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.

Effect of Biochar Dosage and Fineness on the Mechanical Properties and Durability of Concrete.

Biochar (BC), a byproduct of agricultural waste pyrolysis, shows potential as a sustainable substitute material for ordinary silicate cement (OPC) in concrete production, providing opportunities for environmental sustainability and resource conservation in the construction industry. However, the optimal biochar dosage and fineness for enhancing concrete performance are still unclear. This study investigated the impact of these two factors on the mechanical and durability properties of biochar concrete. Compressive and flexural strength, carbonation resistance, and chloride ion penetration resistance were evaluated by varying biochar dosages (0%, 1%, 3%, 5%, 10%) and fineness dimensions (44.70, 73.28, 750, 1020 µm), with the 0% dosage serving as the control group (CK). The results showed that the addition of 1-3 wt% of biochar could effectively reduce the rapid carbonation depth and chloride diffusion coefficient of concrete. The compressive and flexural strength of BC concrete initially increased and then decreased with the increase in biocarbon content, BC with a fineness of 73.28 µm having the most significant effect on the mechanical strength of concrete. At the dosage of 3 wt%, BC was found to promote the hydration degree of cement, improving the formation of cement hydration products. These findings provide valuable insights for the development of sustainable and high-performance cement-based materials with the appropriate use of biochar as an additive.

Substrate modified with biochar improves the hydrothermal properties of green roofs.

Green roof, as an important measure of sponge city construction, is considered as a win-win alternative for alleviating rainwater runoff and urban heat island. The ecological benefits of green roofs are highly dependent on the quality of substrates. Biochar (BC) prepared from agricultural waste biomass has the potential to be used as a substrate amendment for green roofs. However, the influences of BC properties on hydrothermal properties of green roofs remain unclear. We evaluated the effects of natural soils incorporated with two kinds of BCs (particle size and dosage) on runoff retention capacity and roof thermal performance. Results indicated that the runoff reduction benefit of green roofs declines with the increase of rainfall. When the rainfall is less than 10 mm, the green roofs with different substrates hardly generate runoff, otherwise runoff reduction rates of all green roofs reduce below 75%. BC particles have abundant micro-pores and higher specific surface area, significantly improving the water holding-capacity of roof substrate and playing a critical role in the runoff regulation and cooling effect of green roofs. Application of 20% finer BC particles is the optimal for stormwater retention in all BC addition substrates. Moreover, it could reduce the roof upper surface temperature by 3-5 °C and reduced the daily heat gain of the green roof by at least 0.06 MJ/m2 compared with BC-free ones. Overall, adding BC into the substrates of green roofs can achieve better hydrothermal properties, which is beneficial to the design optimization of green roofs.

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.

Performance synergism of pervious pavement on stormwater management and urban heat island mitigation: A review of its benefits, key parameters, and co-benefits approach.

Pervious pavement system (PPS) is a suitable alternative technique for mitigating urban flooding and urban heat island (UHI) simultaneously. However, existing literature has revealed that PPSs cannot achieve the expected permeability and evaporation. To overcome this gap, this study presents an elaborate review of problems associated with PPSs and highlights its benefits to stormwater management and UHI mitigation. We determined key parameters of PPSs that could influence urban flooding and UHI mitigation, including hydrological properties, thermal physical properties, structure design, and clogging resistance. We identified the co-benefits approach of PPS towards performance synergism on stormwater management and UHI mitigation from quality controlled design and fabrication, periodic maintenance, and effective evaluation system based on practice environments. The results indicate that existing studies of PPSs primarily focus on permeability, while little emphasis is given to the evaporative cooling performance, leading to a biased development with a loss of test standards and regulations that cannot control the cooling potential of the system. The performance synergism of permeability and evaporative cooling in PPS should be studied further, while considering quality control of the materials and in-situ practice design. Parameter controls (with commonly used standards) during fabrication, periodic maintenance (during operation), and pre- and post-evaluation processes of PPSs should work collectively to achieve optimal benefits and reduced costs.

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.