ROLE OF MICROSTRUCTURAL CHARACTERISATION IN UNDERSTANDING THE MECHANISM OF EXPANSION DUE TO DELAYED ETTRINGITE FORMATION

摘要

Mortars or concretes that have been exposed to high temperatures, either through the application of external heat or through the endogenous heat of hydration may suffer from expansion during subsequent moist storage at room temperature. This phenomenon is usually referred to as Delayed Ettringite Formation (DEF), because ettringite deposits have been observed in damaged structures. However no direct correlation has been established between the amount of ettringite detected by XRD in expansive heat-cured mortars and the degree of expansion. In the present work, reported in detail elsewhere, various characterisation techniques were used to study the changes occurring heat cured mortars which were either dimensionally stable or which expanded on subsequent storage in water. X-ray microanalyses of the outer hydration products were found to be the key difference between the two cases. These findings are consistent with a mechanism of expansion in which the formation of ettringite from calcium alumino monosulfate in sub-microscopic pores (～50-100 nm) is the origin of expansion.