The use of air entraining/plasticizing admixtures in cement-lime masonry mortars: Effects on fresh and hardened mortar properties

Abstract

Modern day masonry mortars rely on more than just standard constituents, which by definition include binder, aggregates and water. Due to different requirements imposed onto various types of masonry construction, ready mix mortar manufacturers and even masons and labourers on construction sites add certain additives to their mortar formulations. In this study, one standardized admixture is studied – an air entrainer/plasticizer (EN 934-3), coming in two forms – liquid and powder. It is applied to increase the air content and plasticity of cement-lime masonry mortar, formulated in volumetric proportions of 1:1:6 for cement, lime and aggregates. The dosage of admixtures is gradually increased starting with the manufacturer’s recommendations until the excessive air entrainment is achieved in order to determine the optimal dosage. Fresh mortar properties, including consistency, air content and bulk density are used to assess the enhancement of mortar influenced by the addition of the admixture, whereas compressive and flexural testing is performed at 7 and 28 days to monitor the disadvantages brought by reducing density. The results of this study reveal that the efficacy of a liquid admixture is better than that of a powdered air entrainer/plasticizer, albeit it being more difficult to use accurately. In both cases, higher dosage than manufacturer’s recommendations was required to reach satisfactory improvement of the fresh mortar structure, which resulted in a mixing water reduction, increased air content and reduced bulk density. That subsequently influenced the decreased strength, although optimally formulated mortars adhered to their strength class requirements.