Cement hydration inhibition with sucrose, tartaric acid, and lignosulfonate: Analytical and spectroscopic study

The reaction of the cement retarders tartaric acid, sucrose, and lignosulfonate with tricalcium silicate ( C3S), tricalcium aluminate ( C3A), and C3A/gypsum have been studied by Al-27 and Si-29 MAS NMR spectroscopy, SEM, XRD, and XPS to gain an understanding of the effect on the individual minerals prior to studying a typical sample of portland cement. Tartaric acid is the most effective at retarding C3A hydration and ettringite formation, while sucrose and the lignosulfonate accelerate ettringite formation but are more effective at retarding C3S hydration. We have confirmed that sucrose acts via nucleation poisoning/surface adsorption while lignosulfonates involve the formation of a semipermeable layer on the cement grains. The formation of calcium tartrate is clearly the most important step in tartaric acid inhibition; however, tartaric acid only exhibits a dissolution-precipitation mechanism for C3A. Under conditions of excess calcium, the formation of a calcium tartrate overlayer does not require the predissolution of the mineral.