What
is concrete curing?
Curing
is maintaining moisture in concrete following placement so
that the concrete's designed qualities can develop. Curing
influences the concrete's ultimate durability, strength,
water tightness, abrasion resistance, volume stability
and resistance to freeze/thaw cycles and deicing salts. These
properties are reduced significantly when curing is inadequate.
Why
is curing necessary?
When
portland cement is mixed with water, a chemical reaction
called hydration takes place. As cement hydrates,
the strength, durability and density of the concrete increases. The
more complete the hydration, the higher these properties
become. Complete hydration of cement takes a very
long time. The hydration process is far from over
when the surface of the concrete is hard. Theoretically,
the hydration process continues for years. With sufficient
water, the hydration process will be approximately 30%
complete in 3 days, 60% complete in 7 days and 98% complete
in 28 days.Most
freshly mixed concrete contains more water than is required
to hydrate the cement in the mix. Water loss in the
first few days due to bleed water and evaporation reduces
the water content of the mix and slows or stops the hydration
process. It is critical to the long term durability
of the concrete that water evaporation be minimized. Excess
loss of water causes the concrete to shrink, creating
tensile strength, surface cracking results
