From risk study to field evidence: an unprecedented and isolated case of delayed ettringite formation in Brazil

Abstract

This paper presents the first case ever reported in Brazil where delayed ettringite formation (DEF) has been confirmed as the sole cause of deterioration in field concrete. Still under construction and with less than 2 years of age, numerous cracks were observed in the foundation structures of a building located in Recife, a city known for its history of alkali-aggregate reaction (AAR) cases. In addition to the field survey of cracks, microstructural analyses, residual expansion, compressive strength, review of structural design, the determination of the sulfates content in the groundwater and simplified thermal analysis were carried out. Results confirmed that the DEF was the isolated cause of the damages present in those cast-in-place concrete structures, with no evidence of AAR or any other deterioration process. This work corroborates studies previously published on the high risk of the occurrence of DEF in the region, demonstrating the urgent need for a preventive technical standard in the country, considering the chemical composition of cements and mainly prior thermal analyzes to adopt possible preventive measures to limit the maximum internal temperature of the concrete.