The Stability and Chloride Entrapping Capacity of ZnAl-NO2 LDH in High-Alkaline/Cementitious Environment

Abstract

In this work, the ZnAl-NO2 LDH (layered double hydroxide) is investigated as a possible additive for mitigating the chloride-induced corrosion of steel in reinforced concrete. The investigation focused on the stability and chloride binding capacity of this LDH in the pH range typical of cementitious materials. Until pH = 12.5 the material was stable and effective in capturing chloride ions from the surrounding aqueous environment. For higher pH, precisely that of hydrated cement, the LDH was partially dissolved and OH− preferentially entrapped instead of Cl−. These results suggested that ZnAl-NO2 has excellent chloride entrapping capability at neutral pH, but this is reduced with increasing pH. However, when the LDH was incorporated into mortars, the chloride ingress was delayed, signifying that the dissolution of LDH leads to a secondary mechanism responsible for chloride capture.

Tween–80 Coating in Enhancing Physicochemical Stability, Kinetics and Release Mechanism of Layered Double Hydroxide-Ferulate

“…Therefore, these results evidently show that the release behavior of FA from LDH-FA hinges on the pH of the release environment. The high structural stability of LDHs in the high alkaline range is also in good agreement with a previous study [27].…”

“…Due to this reason, Cl − will have a lower affinity towards the positively charged layer of LDH, thereby undergoing an anion exchange process in a slower manner than the polyatomic OH − and PO 4 3− anions. A recent study has reported that LDH tends to have higher selectivity towards OH − than Cl − [27]. The order of anion selectivity can be arranged according to their affinity toward LDH, in the sequence of CO 3 2− > OH − > F − > Cl − > Br − > NO 3 − , with CO 3 2− being the most preferable anions by LDH [28].…”