Investigating the early-age diffusion of chloride ions in hardening slag-blended mortars on the light of their hydration progress

Amor Ben Fraj (1) , Stéphanie Bonnet (2) , Nordine Leklou (2) , Abdelhafid Khelidj (2)

1 Cerema Equipe-projet DIMA - Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement - Equipe-projet DIMA
2 GeM - Institut de Recherche en Génie Civil et Mécanique

The present work seeks to investigate the ingress of chlorides during the hardening of slag-blended mortars that may have been exposed to chlorides since an early age. In order to correlate chloride ingress with the microstructure development, both the hydration reaction and chemical shrinkage of the investigated mixtures are monitored, and their microstructure is characterized through SEM observations. Results indicate a slow hydration reaction in the presence of slag, which decelerates the formation of hydrates and the filling of capillary pores. Despite the decrease in chemical shrinkage, chloride ingress still increases, thus amplifying the risk of corrosion in slag-blended matrices. The hydrates gradually develop within the hardening microstructure and obstruct the chloride diffusion paths, resulting in a lower chloride diffusion coefficient. The apparent chloride-diffusion coefficient measured after 28 days of exposure is 12 × 10−12 m2/s, 14.2 × 10−12 m2/s and 14 × 10−12 m2/s for hardening mortars, with respectively 0%, 30% and 60% of slag. These coefficients are respectively 2 times, 2.8 times and 4.7 times higher than those of hardened mortars.

Mots clés: Chloride diffusion; Slag-blended mortar; Early age; Hydration; Chemical shrinkage; Microstructure

Domaines: Matériaux

Amor Ben Fraj, Stéphanie Bonnet, Nordine Leklou, Abdelhafid Khelidj. Investigating the early-age diffusion of chloride ions in hardening slag-blended mortars on the light of their hydration progress. Construction and Building Materials, 2019, 225, pp.485-495. ⟨10.1016/j.conbuildmat.2019.07.185⟩. ⟨hal-02413028⟩