Development and assessment of fly ash and metakaolin blended geopolymer concrete incorporating expanded vermiculite for masonry units

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Abstract The widespread availability of coal-fired plants and kaolinite deposits has rendered fly ash and metakaolin, respectively, as sustainable alternatives for conventional cement and fired clay-based masonry building materials. Additionally, incorporating lightweight aggregate has been shown to improve the thermal insulation of masonry, which is otherwise poor with natural aggregate. Moreover, the two-part heat-cured low calcium-based FA and MK geopolymer has been researched, while the ambient-cured one-part alternative remains unexplored. This study developed the novel ambient cured fly ash and metakaolin blended one-part geopolymer concrete alternative masonry unit (AMU), substituted with expanded vermiculite (EV) lightweight aggregate at 15% by volume of the sand and synthesised by solid alkaline reagents comprising sodium hydroxide, sodium metasilicate pentahydrate and calcium hydroxide. The microstructure, mechanical properties, density, durability properties, thermal properties and sustainability were investigated. With EV, the 28-day strength decreased from 5.2 to 4.3 MPa, the elastic modulus decreased from 8.2 to 5.6 GPa, the density reduced, the water absorption increased by 6.0% in cold water, and 19.0% in boiled water, and the initial rate of absorption increased from 0. to 0.81 kg/m 2 /min. The overall shrinkage was reduced by 25%, no efflorescence was observed, and the thermal resistance decreased from 0.135 to 0.133 m 2 K/W. When compared to conventional masonry units, the AMU proved to be up to four times more expensive but reduced the carbon footprint by up to 56%. Overall, despite higher costs, the AMUs provide sufficient strength, durability and offer a sustainable alternative to conventional masonry.

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