Effect Of NH₄HSO₄ From Denitrified Fly Ash On Cement Performance And Its Control

The coal-fired power plants have basically completed the transformation of denitration in China,and the traditional fly ash has been basically replaced by denitration fly ash.There are a series of engineering problems in the application of denitration fly ash in cement concrete,which hinder the resource utilization of denitration fly ash.The existence of denitration by-product ammonium bisulfate is the main reason for the frequent problems in the resource utilization of denitration fly ash building materials.At the same time,ammonium bisulfate as a kind of sulfate,the biggest difference between ammonium bisulfate and alkali metal sulfate is that it contains NH₄⁺which will produce ammonia release in alkaline environment.In the presence of the same mole number of sulfate,ammonia will be released The effect of air release process on the hydration and hardening properties of cement fly ash system is also unknown.Therefore,by using the simulation method of adding ammonium bisulfate,based on the systematic study of the influence of denitration fly ash with different ammonia content on the main performance of cement fly ash system,this paper controls a single variable to carry out the influence of denitration fly ash with different sulfate on the hydration and hardening performance of cement fly ash system.Finally,from the perspective of engineering application,the treatment effect of different control measures for denitration fly ash is compared.The results show that:（1）the content of ammonia in the range of 0-5000mg/kg,with the increase of ammonia content of denitrification fly ash,the fluidity of cement fly ash system decreases,the water consumption of standard consistency increases,the setting time is prolonged,the mechanical properties are reduced,the drying shrinkage increases,the porosity of cement fly ash system increases,and the number of large pores increases;（2）hydrogen sulfate with the same mole number as ammonium hydroxide The influence of sodium and sodium sulfate on the flow and standard consistency water consumption of cement fly ash system is not obvious.Sodium sulfate can reduce the setting time of cement fly ash system,and significantly increase the strength of 1 day and 3D,but it will reduce the strength of 7d and 28d,and the dry shrinkage of the slurry is the largest.The results show that the strength of the composite system is 1 day and 3D,but the increase is lower than that of sodium sulfate,and the dry shrinkage of the composite system is increased,but the increase is lower than that of sodium sulfate and ammonium hydrogen sulfate.（3）Sodium sulfate can increase the peak value of hydration heat release and increase the total heat release of cement fly ash system.Both ammonium hydrogen sulfate and sodium bisulfate will reduce the peak of hydration heat release,delay the time of peak heat release,and the total heat release will decrease first and then increase,but the influence of sodium bisulfate is between ammonia sulfate and sodium sulfate.The production of calcium hydroxide in the first day age decreased due to the introduction of H⁺;（4）the comparative study in Chapter 4shows that the adverse effect of ammonium hydroxide on cement fly ash system mainly comes from NH₄⁺;5)the high temperature burning method can significantly reduce the ammonia content of denitrification coal ash,but the strength activity index of fly ash decreases after the temperature is higher than 345℃.The ammonia content of denitrification fly ash can be reduced and its strength activity index can be improved by adding alkali and adding water（oven heating+frying）and constant temperature and humidity method.The processing time of stir frying method is short,energy consumption is low,and the effect is better than other methods.（6）The increase of mixing water temperature and the longer mixing time will lead to the acceleration of ammonia release and decrease of ammonia content in the slurry.When the temperature of mixed water is higher than 30℃,the ammonia gas is released too fast,and the compressive strength of cement fly ash system decreases obviously.