Adsorption Of Sulfate And Chloride Ions By Sepiolite And Its Application

Structural concrete in the marine environment not only suffers damage from loads,but is also corroded by the external environment,damaging the concrete structure.Corrosion damage to concrete structures by the marine environment has exacerbated the deterioration of sea defence engineering damage,not only increasing the maintenance costs of buildings,but also seriously affecting their long-term safe service performance.Therefore,how to improve the corrosion resistance of modern structural concrete,to provide a guarantee of its safe service has become an urgent problem to be solved.The use of special properties of mineral materials to improve the overall service performance of cementitious materials,not only to play the advantages of diversified applications of mineral materials,but also to promote the performance of structural concrete,is the current research trend.As an excellent functional mineral material,Sepiolite has unique advantages in adsorption and has important applications in heavy metal adsorption,but the systematic study of the performance of cementitious materials against sulphate and chloride salt erosion in the context of marine environment has not yet been reported and is the focus of this thesis.The research in this thesis may provide fundamental data and methods for the performance enhancement of concrete for offshore structures.Firstly,the effect and mechanism of physical modification methods on Sepiolite in terms of chloride and sulphate adsorption were investigated.The results show that physically modified Sepiolite has a good promotion effect on both chloride ions and sulphate.Among them,the best effect was achieved by the combined effect of ball milling and calcination;the effect of ball milling alone was relatively poor.The adsorption values were enhanced by 0.4 mg/g and 1.2 mg/g,respectively,compared to the original Sepiolite for them.The adsorption characteristics of Sepiolite were analysed by scanning electron microscopy SEM,BET nitrogen adsorption,X-ray diffractometry and density flooding theory.The results showed that the surface of the modified Sepiolite was relatively smooth and the particle size became shorter in the length direction;the intensity of the IR characteristic peak was slightly increased,and the specific surface area and pore volume were significantly increased.At the same time,the effects and mechanisms of CTAB(cetyltrimethylammonium bromide)modified Sepiolite and ferrous ammonium sulphate modified Sepiolite on the adsorption of chloride ions and sulphate were investigated.The results showed that the adsorption effect was relatively better with the synergistic modification of ferrous ammonium sulphate and CTAB,with ferrous ammonium sulphate alone and CTAB modified being the second most effective,being 1.7 times,1.6 times and 1.5 times higher than the adsorption of the original Sepiolite,respectively.The optimum adsorption sites and mechanism of CTAB on chloride and sulfate were investigated.The results show that the surface morphology of the modified Sepiolite is more "defective",the pore size is larger and the pore volume is significantly increased,and the electronegativity of the Sepiolite is changed.The BET study showed that the pore structure of the modified Sepiolite had been partially intercalated with CTAB and ferrous ammonium sulphate.On the basis of the above studies,inorganic coatings containing Sepiolite in different working conditions were prepared and systematically investigated to characterise the coatings on structural concrete in terms of durability,including the resistance to penetration,freeze-thaw damage and carbonation erosion of the coated concrete.The results of the study show that:(1)The incorporation of different modified Sepiolite into the inorganic coating improved the concrete’s resistance to chloride salts to a greater extent than that of unincorporated Sepiolite.Ammonium ferrous sulphate modified and CTAB synergistically modified Sepiolite coatings significantly improved the resistance of concrete to Cl-penetration by about 10%with their highly dense properties;(2)The microstructure of the inorganic coating infused with modified Sepiolite maintains a fibrous state in the coating,and the gel tissues such as hydrated calcium silicate and calcium alumina formed during the hydration of cement are bonded or wrapped around the surface of Sepiolite fibres,enhancing the bonding performance of the inorganic coating at the concrete interface;(3)The modified Sepiolite mixed into the inorganic coating significantly enhanced the carbonation resistance of the concrete.ctab-modified Sepiolite and ferrous ammonium sulphate plus ctab-modified Sepiolite had stronger carbonation resistance compared with other modifications.Through systematic research,the adsorption patterns of different modified Sepiolite on sulphate and chloride ions were initially obtained,and their mechanism of action was clarified.On this basis,the influence law of Sepiolite-containing coatings on the durability of structural concrete was prepared,providing basic data and methods for the improvement of the performance of marine structural concrete.