Microscopic observations of sites and forms of ettringite in the microstructure of deteriorated concrete

Abstract

The determination of delayed ettringite formation (DEF) in hardened concrete relying simply on the identification of ettringite by electron microscopy or powder X-ray diffractometry can be imperfect because of the high risk of missing other possible deterioration phenomena. The presence of ettringite can be easily biased as an indication of DEF while the actual cause of deterioration is ASR. This paper identifies the deterioration causes and presents different ettringite formation factors based on the petrological observation results. The experiments conditions including depth of carbonation, mix proportions of concrete, curing temperature and others were considered. The deterioration of the samples seem to be correlated to ASR, except for the precast concrete product which presented DEF. In order to determine the deterioration causes and demonstrate the importance of petrological approach, different observations using the same methods were carried out on a concrete specimen blended with fly ash showing some cracks.

Keywords

• Alkali-silica reaction
• Delay-ettringite formation (DEF)
• Scanning electron microscopy (SEM)
• Ettringite
• Petrography