Alternatives to Portland cement in relation to sustainability of concrete

Concrete production is arguably the most active building industry in the modern era. It has been repeatedly shown that this industry, if it continues at the same pace of today, is not sustainable. The current non-sustainability of concrete can be manifested in aspects that range from economic to aesthetic and social. But perhaps the most dramatic are the environmentally adverse effects that concrete production has been causing. In view of this realization, concrete materials scientists have been actively working on ways to reduce the adverse effects of the industry while maintaining its viability. That is,, to restore sustainability to concrete production. Among the most important innovative developments has been research to find credible replacement to Portland cement. This is quite justifiable bearing in mind that Portland cement is both the most expensive component in concrete and the main CO, emitter in this industry. The state of the art now offers alternatives that may well be viable, credible and sustainable. These include using products like metakaolin and natural pozzolana. They also include using industrial by-products such as fly ash, silica fume, blast furnace slag and rice husk ash. Moreover, another direction has been started in the re-exploration and developing of magnesia cement and geopolymers. In this paper, the authors discuss the aforementioned developments pointing to particular issues that concrete technologists need to be aware of when any alternative is considered.