Importance of adsorption compared with complexation for retarding C3S hydration via adding sodium gluconate

Adsorption effect on particle surfaces and complexation effect with free Ca²⁺ mostly determine the retarding performance of organic admixtures on cement hydration. However, it is difficult to identify which effect plays a more important role in retarding hydration by experimental methods. Here, a theoretical model was developed to investigate the retarding mechanisms of sodium gluconate (SG) on hydration of tricalcium silicate (C₃S). Based on obstruction theory and complexation reaction kinetics, effects of adsorption and complexation were simulated to examine the retarding performance of C₃S hydration with addition of SG. The proposed model well predicted the effect of additional dosing of SG on the retarding performance of C₃S hydration. Theoretical parameter studies demonstrated that adsorption ratio contributed much largely to the delays in C₃S hydration, compared with rate constant of complex generation. Therefore, it is confirmed that adsorption plays a more important role in regulating the retarding mechanism of C₃S hydration.