Suitability of different surfactants as air-entraining admixtures for lime mortars

•Study of the suitability of different surfactants as air-entraining admixtures (AEAs) for lime mortars.•The AEAs were sodium dodecyl sulfate (SDS), sodium alfa olefin sulfonate (AOS) and cocamidopropyl betaine (CAPB).•The nature of the surfactants (anionic or amphoteric) was responsible for differences in their performance.•AOS and SDS caused moderate changes in lime mortars, but improved their freeze-thaw resistance.•CAPB had greatest impact on strength and porosity, reducing the freeze-thaw resistance. The paper examines the suitability of three different surfactants as air-entraining admixtures (AEAs) for air lime mortars. The substances tested were based on sodium dodecyl sulfate (SDS), sodium alfa olefin sulfonate (AOS) and cocamidopropyl betaine (CAPB). Results showed that CAPB had the highest air-entraining action of the three, due to its amphoteric nature and, thus, the greatest impact on mechanical strength and porosity, making the mortars more susceptible to degradation by freezing and thawing. Conversely, SDS and AOS caused only moderate changes in lime mortars, but improved their resistance to freeze-thaw cycles. The differences in the performance of the tested surfactants suggest that their use should be carefully assessed as they can have a harmful effect on the already weak and porous air lime mortars, reducing their durability instead of improving it.