Mix design and mechanical properties of geopolymer and alkali activated concrete: Review of the state-of-the-art and the development of a new unified approach

This study presents a comprehensive overview of the design and properties of concrete with alkali-activated binder (AAC). 184 published studies reported on concrete with AAC binder were reviewed critically. A database is constructed containing 1756 individual AAC mixes from 111 studies from the literature, which covers a wide range of AAC mixing parameters and engineering properties. The effects of a set of critical factors (and ratios), including those less understood such as utilizing alkaline activator other than sodium silicate (SS) and sodium hydroxide (SH), adding setting retarder and water reducer, and curing regime, are addressed and the underlying mechanism discussed. The fundamental chemical and mineralogical compositions of source materials and alkaline activators are investigated and used as a solid basis to develop a unified approach for proportioning AAC mixes. Furthermore, by synthesizing the results of the database the relationship between the compressive strength and the mechanical and physical properties of AAC is established. Models provided in major design guidelines for predicting the mechanical properties of ordinary Portland cement concrete (OPCC) are assessed and then modified for their extended applications to AAC. Finally, based on this review, limitations of the existing studies are identified and recommendations laid down for potential future research on AAC.