Effect of Air-entraining and Water-repellent Admixtures and of Their Dosage on the Performance of Lime Mortars

This work explores the short- and long-term effects of admixtures typically used to improve durability on air lime mortars. With that purpose, two air-entraining admixtures (AEA), based on sodium alpha olefin sulfonate (AOS) and sodium dodecyl sulfate (SDS), and a water-repellent admixture (WRA) based on alkylsilicone resin were studied. The AEAs proved not to be detrimental to mechanical strength both in the short- and long-term, when used in an appropriate dosage, and reduced water intake, while improving water vapour permeability, allowing a faster drying. Comparing the AEAs, SDS led to less entrained air and, thus, to higher mechanical strength and lower porosity and pore size than AOS. In turn, the WRA substantially increased mechanical strength in the short- and long-term, despite delaying carbonation, but also increased stiffness. Water intake was reduced, as well as the mortar's drying kinetics, which can hamper its compatibility with old masonries. With increasing dosage, both types of admixtures increased the air content, but different implications in the short-term mechanical strength of the mortars were observed: WRA led to an increase, whereas the AEAs led to a decrease in this property.