Chloride Diffusivity of Concrete Incorporating Rice Husk Ash

Abstract

Effect of rice husk ash addition on the chloride diffusivity of concrete is investigated in the present paper. The concrete specimens, having water-cementitious materials ratio of 0.30, 0.36 and 0.53, with and without rice husk ash are subjected to accelerated chloride penetration using the following two methods: i) Immersion in saturated NaCl at 20 degrees C, ii) Exposure to alternate cycles of 3 days immersion in 3% NaCl solution at 20 degrees C and 4 days drying at 50% R.H. After the accelerated chloride penetration, the total chloride content of concrete specimens at various depths was determined. Consequently, using the chloride content distributions, the chloride diffusion coefficient of concrete is evaluated by applying Fick's second law. In addition, the pore size distribution of concrete is determined in order to assess the effect of concrete microstructure on chloride diffusivity. From the experimental results, the total chloride content of concrete incorporating rice husk ash was shown to be lower than that of the control concrete after accelerated chloride penetration. The concrete specimens incorporating rice husk ash had chloride diffusion coefficients 57% to 25% lower than the control concrete. The effect of rice husk ash on pore refinement in concrete was observed, especially in the pore radii larger than 50nm. The pore size distribution of concrete tended to shift towards the smaller pores with the addition of rice husk ash. The decrease of the chloride diffusion coefficient of concrete incorporating RHA may therefore be attributed to the pore-refinement effect.