Assessment of phase formation in lime-based mortars with added metakaolin, Portland cement and sepiolite, for grouting of historic masonry

Lime-based mortars containing pozzolanic additions of metakaolin, sepiolite and white Portland cement are studied in order to determine their performance as historic masonry conservation mortars. Hydration products on metakaolin–lime blended mortars include stable and metastable phases. The presence of such products has been studied by means of DTA and XRD analysis, concluding that the selection between them is mainly related with the water–lime ratio. Sepiolite addition to metakaolin–lime mortars has shown to inhibit C4AH13 formation. Therefore, the influence of phase distribution on the mechanical resistance is considered. Finally, compounds production on blended lime–white Portland cement was compared to natural hydraulic lime ones, and as a result, no remarkable differences appeared, apart from traces of possible cement Portland addition to the latter, usually not mentioned in the nominal composition supplied by the manufacturers of lime binders.