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Geopolymers are considered to alternatives to Portland cement, providing an opportunity to exploit aluminosilicate wastes or co-products with promising performances in the construction sector. This research is aimed at investigating the strength of fly-ash-geopolymers of different ages. The effect of granulated blast furnace slag (GGBFS) as a partial replacement of fly ash (FA) on the tensile (ft) and compressive strength (fc), as well as the modulus of elasticity, is investigated. The main advantage of the developed geopolymer mixes containing GGBFS is their ability to set and harden at room temperature with no need for heating to obtain binding properties, reducing the energy consumption of their production processes. This procedure presents a huge advantage over binders requiring heat curing, constituting a significant energy savings and reduction of CO2 emissions. It is found that the development of strength strongly depends on the ratio of fly-ash to granulated blast furnace slag. With the highest amount of GGBFS, the compressive strength of geopolymers made of fly-ash reached 63 MPa after 28 days of curing at ambient temperature. The evolution of compressive strength with time is correlated with the development of ultrasound pulse velocity methods, which are used to evaluate maturity. The modulus of elasticity changes with strength and the relationship obtained for the geopolymer is presented on the basis of typical models used for cement-based materials. The tensile to compressive strength ratios of the tested geopolymers are identified as higher than for cementitious binders, and the ft(fc) relationship is juxtaposed with dependencies known for cement binders, showing that the square root function gives the best fit to the results.

The main aim of this article, carried out in relation to ash–cement mortars, is to determine the effect of complex additives of polyfunctional modifiers, including, in addition to superplasticizers, air-entraining and water-retaining additives, at different values of water–cement ratios. With the use of experimental–statistical models, the complex effect on the adhesive strength of cement–ash mortars of water–cement and ash–cement ratios, as well as complex additives of polyfunctional modifiers, including air-entraining and water-retaining additives, is considered. The extreme nature of the water–cement and ash–cement ratios on the adhesive strength of ash–cement mortars are established. Their optimal values are in the ranges of 0.7–0.75 and 0.35–0.4, respectively. The addition of a naphthalene-formaldehyde superplasticizer makes it possible to increase the adhesive strength of mortars by up to 40%. A positive effect is achieved along with the addition of a superplasticizer by introducing optimal amounts of air-entraining and water-retaining additives into the mortar mixtures. Quantitative parameters of mortar compositions that positively affect adhesive strength are established. The influence on the adhesive strength of the fly ash was also investigated, as well as on the binder–sand ratio. In addition, a positive effect on the adhesive strength of modified cement–ash mortars was experimentally shown by increasing the specific surface area of fly ash by regrinding it and increasing the cement–sand ratio.

Due to the need to reduce the CO2 emissions of mineral binders, researchers are considering the use of alkali-activated materials (AAMs) as an alternative to cementitious binders. The properties of AAMs can be more advantageous than those presented by cementitious binders, and thus they can replace Portland cement binders in some applications. Mechanical tests of AAMs are being conducted on an ongoing basis; however, durability issues related to reinforcing steel in conditions in which steel members interact with chloride ions remain unsolved. In this paper, the precursors for AAM preparations are blends of fly ash (FA) and ground granulated blast-furnace slag (GGBFS) in four slag proportions: 0%, 10%, 30% and 50% expressed as a percent of FA mass. Four alkali-activated mortars were prepared, denominated as AAM 0, AAM 10, AAM 30 and AAM 50, respectively. Their basic physical and mechanical characteristics were investigated, as were their gas transport properties. The nitrogen Cembureau method was applied to determine the permeability of the mortar. The transport properties of the chloride ions were determined using the modified NT BUILD 492 migration test. The comparison of results obtained demonstrated a positive effect of GGBFS addition in terms of an increase in bulk density, permeability, porosity and, at the same time, a reduction in chloride ion penetration. The water absorption tests also provided insight into the open pore structures of mortars. The measurements revealed a strong dependence between fluid transport through the mortars and the water absorption and initial water content of materials.

The aim of this article was to analyze the fracture behavior of geopolymer composites based on fly ash or metakaolin with fine aggregate and river sand, with three types of reinforcement: glass, carbon, and aramid fiber, at three different temperatures, approximately: 3 °C, 20 °C, and 50 °C. The temperatures were selected as a future work temperature for composites designed for additive manufacturing technology. The main research method used was bending strength tests in accordance with European standard EN 12390-5. The results showed that the addition of fibers significantly improved the bending strength of all composites. The best results at room temperature were achieved for the metakaolin-based composites and sand reinforced with 2% wt. aramid fiber—17 MPa. The results at 50 °C showed a significant decrease in the bending strength for almost all compositions, which are unexpected results, taking into account the fact that geopolymers are described as materials dedicated to working at high temperatures. The test at low temperature (ca. 3 °C) showed an increase in the bending strength for almost all compositions. The grounds of this type of behavior have not been clearly stated; however, the likely causes of this are discussed.

