Abstract

VARGAS, María et al. Manufacture of geopolymeric mortars from ash coming from the Ubinas volcano, assessment of its mechanical, physical and microstructural propertiesFabricación de morteros Geopoliméricos a partir de ceniza proveniente del volcán Ubinas, evaluación de sus propiedades mecánicas, físicas y microestructurales. Rev. Bol. Quim [online]. 2020, vol.37, n.3, pp.148-175. ISSN 0250-5460.

Abstract In this study, it has been proposed a geopolymerization method that uses a low liquid/solid (L/S) ratio and the pistón as a compaction method which has favored the compression strength achieved considering that the synthesis of geopolymers is characterized by the use of an alkaline solution with a high L/S ratio (greater than 0.45). The volcanic ashes from the Ubinas volcano (Peru's most active volcano) that are rich in Al₂O₃, SiO₂ and CaO were alkaline activated with sodium hydroxide (NaOH) and sodium hydroxide with addition of sodium silicate (NaOH+Na₂SiO₃), both solutions with 12 M concentration, with a low liquid/solid (L/S) ratio of 0.1 and solid:solid (S:S) ratio of 1:1. Volcanic ashes and Portland cement were used as initiators and the local sand was used as aggregate for both of them. The mechanical, physical (density and water absorption) and structural properties were determined by X-ray diffraction and the microstructure was determined by scanning electrón microscope from the mortars. As a result, it has been proven that the use of the NaOH solution favors the dissolution of alumina and silica and therefore the polycondensation, mainly when using an initiator with a high composition of AI₂O₃, SiCh and CaO. Besides, it has been demonstrated that the excess of NaOH (using the sodium silicate solution) inhibits the polycondensations. Therefore, this method has the advantage of a lower use of L/S ratio than the other methods. It has been obtained a compressive strength of 24.6 ± 1.7 MPa with the geopolymer mortars activated with NaOH and 14.2 ± 2.3 MPa with the geopolymer mortars activated with NaOH+Na₂SiO after 28 days of curing being these valúes higher than those for mortars in Norm NTP 334.051.

Keywords : Volcanic ash; Geopolymer; Concrete; Compressive strength.

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