Impact And Mechanism Of Superplasticizer And Retarder On The Performance Of α-hemihydrate Desulfurization Gypsum

The strength of high-strength gypsum (ie, α-semi-aquatic gypsum) is much higherthan physical strength gypsum（ie, β-semi-aquatic gypsum）, so its has a more wider use.The high-strength semi-water FGD gypsum produced by the flue gas desulfurizationFGD gypsum preparation is an effective way. Although the intensity of high-strengthgypsum plaster is higher than normal, but it is also need more water than the actual, andit has a very short setting time. Mixing in the admixture of high-strength gypsum plasterwas modified to be an effective solution to the above problem of high-strength gypsum.As for the high-strength gypsum admixture lack theoretical guidance in the applicationof high-strength gypsum, we can’t choose a suitable additive, so that the admixture can’tplay its due role.Superplasticizer can significantly reduce the gypsum hydration water demand, andsignificantly improve the strength of high strength gypsum oven dry. Shows theinfluence of superplasticizer dosage on the performance of gypsum, the FDN bestcontent is1.0%, the best content of the HC0.6%. Superplasticizer gypsum hydrationprocess and hydration products generally will not have an impact, but will reduce thewater of hydration, and improve the pore structure of gypsum, and other factors tosignificantly improve the plaster strength. Naphthalene superplasticizer increase theresistance between the gypsum particles by electrostatic repulsion of the ζ potential toplay a water-reducing effect. However, with the hydration of gypsum, the hydrationproducts will be attached to the gypsum particles of gypsum crystals between theelectrostatic repulsion shielded its effect rapidly reduced, resulting in loss of gypsumflow through. Polycarboxylate superplasticizer has a branched chain structure, in theplaster surface dressing adsorption, the space between the branched-chain resistance andsynergy with electrostatic repulsion, to play its role of water reduction. As the sterichindrance not affected by hydration, the dispersion is better than the naphthalenesuperplasticizer by loss.Retarders delay the hydration induction period, an postpone the time of hydratiomheat peak. Retarders decrease the early-stage hydration rate of high strength gypsum, byinhibiting the dissolution and crystallization of gypsum, but have no effect on the finalhydration rate hardly. Retarder reducing the cementitious binder liquid saturation,especially early hydration degree of supersaturation to coarsening of crystal and weakening of the matting together, resulting in decreasing of strength of hardenedgypsum paste. Different mechanism of action of the retarder are also differences incalcium in citric acid with gypsum solution (111) of the gypsum nucleation complex,the formation of the chemisorption layer inhibit nuclei growth, slow down the hydrationof gypsum. Calcium phosphate and other inorganic retarder and gypsum in the liquidphase in the surface of hemihydrate gypsum and nuclei network synthesis insoluble salt,the crystal surface coated with gypsum crystals inhibition of early hydration of thegypsum...