Effects of mix design and functional unit on life cycle assessment of recycled aggregate concrete : evidence from CO2 concrete

Relevant studies focusing on the environmental benefits obtained from recycled aggregate concrete compared to virgin aggregate concrete have emerged, but research on the effects of various parameters from the mix design on results is limited. To acquire the potential of recycled aggregate concrete in terms of sustainability, this study evaluates the environmental impact of 57 concrete products by a life cycle assessment approach and conducts a comparative analysis of virgin aggregate concrete, recycled aggregate concrete, and CO2 Concrete under the same mix design. Since the global warming potential of unit volume concrete is between 278.35 and 524.44 kg CO2 eq and the values of other indicators vary greatly, the environmental performance of concrete mix design is disparate. Findings from the study reveal that cement has the biggest environmental impact, while aggregate content and type, chemical additives, and carbon-conditioning treatment of recycled aggregate have only a slight influence on the results. On the other hand, carbon-conditioning treatment benefited to both technical properties and carbon saving of concrete, promoting CO2 Concrete to be best in global warming potential. It was also found that the environmental advantages of recycled aggregate concrete and CO2 Concrete are more pronounced when supplementary cementitious materials are incorporated. A strength-based functional unit was also applied to demonstrate the different interpretations under two functional units. This revealed that the selection of functional units may direct decision making and emphasized the significance of more dimensions being included, such as durability as a functional unit, to reflect the unbiased sustainability performance of the product.