Study On Activation Of Phosphorous Slag And Mechanism Of Its Retardation On Portland Cement

Phosphorous slag(PS) is used as raw materials which can reduced calcinedtemperature of clinker and improve property of clinker, and it also can be used asmixture of cement to improve its property. When PS is used as mixture of cement,there are two disadvantages , low early-strength and long setting time, which aremain reasons that handicap its utilization in cement industry. For better utilization ofPS, reduction of pollution of phosphorous industry and cutting down theenvironmental load of cement industry, we decide to study on how to improve theproperty of setting time and the early strength of phosphorous slag cement(PSC) bymechanical and chemical activation. By research, we know that sodium sulphate,calcined gypsum and calcined alunite can improve compressive strength of PSCabout 2~3MPa at 3 days and 3~5MPa at 28days, but sodium sulphate will harm thelatter strength of PSC and compound usage of these additves will not be better.Effect of man-made additive and calcined dickite using in PSC is good which canimprove compressive strength about 2MPa at 3days and 28days. Increasing specificsurface of PS can improve strength of PSC. The PSC with 341m2/kg PS at content of30% can reach P.O.42.5 level, but the PSC can reach the same level with 502m2/kgPS at content of 40%. The effect of compound usage of additive and mechanicalactivation will be better than that of only usage one of them. The PSC can reachP.O.52.5 level if calcined gypsum and 30% 502m2/kg PS are used. If the content ofPS reach 50%, the PSC can reach P.O.42.5 level yet. When calcinedgypsum(substituted all dihydrate gypsum) will be used ,the PSC can reach the samelevel of the PSC with calcined gypsum and 502m2/kg PS. Setting of portland cement can be retarded severely by PS, and main fact ofretardation is content of PS and its specific surface. The content is higher, the settingtime of cement is longer. When the content of PS in cement increases from 30% to50%, the setting time of PSC delays from about 100 min to about 400 min. And thespecific surface of PS is higher, the setting time of cement is longer too. The isetting time of cement with 502m2/kg PS is retarded about 60 to 100min than that ofcement with 341m2/kg PS at the same content. Additves can improve the property ofsetting time, and sodium sulphate and additve whose main mineral is C4A3 S arebetter than calcined gypsum and calcined alunite when they are used to improve theproperty of setting time of PSC. By study on the mechanism of retardation of PS, we know that absorption of PSby half-permeation film produced at early time during hydration, which results inhard pervasion by water and other ions, so it retard hydration of cement and settingtime is elongated finally. The process of absorption is that P and F in PS are liberatedby Ca(OH)2 produced during hydration of cement, then P will producehydroxyapatite which deposits on the surface of hydration production by absorptionand F will produce CaF2 which combines with hydration by hydrogen bond. We also study on the influence of additves on pore structure, chemicallycombined water and hydration production of hardened paste of PSC. Additives candecrease total porosity of hardened paste of PSC and improve pore diameterdistribution which is reduction of harmful pore whose pore diameter is above 100nmand increase of gel pore whose pore diameter is low 50nm, but sodium sulphate willinduce increase of total porosity at 28days. The relation between total porosity andcompressive strength agrees to Rhyshkewitch equation by mathematically fitted.Sodium sulphate can accelerate depolymerization of PS while calcined gypsum andcalcined alunite can reduce to produce more AFt by research on SEM photoes ofhardened paste of PSC. Additives can increase content of chemically combinedwater of hardened paste of PSC, but effects of additives are different. Both calcined...