Abstract
Layered double hydroxides (LDHs) have gained attention in the concrete research field, appearing as prospective additives for controlling chloride attack, and as micro or nano deliverers of corrosion inhibitors. This work reports the effect of ZnAl-NO2 LDH on the evolution of chloride concentration in the pore solution and on the corrosion resistance of iron in mortar samples exposed to 3.5 % NaCl solution. To this end, Ag/AgCl sensors were used to monitor the ingress of chloride ions into mortar, while the electrochemical state of the iron was evaluated by electrochemical impedance spectroscopy. Furthermore, the mortars were analyzed by XRD and TGA, and the total amount of chloride was measured with a commercial sensor. Mortars with LDH showed a slower increase of chloride ions in the pore solution and the preservation of the passive state of the Fe. The presence of LDHs did not cause a significant structural change in the mortars, which was evidenced by the similar distribution of the high frequency resistance as a function of depth in the samples with and without the additive. Finally, the amount of bound chloride in the cementitious material was higher in the LDH-containing mortars. In conclusion, ZnAl-NO2 LDH exhibited a positive effect on the protection of reinforcement embedded in mortar samples when subjected to chloride ingress.
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