Testing - Concrete Mix Design, Quality Control and Specification - page 151

program automatically calculates the slope of the line joining these two
points (we call this the K value) as the results are entered in the normal test
result entry system (but having selected early age in the setup program).
The program continuously averages all previous K values for the grade in
question as each new result is entered.
Using the previous average K value, the control age strength is predicted
as soon as the early result is entered. When the true control age result is
later obtained, the true K value for that sample is evaluated and included in
subsequent averages.
The system can display and print out the graphs and these can be used
to establish the age at which any particular strength will be attained or
the actual strength at any particular age. However, it is simpler and more
accurate to use dummy results in the test result entry system. The nomi-
nated strength is entered and the age varied until the previous average con-
trol age (and 28-day) strength is predicted. Alternatively the nominated
age is entered and the strength entry varied until the anticipated eventual
strength is predicted.
An important use for the graphs included in the early age section is to
check that the results do conform to a reasonable pattern. If Figure 7.4
shows some lines of distinctly different slope, then a problem exists. If no
bias or particular period causing this can be found, then it may be due to
testing error (the error can be either in the strength or the equivalent age
Figure 7.4 Strength versus log equivalent age graph.