China's anhydrite resources are mainly anhydrite,with high grade and wide distribution,and its reserves rank first in the world,reaching 30 billion tons.The solubility of anhydrite is greater than that of dihydrate gypsum,and its hydration reaction is a thermodynamic spontaneous process,that is,
anhydrite has gelation.However,the anhydrite structure is dense,which is slow to dissolve and low in hydration activity.Activation is the key to the effectiveness of anhydrite resource.At home and abroad,a wide range of studies have been carried out on the active excitation of anhydrite.The use of an activator is the most effective way to improve the hydration activity of anhydrite.It has systematically studied the influence of activator on the dissolution rate,hydration rate and hardening body.Sulfate has a significant catalytic effect on the hydration of anhydrite,and it is a high-efficiency activator of anhydrite.An anhydrite cement with a strength superior to that of a building gypsum can be formulated by sulphate excitation.
Natural anhydrite has hydration gelation ability,but the hardening condensation is very slow.The initial condensation time is as long as 26h20min and 33h5min.The hydration process is slow and the hydration rate is low,and the hydration rate is less than 1% at 8h,and the 28d hydration rate is only 33.8%.Sulfate shortens the setting time of anhydrite and increases the hydration rate.Na2SO4 has the best excitation effect,followed by KAl(SO4)2·12H2O. 2% Na2SO4 shortened the initial setting time of anhydrite to 3h18min and 4h11min.Sulfate significantly increases the hydration rate of anhydrite,and the stimulating effect on the early hydration of anhydrite is particularly remarkable.The anhydrite hydration is an exothermic reaction.Under adiabatic conditions,as the anhydrite hydration progresses,the temperature of the system will continuously increase.Therefore,the hydration temperature rise can understand the hydration process of anhydrite from another angle.The hydration temperature rise curve shows that the anhydrite hydration is very slow,and the temperature rise in the early stage of hydration is mainly due to the dissolution of anhydrite.After a long period of temperature rise platform,it indicates that the anhydrite hydration enters the incubation period and hydrates.The rate is very low.After 8h,the hydration temperature increases slowly,and the anhydrite hydration gradually develops.Sulfate greatly shortens the hydration latency of anhydrite,and the anhydrite quickly enters the accelerated period of hydration after dissolution.With the formation of hydration products and the increase of hydration heat,the hydration temperature increases,and hydrated with 2% sodium sulfate anhydrite.The hydration temperature rise of 3~4h is equivalent to the temperature rise of blank anhydrite hydration for 35h.
Sulfate has a significant stimulating effect on the hydration of anhydrite,which improves the hydration activity of anhydrite and accelerates the hydration process of anhydrite.
