**1. Introduction**

Geopolymers, by definition, are included in the third-generation lime cement and ordinary Portland cement. They are amorphous synthetic alkali aluminosilicates belonging to the group of inorganic polymers, the properties of which depend mainly on the type of base material used, the type and amount of activator used during their production, as well as external factors of the polycondensation process, such as temperature and heating time. In the face of global trends and challenges, developing binders for the manufacture of geopolymer concrete has become a hot topic in construction science [1–5].

Geopolymers are widely regarded as substitute materials for Portland cement. This is due to their good strength and thermal properties, as well as their very good corrosion resistance. These materials are widely used in various industries [6].

One of the most commonly used raw materials in geopolymer production is fly ash. Standard EN-450-1:2012 [7] defines fly ash as fine-grained dust resulting from the combustion of coal dust, which consists mainly of glassy, spheroidal particles.

Basalts, as basic minerals, include intermediate plagioclase feldspars, as well as augite pyroxene with or without olivine, magnetite, and variable amounts of glass. Natural large deposits of basaltic rocks, which are used as aggregate for concrete, are found in Egypt. During the process of crushing and grinding basalt rock, large amounts of basalt powder are produced as a byproduct. Numerous works have investigated the activity of basalt and the possibilities of its use. The reactivity of basalt mainly depends on the surface area of its particles, the content of silica and alteration minerals, as well as the content of volcanic glass [8–13].

The purpose of this study is to investigate the possibility of using basalt flour as a substitute raw material for quartz sand during the production of fly ash-based geopolymers. The effect of the addition of basalt flour and its proportion on the strength properties of

**Citation:** Kozub, B.; Miernik, K.; G ˛adek, S. A Study of Fly Ash-Based Geopolymers with Basalt Flour Addition. *Mater. Proc.* **2023**, *13*, 3. https://doi.org/10.3390/ materproc2023013003

Academic Editors: Katarzyna Mróz, Tomasz Tracz, Tomasz Zdeb and Izabela Hager

Published: 13 February 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

the produced geopolymers was evaluated. The scope of the research conducted includes density measurements, compressive and flexural strength tests, abrasion resistance, and microstructure studies using a scanning electron microscope (SEM).
