Autogenous formation and smart behaviors of nitrite- and nitrate-intercalated layered double hydroxides (LDHs) in Portland cement-metakaolin-dolomite blends

In this work, the influence of sodium nitrite (NaNO2) and sodium nitrate (NaNO3) corrosion inhibitors on the composition, structure, and chloride binding behaviors of layered double hydroxides (LDHs) formed in ternary ordinary Portland cement-metakaolin-dolomite (OPC-MK-DM) systems is studied. The results show that the nitrite and nitrate anions are preferably intercalated in the Ca-Al LDHs (AFm phases), but not in the Mg-Al LDHs (hydrotalcite-type phases) due to its limited formation in these ternary cementitious systems cured at ambient temperature. The autogenously formed nitrate- and nitrite-AFm phases are decomposed upon chloride exposure accompanied by Friedel' s salts formation, potentially releasing corrosion inhibitive ions to the pore solution in a progressive manner. The NaNO2 and NaNO3 incorporation in ternary OPC-MK-DM binders marginally lowers chloride binding capacity but reduces its penetration resistance mainly due to pore coarsening. Nevertheless, a strong linear correlation can be established between the water-soluble and total chloride contents in ternary OPC-MK-DM systems, regardless of OPC replacement level and corrosion inhibitor incorporation.

Automated summary

The study found that nitrate and nitrite ions are more likely to intercalate in Ca-Al LDHs, which are released when exposed to chlorides. The addition of NaNO2 and NaNO3 may reduce the chloride binding capacity in ternary OPC-MK-DM binders, but enhance penetration resistance.