Value stream assessment of the sustainable concrete recycling process with sequestration of CO2 from flue gases

Abstract

The construction industry is a significant contributor to environmental issues, primarily due to the generation of substantial amounts of demolished concrete waste and CO2 emissions resulting from cement clinker production. Therefore, this study aims to assess the feasibility of recycling demolished concrete by-products (waste concrete powder and recycled concrete aggregates) into aggregates suitable for use in concrete mixes by utilizing active carbonation methods with flue gas use, an area that has been lacking in previous research. To conduct a detailed cost analysis, mathematical models based on Cost-Benefit Analysis with the Activity-Based Costing approach have been developed incorporating transportation, recycling, sequestration, and environmental costs based on the current and proposed state of Value Stream Mapping. To validate the feasibility and practicality of the developed models, a case study in Hong Kong has been conducted. The results of the study demonstrate an approximately 29 % greater economic efficiency of the proposed alternative concrete waste recycling method compared to the traditional approach. In the alternative method of concrete waste carbonization using flue gas, there is a significant reduction in the environmental cost of over 51 %, primarily attributed to the decreased reliance on commercially sourced CO2. Furthermore, the ability of waste concrete powder to sequester CO2 generates additional benefits, promoting sustainable recycling. These findings provide valuable insights into the potential for enhancing sustainability in construction material cycles.