Effect of admixture on hydration of cement, adsorptive behavior of admixture and fluidity and setting of fresh cement paste

The adsorptive behavior of admixtures and the hydration of cement in the presence of admixtures were examined and the relationships of them with the physical properties of fresh cement paste including fluidity, variation of fluidity with time and setting time were discussed with the quantitative determination of organic admixture adsorbed on the cement, and with the observation and determination of the surface microstructure and composition of polished clinker dipped in aqueous solution containing a specified quantity of admixture by advanced method of surface analysis. In order to prepare the same fluidity of fresh cement paste, mortar and concrete, the required amount of an easily adsorbed admixture is larger than that of a hard adsorbed one. An admixture having a functional group producing a complex salt with Ca2+ decreases the concentration of Ca2+ in liquid phase at early age and delays the saturation of Ca2+, which influences the morphology of hydrate produced, causes fluidity loss with time and delays the setting time of cement. The microstructural and compositional estimations of the adsorption layer of admixture on the surface of clinker minerals by in-lens FESEM, ESCA-imaging, AES and AFM indicates that the admixture is partially adsorbed to the interstitial phase in a thick layer, forming characteristic three dimensional surface structure.