The effect of metakaolin on the corrosion behavior of cement mortars

In this paper the effect of metakaolin addition on the corrosion resistance of cement mortar is studied. A poor Greek kaolin with a low kaolinite content was thermally treated and the produced metakaolin (MK) was ground to the appropriate fineness. In addition, a commercial metakaolin (MKC) of high purity was used. Several mixture proportions were used to produce mortar specimens, where metakaolin replaced either sand or cement. Mortar specimens were then exposed to the corrosive environment of either partial or total immersion in 3.5% w/w NaCl solution. For the evaluation of the performance of metakaolin, the following methods were used: compressive strength, corrosion potential, mass loss, electrochemical measurements of the corrosion rate by the Linear Polarization method, carbonation depth and porosity. It is concluded that metakaolin improves the compressive strength and the 10% w/w addition shows the optimum contribution to the strength development. In addition, the use of metakaolin, either as a sand replacement up to 20% w/w, or as a cement replacement up to 10% w/w, improves the corrosion behavior of mortar specimens, while when metakaolin is added in greater percentages there is no positive effect.