Synthesis Of Mg-Al Layered Double Hydroxides And Their Adsorption Capabilityof Chloride Ion In Cement Paste

The rapid development of concrete structures in ocean engineering are often served under the environment with multiple factors including ion erosion.The durability problem become more prominent,and the chloride ionsare the main reason for the steel corrosion in concrete.For the present,the research improving concrete durability from the angle of adsorbing or exchanging anions have not been systematic reported.Hydrotalcite-like compounds with larger specific surface area and pore size which can easily accept the objects are often used as adsorbent.Therefore,it has theoretical and practical significance to develop a new modified material to control the external erosion of concrete.The research synthesized different morphologies of Mg-Al-CO3 layered double hydroxides by hydrothermal method,characterized the structure and morphology.The adsorbability of different morphologies of Mg-Al layered double hydroxides of chloride ions in aqueous solution was investigated.The adsorption equilibriumand adsorption kinetic and thermodynamics of the best adsorption performance of LDHs on the adsorbent were studied.The influence of different p H,roasting temperature and the dosage of the adsorbent,adsorption temperature on the binding capability were also studied.The binding capability of LDHs was evaluated by introducing chloride ions into the in cement paste to investigate the binding performance.The results showed that the Mg-Al LDHs could be synthesized by hydrothermal method.Different additives had influence on the morphology and adsorption capability.LDHs calcined within a certain temperature range have been shown to recover their original layered structure in the presence of appropriate anions,with the lower crystallinity.The equilibrium isotherm showed that the uptake of chloride ion by LDO was consistent with the Langmuir equation.The maximum uptake capacity of LDO for chloride ion was 130.97 mg/g,showing its high chlorine ion adsorption capacity.It was also found that the preudo-second-order kinetics model could be used to describe the uptake process satisfactorily,which was controlled by the rate of reaction rather than diffusion.Compared with the ordinary cement paste,the paste added into LDO had a better adsorption capacity of chloride ion.LDO admixed in the cement matrix reconfigured itself with anions in the layered structure.The edges of the reformed LDH in the cement paste were more irregular than those of the raw LDO and the cementitious environment had no effect on the reformed structure of LDHs.Based on the binding capability of chloride ion in cement paste,the LDHs have enormous potential in the concrete to improve durability,which provide a new way that can push the LDHs widely used in concrete.