Life cycle assessment of eco-friendly concrete mixtures incorporating natural zeolite in sulfate-aggressive environment

The incorporation of natural pozzolans into the binder has been considered as an effective method for reducing the climate change impact of concrete mixtures. When quantifying the environmental impacts of concrete mixtures with and without natural pozzolans and with equivalent mechanical properties, their lifespan has been usually overlooked. The importance of lifespan in the life cycle assessment (LCA) is more pronounced when the concrete structure is exposed to an aggressive environment. In this study, the system boundaries of LCA were expanded to a cradle-to-grave scope and the lifespan of concrete mixtures was incorporated into the reference flow calculation. To have a representative experimental result for the lifespan calculation, 54 mixtures with three binder contents and three water-to-cementitious materials ratios with six replacement rates of natural zeolite (NZ) were cast. The hardened specimens were tested against sulfate attack, the prevalent deterioration mechanism in the Caspian Sea. The experimental program was followed by a gene expression programming (GEP) modeling to predict the strength reduction and service life of the mixtures. The contribution of the concrete mixtures with and without NZ to global warming potential (GWP) was evaluated using the characterization factors of the IPCC 2013 model for a 100-year time horizon. The results show that the mechanical and durability performances of NZ mixtures are better than those in the mixtures without NZ. The incorporation of 20% NZ considerably increased the durability properties of mixtures, for example, a 27% reduction in water permeability. Based on the test results, the service life of the modified concrete exposed to a sodium sulfate attack was precisely predicted via the GEP method. The LCA results indicate that replacing 20% of PC with NZ reduced GWP by up to 69.7%, suggesting NZ has the potential to make an eco-friendly concrete mixture. (C) 2020 Elsevier Ltd. All rights reserved.