Chapter 6 Concrete 113
Science
Hydration Process
Hydration is a chemical process in which water combines with other elements from a
compound with different characteristics. In the case of concrete, the hydration process begins
as soon as water is added to the Portland cement. As a result, the concrete needs to be placed
and consolidated before it sets. The concrete is said to be set when it will support weight.
Finishing operations can continue for a short period of time after the concrete sets.
Curing is the final stage of hydration. During this stage, chemical bonds are formed
between Portland cement particles and between the Portland cement and aggregate. The
result is a solid, rocklike mass. There is plenty of water in a typical batch of concrete for
complete curing. However, surface evaporation and absorption into the sub-base may result in
insufficient water being available for complete hydration. Therefore, keep the surface damp by
misting, covering the new concrete for an extended period of time, or spraying the surface with
curing compound.
Most of the hydration and strength gain in concrete takes place in the first month after it is
placed and finished. However, hydration continues at a slower rate, for many years.
Stake
Brace
Footing
Form
ties
2 × 4 or metal
frame
Rebar
Clamps
2 × 4 walers
Plywood
Figure 6-10. Forms are secured with walers and clamping devices attached at the
ends of the form ties. Forms are braced to maintain proper alignment.
STEM Connection