Rebar Corrosion Potential in Alkali-Activated Slag and Pumice Mortars

Previous researches have shown that due to its good adhesion, alkali-activated materials can be used as a protective overlay for concrete structures. However, the mechanical properties and durability of alkali-activated materials are not fully investigated. In this paper, compressive strength, bond strength, water penetration and half-cell corrosion potential of alkali-activated slag and pumice mortars as concrete overlay are investigated. The results show that the performance of alkali-activated slag mortar is better than Portland cement one in above tests and the use of potassium hydroxide as activator and a mixture of 90% slag and 10% pumice as based material result in the highest compressive strength and bond strength and the lowest water permeability and half-cell corrosion potential. The initial half-cell potential reading of alkali-activated mortar specimens was an average of 1.9 times more than Portland cement mortar specimens. This difference indicates that the ranges presented in ASTM C876 and their relationship with rebar corrosion risks are not applicable for alkali-activated materials and it is necessary to provide other criteria for these materials. Also, due to different conductivity of alkali-activated and Portland cement mortars, applying potential difference to accelerate the penetration of chloride ions and comparing the performance of alkali-activated materials with Portland cement is not a correct method. However, this method is suitable for comparing mixes design of alkali-activated mortars and the its results are in accordance with non-accelerated methods.