The role of mathematical modelling and gel chemistry in advancing geopolymer technology

Inorganic alkali aluminosilicate polymers, commonly referred to as geopolymers, have been studied for several decades due to their excellent mechanical and thermal properties, as well as chemical and fire resistance. Such properties make geopolymers suitable for use in a wide range of areas, including construction, building products, and refractory applications. Geopolymers are synthesized via reaction of aluminosilicate materials, such as metakaolin, fly ash (a coal combustion waste) and/or blast furnace slag, with alkaline silicate solutions at ambient or slightly elevated temperatures. Despite the increasing body of research on these advanced materials, little is understood about the underlying gel chemistry, surface phenomena, reaction kinetics or microstructure. It is shown here how reaction kinetic modelling coupled with an analysis of the gel chemistry has led to advances that make the wider acceptance of this technology possible. The ability to model the kinetics of the system allows the design of mixtures for specific applications, and allows better quality control during production. A system of differential equations describing chemical reaction kinetics is formulated and solved, providing a simulated heat flow signal. Validation of the model is undertaken by comparison of this signal with experimental calorimetric data. The process of development of this model is ongoing, but has already provided valuable insights into the reaction processes which, when coupled with understanding obtained from Gel chemistry, provides a framework by which the behaviour of geopolymer-forming systems may be analysed. This is a critical step in the wider commercial acceptance of these materials, and in the development of specific geopolymer formulations tailored to particular applications.