Secondary ettringite formation in concrete subjected to different curing conditions

The large amount of ettringite detected in concrete affected by different f ailure mechanisms (alkali-silica reaction [ASR], freezing and thawing [FT], and wetting and drying [WD]) in sulfate-free environments has been a matte r of concern for many researchers over the past years. Two major lines to a pproach this issue have been defined. One of them considers ettringite as t he main cause of damage and the other assumes that it appears after concret e distress. In order to contribute to the clarification of this phenomenon, research was conducted to cover the above issues. This paper reports on th e conclusions arrived at up to date, from studies conducted on concrete aff ected by different damaging mechanisms:FT, WD, and precracking induced by l oading and ASR. Changes in length and mechanical strength of test concrete are reported, as well as the evaluations made by optical microscopy (OM), s canning electron microscopy (SEM) and energy dispersive X-ray analysis (EDA X). Secondary ettringite formation (SEF) is closely Kinked to pore fluid tr ansport in the mass of concrete. Although it was not possible to define cle arly its participation in the damaging processes related to ASR or to FT, s econdary ettringite crystallization in concretes subjected to WD cycles see ms to be one of the most likely mechanisms to account for the volumetric in stability observed in these concretes. (C) 2000 Elsevier Science Ltd. All r ights reserved.