MORPHOLOGY OF DELAYED ETTRINGITE FORMATION (DEF) AS OBSERVED AND IDENTIFIED BY A SCANNING ELECTRON MICROSCOPE (SEM)

摘要

The development of delayed ettringite formation (DEF) proceeds in several steps and can be detected as two characteristics morphologies: typically, as a "gel-like" material when observed at low magnification, and as a "needle-like" crystals. The "gel-like" material is actually a massive formation of extremely fine ettringite needles, either perpendicularly oriented to cut concrete surfaces, or in parallel orientation to them. These two types of morphology, as observed in cement paste by a scanning electron microscope (SEM), either "in-situ", in cracks ("veins") or at aggregate particle/paste interfaces, are detailed.