Rapid urbanization drives massive construction, which, in return, leads to ever increasing urban metabolism challenges on the provision of raw materials, as well as the disposal of construction and demolition waste. Due to its large volume, the transporting and processing of these materials cause considerable greenhouse gas emissions and land use change. With this circumstance, shortening the supply chains of urban construction by efficient recycling of construction and demolition waste becomes a frontier field for the circular transition of cities. It is particularly important in current China, where the concrete recycling is still rare. This paper aims to map the opportunities and potentials of concrete recycling on the mitigation of greenhouse gas emissions and land use change, with an integrated material flow analysis and life cycle assessment for the case study city e Chongqing, China. For the baseline year 2015, four scenarios representing various recycling routes in Chongqing have been explored: (1) improving brick manufacturing; (2) recycling on-site for road base filling; (3) recycling aggregate for prefabricated concrete component and (4) recycling concrete aggregate for structure use. Results highlighted that different technological routes have different potentials to increase recycling rates but all generate co-benefits on greenhouse gases mitigation and land transformation reduction. Recycling of stony construction and demolition waste for high value concrete aggregate has the biggest potential to bring the co-benefits on greenhouse gases mitigation and land use reduction. Besides, on-site recycling for road-base aggregates also presents a high performance, especially on greenhouse gases mitigation in transport. Based on the sensitivity analysis, policy implications were discussed, highlighting the necessity of to develop the recycling routes that substitute primary gravel with aggregates recycled from the stony waste; unlocking the existing recycling capacity and restricting landfilling.
Conventional acoustofluidics are restricted to manipulation of droplets on a flat surface, and there is an increasing demand for acoustofluidic devices to be performed at inclined surfaces to facilitate multilayered microfluidic device design and enhance system compactness. This paper reports theoretical and experimental studies of acoustofluidic behaviors (including transportation/pumping and jetting) along inclined surfaces using AlN/Si Rayleigh surface acoustic waves (SAWs). It has been demonstrated that for droplets with volume smaller than 3 μL, they could be efficiently transported on arbitrary inclined surfaces. The gravity effect would play a more and more important role in uphill climbing with the increased inclination angle. When the inclination angle was increased up to 90º, a higher threshold power was needed to transport the droplet and the maximum droplet volume which can be pumped also reached its minimum value. Effects of surface inclination angle on droplet jetting angles could be neglected for their volumes less than 2 μL. Moreover, microfluidic and acoustic heating performances of AlN/Si SAWs were further studied and compared with those conventional ZnO/Si SAWs with the same electrode configurations.
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