Study On Mechanism Of Bingding Chloride Ion In Alkali-Activated Slag

As a new environmentally-friendly building material,alkali-activated cementitious materials can not only solve the problem of resource utilization of industrial solid waste reasonably,but also save a lot of energy consumption.Alkali-activated slag is the most widely used one in alkali-activated cementitious materials and has some advantages.For example,the simple manufacturing process,excellent performance,strong durability,good heat resistance and good hydration heat.It also has significant economic and social benefits.However,there is still no systematic theoretical result on the performance and mechanism of various alkali-activated slag for binding chloride ions in the relevant fields.A lot of in-depth research is needed.The work of this thesis mainly focuses on the binding performance and mechanism of chloride ions influenced by alkali-activated cementitious materials,which are dominated by slag and the main hydration products C-S-H and C-A-S-H.We explored the four most common activators,sodium hydroxide,water glass,sodium carbonate and sodium sulfate Ordinary Portland Cement was added for comparison.Acid dissolution method and equilibrium method are chosen to reciprocally verify the influence of factors such as alkali equivalent,soaking chloride solution concentration,gelation material etc.In this way,the performance of binding chloride ions in the alkali-activated slag under different factors is explored;X-ray diffraction analysis?XRD?,Fourier Transform Infrared Spectroscopy?FT-IR?,comprehensive thermal analysis?DSC/TG?,Scanning Electron Microscopy?SEM?and Nuclear Magnetic Resonance?NMR?are used to study the microstructure and hydration products of alkali-activated slag at the microscopic level,aiming to reveal the combination rule of alkali-activated slag and chloride ions.The main results are as follows:?1?Under the same concentration of soaking solution and alkali equivalent,the chloride ion binding capacity of slag activated by four kinds of activators and ordinary Portland cement is:Ordinary Portland Cement>sodium hydroxide activated slag>water glass activated slag>sodium carbonate activated slag>sodium sulfate activated slag.Moreover,the amount of chloride ion bound by the above alkali-activated slag increases as the concentration of the soaking solution.?2?In the case of the same alkali equivalent,the chloride ion binding capacity of sodium hydroxide-activated slag is stronger than that of water glass.And as the alkali equivalent increases,the chloride ion binding capacity of the slag activated by the two activators both increases.?3?In the case of the same kind of activator,the chloride ion binding capacity of water glass activated fly ash is better than that of water glass activated slag.And with the increase of alkali equivalent,the binding capacity of various gelling materials has a corresponding improvement?4?In the net pulp block maintained in a standard environment for 28 days,microscopic analysis revealed that the main hydration products of alkali-activated slag and Ordinary Portland Cement contain calcium silicate hydrate but not calcium hydroxide.C-A-S-H and C-A-H also appear in the sodium hydroxide activated slag.Ettringite and calcium sulphate appear in the sodium sulfate activated slag.After the chloride salt attack,the water glass activated slag and sodium carbonate activated slag of slag do not appear new products.In the Ordinary Portland Cement and sodium hydroxide activated slag,hydrated calcium chloroaluminate?C₃A·CaCl₂·10H₂O?appears,ie Friedel salt.Rusrumite appears in the sodium sulfate activated slag.It is indicated that the binding mechanism of sodium hydroxide activated slag,sodium sulfate activated slag and Ordinary Portland Cement contains physical adsorption and chemical bonding,while the binding mechanism of sodium carbonate activated slag and water glass activated slag is mainly physical adsorption.?5?The main hydration products of alkali-activated slag C-?A?-S-H is mainly physical adsorption for the binding of chloride ion.The structure and chloride ion adsorption capacity are greatly affected by the ratios of calcium to silicon and aluminum to silicon.The chloride ion adsorption capacity is the strongest when the ratio of calcium to silicon is between 1.2and 1.5.When the ratio of calcium to silicon is constant,the higher the ratio of aluminum to silicon,the lower the ability to adsorb chloride ions.