Chloride Ion Curing Properties Of Calcium-Aluminum Hydrotalcite In Cementitious Materials

Due to these advantages of its recognized low price,wide application range,easy pouring and molding,and good durability,cement concrete has almost covered the fields of infrastructure construction such as houses,highways,bridges,airports,rail transit,water conservancy facilities,marine engineering,and military engineering in the past 100 years.It can be said that without concrete,there would be no world today.However,in the process of application,the defects of traditional cement concrete are increasingly exposed,mainly reflected in the durability.Chloride ion penetration is one of the main problems affecting the durability of reinforced concrete structures.Therefore,the chloride ion in cured concrete has become an important aspect of steel corrosion research in reinforced concrete structures.In this paper,calcium aluminum nitrate hydrotalcite（CALN）was prepared from tricalcium aluminate（C₃A）and calcium nitrate tetrahydrate as raw materials.The properties of calcium aluminum nitrate hydrotalcite（CALN）were tested by simulated pore solution test,brown ring test,weight loss rate of steel bar test,X-ray diffraction（XRD）,scanning electron microscope（SEM）,and comprehensive thermal analysis（TGA-DSC）.The chloride ion solidification behavior of calcium aluminum nitrate hydrotalcite in cement-based cementitious materials and alkali activated cementitious materials was studied,and the penetration behavior of chloride ion in CALN-Concrete was simulated by COMSOL simulation software.The conclusions are as follows.（1）The best preparation process of CALN is that the mass ratio of C₃A and calcium nitrate tetrahydrate is 1.5:1,stirring temperature is 20～30℃,stirring time is 1h,synthesis temperature is 70℃,synthesis time is 8h,drying temperature is 105℃.The results show that the CALN can effectively solidify chloride ions and form a stable chemical structure.In chloride environment,the weight loss rate of steel bar is 1/10 of the original.（2）Compared with the blank sample,the compressive strength increased by 21.9%when CALN was added to the cement at 3%.In the 0.5mol/L～0.7mol/L sodium chloride solution,its ability to solidify chloride ions is increased by 15.7%～25.2%.Its electric flux is reduced by27%.Based on the COMSOL simulation results,the diffusion depth of free chloride ions in concrete decreases when the concrete is mixed with CALN,regardless of the compressive stress state or tensile stress state.（3）In alkali activated materials,the compressive strength of alkali activated materials increases with the increase of CALN content.Among them,when the content of CALN is 4%,the compressive strength develops best,which is 47.64%higher than that of the blank sample.When the content of CALN is 4%,the chloride curing performance of alkali activated materials is not improved much.