Research On The Rheological Properties Of Fresh Gypsum Paste And Plaster

The output of gypsum plaster had been rising in China in recent years.With the application of gypsum mortar,different types of calcined gypsum from industrial by-product was also used in the preparation of gypsum plaster.Due to the unstable performance of raw materials prepared by industrial by-products,the performance of gypsum plaster also fluctuated,which increased the difficulty of quality control for gypsum plaster manufacturer and construction enterprises.The performance of gypsum plaster related to its rheological properties.But there were no unified research method and test method for the rheological properties of gypsum plaster,and the suitable range of rheological parameters of fresh gypsum plaster was not clear,so the rheological properties of fresh gypsum plaster could not be controlled according to the properties of the raw materials.As the problem of the rheological properties testing and characterization methods of fresh gypsum paste and plaster were not unified standards,the effects of wall slip,initial test time,maximum shear rate and protein type retarder on rheological properties of fresh gypsum paste and plaster were studied and the rheological parameters from different rheological models were also analyzed comparatively.In view of the prediction and regulation of the rheological properties of the new gypsum paste,the effects of building gypsum,aggregate and cellulose ether on the rheological properties of the new gypsum paste were studied,and the relationship between the rheological parameters of the new gypsum mortar and the application effect was compared and analyzed.The results showed that the effect of the roughening of the test barrel and the propeller rotor could reduce the effect of the wall slip on the test results.When the maximum shear rate was 300s-1,the rheological curve of fresh gypsum paste and plaster could be fully tested.0.1%protein could guarantee the completion of the rheological test without affecting the rheological properties of fresh gypsum paste and plaster,but the impurities in the gypsum would affect the retarding effect of the protein retarder.It was found that HPO42-would react with the amide II band of the secondary amide of protein retarder,so the calcined gyprum from phosphogypsum containing phosphate impurities was suitable for the protein retarder with primary amide as the main component.The results of the analysis and prediction of the rheological properties of fresh gypsum paste and plaster showed that the rheological curves of fresh gypsum paste and plaster were more suitable for the Hershel-Bulkley model,and the critical apparent viscosity and yield stress related to the properties of the raw materials were considered as the characterization parameters of the rheological properties of fresh gypsum paste and plaster.The yield stress of fresh gypsum paste and plaster should be fitted by Bingham model from the Os-1 section of the shear rate to the rheological data of the critical shear rate.The critical apparent viscosity of fresh gypsum paste was predicted by the absolute density of the calcined gypsum,and the relationship between the median radius of the calcined gypsum and the yield stress of fresh gypsum paste was established.The critical apparent viscosity and yield stress of fresh gypsum plaster could be superimposed by the influence of single and particle size aggregate on the rheological parameters of fresh gypsum paste.Based on the relative concept,it was found that the critical apparent viscosity and yield stress of fresh gypsum plaster could be predicted by the critical apparent viscosity and yield stress of fresh gypsum paste,and the yield stress of fresh gypsum plaster was predicted based on the thickness ratio of the slurry(Dd).At the same time,the effect of cellulose ether on the critical apparent viscosity and yield stress of fresh gypsum paste and plaster was mainly related to its concentration.The critical apparent viscosity and yield stress of fresh gypsum plaster with cellulose ether could be calculated by superimposing the variation amount of critical apparent viscosity(??crit)and the variation of yield stress(??crit)related to the concentration of cellulose ether.The prediction equations of critical apparent viscosity(?p)and yield stress(?p)for fresh gypsum paste were:(?)The prediction equations of critical apparent viscosity(?s)and yield stress(?s)for fresh gypsum plaster were:(?)The prediction equations of critical apparent viscosity(?c)and yield stress(?c)for fresh gypsum paste and plaster with cellulose ether were:?c=?+ ?crit?c = ? + ??critThe results of the range of selection and regulation of rheological parameters showed that the suitable rheological parameters of fresh gypsum plaster were,HB-n coeflicient from 0.9 to 1.0,yield stress from 80 to 130Pa,critical apparent viscosity from 1.1 to 1.5Pa·s,thixotropy from 20000 to 35000.The critical apparent viscosity and yield stress of fresh gypsum plaster could be controlled by its prediction equation and the properties and proportions of raw materials.The research results not only provided a set of quantitative and operable quality control methods for the production and construction enterprises of gypsum plaster,but also established a theoretical system for predicting critical apparent viscosity and yield stress of fresh gypsum paste and plaster and laid a theoretical foundation for the design of the rheological properties of the slurry.