Strength of asphaltic concrete

Use this diagram to explain how the no-interaction model implies that changing the level of factor A has the same effect, whatever the level of factor B (and vice versa).

Rotate to y-z. Explain that the lines are parallel since the no-interaction model assumes that the differences (Basalt - Silicious) are the same for all compaction methods.

Similarly, rotate to y-x. Again the two fitted lines (corresponding to the different aggregate types) are all parallel since the no-interaction model assumes that the effect of changing the compaction method is the same for both aggregate types.

An experiment was conducted by a civil engineer to assess the effect of the compaction method on asphaltic concrete. Two types of aggregate and four compaction types were used in the factorial experiment with three replicates. The response measurement was the tensile stringths (psi) of the samples.