Title: DEF-Related Expansion of Concrete as a Function of Sulfate Content in the Clinker Phase or Cement and Curing Temperature
Author(s): M. Collepardi, J. J. 0goumah Olagot, D. Salvioni,
and D. Sorrentino
Publication: Symposium Paper
Appears on pages(s): 77-92
Keywords: delayed ettringite formation; expansion; external sulfate attack; internal sulfate attack; sulfate attack
Delayed ettringite formation (DEF) occurs at late ages and the related heterogeneous expansion in a hardened concrete can produce cracking and spalling. There are two different types of DEF depending on the sulphate source: DEF caused by external sulphate attack (ESA) or internal sulphate attack (ISA). In the present paper only ISA-related DEF is studied with reference to the following three parameters: a) the sulfate content in the clinker phase of the cement; b) the curing temperature; c) the presence of preliminary cracks in concrete specimens. Concretes manufactured at room temperature (20°C) do not show any form of DEF-related expansion independently of the SO3 content of the clinker (1—2%) or the portland cement (2-4%). On the other hand, concretes steam-cured at 90°C and then kept under water show significant expansion related to DEF provided that the SO3 con-tent of the portland cement is relatively high (> 4%). The higher SO3 content in the clinker phases (> 2%) or the presence of preexisting cracks accelerates the DEF-related expansion. Deposition of ettringite fiber crystals occurs in the preexisting cracks or within the new microcracks. Curing at temperatures lower than 80°C, preferably lower than 70°C, is strongly recommended to avoid DEF-related risk. Blended cements with a lower SO3 content should be used in case this limit in curing temperature cannot be safely ensured.