# Replacement of Natural Sand with Expanded Vermiculite in Fly Ash-Based Geopolymer Mortars
###### Abstract
Sodium hydroxide and sodium silicate are two alkaline activators usually used in the production of geopolymers [5]. In the production of sodium hydroxide and sodium silicate, the required heat is about 300 \({}^{\circ}\)C for sodium hydroxide [15] and 1400 \({}^{\circ}\)C for sodium silicate [16], which are both lower compared with the heat required for cement production (\(\sim\)1500 \({}^{\circ}\)C). In addition, the usage ratio of sodium silicate is about 0.5-2%, which is significantly lower compared with that of sodium hydroxide and cement [5]. Therefore, production of sodium hydroxide and sodium silicate needs less energy than production of cement. Many studies exist on cementitious materials containing lightweight aggregates, such as pumice, expanded polystyrene, perlite and expanded clay [12; 17; 18; 19; 20; 21]. However, there are very few studies on the use of expanded vermiculite in cementitious materials [9; 12; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31]. [PERSON] et al. [27] studied the alkali-silica reactivity behavior of lightweight cement mortar containing expanded vermiculite, perlite, expanded glass and expanded clay as fine aggregates. They reported that the mortar containing expanded glass and perlite exhibited high alkali-silica reactivity, whereas those containing expanded vermiculite and expanded clay did not show any potential reactivity [27]. [PERSON] et al. [12] investigated the mechanical and thermal characteristics of cement mortar made with expanded vermiculite and expanded polystyrene as fine aggregates, and they reported that, at the same mortar volume ratio of 55%, the mortar containing expanded vermiculite had a 25% higher 28 day compressive strength and 11% lower thermal conductivity compared with that containing expanded polystyrene. [PERSON] et al. [9; 26] and [PERSON] et al. [24] assessed the influence of an elevated temperature on the mechanical behavior of cement mortar containing expanded vermiculite, and they revealed that mortar with a higher vermiculite content exhibited lower compressive and flexural strength losses at all temperature ranges up to 900 \({}^{\circ}\)C. [PERSON] et al. [30] used nano-metakaolin to improve the mechanical and microstructural characteristics of cement mortar with expanded vermiculite. They showed that incorporating 10% nano-metakaolin (by weight of the vermiculite) led to about a 57% increase in the compressive and flexural strength and a 74% decrease in the capillary water absorption of the cement mortar [30]. It was shown by [PERSON] et al. [31] that incorporating 30% vermiculite as a fine aggregate in cement mortar resulted in a high thermal stability. [PERSON] et al. [22] evaluated the effect of raw vermiculite and expanded vermiculite on the durability and mechanical characteristics of cement mortar at ambient and elevated temperatures, and they reported that mortar containing expanded vermiculite had better high-temperature resistance compared with that containing raw vermiculite. [PERSON] et al. [29] and [PERSON] et al. [23] assessed the influence of FA content on the compressive strength of cement mortar containing expanded vermiculite as a fine aggregate. They showed that the influence of FA content on the compressive strength of the mortar was lower with a larger content of vermiculite, in comparison with mortar with a smaller vermiculite content [23; 29]. Based on the above literature review, the existing studies on the addition of expanded vermiculite as a fine aggregate in cementitious materials focused on cement mortar, and no study has been performed on geopolymers. To address this research gap, this paper presents the first systematic study on different properties of FA-based geopolymers incorporating expanded vermiculite as a sand replacement material. The presented results show significant potential for using expanded vermiculite in geopolymers to improve their physical and thermal properties.