The review describes fentanyl and its analogs as new synthetic opioids and the possibilities of their identification and determination using electrochemical methods (e.g., voltammetry, potentiometry, electrochemiluminescence) and electrochemical methods combined with various separation methods. The review also covers the analysis of new synthetic opioids, their parent compounds, and corresponding metabolites in body fluids, such as urine, blood, serum, and plasma, necessary for a fast and accurate diagnosis of intoxication. Identifying and quantifying these addictive and illicit substances and their metabolites is necessary for clinical, toxicological, and forensic purposes. As a reaction to the growing number of new synthetic opioid intoxications and increasing fatalities observed over the past ten years, we provide thorough background for developing new biosensors, screen-printed electrodes, or other point-of-care devices.

Geopolymers may be considered as an alternative materials to Portland cement ones, providing an opportunity to exploit industrial wastes or co-products with promising short and long-term performances in the construction field, f.ex. for reparation issues. However, these materials are porous and consequently their durability depends on the risk of intrusion of aggressive agents. In order to assess their durability, we propose to investigate in this study gas permeability of sound and mechanically loaded specimens. Loading is performed using a splitting tensile test driven by a crack opening displacement up to a level of 50 microns. Tests are performed on four types of blended fly-ash (FA) and ground granulated blast furnace slag (GGBFS) geopolymer mortars, containing four different levels of GGGBF slag in the binder: 0%, 10%, 30% and 50% wt. Results show a positive effect of blending with slag in terms of modulus of elasticity and tensile and compressive strength, as well as the permeability. However, permeability recovery after cracking is the lowest when blending is the highest.

The paper presents experimental investigations concerning the influence of the cement type (CEMI 42.5 R Portland cement and CEMIII/A 42.5 N slag cement—with 53% granulated blast furnace slag) on the mechanical and transport properties of heated concretes. The evolution of properties due to high temperature exposure occurring during a fire was investigated. High temperature exposure produces changes in the transport and mechanical properties of concrete, but the effect of cement type has not been widely studied in the literature. In this paper, concretes were made with two cement types: CEMI and CEMIII, using basalt (B) and riverbed aggregates (RB). The compressive and tensile strength, as well as the static modulus of elasticity and Cembureau permeability, were tested after high temperature exposure to 200, 400, 600, 800, and 1000 °C. The evaluation of damage to the concrete and crack development due to high temperature effects was performed on the basis of the change in the static modulus of elasticity. The test results clearly demonstrated that permeability increases with damage, and it follows an exponential type formula for both types of cement.

Irreversible climate change, including atmosphere temperature extremes, is one of the most important issues of the present time. In this context, the construction industry requires solutions for increasing the energy efficiency of buildings through feedback between temperature adjustment inside buildings and better isolation of the external parts of buildings. Newly developed thermal insulation materials play an important role in this strategy. This paper presents the foamed geopolymer based on metakaolin that can be used as a modern facade material. In order to further improve its thermal insulation properties, the composition of geopolymer was modified with organic substances, i.e., perlite and cellulose fibers (30% and 50% of the volume). The thermal conductivity and insulation properties, density, mineral phases, absorbability, and compressive strength were improved for composite materials. It has been shown that the final properties of the foamed geopolymer can be controlled to a great extent by modifications, and the final properties determine its applicability.

This work aimed to determine the effect of the addition of different types of reinforcing fibers on the strength properties of geopolymers such as flexural and compressive strength. Geopolymers are an attractive alternative to conventional binders and building materials; however, one of the main problems of their widespread use is their low resistance to brittle fracture. To improve the mechanical properties, reinforcement in the form of glass, carbon, and basalt fibers (as grids) was applied to geopolymers in the following work. Additionally, composites with these fibers were produced not only in the matrix of pure geopolymer but also as a hybrid variant with the addition of cement. Furthermore, basalt grids were used as reinforcement for geopolymers not only based on ash but also metakaolin. An additional variable used in the study was the molar concentration of the alkali solution (5 M and 10 M) for the different types of geopolymer samples. The mechanical properties of geopolymer materials and geopolymer–cement hybrids are the highest when reinforcement in the form of carbon fiber is used. Strength values for geopolymers reinforced with basalt mats depend on the number of reinforcement layers and the concentration of the alkaline solution used. All produced composites were tested for compressive strength and bending strength. When using basalt mesh, it was possible to achieve a bending strength of 12 MPa. The highest compressive strength that was achieved was the value of 66 MPa, while for samples not reinforced with fibers, only about 40 MPa was achieved.

This manuscript investigates the chemical and structural stability of 3D printing materials (3DPMs) frequently used in electrochemistry. Four 3D printing materials were studied: Clear photopolymer, Elastic photopolymer, PET filament, and PLA filament. Their stability, solubility, structural changes, flexibility, hardness, and color changes were investigated after exposure to selected organic solvents and supporting electrolytes. Furthermore, the available potential windows and behavior of redox probes in selected supporting electrolytes were investigated before and after the exposure of the 3D-printed objects to the electrolytes at various working electrodes. Possible electrochemically active interferences with an origin from the 3DPMs were also monitored to provide a comprehensive outline for the use of 3DPMs in electrochemical platform manufacturing.