Freezing and thawing resistance of aerial lime mortar with metakaolin and a traditional water-repellent admixture

• Linseed oil improved the mortars’ resistance to freeze-thaw ageing.
• The compressive strength of lime-metakaolin mixes increased after freeze-thaw cycles.
• The combination of lime-metakaolin with linseed oil produced vaterite.
• Lime-metakaolin with linseed oil showed the highest resistance to frost damage.
• Linseed oil had comparable effectiveness to industrial water repellents.

We prepared four mortar mixtures with lime, metakaolin and linseed oil, the latter added as an admixture to impart water-repellency. The mortar mineralogy, microstructure, mechanical strength and resistance against freeze-thaw cycles were evaluated. The addition of oil reduced the water saturation coefficient and capillarity absorption rate. Oil also hampered crack development during curing, thanks to the development of large spherical pores. The mechanical strength slightly decreased with the addition of oil to lime mortar but increased when added to lime-metakaolin. The mortar composed of lime, metakaolin and oil showed the highest resistance against freeze-thaw cycles.