Effects of Nanomaterials on the Hydration Kinetics and Rheology of Portland Cement Pastes

In this paper, effects of nanomaterials on the hydration kinetics and rheology of ordinary Portland cement pastes were investigated. Three nanomaterials, nano-limestone, nano-silica, and nano-clay (a highly purified magnesium aluminosilicate), were added to a cement paste at the levels of 0.0 %, 0.5 %, 1.0 %, and 1.5 % (by mass) of cement. The heat of cement hydration of the paste was measured using isothermal calorimetry. Rheological behavior of the paste was characterized using a rotational rheometer. The rheology measurements were performed at 10, 30, 60, 90, and 120 min after the cement was mixed with water. Set times of the paste were measured according to ASTM C191 [Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA]. The experimental results indicate that the addition of nano-limestone and nano-silica accelerated cement early hydration, the maximum heat flow increased, whereas the time to reach the heat-flow peaks decreased. The initial and final set times were also reduced. These effects were enhanced with increased nano-addition level. The addition of nano-clay also significantly increased the intensity of the heat flow peaks, and, especially, the peak corresponding to the renewed reaction of the aluminate phase. Addition of these nanomaterials generally increased yield stress and viscosity of the cement paste, especially after 60 min when cement hydration started to accelerate. Nano-clay considerably influenced the rheological behavior of the cement paste. Significantly higher shear stresses were required to initiate the flow.