复合外加剂改性盐石膏的研究

盐石膏的主要成分为无水硫酸钙,其活性差、凝结硬化慢、强度低,需要添加活性剂来激发盐石膏的活性。通过复合外加剂对盐石膏加以改性,并通过XRD和SEM对其作用机理做了分析。结果表明,单掺脱硫石膏和建筑石膏均能缩短盐石膏的凝结时间,建筑石膏的效果较好,但掺量不宜过高。复掺建筑石膏和缓凝剂时,两者比例要控制得当,适宜的建筑石膏和缓凝剂掺量分别为50%和0.10%~0.12%（质量分数）。分析可知,大掺量建筑石膏会增加盐石膏硬化体中二水相和针棒状晶体的含量;缓凝剂掺量的增加,会降低盐石膏硬化体中二水相的含量,棱形晶体增多,从而降低了盐石膏的强度。

Study on composite admixtures modified salt gypsum

Salt gypsum is a waste residue produced in the salt industry.The main component of salt-gypsum is anhydrous cal-cium sulfate.It is necessary to add active agent to stimulate the activity of salt gypsum for its poor activity,slow setting and hardening rate,and low strength.The salt gypsum is modified by composite admixtures and its action mechanism is analyzed by XRD and SEM.The results showed that the single-doped flue gas desulfurization（FGD） gypsum or plaster of Paris could both shorten the setting time and increase the strength of salt gypsum,and the effect of plaster of Paris was better,but the dosage should not be too high.The addition of retarder could retard the setting time and decrease the strength of plaster,thus the amount of retarder should be appropriate as well.When the plaster of Paris and retarder were mixed,the ratio of them should be properly controlled and the suitable dosages of plaster of Paris and retarder were 50%（mass fraction,same as blow） and 0.10%~0.12%,respectively.The analysis showed that the high content of plaster of Paris will increase the amount of the dihydrate phase and the needle and bar crystals in the hardened salt gypsum;the increase of the retarder content will reduce the amount of the dihydrate phase in the hardened body of the salt gypsum,and the prismatic crystals will increase as well,thus reducing the strength of salt gypsum.