Análise multiescala dos danos por reações expansivas no concreto: estudo de caso na fundação de um edifício

Abstract

Concrete structures are subject to deterioration mechanisms capable of compromising their physical integrity and mechanical performance over time. Identifying these mechanisms and assessing the state of deterioration are fundamental for diagnosing and defining intervention strategies in structures in service. Despite advances observed in the international literature, a gap remains in the national context regarding the integrated application of mechanical and microscopic analysis tools, such as the Stiffness Damage Test (SDT) and the Damage Rating Index (DRI), in real structures affected by expansive mechanisms. In this context, this research aimed to evaluate the degree of deterioration of a foundation block of a 21-year-old vertical building, subjected to internal expansive mechanisms, such as alkali-silica reaction (ASR) and delayed ettringite formation (DEF), using a multiscale approach. Mechanical and microstructural tests were performed, including SDT, DRI, and compressive strength, in addition to scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) analyses. The results indicated that the analyzed concrete is in an advanced stage of deterioration associated with internal expansive reactions. The average compressive strength was 33.00 MPa, approximately 29% lower than the estimated strength at 28 days (46.65 MPa) from the technological control at the time of construction, evidencing a significant loss of mechanical performance over time. The integration of macrostructural (SDT: SDI = 0.22 and PDI = 0.18) and microstructural (DRI = 710.23 and SEM-EDS) results revealed intense microcracking in the cement paste, the presence of an alkaline-silicate gel, and evidence of ettringite formation, associated with the combined action of the alkali-silica reaction and delayed ettringite formation. The SDI and DRI values place the concrete in the very high damage range, according to intervals reported in the literature, corroborating the high degree of deterioration observed in situ. It is concluded that the multiscale approach based on the integration between SDT and DRI is effective for evaluating the deterioration of concrete affected by internal expansive mechanisms in service structures, establishing itself as a robust tool for the diagnosis of real structures.