Reatividade álcali-agregado: estudo de caso de materiais provenientes de dois locais do Nordeste do Brasil

Abstract

The first case related to AAR in Brazil was reported in 1946, at the Peti hydroelectric plant, and from that moment on the studies related to the occurrence of expansive reactions gained notoriety in the national scenario. This reaction can be classified into three types: alkali carbonate reaction, alkali-silica reaction and alkali-silicate reaction, the latter being considered as a specific type of alkali-silica reaction. This paper focused on the alkali-silica reaction (ASR), because it is the most common in the country. The main characteristic of ASR is the formation of a hygroscopic gel that expands in the presence of water, generating internal tensile stresses in concrete. Such stresses cause cracking of the structural element, compromising its physical properties and allowing the entry of deleterious agents from the external environment. In view of such problematic, the work aimed to verify the potential reactivity of aggregates of different granulometries. Mortar bar tests were performed by the accelerated method in two aggregates from places in northeastern Brazil. The first was a fine aggregate from a deposit in the state of Pernambuco, which presented a reactivity potential of R0 grade (innocuous), while the second was a coarse aggregate from the extraction of cores from a concrete pile in the interior of Bahia, which presented a reactivity potential classified as R1. Finally, an analysis was made on the limitations of the test method used and the recommendations established by the main standards in force in Brazil, regarding the prophylactic actions on the use of aggregates in the composition of concrete.