Development of wet-cast green concrete prepared from waste materials through multiple carbon sequestrations

Waste concrete powder (WCP) belongs to construction waste that is mainly disposed of at landfills. In Hong Kong, municipal solid waste (MSW) accounts for most waste sent to landfill. Additionally, the management of municipal solid waste incineration bottom ash (MSWIBA) remains poorly defined. Given that Hong Kong is a resource-scarce city with limited land availability, landfilling should be the last resort for waste management.There is thus an urgent need to find sustainable alternatives to landfilling for managing WCP and MSWIBA to mitigate environmental impacts and conserve land resources. Therefore, the proposed project will provide an alternative solution to recycle waste and reduce landfills while reducing CO2 emissions. The project will develop three innovations. The first innovation will be a modified and simplified ambient-pressuremineral carbonation system. This system will convert WCP into supplementary cementitious material (SCM) that can be used to replace cement and turn MSWIBA into valuable aggregates that can be applied to substitute natural aggregates in concrete production. The second innovation will develop an innovative ambient-pressure flue-gas carbonation system to cure already-formed concrete products at early ages directly usingflue gas from industrial plants. The third innovation will combine these two carbonation systems to recycle waste, integrate waste into concrete production, and use CO2 to enhance the properties of the final products. This combination of systems is rare in this research field. The heat treatment of WCP can generate components with hydraulic properties, and mineral carbonation is expected to produce a large quantity of nanoscale calcium carbonates that will provide a seedbed effect for the development of hydration products. Besides, mineral carbonation can improve the properties of MSWIBA-converted aggregates. Most importantly, early-age ambient-pure flue gas carbonation curing is expected to enhance the interfacial transition zone (ITZ) between carbonated aggregates and paste in concrete, densify the concrete surface, and improvethe wet-cast concrete performance. Furthermore, a life cycle assessment (LCA) will be conducted to calculate the global warming potential (GWP) value of the carbonationcured wet-cast green concrete and some environmental assessment tests (e.g., a heavymetal leaching test) will be conducted to confirm its environmental effect before use. Finally, the project will incentivize industrial partners and investors to put the developed techniques into practical applications. In summary, the proposed project will turn waste into a value-added construction material, decrease landfill uses, conserve natural resources, and contribute to emission reductions, a circular economy, and the sustainable development of Hong Kong.