# Replacement of Natural Sand with Expanded Vermiculite in Fly Ash-Based Geopolymer Mortars
###### Abstract  
Increasing the thermal insulation of building components to reduce the thermal energy loss of buildings has received significant attention. Owing to its porous structure, using expanded vermiculite as an alternative to natural river sand in the development of building materials would result in improvement of the thermal performance of buildings. This study investigates the properties of fly ash (FA)-based geopolymer mortars prepared with expanded vermiculite. The main aim of this study was to produce geopolymer mortar with lower thermal conductivity than conventional mortar for thermal insulation applications in buildings. A total of twelve batches of geopolymers were prepared for evaluating their different properties. The obtained results show that, at a given FA and expanded vermiculite content, the geopolymers prepared with a 10 molar NaOH solution exhibited a higher flowability, water absorption and porosity, as well as a lower dry unit weight, compressive strength, ultrasound pulse velocity and thermal conductivity compared with those prepared with a 15 molar NaOH solution. As is also shown, the geopolymers containing expanded vermiculite (15%) developed a lower flowability (-6%), dry unit weight (-6%), compressive strength (-7%), ultrasound pulse velocity (-6%) and thermal conductivity (-18%), as well as a higher apparent porosity (-6%) and water absorption (-9%) compared with those without expanded vermiculite at a given FA content and NaOH concentration. The findings of this study suggest that incorporating expanded vermiculite in FA-based geopolymer mortar can provide eco-friendly and lightweight building composites with improved sound and thermal insulation properties, contributing toward the reduction of the environmental effects of waste materials and conservation of natural sand. expanded vermiculite; geopolymer; fly ash; strength; thermal conductivity; ultrasound pulse velocity +
Footnote †: journal: Applied Sciences  
Geopolymers, as alkali-activated aluminosilicate materials, are an environmentally friendly building and construction material [5]. In a geopolymer, an aluminosilicate binder is used as a replacement material for OPC [6]. Fly ash (FA) is an industrial by-product which contains high-aluminosilicate resources [6]. As was reported previously, the annual generation of FA is about 750 million tons [7], but only 25% of it is currently being recycled [8]. Thus, there is great potential for FA to be used as an OPC alternative in concrete production, with the aim of reducing the negative impact of OPC and FA on the environment. Vermiculate, as a naturally occurring mineral, is a hydrous phyllosilicate mineral [9]. It was reported that the worldwide production of vermiculite is approximately 2.35 million tons annually, with the main deposits being in South Africa, the United States, Australia, China, Russia, India and Uganda [10]. When vermiculite is heated to temperatures of 650-1000 \({}^{\circ}\)C, it expands to up to 30 times its original volume. Therefore, vermiculite in its expanded form exhibits a very low density, high refractoriness, high sound absorption and low thermal conductivity [11; 12]. [PERSON] et al. [13] reported that dehydration of vermiculite occurs at about 100 \({}^{\circ}\)C, which is due to the weight loss of the physically absorbed water. Mass losses between 500 \({}^{\circ}\)C and 900 \({}^{\circ}\)C may be as a result of the loss of chemically absorbed water. As was reported by the United States Environmental Protection Agency (EPA) [14], the primary pollutants in the vermiculite expansion process are particulate matter (PM) and PM of less than 10 micrometers, and there is no data on carbon dioxide emissions corresponding to the vermiculite expansion process. Due to its excellent properties, expanded vermiculite has great potential to be used as an aggregate for producing lightweight concrete with excellent thermal and sound insulation characteristics.