ABSTRACT
Freshly mixed cement paste consists of cement particles suspended in water. As the cement hydrates, forming calcium-silicate hydrate (C-S-H), calcium hydroxide (CH), and various aluminoferrite phases (AFm and AFt), the space originally lled with water is reduced because the volume of the hydrates is greater than the volume of the unhydrated cement. Figure 4.1 shows how the relative volumes of the major compounds change as a portland cement paste (W/CM = 0.50) hydrates and lls up the space originally occupied by water.1 The remaining (originally water-lled) space is termed capillary porosity because it is generally considered that the pores making up this space are of a size in which capillary effects can occur. The capillary porosity clearly reduces as the curing period increases, and it will also reduce as the W/CM is decreased, because with lower W/CM there is less water-lled space to begin with (Figure 4.2).
