Two plain portland cement pastes were made by mixing deionized water in a blender with either T-1H or T-1D cement at w/c = 0.4. The slag blended cement (designated as T-S) was made by mixing 30 % (by mass fraction) slag with 70 % T-1D portland cement at a 0.4 water-to-solid binder (w/s) mass ratio. Both the slag and this cement, T-1D, were supplied by Dyckerhoff. The fly ash blended cement (designated as T-L) was made by mixing 20 % (by mass fraction) fly ash and 80 % T-1H cement at a 0.4 w/s mass ratio. Both the fly ash and the T-1H cement were supplied by Holcim. Overall, four different cement pastes were studied*.
Figure 1 shows the measured cumulative particle size distributions (psd) for the T-1D and T-1H cements. The minimum diameter is 1 µm. These psd curves were measured using a laser scattering instrument, with air dispersion (dry dispersion). A standard methodology for psd determination, worked out in the context of several ASTM round robins, was used [11]. Figure 2 shows similar psd curves for the slag and fly ash materials, with the same minimum diameter of 1 µm. Wet dispersion in propanol was used for these materials. The psd of the blended cements used in this study would of course be a weighted average of the relevant curves in Figs. 1 and 2. In Fig. 1, the T-1D cement was finer than the T-1H cement, and Fig. 2 shows that the slag material was finer than the fly ash material.
In order to eliminate entrapped air bubbles, house vacuum was employed during the mixing and casting processes, and a vibration table was used during casting. To prevent substantial bleeding, samples were cast in sealed plastic molds and slowly rotated for 5 h on a roller. By constantly changing the orientation of the samples with respect to the direction of gravity, bleeding was prevented. After this, the pastes were kept in the molds and put in sealed plastic bags at 20 ºC and 100 % RH until the testing age was reached.
Figure 1: Cumulative particle size distributions for the T-1D and T-1H portland cements. The minimum particle size measured was 1 µm. Air dispersion and laser scattering techniques were used.
Figure 2: Cumulative particle size distributions for the T-1D and T-1H portland cements. The minimum particle size measured was 1 µm. Wet dispersion in propanol and laser scattering techniques were used.