Effect of the addition of the natural and treated açaí stone in structural mortars
Authors: Monteiro Gabriel Pereira ,   UENF-State University of the Northern Rio de Janeiro, LAMAV e Advanced Materials Laboratory, Av. Alberto Lamego, 2000, 28013-602, Campos dos Goytacazes, Brazil, de Azevedo Afonso Rangel Garcez , Marvila Markssuel Teixeira ,   UENF-State University of the Northern Rio de Janeiro, LECIV e Civil Engineering Laboratory, Av. Alberto Lamego, 2000, 28013-602, Campos dos Goytacazes, Brazil
Published: August 2021

<abstract>
<p>The açaizeiro is a palm tree present on a large scale in the northern region of Brazil and in others countries, such as Colombia and Peru, its fruit constitutes one of the main forest products of great economic potential to exportation. However, a generation of large amounts of waste during its processing represents a serious environmental problem, since about 365 tons of açaí stone are discarded in landfills daily in Brazil. The objective of this work was to evaluate the potential of using açaí stone as a substitute of 25% in mass natural sand with filler function, in the development of structural mortars with reference mixture of ratio 1:2:0.45 (cement:sand:water) and waste mixture with1:1.5:0.5:0.45 (cement:sand:açai stone:water), that both mixtures are relationship adopted for structural mortar in the literature. Three different types of mortar were made for evaluation, the reference (without adding stones) and with the addition of natural stone (without treatment and treated with NaOH). After the incorporation of the stones, consistency, water retention, incorporated air content and density in fresh mortars were analyzed, in the fresh state. For evaluation in a hardened state, cylindrical specimens (50 mm × 100 mm) were molded, for compression strength and density tests. The optimum composition was also analyzed with confocal microscopy. It can be seen that in the compression strength tests, mortars with the addition of natural and treated stone showed a reduction, decreasing from 6.25 MPa (reference), to 5.55 MPa (natural stone) and 1.89 MPa (treated stone), this showed that the natural stone mortar was above the minimum of 5.00 MPa reported in the literature. As for density, the evaluations demonstrate a beneficial effect to the incorporation of the stone, which formed lighter mortars, decreasing from 2.12 to 1.79 g/cm<sup>3</sup> in the natural composition and 1.85 g/cm<sup>3</sup> in the treated composition, in both situations with additions, the values were within the maximum limit of 2 g/cm<sup>3</sup> that the literature suggests for structural mortars. In addition, the results of water retention showed an increase in the treated composition (97.28%) in relation to the reference (95.84%), an increase characterized by the treatment in NaOH that reduced the hygroscopic characteristics of the stones, the mixture mortar with treated seed, as well as the reference, presented values above 95%, which is recommended by other studies. The evaluations show that there is a potential for specific structural applications of these mortars, since in all tests the composition with natural stone is within the ideal parameters by Brazilian standard, in addition to helping to solve the environmental impacts caused by discard this waste. As it is a mortar with low compressive strength, its application is suggested for the purpose of repairing specific structural defects that arise in the molding stage of beams, slabs and columns, located in regions with low load demand.</p>
</abstract>