ABSTRACT
Abstract To study the mechanism of expansion which occurs after curing at elevated temperatures, commonly called delayed ettringite formation (DEF), a series of mortars were cured at 90°C for 12 hours and then under water at 20°C. The mortars were made with cements prepared from the same clinker, with additions of calcium sulphate at 3, 4, and 5 wt.% S03 and also with additions ofKOH. Analysis was carried out at times throughout the expansion process by scanning electron microscopy (SEM) and X-ray microanalysis. The results support the view that expansion is caused by relatively uniform expansion of the cement paste as opposed to by ettringite growth at the paste/aggregate interfaces. Sulphate and aluminate ions are incorporated within the C-S-H after heat curing, the concentration of these ions in the C-S-H immediately after heat curing appears to determine the potential for expansion. Keywords: Delayed Ettringite Formation, microstructure, heat curing, temperature, X-ray microanalysis, expansion, threshold, sulphate incorporation.
