Life cycle analysis of recycled aggregate concrete with fly ash as partial cement replacement

Abstract

This paper presents a part of the results obtained within the frame of the SCOPES joint research project - a scientific collaboration between ETH Zurich and Faculty of Civil Engineering, University of Belgrade. One of the goals of the project was to produce recycled aggregate concrete with fly ash as partial cement replacement, which would have mechanical and durability-related properties adequate for structural concrete. At the same time the aim was to replace as much as possible natural resources with waste materials to achieve environmental and cost efficiency. Three mixtures of recycled aggregate concrete were designed with percentages of cement replacement with fly ash equal to 0%, 19% and 38%. Equal compressive strength was set as the design goal and environmental impact assessment was based on that fact. The results of these tests showed that it was possible to reach the same 28-day compressive strength for all three concretes with established mix design procedures. The environmental impacts of the tested concretes types were assessed using the standardized methodology of Life cycle assessment (LCA). The assessment was based mostly on local LCI data and on typical conditions in Serbia. Regarding the impact of fly ash, three different allocation procedures were tested: 'no-allocation', 'mass allocation' and 'economic allocation'. Comparative environmental assessment showed that environmental benefits from replacing a part of the cement with fly ash could be gained in the 'no-allocation' and the ' economic allocation' case. In the case of 'mass allocation', all calculated environmental impacts were higher for recycled aggregate concrete with fly ash.