In addition to solids, the hydrated cement paste contains several types of voids
which have an important influence on its properties. The typical sizes of both
the solid phases and the voids in hydrated cement paste are illustrated in Fig.
2-7a. The various types of voids and their amount and significance are discussed
next. Just for information the size range of several objects ranging from
human height to Mars’ diameter is shown in Fig. 2.7b.
Interlayer space in C-S-H. Powers assumed the width of the interlayer space
within the C-S-H structure to be 18 Å and determined that it accounts for
28 percent porosity in solid C-S-H; however, Feldman and Sereda suggested that
the space may vary from 5 to 25 Å. This void size is too small to have an adverse
effect on the strength and permeability of the hydrated cement paste. However,
as discussed below, water in these small voids can be held by hydrogen bonding,
and its removal under certain conditions may contribute to drying shrinkage and
creep.
Capillary voids. Capillary voids represent the space not filled by the solid components
of the hydrated cement paste. The total volume of a typical cement-water