Effects and mechanism of anhydrite AⅢ on the performance of β-hemihydrate gypsum
Zheng Shaocong , Yu Qiang , Ning Ping , Ma Jinbo , Tian Lin , Zheng Yuanli
DOI:
Received March 25, 2015,Revised , Accepted , Available online January 05, 2016
Volume ,2015,Pages 118-124
- Abstract
The β-hemihydrate gypsum was prepared from phosphogypsum and the effects of the soluble anhydrous AⅢ were investigated. The Conventional analytical methods, TG-DSC, XRD and SEM were used to analyze and characterize the β-hemihydrate gypsum and their products. The thermal analysis results showed that two endothermic peaks in the phosphogypsum dehydration reaction, and those two peaks overlapped partly.The difference between the two peaks was only 6 ℃, which indicated that the dehydration reaction included two steps of different reactions and the β-hemihydrate gypsum existed as mixed phase structure. The optimal conditions for β-hemihydrate gypsum calcinations were 170±5℃ for 2 hours. The content of the crystal water in β-hemihydrate gypsum was about 3.0%. The properties of the gypsum powder could be improved if the content of the crystal water content changed in range of 4.8~5.2% through aging process. The highly activity and fast hydration rate of AⅢ offset the effect of the water reducing agents during the hydration of β-hemihydrate gypsum indication that AⅢ affects the performance of β-hemihydrate gypsum. The addition of water reducing agents could improve the strength of gypsum products. When 0.7% HC polycarboxylate was added, the strength of β-hemihydrate gypsumcan reached to 15.0 MPa, nearly an increase of 64.84%. When 0.7% superplasticizer-FDN was added, the strength reached to 14.8 MPa, nearly an increase of 62.64%, and when 0.7% lignin was added, the strength increased nearly by 52.75% to 13.9 MPa.