Comparison and assessment of carbon dioxide emissions between alkali-activated materials and OPC cement concrete

Geopolymer concrete (GPC) has been developed as a sustainable alternative to traditional cement-based concrete using industrial waste materials. Thus, reducing greenhouse gas emissions in concrete production can be expected. This study employed the life cycle assessment (LCA) method to evaluate geopolymer concrete's cost and life-cycle carbon dioxide (CO₂) emissions. Moreover, the critical transportation radius of the geopolymer is estimated. Then, evaluation results were compared with ordinary Portland cement (OPC), considering three concrete construction methods: cast-in-place, ready-mixed, and precast. In particular, the service life of two types of concrete in sulfuric acid environments is considered. Compared with OPC concrete, the results show that geopolymer concretes can significantly reduce the cost and CO₂ emissions when one or a small amount of alkali activator is used or alkali-containing materials are used to replace some alkali activators. However, the advantages would be reversed by the rising alkali dosages, which account for cost increases and carbon emissions. When considering the service life in special environments, geopolymer concrete in sulfuric acid environments corresponds to fewer carbon emissions, 94%–97% decreased compared with OPC concrete. Finally, compared with OPC concrete, the newly developed limestone calcined clay cement (LC3) avoids high-temperature calcination and dramatically reduces carbon dioxide emissions. Compared to OPC concrete, LC3 concrete has a 19% reduction in CO₂ emissions. And geopolymer concrete that takes alkali-activate materials for superseding alkalis also produces less carbon dioxide emissions. In particular, CO₂ emissions from FA-SF geopolymer concrete are approximately 50% lower than OPC concrete. In addition, the use of alkali activators significantly weakens the cost advantage of geopolymers. But after accounting for waste disposal costs, the average net cost of fly ash-based geopolymer concrete can be more than 30% lower than that of OPC concrete. The average net cost of slag-based geopolymer concrete is 7%–45% lower than that of OPC concrete. The findings of this work provide the basis for further development of geopolymer concretes obeyed environmental protection.