Estabilização de areia descartada de fundição a partir de ligante álcali-ativado: comportamento mecânico, microestrutura e lixiviação

Abstract

Portland cement is a material with a large environmental impact, being responsible for up to 8% of global CO2 emissions. In addition, industrial and agricultural activities results a large volume of waste, such as waste foundry sand (WFS), rice husk ash (RHA) and eggshells. To reduce the impacts of Portland cement production and waste disposal, research is being conducted on the development of alternative cements, such as alkali-activated binders (AABs). These binders can be produced from the alkaline activation of aluminosilicate-rich waste materials. In this context, this study evaluated the mechanical performance of WFS stabilized with an AAB obtained from RHA, hydrated eggshell lime (HEL) and sodium hydroxide solution. Mechanical properties, leaching, and microstructure were evaluated. The durability of the material was verified, as well as the effect of wetting and drying cycles on mechanical strength and metal leaching. For the mechanical performance evaluation, different binder contents, dry specific weights, and moisture contents were tested. The WFS-AAB mixtures with higher binder content and specific weight met the unconfined compressive strength (UCS) and acumulative mass loss (ALM) criteria for use as a pavement layer. The wetting and drying cycles did not significantly compromise the material's strength, and the concentrations of leached metals did not exceed the toxicity limits. FTIR analysis confirmed the formation of CSH gel. SEM-EDS images showed a more compact microstructure at 28 days with increased formation of cementitious products. Chemical maps confirmed traces of the elements silicon (Si) and calcium (Ca) in higher proportions, as well as sodium (Na), aluminum (Al), iron (Fe), and magnesium (Mg) in lower proportions. WFS stabilized with AAB from RHA, HEL, and NaOH solution has potential applications in engineering and geotechnics, representing an alternative for the valorization of the by-products and waste involved.