Testing - Concrete Mix Design, Quality Control and Specification - page 152

Figure 7.5 Early age specimen results. Strength (MPa) versus log equivalent age (hr).
of the early result). K values can be plotted in the normal QC system and it
can be seen which results are abnormal. Such results can easily be excluded
from the analysis by finding them in the table of all results (in Full View in
the ConAd program) and so labeling them.
Figure 7.5 also clearly shows how much scatter of results there are and
whether they are scattered about the correct line. For example the illustra-
tion chosen here does show some tendency to change slope at earlier than
the 7 days selected as a control age.
Figure 7.3 is the kind obtained with multiple test ages and again shows a
change at 2 days rather than the 7 days used. The error due to this assump-
tion is quite small in this example but can be larger in other cases.
7.4.1 Limitations of the equivalent age concept
Concrete that has been heated
1. too early, or
2. too rapidly, or
3. too hot
will attain a lower 28-day strength than the same concrete cured at normal
temperatures. The limiting values to avoid such problems differ for different