Carbonation of blended binders containing metakaolin

Abstract

The pozzolanic materials are often recommended for their very good durability in aggressive environment. Unfortunately, this is not always true and particularly in the case of carbonation by the atmospheric CO 2. Although cement replacement by pozzolanic materials causes a decrease in pore size, the pozzolanic reaction consumes portlandite and decreases the protection potential against CO 2 ingress. This is the case for most pozzolanic materials, including metakaolin. The aim of this study is first to confirm the literature results of carbonation by using flash metakaolin in partial replacement of cements (CEM I, CEM II A-LL and CEM II A-V). Then the concretes with a metakaolin are compared with concretes based on standardized cement in order to assess the carbonation depth of metakaolinbased concretes and concretes used today in the building construction. Even though the cement replacement of CEM I and CEM II A-V by metakaolin increases the carbonation depth, results are not the same with the CEM II A-LL cement. The interaction of metakaolin with the cement limestone filler can explain this better performance, certainly because the hemicarboaluminate allows slowing down the CO 2 propagation through the matrix.