Ettringite Formation in Hardened Concrete and Resulting Destruction


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Title: Ettringite Formation in Hardened Concrete and Resulting Destruction

Author(s): J. Stark and K. Seyfarth

Publication: Special Publication

Volume: 177


Appears on pages(s): 125-140

Keywords: carbon; concretes; durability; ettringite; expansion; sulfate

Date: 1/1/1999

The destruction of concrete attributed to the formation of ettringite was originally seen only as a problem caused by heat treatment. In this field, investigations were done by many scientists. Our long term investigations, started in 1989, into the durability of concrete, showed that damages could also occur in untreated concrete under use conditions. The change in the microstructure of the hardened paste and the degree of damage were assessed by expansion, compressive strength, ultrasonic pulse velocity, loss in E-modulus, variation in mass, depth of carbonation, the crack pattern (net-like crack formation), and microscopical and phase-analytical investigations. After six years the highest degree of damage was observed on heat treated samples with a dense microstructure. It was found also that there was no connection between the degree of damage and the detected ettringite content. It was not possible to determine whether ettringite was the cause of damage, as it is in sulfate attack due to crystallization pressure, or whether ettringite was just deposited and enriched in available spaces in the hardened paste (voids, cracks, gaps and peripheral cracks around aggregates). Probably these primary defects, not affecting the use e.g. of a concrete element, originally caused by the hardening, curing and/or use conditions, will likely increase as a result of the accumulation of ettringite until effective destruction of the concrete.