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1. INTRODUCTION
Geopolymers are a group of cementing ceramic materials belonging to the family of inorganic polymers that are obtained from the reaction between an aluminosilicate (primary precursor) and one alkaline activator. These materials have been widely developed and have gradually attracted the attention of the scientific and industrial world as revolutionary materials. This attention is partly due to their technical and environmental advantages, the ease of implementing new technologies for their production and the versatility of their application to different engineering fields. Despite the excellent properties obtained from the activation of industrial by-products and waste as precursors, the nature of these materials leads to variability in their chemical and mineral compositions, which makes it more difficult to standardise an activation process to obtain specific mechanical and durability properties. These challenges have incentivised the development of studies focused on the production of alkaline activation cements based on different natural resources, such as clays (particularly kaolinites and smectites) and natural pozzolans, which could be a more viable alternative from a commercial standpoint when adopting these materials on an industrial scale.
In particular, the use of natural volcanic pozzolans in geopolymer synthesis is a subject of great interest and economic significance for countries that possess large deposits of these materials, such as Colombia. This type of material could be advantageous as an alternative cementing agent to replace portland cement in certain applications and contribute positively to reducing the environmental impact of its production (1, 2, 3, 4, 5, 6). It is worth noting that approximately 0.84% of soils from tropical regions of the world are composed of volcanic ashes, and in Colombia they occupy approximately 11.6% of the national territory. In Colombia, volcanic ashes are located in areas of higher demographic and economic growth, particularly throughout the entire Andes region and in the centre and southern part of Colombia (7).
Lemougna et al. (8), Tchakoute et al. (9), Bondar et al. (10), and Kani and Allahverdi (11), among others, have used volcanic pozzolans from different sources as precursors in the production of geopolymer cements with satisfactory results. Tchakoute et al. (9) report compressive strength of up to 50 MPa after 28 days of curing at ambient temperature for a volcanic pozzolan from Cameroon. However, other researchers have...