Setting and hardening

Mixing cement with water produces a plastic workable paste. For some time these characteristics of the paste remain virtually unchanged, and this period of time is known as the ‘dormant period’. At a certain stage, however, the paste begins to stiffen to such a degree that, although still soft, it becomes unworkable. This is known as the ‘initial set’ and the time required for the paste to reach this stage as the ‘initial setting time’. The ‘setting’ period follows, in which the paste continues to stiffen until a stage is reached when it may be regarded as a rigid solid. This is known as the ‘final set’ and the time required for the paste to reach this stage as the ‘final setting time’. The resulting solid is known as the ‘hardened cement paste’ or, sometimes, as the ‘cement stone’. With time the hardened paste continues to harden and gain strength, a process known as ‘hardening’. The various stages of setting and hardening are shown in Figure 2.1.