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This study investigated the influence of the steel and melamine fibers hybridization on the flexural and compressive strength of a fly ash-based geopolymer. The applied reinforcement reduced the geopolymer brittleness. Currently, there are several types of polymer fibers available on the market. However, the authors did not come across information on the use of melamine fibers in geopolymer composites. Two systems of reinforcement for the composites were investigated in this work. Reinforcement with a single type of fiber and a hybrid system, i.e., two types of fibers. Both systems strengthened the base material. The research results showed the addition of melamine fibers as well as steel fibers increased the compressive and flexural strength in comparison to the plain matrix. In the case of a hybrid system, the achieved results showed a synergistic effect of the introduced fibers, which provided better strength results in relation to composites reinforced with a single type of fiber in the same amount by weight.

The article discusses the main features fly ashes (FAs) as a raw material for geopolymerisation taking into consideration mineralogical composition and morphology. It is continuation the previous research connected with chemical composition and physical properties. This article is focused on the examination of a FA from the CHP plant in Skawina (Poland) and assessment it as a main component for geopolymers production. The characteristic of the FA is presented, including the morphology and mineralogical structure. The morphology was examined using Scanning Electron Microscopy (SEM). The structure of the FA was monitored also by Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray diffraction (XRD).

The main objective of this article is to develop ceramic-based materials for additive layer manufacturing (3D printing technology) that are suitable for civil engineering applications. This article is focused on fly ash-based fiber-reinforced geopolymer composites. It is based on experimental research, especially research comparing mechanical properties, such as compressive and flexural strength for designed compositions. The comparison includes various composites (short fiber-reinforced geopolymers and plain samples), different times of curing (investigation after 7 and 28 days), and two technologies of manufacturing (casted and injected samples—simulations of the 3D printing process). The geopolymer matrix is based on class F fly ash. The reinforcements were green tow flax and carbon fibers. The achieved results show that the mechanical properties of the new composites made by injection methods (simulations of 3D technology) are comparable with those of the traditional casting process. This article also discusses the influence of fiber on the mechanical properties of the composites. It shows that the addition of short fibers could have a similar influence on both of the technologies.

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The properties of alkali-activated materials (AAMs) depend on both the type of raw material used and their production procedure. This article presents an inexpensive and easily accessible method, based on using thermistors with a negative temperature coefficient, to analyse phenomena during the geopolymerisation process of AAMs. The described method enables prediction of the final physical and mechanical properties of tested materials and allows unambiguous determination of the quality of raw metakaolin materials in terms of their suitability for geopolymerisation processes and AAM production. This statement was proved by comparing AAMs formed based on metakaolin from three different sources. This article also describes the results of the mineralogical analysis, density, particle size distribution and morphology of the three metakaolins. In addition, the compression strength and FT-Raman spectroscopy of the AAM produced are described. Even though all materials were referred to as metakaolin, the results of this study showed that calcined materials can significantly differentiate the geopolymerisation process and final physical and mechanical properties of AAM.

Over the last several years, there has been a large increase in interest in geopolymer materials, which are usually produced from waste materials, and their applications. The possibilities of application of geopolymers seem to be unlimited, and they are used in almost all fields of technology. Their use as insulation materials appears promising due to their complete nonflammability and excellent strength. However, one limitation is their complex manufacturing process and lack of stability of the obtained geopolymer foams as well as difficulties in achieving such good insulation properties possessed by polyurethane foams, polystyrene, and wool. Hundreds of studies have already been performed on insulating geopolymer foams and various types of foaming agents, and their authors reported that foamed insulating geopolymers had a density starting from 200 kg/m3 and thermal conductivity from 0.04 W/mK. However, the repeatability of the obtained results on an industrial scale is questionable. It is still a challenge to obtain a geopolymer material with comparable properties as conventional insulation materials and to overcome the barriers associated with the successful implementation of geopolymer material as insulation in buildings and other applications on a mass scale. This paper provides a comprehensive review of the methods used for the production of foamed geopolymers and the best parameters obtained, as well as a summary of the most important information reported in the scientific literature. It also presents the results of a critical analysis of the feasibility of implementing this technology for mass deployment. In addition, the problems and limitations that are most often encountered with the implementation of geopolymer technology are discussed.

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