Durability of Alkali- Activated Materials: Progress and Perspectives

In the last decade, there has been rapid growth in interest in alternative binders, as part of the toolkit of cement technologies needed to mitigate the carbon footprint associated with the construction industry. Alkali-activated materials (AAMs), including geopolymer binders and other related systems, have been identified as a key component of this move to lower CO2 cements and concretes. These are clinker-free cements which can exhibit comparable performance to conventional portland/blended cements, when they are adequately formulated and cured. However, AAMs have a somewhat limited record of durability in service, and this is one of the main limitations facing their commercial adoption at present. To provide the best possible answers to the question of long-term durability within an experimentally accessible timeframe, standardized accelerated degradation testing methods have been widely adopted, in an attempt to simulate natural processes. It has been identified that the interactions between material and environment, which take place on microstructural and nanostructural levels, have a very significant influence on the outcomes of the durability tests. Here, we present an overview of the results obtained when AAMs are exposed to aggressive testing conditions such as elevated concentrations of CO2, sulfates or chlorides. The key outcome of this article is a broader synthesis of the available data regarding the interactions between these new materials and their surrounding environment, which is then available to be used in the design, development, and implementation of environmentally sustainable, high-performance cements and concretes for the 21st century.