Comparative properties of a lime mortar with different metakaolin and natron additions

• Lime increases (10–30%), on natron-MK adjusted mix, improve resistance.
• In lime-natron-MK adjusted mortars, C-H has not been detected.
• Lime increases on initial geopolymer result in more homogeneous microstructure.

The heterodox hypothesis about the construction of the pyramids in the Old Kingdom of Egypt with cast stone has served as a starting point in the design of several blends of aerial slaked lime mortar for their potential use in restoration events. Aerial slaked lime mortar characteristics with added metakaolin and sodium carbonate were analysed. Increments in the ratio of lime on adjusted initial proportions, corresponding to a theoretical geopolymer, were then made. Seven blends were characterized: two of them corresponding to different a water/binder ratio geopolymer and the rest to 5, 10, 30 and 60% lime increments. Finally, a lime mortar remained without additions.10 and 30% lime increases on an adjusted specimen of sodium carbonate, metakaolin and slaked lime mainly improve Shore C hardness and compressive strength when compared both to the theoretical geopolymer and to conventional lime mortars. These become the most influential factors within a month, and values in this interval are suggested to improve these characteristics. TGA/DSC, XRD and SEM/EDS analyses show absence of portlandite and an improvement in the continuity of the microstructure in these values, yielding closer results to a polymer rather than to a conventional lime mortar.