Delayed ettringite formation (DEF) behavior towards variations in cement matrix and aggregates fabric


The term DEF, “delayed ettingite formation”, corresponds to the expansive reaction pathology identified in concretes (and mortars) that were subjected to high temperatures during curing. Regarding the expansion mechanism caused by delayed etringite, there are two main hypotheses considered: the formation of small crystals of etringite in the cement paste, which results in the appearance of cracks in the paste-aggregate interface, so that etringite recrystallizes in these cracks without significantly contributing to the expansion, and the expansion caused by crystallized etringite and concentrated at the paste-aggregate interface. This work aimed to understand the role of space restriction for accommodation of delayed etringite crystals in cementitious matrix with space restriction by suppression of aggregates, in molded specimens of cement paste, and with different proportions of space, in specimens molded from mortar and concrete, as well as to verify how these characteristics influence the expansion and loss of mechanical strength caused by the crystallization of this mineral phase. Concerning the physical-mechanical results and electron microscopy, it was possible to determine that etringite has a growth preference for empty spaces promoted by porosity, either by the higher water-cement ratio or by the introduction of a paste-aggregate interface. This study indicates the occurrence of the two phenomena, that of expansion by taking advantage of pre-existing voids and generalized expansion of the paste.


1. LEAL, Priscila Rodrigues Melo; CASTRO, Alessandra L.; NASCIMENTO, Lucas C.; GONÇALVES, Karoline M.; PINTO, Natasha da S.; SOUZA, Victor H. Estudo do comportamento de formação da etringita tardia (DEF) frente à variação dos arranjos entre matriz cimentícia e agregados. In: CONGRESSO BRASILEIRO DO CONCRETO, 62., 2021, Florianópolis. Anais… 22p.

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