ABSTRACT
Concrete is an artificial rock made by blending coarse and fine aggregates, cement powder, water and-increasingly-chemical additives. In the wet state it can be poured into complex shapes within formwork, where the cement and water react together by hydration. This forms a gel, referred to here as the ‘cement paste’, which sets (stiffens) within a few hours and then hardens at a diminishing rate over the following days, weeks and even years. About 30% of the ultimate strength is typically achieved within 24 hours, about 50% within one week, and upwards of 80% after four weeks (Figure 8.1).
