Geopolymer

Abstract: A brief history and review of geopolymer technology is presented with the aim of introducing the technology and the vast categories of materials that may be synthesized by alkali-activation of aluminosilicates. The fundamental chemical and structural characteristics of geopolymers derived from metakaolin, fly ash and slag are explored in terms of the effects of raw material selection on the properties of geopolymer composites. It is shown that the raw materials and processing conditions are critical in determining the setting behavior, workability and chemical and physical properties of geopolymeric products. The structural and chemical characteristics that are common to all geopolymeric materials are presented, as well as those that are determined by the specific interactions occurring in different systems, providing the ability for tailored design of geopolymers to specific applications in terms of both technical and commercial requirements.

Abstract: Spectacular technological progress has been made in the last few years through thedevelopment of new materials such as «geopolymers», and new techniques, such as «sol-gel». New state-of-the-art materials designed with the help of geopolymerization reactions are opening up new applications and procedures and transforming ideas that have been taken for granted in inorganic chemistry. High temperature techniques arc no longer necessary to obtain materials which are ceramic-like in their structures and properties

Abstract: Geopolymers are similar to zeolites in chemical composition, but they reveal an amorphous microstructure. They form by the co-polymerisation of individual alumino and silicate species, which originate from the dissolution of silicon and aluminium containing source materials at a high pH in the presence of soluble alkali metal silicates. It has been shown before that geopolymerisation can transform a wide range of waste alumino-silicate materials into building and mining materials with excellent chemical and physical properties, such as fire and acid resistance. The geopolymerisation of 15 natural Al–Si minerals has been investigated in this paper with the aim to determine the effect of mineral properties on the compressive strength of the synthesised geopolymer. All these Al–Si minerals are to some degree soluble in concentrated alkaline solution, with in general a higher extent of dissolution in NaOH than in KOH medium. Statistical analysis revealed that framework silicates show a higher extent of dissolution in alkaline solution than the chain, sheet and ring structures. In general, minerals with a higher extent of dissolution demonstrate better compressive strength after geopolymerisation. The use of KOH instead of NaOH favours the geopolymerisation in the case of all 15 minerals. Stilbite, when conditioned in KOH solution, gives the geopolymer with the highest compressive strength (i.e., 18 MPa). It is proposed that the mechanism of mineral dissolution as well as the mechanism of geopolymerisation can be explained by ion-pair theory. This study shows that a wide range of natural Al–Si minerals could serve as potential source materials for the synthesis of geopolymers.

Abstract: The potential position of and drivers for inorganic polymers (“geopolymers”) as an element of the push for a sustainable concrete industry are discussed. These materials are alkali-activated aluminosilicates, with a much smaller CO 2 footprint than traditional Portland cements, and display very good strength and chemical resistance properties as well as a variety of other potentially valuable characteristics. It is widely known that the widespread uptake of geopolymer technology is hindered by a number of factors, in particular issues to do with a lack of long-term (20+ years) durability data in this relatively young research field. There are also difficulties in compliance with some regulatory standards in Europe and North America, specifically those defining minimum clinker content levels or chemical compositions in cements. Work on resolving these issues is ongoing, with accelerated durability testing showing highly promising results with regard to salt scaling and freeze–thaw cycling. Geopolymer concrete compliance with performance-based standards is comparable to that of most other high-strength concretes. Issues to do with the distinction between geopolymers synthesised for cement replacement applications and those tailored for niche ceramic applications are also discussed. Particular attention is paid to the role of free alkali and silicate in poorly-formulated systems and its deleterious effects on concrete performance, which necessitates a more complete understanding of the chemistry of geopolymerisation for the technology to be successfully applied. The relationship between CO 2 footprint and composition in comparison with Portland-based cements is quantified.