Experimental investigation on chloride diffusion and binding in concrete containing metakaolin

In this paper, the effects of metakaolin addition on the compressive strength and chloride penetrability were studied. The study focused on the diffusion of the free and total chloride in concrete containing metakaolin (MK), which was measured by a potentiometric titration measurement. Effect of MK and sulphate on chloride binding capability was investigated, and Friedel’s salt was identified by X-ray diffraction and differential scanning calorimetry. The compressive strength increased with the addition of MK. Metakaolin decreased both the permeability of concrete and the free chloride, and increased the chloride binding capability greatly. The mechanism is that MK reduced the porosity and optimised the pore structure. The addition of MK favoured the formation of Friedel’s salts. However, sulphate decreased the chloride binding capability of concrete containing MK due to the formation of ettringite.