THE INFLUENCE OF SULFATE CONTENT IN CLINKER OR CEMENT AND CURING TEMPERATURE ON DEF-RELATED EXPANSION OF CONCRETE

摘要

Cement pastes and concrete specimens were cured at 20°C or steam-cured up to 90°C. At curing temperature higher then 70°C, ettringite disappears and then forms again at later ages (DEF). Concretes manufactured at room temperature (20°C) do not show any form of DEF-related expansion independently of the SO_3 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 SO_3 content of the portland cement is relatively high (> 4%). The higher SO_3 content in the clinker phases (> 2%) or the presence of pre-existing cracks exacerbate the DEF-related expansion. Deposition of ettringite fibre crystals occurs in the pre-existing cracks or within the new microcracks. However, no clear evidence was found between the ettringite deposition and the width-change of the cracks. Curing at temperatures lower than 70°C is strongly recommended to avoid DEF-related risk. Blended cements with a lower SO_3 content should be used in case this limit in curing temperature cannot be safely ensured.