Effect of NaCl on stability of C-A-S-H phases

Concrete structural components are exposed to numerous substances which can reduce service life and result in high costs for restoration or replacement. Dissolution and precipitation processes due to changes in the phase composition of the hardened binder lead to changes in the microstructure. Here the properties of the strength-giving C-S-H phases are of primary importance regarding concrete durability.

The current trend towards higher proportions of aluminium-rich supplementary cementitious materials (SCM), such as fly ash, ground granulated blast-furnace slag and metakaolin, is environmentally beneficial because less CO₂ is released by concrete production as a whole. However, this results in an increased aluminium content of the binder and thus in the C-A-S-H phases compared to concrete made with pure Portland cement. Changes in the nanostructure and chemical composition of the C-A-S-H phases due to the reaction of aluminium with deicing salt and/or the incorporation of alkalis into the C-A-S-H nano-structure modifies the phase composition of concrete and consequently its chemical resistance.

New findings are presented on changes in the C-A-S-H nanostructure and the stability of aluminium based on the results of storage tests with NaCl solutions.

Author: L. Irbe, H. Hilbig, R.E. Beddoe, D. Heinz

Section: Science and production

Keywords: phase C—A—S—H, structure, NaCl solution, deicing salt