Data from small-angle X-ray scattering experiments are used to determi
ne the fractal types and dimensions of hydrated portland cement pastes
over a range of length scales. The larger-scale, 200-1500 Angstrom, g
eometry at most degrees of water saturation is found to be that of a r
ough surface fractal. The smaller-scale, 30-200 Angstrom, geometry is
found to be a mass fractal in saturated pastes. This geometry changes
gradually with drying, and becomes a rough surface fractal at saturati
ons less than about 50%. Completely oven dried pastes are found to hav
e a considerably altered geometry.