| Belite-calcium barium sulphoaluminate (C2.75B1.25A $)cement is one type of cement characterized saving resources, energy and environment friendly. Therefore, it is very important to realize its industrial production and application. This paper mainly investigates the adaptability of industrial waste gypsum to be as retarderofbelite- C2.75B1.25A $ cement, also the influence mechanism of early strength agent and water reducing agent on belite-C2.75B1.25A $ were discussed in order to improve its performance. This would lay foundation for its engineering application. The major conclusions were list as following.Industrial waste gypsum(citro-, phosphor- and FGD gypsum) can replace natural gypsum to be as the retarder of belite-C2.75B1.25A $ cement and their appropriate dosage of citro-phosphor-and FGD gypsum in cement was 13%,15% and 15%. At the same time, the early strength of cement with industrial waste gypsum is equivalent to cement with natural gyp sum The late strength of cement is prior to cement with natural gyp sum In addition, the soundness of cement with industrial waste gypsum is good. At the condition of equivalent SO3, the hydration rate of cement with citrogypsum is fast due to its fast dissolution rate. The initial hydration rate of cement with citrogypsum is about two times of the cement with other waste gypsum. The impurity in industrial waste gypsum has big effect on the setting time and hydration process of cement. Small amount of soluble phosphate in phosphogypsumcan form insoluble mineral covering the surface of cement particle. This resulted in delaying the hydration process of cement. The citric acid in citrogypsum can r decrease the alkalinity of the system to promote the hydration of cement.Na2SO4, Ca(NO3)2 and Ca(HCOO)2 can be used as the early strength agent of belite-C2.75B1.24A $ cement. Their appropriate addition content in cement is 0.5%,0.5% and 2.0%, respectively. Meanwhile, the 3d strength of the cement increases by 13.2%,18.2% and 20.9%, respectively. The addition of Na2SO4 generated much secondary gypsum, which is contributed to the formation of AFt; The reason of Ca(NO3)2 mainly increase the ion concentration of the hydration of cement, promoting its hydration reaction; Due to the characteristic of Ca(HCOO)2, which can promote the formation of AFt and hydration of silicate phase; Although TEA can promote the formation of the AFt, but also inhibit the hydration of silicate minerals, so it is not suitable for used as early strength agent of the cement.Polycarboxylic acid, naphthalene series, aliphatic and composite water reducing agent can be used as water reducing agent for belite- C2.75B1.25A $ cement, and their appropriate content are 1.2%,2.0%,2.0% and 1.2%, respectively, along with the corresponding fluidity of paste is 258 mm,282 mm,285 mm and 289 mm. Compared with OPC, the best dosage of all types of water reducing agent in cement is larger. The time loss of cement with polycarboxylic acid is small, but the others are relative bigger. The water reducing agent adsorbing on surface of cement particles could chang the potential of particles and reduce the interaction between particles, which would decrease the slurry viscosity. The water reducing agent could inhibit the early hydration of silicate minerals, but does not affect the late strength of cement. The water reducing agent can meet the need of common projects and the effect of polycarboxylic acid is the best.The erosion of sulphate and chloride ion resistance in belite-calcium barium sulphoaluminate cement is weaker than that in sulphur aluminate cement, but which is far more than that in ordinary Portland cement. Compared with ordinary Portland cement, the Ca/Si and Ca(OH)2 growth orientation of ITZ in belite- C2.75B1.2sA $ cement sample is smaller. |
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