| As one of the concrete admixtures, polycarboxylate-type superplasticizer is widelyused in concrete project and exhibited excellent water reducing performance. However,sulfate of cement and composite materials may cause incompatibility betweensuperplasticizer and concrete raw materials, which have negative effect on the dispersityof superplasticizer. Sulfate was recognized as one of the most obvious factors affectingthe dispersity of superplasticizer, but the impact on its dispersion mechanism is not clearenoughThe paper investigates the effect of Na2SO4and CaSO4·2H2O on the fluidity ofcement paste and divergence of mortar with superplasticizers of different molecularweight. The paper studies the effect of sulfate on the adsorption layer thickness, stericconformation, hydration diameter, aggregation behavior, cloud point and adsorptionamount of superplasticizers. In order to have an insight into the influence of sulfate onthe adsorption and dispersion behavior of superplasticizer, effect of sulfate on the zetapotential of calcium silicate hydrate and concentration of ionic dissolution were alsostudied.By measuring the effect of sulfate on fluidity of cement paste and extension ofcement mortar, a conclusion can be drawn that sulfates have negative effect on the waterreducing performance of superplasticizer. Compared with CaSO4·2H2O, Na2SO4displayed a more pronounced negative effect on dispersity of superplasticizer. What’smore, superplasticizers with larger side chain molecular weight are more sensitive tosulfates.With the help of X-ray photoelectron spectroscopy, fluorescence spectra,nano-particle analyzer, the adsorption layer thickness, chain conformation, aggregationbehavior, hydration diameter, cloud point and change of micro-structure ofsuperplasticizer were investigated. The results indicate that sulfates not only reduce theadsorption layer thickness of superplasticizer notablely, but also affect the stericconformation of superplasticizer. Compared with CaSO4·2H2O, Na2SO4shows moreremarkable influence on the conformation change of superplasticizer. Sulfate lower thecloud point of superplasticier by salting out effect, and changes of micro-structure ofsuperplasticizer as well, which causes the collapse of conformation. Sulfate have littleinfluence on the hydration diameter of superplasticizer. With the aid of total organic carbon analyzer, ultraviolet spectrum, nano particleand zeta potentiometer, atomic absorption spectrum, influence of sulfate on theelectrostatic repulsion and adsorption capacity of superplasticizer were studied. Theresult manifests that the competitive adsorption between sulfate and superplasticizer, theaggregation behavior of superplasticizer and the increase of Ca2+that dissolved are themechanism of effect of sulfate on the dispersity of superplasticizer. Sulfates alsodecrease the electrostatic repulsion effect of superplasticizer by condensing theelectrical double layer on the surface of the particles. Compared with CaSO4·2H2O,Na2SO4reduces the electrostatic repulsion of superplasticizer more remarkable. |
