Argamassas de cal para restauro em áreas próximas ao mar

Abstract

Rendering mortars are essential for the preservation of historical buildings, as they provide protection to masonry while also fulfilling an aesthetic function. Structures located in coastal regions, such as Salvador, are particularly vulnerable to deterioration due to high salinity and humidity. Sodium chloride (NaCl), which is predominant in the ocean, is one of the main agents responsible for this degradation, acting through cycles of crystallization and recrystallization within the pores of the mortar. This phenomenon results in severe pathologies such as efflorescence and subflorescence, cracking, and spalling. The main objective of this research is to develop new lime-based mortar formulations incorporating metakaolin, calcium hydrogen phosphate dihydrate, and potassium silicate additives for restorative interventions in coastal areas, and to test them in order to investigate the role of each additive in the mortar’s properties. The methodological approach involved the preparation and testing of 72 specimens, divided into four distinct formulations. The tests conducted included carbonation, determination of dynamic modulus of elasticity, flexural tensile strength, axial compressive strength, specific mass, porosity, immersion absorption index, capillary water absorption, and resistance to sodium chloride crystallization. The results of the formulations were compared with a reference mixture and with similar studies found in national and international literature. The tests indicated that the lime-based rendering mortar with a 1:2 mix ratio, without additives, demonstrated efficient performance in both mechanical resistance and salt penetration resistance. Even when exposed to extreme salt conditions, the reference mortar did not exhibit significant volumetric changes. The other formulations showed varying performance, suggesting a potentially adverse effect resulting from the interaction between one or both additives – calcium hydrogen phosphate dihydrate and potassium silicate – with metakaolin, with the latter likely being the main factor. The formulation that incorporated all components exhibited severe degradation, suggesting a possible incompatibility among materials. This research holds significant relevance for Conservation and Restoration Technology and Materials Science, as it explores the interactions between additives and lime in mortars exposed to aggressive environments, especially in coastal areas. By investigating these dynamics, the study opens perspectives for the development of reintegration mortar formulations for historical buildings, thus contributing to the preservation of cultural heritage.