The chemical environment of barium in Portland cement which is doped with barium nitrate was investigated using x‐ray photoelectron spectroscopy (XPS) and Fourier Transform Infrared spectroscopy (FTIR). The barium-doped cement showed tremendous increases in carbonate content over the undoped cement. An XPS sulfate signal was observed in the cement doped with 20% w/w Ba(NO3)2 but not in the 0 and 10% w/w doped cement. FTIR and XPS results lead us to believe that the barium exists as both BaSO4 and BaCO3 in the cement matrix.
Ettringite formation was also suppressed, with setting times prolonged, in proportion to the amount of BaCO 3 added. The addition of barium as a soluble salt, such as barium nitrate, also resulted in the precipitation of BaSO 4 and BaCO 3 . It was suggested that the presence of large quantities of insoluble compounds hinders OPC hydration resulting in lower non-evaporable water contents and a greater proportion of anhydrous OPC.
Typically, when small additions of CaCO 3 are added to OPC, the rate of hydration, q max , increases due to the accelerated dissolution of C 3 S and precipitation of Ca(OH) 2 , which contrasts with the decrease in q max observed in this study. Other authors have reported the inhibition of OPC hydration with BaCO 3 additions, due to the formation and presence of insoluble compounds
