction) and RVR(i) (runoff volume reduction), while little effective in increasing PFR(i) (peak flow reduction). Moreover, the ARVR(i) could meet the designed goal of 70% when the SF(i) was more than 7.5 mm/h. For RVR(i), the key variable of precipitation characteristic changes from Ptotal to P4h(max) (maximum precipitation in 4 h) as SF(i) increases, while P4h(max) remains as the key variable for PFR(i) all the time. The sensitivity studies demonstrate that the hydraulic conductivity is more effective in increasing PFR(i) than the berm height. For the bioretention cell under condition of low infiltration underlying soil and heavy storms, in order to simultaneously achieve expected reduction goal of both peak flow and runoff volume, and make the best comprehensive performance of bioretention cell, it requires not only a maintenance action to increase the hydraulic conductivity of soil medium layer, but also a drain pipe to be added in the storage layer, and meanwhile other LID practices should be combined.