**1. Introduction**

In terms of environmental protection, it is critical to creating a sustainable product. The geopolymer mortars were used to reduce OPC use to as an alternative to Ordinary Portland cement (OPC). Cement manufacture accounts for 5–7 percent of global CO2 emissions [1]. This scenario has severe environmental consequences. Finding alternate OPC replacements is essential. Industrial waste materials (slag, red mud, fly ash) were significant replacements. Alkaline activators were used to activate these waste materials in the geopolymer manufacture process. The carbon dioxide emissions are decreased due to recycling waste materials and using less OPC [2].

Additionally, geopolymer mortars have much superior durability and mechanical properties. In this instance, the compact and dense geopolymer microstructure is beneficial [3]. Industrial waste, produced as a byproduct of many technological operations, is a major environmental issue. One of these sectors is the quarry industry which generates a large quantity of industrial waste. The environmental cost for storing waste items rises year after year. The mining and processing of rock raw materials are rapidly expanding. Rock raw materials are treated to cutting and grinding operations in stone manufacturers. The fine-grained waste material generated during processing is transported to and deposited

Tammam, Y.; Kara, S.; Lezcano, R.A.G.The Effect of Basalt Fiber on Mechanical, Microstructural, and High-Temperature Properties of Fly Ash-Based and Basalt Powder Waste-Filled Sustainable Geopolymer Mortar. *Sustainability* **2021**, *13*, 12610. https://doi.org/10.3390/su132212610

Academic Editor: Jose Ignacio Alvarez

**Citation:** Ziada, M.; Erdem, S.;

Received: 26 October 2021 Accepted: 12 November 2021 Published: 15 November 2021

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**Copyright:** © 2021 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/).

in landfills. Therefore, geopolymer was produced using different waste materials, and its properties were investigated in previous studies [4–7]. The sodium hydroxide (SH) and sodium silicate (SS) used in this study were close to the amounts of SH and SS used in these studies. However, it can be stated that using BP instead of sand in this study is more economical than geopolymers using sand. BP is a byproduct of the manufacturing of high-quality aggregates from basalt rocks. Tammam et al. [8] were used industrial waste filler materials such as BP, marble powder, and limestone powder waste in geopolymer mortars. They found that the use of industrial waste enhanced the mechanical and durability properties of the geopolymer specimens. Celikten and Atabey [9] investigated the mechanical and physical characteristics of geopolymer mortars manufactured using basalt stone cutting waste. Geopolymer mortars with four different water contents were created for this purpose. They found that the mortars with the least water content had the highest strength values.

Improving mechanical characteristics using fiber has significant benefits. PVA, basalt, glass, Carbon, and steel fiber have all been used to create geopolymer [10–12]. Previous research used polyvinyl alcohol (PVA) fibers and nano-SiO2 to manufacture geopolymer concrete. The findings showed that PVA fibers enhanced the proprieties' strength, improved toughness, and achieved the optimal value at 0.6% to 1% [13–16]. Significant values were achieved with high temperatures in BF, and PVA contained geopolymer mortars. BF was examined and is among the most widely used concrete fibers [17]. It is a very efficient insulating, non-toxic, low-cost fibrous material formed during basalt rock melting at up to 1400 °C. It is less costly than other fibers since it requires less energy and no additives [18]. Additionally, it was shown that it had a function in strength growth by substantially adding to workability. Several publications have verified the beneficial benefits of BF [19–23]. Ali et al. [24] investigated the impact of boron waste and BF on metakaolin-based geopolymer. Based on the findings of their study, 24 mm BF has more significant beneficial impacts than 12 mm BF. The specimens were found to be stable during high temperatures, sulfuric acid, and freeze-thaw effects.

Previous studies were conducted on alternative binder ingredients in fly ash-based geopolymer. Only a few of them have mixed various ratios of BF and basalt waste aggregate. This study aims to produce a sustainable mortar with high mechanical and microstructural properties and good high-temperature resistance. Thus, this study has led to environmentally friendly geopolymer mortar production using waste materials instead of cement and sand. For this proposal, BF contained fly ash-based, and BP-filled geopolymer mortar samples were produced. The mechanical, physical, and microstructural tests were performed after and before the high-temperature test.

#### **2. Materials and Methods**
