Controlling of the adsorption and dispersing force of polycarboxylate-type superplasticizer by sulfate ion concentration in aqueous phase

The dispersing force of polycarboxylate-type superplasticizer (PC) with poly(ethyleneoxide) (PEO) graft chain has been known to degrade by the sulfate ion in the aqueous phase of concrete. Alkaline sulfate contents and calcium sulfates in cement, mixing temperature and time elapsed after mixing, and other various material characteristics as well as environmental conditions affect the sulfate ion concentration. Therefore, it is generally Very difficult to keep the sulfate ion concentration constant. In this study, the active control of the sulfate ion concentration in aqueous phase by adding soluble salts containing multiple-charged cations, such as CaCl2 and alkaline sulfate, has been attempted. The adsorption of PC is able to be controlled by adding salts such as CaCl2 and Na2SO4. The change of the PC adsorption ratio results directly in the variation of the dispersing force of superplasticizer. It is also indicated that ionic strength in the aqueous phase affects the dispersing force of PC. The dispersing force degrades with the increase in ionic strength and sulfate ion concentration. (C) 2001 Elsevier Science Ltd. All rights reserved.