Himani Acharya, Krutik Patel, Yathiraj Nagaraju
The project on Delayed Ettringite Formation; effects and preventive measures, includes the procedure of reformation of ettringite or can be termed as delayed ettringite, which is basically a destructed form of primary ettringite. The research on DEF states that the predominant surrounding consequences that stimulates the delayed ettringite formation involves: Higher temperature at early age, sulfate & carbonate introduction and adequate moisture serving environment.
Understanding the microstructure of the delayed ettringite in the concrete structure and its adverse effects on the structure along with Research for the other aspects affecting the durability of Structure and allowing DEF such as alkali silica reaction, variations in aggregate (such as limestone aggregate and quartz aggregate), types of cement (Portland cement, high early strength cement etc.) and their characteristic of generation of heat of hydration, use of different supplementary cementitious material and moisture introducing conditions will allow to acknowledge the particular cause of damage due to DEF and the measure to prevent the DEF.
As stated in various research studies, Some of the SCMs were observed to be beneficial to prevent the expansion caused by DEF when the temperature exceeds 70° C. Other ways to forestall this expansion is by using diverse materials like Class F Fly ash, Class C fly ash, Slag, Ultra fine fly ash and Metakaolin in an adequate amount. In addition to that, curing duration and curing temperature also influence the formation of ettringite which will later reform in “Delayed Ettringite formation”.
EDF, French electricity company had claimed that limestone filler can also increase the risk of DEF but the reason was unknown. After several researches to investigate it was concluded that limestone dissolves and the carbonate ions of it react with monosulfate to form hemicarbonate or monocarbonate and releases sulfate ions in the solution. These sulfate ions react with monosulfate in the outer product of C-S-H and cause expansion due to DEF. The tests have shown that Fly ash inhibits the DEF for cement containing high sulfate (SO3), limestone powder and even when the specimen was immersed in carbonate ion solution.
The major problem of DEF can be seen in pre- cast concrete because of their curing procedures and high temperature. Various heating methods were seen advantageous to control high temperatures. Heating with radio waves and direct energy input were found out to be more convincing to reduce the possibility of long term damage than other heat treatment methods.
1 Shingo Asamoto, Kohki Murano, Isao Kurashige, Anura Nanayakkara, Effect of carbonate ions on delayed ettringite formation, Construction and Building Materials 147(2017) 221-226.
2 Yasser Amine, Nordine Leklou, Ouali Amiri, Effect of supplementary cementitious materials on delayed ettringite formation in heat cured concretes, International conference on materials and energy, Tetouan, Morocco, 2015.