Effect of Carbonation in Mortars with Different Types of Metakaolin and Curing Procedures

Abstract

This study aimed to evaluate the influence of different types of metakaolin and curing conditions on mortars depth of carbonation. To do so, prismatic mortar specimens were produced by using three different 1:2 mix proportions (binder: sand): a reference mix proportion (without mineral addition) and two mixes with partial replacement of the cement by metakaolin, in the content of 10% by mass of cement. Two types of metakaolin with different characteristics were used in order to verify their capacity of changing the mortar microstructure and the pore solution, modifying this way the carbonation behavior of these materials. Three curing conditions for the test specimens were defined: no wet curing and wet curing (by immersion in water) for 3, 9 and 28 days. After the accelerated carbonation procedure in a CO2 chamber (in an atmosphere of 10% of CO2), with a relative humidity of 70% and a temperature of 20°C, for a period of 7 days, the carbonation depth was measured by using pH-indicators based on phenolphthalein and thymolphthalein. The results indicated influence of the type of curing in the carbonated depth and the significant interaction between curing and the type of metakaolin. When wet curing was not performed, the carbonation was more intense in the reference mortar. The effect of curing in the mortars with metakaolin was much less significant compared to that in the reference mortar. A global discussion about carbonation behavior of metakaolin modified mortars will be performed, based on the characteristics of the metakaolins.

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