Abstract
In this study, the chloride adsorption behaviors of CaAl-Cl LDH precursors with various Ca:Al ratios were investigated. The optimal chloride ion removal rate was 87.06% due to the formation of hydrocalumite. The chloride adsorption products of CaAl-Cl LDH precursors were further characterized by X-ray diffraction analysis and atomic structure analysis, the adsorption mechanism was considered to be co-precipitate process. The chloride adsorption behaviors of cementitious materials blended with CaAl-Cl LDH precursors were further investigated. Leaching test according to Test Code for Hydraulic Concrete (SL352-2006) was performed to testify the stability of chloride ions in the mortar. The results show that more than 98.3% chloride ions were immobilized in cement mortar blended with CaAl-Cl LDH precursor and cannot be easily released again. The inhibition performance of steel in the electrolytes with/without CaAl LDH precursor was investigated by using electrochemical measurements. The results indicate that CaAl LDH precursor can effectively protect the passive film on steel surface by chloride adsorption. Considering the high anion exchange capacities of the LDHs, synthesized chloride adsorbent precursor can be applied as new inhibitors blended in cementitious materials to prevent the chloride-induced deterioration. Moreover, the application of chloride adsorption on CaAl-Cl LDH could also be of interest for the application of seawater blended concrete.
Highlights
Concrete structures can be deteriorated by chloride and failed to serve the predetermined service lives in marine environments
The formed mechanism of calcium chloroaluminate can be classified into two patterns: A direct chemical reaction among chloride, lime, and calcium aluminate, see Equation (3), and an indirect ion exchange between the OH− ions presented in the interlayers of layered double hydroxides (LDHs) phase Ca4 Al2 (OH)14 and unbounded chloride ions, see Equations (4) and (5) [8]
The results indicate that the chloride ions adsorption rate of mortar blended with CaAl-Cl LDH precursors is the highest
Summary
Concrete structures can be deteriorated by chloride and failed to serve the predetermined service lives in marine environments. The corrosion occurs when sufficient amounts of chloride ions have been accumulated onto the surface of the embedded steel. To enhance the concrete properties, several kinds of inhibitors have been developed and applied in the practical engineering projects [1]. Such kind of inhibitors are usually presented as a thin and weak inertia film that are just attached on the surface of the steel bars to prevent chloride attack, correspondingly serious local corrosion will occur on the unprotected area. Layered double hydroxides (LDHs) are found to be effective chloride adsorbents, effectively preventing chloride-induced deterioration in reinforced cementitious materials [2,3]
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