Influência da adição de resíduos de alumina em massa de solo-cimento

Abstract

Construction materials can be used as an alternative destination for waste, preventing them from being disposed improperly. Soil-cement is a building material that can be used for this, and that also has the advantage of being manufactured without the firing process used in conventional ceramic blocks and bricks, whose manufacturing process by sintering is highly polluting and consumes much energy. Activated alumina is used as an adsorbent for the purification of polyolefins and, after its use, this material becomes a residue that can be indicated to partially replace the soil used in soil-cement admixtures. The addition of other solid waste in soil-cement formulations has been studied in Brazil, especially for the manufacture of ecological blocks and bricks. For these reasons, this work investigated how the adsorbent residue made of alumina can interact with substances present in the cement and soil used in typical formulations of admixtures for the manufacture of soil-cement blocks and bricks. For this, firstly, a study was carried out in two different soils, to verify their suitability to the Brazilian standards (NBR) of the Brazilian Association of Technical Standards (ABNT). The specimens were manufactured in four different compositions, one without addition of residue, and the others with the replacement of the soil by 5%, 10% and 15% (by volume) of residue. The residue was chemically characterized by X-ray fluorescence and the microstructure of the soil-cement from the specimens was analyzed by scanning electron microscopy. The results showed that the addition of alumina residue reduces the compressive strength of the soil-cement, taking it to values below the minimum required by NBR 10834 and NBR 8491, while reducing the water absorption content of the material (and all compositions met the minimum required by the same standard). Observing the microstructure present in the electronic microscopies, it was concluded that the reduction in compressive strength is due to the low adhesion of the alumina residues to the soil-cement matrix, while the reduction in the water absorption content was due to the low porosity of the residue, much smaller than that of the matrix. Therefore, alumina residue is promising as a partial substitute for soil in the preparation of masses for the production of soil-cement blocks and bricks, reducing its negative environmental impacts due its reutilization. However, it’s still necessary to investigate which measures can improve the material’s compressive strength, such as the use of higher strength-class cements, according to NBR 16697.