Impact of hydroxypropylguars on the early age hydration of Portland cement

Hydroxypropylguars (HPG) are used as admixtures in factory-made mortars. These molecules present water retention properties comparable to those obtained with commonly used cellulosic water-retaining agent. The influence of HPG on cement hydration was investigated in order to improve understanding on the delayed effect induced by polysaccharides. Hydration kinetics were characterized by means of conductivity and isothermal calorimetry measurements. The influence of polymer concentration and predissolution was studied. A weak influence of HPG on the germination of hydrates was observed. In contrast, HPG induced a significant decrease in the hydrates growth rate. Strong effects of the polymer concentration and predissolution were noticed too. From these results, we supported the hypothesis that HPG adsorption on hydrated phases via polar interactions should be responsible for the delayed effect observed.