Chloride binding of synthetic Ca–Al–NO3 LDHs in hardened cement paste

Abstract

The chloride binding of synthetic Ca–Al–NO3 layered double hydroxides (LDHs) for the removal of chloride ions from pore solution of cementitious materials is studied. The Ca–Al–NO3 LDHs is synthesized and characterized by XRD, SEM, FT-IR and XRF analysis. Results of direct anion exchange tests show that chloride substitutes nitrate in the interlayer of Ca–Al–NO3 LDHs in aqueous solution and the adsorption model fits the Langmuir adsorption isotherm. Furthermore, the structural change of Ca–Al–NO3 LDHs in simulated pore solution and its transformation after binding chloride are investigated. Cement pastes with Ca–Al–NO3 LDHs are prepared with chloride solution. Microstructural analysis shows that the Ca–Al–NO3 LDHs can immobilize the chlorides in the hardened cement pastes.