Geopolymers - Precursors and properties

Growing awareness of the need to reduce the environmental impact and energy consumption of materials has contributed to the development of alternative materials that consume less energy and pollute less, such as cold consolidated materials. These include sol-gel materials, stabilized soils, hydraulic binders and geopolymers. In particular, aluminosilicate geopolymers, synthesized at low temperatures (< 100°C), are ideally suited to a sustainable development approach. The term "geopolymer" was introduced in 1972 by French chemist Joseph Davidovits to designate materials based on raw materials of geological origin, which are consolidated at low temperatures by polymerization-type reactions. These materials are synthesized from an aluminosilicate source and an alkaline or acid source. The alkaline route is the most widely used, and the most developed in terms of research and commercialization. It is a composition derived from mineral materials available in large quantities and easily recyclable. These materials are characterized by an amorphous three-dimensional structure and possess interesting mechanical and thermal properties. Their formulations can also be modified by adding reinforcements and fillers to give them new properties. These remarkable properties make them ideal for a wide range of applications. Indeed, geopolymers can be a less energy-intensive alternative to Portland cement for construction and building applications, as repair mortars or coatings for shipbuilding. They can also be used as fire-resistant materials and thermal insulators, or for encapsulating toxic or radioactive waste.

Since 2010, geopolymers have attracted growing interest from researchers and industry alike. Indeed, national and international scientific communities have been working extensively on this type of material. The main scientific players are China, India, Australia and the United States. In France, work on understanding raw materials for a given property has been carried out for some fifteen years by the Geopolymer Institute and various research centers, such as the Groupement d'Intérêt Scientifique Géopolymères, Géocomposites, Géomatériaux à base d'argile.

In this article, the reader will find information on the decisive role of raw materials in predicting the process and, subsequently, the desired property for geopolymeric materials in the basic route. In each section dealing with the characteristics of raw materials and the properties presented, the role and impact of a raw material will be explained. Given the diversity of raw materials that can be used, whether natural (clays), synthetic (metakaolin) or recyclable (silica fume), we need to determine the key parameters governing the reactivity of the raw materials used and understand their effect on the raw and consolidated...