A comparative study of the mechanical and life cycle assessment of high-content fly ash and recycled aggregates concrete

In this paper, an extensive experimental work is made to understand the mechanical behaviors, environmental impacts (EI) and resources use of concrete mixtures containing high amounts of fly ash (FA) and/or recycled aggregates (RA). Then, the results of this study are compared with previous studies, and also non-expected results and missing information from those studies are highlighted. For that purpose, the Life Cycle Assessment (LCA) methodology was used to determine the most influential factors, resources use (e.g. non-renewable energy consumption - PE-NRe) and EI (e.g. potential global warming - GWP) for probable scenarios in the center of Portugal, according to EN 15804 and ISO 14040. In addition, the mechanical behavior (compressive and tensile strength, and modulus of elasticity) are also considered. The results show that the use of RA negatively affects all the mechanical parameters of concrete when the binder content is kept constant. The use of FA also affects the mechanical performance of concrete except for the modulus of elasticity. In addition, according to the results of this study, the GWP and PE-NRe of concrete mixtures seem not to be considerably affected by the incorporation of RA. However, in previous studies, the GWP and PE-NRe of RA concrete strongly depends on the transportation scenario. The LCA of concrete significantly decreases with the use of FA, regardless of the transportation scenario. According to the relationship made based on the results of this study (same LCA scenario) and previous studies (different LCA scenarios), there are no clear relationships between the mechanical behaviors, and GWP and PE-NRe of concrete mixtures with and without RA and FA because the incorporation of each of the nontraditional materials differently affects each characteristic of concrete and LCA results may be different for other approaches or assumed scenarios in life cycle inventory modelling. Thus, an optimization method is needed to find the optimum concrete in terms of mechanical performance, EI and resources use point of view.