Alternative cements: Recent developments and future directions

Concrete is the most utilized construction material and the second most consumed material on earth after water. As a consequence, its manufacture and use imparts global durability and environmental consequences. The manufacture of conventional ordinary Portland cement (OPC), the main constituent in concrete, for example, alone accounts for 5-8% of global CO₂ emissions worldwide. In addition, the main durability challenges of OPC are associated with the chemistry of its binder. In recent years, increased demand for sustainable building materials with lower CO₂ emissions and equivalent (or higher) service lifespans have prompted the development of alternative and novel cementitious materials to supplement and/or in some applications replace the use of OPC concrete in a variety of building and infrastructure engineering projects. Many of these alternative and novel cementitious material systems and approaches generally demonstrate lower CO₂ emissions during production (up to 50% CO₂ reductions) and increased durability when subjected to harsh conditions (e.g., lower shrinkage, higher acid resistance) when compared to OPC. This paper synthesizes and presents the general classification, characteristics, and current applications of four promising alternative cementitious material systems, namely (1) high-aluminate, (2) super-sulfated slag, (3) alkali-activated, and (4) carbonate-based cements (e.g., bio-cements). We will highlight the basics of alternative cement chemistries, their environmental impacts, and relevant material properties (i.e., fresh- A nd hardened-state properties) compared to OPC concrete. The discussions presented herein are supplemented with specific case-study examples of real-world applications and aim to serve as an inspiring platform for researchers, educators, and engineering professionals to conceptualize how next-generation cementitious materials can (and will) shape our built environment.