Efeito de aditivos superplastificantes em argamassas de revestimento com fíler calcário e incorporadores de ar

Abstract

The use of superplasticizers can influence the properties of mortars in both the fresh and hardened states, as well as the tensile bond strength when applied to a substrate. This study aims to evaluate the effect of different superplasticizing admixtures on the applicability of rendering mortars. Four base compositions were evaluated: (i) cement (C10), (ii) 30% cement replacement by limestone filler (C40), (iii) an air-entraining admixture (IA), and (iv) a plasticizing and stabilizing admixture (PE); each was tested both without and with the addition of one of three superplasticizers: a lignosulfonate-based (A) and two polycarboxylate ether based types (B and C). The investigation was conducted in three stages: (1) on pastes to evaluate the influence of superplasticizers on hydration kinetics via isothermal calorimetry; (2) on mortars to determine their impact on fresh and hardened properties; and (3) on mortar applicability to evaluate how the admixtures affect rendering application procedures and the properties of the mortar–substrate system. In the first phase, sixteen pastes mixtures with a water–binder ratio of 0.50 were tested. For the mortar phase, a 1:4 (cement: sand) volumetric mix proportion was used as the reference. Fresh mortar properties evaluated included bulk density, entrained air content, and water retention capacity. At 28 days, hardened properties was assessed, including flexural tensile strength, compressive strength, dynamic modulus of elasticity, and capillary water absorption. In the third phase, selected mortars were applied by a professional workmanship onto ceramic brick panels and subsequently tested for fresh and hardened state properties, as well as tensile bond strength tests. The results indicated that the superplasticizer admixtures influenced the hydration kinetics of the pastes, increasing the dormant period and thereby retarding hydration; this retarding effect was most pronounced for the lignosulfonate-based admixture (A). In the mortar study, admixture A yielded lower mechanical strength compared to the polycarboxylate-based admixtures (B and C). Conversely, superplasticizers B and C increased flexural tensile strength. The use of superplasticizers delayed the the setting time in all pastes mixtures.In mortars, the use of superplasticizers improved performance in both fresh and hardened states and increased the tensile bond strength.