Mistura compactada de solo residual argiloso e ligante de cinza de casca de arroz e cal de casca de ovo: comportamento reativo e mecânico mediante ataque ácido

Abstract

The growing production of waste and its respective destination is a serious problem in the current context. Among the responsible sectors, the foodstuff responsible for the generation of large residual volumes, commonly destined to landfills, stands out. The production of rice generates annually tons of a residue called rice husk. This material is often destined for combustion processes, giving rise to a new material, rice husk ash (RHA). Another residue from the highly produced food sector is eggshell, which is rich in calcium carbonate, with high potential for application in the production of lime. Therefore, the objective of this work was to evaluate the application of mixtures of RHA and lime based on eggshell (EL) in compacted clay soil, evaluating its behavior through acid attack. RHA was characterized by chemical, physical, mineralogical, geomorphological and environmental classification tests. The soil-ash-lime mixture, containing 30% RHA and 6% EL, was evaluated for reactive and mechanical behavior. Comparatively, a mixture containing commercial lime was evaluated under the same conditions. Reactivity was studied through the execution of central composite experimental design of three variables (% RHA, % lime and acid attack pH), using acid attack methodology by batch tests with sulfuric acid solution. The physical and mechanical behavior was evaluated by means of compaction tests and unconfined compression strength (UCS), for both mixtures. The residue has a high content of silica oxide (87.6%), containing quartz minerals and cristobalite in crystalline form, fitting as a low reactivity pozzolan. Reactivity tests demonstrated better neutralization of contaminant acidity for mixtures with EL. The incorporation of up to 30% of RHA in the soil, together with 6% of eggshell lime, raised the pH without the solubilization of toxic elements. As for the physical behavior, there was a reduction in the maximum dry specific weight and an increase in the optimum moisture content of the soil. EL proved to be a more efficient binder for the mechanical resistance and reactivity of the mixtures after 28 days of curing. Therefore, it is concluded that the application of RHA and EL in soils subjected to acid attack has environmental viability, however, it is recommended to analyze the processes of grinding the waste together with the study of the resistance of the mixture over time and application tests on impermeable landfill barriers.