Argamassa bastardas à base de cal aérea hidratada: caracterização experimental e implicações para intervenções em sistemas construtivos tradicionais

Abstract

This work departs from the recognition that lime is one of the oldest and most resilient building materials in human history. Before the experimental work, a historical and technical review traces its millennial origins and the chemical processes that determine its performance. Running alongside this trajectory is the evolution of bastard mortars, from traditional empirical formulations to contemporary industrialized products and their compatibility limits with the built heritage. Building on this foundation, the study presents the experimental characterization of bastard mortars formulated with hydrated air lime as the base binder, combined with natural hydraulic lime, Portland cement and metakaolin in different proportions. The tests were conducted at the Construction Materials Laboratory of the Polytechnic Institute of Bragança (IPB), Portugal, during an international academic mobility period. Under controlled temperature and humidity conditions, the evaluated properties included mass variation, shrinkage, flexural and compressive strength, and response to thermal cycles in a climatic chamber. The results demonstrated the complexity of the interactions between binders, aggregates, and curing conditions in bastard mortars. Each composition responded in a singular way to curing and accelerated aging conditions, reaffirming what constructive tradition already knew before any standard: the material converses with the place, with time, and with whoever applies it. Mechanical strength, taken in isolation, is an insufficient criterion for guiding interventions in traditional building systems. The most compatible mortar is not always the most resistant one, and it is precisely this understanding that makes technical knowledge an instrument of care for heritage.