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This study aimed to investigate the mechanical behaviour and microstructure of an environmentally friendly fibre-reinforce alkali-activated composites. The composites were obtained from alkali-activated granulated blast furnace slag reinforced with chopped secondary carbon fibres (SCFs) coming from the aircraft industry carbon fiber reinforced plastics waste. Three types of surfactants and two concentrations of SCFs were investigated. The compressive and bending strengths were measured to evaluate the mechanical behaviour of specimens. Moreover, the polycondensation products, pore structure, and microscopic morphology of the composites were analyzed using X-ray diffraction (XRD), method of standard contact porosimetry (MSCP), and scanning electron microscopy (SEM). It was found that tetraethylammonium bromide and a superplasticizer agent Glenium-51® increase compressive strength for reference granulated blast furnace slag-based alkali-activated matrix approximately by 60 % and lead to lower open porosity from 16 to 5 %. The experimental results showed that the incorporation of 0.7 vol. % SCFs had an optimal influence on mechanical behaviour and microstructure of composite. Based on the test results, it can be clearly said that using of Glenium-51® is improving the compressive strength of slag based alkali-activated composites reinforced SCFs.

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The article describes a study of the physical and mechanical properties and microstructure of geopolymer materials for construction based on low-calcium fly ash from CHP-22, depending on the type of activator, temperature and humidity conditions of curing and the introduction of an additional source of calcium (CaO) in the amount of 10, 15 and 20 wt. %. It was found that for the fly ash under study, the most promising type of activator is a sodium silicate solution with a silicate modulus SiO2 / Na2O = 1; the preferred curing mode is steam treatment at 90 °C. With the introduction of 15 % CaO into the geopolymer mixture, it was possible to increase the compressive strength by more than 2.5 times (to 38 МПа), the open porosity decreased from 24 to 7 %, and the water absorption from 15 to 3 %. However, a further increase in the CaO content leads to degradation of properties due to a significant reduction in the setting time of the raw mixture.

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