Laboratory study of a kaolinitic soil and sodium hydroxide interaction mechanisms and resulting swelling stresses

¹ Universidade Federal do Rio de Janeiro (UFRJ), Civil Engineering Department, Rio de Janeiro, Brazil
² SM Engenheiros Consultores Ltda, Civil Engineering, Rio de Janeiro, Brazil

^* Corresponding author: thiago.silva@coc.ufrj.br

Abstract

The study of prolonged exposure of natural soils to alkaline solutions has been conducted to analyze and control the local soil swelling behavior observed in industrial sites. The occurrence of foundation heave in a Brazilian industrial site prompted a laboratory investigation aimed at understanding the mechanism of interaction between soil and alkali that induced swelling behavior. The study was extended to determine the corresponding swelling stress to be used in reinforcement design, and to investigate the soil response to chemical stabilization with 5% ferric chloride solution. Previously, a comprehensive mineralogical and physical-chemical investigation was accomplished using industrial caustic liquor and four natural soils from local stratigraphy. All soils are mainly constituted by kaolinite and quartz, and one also presents some montmorillonite. Both kaolinite and montmorillonite were degraded by NaOH liquor, and newly formed minerals were identified. The expansion is related to the mechanism of the silica-NaOH reaction. In the study reported here, the local soil with the highest volume change in sedimentation tests with NaOH solutions was subjected to quasi-constant volume oedometer tests with water and with 4N NaOH solution to determine the swelling stresses resulting from the reactions until stabilization. The alternative of chemical treatment with 5% ferric chloride solution was investigated through the same testing procedure. X-Ray diffraction analyses were applied to evaluate the changes in mineralogy. The swelling vertical stress reached 40 kPa under confined conditions, and stabilization took up to 40 days. The chemical treatment was effective in controlling ongoing reactions, but not effective in prevention.