Study On Activation Of Natural Anhydrite And Its Hydration And Hardening Characteristics

Chinese resource storage capacity of natural anhydrite is number one in world, and it reach 300 hundred million tons.Solubility of anhydrite is greater than gypsum, and its hydration reaction is thermodynamics autogenitc process, and have potential jilling property.But its structure is densify, and solution is slow, and hydration activity is very low, so its utilization ratio and utilization level are very low.Activity excitation is key of utilization of anhydrite. In this paper, four technic paths of milling, calcinatin, excitant, and inorganic active materials are used to excite active of anhydrite. By rating hydration ratio, hydrated temperature, ion concentration, degree of supersaturation of gypsum, fineness of powder, normal consistency, setting time, intensity, micro structure, linear expansion ratio and so on, activation of natural anhydrite and its hydration and hardening characteristics are studied.After milling, particle of anhydrite is finer, and contact area increasing, and solution is accelerated, and hydration latent phase is shortening, and its propriety fineness is in 4000～6000cm2·g-1; Grinding aid is well to pulverise, and could improvement particle pattern. The proper dosage of FDN is 0.5%, and The proper dosage of K2SO4 is 1%.Gypsum in anhydrite break down into semi-hydrated gypsum after calcination at 150℃. Structure of anhydrite is looseness, and proper of milling and fineness increase, and mean size is diminution. Semi-hydrated gypsum have high hydrated activity, and it is able to hydrate immediately to generate gypsum. It has seed crystal induction effect to hydration of anhydrite, and crystals nucleating and growing rate are accelerated. Excitant is effective path to increase hydrated activity of anhydrite. Sulfate excitant increase hydration process and concentration of SO42- and supersaturation degree of gypsum, and crystals nucleating and growing rate of gypsum are accelerated. Its size of crystal is refinement, and density of hardenite is increased. Sulfate excitant is better than alkalinity excitant, Na2C2O4 is highly active excitant, and it able to react with anhydrite to formate CaC2O4 and soluble sulfate. Concentration of SO42- is increased and hydration of anhydrite is accelerated. Compound excitant have different effect to anhydrite, and 3% calcinated alum and 1% sodium sulfate mixture is highly active excitant.Afer the inorganic active materials such as slag , clinker and so on being doped in anhydrite, hydration of slag , clinker and anhydrite are mutual promote, and hydraulicity mineral such as ettringite, hydrated calcium silicate and so on formatted. Its hydration latent phase is shortening, and hydration process and density of hardenite are increased, and linear expansion ratio is reduced, and resistance to water is increased.The research supply supporting technology to utilize anhydrite resource rationally and develop building energy-saving product, and it will guide utilization of anhydrite and develop new style jilling materials.