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Geopolymers are ceramic-like materials prepared at low temperatures by reacting natural aluminosilicates (clays) or aluminosilicate wastes (fly ash and blast furnace slag) with alkalis or acids. Like ceramics, they fracture in brittle mode, but graceful failure can be induced by fiber reinforcement. Since geopolymers are processed at low temperatures, organic reinforcing fibers can be used without thermal degradation. This chapter provides a brief description of the synthesis, structure, and properties of the aluminosilicate geopolymer matrix, and reviews the effect on the physical and mechanical properties of plant-based (cellulose) reinforcing fibers and protein-based fibers (wool). The possible degradation of the fibers by the highly alkaline geopolymer matrix is discussed, as well as the comparative benefits benefits associated with the mechanical properties of long and short fibers and woven cloth reinforcement. The literature reviewed here suggests that geopolymers produced at low temperatures (

Aluminosilicate inorganic polymers (geopolymers) can be cheaply and readily prepared from dehydroxylated kaolinite clay and have been successfully demonstrated as a new type of stationary phase in the chromatographic separation of a mixture of three model aromatic compounds (a trisubstituted benzene, an ester and a pyrrole). Grinding and sieving to 105 μm produced powders with a similar particle size distribution and morphology to standard chromatographic silica, although smaller particle sizes and other morphologies can readily be produced. Three compositions of geopolymers were studied here and their performance was compared with conventional chromatography column packing media typically used for simple open-column and flash separations (silica and aluminas). Although the geopolymers were prepared under highly alkaline conditions, washing with acid to bring them to neutral pH before use was found to be unnecessary. The results obtained with the as-prepared geopolymer of standard composition showed it to possess a significantly greater number of plates/meter than any of the other column materials, including acidic and neutral aluminas and silica, and although more of the ester adsorbed to this column than on silica, in all other important respects the behavior of the geopolymer was comparable to silica and alumina. All the geopolymers were shown to be chemically stable to strong solvents such as ethanol, by comparison with conventional media such as silica and alumina, which were decomposed by ethanol; this suggests that unlike conventional silica, the geopolymer media may be cleaned with a strong solvent between runs without being degraded, and re-used. These results indicate that geopolymers represent a promising substitute for the commonly-used silica or alumina chromatography stationary phases, being simpler and cheaper to produce, more stable to strong solvents and showing comparable or better separation characteristics.

This study reports the synthesis and mechanical properties of new inorganic polymer (geopolymer) composites unidirectionally reinforced with 4–10 vol.% natural cellulose-based fibres (NZ flax, phormium tenax). The geopolymer matrix was derived from dehydroxylated kaolinite-type clay. The mechanical properties of the fibre-reinforced composites improve with increasing fibre content, achieving ultimate flexural strengths of about 70 MPa at 10 vol.% fibre content. This represents a significant improvement on the flexural strength of the unreinforced geopolymer matrix (about 5.8 MPa), and all the composites show graceful failure, unlike the brittle failure of the matrix. Scanning electron microscopy was used to study the morphology of the fibre-matrix regions and a combination of thermogravimetric analysis (TGA) and thermal shrinkage measurements of these composites suggests that despite the formation of microcracks due to water loss from the geopolymer matrix, the fibres are thermally protected by the matrix up to 400 °C. The flax fibres do not appear to be compromised by the alkaline environment of the matrix, suggesting new possible applications for these low-cost simply prepared construction materials.

New fibre-reinforced composites of aluminosilicate inorganic polymer (geopolymer) with natural protein-based fibres (carpet and Merino wool) were developed, and their mechanical properties determined. The surfaces of some of the wool fibres used in this study were chemically modified to improve their alkali resistance and reinforcing properties. The flexural strengths and failure characteristics of the composites, determined on bar-shaped samples by a three-point test method, show an approximately 40 % improvement over the unreinforced matrix and graceful failure, unlike the unreinforced matrix that displays ceramic-like brittle fracture. Interaction between the sulphide linkages of the wool and the aluminosilicate matrix produces a blue-green colour in the wool, shown by UV–visible and IR spectroscopy to be related to the formation of the sulpho-aluminosilicate compound sodalite. The thermal behaviour of these composites was studied by thermogravimetric analysis, and scanning electron microscopy was used to study the fibre-matrix interface.