Chloride-Enhanced Delayed Ettringite Formation (CLDEF): An Obscure Process

Abstract

From the historical perspective Delayed Ettringite Formation (DEF) is known to occur usually in cementitious systems made at high cement contents with rapid hardening Portland cements (RHPC) such as Type III cements. Elevated curing temperatures exceeding 70 °C are necessary for DEF to occur. However, there have been controversies, leading to speculations that DEF could occur outside these generally recognized conditions [1,2,3,4,5,6,7,8,9]. For example, large pours of concretes under hot weather concreting could increase concrete temperature levels to DEF critical temperatures. Johansen and Thaulow [10] found that a concrete beam of 1 m × 1 m cross-section developed a peak temperature of 84 °C at ambient temperatures of 35 °C, without heat treatment. Hobbs [11] also suggested that large sections of field concretes made with high cement contents of about 500 kg/m³, could attain maximum temperatures in the range of 85 °C. So in hot or tropical climates, concreting conditions similar to those found under heat curing, could arise as a combined effect of the following factors:- use of RHPC/Type III cement, mix designs of high cement contents such as 500 kg/m³, large concrete pours or casting of large sections, and ambient temperatures exceeding 30 °C. In laboratory studies, however, there are no reports of DEF occurrence in the absence of heat curing.