The influence of limestone filler on delayed ettringite formation in concrete

One of the most popular preventive measures to minimize the occurrence of chemical expansive reactions, namely the internal sulphate reaction (ISR), in hardened concrete is the use of mineral additions. This pathology is due to the formation of expansive ettringite (delayed ettringite formation - DEF) inside the material and is very difficult to deal with, because presently there is no efficient method to repair concrete structures affected by DEF. Hence, there is an urgent need to find preventive methods that may enable the inhibition of DEF in new constructions.
The research work presented in this paper deals with the influence of limestone fillerin the inhibition of DEF. The filler influence was followed by expansion and microstructure evaluation of concrete mix at several ages. These studies showed an interesting behaviour of limestone filler. According to these results it seems that the limestone filler does not inhibit rather it promotes the expansion due to DEF. Thus, for concretes subjected to high temperatures in early ages, the limestone filler is not adequate to sustain DEF development rather it may even increase the expansion behaviour in concrete mixes. According to these findings, it was proposed that the ISR recommendations must prohibit this kind of mineral addition.

Author: A. Santos Silva, D. Soares, L. Matos, M. Salta, A. Gonçalves, A. Bettencourt Ribeiro, A. Pavoine, L. Divet

Section: Concrete

Keywords: internal sulphate reaction, delayed ettringite formation, limestone filler, mineral additions, microstructure