This study investigated the effects of a common superplasticizer, ligno-sulfonate, on the hydration of Portland cement Type V. Samples of plain cement and superplasticizer-treated cement have been examined by x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Lignosulfonate has been observed to retard the hydration of cement through specific surface chemical reactions which involve Ca2+ions in pore solution. The admixture has been found to retard the formation of Ca(OH)2and stabilize ettringite [Ca6(Al22O6)(SO4)3.32H2O]. The inhibition of the rate of conversion of ettringite to monosulfate [Ca4Al2(OH)12.SO4.6H2O] is attributed to charge-controlled reactions caused by large quantities of Ca2+ions from initial hydration reactions. Leaching of the admixture doped cement by water-removed lignosulfonate and caused complete hydration of cement. A charge-controlled-reaction model involving the Ca2+ions is proposed to explain the role of the admixtures during hydration of cement.