Modification Of Mineral And Chemical Admixtures On Building Gypsum

Buiding gypsum is a kind of material with recycling utilization,environmental protection and energy-saving characteristics.It is one of research and development issues of building gypsum to improve the characteristics and reduce the cost by means of the modification of admixtures.This article focus on the effect of different mineral admixtures(fly ash,blast fumace-slag,cement and activator of calcium oxide)and different chemical admixtures(the water reducers:lignosulfonate MG, naphthalene sulfonate FDN,polycarboxylate KH;.the retarders:inorganic salt retarder NP,organic acid retarder CR,protein retarder GJ,organic sugar salt retarder PT)on the physical and working characteristics of building gypsum,and the miscibility between mineral admixtures and chemical admixtures in building gypsum was also studied, the course of its hydration and the modification mechanism were analyzed,the main achievements were listed as follows.1.The effect of mineral admixtures on the characteristics of building gypsumIn the three kinds of mineral admixtures-fly ash,blast furnace slag and cement, the activity of fly ash and blast furnace slag stimulated by gypsum was not so violence in 28 days.Adding cement in the cementitious material,the activity of fly ash in it would be enhanced,when added fly ash and blast furnace slag in building gypsum,they could prolong the setting time,but the cement would accelerate the setting time.For the fluidity,cement and blast furnace slag could enlarge it,but fly ash would decrease it.Adding activator in the compositely cementitious material of mineral admixtures and building gypsum,it could prolong the setting time and enlarge the fluidity,but it decreased the 3th's strength.To the volumetric stability of building gypsum,the influence of adding fly ash and cement was very little,but influence of activator was very heavy.Adding activator to the compositely cementitious material of fly ash, cement and building gypsum,it could make the volume violently expand.The change of volume expanding would happen in 20 days.2.The effect of chemical admixtures on the characteristics of building gypsumThe hydrate system which contained KH had the biggest fluidity,but its early fluidity was samll,next was the FDN,and its early fluidity was the biggest,the system which contained MG had the lest fluidity.MG had the most efficiency on the setting time of gypsum,next was the KH,FDN had no effect on the setting time.The more effect on the setting time,the longer time of fluidity would be maintained.In the range of 0.5%and 2.0%,when it was no change in the ratio of water and solid,the 28th-day's strength of building gypsum would decrease along with the content of water-reducing agent,and the hydrate system which contained FDN had the lest decrease in the strength.In the four retarders,CR was the best in prolonging the setting time of gypsum, next was the PT,again was the NP,the worst retarder on setting time was the GJ.To the 28th's strength of building gypsum,low content of GJ could increase it.when the content exceeded 0.10%,the strength of gypsum would decrease along with the increase of retarders,and the influence on strength for the retarders was opposite to the effect on setting time.Basing on the morphology of hydrating system,the better effect of chemical admixtures on the setting time,the bigger change would happen in the crystal morphology,and the ratio with diameter and length of crystal would increase.3.The effect of the miscibility between mineral admixtures and chemical admixtures on the characteristics of building gypsumTo the materials of compounding different mineral admixtures and different retarders in building gypsum,its 28th's strength that contained NP or CR would be increased with the adding of activator and cement,but to the strength that contained PT or GJ would be decreased with the adding of activator.Adding activator,it could prolong the setting time of all the materials.With the adding of activator and cement, it could make a relative increase in the setting time of the materials which contained CR.Activator could decrease the fluidity of the materials which contained PT,and FDN had no effect on the fluidity of materials containing GJ.The effect of compositely adding activator and retarders on the strength of building gypsum connected with the crystal morphology of dehydrate gypsum and the degree of fly ash stimulated.