"Three important variables, the proportion of silica-fume replacement, the type of HRWRA, and the w/c, were evaluated... A methocellulose thickening agent (Methocel F4M, Dow Chemical Co...) was added to each batch to reduce the rate of settling of the cement particles. The mixing operation... involved dry blending the Methocel with portland cement in a 7-to-l by volume mixture prior to adding the cement to the water in the high-shear mixer. The paste was prepared by combining the water, HRWRA, dispersing agent, cement, and silica fume in a 0.36-m3 (12-ft3) capacity high-speed shear mixer. The addition of foam adds water to the mixture, and the quantity of the water depends on the density of the foam. ...[I]t was necessary to add sufficient water to the high-shear mixer to get the cement paste to mix efficiently and to flow out of the mixer."