Chloride Diffusivity in Red Mud-Ordinary Portland Cement Concrete Determined by Migration Tests

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Red mud, which is a solid waste produced in the alumina production process, is classified as dangerous dueto its high pH. In this work, the concentration of chlorides was monitored by measuring the conductivity of theanolyte, which initially was distilled water. The steady and nonsteady-state chloride diffusion coefficients wereestimated from the “time lag” and “equivalent time” between diffusion and migration experiments. The capillarywater absorption, apparent porosity and pore size distribution of concretes were also analyzed. The additionof red mud apparently ensured lower chloride diffusion in the tested mixtures due to its superfine particle-sizedistribution and its “filler” effect. Red mud lengthened the service life of the concrete to 35 years (double that ofthe reference concrete). This finding is very positive since it indicates a delay in the onset of the rebar corrosionprocess caused by the migration of chloride ions.