ETTRINGITE - CAUSE OF DAMAGE, DAMAGE INTENSIFIER OR UNINVOLVED 3RD-PARTY

Concrete damage in conjunction with the formation of ettringite in har dened concrete is the result of complex long-term processes, in which concrete composition, technological factors during concrete production , and ambient effects are important. When taking preventive measures i t is therefore not sufficient to take only one influencing factor; e.g . the chemical composition of the cement, into account. All factors wh ich lead to disruption and damage of the microstructure can also promo te ettringite formation in hardened concrete. The occurrence of large ettringite crystals in concrete cracks is as a rule only a consequence , and seldom the cause, of the cracks. It has not been proved whether, they can have a damage intensifying action, e. g. by preventing moist ure- or temperature-induced changes in volume of the concrete. It is a lso unclear whether microcrystalline ettringite can, initiate damage i n concrete or increase damage which is already present. Experience so far indicates that compliance with the rules for the warm-curing of co ncrete given in the guidelines issued by the DAfStb (German Committee for Reinforced Concrete) ensures that no harmful ettringite formation is to be expected as a result of warm-curing. Problems can, however; o ccul if concreting is carried out at very high ambient temperatures or if large amounts of heat are liberated during the hydration of the ce ment in massive concrete components with very high cement contents.