Sustainable design of pavement systems in highly urbanized context: A lifecycle assessment.

Substantial amount of resources is consumed by pavement systems, which have resulted considerable environmental impacts. Understanding the environmental impacts would provide opportunity for reducing resource consumption and informing decision-makers in the process of designing sustainable pavement. There is a lacking of comprehensive and comparative sustainability assessment of pavement systems in highly urbanized context currently. Therefore, this study aims to design and comprehensively evaluate the environmental performance of the commonly adopted pavement systems in highly urbanized context using lifecycle assessment (LCA) technique through a case in Hong Kong. According to the codes and practices of Hong Kong, two pavement systems including flexible and rigid pavements were designed based on the same road section. After that interviews with structured questionnaire were conducted to collect relevant practical information of pavement construction and maintenance from the relevant professional bodies and experts for the subsequent LCA of such designs. The LCA results reveal that the two mid-point impacts of global warming potential and mineral extraction are 21% and 54% higher for rigid pavement than for flexible pavement. Yet, the end-point results indicate that flexible pavement is associated with 64%, 65%, and 69% higher human health impact, ecosystem quality damage, and resource damage, respectively. Material production and transportation contribute significantly to the total impact in the two pavement systems. For instance, it is about 57% and 97% of the total global warming potential for flexible and rigid pavements, respectively. The overall results demonstrated that 49% higher total impact was found for flexible pavement than rigid pavement. Therefore, the use of more recycled and environmentally friendly materials can potentially enhance the environmental sustainability of both pavement systems. The findings should provide useful information to the design and selection of sustainable pavement structures in resource-scarce highly-urbanized cities.

High frequency dielectrophoretic response of microalgae over time.

The high frequency dielectrophoresis (>20 MHz) response of microalgae cells with different lipid content was monitored over time. Chlamydomonas reinhardtii was cultured in regular medium and under nitrogen-depleted conditions in order to produce populations of cells with low and high lipid content, respectively. The electrical conductivity of the culture media was also monitored over the same time. The upper crossover frequency decreased for high-lipid cells over time. The single-shell model predicts that the upper crossover frequency is dictated primarily by the dielectric properties of the cytoplasm. The high frequency DEP response of the high-lipid cells' cytoplasm was changed by lipid accumulation. DEP response of the low-lipid cells also varied with the conductivity of the culture media due to nutrient consumption. Relative lipid content was estimated with BODIPY 505/515 dye by calculating the area-weighted intensity average of fluorescent images. Finally, microalgae cells were successfully separated based on lipid content at 41 MHz and DEP media conductivity 106 ± 1 µS/cm.