Effect of filler on early Portland cement hydration

Knowledge of the microstructure of hydrated cement paste is essential for forecasting their performance. «Inert» mineral admixtures such as quartz or titanium dioxide are considered to influence the rate of dissolution mainly due to heterogeneous nucleation. They may have an influence on the calorimetry curve during the first days and particularly on the peak associated with C3A hydration products. It may be related to the nucleation of hydrates on foreign minerals particles which catalyzes the nucleation process. However, the relation between the effect on calorimetry curve and the C3A consumption and/or nature of hydrates formed is not clearly established.
The X-Ray Diffraction (XRD)/Rietveld method has been used to follow quantitatively the reaction of cement phases as a function of time for cement with and without titanium dioxide (TiO2) in the anatase form. We can observe a quicker consumption of C3A due to the filler effect, associated with the peak intensity enhancement in the calorimetry curve. As the hydrated products of C3A were difficult to study by XRD as AFm is an ill-crystallized phase, 27Al Nuclear Magnetic Resonance (NMR) was employed to follow the variation of ettringite and AFm as a function of hydration time in the presence and absence of TiO2. The consumption of C3A can be clearly related to the formation of AFm phase. Scanning electron microscopy (SEM) with Ti, Si and Al mapping were applied on hydrated samples using backscattered electron images to show the location of hydrated products containing Al around TiO2 particles.

Author: G. Le Saout, M. Ben Haha

Section: Science and production

Keywords: cement, NMR, XRD, calorimetry