Civil Engineering Reference
In-Depth Information
50
40
28 day
30
3 day
20
10
0
0
10
20 30
Curing Te mperature (°C)
40
50
60
Figure 2.7
The 3-day and 28-day strength of concrete cured at various constant curing
temperatures.
Despite minor changes in the composition of C-S-H, the stoichiometry of
hydration remains the same up to about 100°C. However, although the
reasons for the increased strength development rate of concrete at elevated
temperatures are mostly known, the reasons behind the decreased long-
term strength of the concrete when cured at elevated temperatures are not
as clear. This is partially because an increase in temperature of up to 45°C
is considered to have no or negligible effects on the physical or chemical
structure of the hydration products. It has been suggested by some studies
that the negative effects of elevated temperatures on the long-term strength
of concrete stem from the nonuniform distribution of hydrated cements
within the paste at elevated temperatures, which results in weak parts pres-
ent in the matrix [1].
The inverse relationship between the early and ultimate strength of
concrete is usually considered as a general rule; i.e., the higher the initial
strength of concrete, the lower the long-term strength will be. The det-
rimental effects of higher curing temperature and higher initial strength
development rate on the long-term strength of concrete are also seen even
when the concrete is initially cured at elevated temperatures and then kept
at ambient temperatures (Figure 2.8). A similar inverse relationship between
early and long-term strength of concrete is also observed when curing the
concrete at lower temperatures. This has been shown to result in a decrease
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