Biases in life cycle assessment of circular concrete

Abstract

This investigation constitutes the fourth phase of a conceptual framework designed to produce circular concrete upon the main principals of circular economy reduce, reuse and recycle. Comparative life cycle assessment is carried out for conventional and circular concrete mixtures to identify biases in the results of common life cycle assessments. Ten midpoint and four endpoint indicators are assessed using the impact 2002+ method. In baseline scenarios, environmental performances of conventional and circular concrete mixtures are compared over identical service lifes, considering cradle-to-grave and cradle-to-cradle (closed-loop) system boundaries, respectively. Results reveal that by using optimal amounts of two industrial wastes i.e. Silica fume and ground granulated blast furnace slag, as binder materials, and recycled concrete aggregate, the environmental performance of concrete is significantly enhanced. Such condition is obtained by remarkable reduction of environmental indicators (up to 44%) at both midpoint and endpoint levels. Also, circular concrete embraces a considerable amount of Non-Renewable Energy saving (40%). Investigating the impact of different end-of-life scenarios indicates that limiting boundary conditions in the cradle-to-gate approach (lack of considering end-of-life stage) has offset the results. Furthermore, the comparison trends were completely reversed in some environmental indicators upon considering the impact of service life.