Evolução textural e mineralógica de concretos submetidos a diferentes estágios de degradação de reação álcali agregado e formação de etringita tardia

Abstract

The present study aimed to study the textural and mineralogical evolution of 29 concrete specimens. These specimens were subjected to deterioration processes, such as alkali-aggregate reaction and late ettringite formation, for periods of 28 and 200 days. The mineralogical characterization aimed to infer which minerals participated in the reactions, as well as the evolution of the modal composition of the samples in relation to time. The textural analysis, performed on the same specimens applying the Damage Rating Index (DRI) method, allowed the evaluation and identification of the degree of concrete deterioration and the pathologies involved, by quantifying the fractures. The study was divided into the following stages: literature review (1), application of the DRI (2), petrography (3) and analysis and discussion of the data (4). The textural analysis revealed the predominance of unfilled fractures in the coarse aggregates, in the 28-day specimens for the AAR. In the 200-day period, fractures filled by the reaction product in the coarse aggregates are formed, reaching an expansion of 0.06%. The same textural characteristics were observed in the test specimens subjected to late ettringite formation at 28 days, mainly fractures found in the aggregate because the reaction does not occur in the stipulated time, but at 200 days the fractures develop in the paste, reaching an expansion of 0.03%; however, with a predominance of fractures in the aggregate, it is noteworthy that these fractures are not due to the formation of late ettringite. From the petrographic analysis, it was possible to verify the presence of deleterious minerals such as quartz and devitrified material, as well as the reaction products at 200 days. In view of this, it was argued that the alkali-aggregate reaction occurs more effectively than the DEF pathology, since the DRI values found at 200 days were at least 219, while the DEF reached its maximum at 154.75; The RAA samples exhibited an average DRI value of 225.75 at 200 days, and the RR samples 238.5, showing similar DRI values, although the RR specimens were not manufactured with the intention of the reaction occurring in an accelerated manner, indicating high reactivity of the material. For DEF, the initial heat treatment proved to be important, since an effective difference was observed in the average DRI values (148), when compared to the RI values of 108.5 at 200 days. It was also possible to define the reactive potential for the pathological manifestation of RAA even in DEF concretes, due to the presence of deleterious minerals that can help the reaction. In this way, it was possible to identify the mineral phases that contribute to the reactions, as well as the modal relationship of the specimens that do not show an effective change in the coarse aggregates and in the paste.